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Old 09-12-2006 | 09:10 PM
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blw
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From: Opelika, AL
Default RE: full scale chopper


You could get into the same sort of destructive situation with the OH-58 A and C models. I did see a flight test video of that happening in the air during autorotation. That mainly has to do with dynamic resonances and the transmission pylon mounts bouncing.

bdavison- I think you are talking about articulated rotor systems which have dampers for the blades to lead and lag. You can get into ground resonance with those if you hit one oleo strut hard, and then let the other struts start a bouncing (tap dancing) sequence. This in turn starts the blades to slamming against the damper stops, which transfers more energy to the oleo struts. It is a cycle that can't be stopped most of the time unless you take off to a hover. At least that is what they taught us in flight school for helicopters with skids. That site mentions tire pressure being important.

FBD- It's a real test. They do all kinds of things like that before any aircraft is released into the inventory. That's how they make the performance limitations, charts, dead man curves, etc. I've seen videos of aircraft being crashed to determine correct autorotation profiles. I have a video somewhere of an overgrossed Huey doing a steep autorotation. The tail boom broke off and the fuselage spun on the runway. You can see the test pilots white helmets slam forward as they went forward against the straps.

You can see the pilot apply full collective pitch once that rear pylon started breaking apart. This helped save more damage from the blades, especially the front rotor system.