How an Aircraft Flies: Control Surfaces

The basic rules of flight state that for an aircraft to fly straight, at a continuous speed, then lift must equal weight, and thrust must equal drag.

But, of course, it wouldn’t be much use if an aircraft could only fly straight would it?! So, how does a plane ascend, descend, turn and increase/decrease speed?

Firstly, let’s look at a diagram of a modern airliner’s control surfaces; 

As you can see, the main controls used are; flaps, ailerons, rudder, and elevators.

Flaps: You will see that flaps can be found on both the leading edge, and the back of the wing. They are used to give more lift during take-off and landing. Increasing the surface of the wing increases lift to allow the aircraft to take-off and land at slower speeds – therefore needing less runway.

The flaps also increase drag, therefore, during the cruise they will retract to decrease drag. This means that less thrust is needed to maintain speed, and therefore less fuel is used.

Ailerons: These are used to tilt or bank the aircraft (i.e. turn). As an example, to turn left the left aileron is raised. Natural lift on an aircraft points straight up, so by raising the aileron there is effectively less lift on that wing.

The effect of having more lift on one wing than the other forces one to rise – and therefore the aircraft tilts and turns in that direction.

Back to our example; Raising the left aileron will result in less lift on the left wing. Therefore, the right wing will rise, and the aircraft will tilt to the left – and turn.

CLICK HERE FOR ANIMATED DEMONSTRATION OF AILERONS

Rudder: This is used to assist in turning the aircraft. It works in a similar way to the ailerons, but it alters the level of drag on the chosen side of the aircraft.

If we use the example of a left turn again, the rudder would move to the left which would create more drag on the left hand side. In effect, this means that the right hand side can move faster than the left and therefore the aircraft turns that way.

CLICK HERE FOR ANIMATED DEMONSTRATION OF THE RUDDER

Elevators: Much the same as both ailerons and the rudder works, elevators point the nose up or down. To climb, the elevators are moved upwards, and to descend, they move downwards.

When climbing, thrust is increased so that the speed of the aircraft does not alter (just like a car going up a hill, the plane naturally wants to slow down when pointing upwards, and go faster when doing the opposite).

CLICK HERE FOR ANIMATED DEMONSTRATION OF ELEVATORS

In essence, flying sounds much more complicated than it really is. Wings provide lift, engines provide the thrust to move us forward, and the controls explained above enable us to change direction (either horizontally or vertically).

Any questions? Just ask…..

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