PPRuNe Forums - View Single Post - Static / Dynamic rollover definitives required...
Old 8th January 2007 | 04:22
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Shawn Coyle
 
Joined: Dec 2001
Posts: 1,835
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From: Philadelphia PA
I think you'll find that dynamic rollover almost universally happens to teetering rotor helicopters.
The few occasions it's happened to articulated or other, non-teetering rotor helicopters, it's been with something snagging the undercarriage. The movie of the Ch-46 on the aft deck of the ship comes to mind for that.
For the teetering rotor helicopters, it also appears to happen mostly when lifting off - and when something has snagged the skids.
The unfortunate thing in a teetering rotor helicopter with dynamic rollover on liftoff is that nothing you do with the cyclic is going to help you - there is only one solution if a roll rate develops that you don't like, and that's to bottom the collective.
The reason the lateral cyclic doesn't help you in this situation is that tilting the thrust vector to the side only slightly changes the vertical component of the thrust vector, which is the main thing rotating you around the skid stuck on the ground. There is no rolling moment to the airframe from the rotorhead to stop the roll with a teetering rotor head.
Unfortunately, not well described in any book (including my current one).
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