Chapter 2 - Aerodynamics of Flight
Lift
Lift opposes the downward force of weight and is produced
by the dynamic effects of the surrounding airstream
acting on the wing. Lift acts perpendicular to
the flight path through the wing’s center of lift. There
is a mathematical relationship between lift, angle of
attack, airspeed, altitude, and the size of the wing. In
the lift equation, these factors correspond to the terms
coefficient of lift, velocity, air density, and wing surface
area. The relationship is expressed in Figure 2-11.
This shows that for lift to increase, one or more of the
factors on the other side of the equation must increase.
Lift is proportional to the square of the velocity, or
airspeed, therefore, doubling airspeed quadruples the
amount of lift if everything else remains the same.
Small changes in airspeed create larger changes in
lift. Likewise, if other factors remain the same while
the coefficient of lift increases, lift also will increase.
The coefficient of lift goes up as the angle of attack
is increased. As air density increases, lift increases.
However, you will usually be more concerned with how lift is diminished by reductions in air density on
a hot day, or if you are operating at higher altitudes.
All wings produce lift in two ways:
1. Airfoil shape creating a higher velocity over
the top of the wing and a lower velocity over
the bottom of the wing with Bernoulli’s venturi
effect.
2. Downward deflection of airflow because of
the curvature of the wing with the principle of
Newton’s Third Law of Motion: For every action,
there is an equal and opposite reaction.
Both principles determine the lifting force. Review
Chapter 2 in the Pilot’s Handbook of Aeronautical
Knowledge to understand Newton’s laws of motion
and force and Bernoulli’s principle of pressure. |
