5. 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.
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.
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
•Weight (Gravity)
•Thrust
•Drag
7. 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
As speed increases, drag increases, until a point is reached where drag again equals thrust, and the airplane will
continue in steady flight at a higher speed. As another example, if power is applied while in level flight, and a
climb attitude is established, the force of lift would increase during the time back elevator pressure is applied; but
after a steady-state climb is established, the force of lift would be approximately equal to the force of weight. The
airplane does not climb because lift is greater than in level flight, but because thrust is greater than drag, and
because a component of thrust is developed which acts upward, perpendicular to the flightpath.
9. The primary controls are the ailerons, elevator, and the rudder, which provide the aerodynamic force
to make the aircraft follow a desired flightpath.
10. Elevator
When the pilot moves the controls forward, the elevator surface is deflected downwards. This increases the
camber of the horizontal stabilizer resulting in an increase in lift. The additional lift on the tail surface causes
rotation around the lateral axis of the aircraft and results in a nose down change in aircraft attitude. The opposite
occurs with an aft movement of the flight deck controls.
11. Aileron
Ailerons control roll about the longitudinal axis. The ailerons are attached to the outboard trailing edge of
each wing and move in the opposite direction from each other. Ailerons are connected by cables, bellcranks,
pulleys, and/or tubes a control stick.
12. Rudder
The increase in camber of the wing results in an increase in lift but this, in turn, also causes an increase in
drag. This added drag causes the wing to slow down slightly resulting in rotation, referred to as yaw, around
the vertical axis. To overcome this yaw rudder input is required while entering and exiting a turn. To minimise
the amount of adverse yaw produced during a turn.
18. From the shape of the airfoil it is clear that
the upper surface is more curved than the
lower surface. This means the particles on
the upper surface should travel a greater
distance than the particles on the lower
surface. Since both particles should reach
the trailing edge at the same time, the upper
surface particles should have more velocity
than the lower surface particles. This means
that according to Bernoulli's principle, there is
more pressure at the bottom and less
pressure at the top surface. The difference in
the pressure generates lift.
How the aircraft wing generates Lift?
24. To be a competent pilot
first requires that the pilot
is skilled in the basics of
fundamental airmanship.
This requires mastery of
the four basic flight
maneuvers upon which all
flying tasks are based:
straight-and-level flight,
turns, climbs, and
descents.
