RIGGING THE FLIGHT CONTROLS
“Rigging” refers to the installation and adjustment of the rods that move flight surfaces in response to inputs from the controls of the helicopter. These rods are cut to length, threaded, and fitted with rod ends to allow rotating movement. Correctly rigging your helicopter will have an enormous impact on the safety and performance of your helicopter.
WHEN INSTALLING A ROD END TO ONE SIDE OF A CONTROL ARM, IT MUST BE HELD ON THE OTHER SIDE BY A PENNY WASHER (AN970-4) WITH THE BOLT HEAD ON THE WASHER SIDE.
If possible, the bolt should be installed from the front of the aircraft with the nut on the aft side. In the event that the ball separates from the rod end, the penny washer will hold it captive and allow partial control authority. Otherwise, the rod end can fall off the control arm and all control authority is lost.
When installing a rod end between two surfaces that are larger than the size of the moveable area of the rod end, use an AN960-416 washer under the bolt head and an AN960-416 washer under the nut, secured with an AN380-2-2 cotter key.
We recommend that you finger tighten the nuts securing the rigging and wait until it is complete before torqueing and cotter pinning the nuts.
It is critically important that you understand how the flight controls work together to produce the desired effect. Careful fabrication, installation, and adjustment of the rigging will allow you to control your helicopter through its entire range of operation.
BEFORE COMPLETING THE RIGGING, THE HELICOPTER MUST BE LEVEL ON ALL AXES. The bottom tubes of the cabin frame are on the same plane and can be used for leveling.
The long control rods that pass from inside the cabin to the main transmission swashplate are fabricated from 4130 Chromoly and are powder coated along with the frame. If you have purchased a Base Kit, they will require painting. In a Complete Kit, the control rod from the base of the pilot’s cyclic to the rear of the cabin is provided in the Electric Trim Kit, and it is ready to install.
All of the control rods that are fabricated by the builder are made from aluminum tubing that may be painted after completion. DO NOT ANODIZE THE ALUMINUM CONTROL RODS. While the side walls of the tubing are substantial, anodizing weakens aluminum tubing and should not be done on the control rods.
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The procedure for fabricating the control rods is as follows:
From the Control Kit, locate the package of 22 HXAM-4T rod ends. Using a felt tip marker, make a circular mark around the threads of each rod end ¾” from the end of the threaded shaft. In all instances, there must be at least ¾” of the threaded shaft of the rod end engaged in the end of the control rod, with a right-hand pal nut to lock it into position. (The two smaller MM-4T rod ends are used for the throttle linkage.)
Thread AN316-6R pal nuts onto the shaft of each rod end.
Loosely install HXAM-4T rod ends from the Control Kit using AN4 bolts at each location where the control rod will connect.
At each location, measure the distance from the ¾” marks on the rod ends.
Cut to length the ½” x .155” aluminum tubing found in the raw materials shipped with your Kit to length, square and de-bur the ends, and thread using a 3/8” NF tap.
When the correct position of the rod is determined, it is locked into place by tightening the AN316-6R pal nuts on the shaft against the end of the control rod.
NOTE: New rod ends can be very tight. If you find that they are too tight to move freely, they can be loosened up by placing a long bolt through the ball and, using washers to shim it up, tighten a nut down to the washers. Have a cup of water at hand to cool the parts. Tighten the bolt into the chuck of your drill and spin the ball with the drill until you feel the drag lessen. Quickly cool the parts in the water. You want the rod end to rotate freely, but no side to side play. Repeat as required.
The cyclic allows you to change the direction of flight left, right, fore and aft. Left and right rotates the cyclic torque tube which has a bell crank bolted to it just behind the slider sleeves. Both cyclic sticks are linked together at the bottom forks of the bell cranks. The horizontal forks of the bell cranks have control rods extending up to the swash plate spider arms.
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FINISHING THE CYCLIC LOCK
Your cyclic lock is sent to you unpainted, because it must be fit to your helicopter. The rod should be cut if necessary and bent to secure the cyclic stick in the center. Once it is modified to fit, it can be removed for paint or plating; however, it will be easier to rig the helicopter if you leave it in place until that task is finished.
Beginning on pilot’s side, lock the collective stick down as far as it will go. A plastic zip tie will serve the purpose.
Put a piece of masking tape on the front of the kick panel over the future location of the cyclic lock to protect the paint. Position the cyclic lock on the front of the kick panel directly behind the cyclic stick and clamp it temporarily while its exact location is determined.
Center the pilot’s cyclic stick vertically and horizontally as measured with an angle finder or protractor. Do this carefully, because all of the rigging is based on the position of the cyclic stick.
Determine how long the hook should be to lock into the tab on the side of the pilot’s cyclic and hold the cyclic centered forward/aft, and laterally. Also determine the exact placement of the cyclic lock on the front of the kick panel. Mark and drill 1/8” pilot holes in the center of the holes in the cyclic lock mounting plates and the tabs welded onto the seat frame. Drill the holes out to ¼”.
Bend and cut the rod on the cyclic lock to hold the cyclic stick in the center, and re- install it on the front of the kick panel. Secure the cyclic stick with the hook and begin fabrication of the control rods.
CYCLIC PITCH RIGGING
Remove the cyclic pitch rod provided in the Electric Trim Kit. If you have purchased a Base Kit without the Electric Trim Kit, you will fabricate a control rod of the appropriate length from the aluminum tubing provided in the raw materials.
Position the pilot’s side cabin pitch horn so that it is vertical.
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Install the cyclic pitch rod between the bottom of the cyclic stick and the pitch horn, adjusting the distance between the center of the rod ends to keep the cyclic stick and the pitch horn vertical. Attach the rod to the pitch bell crank (horn) using AN4-14 bolts, with AN960-416 washers under the bolt head and nut and loosely secure with AN310-4 nuts on this rod and the corresponding rod on the co-pilot’s side. Use AN4-15 bolts, AN960-416 washers under the bolt head and AN310-4 nut and loosely secure the other end of the rod to the lower end of the cyclic sticks. Be certain there is at least ¾” of the rod end shaft engaged in the control rod. The small tab welded on the rod from the Electric Trim Kit should be positioned pointing upwards.
Fabricate an aluminum control rod for the co-pilot’s side using the procedure described previously.
Adjust the control rod at both ends until the cyclic sticks are parallel fore/aft.
CYCLIC ROLL RIGGING
If the cyclic lock is still in position, the sticks should be centered horizontally and vertically.
Install rod ends in the vertical end of the cyclic roll bell cranks, using AN4-14 bolts, AN960-416 washers under the bolt head and under the AN310-4 nut. Finger tighten the nut.
Fabricate and install the control rod, and adjust to center it between the bell cranks. Confirm that both cyclic sticks are parallel in the left-right axis.
COLLECTIVE/THROTTLE RIGGING
Position the collectives so that the collective bell cranks are vertical and centered.
Install a rod end on the aft side of the collective bell crank on the aft end of the pilot’s collective. Install another rod end on the aft side of pilot’s side of the double bell crank attached to the co-pilot’s collective. Use AN4-15 bolts with AN960-416 washers under the bolt head, an AN970-4 washer against the rod end, and an AN310-4 nut with an AN960-416 washer under the nut.
Fabricate and install the control rod, and adjust to center it between the two bell cranks. Verify that both horns of the bell cranks are exactly vertical.
Locate the throttle control rod shown below and the two smaller MM-4T rod ends from the Control Kit. The end of the control rod with the shortest length of tubing past the bell crank goes forward. On an AN4H-10A bolt, thread an AN960-416 washer, an AN970-4 washer, an AN960-416 washer, an MM-4T rod end, and an AN960-416 washer. Install the AN4H-10A bolt in the end of the control rod. Torque the bolt and safety wire. Repeat the procedure for the opposite end of the control rod.
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The throttle linkage rod ends are threaded up through the mounting tabs welded to the frame. The forward tab is located on the lower cabin frame below the co-pilot’s collective bell crank. The aft tab is located on the co-pilot’s side of the rear of the frame as pictured below. With the AN316-4R pal nut close to the head of the rod end, pass the rod end up through the tab and use an AN365-428 Nylock nut to secure the rod end to the tab. When there are at least 2 threads of the rod end above the Nylock nut, tighten the pal nut securely against the bottom of the tab.
The remainder of the interior rigging requires that the engine with carburetor be installed.
COMPLETING THE THROTTLE RIGGING
Remove the carburetor throttle arm and drill the center hole out to ¼”.
Using the nut and cotter pin provided with the carburetor, re-install the arm positioned so that when the carburetor stop is at idle, the arm is angled down and forward roughly 25 degrees. All further adjustments will be made with the carburetor stop at idle.
Install a rod end on the forward side of the rear bell crank of the throttle control rod using an AN4-11 bolt threaded through the last hole in the bell crank and the rod end, with an AN970-4 washer under an AN310-4 nut.
Install a rod end in the middle hole of the carburetor control arm, using an AN4-13 bolt, with an AN970-4 washer under the head threaded through the rod end and through the
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hole you drilled out earlier in the carburetor arm. Secure with an AN310-4 nut with an AN960-416 washer under the nut.
With the carburetor throttle arm positioned forward at 25 degrees and the throttle control rod bell crank positioned down 45 degrees from level toward the pilot’s side, measure the distance between the markings applied to the threaded ends of the rod ends and fabricate and install a control rod of that length.
Install a rod end on the aft side of the forward bell crank of the throttle control rod using an AN4-11 bolt threaded through the last hole in the bell crank and the rod end, with an AN970-4 washer under an AN310-4 nut.
Install a rod end on the forward side of the co-pilot’s collective bell crank. Use AN4-15 bolts with AN960-416 washers under the bolt head, an AN970-4 washer against the rod end, and an AN310-4 nut with an AN960-416 washer under the nut. The bolt head should be on the aft side of the horn to provide clearance for collective movement.
With the collective control bell crank angled 45 degrees down and pointing outboard, and the throttle control arm bell crank angled 25 degrees down, measure the distance to the markings on the rod ends. Fabricate and install a control rod of that length.
Verify that the throttle will open and close completely when collective is full down by fully rotating the collective grip from stop to stop. Inspect the carburetor at each position to make sure there is full travel.
Raise collective full up, and perform the same test.
Torque and cotter key all fasteners, except the throttle correlator connection described below.
THROTTLE CORRELATOR
Throttle correlation can be achieved by adding a longer bolt with a ½” to ¾” spacer at the co-pilot’s collective control bell crank and the rod end. The length of the spacer and bolt can be adjusted to the builder’s preference for the amount of correlation provided.
Correlator linkage
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PEDAL LINKAGE
The control rods linking the pilot’s and co-pilot’s pedals must be exactly the same length when completely installed. Within the requirement of ¾” of thread in the control rod, the length can be adjusted by threading the rod end in or out.
Fabricate two control rods 2-5/8” in length. Thread a rod end with AN316-6R pal nut positioned near the head of the rod end into the four ends of the control rods.
On the side of the pilot’s right pedal mounting tube and the co-pilot’s left pedal mounting tube, drill out the existing holes to ¼”.
Attach one rod end at this point using an AN4-20 bolt through the ¼” hole, with an AN960-416 washer under the bolt head, through the rod end, followed by an AN970-4 washer, then an AN310-4 nut.
Rotate the pilot side bell crank to vertical with the grease fitting upward. Install the rod end in the other end of the control rod through the pilot’s side of the bell crank using an AN4-11 bolt, with an AN960-416L thin washer under the bolt head. On the outside of the rod end, use an AN970-4 washer, with an AN310-4 nut.
With the pilot’s side bell crank still in the vertical position, install the remaining control rod between the co-pilot’s bell crank and the hole in the side of the co-pilot’s left pedal mount using the same hardware used on the first rod.
Torque and cotter key all nuts.
TAIL ROTOR CONTROLS
Installation of the tail rotor control cable will be covered in Section 25 External Rigging.
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