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Flaperons on Model Aircraft

September 17, 2011

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Flaperons are a mix of Flap and Aileron to allow these control surfaces to improve flight efficiency or aerobatic capability.

Unfortunately, the concept of Flaperons seems to have confused some people which has resulted in incorrect and misleading information being passed around.

Some people believe that mixing flaps to the elevator is Flaperons.  This is absolutely untrue.  Flaps can be mixed to the elevator, but this mix is simply called an elevator/flap mix.  It is not Flaperons.

The only correct definition of Flaperons is flap/aileron mixing.

The reason for this confusion is that some people create a Flaperon mix for the sole purpose of mixing the flaps to the elevator.  An elevator/flap mix will, in most cases, allow an aircraft to perform tighter (smaller radius) loops and related pitch maneuvers - such as square corners.

Although any number of surfaces on the trailing edge of the wing can be mixed to create Flaperons, it is most common for a pair of strip ailerons to be mixed.  To create the mix, a servo is required for each aileron.  You will need a computer transmitter or a separate mixing module.

Each servo must be on its own channel.  If you use a Y-harness to connect the two servos, then they can not be used as flaperons.

The way the mix works is that the ailerons perform normally when giving aileron commands (ailerons move in opposite direction).  Flaps can also be used which will raise or lower both ailerons simultaneously.  The flaps can be used by themselves or can be mixed to the elevator as explained above.

A more efficient type of Flaperon is to have two surfaces on each wing - an aileron and a flap.  This setup is often called "Quad Flaps."  Again, a servo on each surface is required - four in total.

There are a variety of ways to set these up depending on the capabilities of your transmitter and what you are trying to do.  In fact, you can have several modes programmed in for various flight conditions.

For example, you can have all four surfaces act as ailerons or as flaps.  You can also have only the two ailerons act as ailerons while all four surfaces act as flaps.  The inverse can also be used - all four surfaces work as ailerons but the two inboard surfaces act as flaps.

Any of these mixes can also be mixed to the elevator as well.  When you consider the number of possibilities, it is easy to see that most transmitters are not capable of having every mode available for a single model memory, so you have to choose which ones you want to use.  Of course if you do not like a particular mix, you can adjust it, turn it off or replace it with a different mix.

You might want all four surfaces working as flaps for aerobatics, but only the inboard flaps working for landing.  The reason is that when flaps are lowered, it raises the angle of attack of that section of the wing which puts the wing closer to its stall angle.

If the flaps are full-span, as when using strip ailerons, then lowering the flaps can make the aircraft more prone to wing tip stalls which can lead to catastrophic results - especially when low and slow such as during a landing approach.

Using four surfaces allows the outboard ailerons to assume their normal angle of attack while the inboard surfaces are lowered.  This flight condition will cause the inboard section of the wing to create more lift at lower speeds.  It also means the inboard section of the wing will stall before the tips which will cause the nose to pitch down rather than the aircraft rolling over as in a tip stall.

Another flight condition possible with quad flaps is called Crow (aka Butterfly).  This is an extremely efficient landing configuration because both ailerons are simultaneously raised which lowers their angle of attack.  At the same time, the inboard flaps are lowered which raises their angle of attack and creates more lift as previously stated.

This configuration greatly increases drag which slows the aircraft while creating a great deal of lift allowing the aircraft to continue flying at this reduced speed.  The lower angle of attack at the tips provides an excellent safety margin to avoid tip stalls.

As with a dual aileron setup, all four surfaces can be mixed to act as flaps and then mixed to the elevator.  Therefore, with a capable transmitter (one having many channels and available mixes), an aircraft can be setup to fly extremely efficiently in many different flight conditions.


Videos demonstrating various Flaperon mixes

Please do not e-mail me asking how to set up these mixes with your transmitter.  Consult the manual or call the manufacturer for guidance.

Horizon Hobbies has the manual for the Ultra Stik available for download which explains how to set up quad flaps for a couple different type transmitters.

Note that in all modes the ailerons still work.  However, when a mixed control is at its extreme in either direction it will not move any farther in that direction no matter what command is given.  Watch the videos to see what I am talking about.

Another thing to note is that some of the controls lag behind others in certain modes.  I have no clue what that is about.

In at least one of these videos you will see the elevator move.  The elevator is not included in any of these mixes - I just bumped the stick.

Elevator can be included in any of these mixes if your transmitter supports it or you have enough manual mixes to include it.  For example, my transmitter has a built-in Butterfly mix that includes elevator.  I have the elevator turned off for now because the plane hadn't been test flown when these videos were shot.  After flight-tests of the Butterfly mix, I will include elevator if it is needed.



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