CarterCopter
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The CarterCopter is an advanced aircraft, a combined fixed wing aeroplane/autogyro currently under development by Carter Aviation Technologies, a privately owned company based in Wichita Falls, Texas.
The design has a gyroplane rotor mounted on top which is unpowered in flight, but it also has short fixed wings like a conventional aeroplane. Unlike a helicopter, the aircraft is entirely powered by a pusher propeller at the rear.
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[edit] Concept
The Cartercopter concept is a gyrocopter with an unusually stiff, relatively heavy rotor, supplemented with conventional wings. At low speed, the vehicle flies as a gyrocopter, and can pre-spin the rotor for a vertical takeoff and very brief hover, and can land more or less vertically.
At high speed (above about 100 mph) the aircraft flies mostly using the fixed wings, with the rotor simply windmilling. Unusually for a rotorcraft, the rotor spins with a tip speed below airspeed, which means that the retreating blade flies completely stalled. Normally this would cause massive lift asymmetry and insoluble control issues on a helicopter, but the fixed wings keep the aircraft in the air and stable.
The low rotation speed and flat feathering of the rotor means that it causes little drag, and the company claim that the aircraft would be potentially able to leverage the advantages of fixed wings as well as gyrocopters, giving almost all the capabilities of helicopters but with a mechanically relatively simple system and probably safer system capable of higher airspeed that fixed wings can achieve, but capable of landing in any small area in an emergency.
[edit] Takeoff
At takeoff the pilot angles the rotor flat and spins it to very high speed, then disconnects the engine and flips the angle of the main rotor blades so that the vehicle leaps into the air. The aircraft's main rotor then has enough momentum (due to heavy counterweights in the tips) that it can hover for a short time safely. The pilot then applies full power to the pusher and the vehicle starts to move forwards. As it does so, the air gets forced through the main rotor spinning it faster and giving more lift. The vehicle climbs into the air.
[edit] Cruising
Once the CarterCopter gets up to a forward speed of about 90 miles per hour (145 km/h), its stubby, lightweight wings provide most of the lift. The pilot then flattens the angle of the main rotor so it produces hardly any lift and this drastically reduces the drag. The CarterCopter then surges forwards in the air. Although the rotor is unused at high speed, the rotor is kept spinning as it keeps the rotor rigid, preventing excessive flapping.
Normally a helicopter or gyrocopter cannot go as fast as its rotor tip speed. This is because the retreating rotor blade would stop in the air, whilst the leading rotor blade would be travelling at twice the speed. The vehicle would 'fall over' due to retreating blade stall.
However, with the CarterCopter, the fixed wings are keeping the vehicle at the correct angle to the horizon and providing the lift. Since the rotor is unloaded, the aerodynamic forces on the rotor are very minor. This means that a CarterCopter can theoretically fly much faster than the tip speed of the rotor. The rotors would flap a little as they rotate to deal with the difference in lift between the two sides of the vehicle, but this is manageable.
The theoretical maximum speed of a CarterCopter is around 500 mph (800 km/h), which would be twice as fast as any helicopter has ever gone.
[edit] Achievements
At present, the prototype's engine is normally aspirated, and hence is limited to just 320 hp (240 kW) and the fastest Carter Aviation Technologies prototype has achieved is about 173 mph (270 km/h); which is still ~40% faster than a conventional autogyro but slower than gyrodynes of the 1950s.
A helicopter to go the same speed would need almost twice this power.[citation needed] Thus the CarterCopter seems to be about twice as efficient.
The maximum mu that has been achieved (mu is the ratio of airspeed to rotor tip speed) is 1.0 for a brief moment on June 17, 2005, the first time any rotary aircraft has reached this level. (CarterCopter's pilot claimed that there was no great drama, and mu -1 was reached accidentally due to normal variations in rotor RPM and vehicle airspeed; the pilot described it as 'smooth' with no significant vibration.)
However, on the next test flight the same day, the CarterCopter made a hard landing (crashed), causing significant damage, but the pilot was unhurt. The crash was caused by a partial loss of control of the rotor due to a hardware failure. It was initially believed that the CarterCopter was unrepairable; later inspection showed that it could be repaired, but the company has chosen to work on other projects at this time.
[edit] Potential
The bottom line is that the vehicle architecture potentially outperforms helicopters on every dimension except sustained hover, and should be much cheaper to buy and maintain. It also very nearly matches fixed wing aeroplanes- but with near-vertical takeoff and landing; and at only modestly higher cost to buy and maintain than a fixed wing aircraft.[citation needed]
[edit] See also
[edit] External links
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