The Basics of Flight

The concepts of flight should be understood by a beginner. 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.

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

 Airfoil - The cross section of the wing Angle of Attack - The angle between the chord line and the relative direction of flight Chord Line - The line between the leading edge and the trailing edge of the airfoil Direction of Flight - The relative direction of the wing in relation to stillair Leading Edge - The most forward edge of the wing Trailing Edge - The most rearward edge of the wing

There are four (4) primary forces which 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 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.

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.