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September 4, 2002
Piasecki Aircraft Corporation has a better idea: the compound helicopter. The idea is to take a modern military helicopter (such as the UH-60 BlackHawk) and add wings with flapperons and a thrust-producing ducted tail rotor. This would push the speed of the helicopter well beyond 200 mph, considerably more than its currently possible. The limit on helicopter speed is the stall on the "retreating blade" (the one moving backwards). This limits conventional helicopters to about 150-160 knots. The Russians used winglets on some of their helicopters to unload the blades, pushing speeds beyond 175 knots. The Piasecki plan also uses wings, but changes the conventional tail rotor from one that spins sideways (purely to counteract the torque of the main rotors) into one that rotates like a normal aircraft pusher propeller. This gives thrust (pushing speed over 200 knots, perhaps as high as 240 knots in designs that need more speed than lift); the torque issue is handled by ducting some of this thrust sideways through louvers, a rudder, or other systems. By unloading the rotors, the wing extends their lifetime (always the critical issue for helicopter maintenance). Piasecki says that existing (legacy) aircraft could be easily modified into these compound helicopters for a fraction of the price of new aircraft, giving a major increase in performance.--Stephen V Cole
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