Which of the following is NOT one of the four forces acting on an airplane?

In aviation, the four fundamental forces acting on an airplane during flight are lift, weight, thrust, and drag. Each of these forces plays a critical role in the dynamics of flight.

• Lift is the upward force generated by the wings, allowing the aircraft to rise off the ground.

• Weight is the downward force due to gravity acting on the mass of the airplane.

• Thrust is the forward force produced by the engines that propels the aircraft through the air.

Speed, while it is an important factor in the performance of an aircraft, is not considered one of the four primary forces. Instead, speed affects the generation of lift and drag as the airplane moves through the air. In essence, speed is a result of the interaction between thrust and drag, rather than a force acting on the airplane itself. Thus, identifying speed as not being one of the four forces accurately reflects its role within the principles of flight.