Ground School - Aircraft Controllers and Control Surfaces

Note:  All illustrations in this section, and edited text, are copied from, and used with the permission of , Pete Carpenter, . Visit the web site for a wide variety of RC information and more detail of what is ( and is not ) covered here.

Radio control functions and features vary depending on the complexity of the rc system, but the majority of rc systems do all share the same basic concepts.

The fundamental purpose of the rc system is, of course, to control the directional movement of your aircraft.  There are 2 channel systems, available for simple aircraft such as gliders, and those going up to as many as 12 channels for complex airplanes.  The word 'channel' refers to each separate function of the rc system,  like a channel for the throttle, a channel for the rudder, etc.

Because of space limitations, we will concentrate on 4 channel systems.

Just to add to any confusion, in addition to systems with different numbers of channels, transmitters are available in 4 different “Modes” ( Mode 1, Mode 2, Mode 3, and Mode 4).  The mode of a transmitter refers to what functions the two “sticks” control.  In North America, most transmitters with 4+ channels use Mode 2 functionality.

A Mode 2 transmitter with 4+ channels is shown in the illustration below.

Each stick on a Mode 2, 4+ channel transmitter moves up and down and left and right...

The right hand stick moves forward and backward to control the up/down elevator movement and it  moves left and right to control the ailerons.

The left hand stick  moves forward and backward to control the throttle  and it moves left and right to control the rudder.
Learning to control two actions with one stick may sound complicated but is quickly mastered and with practice quickly becomes second nature.

RC airplane controls are the same as those found on full size airplanes and they control the model in exactly the same way.

The four primary controls of an rc airplane are throttle, elevator, ailerons and rudder. The elevator, ailerons and rudder are known as control surfaces and the picture below shows where these main controls are located on a typical 4 channel aerobatic rc airplane....


The Throttle

Throttle assembly of a glow plug engine

The throttle ( or electronic speed control – ESC on an electric powered model)  controls the speed of the engine.

In the air throttle/motor power not only controls the forward speed of the airplane but also, more importantly, the rate of climb and descent, because different amounts of lift are generated at different airspeeds. For example, if your landing approach path is too low you can make the airplane rise slightly without changing speed much, simply by opening the throttle instead of using up elevator. Conversely, closing the throttle will cause the airplane to sink before the speed reduces.

Using throttle/motor power in this way is the correct way to fly your rc airplane, but many pilots just rely on elevator inputs to adjust altitude and rates of climb and descent.


The Elevators

The elevators are the hinged section of the tailplane, or horizontal stabiliser, at the very rear of the airplane. Elevators control the horizontal pitch attitude of the airplane, in other words whether the nose of the plane points upwards or downwards.

When elevators are in the up position (upward deflection) the nose of the airplane is forced to point upwards, and with the elevators deflected downwards then the nose is forced downwards.


Elevators are used in conjunction with rudder and/or ailerons when making a turn.

 The Ailerons

Ailerons control the roll of the airplane about its longitudinal axis (imagine a straight line running from nose to tail).

Ailerons come in pairs and are found on the trailing (rear) edge of the wing, and they work opposite to each other i.e. when one aileron moves up, the other one moves down and vice versa.

Using ailerons changes the airplanes roll

When used to turn the plane aileron input is applied first to roll the plane in the desired direction, and then up elevator, and/or rudder, is applied to pitch the nose around in that same direction; the end result is a banked turn. Ailerons are also used in many aerobatic maneuvers where rolling the airplane is necessary.


The Rudder

The rudder is the hinged section of the fin, or vertical stabilizer, at the rear of the airplane.
It's used for directional control by changing the yaw of the airplane and works in a positive manner i.e. moving the rudder to the left causes the airplane to turn left and vice versa.


Applying rudder makes the nose of the airplane point to the left or right, but rudder alone does not make the airplane roll like ailerons do. It's actually the dihedral, or the upward 'V' angle of the wing when viewed from the front, that makes the plane roll when rudder is applied; a plane with very little or no dihedral will have a much flatter turn when rudder is applied.

Rudder is also very important on the ground, it's the one control that will keep your rc airplane tracking straight during a take off run or landing roll. Nose wheels are often connected to the rudder servo and tail wheels directly to the rudder (or its own servo) on many planes, making the wheel steerable and ground handling much easier.

The trimming function

 trimsSmall trim levers, also called trim tabs or simply trims, are located adjacent to each stick, one for each direction in which the stick moves. The trim levers have exactly the same effect as the main sticks, only to a much finer degree.

Essentially the trims fine tune the servo deflection for control surfaces or the motor idle speed of the model. With rc aircraft, the aim of trimming is to get your model flying as straight and level as possible with the main transmitter sticks in their central positions, and with no input from you.

All rc transmitters, with the exception of the cheapest toy ones, have a function that allows you to 'trim' your model before  or while it is being flown.

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