CarterCopter

The CarterCopter is an experimental compound autogyro developed by Carter Aviation Technologies to demonstrate slowed rotor technology. On 17 June 2005, the CarterCopter became the first rotorcraft to achieve mu-1 (μ-1), an equal ratio of airspeed to rotor tip speed.

Design and development

The Carter copter is a pusher configuration autogyro with wings and a twin boom tail. The rotor is a two-bladed design weighted with depleted uranium at each tip.It is an all-composite design

The tricycle undercarriage is retractable. The undercarriage has a large travel to allow for landing at up to 20 ft/sec.

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. Several technical challenges make flying a slow rotor difficult.

At high speed (above about 100 mph) the aircraft flies mostly using the fixed wings, with the rotor simply windmilling. The rotor spins with a tip speed below airspeed, which means that the retreating blade flies completely stalled. On a helicopter this would cause massive lift asymmetry and insoluble control issues 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 claims 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 (except hovering) but with a relatively simple mechanical system. Carter Aviation also claims the system is safer than a typical helicopter. The CarterCopter should be capable of the higher airspeeds that can only be achieved by fixed wing aircraft, but also able to land in any small area in an emergency.

Takeoff

At takeoff the pilot angles the top rotor flat (zero angle of attack) and spins it to very high speed. The rotor is then disconnected from the engine and the angle of attack of the main rotor blades is increased suddenly so that the vehicle leaps into the air. The aircraft's main rotor 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 rear pusher propeller and the vehicle starts to move forwards. As it does so, air is forced through the main rotor, spinning it faster and generating more lift. The vehicle climbs into the air, flying as an autogyro .

Cruising

Once the CarterCopter gets up to a forward speed of about , its stubby, lightweight wings provide most of the lift. The pilot can then flatten the angle of attack of the main rotor so it produces very little lift, dramatically reducing the amount of induced drag created by the rotor. 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 fly forward at the same speed (or faster) as its rotor tip speed. This is because the retreating rotor blade would stop in the air, whilst the leading rotor blade would be traveling at twice the speed of the aircraft. The vehicle would 'fall over' due to retreating blade stall and the dissimilar lift.

However, with the CarterCopter, the fixed wings keep the vehicle at the correct angle to the horizon and provide the lift required to remain aloft. 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 still experience flapping as they rotate due to dissymmetry of lift lift between the two sides of the vehicle, but Carter Aviation claims this is manageable.

The claimed theoretical maximum speed of a CarterCopter is around 500 mph (800 km/h), which would be about twice as fast as any helicopter has ever gone.

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 gyrodyne s of the 1950s. A custom gyroplane can go 168.29 km/h (104.6 mph).

A helicopter to go the same speed would need almost twice this power. Thus the CarterCopter seems to be about twice as efficient.

From 1999 to 2001 there were 4 recorded instances of non-fatal crashes.

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 pilots were unhurt. The crash was caused by failing propeller bolts which damaged wires controlling the rotor. It was initially believed that the CarterCopter was unrepairable; later inspection showed that it could be repaired, but the company chose to work on a small open autogyro demonstrator instead.

The company claims that the testing indicated

that the vehicle architecture could potentially outperform helicopters on every dimension except sustained hover, and should be much cheaper to buy and maintain. The company also claims that it also very nearly matches the L/D of fixed wing General Aviation aeroplanes at cruise speed - but with near-vertical takeoff and landing.

Specifications

|crew=|capacity=5 |payload main=|payload alt=|payload more= |length main=|length alt=|span main=32 ft|span alt=|height main=|height alt=|area main=77 sq ft|area alt=|airfoil=|empty weight main=2,000 lb|empty weight alt=|loaded weight main= ~3800 lb inc. 30 gallons of fuel

|loaded weight alt=|useful load main=|useful load alt=|max takeoff weight main=|max takeoff weight alt=|more general=|engine (prop)="V6 NASCAR racing engine". |type of prop=piston engine|number of props=1|power main= 600 hp |power alt=|power original= rated for short duration

|propeller or rotor?=rotor

|propellers=two-bladed

|number of propellers per engine=|propeller diameter main=33 ft 6 in|propeller diameter alt= |max speed main=|max speed alt=|max speed more=|cruise speed main=173 mph|cruise speed alt= |cruise speed more=|never exceed speed main=|never exceed speed alt=|stall speed main= |stall speed alt=|range main=|range alt=|range more=|ferry range main=|ferry range alt=|ferry range more=|ceiling main= 10,000 ft|ceiling alt=|ceiling more=|climb rate main=|climb rate alt=|climb rate more=|loading main=|loading alt=|thrust/weight=

|power/mass main=|power/mass alt=|more performance=

* L/D of 7 @ 170 mph

|avionics=

}}