The Basics of Flight

A beginner should understand the basic concepts of flight. The theories behind the physics of flight are covered in many volumes of books. There are different and sometimes conflicting theories and arguments as to how airplanes fly, but the one accepted principle is that lift is generated as a result of the air pressure on the bottom of the wing being higher than the air pressure on the top of the wing.

Lift Diagram

The Lift Diagram shows some of the basic terms relating to a wing section.  These terms are common to R/C flight.

There are four (4) primary forces that act on an aircraft in flight; thrust, lift, drag, and weight. Thrust is the force applied by the combination of engine and propeller acting to pull the aircraft forward.  Drag is the resistance against the aircraft by the force of the air against the forward facing surfaces. Weight is caused by gravity. In order for a constant speed to be maintained, thrust and drag must be equal. In order for a constant altitude to be maintained, lift and weight must be equal.

Lift and Angle of Attack

Lift increases as the velocity of the air passing over the wing increases or as the angle of attack increases as long as the flow of air over the wing remains smooth. Actual flight is attained when the force of the lift equals weight.

An aircraft pivots about three (3) axes; the yaw or vertical axis controlled by the rudder, the pitch or lateral axis controlled by the elevator, and the roll or longitudinal axis controlled by the ailerons.  It can pivot about any one of these individually or in combination based on the control surfaces that are moved and the direction of the movement.

Axes of Rotation

When the rudder is moved to the right, the aircraft will rotate to the right about the yaw axis and vice versa.  When the elevator is moved up, the aircraft will pitch the nose upwards. The ailerons move in opposite directions.  When the left aileron is moved up and right one down, the aircraft will rotate to the left and vice versa.

Effects of Control Surfaces

The new radio systems are proportional control meaning that the control surfaces move in proportion to the amount of movement of the stick.  If the stick is moved half of its total travel in one direction, the corresponding control surface will move half of its total travel in the corresponding direction.  A beginner must first know the effect that a stick movement has on the model.  During normal flight, the throttle is set so that a constant speed is maintained. This means that thrust is equal to drag and lift is equal to weight. From this stable condition, the effects that the stick movements have on the trainer are described.

Elevator Stick – Pull Back

When the right stick is pulled back, the elevator moves up.  This causes the nose to pitch upward increasing the angle of attack of the wing and increasing drag.  If power is not applied, the airplane will slow down and eventually stall.  This means that the air passing over the wing becomes turbulent and lift decreases until weight exceeds lift and the airplane will begin to drop.

Elevator Stick – Push Forward

When the right stick is pushed forward, the elevator moves down. This causes the nose to pitch downward reducing the angle of attack of the wing and reducing drag. As the airplane descends its speed increases until drag and thrust are again in balance.

Aileron Stick – Move Right

When the right stick is moved right, the left aileron moves down and the right aileron moves up. This causes the airplane to roll to the right meaning that the left wing moves up and the right wing moves down. It will continue to roll as long as the stick is held in the same position. When the roll takes place, lift is no longer oriented vertically so the effective lift decreases.  As the angle of the roll increases, effective lift continues to decrease and the airplane will begin to drop.

Aileron Stick – Move Left

When the right stick is moved left, the left aileron moves up and the right aileron moves down.  This causes the airplane to roll to the left meaning that the right wing moves up and the left wing moves down. It will continue to roll as long as the stick is held in the same position. When the roll takes place, lift is no longer oriented vertically so the effective lift decreases.  As the angle of the roll increases, effective lift continues to decrease and the airplane will begin to drop

Rudder Stick – Move Right

When the left stick is moved right, the rudder moves to the right. This causes the airplane to swing or yaw to the right. This causes the left wing to move slightly faster through the air causing an increase in lift. The combination of the yaw and the lift increase on the left wing results in a gentle turn to the right as long as the stick is held in position.

Rudder Stick – Move Left

When the left stick is moved left, the rudder moves to the left. This causes the airplane to swing or yaw to the left.  This causes the right wing to move slightly faster through the air causing an increase in lift. The combination of the yaw and the lift increase on the right wing results in a gentle turn to the left as long as the stick is held in position.

When the left stick is moved forward, the throttle is opened resulting in an increase in speed of the airplane.  This causes an increase in lift and results in a tendency for the aircraft to climb.  When the left stick is moved back, the throttle is closed resulting in a decrease in speed. This causes a decrease in lift and results in a tendency for the aircraft to descend.

It is obvious from the descriptions of the effects of stick movement, that any movement can adversely affect the flight of a model.  These effects can be overcome by using a combination of control surfaces to achieve the desired results.  For instance, the right stick can be moved back when it is moved left. The result of this action would be that the nose of the airplane would be raised to overcome the loss of lift resulting in a banked turn without a loss of altitude.

In order to understand how to properly use the controls, a change in thinking may be required of a beginner who has some basic knowledge of control surfaces.  A beginner must remember the forces acting on a model in flight and how they affect the model.