The Israeli air force may replace the tailrotor shaft on its Bell AH-1 Cobra helicopters with that from the Bell 212 to avoid tail disintegration caused by fuselage resonance.
The idea follows the fatal crash of an Israeli air force Cobra during a flight over the Mediterranean in 1998.
The inquiry showed that as engine speed was increased, tailrotor shaft resonance matched that of the fuselage, cau sing the tail to break off. The resonant point was reached when the engine was at 113% power. When replaced with the larger- diameter Bell 212 tailrotor shaft, the critical resonance occurred at 131% power.
Source: Flight International
