An RC plane flaperon is a form of an aircraft control surface. It is a perfect combination of ailerons and flaps. Flaps are used to build, lift or drag depending on how it is used, while ailerons stop the plane from sloping over. Flaperons support and stabilize the RC plane, mainly during low-speed flying when taking-off and landing. Flaperons answer to roll directions made by the pilot using the control wheel as ailerons do. However, flaperons can both be lowered to work as a set of flaps.

The pilot’s controls for raising or lowering the flaperon are separate from the controls responsible for the ailerons' functionality. This is where a mixer is integrated into the design to link and associate the two inputs accordingly.

Some pilots prefer using flaperons instead of the separate ailerons and flaps because it reduces the overall weight of the RC plane.  Flaperons are usually attached away from the wing's trailing edge to make sure that airflow through the flight control surface is uninterrupted and continuous, especially while at low speed or high angles of attack. This helps in reducing the stall speed and enhances low-speed handling properties.

Flaperons were fused into a couple of World War II-era creations like the Junkers Ju 52 and Ju 87 Stuka dive bomber. But today, its utilization is limited and is confined to homebuilt planes and RC planes.

Configurations of a Flaperon

Your flaperons will use both your ailerons, with one using a channel each as both ailerons and flaps. For the input and output channels, the frequencies from your transmitter or remote control to the receiver on the plane and then the autopilot on your motor are considered your input channels. Meanwhile, the channels coming from your auto-pilot to your servos are classified under your output channels.

Flaperons are the perfect example of a structure where the input and output channels are not mapped directly to one another. The autopilot will use the aileron's input on Channel 1 and the input of the flap on Channel 5, for example. The mixer will then 'mix' the two inputs and forecast and calculate how the RC plane flaperons move. This measured result is sent out to each of the output channels of the flaperon.

Flaperon Set-Up

Note that on your transmitter, you don’t do any aileron mixing.

For the Input:

  1. Leave the regular aileron input on Channel 1.
  2. Add an input channel on your transmitter or controller for flaps control. You can use any of the available input channels for this, but for this guide, we will set it to Servo output channel 5. Once you have selected your channel, you have to configure your controller to use Channel 5 (or whatever channel you selected) for flaps via a rotary button or a switch. Set ‘Flap_In_Channel’ to 5.
  3. Transfer your ailerons to two available output channels on your autopilot. For this reading guide, we will set it to Channels 5 and 6.

For the Output:

  1. Set ‘Servo5_Function’ and ‘Servo6_Function’ to 24 and 25. This is for Flaperon 1 and 2 correspondingly. Note which channel has zero bearings.
  2. Set the ‘Servo5_Min,’ ‘Servos5_Max,’ and ‘Servo5_Trim’ to 1000, 2000, and 1500. Set the same values as well to the ‘Servo_6’ equivalents.
  3. Switch to 'Cruise' or 'FBWA.' Roll your RC aircraft back and forth and ensure that the ailerons are moving in the correct direction, which is going down on the wing that you roll down. If it is not moving as intended, use 'Servo5_Reversed' and 'Servo6_Reversed' so the channels can be reversed.
  4. Once the ailerons are moving right, try the flaps control using your transmitter. The flaps should go down. If otherwise, you need to switch the two output channels and adjust the reversals.
  5. Try the ailerons stick of your transmitter. If the direction is wrong, use 'RC1_Reversed' so the input channel's directions can be changed. The expectation is if you put your stick to the left, then the left aileron should go up.

Flaperon Tuning

Here are the steps in tuning your flaperon:

  1. In your Mission Planner, go to failsafe set-up and check the maximum and minimum values match Servo5_Min and Servo5_Max. If it is already matching and it is still not working, you can adjust the values accordingly until your flaps move all the way. Setting your 'Flap_Slewrate’ to 100 allows your flaps to move from 0 to 100% in a single second. If you lower this value, your flaps will also react and move slower.
  2. Modify the ‘Flap_x_Percnt|Speed’ as needed for auto-modes.
  3. Check if you need to adjust any settings in 'Tkoff_Flap_Pcnt’ and ‘Land_Flap_Percnt’ for taking off and landing.
  4. If flying manual mode, it is highly recommended that you set-up an elevator downmix in your transmitter when you set your flaps. This means that the more flaps you send, the more elevator down should be sent to pitch up from the flaps correctly.

Never rush flying your RC plane without double-checking that your flaperons are working. On the initial set-up, it might take you more time than planned, but eventually, you'd know what needs to be tweaked for your flaperons to work seamlessly.