Originally Posted by
Reely340
Thx for the detailed reply, but those "vibrations" occurred way before translational lift, even before hovering, they were pratically still on the ground when everything was rocking wildly. So no lateral airflow, everything should be perfectly balanced at that stage.
I find it truly amazing that these vibrations happen early on, at low rpms, stationary, at or before hovering and precisely NOT in horizontal flight with all it asymmetry.
It’s a long video so I’m not sure which minute mark you’re referring to, but I did scrub through and see the cockpit video when the ship was at some ground idle condition with the crew clearly bouncing in their seats. At that condition, the rotor isn’t tuned well to that condition and quite possibly the airframe/gear/ground system isn’t either. Often, a helicopter is tuned for only a few specific rpm/operating conditions and away from those targeted conditions structure is nearer or in resonance, etc. The UH-1 is a tad before my time so I don’t know much about the airframe/gear frequency placement but I do know something about the rotor.