An important topic, as I see quite regularly suboptimal linkages.


I like to make all my linkages with maximum mechanical advantage, that is, using ALL available servo throw to achieve the desired surface deflections.

I got asked how to do this on a flaperon that has asymmetric deflections (i.e. more down than up).

Here is my procedure how to design a flaperon linkage that uses all servo throw:

1) On your transmitter, make sure that you unlock all available servo throw. On Futaba, that means 140% dual rate, max rate on diff and max endpoints and travel. The aileron servo should now move from around plus to minus 50 degrees. See Figure 1.

2) Mount the servo horn at neutral transmitter trim such that it points vertically down

3) Using a balsa wedge, fix the aileron in the maximum upward deflection position. Since this will be max up, be generous (i.e. if you want 15mm up, fix it at 18mm up). See Figure 2.

4) Bring the servo to the end point corresponding maximum aileron up. The arm should now point 50 degree backwards in a bottom drive system, as shown in Figure 3. For a top drive linkage, the arm has to point forward, see Figure 6.

5) Hook up the linkage to wing and servo and glue in the L wires into the carbon rod, while aileron is fixed and servo is in full deflection for aileron up.

7) Once it is well cured, move the servo on the transmitter to neutral. You will notice that the flaps are already partially deflected downwards (see Figure 4). This is as it should be,...Continue Reading