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GYROPLANES AND OVERHEAD ROTOR DISC
AREA USED TO CREATE PLANE / DISC

Identifying the Mechanics of Lift and Control

  • The mechanics of lift
  • What are the benefits of autorotation?
  • What is actually being flown, the overhead rotors or the airframe?
  • What is a big danger of low rpm?
  • Flying backwards in high winds?
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The mechanics of lift are created by two wings set end to end with opposite pitch. They are attached to a teetering, gimbal head for controlled movement, both automatic and pilot input. Like a regular aeroplane wing, the movement of air across top and bottom surface of the wings creates lift. In a gyroplane the lift is created by the two wings spinning at high rpm through the air rather than the air being forced over stationary wings. This is achieved by autorotation.

The benefits of autorotation are many. Unlike a stationary aeroplane wing, the autorotation of the blades of a gyroplane are less affected by gusts of wind. This is true because the blades are moving at more than ten times the speed of the gust of wind. So they cut through it easily while still providing lift. Gusts of wind through the rotor disc area simply add to the rpm, which is good. Helicopter blades do not benefit from this as they are pushing air rather than using aeroplane wing style lift. Another benefit of autorotation on the gyroplane is that it is not created by engine power, but is a result of forward motion and air movement up and through the disc area. This is the big safety issue that the Spanish inventor: Juan de la Cierva invented / designed, as a method to stop aeroplanes from falling out of the sky, (because of wing stalling on regular aeroplanes). It's important to keep flight motion in a positive manner to maintain rotor disc speed and autorotation. The diagram is shown as in flight with the gyroplane moving in the same direction as the wind. Therefore the gyroplane must be flying much faster than the wind speed.*1 So if the ground speed is 40 knots and the wind speed is 15 knots, what is the forward airspeed of the gyroplane? 25 knots or 55 knots?

Actually, what is being flown, on a gyroplane, is the overhead rotor disc (the two spinning blades form the 'disc'. This is essentially the 'wing' that the gyroplane flies on. The body, engine, wheels and pilot are a mass hanging below the flying disc. The vertical tail is there to keep the airframe (pilot) pointed in the same direction as direction of travel. The pilots use of the stick against the resistance of the gyroscopic effect of the rotor is how the rotor disc is adjusted in flight. If you think of a 'Frisbee' disc spinning through the air, propelled by the last movement of the thrower, then you can imagine the rotor disc on a gyroplane. So, the most important thing in flying a gyroplane, is to keep the rotor disc in the proper attitude through calm air and gusty conditions. Generally you want to increase air speed the closer you get to the ground. This is because air speed is a source of energy should the engine quit.

Low rpm on a rotor disc can be dangerous to the flying state of the gyroplane. Imagine you have a rope with a small weight on it and you're spinning it above your head. The slower you spin the rope the lower the end of the rope drops. This happens in reverse on a spinning rotor disc. The faster the rotor spins the more lift is balanced on a horizontal plane. The slower the rotor spins the more coning occurs which puts strain on the blades, twists them more, forcing more face towards the air flow which slows them down. *1 Another effect of coning is the reduction in disc area, reducing the area of lift.
Flying with the direction of the wind, on a very windy day can also cause a reduction in lift, even though the rpm is up. The gyroplane can loose a hundred feet of elevation in seconds caused by a reduction of the wind going up and through the disc plane. Thus the practice of flying higher, giving more time to correct the situation. It's also more beneficial to have shorter rotor blades than longer ones as shorter ones spin faster cutting through uneven air layers.

The number one fact to remember with gyroplanes is that you're really flying the rotor disc above your head. Be knowledgeable about it, and it will behave properly for you.

What's the difference between how a helicopter's overhead rotors work and how a gyroplane's rotors work?
A helicopters rotors work like a fan blowing air downward to create lift. A gyroplanes rotors work by receiving air upwards and creating lift just like an aeroplane wing does, only it spins. In fast forward speeds the leading edge of the disc is right on the edge of "going under".

 

   
   
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Revisions: *1 Revised Jan. 17, 2009