This is similar to aircraft. While many have "bells and whistles" thanks to new technology, the fundamentals never change. The four forces of flight—thrust, drag, lift, and weight—are always acting on every aircraft in flight. Having a solid understanding of those forces helps pilots safely control their aircraft and avoid safety-related issues such as exceeding the critical angle of attack or operating outside of the aircraft's weight and balance limits.

The first force, thrust, is controlled by the pilot by applying or reducing power. In level flight, thrust must be greater than drag for the aircraft to accelerate. If thrust is reduced, the aircraft will slow down until more power is applied. For an aircraft to move faster, the amount of thrust must be greater than the amount of drag. If thrust and drag are equal, the aircraft will maintain a constant airspeed. Pitch and power work together to manage airspeed and altitude, especially during takeoffs, approaches, and go-arounds.

Two types of drag affect an airplane in flight: parasite drag and induced drag. Induced drag is related to the aircraft developing lift, while parasite drag is not. Antennas, landing gear, and other protrusions disrupt airflow around the aircraft to create parasite drag. As an airplane slows, the wing must work harder to produce enough lift to maintain altitude, increasing induced drag. That means flying slower can actually require more power to maintain level flight, an important consideration during slow flight and approaches.

The pilot controls lift by moving the control yoke or stick forward or aft, changing the angle of attack. In general terms, when the aircraft is climbing, lift increases along with the wing's angle of attack up to a point. Once the critical angle of attack is exceeded, the wing stalls. Knowing how to recover from an aerodynamic stall is an essential skill for pilots. It's most critical to know how to avoid (and potentially recover from) such a stall when at lower altitudes, such as while flying the traffic pattern. Remember, an airplane can stall at any airspeed or attitude, not just when flying slowly.

The weight of an aircraft is a function of gravity. The center of gravity is the point on the aircraft where weight is concentrated and, if placed on a pinhead, the airplane would balance. In flight, when weight is greater than lift, the airplane descends. Conversely, if lift is greater than weight, you will climb.

This simple overview is just the tip of all there is to learn about the four forces of flight, how they interact together, how they are affected by the environment, and how pilots can control them to fly safely.

More information can be found online from the AOPA Air Safety Institute and in Chapter 5 of the Pilot’s Handbook of Aeronautical Knowledge.