Helicopter Accident Damage

[jalbert]

A question from a fixed wing pilot.. .Why do so many crashed helicopters seem to have their tail booms severed.Is it the main rotor striking the tail or more to do with the attitude at impact? Also many force landed helicopters then seem to roll over-why?. .Apologies for looking like an idiot.

[voodoo2]

Just before the helicopter touches down in an autorotation(enginefailure)the pilot will lift the collective to soften the toutchdown. By doing this the rotor rpm will decrease and if your timing is not perfect, you will hit the ground hard and the blades will flex down and hit the tailboom or you will rollover. Easy in training but a harder when an actul failure occur. As helicopter normally fly low this will not give you mutch time to turn into the wind, find a nice open and flat area. If you walk away from an enginefailure, you done a good job.

[Droopy]

There are a number of contributing factors:-. .. .The tail boom is relatively long and is vulnerable to a bending moment, caused either by downward decelerative forces at impact or by contact with the ground on rolling over; if the tail boom has been struck on impact then it will at least be weakened if not severed. Contributing factors to rollovers are the relatively high C of G with engines and gearbox often above the cabin, and the fact that run-ons are often not straight. Once the aircraft begins to roll the main blades will touch the ground and their sudden deceleration will cause a turning force on the airframe again swinging the tail boom around. . .. .There's an awful lot of energy looking for somewhere to go when it happens - definitely best viewed from a distance

[talkturn]

Another factor maybe that the aircraft is not level on touchdown. The pilot still trying to reduce his groundspeed and still flaring as he touches the ground. Either the tail hits the ground (long arm and large moment) or the backs hit first of the skids resulting in a forward rolling movement.

[Grainger]

Also due to the fact that - just like fixed-wing aircraft - those that have landed intact don't make the papers.. .. .Crashed light aeroplanes are nearly always seen flipped over or buried in a hedge. Helicopters have different bits to break off but the end result is the same - smashed up gets you in the news, successful forced landing is not so dramatic so no-one hears of it.