To: Nick Lappos
You said,” Your belief that somehow the rotor blade loses lift when aligned with the fuselage is not based on fact! The tips of a Huey's blades are moving at 485 knots in a hover, and at 100 knots of airspeed on the helicopter, the blades are also doing 485 knots when they align with the fuselage, quite enough to produce their share of the lift”.
The tip speed is constant but the relative wind generated by that tip speed is not. In a hover in a still air day the lift generated by the rotor is constant but at speed the relative wind is not the same across the disc. That is why I used the retreating blade stall analogy. In that comparison there is a loss of lift due to the rotational velocity of the blade at a given point being less than the air stream passing over the blade. I can’t speak from detailed engineering analyses but it seems to me that as the blades are aligning with the longitudinal centerline and as they pass through and slightly past that point the blades are in an airstream that is equivalent to the forward speed of the helicopter. That can be on some two blade helicopters as high as 150 + Knots. In retreating blade stall the retreating blade loses lift due to the reverse airflow on the blades. I believe that a blade with a tip speed of 485 Knots will lose some lift when passing through an airstream that is passing down the span of the blade which would reduce the lift generated by the blades.
You can address the end result and quote all types of engineering speak but until I can get this question resolved by Bell I will continue to believe that the 2 per rev bounce is caused by the intermittent loss of lift as the blades rotate. If Bell says it ain’t so I’ll go on to other pastures.
The reason this doesn’t happen on a multi blade system is that at least two of the blades are lifting and on helicopters like the CH-53 there are five or more blades lifting.
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The Cat