Setup Snap Flaps

Snap Flaps

Purpose

Aerobatic gliders with (near-)full-span ailerons can be set up to move the wing trailing edge slightly downwards (camber) when the elevator is pulled, and upwards (reflex), when the elevator is pushed. See this article at slopeaerobatics.com for the details.

In addition, we want to be able to control the camber/reflex of the main wing also with a potentiometer, independent of the elevator stick.

Set up

The main challenge is to overcome the limit of FS-i6, only three usable mixes. But wait - there is an additional powerful mix which we can (ab-)use, the elevon mix.

Plug the right aileron servo to Ch1, the left aileron servo to Ch2, and the elevator servo to Ch5.

Set up the auxilliary channels as follows:

Key → Aux Channels
   Channel 5: None
   Channel 6: VrA

Then set up both ailerons as elevons. Note that we want the full travel across the aileron stick range, instead of what is commonly used with elevons, having the full travel in the diagonal stick positions only. The value for CH2 below represents the movement of the snap flaps. When less movement is desired, it is possible to lower the value to e.g. 30 % (which is what I originally started with):

Key → Elevon
   Elevon: On
   CH1: 100 %
   CH2: 50 %

Copy the elevator value also to Ch5, where the elevator servo is:

Key → Mix → Mix #1
   Mix is     On
   Master     Ch2
   Slave      Ch5
   Pos. mix   100%
   Neg. mix   100%
   Offset       0%

Use the potentiometer to control the trailing edge, with more travel downwards (flaps) than upwards:

Key → Mix → Mix #2
   Mix is     On
   Master     Ch6
   Slave      Ch2
   Pos. mix    40%
   Neg. mix   100%
   Offset       0%