How RPAS Fly
A little aerodynamics makes you a safer pilot — you'll anticipate how your aircraft behaves instead of being surprised by it.
Lift and the four forces
- Lift comes from smooth airflow over an aerofoil (wing or rotor blade) — explained by both Bernoulli's principle and Newton's third law.
- Four forces act on every aircraft: lift, weight, thrust, drag. Steady flight is a balance between them.
- Angle of attack is the angle between the aerofoil and the oncoming air. Too high and the airflow separates — a stall, and lift is lost.
Aircraft types
- Multirotor (e.g. quadcopter) — varies the speed of each motor to control lift and direction; can hover, but relies heavily on sensors and has shorter endurance.
- Fixed-wing — efficient and long-range, but cannot hover and needs space (or a launcher/recovery system).
- VTOL fixed-wing — combines vertical take-off/landing with efficient forward flight.
- Helicopter / single-rotor — long endurance, mechanically complex.
A fixed-wing aircraft cannot stop and hover, so the pilot must always keep it moving and stay ahead of its flight path.
Because multirotors depend on sensors (IMU, GNSS, compass) for stability, a sensor or GPS problem affects handling directly — practise flying in a lower-assistance mode so you're ready to take manual control.
Load factor
Turns, gusts and abrupt inputs increase the load on the airframe — aggressive manoeuvres in turbulence can exceed structural limits.
Check your understanding
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Key takeaways
- Lift = smooth airflow over an aerofoil; balance lift/weight/thrust/drag.
- Too much angle of attack → stall.
- Multirotors hover but lean on sensors; fixed-wings are efficient but can't hover.
- Turns and gusts raise load factor — be gentle in turbulence.
Sources: RPAS 101 pp.15, 67–69 · TP‑15263 §7 (Theory of Flight).