OpenTX - Application Note 12
Mix Flap Into The Elevator Channel
Mix a percentage of the flap channel with the elevator channel.
When flaps are lowered they cause increased drag on the wing. Lowering the flaps causes the nose to pitch up. This effect varies for different aircraft. The effect is greater for high wing aircraft, for example. Adjust the amount of mix until the nose does not change pitch when the flaps are deployed.
This mix is for a high wing aircraft which requires some down elevator to be automatically applied when the flaps are lowered. This keeps the nose from pitching up. The amount of compensation added to the elevator is proportional to the flap deployment.
Mixer Set Up
The mixing is done on the mixer screen by adding a line to the elevator channel. In this example, the elevator is channel 3. The flap is channel 5.
Curve CV1 converts the –100% to +100% range of the flap channel to 0% to +100% range so only positive values are added to the elevator. The actual value is scaled by the weight in the second line.
The first elevator line, if it was set up by the model wizard, may look like this.
This first line passes the IEle signal through to CH3.
Add a second line which is configured as follows.
When the flaps are up, channel 5 is +100%. When flaps are fully down, channel 5 is –100%. This means that as flaps go down, channel 5 goes down, but to lower the elevator, channel 3 must go up. Curve CV1 is used to invert the signal and also only produce a positive output. Only 2 points are required to define the curve that does this.
Curve CV1 is as follows.
As the flaps are lowered, the elevator is also lowered. When the flaps are fully down, the elevator is lowered by 10%. This percentage is set by the weight in the second line. A flight test is used to set the best mix percentage to maintain level pitch as flaps are deployed.