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INTRODUCTION
There are certain laws of nature or physics that apply to any object that is lifted from the Earth and moved through the air. To analyze and predict airplane performance under various operating conditions, it is important that pilots gain as much knowledge as possible concerning the laws and principles that apply to flight. The principles of flight discussed in this chapter are intended primarily for beginning pilots, and are not intended as a detailed and complete explanation of the complexities of aerodynamics.
FORCES ACTING ON THE AIRPLANE IN FLIGHT
When in flight, there are certain forces acting on the airplane. It is the primary task of a pilot to control these forces so as to direct the airplane’s speed and flightpath in a safe and efficient manner. To do this the pilot must understand these forces and their effects. [Figure 1-1] Among the aerodynamic forces acting on an airplane during flight, four are considered to be basic because they act upon the airplane during all maneuvers.
These basic forces are :
• Lift
• Gravity (Weight)
• Thrust
• Drag
While in steady-state flight, the attitude, direction, and speed of
the airplane will remain constant until one or more of the basic forces
changes in magnitude. In unaccelerated flight (steady flight) the opposing
forces are in equilibrium. Lift and thrust are considered as positive forces,
while weight and drag are considered as negative forces, and the sum of
the opposing forces is zero. In other words, lift equals weight and thrust
equals drag. When pressure is applied to the airplane controls, one or
more of the basic forces changes in magnitude and becomes greater than
the opposing force, causing the airplane to accelerate or move in the direction
of the applied force. For example, if power is applied (increasing thrust)
and altitude is maintained, the airplane will accelerate.
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