Control System Rod-Ends

April 1979

The VariEze control system is unusual in that it uses the small HM-3 rod-ends in its primary controls. Aircraft normally use the 1/4" hole HM-4 as the minimum size. Justification for this is that the control surfaces are small, sized for the low forces required for a side-stick control. Thus, the design safety factors are still larger than in normal control systems. However, the small HM-3 rod-ends are relatively fragile if they are subjected to bending or twisting loads.

These loads do not exist in operation, but they can occur when the canard is being removed, or at the stick if the roll stops are not adjusted correctly. We recently heard from a builder who broke an HM-3 while he was installing his controls! This is a very serious concern, since there is no redundancy in the pitch system to save the airplane if one should fail in-flight. This is not as serious in the roll system, since the airplane can be steered with rudder or the other aileron.

Due to the relative frailty of these rod-ends, we are recommending that you immediately replace the four primary pitch rod-ends with HM-4’s as shown in the adjacent drawings. This includes both ends of the CS136 tube and both ends of the CS102 tube. Note that two CS201 spacers are required for each rod-end on the CS102 push-rod to allow sufficient roll travel. They are steel, 5/16 OD x 1/4 ID x 0.1 long. Also, the two CS111 spacers are replaced by CS202 spacers.

Four of the CS1 inserts now are CS1A (1/4’ x 28 thread). Note that this change also affects the parts list on several bolts, washers and nuts. Drawings for CS1A, CS201 and CS202 have been supplied to Brock so he can manufacture them. Aircraft Spruce and Wicks have all the new hardware in stock. If you are retrofitting, you can drill (#3 drill) the CS1 spacers and tap 1/4 x 28 thread.

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