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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.

 

Channel Number

 

Weight

 

Source

 

Curve

 

Trim

 

Switch

Delay /

Slow

Mix Name

CH3

100

IEle

ele

+=

10

CH5

CV1

Flap Mix

 

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.

 

FIELD

Parameter

Description

Mix Name

Elevator

Source

IEle

Weight

100

Default setting

Offset

0

Default setting

Trim

ticked

Default setting

Curve

Diff 0

Default setting

Modes

0 1 2 3 4 5 6 7 8

Default setting

Switch

---

Default setting

Warning

OFF

Default setting

Multplx

Add

Default setting

Delay Up

0.0

Default setting

Delay Dn

0.0

Default setting

Slow Up

0.0

Default setting

Slow Dn

0.0

Default setting

 

This first line passes the IEle signal through to CH3.

Add a second line which is configured as follows.

 

FIELD

Parameter

Description

Mix Name

Flap Mix

Source

CH5

+100%

Weight

10

The amount of flap mixed is set here.

Offset

0

Trim

Not ticked

Curve

Cstm CV1

Use curve CV1

Modes

0 1 2 3 4 5 6 7 8

All modes enabled.

Switch

---

Warning

OFF

No warning beeps required.

Multplx

Add

The value of this line is added to the one above.

Delay Up

0.0

Delay Dn

0.0

Slow Up

0.0

Slow Dn

0.0

 

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.

 

FlapElevatorMixCurve

 

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.

 

Phantom Divide

 

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