Basic Aerodynamics
What you must know
Basic aerodynamics covers the atmosphere and its properties, airflow and Bernoulli's principle, the generation of lift and drag, angle of attack, stall, and the four forces in flight (lift, weight, thrust, drag). You should understand airspeed terms (indicated, calibrated, true, ground speed), the relationship between altitude and air density, and the effects of temperature and pressure on aircraft performance.
Traps to watch
- Angle of attack versus attitude: stall depends on angle of attack, not airspeed or pitch attitude alone; an aircraft can stall at any speed if AoA is excessive.
- Bernoulli misconceptions: lift arises from pressure distribution over the wing, not simply from unequal path lengths; questions often test the pressure difference concept.
- Airspeed types: IAS is what the instrument shows; TAS corrects for density and position error; GS is TAS adjusted for wind.
- Density altitude: high altitude, high temperature, and high humidity all reduce density and degrade performance.
- Induced versus parasite drag: induced drag increases with lift (high AoA); parasite drag increases with the square of speed.
Worked example
An aircraft at high altitude in hot weather has a high density altitude. Although the indicated airspeed may be normal, true airspeed is higher because the air is less dense. Take-off run lengthens and climb performance decreases. Rule of thumb: as density decreases, for a given IAS the TAS increases by roughly 2% per 1000 ft of altitude.
Rule of thumb
Stall is a function of angle of attack; density altitude, not pressure altitude alone, governs performance.