Tiltrotor
A tiltrotor aircraft combines the maneuverability of a helicopter with the speed and efficiency of a turboprop aeroplane.
Basically, for vertical flight, large counter-rotating rotors support the aircraft. As the craft shifts to full-forward flight, the rotors tilt forward, acting as propellors.
In vertical flight, yaw is controlled either by differential rotation of the rotors, (using a differential powered by a hydraulic or electric motor), or by thrusting the rotors in opposite directions. Vertical motion is controlled with conventional pitch and collective controls.
Tiltrotor aircraft interest military planners because of their unique traits.
They are faster than a helicopter, because in full-forward flight, there are no forward-going rotor tips to induce drag or asymmetric lift.
The speed means that a given weight of tiltrotor craft can transport more men and equipment in a given time than helicopters can. This translates directly into smaller hanger spaces in aircraft carriers, lowered weight and volume of logistic spares, less total cost, including pilot training costs, and greater mission flexibility.
The speed also means that a tiltrotor can refuse battle to enemy helicopters. This increases security.
The speed aids medevac, and allows more centralized medical faclities. This results in higher standards of care, not least from reduced physician fatigue.
The greater fuel-efficiency means that a tiltrotor has both a longer range and a longer loiter time over an LZ.
The longer range means that tiltrotors can directly increase the security of a carrier operating group or forward air base. They increase the stand-off distance, increasing the warning time and thus the security of an air base or carrier group from hostile aircraft.
The longer loiter time theoretically allows a tiltrotor to mount suppressive fire weapons similar to the howitzer and vulcan loads of an AC-130. However, since the tiltrotor can operate from a carrier or forward airbase, airborne suppressive fire can be provided in areas lacking friendly airfields.
See also V-22 Osprey