Manual
Setting
Helicopter Setting up a helicopter
Setting up a helicopter for its first flights can be a daunting task, even after you've done it a few times. There is more than one "right" way to do it, and a lot of room for personal preference s, so I don't claim that this page describes the "one true setup" for everyone. What it does describe is the process I use to set up my own helicopters, as well as those of beginners who ask for my assistance. I will walk though the setup, step by step, ex plaining what I do and why I do it.
General principles...
• 90 degree angles are your friend. With the controls centered, imagine a short line from the center of the servo horn to the ball link. This line should be perpendicular (at 90 degrees to) the link age attached to that ball. If it isn't, you'll find that you get more control throw in one direction than the other, which will leave you with a helicopter that feels different depending on which way you're turning or tumbling. Helicopters are hard enough to fly already; bad setup only makes them more difficult still. • Slop is not your friend. Grab the swashplate and wiggle it up and down... try to tilt it in every direction. Notice any slop? Find and fix the sources. Grab the blade grips and twist them. No tice any slop? Find and fix the sources of the slop. With all those linkages and pivots between the blade grip and the servo horn, there's bound to be some slop, but do everything you can to minimize it. • This document assumes that you have a radio with 5 -point curves . If you have fewer (e.g. JR 8 - channel radios have 3 point throttle curves and tail rotor curves), just ignore the "1/4 stick" points. If you have more (e.g. JR 10 -series and Futaba 9 -series), do the best you can to fill in the blanks. • If you follow all of these instructions to the letter, you'll probably end up with a very flyable helicopter. If you only follow half of the instructions here, and borrow from someone else's setup scheme for the rest, you'll probably end up with a rather uncooper ative beast. You're best off sticking with a single setup paradigm until you're confident that you can experiment, recognize the results (both intended and unexpected results!), and compensate for the side effects of the changes. • That said, a computer rad io is like an etch -a-sketch. If you don't like what you end up with, you can start over as many times as you like. Even better than the etch -a-sketch, you can erase only the part you don't like, and you can restore your old setup perfectly if you just take good notes. There's a lot of room for personal preference in helicopter setup. You find your preferences by experimenting, so don't be afraid to experiment. Just start with something that works, and make one change at a time so you can learn from each lit tle change. • This is an iterative process. Unless you're really lucky, you won't be able to execute each step in sequence without running into a problem that forces you to back up a couple steps, make a change, and work your way forward again. It can be te dious and time -consuming. Set aside an entire evening, and don't be surprised if you need two. This process assumes that you'll be doing 3D, which assumes that you'll need quite a bit of pitch range, which inevitably means that you'll need to fuss with you r linkages to find a combination of lengths and angles that gives you full positive and full negative without binding anything.
You'd think that after all these years of all these people doing all these crazy aerobatics, you'd be able to build any kit acc ording to the instructions and get +/ - 10 degrees on the first try. Unfortunately, you'd be wrong. If you're not wrong, you're lucky! I'm sure this will change as manufacturers come to grips (so to speak) with the fact that everyone wants to do 3D these da ys, but I don't think we're there yet.
• This document assumes that you're past the training -gear stage and into forward flight . If you're still learning to hover with training gear, a some modifications are in order: 1. Don't bother setting up idle -up -2. 2. Us e a pitch range of 0 to 8 degrees for normal mode and idle -up -1. 3. Set your 5 -point pitch curve for 0, +2, +4, +6, +8 (nice and linear). 4. Start with a throttle curve of 0, 30, 50, 70, 100 for normal mode 5. Start with a throttle curve of 25, 30, 50, 70, 100 f or idle -up -1 6. Get into the habit of using normal mode to start the engine and end your flights, and using idle - up -1 for all of your flying. 7. When the training gear comes off and you start getting into forward flight, switch over to the -4 to +8 collective setups for normal mode and idle -up -1. You'll find it a bit tedious to bring the helicopter back downstairs into a regular hover when you only have 0 degrees of pitch at low stick. It will slow down and descend, but only slowly. 8. When you get into forward f light, get rid of the training gear. With altitude and distance, they will only serve to confuse your eyes like an Escher drawing.
What to do Why to do it
Start with a blank slate . Any asymmetrical settings in your radio are only going to cause headaches later. The pitch curve - Set all of y our trims and subtrims to zero. settings will be explained later, but for now just note - Set all of your ATVs t o 100%. that there's ten percent at either end of the idle -up -2 range that goes unused, and the 1/4 points (30 and - Set your 'high' dual rates to 100% and your 'low' dual 70%) are moved in five percent to keep things linear. rates to 75%. This will allow throttle hold to have a little bit of extra - Set your idle -up -2 pitch curve to 10, 30, 50, 70, and pitch on top . 90 % from low -stick to high -stick. - Set your idle -up -2 throttle curve to 100,60,50,60,100. These curves will need to be refined later, but they provide a pretty reasonable place to start. You'll fine - - Set your normal -mode pit ch curve to 30 , 45,60,75,90 . tune the pitch curve with a pitch gauge, and you'll fine -tune the throttle curve with a tach (if you're - Set your normal -mode throttle curve to 0 , 30, 40, 60 , lucky) or by ear (which also works). The n you'll fine - and 100 % from low -stick to high -stick. tune both of them all over again a couple times. Its almost inevitable.
Center the servo horns. Remember, 90 degree This should be obvious. If it isn't, just trust me. angles are your friend. Get the servo horns as close to straight as you can get them mechanically, and then use the subtrim to get each one perfectly centered.
Do this for all five channels: throttle, collective, both cyclics, and the rudder.
Level the swashplate. If the swashplate isn't level, this will confuse the pitch gauge in later steps. Adjust linkages as necessary. This will vary from one helico pter to the next, so I can't offer any specific suggestions.
Level the chassis. If the cha ssis isn't level, all of your pitch gauge readings will be skewed correspondingly. This will Put a bubble -level on the sideframes, servo tray, tail leave you with a helicopter that lugs down when you boom, or whatever you can find. Shim un der the skids climb upright and overspeeds when you climb as necessary to get the heli level. You only need to do inverted, or vice versa. one axis (e.g. looking from the side or looking from the front), just remember to make all of your pitch gauge readings while you're looking at the helicopter along that axis.
Zero the collective. For 3D flying, you want the helicopter to behave identically whether it's right -side -up or inverted. This Hang a pitch gauge on a blade and a bubble -level on requires a pitch curve that provides zero pitch at the flybar. If you have a "flybar alignment" pitch gauge center stick, and equal amounts of positive and like the Miniature Aircraft or Helimax gauges, set it for negative pit ch at high and low stick. zero degrees and tinker until the flybar is parallel. Even if you're not into 3D flying just yet, centering Set your radio to idle -up -two, and center the collect ive the collective setup at zero degrees will still make stick. the rest of the setup process a bit easier.
This part varies from one helicopter to the next, but There is an exception to this guideline, however. there are typically three sets of links to consider. First, Some helicopters, designed specifically for look at the links between the collective servo and beginners, will not have enough collective range to whatever it works on - a rockin g servo in the case of allow a symmetrical pitch curve. If you can only get the Futub a and XCell, a t ilting servo in the case of the 12 degrees of total pitch range, for example, you're Intrepid and Raptor, a simple bellcrank in the case of better off with +8 to -4. A symmetrical range of +/ -6 the Concept, and so on. Shoot for a 90 degree angle degrees will barely get off the ground. between the linkage arm and this mechanism (rocking servo, bellcrank, whatever). Second, look at the links The rest of this page assumes that you have enough between th e collective mechanism and the pitch range available to set up a symmetrical pitch swashplate. Again, aim for 90 degree angles where curve. If you don't, skip the idle -up -1 and idle -up -2 possible. Third, look at the links between the pitch setups, and just aim for +8 to -4 in normal swashplate and the mixer, or (in the case of the mode and idle -up -1. This will get y ou all the way into Concept) between the mixer and the blade grip. basic aerobatics.
It's nice if you can get zero c ollective without touching your subtrim, but I think the backlash against making electronic adjustments is sometimes taken too far. However, if you run into a mechanical limit (a link that can't get any shorter, servo splines that aren't quite centered, et c) you may need to resort to subtrim.
Get +/ - 8 degrees of collective throw. The 8 degree figure is mathematically friendly, as we'll see when we set up normal node. If you're Ideally this should just be a matter of adjusting the running a modified motor, high -nitro fuel (e.g. Cool ATVs on the pitch channel, though you may find that Power 30%), or short blades, you may be able to take some mechanical or subtrim adjustment is necessary if advantage of more pitch, but we'll sort this out later. you find somethi ng binding in the rotor head before the For the moment, just stick with +/ - 8 degrees. blades reach 8 degrees in either direction. Do not change the middle or end points of pitch curve - stick with the 10, - ,50, - ,90 settings we established earlier. You need to leave the compressed pitch curve in Feel free to adjust the 2nd and 4th points though, so place because later we'll use 100% pitch to get a you get -4 and +4 degrees, respectively. little extra top -end for throttle hold.
If you need to change the zero -degree / half -stick point, use your subtrim. If you need to change end 8 - degree / full - or low -stick points, use your ATVs.
Get -4 and +8 for normal mode. I like linear pitch curves. While I like a symmetrical pitch range in for 3D flying, I only want half as much At this point, your subtrim and ATVs are set, and you negative pitch for precise hovering. I'm not picky don't need to change them. This ca n all be done with about where the stick is when I'm hovering, so the the normal -mode pitch curve. Shoot for a five -point hover point falls where it may . With a pitch range of -4 pitch curve like -4 -1, +2, +5, +8. Ideally, your to +8, I end up hovering at about 5/8 -stick instead of transmitter's pitch curve settings would be 30 , the 1/2 -stick position many folks recommend. So be 45,60,75,90 , so that's a good place to start. it.
Note that there's three degrees of pitch change The linear pitch curve gives a very consistent 'feel' between each of the five pitches - that should give no matter where the collective stick happens to be you a very linear "feel" no matter how much collective at, and I thi nk this is preferable to an artificially - pitch you're using. Note also that there's a 15% skewed 1/2 stick hover. If you've got 12 degrees of change between each pitch curve percentage. pitch range and you're hovering at 1/2 stick, you're Theoretically, it should be that simple... Howev er, with 5-point pitch curve probably looks like -4, 0, 4, 6, 8. all those links and levers and their non -linear That's bound to over -sensitive below half -stick characteristics, your transmitter settings are bound to (where 1/4 stick movement covers 4 degrees of need a bit of tweaking from that "mathematically ideal" pitch), while it's going to be mushy above half -stick starting point. Don't worry about the transmitter's (where 1/4 stick movement covers 2 degrees of numbers; it's the pitch gauge that matters most. pitch).
Pick an idle -up -1 pitch range . The reduced pitch range we just set up for normal - mode acts almost like a 'dual rate' for your collective If you spend a lot of time doing forward flight and control. With only 75% degrees of the total pitch simple aerobatics (loop s, stall turns), the normal -mode range under your thumb, small precise changes are pitch range is probably your best bet. Duplicating it in easier than idle -up -2 where you've got the full range your idle -up -1 mode will allow you to switch between at your disposal. I find that this reduced pitc h range the two modes seamlessly. makes it a bit easier to get a solid hover out of a lightweight 30 -class heli. With a 60 -class helicopter, No matter what you're doing with a 30 -class everyday hovering is no problem in idle -up -2, but it helicopter, I still recommend copying over the normal - doesn't hurt to have a reduced pitch range available mode pitch settings. for contest hovering.
If you're flying a 60 -class helicopter, or if you're getting I've general ly had idle -up -1 set up just like idle -up -2 beyond 'airplane -style' aerobatics, I recommend in my Futura SE, but at a recent contest (two days tossing a coin unless you feel strongly one way or the before I wrote this) I switched to normal mode about other. 1/3 of the way into a precision hovering segment. I can't say for sure if it was a just a mental crutch or i f it really helped, but I did much better than I expected in the contest. I'm going to copy my normal -mode settings into idle -up -1 as soon as I finish writing this. This is strictly a matter of personal preference though.
Pick a throttle -hold pitch range . If you're not doing aerobatic autos, you don't need the wide pitch range and you'll probably be more If you're new to autorotation , or if you're not interested comfortable just holding the collective at the bottom in inverted autos, copy the normal -mode pitch curve during the descent. If you are doing aerobatic autos, over to your throttle -hold curve. If you're doing (or you might as well have a symmetrical pitch curve for learning) inverted autos, copy the idle -up -2 pitch curve those, too. This will allow you to better control the over to your throttle -hold curv e. inverted portion of your descent, and it lets you do your autos with a pitch curve that you're already familiar with.
If you copied the normal -mode curve, try to practice your autos from norm al mode. If you copied the idle - up -2 curve, practice them from idle -up -2. This will minimize the bobble that tends to happen when you enter throttle hold. It will also minimize the bigger bobble that will happen if you need to bail out of an auto gone wron g.
Tweak throttle -hold just a bit. This will give you just a touch of extra top -end pitch at the ends of your autos. You should end up with about Take that top point and crank it up from 90% to 100%. 10 degrees. Anything more is probably not going to he lp any; you may find that using less doesn't really change things much either. By the time your stick is up that far, your head speed is probably so low that you're about a quarter -second away from touchdown no matter what you do.
Set your cyclic throws. It's a long story! I've got a whole web page on this topic.
Check for binding at the extremes. At best, binding will shorten the life of your collective or cyclic servos. At worst, it will strip them out in a Select the idle -up -2 flight mode. With the radio off, heartbeat. Neither of these are optimal, of course. move the servos to full positive c ollective and full forward cyclic (it doesn't really matter which direction actually, as long as the swashplate is a full tilt). Slowly Many folks are content to allow a bit of binding, on and gently rotate the rotor head by hand. Watch for any the assumption that they will never actually binding in the rotor head linkages. Feel carefully for any command full collective and full cyclic at the same resis tance as you turn the rotor. Keep an eye out for time. I personally think that's optimistic - or maybe servo movement - if the something starts to bind up, it's just that I know I can't be relied upon to follow the they will be forced away from their present positions. rules all the time. I prefer to solve the binding problem while I'm setting up the helicopter, rather than while I'm flying the helicopter. Make at least two full rotations of the rotor head, just to be sure. Th is can take a lot of tweaking, depending on the helicopter. Specific instructions for each helicopter Now go to full negative coll ective and full cyclic, and would easily double the size of this document, so I watch for the same thing. suggest you get in touch with other folks who fly your favorite model of helicopter and ask them what With any luck, you'll encounter no binding in either they've done to maximize their pitch range. case. If you run into binding at both ends, try to find a way to get more blade pitch change with less If you cut back on swashplate tilt, you may find swashplate movement. Depending on your helico pter, yourself needing to change the Bell -Hiller ratio or you might want to change the Bell -Hiller ratio, or lightening the flybar paddles to get the roll rate you install longer mixing levers, for example. want. In either case, you're sacrificing some flybar st abilization. It's not the end of the world, but it's not If you find binding at just one end, try to find a way to ideal. move the swashplate away from the bind without changing the blade pitch. Are there any links you can If the washout mixer is slamming into the top of the lengthen and shorten to move the swashplate away swashplate twice per revolution at 1700 RPM, how from the binding zone without changing the blade long are the cyclic servo's gears going to hold out? pitch? As a last resort, consider using less swashplate My guess is not very long, so I pers onally can't stand tilt to get the roll rate you want. the thought of linkages binding when I'm in flight.
Set up the throttle linkage. You'd be surprised how silly your throttle curve will look if you don't have the linkage set up right. After I This is surprisingly easy if you do it right. For starters, installed a new YS ST2 in my Futura, I was beginning take the throttle linkage off of the carburetor throttle to think the motor w as a dog because at "70% arm and the servo horn. Hold the thr ottle link in your throttle" it was only pulling 1450 RPM in a hover, and fingers such that the ball links are directly over the when I give it full throttle it could only manage 1400 centers of the arms they connect to - the engine side of RPM at 8 degrees. After re -doing the throttle linkages, the link should be right over the center of the throttle I found it hovering at 1650 RPM and 65% throttle. barrel, and the servo side of the link should be right With the engine running up in its power band , over the cent er of the servo output shaft. climbing out at 8 degrees and 1650 RPM was no problem. Lengthen or shorten the linkage as necessary until you can have the links centered over the carburetor Unless you set your throttle curves right, you have barrel and the servo output shaft. You're not going to no idea what your throttle setting really is. I could connect it to either of these, of course - this exercise probably have solved the problem by setting my is just to get the linkage length set right. throttle curve f or 85% in a hover, but fixing the linkages is really the "right" way to address that Put the ball on the servo horn so that the servo arm problem. length is equal to the carburetor arm length, or as close as you can get them. Set the middle point of your normal mode throttle curve to 50% for a moment, set the thr ottle at half stick, and install the throttle servo arm on whatever spline makes the servo arm perpendicular (90 degrees) to the linkage. Use the throttle channel subtrim if necessary. Install the linkage.
Set the throttle ATVs such that the throttle link age almost binds at 100% and almost binds when you hit the kills switch or bring the throttle trim all the way down (depending on how you prefer to stop the engine). You should end up with ATVs that are almost equal. If not, use the subtrim to change the c enter of the throttle servo's throw, and balance the ATVs accordingly.
This is quite involved... I've actually got an entire page Set up the gyro and rudder linkage. devoted to heading -hold gyro setup, and a separate page for standard gyro setup.
Got a GV -1? Here's a quick overview of GV -1 setup. Yes, I only use two speed settings, not thre e. A This isn't everything, but it doe s cover the things I look 'hovering' headspeed and a '3D' headspeed is all I for when I'm troubleshooting someone else's bother with. In fact I hardly ever use the 'hovering' installation. speed... But I do use the 'off' position at the start of every day - the GV -1 will adjust the throttle to Connections - connect the GV -1's throttle input to the compensate for any mixture issues, so I prefer to fly throttle channel of the receiver , and connect the without it for a couple minutes, or until I'm happy with throttle servo to the GV -1's throttle output. Connect the mixture. the GV -1's " speed" input to a channel controlled by a three -position switch. Do not bother with the GV -1's The 1500/1700 settings are just a place to start. "on -off" connection. If you want to use the GV -1's Adjust them to suit your tastes. I fly my Futura SE at mixture control features, you're on your own - I haven't 1675 and my Concept SRX at 1900 or 1950. The tried them yet. Futura has a 'hover' headspeed of 1450, which I hardly ever use. Pick speeds that suit you and your Gear Ratio - set it to match your he li's gearing helicopters.
Speeds - Set S1 for " -off -", set S2 for 1500, set S3 for StSw is a key. With this turned on, the GV -1 will 1700. automatically disengage when the throttle goes below about 25%. This simplifies throttle hold setup, Servo Travel Limit - the most -overlooked aspect of and makes it easy to stop the motor at the end of a flight - just select normal mode and bring the throttle GV -1 setup. Put the transmitter in normal mode. Press down to an idle like you normally do. So long as your the "func+" key until you get to a screen that says "Lmt Idle." Bring the throttle stick all the way down idle -up curves are set so they never go below 25% (with the trim set for a good idle) and press "data+" (and they shouldn't!), the governor will work just fine for aerobatics. Using StSw for all this also enables The GV -1 will read "Lmt High." Bring the throttle all you to skip the on/off channel, and does away with the way up and press "data+" The GV -1 will read "Lmt any need you might have had for transmitter p -mixes Stop." Bring the throttle all the way down and hit the to disable to governor in throttle hold or normal kill sw itch or bring the trim down, as you would to stop the motor, and then press "data+" once more. mode.
StSw - Set this to "on." The SwCd check just ensures that the GV -1 r eally does what I expect it to do. Verify Switch Conditions - go to the "SwCd" or "switch condition" screen. This will read "on" if the GV - The 'limit' settings tell the GV -1 where the throttle servo is allowed to go. Since the GV -1 takes over 1 sees the settings it needs t o engage itself, and "off" the throttle servo control, just setting your if it sees the settings in needs to disengage it . transmitter's ATVs isn't enough - you also have to tell the GV -1 where the throttle servo's limits are. First, set the 'speed select' switch to something other than the 'off' position. Select normal mode and verify To verify the setup, go to the "Test Idle" screen. that the governor turns off at low stick and turns on at Pressing the "data+" key will cause the throttle servo high stick . Select idle -up and verify that the governor to go to the idle setting for a moment. Pressing it stay on at all stick positions. Repeat for idle -up -2. Hit the throttle hold switch and verify that the governor again will cause the servo to go to full throttle, turns itself off from any flight mode. pressing it once more will cause the servo to go to the 'off' position. You're done. Pick a head speed The throttle curve values I suggested above are only You might be tempted to skip this step if you have a start ing points. They will need some fine -tuning to suit GV -1, but I suggest setting up your throttle curves your own particular combination of engine, rotor anyhow, just in case. If the magnet is ejected from the blade, gear ratio, fuel, exhaust system, altitude, fan, or if the sensor fails, or if anything else goes humidity, phase -of -moon, and so on. wrong, you'll be flying with your radio's throttle curves. Sensor failures are pretty rare, but disappearing Don't be too worried if you don't have a GV -1 or a magnets are not. friend with a ta ch. They do make things a bit easier, but we all got along quite well without them before If you have a friend with a tach, pick a head speed, they came along. hover, and tweak the throttle curves until you can hover at that head speed in all flight modes (and inverted in idle -up -2, if you're able).
If you have a GV -1, but not a tach, set the GV -1 for your preferred head speed, and switch it on and off during a hover. Your ears will tell you if yo u head speed is higher or lower without the GV -1 engaged.
If you don't have a GV -1 or a tach, hover, and check your collective at that stick position. You should be between four and five degrees.
Fine -tune the collective range. Naturally, not everyone will find +/ - 8 degrees of collective to be ideal. I find that it works pretty well If you're not comfortable flying inverted, have someone with my Futura SE and its 710mm blades, but my else help you out with this phase. Read this all the way Concept runs better with 9.5 degrees in either through, and remember that sometimes it makes sense direction. to carry out these two adjustments in the opposite order they're presented here. And, pitch gauges lie. Due to linkage slop and rotor blade variations, you'll probably find that no matter If you have a GV -1, set the speed select to the 'off' how hard you try to set up the pitch range position. Hover right -side up for a moment, and then symmetrically, you end up with a helicopter that lugs punch it, climbi ng vertically with 100% throttle and full down when you climb in one direction and collective. Roll it over and climb inverted with 100% overspeeds when you roll it over and climb the other throttle and full negative collective. direction.
Chances are, you'll find that one orientation gives you By moving the su btrim, you add a little pitch on one a faster climb rate and a lower head speed, while the side while subtracting an equal amount of pitch from other orie ntation climbs more slowly and overspeeds the other side. The nice linear pitch curves we set up a bit. If both orientations are overspeeding or lugging earlier will remain just as linear. If you use the ATV's drastically, skip the next paragraph and come back to to balance out the pitch range, you will end up it later. puttin g "knee" in the pitch curve, and you'll end up with more sensitive response upright and less Use the pitch channel subtrim to shift the entire pitch sensitive response inverted, or vice versa. Stick with range. Don't use the ATVs. Make subtr im adjustments subtrims to equalize the climb rates in either until you can carry out the experiment above with the orientation. same head speed and climb rate in either direction. By making equal ATV adjustments in both directi ons, Once you get the head speeds and climb rates you can increase and decrease your overall equalized, consider the head speed you're getting in collective range without disturbing the linear pitch your climbs. Are both directions ove rspeeding a bit? If response we've worked so hard to achieve. so, add an equal percentage of ATV in both directions to add some pitch in both directions. If you end up lugging the motor no matter which way you climb, subtract an equal amount of ATV in both directions.
Rethink your head speed choices. Don 't get too concerned with the figures other people are using for their helicopters. There are so many variables involved; it's very difficult to compare figures You may have found, in the above exercise, that your meaningfully . engine can carry more th an 8 degrees of pitch. If this is the case, you might consider going back to 8 degrees of pitch and using a higher head speed. Or, if you I recently saw Bob Johnston, for example, running found that 8 degrees of pitch was too much, you might 1650 RPM and +/ - 8.5 degrees o f pitch. He's got want to use a lower head speed for an increased pitch 710mm blades so he isn't lacking for thrust. I've range. been running 690mm tapered blades lately, and even with +/ - 9.5 degrees and 1750 RPM, I don't think I have his top speed or climb rate.
Fine -tune the cyclic response. If the helicopter Light flybar paddles are a low -cost way to get faster doesn't roll fast enough, even with full swashplate tilt, rolls. If your helicopter has adjustable Bell -Hiller put on some lighter flybar paddles or shift the Bell -Hiller mixing, you may have a zero -cost way to tune the roll ratio for more Bell (direct) input and less Hiller (flybar) rate to your liking. input. Check your helicopter's manual for help with the Bell -Hiller ratio, it's beyond the scope of this document. If your roll rate is faster than you want it, you might consider taming the response mechanically. This Note that changing the Bell -Hiller ratio will probably has the added advantage of making the helicopter change your pitch range as well, so you'll want to more stable against wind and air -speed trim repeat the 'check for binding' and 'fine tune the changes. However, I prefer to fly in low rates. This collective range' steps. As I said, this is not a linear way I can get my full cyclic authority back just by proces s. going into high rates. Having snappy cyclics can give me the extra confidence I need to try something If it rolls too fast, or faster than you want it to, consider new. The quicker the heli rolls, the quicker I can get flying in low rates. That's my favorite approach. Or, out of whatever trouble I've gotten myself into. shift the Bell -Hiller ratio for more Hiller, or move your flybar weights out until the roll rate is just where you want it. If you don't have flybar weights, get some. They're relatively cheap and they allow you to tailor the roll rate with just a couple minutes of work.
P o w e r First, let's look at the things that determine how much power you have available: Engine
Some engines just make more power than others. Head Speed
Some engines, like the YS 6 1 ST2, make the best power at higher speeds. Others, like its predecessor the ST1, make the best power at lower speeds. Your own engine's 'happy range' will also be affected by the other factors, most notably the exhaust system you pair it with. Exhaust
Mufflers are typically quiet, but not remarkably powerful. Tuned pipes are typically more powerful, but not as quiet. Unfortunately it's not as simple as bolting on a tuned pipe though - a YS ST2 with a Muscle Pipe can be exceptionally powerful, but a con sistent mixture is next to impossible and the combination is prone to extremely high vibration, particularly when hovering. Fuel
Some fuels will make more power that others. The percentage of nitro methane is the most obvious factor, with 30% nitro fuel s producing more power than 15% or "straight" 0% nitro fuel. Mixture An engine with a lean mixture will produce more power than an 'ideal mixture,' up to a point - too lean, or too much time spent lean, will result in overheating and loss of power, as w ells as possible engine damage. An engine that is run rich will run cooler and will likely last longer, but this comes at the expense of power. Weather
On hot days, the air is relatively thin, which means that the mixture screws need to be turned in to maintain a proper air/fuel balance. In the end, you have less fuel and less air to work with, so power goes down. On cold days, the reverse is true and the power output is increased. Personally I've never seen as much power from my own helicopters as when I flew at night shortly before Christmas. The difference then was dramatic! Now let's look at what power affects:
Top Speed
This is pretty obvious: more power means faster climbs and higher speeds in level flight. Pitch Range
With more power, you c an use a greater pitch range for a given head speed; with less power, you need to reduce the pitch range if you wish to maintain a given head speed. Head Speed
With more power, you can use a faster head speed for a given pitch range; with less power, yo u need to reduce the head speed if you wish to maintain a given pitch range. Pitch range and head speed are inversely proportional to one another. If power is constant (e.g. if you don't switch fuels or exhausts or climates or anything else on this page), choosing one will effectively determine the usable limits for the other.
Tuning pitch and throttle curves
Setting the pitch and throttle curves "correctly" for the different flight modes took me a while. If the messages in rec.models.rc.air and the heli mailing list are any indication, this is a common issue for neophytes in general. In an effort to keep people from spending any more fuel than necessary while tuning their own pitch and throttle settings, I thought I'd document what I learned here. If you have suggestions, or would like to share your experiences, please use the form at the bottom of this page.
What are the different flight modes?
This depends upon which trans mitter you're using. It is my understanding that older and/or inexpensive radios had two modes, referred to as "normal" and "idle -up," at the other end of the spectrum, the newer, more expensive computer -based radios may allow for several different modes. My own Futaba 8UH has three flight modes, labeled to as normal, idle -up -one, and idle -up -two . I tend to refer to normal mode as idle -up -zero , but it might just be me.
Each flight mode h as its own settings for the throttle and collective pitch curves, as well as a tail rotor compensation curve (a.k.a. revolution mixing, or anti -torque system). With my radio, these curves are set be assigning servo positions to the position of the left sti ck at five points (top, bottom, mid -stick, and the 1/4 and 3/4 positions).
There is also a throttle hold mode, which is to facilitate autorotation practice. You might think of this as a degenerate case of a flight mode: this mode has its own pitch curve, but the throttle is held at a pre -set value (typically just below the point at which the centrifugal clutch engages) and there is only one rudder trim value (rather than a 5 -point curve as in the other flight modes). While I was learning autorotation , I wo uld set the throttle to a point just above where the clutch engages - this effectively gave my Concept 30 a driven tail, without affecting the main rotor. It's cheating, but it helped a little bit.
When I first created this page, I was flying with an old -fashioned mechanical gyro, which required quite a bit of tail rotor compensation to perform well. I'm now using heading -hold piezo gyros in all of my aerobatic helicopters, which require no tail rotor compensation at all. In fact, any tail rotor compensati on curve will only make things more difficult than they should be.
The tail rotor compensation curves shown here are only useful if you're using a standard gyro. If you're using a heading hold gyro, you should set all of your tail rotor curve values to ze ro. The curves shown here are only here to serve as guidelines for people who still use standard (i.e. non -heading -hold) gyros.
The curves shown below all assume that your helicopter maintains a reasonable head speed at 100% throttle and 8 degrees of pitc h. This is not unusual for a 30 -class helicopter using 15% nitro and a muffler. If your engine is stronger, increase the pitch range accordingly.
What are the different flight modes for?
With my Concept, normal mode is used when starting the helicopter and hovering. Idle -up -one was for forward flight and mild aerobatics. As I got more and more into inverted flight and hovering, and 3D aerobatics, I began spending more and more time in idle -up -2. Now, I spend almost all of my time in this mode. Idle -up -1 is now a mode I only use for experimental setups - currently I've got it set up with a slightly reduced pitch range for slow -and -low 3D flight.
With my Futura, I only use normal mode when starting and spooling up after an auto. I used idle -up -one for hov ering and idle -up -two for everything else at first, but soon realized that the 60 -size machine hovers very comfortable in idle -up -2... so, like the Concept, I use normal mode to spin the blades up to speed, I use idle -up -2 for everything else, and idle -up -1 is basically just a scratchpad for new ideas. I haven't had any new ideas lately, so it's identical to idle -up -2.
The Concept's collective control feels somewhat more more sensitive than the Futura's - 30 -class helis are like that because they are light er and therefore quicker to respond to tiny changes. I compenate for this by using an idle -up -zero flight mode that has a reduced pitch range as compared to idle -up -2. The reduced pitch range is similar to a 'low rate' on aileron or elevator but here it ma kes the collective a bit softer. With the Futura, I can do most of my hovering exercises in idle -up -two without much trouble, so I don't use the milder flight modes very much at all.
Keep your pitch curves linear. Forget half -stick.
Once upon a time, so meone suggested setting up your pitch curves so that you hover at half stick. Sometimes, that's a great idea. Other times, it just causes trouble. Forget you ever heard that suggestion. There are really only two variables when you're setting up a flight mo de: 1. How much positive pitch do you want? This usually is just a compromise between how fast you want to climb (this means more pitch), and how fast you want the rotor to spin (this means less pitch). 8 to 10 degrees is typical. 2. How much negative pitch do you want? If you're learning to hover, you don't want very much. The more negative pitch you have, the more sensitive the collective will feel (you don't want that), and the faster you'll be able to descend (you probably don't want that either). Zero to negative two degrees is typical. If you're into fast foward flight, loops, and stall turns, you'll want more negative to allow you to slow the helicopter down and transition from fast flight upstairs to hovering downstairs; -4 or -5 is typical. If you're in to inverted flight or 3D aerobatics, you'll want just as much negative pitch as positive pitch, and again, -8 to -10 degrees is typical. Once you've decided on the positive and Let's assume you've picked -4 and +8 . negative extremes, the middle points are easy to set up. Figure out the total pitch range. 12 degrees total (8 + 4) Divide the total by two, and subtract that much 12 / 2 = 6 from your top end pitch, and this tells you how 8 - 6 = +2 at center stick much pitch to use at center stick. -4 + 6 = +2 at center stick Divide that number by two, and use it to 6 / 2 = 3 determine how much pitch you want at the 1/4 -4 + 3 = -1 at 1/4 stick stick and 3/4 stick positions. +8 - 3 = +5 at 3/4 stick
Just to be sure, make sure that the pitches start with -4 on the bottom you' re about to set up will give you the same -4 + 3 = -1 amount of pitch change between any two -1 + 3 = +2 points on the curve +2 + 3 = +5 +5 + 3 = +8
(I like to start by setting up idle -up -2 with -4 to +8 just because you get a nice whole number at each step, but it's not necessary.) Mailing lists and message boards will show lots of people with awkward pitch curves like -5, 0, +5, 7.5, 10. OK, so you hover at half stick, but below half -stick you have 10 degrees of pitch ra nge and above half stick you have only 5 degrees of pitch range. This means you'll get a very soft feel above half stick, and a rather twitchy feel below half stick. And you'll be hovering right on the edge... If the helicopter starts descending slowly, yo u'll need to move the stick quite a bit to stop it... but if the helicopter starts rising slowly, you'll need to move the stick half as much to get the same effect. This just makes things harder than they need to be. Do not worry about hovering at half sti ck. Worry about the top -end and bottom -end extremes, and just set the rest up for a linear response.
Examples.
After you've had some time to experiment with different flight modes, you will decide for yourself what works best. In the meantime, you should try some different setups... Following are the setups that I used while I was learning. Idle -up -zero a.k.a. "normal" mode
Since I use this mode when I'm starting the engine, the throttle curve has to start with a 0% value at low stick. As with all flig ht modes the throttle is at 100% when the stick is pushed all the way forward, to facilitate rapid climbing in case I find myself approaching terra firma too quickly. To keep things simple, the throttle curve started out as 0, 25, 50, 75, 100%. The middle values were later changed slightly to maintain a constant rotor speed, and the end result was something like 0, 30, 65, 80, 100%.
It's difficult to do stall turns and figure eights in this mode, so I I started running -3 or -4 degrees pitch in this mode.. . Then I found it difficult to hover because of the increased sensitivity (more degrees of collective pitch change for the same stick deflection). Eventually I realized that what I needed to do was learn to switch to idle -up -one when not hovering. It seems obvious now, but it actually took me a while to realize the real purpose of the idle -up switch - I can have the 'soft hover' and the forward flight performance, I just had to learn to toggle the idle -up switch as appropriate.
Throttle : 0, 30, 6 5, 80, 100 Pitch : 0, 2, 4, 6, 8 Tail rotor: -30, -20, -1, +4, +9
If you use a heading hold gyro, all tail rotor mixing values should be set to zero. Idle -up -one
When I was doing a lot of forward flight and some basic ae robatics, I would switch into this mode as soon as I left the helipad, (well, not 100% of the time, I must admit...). I wanted to be able to do loops, rolls, and stall turns, the coll ective pitch is -4 degrees at low stick. To keep the rotor speed up at in the middle of a roll or at the top of a bit loop, the low -stick throttle is 60%. To keep it from overspeeding in upright descents, the throttle goes down to 25% at 1/4 stick, when th e pitch is closest to 0 degrees, and where the rotor is actually autorotating a little bit in a descent.
The pitch "curve" is linear, so the point at which the helicopter hovers is a between 1/2 stick and 3/4 stick. Note that there are three degrees of p itch change between each of the points - this gives a consistent feel to the collective control. Throttle : 60, 25, 40, 65, 100 Pitch : -4, -1, 2, 5, 8 Tail rotor: +4, -3, -1, +5, +8
If you use a heading hold gyro, all tail rotor mixing values should be set to zero. Idle -up -two
This is the mode I use for 3D flight, so I want the response to be identical whether I'm right side up or inverted. This means 0 degrees pitch in the middle and equal amounts of positive a nd negative pitch at either end. Smooth hovering in this mode is more difficult than the others, since the same stick movements now yield almost twice the pitch changes.
I initially had this set to +/ - 10 degrees, but the motor was definitely struggling a t the extremities. So, I dialed in the following +/ - 8 settings and found that the helicopter was much happier this way.
Throttle : 100, 60, 50, 60, 100 Pitch : -8, -4, 0, 4, 8 Tail rotor: +8, -2, -7, -2, +8
If you use a heading hold gyro, all tail rotor mixing values should be set to zero.
After I upgraded to 30% nitro and a tuned pipe, my Concept was able to use all of the available pitch range comfortably, so I expanded all of the curves to use +/ - 9.5 degrees. C oupled with a head speed of about 1950 RPM, this makes for a very sensitive helicopter, but that sensitivity serves to boost my confidence as I learn new maneuvers.
My idle -up -1 pitch range is now set up with +/ - 8 degrees, exactly as idle -up -2 is describ ed above. I use it sometimes to remind myself that you don't really need tons of power to do 3D well. I'm hoping to get more comfortable flying this way. The collective control is a bit less sensitive, which helps smooth out my flying a little bit. The max imum pitch is reduced, which reduces my top speed, which helps me keep the helicopter closer and lower. I am still most comfortable in idle -up -2, with the extra pitch at my disposal, but I'm working on using the extremes less.
Throttle Hold
I've used tw o very different approaches to my throttle hold pitch curve. The first, which I used to learn autos and continued with until I got into inverted autos, is all about keeping things simple. Low stick provides about -3 or -4 degrees of pitch, and the curve is linear up to about 9 degrees of pitch. From the start of an auto until the flare begins, I left the stick all the way at the bottom. If I wanted to adjust my rate of descent, I did it between flights, by adjusting the pitch setting at low stick.
Later, f ollowing a suggestion from Gary Wright, I moved to a symmetrical pitch curve - currently set to +/ - 9.5 degrees (all that my Concept allows). This is identical to my idle -up -2 curve. The advantages are that I can enter and exit throttle hold from idle -up -2 without collective hiccups, and I can vary the rate of descent all I want whether I'm upright or inverted. The drawback is that I must now actively pay attention to the collective during an auto. It requires a little more brain -power to do this, so I don' t recommend it until you can work the rest of the controls in your sleep. However, when you're ready for the extra control, you'll appreciate it. Keeping the head speed up during a rolling auto is all about collective control, and the more familiar that cu rve is, the better off you will be.
Some folks advise +12 degrees of pitch at high stick in your throttle hold pitch curve. I'm not one of them. By the time you've got that much pitch in your blades, they will probably be generating more drag than lift. A fter more than a half -second at this pitch, they will almost certainly have stalled out. I've experimented with extra pitch at the top, and have not found it useful. The theoretical advantage of additional lift is offset by the rapidly decaying rotor speed , and you do yourself no favors by making the collective control more sensitive.
I've also experimented (accidentally...) with a range as limited as -3 to +6, and surprisingly enough, I've never done smoother autos. Sure, there was no hang time at the end , but it touched down as gently as you could ask - which is not consistent with my normal flying style, I admit! The extra -fine collective control made things a little bit easier, and the limited negative pitch made for a relatively slow descent.
I think that using the same amount of pitch as your idle -up -2 pitch curve is a good compromise. For starters, remember to descend with about the same pitch you'd use to hover if the skids were on the other side of the rotor disk. If you're descending upright, put the stick in the inverted -hover position. If you're descending inverted, put the stick in the regular hover position. While you're rolling, put the stick in the center, at zero pitch, to conserve rotor energy during the roll. With practice you'll find your self adjusting the pitch in response to the rate of descent, the sight and sound of the spinning rotor blades, and so on.
From the h -list, December 1996: I haven't seen a lot of discussion on this subject. What expo setting do most of you use on your rad ios? How about dual rates? I use the above settings base on a guesstimate. I have found them to be OK for me but I would appreciate other ideas and explanations (examples) for using them. The manual (Futaba 8) doesn't do much explaining. Ask a dozen peopl e, and you'll probably learn about at least 15 different ways to make use of dual rates. What follows is my own preference. What are rates? For background, "Rate," in this context, refers to the amount of servo movement you get with a given movement of t he control stick. The key thing is this: The higher the rate, the most sensitive the controls are and the more rapidly the model will respond. You'll have a more 'twitchy' hover, tighter loops, faster rolls, and so on. Lower rates make the sticks less sen sitive, which makes it easier to hover and to fly smoothly but more difficult to do most aerobatic maneuvers. Rates are measured in percentages. 100% is just a middle -ish value that the radio manufacturers picked arbitrarily, as a point of reference. Most Futaba radios allow you to choose a rate between 30% and 140% - I believe JR radios allow 10% to 150%. This doesn't make JR radios somehow better; Podunk radios might just as well pick a 100% rate that allows 180 degrees of servo movement, and ask you to pick values between 5% and 100%. Rates are related to ATVs (adjustable travel volume), but rates affect both servo movement equally in either direction. ATVs have a separate adjustment for travel in either direction. Adjusting the rate changes how far th e servo will move from its center when you move the stick to one side or the other. If the rate is too high, the linkages or other parts of the model may bind; if the rate is too small, the linkages has not move enough to make any difference at all.
What are dual rates? Dual rates indicates that the transmitter has a switch that can select between two different rates, typically referred to as "high" and "low." Every channel on the radio has a rate, but not all have dual rates. Typically, dual rates are available on the rudder, elevator (or fore -aft cyclic), and aileron (side -to -side cyclic). Dual rates for the throttle just wouldn't make much sense - why would you want to limit your high throttle setting and raise your idle at the same time?
What do you do with dual rates? Personally, I spend 99% of my time flying in the "low" rates, which I gather is different from most folks. Using "low" rates most of the time, I feel less at risk should I accidentally find myself flying with the switch in the wrong position. One of the most convincing arguments against the use of dual rates is that if you think you're in your normal "high" rates, you can get into trouble if you start a knee -high roll and find that you're actually flying on "low" rates. This has led to many a crash and many a curse to the sky. So, for me the "low" rates are normal. I find the "high" rates useful when I'm trying to learn something new. Faster response allows me to bail out of a botched maneuver more quickly. The drawback is that I ca n't fly at all smoothly this way, and it takes a bit more concentration to keep the heli on the path I have in mind. The advantage is that if I start a maneuver in the "wrong" rate, I can return to a safe orientation faster than I expected, so I'm not like ly to crash as a result of using the wrong rates at the wrong time. How do you set up dual rates? The high cyclic rates are set up so that the swashplate will almost bind if I move the cyclic stick all the way forward, all the way back, or all the way to either side. The swashplate will bind if I move the stick into the corners of the gimbals (top -left, bottom -right, etc). The low cyclic rates are set so that the swashplate will almost bind when I move the cyclic stick into the corners. There is a bit of unused travel available when I move the stick straight forward or to either side. My radio - Futaba 8UH - allows me to put both the aileron and elevator cyclic rates on the same switch. With the radio configured his way, I'm either using high rates for b oth channels or low rates for both channels. This makes one less switch to mess with, and it frees up another switch for another purpose (for example, to turn my cyclic ->throttle mixing on and off, or to adjust the governor settings, depending on the model ). The nice thing about the low rate is that I never need to worry about binding anything. With high rates, it's possible to bind the swashplate against the main shaft if the stick moves too far into the corners. I find that a little scary because with mo st machines, when the swashplate is locked against the main shaft, collective control binds up as well. Concepts and Barons are immune to this, but virtually every other machine on the market depends on a (smoothly) sliding swashplate for collective contro l. Once I'm satisfied with the radio setup, I adjust the mechanical setup to get the amount of cyclic authority I want. So far, with my Concept and Futura, I've found that when I'm happy with the authority when the low (unbindable) rates are in effect, I' m also happy with the extra authority provided when the high rates are in effect. What about the rudder rates? Back in the days of mechanical gyros, I set the "high" rate to the maximum allowed by the radio (with maximum ATVs, too) and was barely satisfi ed with the pirouette rate. This led to lots of binding while the heli was on the ground of course, so I used the low rate to set the travel to where it wouldn't bind if I bumped the rudder stick. Today, in the age of "yaw rate demand" or "heading hold" g yros, I have a little more flexibility... My initial "heading hold" setup used a low rate that was just fast enough for a clean 540 stall turn, and a high rate that allowed extremely fast pirouettes for zing -zing -zing -zing stall turns and ripper -esque plu mmeting pirouettes. I found that pirouetting fast for the sake of pirouetting fast wasn't very interesting to me though, and didn't use high rates much. I spoke briefly with Curtis Youngblood about pirouetting aerobatics a couple of years ago, and he offe red the following practice suggestion: set your low dual rate to get slow pirouettes that you're comfortable with when you hold full rudder. It seemed like a good idea - if you commit to holding full rudder, you have only three controls to worry about, not four. I set the "low" rate for very slow pirouettes, and set the "high" rate for a clean 540. Then , practiced holding full rudder and keeping the helicopter in one place, later circling around myself, and later flying circuits. Then I gradually started tu rning up the pirouette rate... Then I had an idea of my own, for learning pirouetting tumbles. I set the low rate for pirouettes that were exactly as fast as my tumbles. This way, a forward flip with full rudder results in a flip with a single pirouette. At the halfway point, the helicopter is inverted and pointed in the same direction it started in (nose -in or tail -in, depending). The cyclic stick basically moves in a single smooth circle over the course of the tumble. With some simulator practice, this h elped me take a big step forward. What to do with high rates? Why, set the pirouettes to be exactly twice as fast as the tumbles. One full pirouette - and one circle with the cyclic stick - per half flip. More simulator practice and another big step forwa rd! I'm almost starting to get comfortable doing this in real life, three mistakes high. What about expo? Exponential response allows you to make the controls softer around the center (for smoother flying) without reducing the total servo throws (so you don't lose aerobatic potential). The stick sensitivity increases at the extremes, which some people find unsettling. Personally, I'm all for it. When I switched to lighter flybar paddles, I cranked up the expo to about 55% at first, then down to 45% and l ater to 35%. It was a nice way to compensate for the change until I became more comfortable with the increased response. Now I find that 35% is a nice compromise that allows smooth hovering and predictable aerobatics. Conversely, you can also use expo mak e the stick more sensitive around the center, and less sensitive at the extremes. I have no idea why you'd want to, though.
"What head speed should I use?"
Everyone faces this question from time to time. Like most questions about RC helicopter setup, there is more than one correct answer. I hope this document will help you find a head speed that makes you happy.
First, a word about safe operating limits. Generally speaking, you should not exceed 2000 RPM with a 30 - class helicopter or 1900 RPM with a 6 0-class helicopter. There are exceptions to every rule, but generally speaking you'll be better off if you stay within these guidelines. When a rotor head fails, the entire helicopter is usually destroyed. Not just damaged, but destroyed beyond repair. In addition, many pieces typically fly in many directions, posing a safety hazard for everyone within 50 yards or more.
Next, a word about exhaust systems, If you're using a tuned pipe, your engine will probably only be happy within a narrow RPM range. This complicates things a bit. If you're using any other sort of muffler, you can probably run the engine happily over a wipe RPM range.
Some answers:
The short answer, if you're running a muffler:
If you're using the same size engine your helicopter was des igned for, it doesn't matter what heli or blades or fuel or whatever... go with 1700 for starters. Really, I can just about guarantee that 1700 RPM will work just fine.
If you get much slower, the engine is probably out of its powerband. If you get much f aster and you may not be able to pull enough pitch to climb reasonably fast without losing head speed. 1700 is a safe place to be.
The short answer, if you're running a tuned pipe:
there is no short answer. You just have to find the right RPM range by tr ial and error, or by comparing notes with someone who is already using the same engine, tuned pipe, tuned pipe length, etc, etc.
The short answer, if you're running a monster motor:
If you've done something creative like stuffing an OS 50 into a Raptor 3 0, or YS80/OS90 into anything at all, then I don't know the "short answer" to this question. Go find someone using the same engine and gear ratio you're using, and see what they're doing. If you're running a monster motor and a tuned pipe, I salute you, bu t I can't help you. If you find something that works, do let me know, that sounds like a fun combination.
Medium answer for muffler systems:
It depends on what kind of flying you do. For precise hovering or scale flying, 1500 is a good place to start. Fo r cruising around, the usual range is 1600 -1750. For aggressive aerobatics, the usual range is 1750 -1850 for 60s and 1850 to 2000 for 30s.
Medium answer for tuned pipes:
You've got to find the RPM at which the tuned pipe resonates with the motor.
As you raise the throttle slowly at the start of a flight, you will probably notice a point at which the motor gains speed faster than you raise the stick - and it might even continue gaining speed if you hold the stick still or even back down a hair. This is ha ppening because the pipe tuning is starting to increase the motor's power. When the speed stabilizes, you have found the lowest speed at which the engine and pipe are likely to run cheerfully. Add around 10% to this RPM and the result is probably a good ta rget head speed. If you get a lot of overspeeding while flying around, that's the pipe's way to telling you that you're trying to run too slowly - step up the RPM a bit. If you get a lot of under speeding , you're probably either loading the engine way too much, or you're trying to run it too fast. Try changing your flying style and/or or reducing your rotor speed.
The long answer:
There are a few things to ponder when choosing a rotor speed. They are presented here in no particular order...
1. Lower head s peeds typically make for a less responsive helicopter. The collective, cyclic, and tail rotor controls will feel softer. The roll rate will be reduced. This is preferable - to a point - for precise hovering, especially for beginners and contest flyers. 2. Hi gher head speeds typically make for more a responsive helicopter in every way - more responsive collective, cyclic, and tail rotor control. This is preferable - to a point - for aerobatic flight. 3. Generally speaking, a higher head speed will require a smal ler collective pitch range. Conversely, a lower head speed will allow a greater pitch range. For example, full throttle might allow you to pull 9 degrees at 1750 RPM, or 10 degrees at 1600. 4. Higher head speeds waste power overcoming drag. Though you can ge nerate the same lift with less collective pitch, it will typically take more power to generate the same amount of lift at a higher head speed. The 10@1600 setup will probably climb faster than the 9@1750 setup. 5. In some cases, a higher head speed may allow the engine to generate more power, by virtue of the higher crankshaft speed and nature of the engine's power curve. In some cases, the increase in engine power may be greater than the increase in drag, allowing for a faster rate climb and higher top speed . In other cases, the increase in power may be smaller than the increase in drag, resulting in poorer performance.
The final point is most important because it's the least obvious. If engine power were the same across the RPM range, picking a head speed w ould be a simple matter of choosing a tradeoff between faster cyclic response (high RPM, lower allowable collective pitch) and faster top speed (lower RPM, greater allowable collective pitch).
But alas, it's not that simple. This point was most clearly il lustrated when during the first flights on a YS 61 ST2 that I just purchased. With a hovering head speed of only 1450 RPM, I was only able to pull about 8 degrees of collective pitch, and even then the engine was struggling and the rotor was slowing into n eighborhood of 1400 RPM. After raising the hovering RPM to 1650, I found that the engine was able to carry more than 8 degrees of collective pitch without slowing down.
How can you tell if the rotor is staying at a constant speed if the heli is in flight?
By ear, mostly, keeping the Doppler Effect in mind, if it sounds constant, it's close enough. At least, that works well enough for me. : -) Initially, I think it might be best to have someone else watch and listen when you're flying, so you can concentrat e on flying and they can concentrate on listening.
If you're picky and you have access to a tach, you can have someone watch your head speed in different situations, like hover, fast forward flight or vertical climb, inverted hover and climb, knife -edge s tall. I've done this a couple times; it's good for a little fine tuning.
You'll always lose speed if you push it hard enough, especially when you add cyclic stuff to the picture, but IMO if you have the same head speed in a hover and fast forward flight y ou're 80% of the way there.
What if you don't have a tach?
Set up your heli so you hover at 4 -5 degrees, and make sure you have 100% throttle at full stick. Make the pitch curve linear - something like -5 to +2.5 to +10, or -10, 0, +10. Listen to the hea d speed. Go to full stick (max throttle and collective). If it's slower when it's climbing, reduce your top -end pitch. If it's faster when it's climbing, increase your top -end pitch.
Having chosen and dialed in your head speed with climb out tests, adjust your hovering throttle percentages until you can hover with the same headspeed as your climb outs . From a hover, go to full stick. Did the head speed seem to change? If so, raise or lower your hovering head speed with the throttle curve - remember, you're done with the pitch curve now. You will get some overspeeding when you descend "elevator -style" with the rotor level. In a flight mode used mostly for upright flight (e.g. the -5, 0, +10 setup I mentioned earlier), you can tune this out by reducing the throttle values at or near low stick. If you're using a "3D" flight mode (e.g. -10, 0, +10), so far as I can tell, a governor or a well -tuned exhaust is the only way to solve this without creating bigger problems. A governor will help by backing off on the throttle as the engine attempts to over speed . A tuned pipe will help if your head speed is set near the top end of the pipe's tuned RPM, because increases in head speed will cause a decrease in horsepower.
Mixing cyclic to throttle
For my Concept SRX and OS32sx, I use 100% cyclic to throttle mixing. Yes, you read that right. One day I figured I'd add more and more mix until it started to overspeed during rolls, and then back off a little (sort a like dialing in gyro gain - you don't know you have enough un til you've seen too much). I never saw the overspeeding happen during aerobatics, so I just left it at 100%.
I DO see a little bit of overspeeding when I wiggle the cyclic stick in a hover, but it's no big deal. I'm also running a tuned pipe with that eng ine though - a muffler might allow enough overspeeding to be annoying.
For my Futura SE and YS61st2, I let the governor take care of the throttle for me, and I don't use any mixing for the throttle.
For my Concept SRX and OS32sx, I use the tuned pipe and cyclic -to -throttle mixing to get a consistent head speed.
The narrow powerband of a tuned pipe makes them work pretty well without a governor (or even without mixing, if you ask some folks). As the engine overspeeds, power drops off to keep the overspeed ing in check. If the 'normal' speed is on the high -rpm side of the curve, bogging the head speed down a bit will open up more power to keep the speed from dropping further.
Governors aren't perfect... Even with a governor, my Futura overspeeds in descents . The YS midrange is plenty rich, it's the idle that I can't get rich enough. Or rather, when I do set the low -end valve rich enough to stop overspeeding, the engine loads up at idle. I have mixed feelings about this engine. It's strong, but the mixture cu rve kind of ***** . At least mine does. Maybe I should try a new throttle barrel.
Anyhow, if you fly 3D without a governor or tuned pipe, you will benefit from cyclic ->throttle mixing. If you have a tuned pipe, you probably don't want a governor, but you will probably still benefit from mixing. Try 50% mixing. If it helps, keep it. If it doesn't, set it back. You've nothing to lose by trying it for yourself. Then draw your own conclusions.
Servo Speeds
There's a widespread (mis)conception that the throt tle servo should be really fast. I think this is bogus.
The way I figure things, the GV -1 servo doesn't have to be any faster than the collective or cyclic servos, since they are the ones that end up changing the rotor torque that the GV -1 has to respond to.
And besides, the throttle servo is going to be centered at around 65%, moving between 40% and 100%. That gives it about half as much distance to cover as the collective servo. So effectively the throttle servo is twice as fast as the rest of them to b egin with.
Tail rotor servos need to be extremely fast, but a) the tail rotor mostly just responds to collective and cyclic loads, and b) the tail rotor has a relatively small effect on engine load, and it's biggest demands are transient anyhow (starting/ stopping pirouettes, basically).
And, if you're not using a governor... no matter how fast your throttle servo is, it will never move faster than you ask it to. That is, it will never move faster than your thumb moves the throttle stick. There are people who suggest using a really fast throttle servo because then the throttle will 'lead' the collective, and this is why I think they're wrong. Throttle will only lead the collective if you're slamming the stick faster than the collective servo can move. How o ften does that happen? For my Futura, I'm using a non -digital throttle servo with .18 transit time and 40 oz/in torque, and it works just fine
Rotor head Dynamics 101
It seems that rotor dynamics get a little bit more complicated every time I tak e a good look at my rotor head and the associated linkages and levers. There are a lot of variables, a lot of interactions, and a lot of different results for seemingly simple changes.
Chapter One: what is the rotor head
The rotor head in most modern helicopters is a complex mechanism that turns swashplate movements into pitch changes in the main rotor blades and flybar paddles. Collective pitch change - chan ging the pitch of both blades together to make the helicopter climb and fall - is relatively straightforward. Cyclic pitch - changing the pitch of both blades is different directions at a specific rotor head orientation to make the helicopter pitch and rol l - is much more complex.
Notice the path of the linkages in the Futura SE rotor head pictured above. Start from the blade grip and working downward. The blade grip ends with a "mixing lever" from which two links extend downward. The link on the left side of the mixing lever (attached to the back of the mixing lever and thus partially obscured by it) extends down to the swashplate; this link is commonly referred to as the "direct link" since it provides the pilot with direct control over the blade pitch. O n flybar less helicopters, this is the only link between the swashplate and the rotor blade grip. The link on the right side of the mixing lever attaches to the flybar. We'll refer to this as the "flybar link" for the purpose of this discussion. The flybar 's pitch is also controlled by another set of links (sometimes called Hiller links), which extend downward from L -shaped arms. The Hiller links on the Futura SE are connected to the swashplate via a mechanism known as a "washout" or a "collective pitch co mpensator," depending who you ask. I'm fond of the latter myself, since I'm not sure what "washout" means and I think "collective pitch compensator" describes the mechanism perfectly. Its function is to translate swashplate tilt into flybar pitch, even as the swashplate slides up and down on the main shaft. In other words, it compensates for the swashplate's collective pitch movements.
Both the direct link and the flybar link influence the pitch of the main rotor blade. The mixing lever "mixes" the influen ce of each link and determines the resultant rotor blade pitch. The Futura SE rotor head above has a 1:1 mixing ratio and is not adjustable. Some helicopters, including the XCell series, Bergen Intrepid, and Concept 30s with Zeal upgrades, have adjustable mixing levers. This allows you to set the relative influence of the flybar links (flybar movements) and the direct links (swashplate movements).
Note that the design described above is not the only way to do things - while the Futura SE (and the XCell and Raptor and many other helicopters) use a sliding swashplate to control collective pitch, the Kyosho Concept (and some Kalt helicopters) uses a fixed swashplate that can only tilt. On these helicopters, the collective pitch is controlled by linkages that r un parallel to, and spin with, the main shaft. Though the changes the configuration of everything else between the swashplate and the blade grips as well, the resulting functionality is basically the same. Perhaps I'll take some pictures of my Concept's ro tor head and go into more detail here later.
Chapter Two: why is the flybar
The flybar serves two purposes:
1. turning servo motion into main blade cyclic pitc h changes 2. stabilizing the rotor disk against pitching and yawing motions
The flybar is free to move in two directions.
First, it can twist along its length, changing the pitch of the paddles mounted at the ends of the flybar. Flybar pitch is controlled by the cyclic servos, via the swashplate. When the one paddle's pitch is increased, the pitch of the opposite paddle increases. The swashplate "cycles" the flybar pitch - the pitch varies as the rotor head turns. For example, if you hold forward cyclic, th e flybar paddle pitch will be decreased on the left side of the helicopter, increased on the right side of the helicopter, and neutral when the flybar is aligned front -to -back (if you're looking at a counter -clockwise rotation helicopter, exchange the word s "increase" and "decrease"). As a result, this cyclic flybar pitch causes the flybar to deviate from its plane of rotation, just as main rotor cyclic pitch causes the main rotor to change its orientation.
Second the flybar can tilt, moving the flybar pad dles up and down. This tilting action is controlled by the gyroscopic effect of the flybar paddles, and by the aerodynamic effect of the flybar paddles, when they have pitch applied as described above. When the helicopter is at rest, both of these forces g o away, and the flybar is free to flop around.
The aerodynamic behaviors of the flybar and the main rotor blade grips, and the geometry of the linkages between the flybar and the main rotor blade grips, are designed to keep the main rotor and the flybar r otating in the same plane. If the flybar's plane of rotation changes, the flybar link and mixing lever cause corresponding changes in the pitch of the main blades as the rotor head turn. These pitch changes are proportional to the difference between the pl anes of rotation of the flybar and the main rotor grips, so they act to bring the main rotor blades into the same plane of rotation as the flybar, and vice versa.
In practice, this behavior has at least three obvious results:
1. When the pilot applies a til t to the swashplate, the flybar's cyclic pitch causes it to lean in the direction commanded by the pilot. The main rotor's cyclic pitch causes the main rotor to lean in the same direction. Watching my Futura SE's rotor as I give it quick stabs to cyclic, i t's quite clear that the flybar's orientation "leads" the main rotor's orientation. The flybar's orientation changes first, and the main rotor quickly catches up
2. When external forces conspire to change the helicopter's orientation against the pilot's wis hes, the flybar acts to damp these forces.
This can be demonstrated (dangerously) by holding onto an LMH while the rotors are spinning at flying speeds, and rolling the helicopter by hand with the cyclic centered. You should never actually attempt this of course, as it's very dangerous and you will put your eye out.
This can also be demonstrated (less dangerously) by comparing the fast forward flight characteristics of your helicopter with heavy and lighweight paddles fitted.
When the helicopter is in fa st forward flight, the advancing blade generates more lift than the retreating blade. Due to gyroscopic precession, this manifests itself 90 degrees later as a tendency to "pitch up." On most helicopters (the Lite Machines LMH series being the sole excepti on that I'm aware of), the flybar does not generate lift and is not so affected by the advancing/retreating differential.
Helicopters set up for novices or scale flight typically use heavy, gyroscopically stable flybars and/or mixing levers that favor the flybar link, and the "pitch up" tendency is negligible. On helicopters set up for aerobatic flight, lighter flybars and mixing levers that favor the direct link make the flybar less effective at countering the pitch -up tendency.
It has been suggested tha t the advancing/retreating lift differential that causes the main rotor blades to pitch up may in fact have the opposite effect on the flybar. The advancing flybar paddle is pushed downward by the oncoming air, and this further counters the tendency to pit ch up. I can only guess as to how effective this is in practice. Logically, one should be able to adjust flybar paddle size to create a helicopter that pitches down in forward flight, but I have yet to hear of anyone doing this.
Chapter Three: how do the variables
Much of the rotor system's complexity centers on the flybar.
The Holy Grail , I suppose, would be a system that gives maximum cyclic response (or at east, as high a roll rate as the pilot can handle) yet maximum stability as well, (one that stops rolling or pitching as soon as the swashplate is leveled).
The most obvious benefit of a highly stable system is that the helicopter should hover easily, with no tendency to drift or to change attitude without pilot input. A less obvious benefit (less, o bvious, until it goes away!) is that the helicopter exhibits less pitching up during high -speed flight. When I tweaked my setup for more roll rate and less stability, I was somewhat surprised at the tendency for the helicopter to want to slow down and clim b after I built up significant speed.
What follows is a work in progress that reflects my understanding of what's going on ?
I welcome your corrections, additions, and suggestions.
Flybar paddle mass This is probably the most commonly adjusted variable . Generally speaking, lighter paddles give strong cyclic response faster roll rates, and less stable hovering.
Flybar paddle area
A larger paddle area will make the flybar more responsive for a given flybar pitch change, and thus increase the cyclic re sponse.
Flybar paddle airfoil
This is one variable that I don't understand very well, as I haven't experimented with it.
Flybar length
A longer flybar should make the flybar deflect more with a given flybar pitch change, due to increased airspeed of paddles. Increased flybar length leads to increased flybar moment, like adding heavier paddles, but the end result is an increase in flybar effectiveness. I have experimented with an extremely long flybar setup (710mm JR flybar and Schluter Futura SE p addles) and found that flybar weights were necessary to tame the cyclic response.
Flybar link placement
This is the link that connects the flybar seesaw to the mixing levers, and the variable that inspired this web page.
Many of us tend to assume that the flybar enhances the pilots authority over the rotor disk, but this is not necessarily the case. In fact the flybar reduces the pilot's authority. Reducing the flybar's authority on the main blades will increase the roll rate and make the helicopter mo re sensitive in a hover.
Hiller lever length
A shorter Hiller lever should yield increased flybar pitch changes for a given swashplate angle. This should mean more cyclic response, with no change in stability. However, one must wonder when the flybar pa ddles begin to stall, causing more drag than useful leverage.
Rotor speed
Higher head speeds give more cyclic response due to increase air flow over the flybar paddles and main blades as well as more stabilization, due to increased gyroscopic effect of both the flybar and main rotor. This is desirable for aerobatic flight. However, an excessively high head speed can contribute to rotor head failure, so don't get too carried away.
Main blade moment
I would call this 'main blade mass,' but the distrib ution of the mass along the blade is critical. Greater moment (more mass, or center of mass closer to blade tip) yields increased stability (and better autorotation , but that's beside the point).
Tail Rotor Adjustment
In mid -June 1996, the helicopter mai ling list just about exploded with discussion (to put it politely) over how best to dial in one's tail rotor. One reason this is such a hot topic is that there are so many variables involved. Another is that tail rotor adjustments seeks to achieve two seem ingly incompatible goals: on one hand, we want the tail to 'lock in' and remain as steady as possible when hovering. On the other hand, we want the tail to be powerful enough to pirouette like a banshee in fast forward flight. We want to be able to do big high speed sideways loops with the tail sticking out... stable enough to keep the heli from yawing in mid -loop, yet strong enough to keep the tail from ' weathervane ' into place behind the canopy, thus straightening out the formerly sideways loop.
Variabl e Effect upon stability Effect upon authority positive negative As the gyro gain is increased, the With a "standard" gyro, as the tail rotor becomes more resistant gain is increased, the gyro to wind buffeting, changes in 'robs' the pilot's authority as a engine speed or main blade pitch, result of its attempt to keep th e and so on. This is the reason we heli from pirouetting too fast. Gyro gain use gyros in the first place. With a "heading hold" gyro, If the gyro gain is set too high, the there is no drawback to tail will wag back and forth, increased gain, unless you oscillating and overcompensating turn it up far enough to induce for itself. oscillation (wagging). negative As the servo arm length is increased, the effective gain o f the gyro is also increased, leading to the same problems noted under the gyro gain section.
With a standard gyro, the control will become touchier from the pilot's point of view for the same reason - small movements of the servo cause larger changes in tail positive rotor pitch. As the servo arm length is increased, the servo is able to With a heading hold gyro, the cause larger changes in the tail rotor pitch. With a standard Servo arm length control sensitivity is determined by the gyro itself so the difference gyro, this allows for faster 540 here is negligible. stalls, pirouettes, and the like. With a heading hold gyro, the Lengthening the servo arm will over overall effect is typically typically require a lower gain negligible. setting in the gyro, but the two will balance out and the overall stability will changed very little, if at all. Because the servo will be able to cause a greater tail rotor pitch change in a given time period, the servo is effectively made faster this way, which can effect a net increase in stability even t hough the electronic gain is reduced. negative As the area of the tail rotor is increased, the tail rotor's strength positive is increased. This causes gyro As the tail rotor area is Tail rotor diameter and/or inputs to be magnified as if the increased, the tail rotor is blade chord gyro gain had i ncreased. This also better able to force the causes pilot inputs to be helicopter to yaw, which allows magnified in the same way. Both for faster pirouettes and so on. factors contribute to a tail boom that doesn't want to sit still. Increasing the tail rotor diameter, like increasing the servo arm length, will require a corresponding reductio n in gyro gain. However, as with a longer servo arm and a reduced gain, the overall effect is usually a small increase in stability. negligible In theory, the vertical fin should negligible help keep the helicopter pointed The only practical purpose of straight ahead in forward flight. the vertical fin is to keep the Vertical tail fin area However, in my experience (flying tail rotor blades from with solid fins, skeletal fins, and contacting the ground in less - even no fin at all), the fin's effect is than -perfect landings. negligible. They just aren't large enough to matter. With a heading hold gyro, the transmitter ATV values determine the maximum pirouette rate of the helicopter. In conj uction with the exponential setting, they also determine the sensitivity of the rudder With a heading hold gyro, the transmitter control around center. ATV values determine the maximum pirouette rate of the helicopter. In With a standard gyro, more servo conjuction with the exponential setting, travel means more authority to yaw they also determine the sensitivity of the harder and faster. Because the gyro rudder control around center. will, in flight, reduce the servo throw Servo travel (using ATV ) (due to the rotation of the helicopter With a standard gyro, an in creased ATV itself), it is common to set the travel percentage will have a negative effect on volume of the rudder servo to go 20% preceived stability, as since smaller to 40% past the limits of the rudder control movements lead to more servo linkages. movement. This will allow you to stall the servo when testing on the bench, but unless you really overd o it, the servos won't hit their limits in flight unless you turn the gain down low enough to get blindingly fast pirouettes. positive, but insignificant A faster servo will allow you to positive enter pirouettes more rapidly A faster servo will allow the gyro (i.e. go from standstill to system to react more quickly to pirouette in l ess time), but... destabilizing forces such as The 0.1 second you save Servo speed torque, wi nd, and the like. Faster entering the pirouette isn't servo response means faster tail likely to make a noticeable rotor correction, which means difference. Moreover , the faster damping of undesired yaw. maximum rate of yaw (how fast the heli spins pirouettes) will not be affected at all.
Standard Gyro Setup Examples
Note that the following setup ideas predate the advent of heading hold gyros. They are retained here in order to assist in the setup of standard gyros only. If you are setting up a gyro for heading hold operation, follow the instructions provided by the gyro manufacture r. Gary Wright, a competitive helicopter flier of some note, shared some information on his standard -gyro tail rotor setup scheme with the heli -list. Gary suggested using smaller tail rotor blades with standard gyros because:
o you can raise the gyro gain without causing wagging o you can use a longer servo arm, again without causing wagging o you can overdrive the tail rotor servo further o it takes less power overall to cause the helicopter to yaw
Chief among his claimed advantages of the smaller tail rotor disk was a lessened "translational lift." The air flowing over the tail rotor disk at high forward speeds causes an increase in tail rotor strength, which can cause the heli to wag in forward flight. A smaller tail rotor will have an ameliorating effect.
He also believes in higher gyro gain (presumably made possible with the smaller tail rotor) and a smaller tail fin area. The higher gyro gain reduces the tail rotor strength, but I assume that the longer servo arm and even - more -overdriven rudder servo mak e up for this.
It seems to work for him; he came in second at a national event recently. Now, how did the first place guy set up his tail rotor?
Another heli -list member put it another way. Doug Adams suggested using the smallest tail rotor that will del iver "enough" authority [for pirouettes, 540s, and the like]. When using smaller tail rotors, it is key, he said, to get the maximum possible tail rotor pitch when in flight. This combination, he says, will allow the gyro to work better, will reduce transi tional lift (the natural tendency of the tail rotor to yaw the helicopter when in fast forward flight), and will reduce weathervane .
However, as of this weekend, I've pretty much stopped using the low r ate setting at all (I leave the aforementioned p-mix turned off). I found that I can do 540s even with the gyro gain set as high as possible without wagging the tail in forward flight. The yaw rate starts slow, but if I keep the rudder pushed all the way over, the yaw accelerates to a 540 -able rate. It loo ks kind of neat, too. :) With the rudder centered, the heli locks straight again nicely. I am surprised that you have enough gain to hover as stable as the gyro will let you and still have enough rudder authority to give you a good rate for a 540 ST. Very interesting...... is there a secret you aren't telling us about???
I'm not sure which part is the secret, but my setup is pretty straightforwa rd. Well, I guess the dual rate it.
o Concept 30 SRX with unmodified tail rotor o Futaba 153BB gyro, o S3001 servo, o ATV is set so that with dual rate at 100% I can't bind the linkage o I generally fly with the dual rate setting at 140% o gyro gain is just under 50%, probably 45% or so o The tail wags at 50% gain... o ...probably due to the length of the servo arm - it used to be at about 75% gain, without wagging, when I was using a small servo wheel on the rudder servo. It was wagging all over the place after I put the arm on, until I turned the gain down. I don't think I ever did 540s with that setup without using low gain (~40% at the time).
When talking about overdriving the rudder, people usually suggest something in the +20% area. +40% might be my 'secret.' It still doesn't pirouette anywhere near as fast as it can, so I'm not too worried about overdriving the linkage.
When doing range checks, I set the rudder back to the 100% rate so I can wiggle the rudder stick with impunity.
This might be part of the secret too:
The yaw rate starts slow, but if I keep the rudder pushed all the way over, the yaw accelerates to a 5 40 -able rate. Leave your heli in high gain, and try a 540 at something like a 45 degree angle (this way, if you don't make it all the way around, you won't lose too much altitudes (hopefully)). That's how I discovered the secret. It starts yawing at a ra te so slow it doesn't look like it will ever make 540 degrees. By the time it's gone 180, the rate is fast enough that a 540 looks possible. By the time it's gone 540, the rate looks fast enough that a 900 might not be out of the question, but I haven't tr ied that yet.
Maybe this only works with old -fashioned mechanical gyros and slow rudder servos. I guess it also helps to have lots of forward speed, to maximize the 'stall time.'
It's nice to be able to do 540s without adjusting the gyro. Last time I wen t flying, I set the gyro gain to channel 8 (this is the mixture channel on the 8UHx). Someone mentioned this idea on the list a while back, and I think it's pretty neat.
What was my 'high' gain is now my 'low' gain, since I never used the low gain setting anymore. High gain now means 'so high you can't do anything but hover.'
I've programmed it to be at low gain in idle -up, and extra -high gain in normal mode, for hovering. In normal mode, it switches to lower gain at full collective so I don't wag when I' m launching into forward flight.
It's a little bit more resistant to crosswinds now when I'm hovering, but that's all. Low gain is high enough for a stable hover anyhow, so high gain does not make a very pronounced difference...
Other heli fliers are en couraged to send their tail rotor schemes to the heli -list, to me directly, or to simply describe them below.
Servos and gyros and rotors, oh my!
Proper tail rotor setup is one of the most frequent topics on the h -list. It was complex enough when everyone was using honest -to -god gyroscopes, (little metal flywheels in little plastic boxes!). When heading hold gyros came out, the issue got twice as confusing.
And it's no wonder. Now you have to set up your gyro twice , once in heading hold mode and once in standard mode. And the setup for heading hold mode is dramatically different from everything you might have learned about standard gyros. Egads! What's a chopper mechanic to do?
Don’t panic
Gyro setup isn't that difficult, if you follow the instructions. H owever, instructions aren't famous for their universal comprehensibility and crystal clarity.
For most satisfactions, one is frequently wished to locate instructions proofreader, and with him replace one who can assemble sentences of your native country's most pleasing grammatical correctness.
I've created this web page to address some of the most common pitfalls of gyro setup. Though gyros come in varying shapes and sizes, and they all have their own quirks about them, some things are true for all of the m. If you follow the instructions here, you'll at least be flying. The various tips and tweaks for your particular gyro are beyond the scope of this document.
First, know this: When the gyro is in heading hold mode, the rudder servo does what the gyro tel ls it to do, not what the transmitter tells it to do. Most notably, the transmitter features that once controlled servo travel (adjustable travel volume (ATV), dual rates, etc), won't do squat. Why?
This has probably led to more botched heading hold gyro setups than any other factor. The instructions that came with the first heading hold gyro - the CSM 360 - were actually quite good, but I quickly lost c ount of the number of people who read their instructions, filtered everything through what they knew of standard gyros, set things up creatively, and then complained that their highly sought -after whiz -bang super gyro wasn't any better than their old 153BB . Don't get caught in this trap. Trust me. Heading hold gyros are weird. Follow these instructions to the letter.
Step One: Electrical Connections
1. Plug the gyro's "rudder input" lead to the receiver's rudder socket.
2. If the gyro has a remote gain lead, connect it to an unused channel on your receiver. For the simplest setup, this should be a channel with a two -position switch. If you want to get creative, more power to you , but you're on your own.
3. If the gyro's sensor is packaged separately from the gyro's "brain," connect the sensor to the brain in accordance with your gyro's instructions.
Step Two: Transmitter Setup
1. Set the rudder channel's ATVs to 100% 2. Set the gyro channel's ATVs to 50% 3. Set your rudder dual rates to 100% (high) and 50 % (low). 4. Adjust the rudder trim so that the rudder servo remains motionless while the gyro is in standard mode.
We'll refine these later. First, make sure everything is set correctly so far. Make sure that the rudder servo moves from side to side when you wiggle the rudder stick. Next, the figure out which gyro gain switch position is normal and hold heading . In normal mode, the gyro will always center itself when you center the rudder stick. In heading hold mode, the servo will act a bit more strangel y, lagging behind the rudder stick movements, not centering itself, etc. Why?
You may end up adjusting the rudder trim on your first flight. Set it to wherever it needs to be to keep the heli from yawing. After this the rudder servo will probably wander to one side of the other while the heli is sitting on the bench in heading hold mode. Why?
Step Three: Gyro Direction
Make sure that your gyro isn't reversed. Push the rudder stick to the left, and watch which way the tail rotor servo moves. Return the rudder stick to center. Pick up t he helicopter, and hold it with a finger or thumb atop the rudder servo horn. Yaw the helicopter to the right, as violently as you can (within reason of course). You should feel the rudder servo moving just as it did when you commanded left rudder. If it m oves the opposite direction instead, do not fly until you have reversed the gyro and completed this test successfully.
Step Four: Mechanical Setup
Let's get the mechanical setup right. We'll do this in heading hold mode. If the mechanical setup is correc t in heading hold mode, it will also be correct in standard mode. The reverse is not true - if you set everything up nicely in standard mode, it might be terribly wrong when you switch to heading hold mode. Why?
Some gyros have adjustable servo travel in heading hold mode, and some do not. No matter. Leave it where the factory set it, and we'll get back to it later if you want. For now, let's keep th ings simple.
When the gyro is in heading hold mode, the gyro has built -in travel limits. The servo may move all the way to these limits even with your ATVs and dual rates turned all the way down. We're going to set up the tail rotor control system within the parameters of this built -in travel limit. For starters, connect the rudder pushrod to the middle of the rudder servo arm - maybe 10mm away from the center of the servo's output shaft.
Put the gyro in HH mode, put the rudder to full left, hold it ther e, and observe the travel of the tail rotor pitch slider. Put the rudder to full right, hold it there, observe. If it's not hitting the limits on either side, move the rudder pushrod ball further out along the servo arm, or use a longer servo arm if you ru n out of room. If it's binding on both sides, move the ball closer to the output shaft, or use a shorter servo arm.
If it's hitting on one side but not the other, adjust the linkage length until its equal on each side - either binding equally hard, or lea ving an equal amount of unused travel.
Err on the side of caution - it should almost -but -absolutely -not -quite -bind on either side when you do this test. If moving the ball between two adjacent positions on the servo arm means binding on both sides or leav ing a sliver of unused travel on both sides, opt for the sliver of unused travel.
Oh, and with some helis (Futura SE, for one), you have a couple of different place to attach the rudder pushrod to the tail rotor bellcrank - these will have the same sort o f effect as changing the rudder servo arm length, so experiment a bit.
When you're done, you'll be able to move the rudder stick to either side, hold it there until the servo stops moving, and you'll observe that you'll have no binding on either side, or maybe just a sliver of unused tail rotor pitch travel remaining.
Once you get this set up, don't touch the mechanical setup again . People often suggest messing with the mechanical setup to tune out a slight bobble that might happen when switching between standard and heading hold modes. I've heard some gyro manuals even suggest it. I think that's a terrible idea. Don't. Why?"
Step Five: Tail Rotor Compensat ion
When in heading hold mode, you want no tail rotor compensation mixing going on (this is also commonly known as revolution (or revo) mixing). Turn off the mixes, or set them to 0% everywhere, depending on your radio.
When in standard mode, you want ta il rotor compensation mix percentages similar to those used with your previous gyro.
Due to the tremendous variety of radios out there today, I can't tell you how to make this happen. For this step, you're on your own. Just trust me when I tell you that y our tail rotor compensation mix must be doing nothing while you're in heading hold mode. Why?
Step Six: Set the gyro gain
For this step, you need to f ly the helicopter. Set the gyro to heading hold mode, disable your revo mixing, and hover.
Rule 1: If the gyro wags, turn the gain down until it stops Rule 2: If the gyro doesn't wag, turn the gain up until it starts to wag, and then refer to rule 1.
Se t the gyro to standard mode, with some revo mix if you like, and repeat.
Step Seven: Fine Tune the Rudder Trim
Skip this step if you have a Futaba 401, 502, 601, or anything more recent. You can probably skip this step if you have a Futaba GY501 too, but I'm not 100% certain.
For this step, you need to fly the helicopter. Set the gyro to heading hold mode, disable any revo mixing and lift into a hover. If the helicopter holds its heading, you're done. Go to the next step. If the helicopter drifts, adjust the rudder trim until the helicopter does not yaw. I like to point the helicopter directly away from myself and center the rudder. If the tail rotor wanders to one side or the other, add some trim and re -center it. If the tail rotor stays behind the chass is for 20 seconds or so, you're done.
You will probably never need to adjust the rudder trim again. If you do, you'll probably find that you soon need to re adjust it back to where you just put it.
Step Eight: Adjust the Tail Rotor Mixing
You may wish to set up a tail rotor mixing curve (or two or three) to make the heli easier to fly when the gyro is in standard mode. Or you may not. I almost never use standard mode these days, so I've taken to leaving all tail rotor mixing off, and just flying the tail myself (call it the "mental mixer") when I'm in standard mode.
This part works just like with regular gyros. Fly around, hover, climb, descent, and fiddle with the mixing percentages until the heli quits changing direction on you.
Just don't touch the ru dder trim.
That will mess up your heading hold performance. If you find yourself wanting to change the rudder trim, change the mix percentages instead. It will have the same effect, but without interfering with heading hold performance.
Step Nine: Adjust the Pirouette Rate
I suggest making these adjustments in heading hold mode. But that might just be because I fly in heading hold mode almost all the time. Maybe you should do this in whichever mode you plan to fly in most often.
First, use the dual rate s to get a couple of pirouette rates you're happy with.
For a long time, I used a "low" rate for normal flying, and a "high" rate for blindingly fast pirouetttes, just to spice up the occasional stall turn. Lately I've been using a "low" rate that's slow enough that I can hold full rudder and do pirouetting circuits - "high" rate is the normal -flying rate I described above, just fast enough for a clean 540.
Pick rates that suit you. Fiddle with them all you want later. It's just numbers; you can change th em all you want!
Most modern heading hold gyros will have equal pirouette rates in either direction. But, if not.... use the rudder channel ATVs get the pirouette rate equal on both sides. Select your low dual rate, and hold full left rudder. Then hold fu ll right rudder. If one direction seemed to pirouette faster than the other, adjust your ATVs until both directions feel the same. You may end up with something like 105% in one direction and 95% in the other direction. No worries. If it feels the same in flight, then go with it. Don't worry too much about the numbers.
Step Ten: Fly
Do all the stuff you normally do.
Step Eleven: Tinker
If you want a faster or slower pirouette rate, adjust the rudder channel ATVs or dual rates.
If you get unwanted yawin g in standard mode, adjust the tail rotor compensation mixing, just like you with a regular standard gyro.
Do not change the rudder pushrod length. You took great pains to set this precisely (step four). If you change it, you'll just end up binding the li nkages in one direction, and losing tail rotor authority in the other direction.
Do not change the rudder trim to "fix" a problem in standard mode. When you switch to heading hold mode, that trim change will manifest itself in reverse. Set your trim in he ading hold mode, and make standard mode adjustments with your tail rotor compensation mixing. Step Twelve: Get Serious (only if you want to)
Some gyros (most notably the CSM 360 and 540) work well with longer servo arm. If you put on a longer arm, you'll need to turn down the gyro's travel limiter - this is not the same as the transmitter's travel limiters (ATVs).
Some gyros have fun parameters like " look ahead " and "tracking" and "input delay" to play with. These are beyond the scope of this document. Why?
Some gyros work better with some mounting tapes or foams. Some don't seem to care much. Experiment all you want. Use the factory -supplied ma terial as a baseline.
A few words about drift
But let's make sure we're talking about the same kind of drift. You may (probably will) need to add a touch of rudder trim in order to get the heli to maintain a perfect hover with no manual rudder correction s. That's normal. Set your trim resolution to the finest setting possible just to be sure.
Drift means different things to different people, but the drift problem that indicates a bad HH gyro goes like this: You hover for 30 seconds and dial in the rudder trim for a perfect tail lock. You fly around for a couple minutes and find that you need to add a little bit of trim to get that lock back. Then, you fly around for a couple minutes and find that you need to add a little bit MORE trim to get that lock aga in. And so on. And then for your next flight you find you need to undo all that trim at the start of the flight, and add it back in over the course of the flight, just like last time. This is bad, and this indicates a defective gyro (or a telebee (cheap sh ot but how could I pass it up?)).
If you can make the gyro hold center for a whole flight just by making a small trim change at the start of a flight, then you've got a good gyor - leave the trim in that precise spot and don't let yourself touch the rudde r trim again!
But, if you have to constantly add trim during a flight, you got a bad one. Send it back and get a good one. You'll be glad you did.
I had a CSM 360 that drifted. I sent it back and got one that's perfect. If you need to add rudder trim ove r the course of the flight it's possible you just got a bad one.
If that's the case, I'd send it back.
Why?
Why don't the transmitters travel limiters and dual rates work like they used to?
In the old days of proportional -feedback (aka "standard") gyros , the rudder travel limiters and dual rates worked like they did for every other channel - they set the limits of the servo's travel range. With heading hold gyros, the transmitter doesn't tell the servo where to go. The transmitter just tells the gyro how fast you want the heli to yaw. The gyro then decides where to put the servo. In order heading hold gyros to work their magic, the gyro needs to work the servo for you. So the gyro needs to know what the servo's limits are.
Why does the servo behave so od dly when it's in heading hold mode?
It's trying to control the helicopter's yaw, but since its actions don't do anything hen the heli is on the bench, it gets confused and just tries harder - hence the tail rotor pitch slider wanders off to one extreme or the other. If you pick up the heli and yaw it like the gyro is trying to do, you can center the slider without touching the transmitter. It's kind of neat, try it some time.
Why doesn't it work if you set things up in standard mode first? See the note a bove about the travel limits. If you have the gyro in standard mode, the travel limits you see might be affected by the transmitters ATV and dual rate settings. You want to get those out of the picture while you set things up, so switch to heading hold mod e for the travel and linkage -length adjustments.
Why is it that, in heading hold mode, when I trim the rudder so that the servo holds still on the ground, the heli yaws in a hover? And when I trim the rudder so that the heli remains motionless in a hover, the rudder servo creeps off to one side when the helicopter is on the ground?
I honestly don't know. But I have observed this with every heading hold gyro I've seen so far.
Why am I so certain that the tail rotor mixing must be disabled when the gyro is in heading hold mode?
I've used three different heading -hold gyros for extensive 3D flying in two different helicopters. I've found this to be the case. The gyro is capable of adjusting itself to what revo mixing does. It notices that you're holding cent er stick and the helicopter is yawing, so it adds some 'trim' for you. This happens faster than you can see it, so basically what you have is built -in revo mixing that tunes itself automatically .
Why not play with the mechanical setup to get rid of a yaw twitch that happens when switching between standard and heading hold modes?
Because the mechanical setup must allow the tail rotor pitch slider to get full travel in order to make the fullest possible use of the available tail rotor thrust. The steps abov e will show you how to get full travel without binding. If, after you've set up the mechanical linkages for full travel without binding, you adjust the length of the tail rotor pushrod, guess what happens? You'll now be getting binding in one direction, an d in the other direction you'll no longer getting full tail rotor thrust.
Not having full thrust will give you poorer pirouette stops and poorer holding power in sideways flight.
Allowing the linkages to bind stands a very good chance of burning out the servo prematurely. This was less of an issue in the days of standard -mode gyros, because the servo would center itself if you let go of the stick, and would generally avoid full travel in flight. With heading hold gyros, the servo is apt to wander off to o ne side if you let go of the rudder control while the heli is on the ground. It will stay that way indefinitely. If the gyro's travel adjustments allow the linkages to bind, the servo will work itself to death.
Why not adjust the revo mixing while in HH m ode?
Because the gyro doesn't know revo mixing from rudder stick movements. It will interpret the revo mix as a command to yaw. This will cause your heli to yaw one direction or the other when you vary the collective. If you want the heli to stay on the s ame heading while the rudder is centered (trust me - you do), you need to leave the revo mixing inhibited, or set to zero at all points.
Why no suggestions about the more exotic parameters of the newer gyros?
Because I haven't had enough time to experime nt with them yet - I'm not quite sure what they do or how they work. Rest assured, when I know, I'll add more to this page.
Futaba's heading hold gyros have a parameter that Futaba calls "delay." Other gyros I've had (CSM, Arcamax) have called this same parameter "acceleration," rather than delay, but Futaba wanted to be different.* The biggest difference you'll see from adjusting the delay parameter comes when you're stopping fast pirouettes, or just giving quick stabs with the rudder stick. Set the de lay to zero, hover tail -in at eye level, and poke the rudder stick to each side, letting the stick 'snap' back to center as quickly as possible. With the delay set too low (and 0% is probably too low for most cases), you'll see a bounce when you center the rudder. The gyro tries to stop the yaw immediately, but the heli overshoots a little bit, and then snaps back into place. If the delay is way too low, you might see a little back -and -forth before it settles down. Turn up the delay until this bounce goe s away. Or start with lots of delay, and turn it down until you see bounce, then turn it back up a hair - sorta like you do with gain, but you're shooting for a lower number, rather than a higher number. With gyros that call this parameter by its proper na me ("acceleration") you'll be aiming for a higher number, just like with gain. The goal is to get the acceleration parameter as high as possible without causing the system to oscillate (bounce) when you start or stop a rapid yaw movement. Regular gain sho uld be set to stop the system from oscillating in a steady state (like hovering), but delay can be used to fine -tune the transitions between yawing and not yawing (or vice -versa). Best performance comes when you get both parameters dialed in. If you've be en running the delay at zero, you might try adding a little bit of gain after you raise the delay. I haven't noticed much difference here with my Futaba gyros, but my Arcamax PI Pro was able to run more gain after I turned down the acceleration a bit ("tur ned up the delay" in Futaba speak). I'm curious if other folks are able to run more gain after turning up the delay a bit. Theoretically I'm pretty sure you should be able to run a little bit more gain, but in practice the difference may be negligible. * That's kind of annoying, because acceleration is measured in degrees per second per second, so you have an objective number that you can work with and compare between gyros, even between gyros of different brands. Delay is expressed as a percentage of some arbitrary baselines , so it's completely useless as objective criteria - you can't compare it from one gyro to the next, even between two gyros from Futaba. Argh.
Carburetor Tuning
Setting the fuel/air mixture of a radio controlled helicopter's engine is often one of the most challenging - and frustrating - tasks that novices run into. Even experienced flyers are sometimes stumped by this one when they get an engine they're not familiar with. I don't have all the answers, but I've created this page in hop es that what I have learned will help others.
Symptoms of poor mixture settings include:
• Difficulty starting the engine • Difficulty maintaining a consistent idle • Difficulty transitioning from idle to hovering RPM • Excessive vibration (often mistaken for clutch or fan imbalance - and vice versa) • Unsteady tail in a hover (often mistaken for gyro trouble - and vice versa) • Difficulty transitioning from hover to fast forward flight • Low power • Intermittent power loss • Hovering RPM too high or too low (a gov ernor can hide this, but the problem will manifest itself elsewhere) • Short glow plug life • 'Hanging' onto high RPM after engaging throttle hold • Wagging in fast forward flight (due to vibration and/or excessive rotor RPM) • Engine quits in flight
Differen t symptoms will be more evident under different circumstances :
Starting and Idling
If the idle mixture is too rich, the engine will be difficult to start, and/or it will "load up" if left idling for more than a few seconds. You may also notice an excessi ve amount of fuel spraying from the exhaust.
The most reliable test for the idle mixture is to pinch the fuel line between your fingers, stopping fuel flow to the carburetor. If the idle mixture is too rich, it will idle even better for several seconds be fore revving up and dying. If the idle mixture is too lean, the engine will simply quit after just a couple seconds. If the idle mixture is right, the engine will idle normally for just a couple/few seconds before revving up and dying. It takes practice to recognize the difference between 'too rich' and 'just right' during the pinch test. However, if you find that the engine loads up after 10 seconds of idling (without restricting the fuel flow), and if pinching the line for a few seconds improves things, y ou're too rich. Hovering
If the hover mixture is too lean, the tail rotor will not hold still, possibly leading you to suspect gyro problems. In extreme cases (less common with modern gyros and tail rotor servos), the tail may swing as much as 90 degrees off heading. If the hover mixture is too rich, the head speed will be low and fuel consumption will be increased.
Listen to the exhaust sound when hovering. A proper mixture will simply drone, with no variation. A slightly rich mixture will go in and out of a "four -stroking" mode, resulting in an exhaust note that sometimes 'burbles,' for lack of a better word. An overly lean mixture will often cause the engine to switch to an 'overheated' mode, during with the exhaust sound becomes quiter and engine powe r drops off drastically. If you're overheating, these drops will become more and more frequent, and power will decline steadily. The oscillations into four -stroking tend to be very brief, lasting only a fraction of a second, while overheating causes a chan ge in the exhaust sound that lasts a second or more.
At first it may be easy to confuse the sounds of rich and lean mixtures. If you're not sure, it's best to assume it's too lean, and richen things up a bit. If the problem gets worse, at least you won't hurt anything this way. If the problem is reduced, you're on the right track.
You should also look at the smoke trail when you're hovering. It may take some time to get used to the amount of smoke produced by a particular engine/fuel combination, but with practice this can be a useful indicator.
Fast Forward Flight and Vertical Climbs
All of the symptoms described above will be evident in fast forward flight and in full -throttle vertical climbs, but they're more difficult to detect because the helicopter is further away (harder to see) and moving fast (harder to hear).
If the hovering mixture is reasonable, watch the smoke trail as you ease into full throttle. If you see less smoke, your high -end mixture is probably lean. If you see more smoke, your high -end mixture is probably rich.
You should note, however, that YS ST -1 and ST -2 engines running 30% nitro are notoriously intolerant of lean settings at full throttle. They tend to simply quit.
Autorotation
When you hit throttle hold for an autorotation - even just a 'baby auto' from a hover - the engine should settle down to a smooth idle after just a second or so. If the engine remains at a very high idle (often called "hanging"), your idle mixture is probably a bit on the lean side.
Descending
When d escending with the rotor disc level, the engine has very little load (possibly none at all, in fact) and thus it tends to overspeed. A lean midrange or low -end mixture will make the overspeeding problem even worse. The smoke trail provides additional evide nce - if the smoke disappears during level descents, you need to richen up your midrange and/or idle adjustment. This sort of problem typically goes hand -in -hand with the autorotation problems described above.
Weather
You will inevitably find that after painstakingly perfecting your mixture, it will be off a day or two later. This is because the mixture is determined not only by the amount of fuel flowing into the engine but also by the amount of air flowing into the engine. The fuel intake can be varied by adjusting the valves, and the air intake can be varied by changing the density of the air. Unfortunately, air density is generally out of your control, so you just have to adapt to it.
The air will be less dense on a hot day than on a cool day. In orde r to keep the air: fuel mixture consistent, you need to restrict the fuel low on hot days, and increase the fuel flow on cold days. It's important to bear in mind that the ideal mixture ratio does not change ; you're just varying the fuel flow to compensate for the variation in air density.
You'll find that the engine runs strongest on cold days, when the higher air density allows a great deal of air and fuel to be drawn into the carburetor. On hotter days, the low air density requires you to restrict the f uel flow, which reduces power somewhat.
Temperature Gauge
In addition to all this, I found it very helpful to have a temperature gauge mounted on my engine when I was getting started with RC helicopters. I've tried both the MIP and PC/RC gauges... The P C/RC gauge failed after just a few flights, and was very difficult to read on all but the cloudiest of days, I don't recommend it.
Unfortunately, even with the MIP gauge you have to land the helicopter to read the display safely, but I found that the engi ne cooled slowly enough that I could still get a pretty good idea of how hot it was running upstairs.
One thing you should know about on -board temperature gauges is that the reading depends as much on the placement of the temperature sensor as anything el se. It's probably not useful to compare figures with someone else's temperature gauge unless you've got the same type of sensor mounted in exactly the same place. With the MIP gauge and a lug -style sensor mounted on an exhausts bolt opposite the muffler, I found that temperatures around 260F yielded the best performance from my OS32sx.
Even if you don't know exactly what temperature to aim for, just having the gauge there gives you another piece of information to consider when making mixture adjustments. W ith some experimentation you'll notice correlations between different temperature ranges and different operating characteristics. With more experimentation you'll eventually find the temperature range in which the engine runs best. With a little practice you'll see the relationships between different engine behaviors and different temperatures, and as time goes by you'll find yourself using the gauge less and less as you become better able to recognize the other signs of an engine that's too rich or too lea n.
Valve Interaction
This has been one of the hardest things for me to understand, and that's partly because it's different for every engine. This is why the same approach to tuning one engine might not work so well when tuning another.
Most of our carb uretors have at least two and often three different values to adjust the fuel flow at different throttle ranges. That would be no problem in itself if it were obvious what the throttle range really was for each valve. Unfortunately, you don't get nice over lapping bell curves for each adjustment.
Typically one of the valves will impact all of the throttle range, or most of the throttle ranges above idle. This is the valve you should use to compensate for temperature changes, since a change in ambient air te mperature will impact the mixture across the entire throttle range.
It's helpful to know where each valve's effective range begins and ends. With the YS 61 ST2, for example, the "midrange" adjustment affects the mixture across the entire throttle range. T he "idle" adjustment affects only up to about 20%, at which point the midrange adjustment takes over rather abruptly.
For weeks I thought my idle was too rich because of the way the engine would load up and stumble when I transitioned from idle to a hover . It turned out the idle was way too lean - in order to get a proper hover I had set the midrange richer than was really appropriate. Fattening up the idle and leaning the midrange just a hair smoothed the transition and also cured me of an overspeeding pr oblem I had with descents.
With the OS 32 SX , it's common to drill an air bleed hole to lean out the idle (more on this later). The usual approach is to drill a very small hole in the front of the carb, in positioned so that when the engine reaches about half throttle, the throttle barrel closes off the hole. Intuition suggests that placement of the hole would be important, and that the engine would get noticeably richer when the hole is closed off. Closer examination suggests that neither is true. The eff ect of the air bleed hole is proportional to the ratio between size of the air bleed hole and the size of the regular throttle opening. This means that when you're at an idle, and the air bleed hole is 15% of the size of the regular throttle opening, the a ir bleed hole will lean out the mixture by roughly 15%. Conversely, when you're at half throttle, the air bleed hole is only 1% of the size of the throttle opening, so closing it off makes a negligible difference.
This is why I think the servo -actuated ai r-bleed cutoff featured in MHT a while back is unnecessary. You don't need to close off the air bleed to get a rich midrange - the air bleed simply becomes irrelevant by the time the throttle is halfway open. My own Concept works well enough without a serv o controlling the mixture, and I know I'm not alone in this.
Carburetors That Suck
Every carburetor sucks. The suck fuel in from one side, they suck air in from another side, and the blow a mixture into the engine. But, some carburetors also really don't work very well. This is the most maddening thing, as there may be no combination of valve adjustments that gives you a proper mixture at idle, hover, and full throttle.
Consider the OS 32sx for example. It's got an idle adjustment and a high -speed (full throttle) adjustment. And yet, when tuned for easy starting and reliable idling, plus optimum full -throttle performance, the midrange is lean and the helicopter behaves like crap in a hover. So what do you do if you want to richen the midrange?
If you ric hen up the top end, you get a very nice midrange mixture, but full -throttle performance will suffer (see above i.e. valve interaction). If you richen up the bottom end instead, you can get a nice midrange but the engine will be troublesome to start and dif ficult to idle for extended periods. You're screwed either way.
The solution here is to drill a small "air bleed" hole in the carburetor (link to a diagram coming soon...). Now you can "richen" the low -end valve until you get a satisfactory hover, and yet the air bleed will keep the idle lean enough for to quick starts and prolonged idling.
The throttle barrel (the carburetor's main moving part) that came with my YS ST -1 was poorly machined, and had a rich spot around 3/4 throttle that could not be dialed out with the main needle valve or the high -end valve. When transitioning from hover to fast forward flight, the engine would briefly lug down and belch smoke at twice the normal rate. In this case, the only solution was to replace the throttle barrel with a new one. Fortunately, the first replacement barrel I tried had a properly -shaped fuel passage and yielded a consistent mixture from idle to full throttle.
Dealing with a rich idle
Sometimes, a rich idle is difficult to avoid. Before drilling out my OS 32 SX carb, I had to deal with it on a regular basis. I learned a couple things from friends that make it somewhat easier to manage.
First, before attempting to start the engine, take off the glow plug, go to full throttle, and spin the crankshaft for a several seconds. This clears residual fuel from the carburetor and crankcase. Remember to bring the throttle back to an idle before you put the glow plug igniter back on!
Second, hold the transmitter in your left hand, with your thumb over the throttle gi mbals . This way you can carry the helicopter in your right hand while still working the throttle to keep the engine from sputtering out.
Third, pinch the fuel line periodically to lean the mixture. This is especially useful when the heli is on the bench o r on the ground, and you can pinch with one hand while holding the transmitter and working the throttle with the other hand.
It takes practice to be able to tune an engine by ear. I've been at this for almost five seasons, and I still don't always get it right the first time when someone comes to me with an engine problem. Hopefully what I've written here will help you get thing hang of things just a little bit more quickly.
Important Notice It has come to my attention that the radio/gyro setup detailed below does not work well when the CSM ICG -360 is used with the 8U's PCM mode . Plugging the gyro gain lead into channel five works is much better. I have not yet tested this setup technique with the ICG -360 and FM/PPM mode, so I can't say whether that works or not. It does seem to work will with the Futaba GY -501 and FM/PPM, and with the Arcamax PI Pro/Interface and PCM, so I suspect that it's the specific combination of the ICG -360 and PCM that has trouble.
All I know for certain right now is that when usi ng this setup with the 148DP receiver , the gyro did not work at its best. It was prone to over -rotating at the end of fast pirouettes, and to occasional weathervane during fast backwards flight. These symptoms went away when I connected the CSM's gain lead to channel 5. Two people have reported similar problems, and that the problems went away when channel 5 was used to control the gyro gain.
It has been suggested to me that the 7th and 8th channels of Futaba PCM receivers are not updated at the same rate as channels 1 through 6, but I have not been able to verify this myself yet. I suspect that the ICG -360 may "expect" the gain pulse to come right after the rudder pulse, and the delay introduced by moving the gain from channel 5 to channel 8 might be just enough to confuse it.
Background
Or , what's the big deal?
The CSM gyro is a big step forward in model helicopter technology, but it brings a bit of additional complexity to the setup process. First there's the fact that the gyro has two different modes o f operation; then there's the fact that it uses a single auxiliary channel to set the gain and the mode of operation; then there's the fact that in standard mode the CSM gyro requires the same sort of tail rotor compensation mixing as any other high -end pi ezo gyro while in heading hold mode it works best with all tail rotor mixing turn off completely.
Many people prefer to fly with the CSM in heading hold mode all the time, but I'm not one of them. It seems to me that the CSM acts weird when spooling up in heading hold mode. The heli will yaw before it lifts off, which gives me the creeps, especially on uneven ground. Standard gyro also tend to allow some yaw during spool -up of course, but I've been flying with a standard gyro for some time now and I've lea rned to compensate with the rudder control so it's no big deal.
For a while I had the CSM's aux channel hooked up to the 8U's gyro channel. This allowed me to switch gyro modes easily. Since tail rotor mixing on the 8U is programmed on a per -flight -mode b asis and cannot be turned on and off with a free switch, I wound up having to toggle two switches to switch the revo mixing off and enter heading hold mode on the gyro. This was tedious and error -prone.
The solution I found was to use channel 8 to control the gyro gain and flight mode. The 8U has two built -in 5-point mixes that operate channel 8 as a function of the throttle stick position; one curve is active in normal mode and the other curve is active in both idle -up modes, which turns out to be more th an adequate for solving the gyro control problem.
And, for what it's worth, I don't think the built -in mixes are going to be particularly useful for controlling a carburetor mixture as Futaba apparently intended. A proper fuel control circuit would mix fr om the throttle servo position, not the left stick position. With different throttle curves in idle -up -one and idle -up -two, there's no possible way to get the right mixture control in both modes.
Also note that channel 8 goes to 100% (or 0%, depending on the reverse switch) when you activate throttle hold. Unless you can achieve the proper fuel/air mixture at idle with the mixture servo set to 100% (or 0%), you're going to be "practicing" autorotation with an unhealthy engine. Practice might then become re ality in short order, which sort of defeats the purpose of practicing, don't you think?
The idea behind my setup is to get the CSM to act like a standard gyro when the transmitter is set for the normal flight mode, and get the CSM to act like a heading ho ld gyro when the transmitter is set for the idle -up (stunt) flight modes. Tail rotor mixing for normal mode would be the same as for any other high -end piezo gyro, whereas tail rotor mixing for the idle -up flight modes would be set to zero at all points. Implementation
Or , how do you do that?
First of all, connect the gyro's gain wire to channel eight on the receiver. Set the "TH ->NDL" curves to 0% at all five points in normal mode, and to 100% at all five points in idle -up. Use the channel 8 ATVs to adjus t the actual gain in each mode, just as if you were using a two -position switch to control the gyro gain.
Because of the undocumented channel -8 / throttle -hold behavior described above, you get standard gyro behavior when you activate throttle hold, no ma tter which position the flight modes switch is in.
If you'd rather have heading -hold gyro action in throttle hold, reverse channel 8, and set the TH ->NDL curve to 100% at all five points in normal mode and 0% at all five points in idle -up.
Verify everyth ing on the bench before you fly, of course. This rule holds true for any major setup change. Go into normal mode and make sure that the gyro acts like a standard gyro. Select an idle -up flight mode and make sure the gyro acts like a heading -hold gyro. Hit throttle hold and make sure the gyro acts like you expect it to. Set the channel 8 ATVs to reasonable values (50% if you're setting the CSM up for the first time, otherwise use the values you had been using for whatever other channel you had the gyro conne cted to). Make sure you have a reasonable tail rotor mixing curve in normal mode, and make sure you have no tail rotor mixing at all in either of the idle -up flight modes (zero at all five points in both curves).
The Big Picture
Or , how does it all fit to gether?
When I started thinking about setting up the CSM, I would have preferred a way to toggle gyro modes and enable/disable revo mixing with one switch in any flight mode. As far as I can tell, the only way to enable/disable revo mixing on the 8U is thr ough the front -panel programming buttons, which isn't something I want to mess with in the air.
The "solution" I came up with turned out to be less flexible but - my personal preference of course - more con venient. Standard gyro behavior is spooling up th e blades (in normal mode) and heading hold gyro behavior for everything else (idle -ups). One switch, no brains required, I like that. :)
Flight modes on my Futura SE are set up as follows:
Flight mode Pitch curve Throttle curve Gyro mode The top four points of the throttle curve linear, with half negative pitch at the are set for a constant head speed of idle -up -zer o bottom and full positive pitch at the top. standard 1700 RPM. The bottom point is set for The heli hovers just under 3/4 stick. a smooth idle.
linear, with half negative pitch at the all five points of the throttle curve are idle -up -one bottom and full positive pitch at the top. set for a constant head speed of 1700 heading hold The heli hovers just under 3/4 stick. RPM.
linear, with full negative pitch at the all five points of the throttle curve are bottom and full positive pitch at the top. idle -up -two set for a constant head speed of 1700 headin g hold The heli hovers at about 3/4 stick upright RPM. and 1/4 stick inverted
I use normal mode (idle -up -zero) for starting the engine, spooling up the blades, and recovering head speed after an auto. With the similar pitch and throttle curves, I can switch into idle -up -one at any time after the blades come up to speed, wi th no visible effect. Idle -up -one is what I use for hovering stuff and purely upright flight. Idle -up -two is where I spend 90% of time, as it allows all sorts of aerobatic fun. The bottom line is that I haven't had to change my flying habits with this gyr o setup. I still lift off in normal mode, I still fly with the same idle -up modes, and I still have only one switch to think about. That's good, because when the heli is airborne I don't want to have to think about anything else...
Thoughts on Radio Setu p
For a while when I was using non -heading -hold gyros, I moved Gyro sensitivity to channel 7 which uses a 3-position switch on the front of the transmitter. In the bottom position, the gyro is set to low gain for pirouettes and the like; in the top positi on, it's set to high gain for hovering; in the middle position, it activates a rudder -to - gyro programmable mix which allows for fast pirouettes and 540 - 900 - 1080+ stall turns.
I have also been using channel 8 to control the gyro gain. This is really ha ndy when dialing in a new piezo for the first few flights, since you can tweak the gain quickly using the knob on the front of the transmitter.
The 8U transmitter includes a pair of dedicated 5 -point mixers originally intended for control of a remote need le valve. The master 'channel' is the throttle stick position, the slave is channel 8, and there are separate curves for normal and idle -up flight modes. If you hook up your gyro gain to channel 8, you can have a high gain in hover, and a slightly reduced gain in idle up to keep it from wagging in fast forward flight. That makes for one less switch to flip while keeping the highest possible gain at all times, which appeals to me.
The 8U allows you to assign dual rate functions to different switches, so I p ut both aileron and elevator rates on the "A" switch (rather than A and D). This allows me to adjust the entire cyclic response at once, which suits the way I think of things. This also frees up the "D" switch for other things...
If you've given your heli copter a new engine, or new blades, you might be wondering how much pitch is appropriate. If you have a spare p -mix, you can set up something 'dual rates' for your collective. This lets you try two different pitch ranges in each of the flight modes, which I find helpful when evaluating pitch < -> RPM tradeoffs.
PMIX -2: Channels: PIT -> PIT Percentages: +20 / +20 (for starters, use more or less as you please) Turn off all the mixing options; link off, etc Assign the mix to switch D
When you're satisfied with a pitch range, it's probably best to either disable the mix or set the ATVs to give you the range you want, or set things up so that the 'low' rate is what you fly with 90% of the time and the 'high' rate is just extra pitch for drag racing or whatev er.
In my opinion, flying around on 'high' rates is somewhere between a potential annoyance and a potential disaster. The other day I was wondering why my heli wasn't performing, and it turned out I had the collective on the 'low' rate... annoying. Had I starting doing low tumbles at the start of a flight, it might have been enough to cause a crash. On the other hand, if you normally use 'low' rates and accidentally hit 'high' rates, you'll be more responsive and thus more able to recover from the surprise .
Your mileage may vary, but that's my take on things.
Got drill?
Roughly three years after this web page was created, OS revised the OS32sx carburetor. The newer carbs are rumored to have solved the rich idle / lean midrange problem entirely. However, if you have one of the earlier models (not unlikely, considering they were in production for about four years before OS to ok action to fix this problem), this following information might be useful to you.
Standard disclaimer: all tests, observations, and a djustments should be done when the engine is in its normal operating temperature range.
Setting the low -end mixture You need the low -end mix to be very rich in order to get a decent midrange and top end. Unfortunately, the engine can be a bear to star t when it's tuned 'right.' Basically, you should set it as rich as possible. This means that after then engine has warmed, if you idle for a while it wil sputter a lot when you try to run it up again. It will die if you just punch it, so you have to be car eful.
OS 32 SX mixture peculiarities
The OS 32sx midrange is a bit lean as compared to the rest of the throttle range. It has been suggested that, when learning to hover, the high needle should be set a bit rich to compensate for this. For more adventu rous flight, set the low needle rich; this will allow the high needle to be leaned correspondingly, for better top -end performance.
With the careful use of a very small drill bit and instructions from Doug Adams, the lean midrange / rich idle problems can be cured.
Starting
Due to the rich low end, this is more trouble than it really should be. I find that it starts better if I kill it by pinching off the fuel line rather than simple cutting the throttle all the way off. This effectively leans the mixtu re the next time you turn it over.
If you're having a tough time starting it, get a friend to pinch off the fuel line right at the carb while you turn it over. Instruct the pincer to let the fuel flow again as soon as the engine fires, lest the engine sta rve and die again. It will want to run faster for a moment until the mixture is restored, so be ready to modulate the throttle accordingly.
If the engine is cold, it will probably die as soon as you take off the glow driver. If it doesn't die, you're prob ably too lean and asking for trouble (BeenThere And DoneThat). Before you take off the glow driver, put the heli on the ground and run up to 1/3 throttle or so for a little bit - practice will tell you how long you need to do this. Some guys around here wi ll hover up and down a couple times. No real harm in doing this too long, but if you pull the glow driver off too soon, the engine is likely to die.
Glow plugs
From Doug Adams: Glow plugs are cheap, try a new one. If there's no change, then the old one is usable.
He's got a point, and it seems like something to keep in mind when looking for glow plug wear.
Drill that carb!
Check this out: Here's a quote from Doug Adams, who I understand developed the mod: I've tried a couple of different air bleeds. So far the best one is described below: ======| ()< -.055" | drilled square to the body. | OOOOOOOO SSSSSSSS | | OO OO SS SS | | OO OO SS | | OO OO SS | | OO OO SSSSSSSS |<-Raised Rectangular Boss on Carb | OO OO SS | | OO OO SS | | OO OO SS SS | | OOOOOOOO SSSSSSS S | | | ======
The air bleed is centered above the "S" and is tangent to the top of the "S". It doesn't overlap the "S". Problem is, the S on my carb doesn't look quite like the S on hi s artwork. It's more italic, like: (x) SSSSS SSSSS SSS SSSSS SSS SSS SSSSSSSSSSSSSSS SSSS SSSS SSS SSSS SSSSSSSS
Well, that's kind of lop -sided... Drill in position (x), .055"
This will increase the amount of air going into the carb at low throttle settings, thus leaning the idle a great deal. Compensate by richening the low -end mixture valve. Presto: a reasonable idle mixture (so you can stat it) AND a reasonable midrange mix ture (so you can hover smoothly).
Vibratory Annoyances
Vibration is the enemy. It foams fuel, confuses gyros, cracks solder joints, cracks metal and plastic frame components, and it looks bad too. Every drive train component, from the piston to the rotor blades, is a potential source of vibration, so figuring out what's shaking your helicopter can be a monumental undertaking.
It can help to consider the frequency of the vibration, and then consider what parts of the helicopter are spinning at speeds that would produce vibrations of that frequency...
Frequency Source Destination
High 200 -300 Hz High frequency vibrations usually emanate from the beginning High frequency vibrations often (12,000 - of the drivetrain, where things are spinning fastest. This means cause a "blurring" of the 18,000 RPM everything from the piston to the pinion, and the cooling fan is horizontal and vertical tail at the a common culprit. feathers, and foaming of the fuel. crankshaft)
Watch the end of the tail boom. If Medium The tail rotor spins at about half the speed of the engine. The it's shaking differently from the 6000 - drivetrain is probably pretty well balanced, but a bent tail rotor rest of the heli copter, something 9000Hz output shaft or tail rotor hub can cause plenty of trouble. is probably amiss back there.
Major imbalances will not go The main rotor is the slowest -turning thing on the helicopter. unnoticed. I've seen a helicopter Low It's also the heaviest spinning part, and thus it's the one with that couldn't even get the main 20 -35Hz the most obvious symptoms when it isn't perfectly balanced. rotor up to speed before putting (Rotor head The blades must be matched, and must track perfectly; the Middle Eastern bellydancers to RPM ÷ 60) flybar must balance, and the paddles must be parallel not only shame with its gyrations. Minor to each other but to the swashplate as well. imbalances will be evidenced by shaking skids and canopy ears.
Kyosho Concepts are especially prone to this, bu t it's not You'll see a very distinctive slow Ultra -Low unheard -of in other helis. I don't fully understand this myself, wobble of the e ntire helicopter, 2-5 Hz but it's believed to be a resonance of the feathering spindle best described as "the hula dampers. A higher head speed (1700 RPM or so) will usually dance." cure it.
Here's a checklist, sorted by vibration frequency:
High cooling fan run out cooling fan balance engine bearings engine mixture Medium tail rotor blades tail rotor output shaft tail rotor hub tail rotor drive shaft Low main blades main shaft flybar weights/paddles blade axle
More food for thought
Any time a bearing goes bad, it becomes a potential source of vibration. The speed at which the bearing turns will not necessarily determine th e frequency of the vibration, which’s makes tracking down a bad bearing time -consuming process.
Curtis Youngblood suggests placing tail drive shaft supports un evenly along the shaft. This way each section of the shaft oscillates at a different frequency, which in turn keeps a vibration in one section from inducing vibrations in adjacent sections, which in turn keeps overall vibration levels down.
Boom supports are susceptible to vibration, and two or three different manufacturers will be happy to sell you a boom support brace that brings them some additional rigidity.
Got more ideas? Use the form below to add them to this page.
In late August 1996, the heli mailing list fairly exploded with discussion (to put it mildly) about whether or not blades could be balanced properly without having identical weights and identically placed centers of gravity. It started with a suggestion that if blades are balanced on a see -saw arrangement, their moments will be the same (nobody disagreed with that assertion) and if their moments are the same, the centrifugal forces they exert on the rotor head will also be the way (this is where we disagreed).
One camp firmly believed that the only way to achieve a truly balanced rotor was to ensure that the two blades The other camp was equally firm in their beli ef that the weigh exact ly the same and the two blades' centers of centers of gravity and weights need not be identical, but gravity at exactly the same difference from the rotor must only result in the same moment when balanced in head (or from the mounting bolt, really). It was see -saw fashion. impossible to balance the rotor system otherwise, they claimed.
When the dust settled, some of the first camps were convinced that, surprisingly enough, it is possible for a roto r system to be balanced without using blades whose masses and CG's were truly identical, or even remotely close!
The forces that act on a seesaw are 'moments.' Moment is equal to the product of mass and distance (radius) from the center of rotation:
Mome nt = M x R The forces that act on a rotating rotor head are centrifugal forces. (some prefer to use the term centripetal, which is a bit more to the point but boils down to effectively same thing). This force is equal to the product of the mass and the squ are of velocity, divided by the radius of the center of mass:
Central {fugal petal } force: M x V x V / R
Velocity is distance over time, and in this case distance is the product of two, pi, and radius.
Velocity = 2 x pi x R / T
The question then is - c an the equation for centrixxxx force be reduced to the equation for moment? The answer is yes. I'm now kicking myself for throwing away the proof, but I do have a counterexample below. Consider a 10 gram blade with a CG 1 centimeter from the root, and a 1 gram blade with CG 10 centimeters from the root. It's trivial to prove that their moments are the same: 10 x 1 is equal to 1 x 10. But will they exert the same centrifugal force on the rotor head?
F = M x V x V / R
F = M x (D/T) x (D/T) / R
F = M x (2 x pi x R / T) x (2 x pi x R / T) / R
So now we substitute real numbers into each equation... T has been set to 1 for simplicity.
Blade 1: m = 10 grams, r = 1 centimeter, v = 2 x pi x 1 Blade 2: m = 1 gram, r = 10 centimeters, v = 2 x pi x 10
F1 = 10 g x (2 x pi x 1 ) x (2 x pi x 1 ) / 1 F2 = 1g x (2 x pi x 10) x (2 x pi x 10) / 10
Divide by (2 x pi) x (2 x pi) to get:
F1 = 10g x 1 x 1 / 1 F2 = 1g x 10 x 10 / 10
Multiply to get:
F1 = 10g x 1 / 1cm F2 = 1g x 100 / 10cm
Divide to get:
F1 = 10g / 1c m (note that this looks a lot like the equation for moment) F2 = 100g / 10cm (that is definitely not a coincidence, I assure you!)
Reduce the fraction in the second equation to get:
F1 = 10g / 1cm F2 = 10g / 1cm
And note that:
F1 = F2
Myths
Hu mans use only ten percent of their brains. This may be true of certain politicians, but when's the last time you heard something like, "he got shot in the head, but fortunately it missed the 10% of his brain that he actually uses?"
It's always best to use a higher gyro gain percentage.
You cannot compare the gain percentage you see on one helicopter with the gain percentage you see on another helicopter. A shorter rudder servo arm will allow you to use a higher gain percentage, but you might actually get poorer performance . A larger tail rotor will require you to use less gyro gain, but you might actually get better performance. Even if you have two helicopters set up identically in every way, if they have different gyros the gain percentages will pro bably be different.
Ask yourself - if you gyro gain is at 64%, that's 64% of what? There is no standard unit of gyro gain. It's not measured in inches, pounds, or pints (nor meters, grams, or liters). It's a measurement of how much the tail rotor thrust c hanges when the gyro sensor rotates at a given rate. When you factor in different servo arm lengths, different tail rotor bellcrank dimensions, different tail rotor blade grip dimensions, and different tail rotor blade dimensions, it's clear that the perce ntage on your screen doesn't mean much. And what's more, every gyro manufacturer has a different idea of how much servo movement you get at 100% gain in the first place.
Just turn the gain up 'til the helicopter wags, then turn it down a hair, and don't c oncern yourself with the number you end up with.
You should hover with the throttle at half -stick. I f your pitch range is 0 to 10 degrees, this makes sense. If your pitch range is -4 to +10 degrees, don't use +5 at half stick. The bottom half of the sti ck will give you a range of -4 to +5, and the top half of the stick will give you a range of +5 to +10. It will work, but it could work better. The problem is that the same movement of the collective stick will cause different amounts of pitch change, depe nding where the collective happens to be. The collective will feel mushy and insensitive while you're climbing, but twitchy and oversensitive while you're descending.
You'll get a consistent collective "feel" if you use a linear pitch curve. For a pitch r ange of -4 to +10, set half -stick to be +3 degrees. You'll end up hovering a little over half stick. So be it! There is nothing magical about half -stick.
The throttle servo should "lead" the collective.
Short flybars give you faster rolls
I've heard t his so many times I'm starting to believe it. Well, not believe it, but at least wonder if there's some way this could be possible. But I've run three different flybar lengths on my Futura SE, and in my experience, longer flybars have always caused faster rolls.
A longer flybar means increased paddle airspeed (which should speed rolls) and increased paddle leverage (which should speed rolls) and increased gyroscopic forces (which should slow rolls). Two of those cancel out, but you still get a positive cor relation between flybar lengths and roll rate, and that is what I have observed. Several people have claimed otherwise, and I wonder what's going on. It definitely does not match my experience.
Header tanks solve mixture problems
As long as there's fuel in the main tank, the header tank is just a wide spot in the fuel line. You might think that if you mount it up high, it will make the mixture richer, because fuel will 'flow downhill' to the carb... but you have to remember that the carburetor still as t o 'suck' fuel uphill as the fuel moves from the main tank up to the header tank. In the end, it doesn't matter. I moved the header tank on my Concept 30 SRX back and forth between positions well above and well below the carburetor, and it made no differenc e at all. Header tank location will make a difference when the main tank is empty, but that's only going to be the case for the last 30 seconds of your flight.
The sole function of a header tank is to trap air bubbles that find their way into the fuel li ne from the main tank. Without a header tank, those bubbles will go straight to the carburetor, where they will lean out your mixture and possible even put the fire out. With a header tank, the bubble gets trapped in the header, and the engine continues to receive a steady flow of pure unadulterated fuel.
Thoughts on throttle servos People periodically ask if the model XXXX(X) servos is adequate for use as a throttle servo. Chances are, the answer is yes, no matter what the Xs happen to be. Here's my thin king:
You don't need much torque. The throttle servo is only going to be working the carburetor. Grab the throttle arm with your fingers and give it a wiggle. It's probably the most free -moving control on the helicopter, unless you've done a stellar job setting up your tail rotor linkages. Torque is no big deal. You don't need much speed
There's a common (mis)conception that the throttle servo needs to be at least as fast as the collective servo. Some people go as far as to suggest that the throttle s hould be faster than the collective so that it will 'lead' the collective. These ideas don't hold up to close scrutiny. The collective will only 'outrun' the throttle servo if you're slamming the stick up and down faster than the throttle servo can keep u p. The throttle servo will only 'lead' the collective if you're slamming the stick up and down faster than the collective servo can keep up. In normal flying, the collective is moves smoothly and gradually from top to bottom, at a speed that's pretty much in sync with the helicopter's roll rate. Neither servo is being asked to move faster than it's capable of moving, so both servos are always right where they need to be. The servo will be under great vibration
Possibly, should not more than any other ser vo in the helicopter. The only thing that would cause the throttle servo to get more vibration than the rest of the servos is the throttle linkage. If you've got ball joints at each end of the throttle linkage, this is probably nothing to worry about. Side -to -side and up - down movements of the engine will just cause the ball joints to change their angles; they won't be transmitted to the servo. Any engine movements in a direction parallel to the linkage itself will be soaked up by the rotation of the throttl e barrel. The remaining vibrations will be coming from the chassis itself - just like the rest of the servos. So, in the end, it doesn't make much difference. My Concept has had a Futaba 3001 throttle servo for about four years. I just bought my Bergen In trepid 3D, and bought another 3001 for its throttle. My Futura has the nicest throttle servo - same torque as the 3001, but a speed of .17 instead of .22 - and I think I spent more than I should have!
Field Tips
Handy things to make life easier before and between flights:
Range check!
For some reason, helicopter flyers seem to do this a lot less consistently than airplane flyers. Perhaps it's because we tend to fly closer. When you consider the increased potential for RFI with all the metal and carbon parts we use and the increased potential for disastrous crashes with five -foot -diameter rotors spinning away at 1700 RPM, I think that equal caution is in order.
Turn on the Tx and Rx (and wait for the gyro to initialize), compress the Tx antenna to a stu b, and walk away from the helicopter. Count off 30 paces or so, turn around, and wiggle the sticks.
I like to point one of the rotor blades in the direction I'm going to walk, as this gives me a perfect edge view of the flybar paddles. This makes it very easy to see the flybar paddles tilting when I move the cyclic stick. If you're looking at the nose or tail of the helicopter, wiggle the elevator - if you're looking at the side, wiggle the aileron.
If you give the tail blades 45 degrees of 'lag,' you can see them quite well at a distance too. Put the gyro in standard mode (not heading hold) to make interference most visible.
With an FM/PPM system, you're looking for glitching and jittering, so you can just leave the controls centered, and occasionally ci rcle them to verify that you still have good signal transmission. With a PCM system, you're looking for the system to enter failsafe. If you have it set to 'hold last position,' move the sticks in slow circles and watch for pauses in the helicopter's movem ents. If you have failsafe set to move the controls to center, hold the sticks in the corners. Be aware that the servos will probably hold their last position for a couple of seconds before snapping to center, so watch for pauses.
Typically, interference will show up in the tail blades first, since that servo is fastest and least loaded. If you can't see any interference in any channel, try tilting the transmitter through several different orientations - point the antenna directly at the heli, straight up, straight down, directly away, to either side, and so on. If you still see no interference. walk another 5 -10 paces, or until you can see interference.
Do this at the start of each day. Eventually you'll get a feel for how far away you can get on an avera ge day, a bad day, and a good day. Every now and then, you'll probably find that you can't get very far at all before interference makes itself known. Find the problem before you fly!
If the engine is flooded...
If the engine is flooded, it won't start. Remove the glow starter before doing this!!!! I cannot stress this enough. Here's the procedure:
1. remove the glow starter 2. open the throttle all the way 3. blip the starter a few times 4. if you see fuel spattering out of the muffler, you were flooded if you don't, you weren't flooded; skip the next step 5. continue to blip the starter until no more fuel comes out of the muffler 6. close the throttle down to idle
Try starting the engine as usual.
How not to kill a cold engine, part I
Does the engine die as s oon as you start to carry the helicopter out to the pad? If you leav e the glow starter on it. If your hands are big enough, you can hold the left side of the transmitter with your left hand, and give it a bit of throttle with your left thumb, pressing it i nto the gimbal and manipulating the base of the joystick. Carry the helicopter by the rotor head with your right hand.
How not to kill a cold engine, part II
I find that, early in the day, my engine dies when I remove the glow starter. It can be a real drag to start the engine, carry the heli out to the pad, pull the glow starter, step back and hear the engine die. This is an even bigger drag the third time in a row, I assure you.
Piching the fuel line will cause the engine to run lean - running lean w ill cause the engine to accelerate. The engine will return to idle after a few seconds. Here's the procedure:
1. Set the heli down, and set the radio down at an arm's length. 2. Hold the head with one hand, and pinch the fuel line with the other hand 3. As the e ngine revs up, pull the glow starter off with the hand that was pinching the fuel line. Don't let go of the rotor head yet. 4. Let go of the rotor head and step back. I will not be held liable if the blades whack you in the shins. It hasn't happened to me, b ut I suspect it might if you've pinched the fuel off for too long and/or your idle is too high. 5. As you step back, pick up the transmitter and give the heli a little throttle before the engine settles back to idle and/or quits. 6. Pocket the glow starter and have a nice flight.
Don't drip fuel all over the place
It's a waste of fuel, it's bad for the grass, and it's probably worse for the moles that live under that grass (dunno about you, but we have lots at our field). The local field has picnic tables se t up for between - flight maintenance/fueling/etc. If find that if I set the jug on the seat and the heli on the table, I'm less likely to drip fuel from the filler nozzle after removing it from the heli - instead, the fuel tends to run back down to the pump /jug. Exercises and Yardsticks
Alan Kait started a long -running thread on the h -list when he mentioned that he had a list of basic 'control' exercises that he used to polish his skills. It turned out that there was quite a bit of interest in both them, f or many reasons. Some folks are looking for a set routine to practice; some are interested in a way to measure their abilities over time; some (including me) found them interesting as a way to identify personal weak spots and bad habits, and so on.
Credit where credit is due:
The table of 38 orientation exercises is the work of Alan Kait. The points system and following exercises were developed by Mike Davis. It generated a lot of interest on the h-list , so when Mike asked if anyone wanted to put it on the web, I volunteered. I hope you find it interesting.
HOVERING AND SLOW FLIGHT MANEUVERS
Maneuver View is Position or view of helicopter toward: (numbers indicate relative difficulty)
Tail In Nose In Left Right Constant Side Side Heading
Hover Pilot 1 12 8 10
Straight Out & Back Pilot 2 19 13 14
Lateral Left and Right Pilot 3 20 23 24
Circle Around cc - Pilot 6 21 9 18 3 36 5 wise 1
Circle Around c -wise Pilot 7 22 17 3 11 35 5
Circle Outside cc - Center 31 34 15 38 3 wise 2
Circle Outside c -wise Center 32 33 37 3 16
Circle Outside cc - Pilot 4 29 25 27 wise 4
Circle Outside c - Pilot 5 30 26 28 wise 4
FLIGHT MANEUVERS Maneuver Speed Direction Turn towards Rating
FF (stop) slo w R to L & L to R away 2
FF (stop) slow R to L & L to R toward 4
FF (8’s) fast R to L & L to R away 6
FF (8’s) fast R to L & L to R Toward 8
Pirouette fast N/A c-wise 14
Pirouette fast N/A cc -wise 16
Pirouette slow N/A c-wise 18
Pirouette slow N/A cc-wise 20
Approach to hover right side N/A 10
Approach to hover left side N/A 12
Approach to hover nose in N/A 22
Stall turn fast N/A c-wise 24
Stall turn fast N/A cc -wise 26
Full auto N/A right side N/A 28
Full auto N/A left side N/A 30
Full auto N/A right side 180 32
Full auto N/A left side 180 34
Full auto N/A nose in N/A 36
Loop N/A N/A N/A 38
Roll N/A N/A N/A 40
OTHER FACTORS
Flights since crash 25 +10
Flight out of control over pits/flight line per incident -10
PILOT RATING
Level Diffic ulty Factor
Boot camp 0-166 Novice 167 -332
Basic 333 -498
Intermediate 499 -664
Advanced 665 -830
Competition level 831 -996
Master 997+
Notes ;
1. Circle Around --- pilot is center
2. Circle Outside --- pilot is not center
3. Reminder for backward
4. Co nstant heading
5. all views
Overview
You’ll find a long list of basic "precise control" exercises, put together by Alan Kait and Mike Davis. What follows is my effort to extend their ideas into aerobatic flight.
From here the possibilities increase radi cally (pun intended). For each maneuver listed in the "Sequence" and "Simultaneous" sections, there are a host of variations possible if you start from an orientation other than the basic "spinning side up, canopy forward" stance.
Basics
For those of you just getting comfortable with the essentials of hovering and forward -flight circuits, basic aerobatics might just be your logical next step.
The most obvious basic maneuvers are the classics borrowed from airplane aerobatics: loop, roll, stall turn, and pirouette.
In addition, I think the moon slide (a.k.a. " tumbleweed ") belongs in this category, since it's a close cousin to the loop and you learn a lot about using rotor thrust in tumbling maneuvers. A moon slide is essentially a back flip in fast forwar d flight. It works something like a loop, but you time the collective movements so that your speed and altitude remain constant. From fast forward flight, try dropping to full negative pitch and pulling full back -cyclic - as the rotor disk passes through t he knife -edge orientation, the negative pitch acts to "suck" the helicopter forward. Bring the collective back to full positive as the heli continues to flip, and practice until you can tumble during a fast pass, losing as little speed and altitude as poss ible.
As you learn these basic maneuvers, you'll probably also be learning about (and just plain working on) your helicopter's setup. Flight modes , main rotor setup, and tail rotor setup all become much more interesting as you begin to ask more and more from your helicopter. Orientations
And you thought nose -in was a milestone! Inverted hovering, backwards circuits, inverted circuits, sideways circuits, and backwards inverted circuits, backwards sideways circuits... Just hovering and forward flight become challenging all over again . When you flip the helicopter over or point it another direction (or both).
Sequences of Basic Maneuvers
What to do when you've become comfortable with basic aerobatics? Take them apart, mix and match at will. Build aerobatic sentences from the vocabulary of basic maneuvers...
540 Stall Turn
A stall turns with an extra pirouette.
Rolling Stall Turn
Essentially a stall turns with a half -roll between the entry and the 180. Consider the sequence: 1/4 -loop, 1/2 -roll, 180, 1/4 -loop.
Immelmann
Sequence: 1/2 -loop, 1/2 -roll.
Fickle -540
1/4 -loop, 180, 360 in the opposite direction, 1/4 -loop.
Markingover Kinerturn
1/4 -loop, 1/2 -outside -loop in the opposite direction, 1/2 -roll, 1/4 -loop. Think of it as a rolling stall turn, but with a half -outside -loop in place of the half -pirouette. Ideally the helicopter is traveling straight up, backwards, during the beginning of the half roll. Mark Kiner watched someone do this, mentioned it on the h-list, and got everyone enthused about it. I'm not sure who dubbed it t he "Markingover Kinerturn," but that stuck in my mind...
Cuban Eight
5/8 -loop, 1/2 -roll, 5/8 -loop, 1/2 -roll. This move was taken directly from airplane aerobatics.
Wadd -ooops
1/2 -loop, 180, 1/2 -roll. If you do it right you'll maintain the same spee d, altitude, and heading through the maneuver. I made this up and asked the h -list for ideas to name it. My last name made the answer obvious...
Moonstall Starts with a moonslide, but hold full negative cyclic so the heli starts to climbs tail -first thr ee -quarters of the way into the slide. Let momentum carry the heli straight up tail -first until it stalls. Then do a half -roll and exit as if from a rolling stall turn. I made this up too, but I didn't ask for help naming it.
Basics with new Orientations
Imagine the rotor disk following a familiar path - as in a roll, for example - with the tail boom pointed in a non -standard direction. Sideways Traveling Flip Begin with wide -open -throttle fast forward flight, yaw 90 degrees to get the boom sticking out sideways, apply full back cyclic and work the collective to keep the heli traveling in a straight line. With a heading -hold gyro, it's really no more difficult than a simple roll (but still easier said than done). Half -Axel I want to describe it as a kni fe -edge moonslide... From fast forward flight, pull up to knife -edge like the first quarter of a moonslide, with full negative collective. Half -roll, reversing the collective to keep your momentum up, push forward and exit upright and tail -first, ideally w ith the initial speed, altitude, and heading.
I'm pretty sure you could do a full axel, but I haven't been able to do one with any smoothness at all. You have to work the collective like a moonslide, but the tail boom points straight down the whole time. I'll be working on this one during the coming summer...
Simultaneous Basic Maneuvers
Ready to really start taxing your brain cells? If five basic tricks in a row sounds too easy, try doing just two of them at once.
Rolling Circle
Sounds plain enough - just do a bunch of rolls (easy enough) while doing a forward -flight circle in front of you (easy enough). What a pain in the brain. I'm still struggling with this. I've never made it more than three quarters of the way around the circle before running ou t of speed or running out of nerves.
Pirouetting loop
It's possible to do a single loop with several pirouettes throughout. I've never managed, but it looks like you basically move the cyclic in circles while working the collective just as with a stand ard loop.
A loop with a single pirouette wasn't as hard as I had feared. You can take it one quarter at a time... Note that through this process you still need to work the collective as with a standard loop:
1. First quarter: pull back. add left rudder, gra dually move from back -cyclic to left -cyclic. At this point if you want to bail out you can exit as if you were in the middle of the 180 of a stall turn. 2. Second quarter: hold the left rudder, gradually move from left -cyclic to forward cyclic. At this point , you're coming over the top of the loop tail -first. If you want to bail out, you can release the cyclic, add more rudder, do an inverted 180 and fly away nose -first inverted (half -roll at this point makes it rather like a fancy immelmann). 3. Third quarter: continue holding left rudder, gradually move from forward cyclic to right cyclic. A non - heading -hold gyro, is helpful here, since after this point you can ease up on the rudder and let the helicopter weathervane for the rest of the loop. If you've made it three quarters through the loop, it's easier to complete the maneuver than it is to attempt some sort of bail -out. 4. Fourth quarter: are you seeing a pattern yet? Gradually move from right cyclic to back cyclic and exit as if from a standard loop. Again, a standard -mode gyro will allow the heli to weathervane, which makes the last half of the pirouetting loop a little bit easier.
Rolling Loop
I watched Curtis Youngblood do one of these at a fun -fly a while back, and was amazed. He set up the move with a dive from left field to build up tons of speed, and proceeded to amaze me. I'm still trying to figure this out, but here's my approach so far:
1. start with as much speed as possible - a diving approach from left field works quite well 2. straight and level fa st forward flight 3. half -roll to inverted (it's a rolling trick, so start now!) 4. push forward, aiming vertical (like an outside loop) 5. half -roll 6. pull back, aiming over the top of the loop (like an inside loop) 7. half -roll, so you're upright over the top of the loop 8. push forward, pointing straight down (like an outside loop) 9. half -roll 10 . pull back, aiming back along the way you started (like an inside loop) 11 . that's the end of the loop, but another half -roll (or more) continues the theme nicely.
The most diff icult part (for me) is around step 6. At this point, the momentum is running out and the helicopter is too busy changing orientation to keep its speed up. Keeping a circular trajectory is a challenge. More initial speed helps. A fast roll rate helps. Cheat ing helps: before pulling back, give it full positive collective to get it moving over the top of the loop (looks bad because the boom is pointing straight down). Or pull back almost 180 degrees and use lots of negative pitch to add speed and altitude (loo ks bad because it's a snappy half -flip in what should be a slow, graceful maneuver).
'round the world
This is something I came up with when I was working on the pirouetting loop. My brain froze, but it looked cool anyhow so I kept working on it (thank g oodness for simulators!). From fast forward flight, pull up to about 45 degrees, give a bit of rudder and a bit of aileron in the same direction, and hold both while working the collective somewhat like a loop.
The helicopter's trajectory is next to impos sible to describe with text, since it happens in three dimensions... It looks a bit like a sideways loop, only the loop is perpendicular to the entry and exit; if you enter the trick flying away from you, the loop is a vertical circle in front of you. Be r eady to give it a stab of forward cyclic and a quick 180 at the end of the loop, and exit the way you came. This is a nice "turn - around" trick, try doing them back -to -back at opposite ends of the field.
Stay tuned, I'm still working on this...
Hovering O rientations
Tail -in Nose -in Left side Right side Pirouetting
Circuits
"T" Box Circle Eight
Stall Turns
Start from straight -and -level fast forward flight, pull up to vertical, gaining altitude. As the heli reaches vertical, center the collective . Many maneuvers are possible during the 'stall.' When exiting the maneuver, the helicopter should retrace the entry path as closely as possible.
For extra variations, do the whole thing tail -first, or sideways. Or just exit tail -first or sideways. Or jus t start out tail -first or sideways, and exit normally. Or whatever. You get the idea...
Variations:
Standard 180 Standard 540 no pirouetting, just exit backward 360 540, then back 180 to exit backward 360, then back 180 to exit forward no pirouett e, just a half -roll (e.g. start inverted, exit upright and backward) McTwist - essentially a 540 with flair, as the helicopter passes through a perfectly inverted orientation in the middle of the 540.
Loops and Tumbleweeds
These are related in that the y both start and end with straight -and -level forward flight along the same path, and they both involve continuous back -cyclic and a full -down -full collective action while the helicopter completes a backward flip. The differences: how much cyclic, how far t o pull down on the collective, and what path the helicopter describes during the back flip.
Loop - From straight -and -level forward flight, pull halfway back on the cyclic and don't ease up on it until you're upright again. When seen from the side, the hel icopter follows a circular path. The collective goes from full positive (on entry) to roughly zero (over the top) back to full again (on exit). With practice you'll find yourself working the cyclic a bit, and perhaps using more negative pitch, to get large r and more circular loops.
Variations:
backward inverted (or "outside loop") sideways with an inverted pirouette at the top with a single continuous pirouette with multiple pirouettes rolling square
Tumbleweed - Also called a "moonslide." From s traight -and -level forward flight, pull all the way back on the cyclic, quickly bring the collective to full negative, so that when the nose is pointing straight up, the rotor thrust is simply propelling the helicopter straight forward, then back to full po sitive just as the helicopter's nose points straight down. From the side view, the helicopter continues traveling along the same straight - and -level path the whole time. Ideally, you don't lose or gain any speed or altitude, you just flip backward while tra velling forward.
Variations:
backward inverted sideways pirouetting four -point continuous travelling tumbling circuits (circles, eights, etc)
Markingover Kinerturn
From straight -and -level fast forward flight, pull up to vertical as with a stall turn. When the heli reaches vertical, go to full positive collective and push forward, so the heli climbs while doing half a forward flip. The helicopter should now be pointing straight down, with the skids facing you. Do a half -roll, then exit as you with with a simple stall turn.
For variation, do something with the rudder during the stalled moment right before the half -roll.
Standard (described above) With 360 before the half -roll With 180 before the half -roll, exiting backwards Backward Inverted Skip the half -roll and exit inverted Other "Turnaround" Maneuvers
Immelman
The classic airplane maneuver - starts with half a loop, then half -roll to upright, and continue from there. You'll have gained some altitude in the process.
Cuban Eight
Much like two back -to -back Immelmans, but ideally it's a 5/8 loop, and the roll is done while flying downward at a 45 degree angle. This way you start the next Immelman at the same altitude as the first.
Split -S
From straight -and -level forward flight, pull up to 45 degrees, half -roll to inverted, and pull back until upright again. Ideally you finish the maneuver at the same height you began, but travelling the other direction.
Blunt
Like a split -S, but without the half -roll. Pull up to 45 degrees, dive, and finish inverted (also at the same height you began and travelling the other direction).
Tumble Reversal
Much like a tumbleweed, but don't let up on the negative pitch until the helicopter shoots straight up, tail -first (and it will, if you start with suf ficient foward speed!). Center the collective and let the heli stall out, then half -roll, then pull back to straight -and -level forward flight.
Roll
A basic aerobatic staple, Start with straight -and -level forward flight, give it 100% cyclic to one side, cycle the collective from full up to full down and back to full up, and exit upright along the same path you started. Ideally you don't gain or lose any altitude or speed.
Variations:
Standard Backward Sideways Four -point With knife -edge piroeuttes With a continuous pirouette Rolling Circuits - circles, figure -eights, etc Async Loops
It begins like a loop, but rathen than flying inverted across the top of the loop, you keep the rotor disc vertical (or close to it), and use rotor thrust to draw the helicopter over the top with the cyclic centered. Then feed in more cyclic and reverse the collective, so you exit as if you'd just done a half -flip.
The term 'asynchronous loop' comes from the fact that while the helicopter describes the path of a full loop, the orientation only changes like a half -flip. If you do two async loops in a row, the helicopter follows the path of two loops while doing only one complete flip. For extra style points, you can throw in a 180 or 360 while the cyclic is centered an d the collective is pulling the helicopter over the top of the loop.
For me, it's almost an entirely different maneuver when you do the loops front -to -back (so that a person would need a side -view to see the shape of the loop) or side -on (so that it looks like a loop from where I'm standing). This is basically because I need a lot more practice with my side -on control... : -)
Standard async loops:
Nose -in inverted / tail -in upright Tail -in inverted / nose -in upright Side -on, pointing left Side -on, poi nting right
Front -to -back, with occasional 180s over the top
Nose -in inverted, 180, nose -in upright Nose -in upright, no 180, tail -in inverted Tail -in inverted, 180 tail -in upright Tail -in upright, no 180, nose -in inverted (see how you could do these all day long?) Knife- Edge
This is one of my favorite aspects of 3D flight. Theoretically (and practically) there's no way a helicopter can remain airborne for any length of time while it's knife -edge. But with a bit of creativity and optical illusion, y ou can fake it pretty well.
Funnel - The helicopter travels in tight circles, using a balance of centrifugal force and rotor thrust to maintain a very steep angle for an extended period of time (indefinitely!).
Full Collective Circle - Same thing as a fu nnel, but bigger. Use maximum collective, but counter that with a steep bank angle to keep from gaining altitude... The traditional funnel is done in very tight circles, on the order of 1 -5 foot radius, this one is done with bigger circles, on the order of 10 -50 foot radius. There's a fuzzy line between a funnel and a circle. For extra points, start with a dive to build up speed. This will allow a steeper bank (approaching knife -edge) until your speed runs out.
Metronome - Also called a "tick tock." You ca n ease into this by alternating backward half -flips and forward half -flips. Do them in faster and faster succession, and instead of coming all the way upright or inverted, aim for a only 60 degree angle. Then 45 degrees. 30 degrees? Ultimately you'll be li mited by your helicopter's power -to -weight ratio.
Like any other maneuver, this can be done nose -up, node -down, sideways, skids -up, skids -down, traveling , pirouetting, whatever.
"Hesitation Roll" - Think of this as a four -point roll with an extended hesi tation during the knife -edge points. Actually I mostly just do a half -roll with a very extended knife -edge point. There are a couple of tricks you can use to extend the knife -edge period. First, use a touch of back -elevator to 'toss' the helicopter upward just as the roll begins. Second, instead of going fully knife -edge, go just short (or just beyond) knife -edge, and use full collective. This will give you just a little bit of lift. Not much, but look at it this way: if it can add a half -second to the knif e-edge period that makes the knife -edge twice as long. The helicopter will travel sideways as a result of the collective, but hopefully the crowd won't notice this too much. Think of it as a remote controlled slight -of -hand trick. : -)
Twisting Plummetin g Knife -Edge These tricks all have the same basic premise: start high, set the rotor on edge, plummet earthward while revolving. The higher you start, the more twisting you can get in on the way down. The only drawback is that it's kind of boring climbing way up there before you do a triple -rolling death -defying terminal -velocity tailslide. I usually just do a big stall turn and content myself with a single roll on the way down, but that's just me.
Nose -first (the basic)
Start like a really big, really high stall turn, do a 180, leave the collective centered, and do a complete roll as you plummet straight down. Pull back and give it full collective to exit into straight -and -level flight.
Rolling tailslide (the backward) Start like a stall turn, and sk ip the 180. When the heli gets knife -edge, center the collective (zero degrees), and use full right cyclic (or left) to get the heli rolling. As terra firma approaches, use forward cyclic and full collective to get upright and stop the descent.
It could j ust be me, but I think this is one of the prettiest maneuvers yet devised.
Death Spiral (the sideways)
Start like a stall turn, yaw 90 degrees so the boom is sticking out sideways. Use forward or backward elevator to 'roll' during the plummet. This tim e you get out with side cyclic. Think it through and you'll know which side - it depends which way you take that 90 degree turn at the start.
I started doing these with back -cyclic rolls since I didn't know any better. It looks a little cooler with forwar d cyclic rolls, though. Take your pick. 45 -degree (the wacky) Start like a stall turn, yaw 45 degrees, and put the stick into the corner to 'roll' on the way down. Recover by stuffing the cyclic into another corner. : -)
One of the key things to remember is that no matter what point you're at during the roll, getting upright and level again is always going to require the same control inputs. For the rolling tailslide version, that's forward cyclic and full positive collective. Burn that idea into your min d before you begin the trick. No matter whether you complete exactly one full roll, or only 3/4, or one and a half, the pullout is the same. Be ready for it. Pull out when the ground gets too close, not at some predetermined number of revolutions. You may not have time to finish that last roll!
Oh yeah, and you can also pull inverted out with negative collective and the opposite cyclic input described above. Extra style points for this. : -)
Combinations Rolling Loop Rolling Circle Pirouetting Circle Pirouetting Loop Pirouetting Stall Turns Pirouetting Tumbles (Chaos)
It slips when it flips
My Futura SE and Concept SRX both do this to some degree. Not much, probably not enough to be noticed by more observers, but enough to be noticed by me, and it bugs me. A lot. I notice it most during async loops and simple forward half -flips inverted. Just before the helicopter gets level again, it 'slips' just a little bit on the yaw axis. If I do a forward half -flip from an upright hover, I need to give it a touch of left rudder right after I get into the inverted hover. This is so predictable i t's almost automatic now. Still really aggravates me during asyncs, because to me this maneuver is all about smoothness, and the slip+correction just interrupt the fl ow of the maneuver. Drives me nuts!
I had some vibration issues with my Futura SE last summer and this was one of the symptoms. When it had the vibration problem, the gyro slip during a flip was more pronounced. When it was running smooth as glass, it wou ld still slip, but only just barely.
Unable to solve the problem, I started looking at other peoples' helis. I've observed the same thing while flipping friends' helicopters so I know it isn't just me. In fact, I've made a point of watching for this at fu n-flys, and as far as I can tell this happen to everyone, whether they realize it or not.
What follows is something that's been on my mind for a while but I haven't posted about it yet. These are my observations and conclusions so far, and if anyone has a nything to add, please do. This has been bugging me for a couple of seasons. I don't fully understand what's going on here, and I'd like to!
I think it's a side effect of the ring vortex that happens when the helicopter descends through the turbulent air b elow the rotor.
For a textbook example of a ring vortex, try hovering upright at 12 feet, then descend to 5 or 6 feet, and then stop the descent. Depending on the rate of descent, you may have trouble stopping the helicopter because the blades are flying through turbulent air (the vortex ring). I understand that in full -scale this can become a serious problem ("settling under power"). With RC helis you can just slam the collective and power out of it, but you will notice a lag between slamming the collecti ve and seeing the helicopter rise up.
If you watch the exhaust smoke during the "settling" phase, you can see the smoke hanging around in the rotor disc during the descent. Then you add collective, there's a slight lag while all the smoke is ejected out t he bottom the rotor disc (you hear a soft "whump" sort of noise), and suddenly you're in control again.
I think the same thing happens during a flip. I'm definitely hearing the same noise just before the helicopter gets level, and this is the moment when the gyro slips. I'd like to videotape this in the right conditions and see if the smoke shows the same "vortex ring" behavior.
I wasn't deliberately trying to capture evidence of this stuff, when I shot my last round of videos, but I think this footage in dicates that I'm onto something.
About 17 seconds into Nate_03, you can't see the vortex ring well at all, but you can see the ejection of the smoke just as the blades bite into clean air and the descent stops.
About 7 seconds into Nate_05, a vortex just begins to form on the left edge of the disc before being blown out. Wind and sideways moveme nt stop it from getting significant (in full scale helis, translation (forward speed) is recommended to escape the vortex, since they don't necessarily have the power to just blow it out).
All in all, the video I have so far is not real useful when it com es to illustrating this phenomenon . I'll have to deliberately try to capture this on tape some time...
During the transition from the vortex ring to regular airflow, the gyro slips. I don't know if this is due to the sudden torque change when the main rot or blades finally bite into some clean air, or if the tail rotor loses traction because it's in the vortex, or what... You might see this a little bit in the descending hover exercise I described above, but when you're doing a flip or an async loop, the sl ip is much more pronounced - possibly because the cyclic input adds vibration and make things worse for the gyro.
When I get a chance to fly a heli with a 5000T gyro, this is **THE** test I have in mind. If that gyro can solve this problem, I might buy on e. Even when I had my Arcamax PI Pro working at its best (may it rest in peace), this problem was still there - just barely, but still there. Short of the PI Pro, the best gyro I know of is a CSM ICG -360 that doesn't drift. I have one and I won't sell it a t any price. But when I find a gyro that solves this problem, I'll buy one in a heartbeat. This is derived from something I received a while back, originally about full -scale aviation...
Rules of Flight 1. Every takeoff is optional. Every landing is man datory. 2. If you push the stick forward, your blood pressure goes up. If you pull the stick back, it goes down. That is, unless you keep pulling the stick back, then your blood pressure goes way up again. 3. Flying radio controlled helicopters is not an expensive hobby. Properly cared for, your equipment will last forever. Crashing radio controlled helicopters is what's expensive. 4. It's always better to be at home wishing you were at the field than at the field wishing you had stayed home. 5. The ONLY time you have too much fuel is when it's on fire. 6. The rotor is just a moveable derivative of a ceiling fan, used to keep the owner/operator cool. Notice how much they sweat when it stops. 7. When in doubt, hold on to your altitude. No one has ever collided with the sky. 8. A 'good' landing is one after which no spectators need medical attention. A 'great' landing is one after which you can fly the model again. 9. Learn from the mistakes of others. You won't live long enough to make all of t hem yourself. 10. You know you've landed with the wrong side up when the tail boom is spinning faster than the rotor blades. 11. The probability of survival is inversely proportional to the angle of arrival. Large angle of arrival, small probability of survival and vice versa. 12. Never let the helicopter assume an orientation your brain didn't prepare for several seconds ago. 13. Fly over tall grass if at all possible. It takes a lot longer to find the wreckage, but it's usually in fewer pieces, an d much easier to carry. 14. Always try to keep the number of landings you make equal to the number of take offs you've made. 15. There are three simple rules for a perfect auto. Unfortunately no one knows what they are. 16. You start with a bag full of luck and an empty bag of experience. The trick is to fill the bag of experience before you empty the bag of luck. 17. Helicopters can't fly; they just beat the air into submission. Raptors fly better than most because they're so ugly the earth repels them. 18. If the helicopter's movements are exactly the opposite of what you expect, don't panic. If the people who were admiring your flight are scrambing to get underneath the picnic tables behind you, panic. 19. In the ongoing battle between hordes of 6 -to -12 pound objects made of plastic and aluminum, and a single 13.2 x 10 24 pound object made of dirt, the dirt has yet to lose. 20. Good judgment comes from experience. Unfortunately, the experience usually comes from bad judgment. 21. Between fli ghts, keep looking at the helicopter. There's always something you've missed. 22. Remember, gravity is not just a good idea. It's the law. And it's not subject to repeal.
Full -Scale Inverted Pirouetting Autorotation
Yes, this really happened. "Helig ator" (heligator(at)worldnet.att.net) posted the following to the uspilots.net h-list on July 2, 1999. Gordon Mills of PHI (that's "Petroleum Helicopters, Inc," the full -scale helicopter operator, not "Precision Helicopters, Inc," the radio controlled heli copter manufacturer) verified the story, adding that the helicopter had later been pulled up from the bottom of the sea and was being examined "across the street" at one of PHI's facilities.
NTSB Identification: FTW99LA162 Accident occurred JUN -09 -99 at EI -313, GM Aircraft: Bell 412, registration: N3893S Injuries: 2 Uninjured.
This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. On June 9, 1999 , approximately 1535 central daylight time, a Bell 412 helicopter, N3893S, was substantially damaged while in cruise flight near EI -313, an offshore platform located in the Gulf of Mexico. The two airline transport rated commercial pilots, sole occupants, were not injured. The helicopter was owned and operated by Petroleum Helicopters, Inc., of Lafayette, Louisiana.
Visual meteorological conditions prevailed and a company flight plan was filed for the 14 Code of Federal Regulations (CFR) Part 91 reposition ing flight. The flight originated from the GB -172 offshore platform and was destined for Morgan City, Louisiana.
According to written statements provided by the pilots, the helicopter was level at 5,500 feet msl with a cruise power setting of 70 -75 percen t torque, when they heard a "loud bang." The flying pilot reported that the helicopter "immediately and violently tucked down and left then rolled over inverted and [was] spinning to the right." The helicopter reportedly entered a dive with the nose pitche d "straight down and still turning."
The flying pilot stated that he "rolled the throttles to idle and bottomed the pitch," along with placing the cyclic to the right and applying full left pedal. Approximately 1,000 feet above the ocean, the helicopter " leveled out." Just prior to set down in the water, the non -flying pilot inflated the emergency floats. The helicopter came to rest upright in the water and the two pilots escaped from the right side cargo window and entered a life raft.
The helicopter rol led over to the left inverted, due to the ocean waves. Prior to the helicopter rolling inverted in the water, both pilots saw that the 90 degree gear box and vertical fin cowling were missing along with a 12 -16 inch section of drive shaft.
The flying pilo t reported that, at the time of the accident, there were scattered clouds at 3,500 feet, the visibility was at least 20 miles, and there were a few isolated thunderstorms in the distance.