V22 Osprey discussion thread Mk II
Much of the concern over LTE comes from an early design flaw built into Bell 204 and 205 tail rotors and later carried over to the AH-1G Cobras. These early Bell tail rotors were situated on the left side of the tail boom and turned in an anti clockwise direction. This combination resulted in the tail rotor blade traveling down through the main rotor flow rather than up through it. Certain low speed and cross winds situations dramatically degraded tail rotor performance resulting situations identified as LTE. Bell rectified this by retaining the same tail rotor but relocating it on the right side of the tail boom. In this configuration the tail rotor blades travel up through the main rotor flow and were less susceptible to LTE.
There have been many instances where modern helicopters have experienced some form of LTE. The Blackhawk rolling down the hill and Erickson Aircrane rotating out of control during a water pickup are two recognizable examples. In these examples main rotor torque required exceeded tail rotor anti torque available. The tail rotors were operating as designed but in excess of there capabilities resulting in a loss of directional control.