Man's physical universe

xanabras

UNIT V

SECTION 8

FLYING AN AIRPLANE CONSISTS OF PROPERLY CON-

TROLLING THE FORCES OF THRUST, DRAG, LIFT, AND

GRAVITY

Introduction.

Aerodynamics is the study of the forces produced by the relative

motion between the air and a soUd body. An airplane is a mechanically

driven heavier-than-air craft, fitted with wings which support it in

flight by the dynamic action of the air which results from the forward

motion of the airplane relative to the air. The forward motion of the

airplane is the result of a force, called the thrust, which is produced

by the airplane propeller.

The dynamic action of the air resulting from the forward motion of

the airplane may be resolved into two forces, the lift and the drag.

The force of gravity is a static force, i.e., it acts without any motion

of the airplane.

It is the purpose of this Section to study how the forces of thrust,

drag, lift,

and gravity are controlled so as to enable one to fly.

The Thrust Is the Force Which Propels the Airplane.

Birds use their wings to attain forward motion in the air as well as to

maintain their position in the air.

In the airplane these functions are

separated; and the propeller, which is really a specialized wing, is used

to maintain forward motion.

In the helicopter, however, the propeller

has the dual action of the wings of a bird.

The propeller produces the force called the thrust in accordance with

Newton's third law of motion, which states that to every action there is

always an equal and opposite reaction.

A rocket is propelled through the air by the thrust which the escaping

jet of gases produces against the rocket. The backward force of a

propeller against the air is what forces it forward. The propeller may

be placed in front of the engine or behind it.

In the first case the airplane

is called a tractor, and in the second case it is called a pusher.

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