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Other RC Airplane Controls
 

Other RC airplane controls

Other important controls found on more complex rc airplanes include flaps and retractable landing gear, or 'retracts'.

 

Flaps

Flaps are located on the trailing edge of each wing, between the aileron and fuselage. They're used to generate more lift at slower flying speeds and, at greater deflection, to slow the airplane down close to landing by causing excessive drag.
Unlike ailerons, flaps are connected in such a way that they both drop exactly the same amount together so as not to upset the roll attitude of the plane when they are deployed.

Flaps are typically operated with a toggle switch or rotating dial on the transmitter. A dial is the better option because this allows the pilot to use as little or as much flap as he wants, according to the situation. Flaps operated by a single position (on/off) toggle switch will be all or nothing.

When a lesser amount of flap is used (for example, 10° or so) it's quite common for the airplane to pitch upwards as soon as the flaps are lowered. This is a result of the extra lift being generated and the pilot needs to be aware of this happening before he activates the flaps.
The trick here is to use elevator compensation, either manually or have it mixed in the radio so that when flaps are lowered, the elevator automatically drops slightly to help maintain the plane's path.

Flaps lowered for landing

 

Retracts

Retractable landing gear (undercarriage) is landing gear that folds away into the airplane's wings or fuselage once the plane has taken off.

Retracts are often used on larger rc airplanes, particularly scale models where the real airplane has retractable undercarriage. Larger non-scale airplanes can also have retracts, particularly competition rc airplanes where it's necessary to reduce the amount of drag on the plane in the air. Obviously an airplane with no landing gear hanging below it experiences a lot less drag than one with.

Retractable landing gear, or retracts

Retracts can be operated mechanically by a servo, driven by compressed air or more recently electric worm-drive. The retraction of the landing gear is operated by the flicking of a single switch on the transmitter, typically either on the 5th or 6th channel.

 

 

Control surface mixing

Some rc airplanes are designed in such a way that they cannot have separate controllable surfaces. Planes with a large delta wing and no tailplane, for example, such as the Weasel shown below:

My Weasel Evo

When this is the case control surface 'mixing' is necessary and this is only possible on computerised rc transmitters that offer a mixing capability. These days, most radios offer at least basic mixing.

The secret of control surface mixing is that each control surface must be able to work together with its partner surface (i.e. both up and down together), and opposite to (i.e. one up, one down).

Common control surfaces that are mixed ones include...

Elevons, when elevators and ailerons are combined together on a flying-wing or delta type plane. Elevons move up and down together, as elevators do, and individually, as ailerons do. In short, one pair of elevons does the job of elevators and ailerons.

Ruddervators are the control surfaces found on 'V' tail airplanes - like elevons except that rudder and elevator control is combined, rather than aileron and elevator.

Flaperons are control surfaces that mix the actions of ailerons with flaps. In other words, one pair of control surfaces along the trailing edge of the wing take on the job of aileron control and flap control, when needed.

Spoilerons are, in effect, the inverted version of flaperons. Spoilers are often found on large rc gliders and operate by the control surfaces moving upwards as opposed to flaps that drop down. When spoilerons are deflected, the amount of lift is drastically reduced and so the glider's rate of descent quickly increases, enabling the pilot to land it in a smaller space.

There are other types of rc airplane control mixing too, but those listed above are by far the most common that you'll encounter.

RC channel mixing.

Channel mixing is another type of mixing supported by modern computer radios, whereby two separate channels can be mixed to operate together.

A common example of channel mixing is an aileron and rudder mix; a small amount of rudder is automatically applied when you operate the ailerons. The purpose of this is to produce a cleaner turn and can prevent the effects of adverse yaw, a common situation whereby the tail drops during a turn due to increased drag over the higher wing. Aileron Differential is the 'mechanical' answer to this issue.

Another example of a popular channel mix is to have elevator compensation with flap operation - as the flaps are lowered, the elevators automatically deflect downwards to counteract the natural tendency for a plane to pitch up as flaps are lowered (a result of extra lift being generated by the lowered flaps).

 
Proportional RC airplane controls

You'll often see the word proportional when looking at radio control systems.

By proportional control, we mean that the control surfaces respond directly to how much you move the stick of your transmitter. In other words, if you only move the stick a small amount then that channel will only respond a small amount. Moving the stick to the maximum position will move that channel to its maximum.

Apart from the cheapest rc toys, all modern-day radio control systems are proportional. Non-proportional functions of an rc model or toy will be simple 'on/off' or 'left/right' functions.

It's so important to have proportional control of your rc airplane, as this ensures accurate control. And bear in mind that most radio control planes will respond to the slightest control surface deflection - just a few millimeters deflection will be enough to change the plane's path through the air.

Understanding your rc airplane controls, or indeed the controls of any rc model, is of paramount importance if you want to enjoy your model to its fullest and get the most out of the hobby.
Always take a bit of time to understand how your new rc airplane, helicopter or vehicle is operating and responding to your transmitter inputs, rather than just moving a stick and watching the model change direction. You'll be a much better rc'er for it!

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