Aerodynamics and Principles of Gyroplane Flight
Aerodynamics questions for the gyroplane rating test whether you understand a rotor turned by the air, not by the engine. The exam concentrates on autorotation, dissymmetry of lift, the reversed pitch/power relationship, and the low-airspeed region where gyroplanes get into trouble.
Autorotation
A gyroplane rotor has no engine drive. Air flows upward through the disc, and the resultant relative wind meets each blade at a positive angle of attack, producing lift and the force that keeps the rotor turning. Because the rotor freewheels, there is no torque to counteract and no tail rotor is needed. Rotor RPM is self-regulating: raise airspeed or load and the blades accelerate until forces balance.
Lift, flapping, and coning
- The advancing blade sees a higher relative wind and produces more lift; it flaps up.
- The retreating blade sees less and flaps down, equalizing lift across the disc. Dissymmetry of lift is handled by flapping, not by powered pitch changes.
- Coning is the upward bend of the blades under lift; excessive coning signals low rotor RPM or overloading.
The pitch/power reversal
In a gyroplane the cyclic controls airspeed and the throttle controls climb and descent, the opposite of an airplane. Lower the nose to go faster; add power to arrest sink. Because the rotor must always see airflow, a gyroplane cannot hover. Pitch up too far and you enter the region behind the power curve, where airspeed decays, sink rate climbs, and full power may not stop the descent until the nose comes down.
Worked example
On short final a pilot raises the nose to slow from 60 to 45 kt. Airspeed decays to 30 kt, sink rate doubles, and full power barely holds altitude. The fix is forward cyclic to rebuild airspeed; power alone cannot help because the rotor is starved of airflow.
Traps
Applying airplane pitch-for-airspeed logic; assuming the rotor stalls like a wing; unloading the rotor in a pushover so RPM decays and blades flap; and misjudging turns in wind, where a downwind ground-speed increase tempts over-banking.