A SECOND FLIGHT of the Boeing Sikorsky RAH-66 Comanche scout/attack helicopter has been delayed until after completion of tests to determine why a gear failed on the propulsion-system testbed. The YRAH-66 prototype has been grounded since its first hover test on 4 January.

Resonance is blamed for the failure of the left input-bevel-gear, a piece of which punched a hole in the main-gearbox housing. The testbed was running at 110% power when the failure occurred, in a test intended to verify modifications to the spring clutch made after the first flight.

The team planned to complete a dynamic-strain survey on the testbed by 15 August, to determine where the resonance occurs. The propulsion-system testbed, at Sikorsky's West Palm Beach, Florida, flight-test centre, has the same engines and transmissions as the Comanche prototype.

If no resonance is discovered, the aircraft could fly almost immediately; otherwise the second flight will be delayed until a solution is developed. The prototype was grounded following its 34min first flight to allow the transmission to be upgraded.

Source: Flight International