strike a balance between blades vertical flight and those for forward engineers at the Office of Naval Research, the Naval Air Systems Command, and Boeing, Chicago (boeing.com), are successful, there will soon be torsional actuators for twisting rotor blades while in-flight, thereby optimizing the angle for different modes of flight to increase range and efficiency.

The device relies on NiTinol, which stands for nickel, titanium, and Naval Ordnance Lab, where it was developed. The compound is a shape-memory alloy that, if bent out of shape, will return to its original shape when heated. The torsional actuator sits inside the blade spar near the hub and uses NiTinol torque tubes running the length of the rotor. The tubes twist when heated by an electric current. An energy shuttle developed by Boeing amplifies the force behind the twist and applies it to the blade, twisting the rotor blade to the correct angle for a specific flight mode. The twisting action can be made part of the flight controls, and pilots could engage or disengage it.

The program began in 2001, and culminates in 2008 with a onequarterscale wind-tunnel demonstration and full-scale component test. Since the project started, system weight has gone from 52 to 18 lb, power requirements fell from 3,500 to 700 W, and deployment time shrunk from 3 min to 25 sec. The system is compatible with blade and hubs on many Defense Dept. helicopters, as well as the V-22 Osprey tiltrotor, so retrofits should be straightforward.