Overview
This lesson introduces the four fundamental forces acting on an airplane in flight, establishing a foundation for understanding aerodynamics necessary for private pilot training.
The Four Forces of Flight
- Four forces act on an airplane in flight: lift, weight, thrust, and drag.
- Lift is the upward force that raises the aircraft, generated by relative wind and wing design (airfoil).
- Weight is the combined mass of the aircraft, occupants, fuel, and cargo, acting downward through the center of gravity.
- Thrust moves the aircraft forward and is created by the engine and propeller.
- Drag opposes thrust and resists forward movement.
Types of Drag
- Parasite drag increases exponentially with airspeed and consists of form, interference, and skin friction drag.
- Form drag results from air moving around the shape of the aircraft.
- Interference drag is caused by turbulent airflow meeting at aircraft intersections.
- Skin friction drag is due to microscopic roughness on the aircraft’s surface.
- Induced drag is directly related to lift and decreases as airspeed increases.
Balancing Forces in Flight
- In steady, unaccelerated flight, lift equals weight, and thrust equals drag.
- Increasing thrust causes the airplane to climb because lift exceeds weight.
- Raising the nose to increase lift also increases induced drag, causing airspeed to decrease as drag exceeds thrust.
Key Terms & Definitions
- Lift — Upward force created by airflow over the wings (airfoil).
- Weight — Total mass of aircraft and contents, acting downward.
- Thrust — Forward force produced by engines and propeller.
- Drag — Force opposing forward movement; includes parasite and induced drag.
- Parasite Drag — Drag not related to lift, increases with speed; includes form, interference, and skin friction drag.
- Induced Drag — Drag created as a byproduct of lift, decreases with higher airspeeds.
- Center of Gravity — Point where the aircraft’s weight is balanced.
- Lift to Drag Ratio (LD Max) — Airspeed where lift is maximized compared to drag, minimizing total drag.
Action Items / Next Steps
- Watch lesson two in the series to continue learning about aerodynamics.
- Review and understand definitions and relationships between the four forces.
- Prepare for questions on these concepts in the written test.