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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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