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Home , Adverse yaw, Aileron, Rudder

Aileron- Mixing Explained “Building Good Habits for a Better Future” By Dave Scott. Instructor, 1st U.S. R/C School Illustrations by Dave Scott

Drag Dave Scott is a champion full-scale aerobatic competitor and airshow pilot. He founded 1st U.S. R/C Flight School and has professionally training more than 1500 R/C pilots of all skill levels. His groundbreaking S ..RCFIH SCHOOL FLIGHT R/C U.S. 1ST 1ST U.S. R/CFLIGHT SC training manuals and articles feature the accelerated teaching techniques developed during his 14,000 hours of instruction and

HOOL experience setting up and test flying over 1000 at his school. More information about his books and school can be found at www.rcflightschool.com

The following article details the use of pre-flight preparation. As a result, Adverse yaw is most pronounced on programmable -Rudder mixing most pilots learn to fly by “reacting" to high flat-bottom and to eliminate “adverse yaw”. While what the plane does. Consequently, gets worse at slower airspeeds and/or primary aimed at eliminating adverse many pilots naturally think that when making larger aileron inputs. yaw on a primary trainer, the getting better at making corrections, (Adverse yaw is so severe on a scale descriptions and explanations should good reflexes, and more stick-time are Piper Cub for example, that when flown help cement your grasp of a subject the keys to becoming a better flyer. near speed it will actually turn left that few in the sport understand, even Thus, rarely does adverse yaw or the when right aileron is applied, and vice- through all pilots experience the effects advantages of A/R mixing when versa.) Also, since the principle effect of adverse yaw every time they fly. learning to fly ever come up. However, of wind is exaggerating deviations that if you where to objectively compare the would otherwise be minor on calmer Introduction results achieved training with A/R days, adverse yaw creates a whole slew Nearly 100% of computer radios mixing versus without, you would of problems when trying to fly a trainer today feature Aileron-Rudder (A/R) discover an immediate improvement in in windy conditions. mixing to reduce adverse yaw, i.e., the consistency and therefore the rate of inherent opposite yaw or skid that is Some common approaches to reduce learning. In fact, as you will soon see, especially pronounced during aileron the effects of adverse yaw in R/C have learning to fly with A/R mixing can be deflections on flat-bottomed wing been: Flying at higher speeds; making credited for helping to instill proper aircraft, such as those used for primary the trainer less stable and more control habits that actually accelerate flight training. maneuverable by lessening wing future progress. dihedral; differential aileron travel As the name implies, adverse yaw is an AdverseYaw (more up aileron travel than down); adverse or unfavorable condition that, Space does not permit going into all avoiding wind; accepting it as how among other things, inhibits progress. the involved during trainers fly; and continued reassurance Traditionally, struggling and aileron deflections, so put simply; from club members that the student will committing to many hours of practice adverse yaw is caused by the wing with eventually get it with more practice -- all before soling has been the assumed the down aileron generating more lift of which only help to small and varying normal burden of the novice pilot until and therefore more than the wing degrees. his or her skills improve. However, with the raised aileron (figure 1). The they have unknowingly been fighting Aileron-Rudder (A/R) Mixing drag differential causes the to the additional challenge of flying with The logical solution to counter yaw/skid in the opposite direction that adverse yaw as well. Indeed, pilots adverse yaw is with the surface that the are applied while banking have always assumed that the lack of controls yaw, i.e., the rudder (figure 2). into turns, making course corrections, correlation between their control Coordinated rudder deflections along exiting turns, etc.. Pilots therefore have inputs/intentions and the response of with and in the same direction as the to in the aileron longer to overcome the plane to be strictly the need for more ailerons prevent the plane from the adverse skid, thus increasing the practice, and sometimes wind, when in skidding in the opposite direction while potential for over-controlling, as well as fact adverse yaw has been a big reason! banking into and out of turns, making deal with a lack of consistency caused course corrections, rolling, etc.. Most It’s probably safe to say that most of the by the out-of-sync relationship between importantly, with adverse yaw people reading this learned to fly by their control inputs and the response of eliminated, the airplane response more trial-and-error or at the side of a the plane. closely matches the inputs and recreational flyer/instructor with little intentions of the pilot! Acoordinated rudder deflection in the same direction as the aileron prevents the nose from yawing in the Adverse yaw: An inherent opposite direction during aileron deflections, thereby ath opposite yaw or skid during keeping banks and rolls axial. aileron deflections that is especially pronounced on flat-bottom wing airplanes.

Original flight p

Axial

Coordinated Right Bank Right Bank

Increased drag on the lifting wing drags the wing rearward, causing the nose to yaw left as the plane is banking right. Rudder deflecting in the same direction with the ailerons prevents the nose Lift from skidding to the left.

Be clear, the function of the rudder here going to learn proper control earlier. rudder control on the left stick for left- is not to turn the airplane. Rather, the However, as a bonus, A/R mixing also hand ground and maneuvers purpose of the rudder is strictly to expands the aerobatic capabilities of a requiring independent rudder. In fact, prevent adverse yaw in order to achieve primary trainer airplane by helping learning to use independent rudder on a precise “axial” bank and roll aileron rolls remain axial and on the left stick proves easier after response. heading throughout. Furthermore, the learning to fly with A/R mixing because improved control achieved with A/R much of the right stick control will have 1st U.S. R/C Flight School trains its mixing permits flying in winds that become routine or automatic thanks to students on planes setup to would normally ground most trainers. the consistency achieved with the mix. automatically coordinate the rudder E.g., The main challenge of flying in with the aileron through the A/R Aileron-Rudder Mixing wind is that it tends to exaggerate mixing function in the radio. Radio Setup Rules-of-Thumb manufacturers have in fact been deviations, however, the positive Upon activating A/R mixing, you providing A/R mixing for the purpose of control achieved with A/R mixing need to confirm that the rudder moves countering adverse yaw since the makes it possible to more precisely and in the same direction as the aileron 1980’s, but since most people are promptly correct deviations before the (rudder moves toward the up aileron). inclined to keep passing down the way wind has a chance to exploit them. The rule-of-thumb on a flat-bottom they were taught, it is still not widely Thus, even experienced sport flyers wing airplane is to adjust the A/R used or even understood in R/C. have good reasons to utilize this setup mixing percentage so that the degree of on their flat-bottom wing planes. Those who learn to fly an honest trainer rudder deflection matches the degree of set up to more accurately reflect the Of course, when A/R mixing is being aileron deflection 1-to-1 (figure 3). At control inputs they make are obviously used, pilots still have independent 1st U.S. R/C Flight School we simply gauge the degree (angle) of aileron deflection visually, and visually match an equal degree (angle) of rudder. If for Full deflection some reason we are unable to set a 1-to-1 relationship, we’ll get it as close as we can, knowing from experience that a few degrees more or less is not going to make any appreciable Rear view difference. We then check the setup by flying the airplane directly at or away from us while banking left and right to Right wing confirm that the banks are axial and view the pointed in the same direction throughout. 1-to-1 equaldegree aileron-rudder deflection Of course, if you are hesitant to use A/R mixing, you can always start with less, On a flat-bottom wing airplane, and then keep increasing it until the adjust the A/R mix percentage so bank and roll response is finally axial. that thedegree of rudder Semi-symmetrical Although, you can be confident that deflection matches the aileron deflection 1-to-1. On a semi- after applying the 1-to-1 rule-of-thumb 2-to-1 aileron-rudder deflection to a flat-bottom wing airplane adverse symmetrical wing plane, setup yaw will be virtually undetectable: the A/R mix so that the rudder deflects half as far as the Banks, corrections, and rolls will be ailerons. Using A/R mixing on a smooth and axial, and you will feel fully-symmetrical wing plane is more connected to the plane when you optional, and typically no more Fully-symmetrical fly. By comparison, adverse yaw is than a degree or two when minimal during aileron deflections on activated. Minimal aileron-rudder mix fully-symmetrical wing airplanes (except during slow flight), and thereforefully- symmetrical wing airplanes require little or no A/R mix. Symmetrical wing airplanes exhibit That means that a semi-symmetrical minimal adverse yaw and remain almost wing (in-between flat-bottom and fully- Axial perfectly axial while banking and rolling symmetrical) requires approx. half as (except when the airspeed is low), and thus much rudder deflection as aileron to there is little or no need for A/R mixing with eliminate adverse yaw. this type. Symmetrical DifferentialAileron Flat-bottom wing airplanes exhibit significant adverse yaw and thus require If your airplane utilizes 2 aileron significant A/R mixing to achieve an axial servos, you can program a small bank/roll response. amount of differential aileron travel (more up aileron deflection than down) In short, learning to fly a flat-bottom wing to help further reduce the chances of Axial trainer utilizingA/R mixing leads to learning adverse yaw occurring, particularly at the same control habits used to fly a slower airspeeds. symmetrical wing aircraft, thus making the transition easier because pilots are flying Flat-bottom While differential aileron travel is a without adverse yaw in both cases. common practice used to reduce adverse yaw, its effect is slight, and the only way to fully eliminate adverse yaw is with simultaneous rudder. Note that Once again,s ymmetrical wing without adverse yaw and maintaining a if you did attempt to reduce adverse airplanes require little or no A/R direct correlation between their inputs exclusively with differential, you would mixing because adverse yaw is and the response of the plane (figure 4). end up with so much up aileron travel negligible with this type (until slowed). Conversely, those who learn to fly with that the airplane would be unduly adverse yaw (un-mixed) will have to re- Those who learn to fly a flat-bottom prone to dropping at the start of turns train their habits when flying an wing trainer with A/R mixing will and rolls. Thus, a little differential is aerobatic model without much adverse actually find the transition into good, just don’t get carried away. yaw. Thus, the aim of A/R mixing a symmetrical wing models easier than primary trainer is not only to facilitate A/R Mixing for the Future most. That’s because the control learning to fly, but ultimately to Many new flyers eventually go on to habits learned flying an A/R mixed compliment the transition into higher enjoying the “flying on rails” handling basic trainer are the same techniques performance airplanes that require and increased capabilities of used to fly symmetrical wing airplanes, little or no A/R mixing. symmetrical wing aerobatic models. since in both instances pilots are flying It’s important to note that if you’re but remember that technique only corrections may not even exist. That’s inclined at some point to switch off the applies to flat-bottom wing airplanes when a pilot becomes free to think A/R mixing on a flat-bottom wing and would not be appropriate when ahead of the airplane and more airplane, expect to need a lot more flying symmetrical wing airplanes. efficiently take on new challenges. control inputs to overcome the sloppier Thus, by removing the obstacle of Conclusion responses (something that you do not adverse yaw, A/R mixing proves to be As stated, maintaining a direct want to make a habit of if you also plan one of the most effective tools to ensure correlation between control inputs and to fly less encumbered aerobatic that pilots learn proper control from the the response of the plane is models). Of course, you could instrumental to developing optimum start and therefore continue to enjoy physically coordinate the aileron and control habits. Consider that when steady advancement and a more rudder control sticks using 1-to-1 the initial control inputs are applied successful future. Happy flying! movements to eliminate adverse yaw, correctly, the need for additional