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An open-frame gyroplane in flight showing its rotor

Ground school lesson

Rotor principles for the checkride

The first aerodynamics lesson explained why the rotor turns. This one explains what the rotor is quietly doing every second it turns, which is what the practical test's principles-of-flight task actually asks.

My Hangar

Lesson 4 of 27 · 3 steps · about 8 minutes · ends with a quiz

What you will be able to do

  • Explain dissymmetry of lift and how flapping fixes it.
  • Explain coning, load factor in turns, and retreating blade stall.
  • State why airspeed, not groundspeed, rules turns near the ground.

  1. Step 1 of 3

    Dissymmetry of lift, and flapping

    In forward flight the blade swinging toward the nose (the advancing blade) meets the airflow faster than the blade swinging toward the tail (the retreating blade). More airspeed means more lift on one side of the disc: dissymmetry of lift. Left alone it would roll the aircraft.

    Dissymmetry of lift on a rotor disc in forward flight A rotor disc viewed from above, aircraft flying up the page. The advancing blade side meets more airflow and makes more lift; the retreating side less; blade flapping equalises the two. flight direction advancing: more lift, flaps up retreating: less lift, flaps down Flapping changes each blade's angle of attack and evens the lift out.
    The disc's fix is built in: blades flap up and down as they circle, equalising lift.

    The teetering rotor most gyroplanes carry lets the blades flap as a unit: the advancing blade rises, reducing its angle of attack; the retreating blade descends, increasing its own. The lift evens out automatically, hundreds of times a minute, with no input from you.

  2. Step 2 of 3

    Coning, load factor and retreating blade stall

    Three more the examiner may pick

    • Coning: spinning blades ride where lift pulling up balances centrifugal force pulling out, so the disc forms a shallow cone. Low rotor RPM means less centrifugal force and more cone, part of why RPM below limits is dangerous.
    • Load factor: banking multiplies the load the rotor carries: about 1.15 g at 30° of bank, 2 g at 60°. The rotor speeds up slightly under load in a gyroplane, but the structure and the descent rate both feel every g.
    • Retreating blade stall: push forward speed high enough and the retreating blade, flapping ever further to keep up, finally exceeds its stalling angle. It sets the practical ceiling on speed; the flight manual's never-exceed speed respects it.

  3. Step 3 of 3

    The downwind turn trap

    The practical test names this one explicitly. Turning from upwind to downwind near the ground, the groundspeed rises as the tailwind takes over. The eye sees the ground rushing faster; the untrained instinct is to slow down. But the rotor flies on airspeed, which has not changed, and yielding to that instinct trades away the margin above minimum flying speed at exactly the height where there is no room to recover.

    The discipline: in turns near the ground, fly the airspeed indicator and the aircraft's attitude, not the ground rushing under you. The wind does not care which way you are pointed, and the rotor only ever feels the air.

Check yourself

3 questions. Pick an answer to see whether it is right and why.

  1. What corrects dissymmetry of lift in a teetering-rotor gyroplane?

  2. In a level 60-degree banked turn, roughly what load factor does the rotor carry?

  3. Turning downwind close to the ground, the ground appears to speed up. What should you do?

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FAA Rotorcraft Flying Handbook FAA-H-8083-21, gyroplane aerodynamics chapters (public domain). Your never-exceed and minimum speeds are in the flight manual.