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 condition, it is important that pilots
gain as much knowledge as possible concerning the laws and principles that
apply to flight.
Forces
Acting Upon an Airplane in Flight
During flight
there are different forces that are acting against and with the airplane.
These forces are described as positive (+) forces and (-) forces. It is
the task of the pilot to keep these forces equal with each other to maintain
straight and level flight.
While in steady
flight the attitude, direction and speed of the airplane will remain constant
until one or more of the basic forces changes in magnitude. In un-accelerated
flight the opposing forces are in equilibrium. Lift and thrust are considered
positive forces, while weight and drag are considered negative forces,
and the sum of opposing forces is ZERO, in other words lift equals weight
and thrust equals drag.
Angle
of Attack
The acute
angle between the chord line (the imaginary straight line drawn from the
leading edge to the trailing edge of a cross section of an airfoil), of
the wing and the direction of the relative wind.
Principles
of Flight
To understand
how an airplane flies and creates lift, two principles need to be reviewed.
These laws are Bernoulli's principle and Newton's law of Motion. Bernoulli's
principle states that the internal pressure of a fluid decreases at points
where the speed of the fluid increases. In laymen's terms, high speed
flow is associated with low pressure and low speed with high pressure.
Newton's 3rd law of motion, for every action there is a equal and opposite
reaction, as the wing directs the air downward an upward force is generated.
Reference
Pilot's Handbook
of Aeronautical Knowledge. 1. Basin, Wyoming: Aviation Maintenance Publishers
Inc., 1980.
|