Tutorials : Setting up Spoiler / Elevator Compensation
Many gliders experience a change in pitch trim when spoilers are applied, and most advanced computer radios provide a way to compensate for this by mixing in an elevator correction ('compensation').
This article shows two ways of doing this on the mc4000. The first method uses a built-in mixer and is simple to set up. The second method is more complex to set up, but allows very easy adjustment on the field when the compensation employs a multi-point curve.
Both methods support simultaneous use of the COMBI mixer.
Solution 1: Using VTAIL+ mixer
The first method uses the VTAIL+ built-in mixer.
VTAIL+ Mixer Overview |
--------------- Elevator --> | | Rudder --> | VTAIL + |--> V-tail 1 Spoiler --> | mixer |--> V-tail 2 | | --------------- |
Mixer set up
VTAIL+ | ||||
Input | Control/Mixer | Switch | Curve | Remarks |
1 | Elevator | ON | -100/0/100 | Adjust movement using Control Travel screen, for Elevator |
2 | Rudder | ON | -100/0/100 | Adjust movement using Control Travel screen, for Rudder. |
3 | Spoiler | ON | x/y/z | Set x,y,z to required elevator compensation. |
The two Vtail servos are assigned to this mixer. Each servo will 'see' its own set of curves for Elevator, Rudder and Spoiler.
To change the elevator trim compensation, it is necessary to adjust and balance two Spoiler curves (one for each servo).
Solution 2: Using servomix and multimix
Solution 1 uses two curves which must be matched. Making adjustments is easy if you're using 3-point curves, but it becomes awkward if the curves employs more points.
The second method is more complex to set up, but is easier to adjust on the field since adjustment involves one curve only.
Mixer Setup |
---------------- | | Rudder -----------------------> | "LEFT_VEE" | Elevator----------------------> | Servomix | --> Left V-tail |-------------| | | Servo | |---> | | Spoiler --> |"COMPENSATE" | |--------------| | Multimix | | | |--------------| | |---> | | |-------------| | "RIGHT_V" | --> Right V-tail | Servomix | Servo Rudder -----------------------> | | Elevator----------------------> | | |--------------| |
The COMPENSATE multimix has a single Spoiler input. The relationship between Spoiler movement and elevator compensation is set up in this mixer.
The LEFT_V and RIGHT_V servomixs add the Rudder, Elevator and Compensate values and send them to the V-tail servos.
Multimix set up
"COMPENSATE" multimix | ||||
Input | Control/Mixer | Switch | Curve | Remarks |
1 | Spoiler | ON | a/b/c/d/e | Use the curve to generate the elevator compensation signal. It can be non-linear as required. |
Notes:
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Servomix set up
LEFT_V & RIGHT_V servomixes | ||||
Input | Control/Mixer | Switch | Curve | Remarks |
1 | Rudder | ON | -100/0/100 | To reduce movement, use the Control Adjust -> Travel screen. |
2 | Elevator | ON | -100/0/100 | To reduce movement, use the Control Adjust -> Travel screen. |
3 | COMPENSATE | ON | -100/0/100 | To alter the elevator compensation, adjust the curve in the COMPENSATE mixer. |
Vtail servos are assigned LEFT_V and RIGHT_V mixers. Each shares similar setup above.
-100 / 0 / 100 is a "do-nothing" curve. It may be necessary to adjust the exact end points to balance the servos (it may also be necessary to reverse the curve (i..e change it to +100/0/-100)).