Theory of flight
Four forces act on every airplane in flight: lift, produced by the wings; thrust, created by the engine; weight, which you could think of as gravity; and drag, caused by several factors that resist the airplane's forward progress. The relationship between them is important — in steady, level flight, these four forces must balance each other.

The four forces

Flight controls
Just exactly how does an airplane navigate through the air? Flight controls deflect the airflow around the plane, allowing it to climb, descend, or turn. An elevator (or a stabilator, which does the same thing a little differently) allows the pilot to pitch the nose up or down. A rudder turns the nose left and right. Ailerons permit an airplane to roll about its longitudinal axis. Like the four forces, however, a pilot must use the flight controls together to get the desired results.

Flight controls
Flight control forces
Retractable landing gear

Propeller safety
It's very important that you inspect and take care of the propeller on the airplane you fly. The AOPA Air Safety Foundation offers tips on what to look for in your preflight inspection, operational considerations, maintenance, and other steps you can take in order to ensure a safe flight.
The full range of Safety Advisors is available on the AOPA Air Safety Foundation's website.

Propeller Safety
(Online Version)

Propeller Safety
(PDF Version, 798 KB)