Tutorials : Enhanced Spoiler/Elevator Compensation

Simon Hall    30 July 2005 (intro by Mike Shellim)

Introduction (by MS).

Some gliders undergo a violent trim change when deploying crow. The standard mix to deal with this is using spoiler->elevator compensation. However this may not be enough - the amount of up elevator travel may also be required to be increased.

For example, there may be 50 units of up elevator movement in normal flight. It may be required to increase this to 75 units when deploying full crow. So we may want not just the spoiler compensation to change, but the amount of elevator travel as well.

Over to Simon...


The solution described here is to add another spoiler input to the elevator servo mixer. Set the curve to mirror the original spoiler curve, but with an analogue switch so that it's attenuated by the 'up' half of the elevator stick.

The result is that the extra mix cancels the spoiler compensation when full up is held, but still lets the compensation work (proportionally) at anything less than full up stick.

Details of stick, multimix switch and servo configurations.


Stick Control
B Spoiler
D Elevator


Multimix 1
Input  # Control Remarks
1 Elevator + T trim active
2 Spoiler  
3 Spoiler  

Analogue switch A-1

Servo 1 Travel and Curves

Input Control/Mixer Switch  Curve        Remarks
1 Elevator + T   -100 / 0 /100  
2 Spoiler   24 / 12 / 0
3 Spoiler A1-D -24 / -12 / 0 you will probably have to reverse the switch input. e.g. Select A1-D* and press the R key

In this simple setup you still get full up even with the spoilers activated. For less than full up the elevator compensation still has an effect.

Other notes - You will probably need a seperate multimix if your spoilers are switched (can't have an analogue switch plus an on/off switch on the same input into a multimix) but otherwise the logic is roughly the same. I haven't checked to see what effects servo or control limits have but you should be able to work around these using the curves.