ALTHOUGH rare, engine failure is a stressful thing for a helicopter pilot to have to deal with. The pilot of a fixed-wing aircraft that loses power can at least rely on those wings to provide him with lift until his plane's forward velocity falls below its stall speed. A helicopter, by contrast, derives both propulsion and lift from its blades. If they stop rotating, a rapid and terminal encounter with the ground beckons.
To prevent that, the blades of most helicopters have a special clutch that disengages them from the engine if the engine stops. The pilot has then to change the pitch of his craft to allow it to enter a mode called autorotation, in which the rush of air as it descends keeps the blades whirling, thus providing lift that slows the fall. The transition to autorotation is perilous, though, because it involves a reversal of the airflow through the blades. And even if he survives that, the pilot has to perform a second manoeuvre, known as flaring, just before he hits the ground. This involves pitching the machine's nose up, in order to reduce its forward velocity and increase the speed of rotation of the blades—and thus the amount of lift they provide—to soften the landing.
Both of these maneuvers would be less hazardous if the pilot could call on a second source of power to turn the blades for a few seconds while he was performing them, and Jean-Michel Billig and his team at Euro copter (part of EADS, an aerospace and defence group) hope to provide just that. They are introducing into helicopters the fashionable concept of hybrid-electric drive.
