To: Nick Lappos
I had stated previously that when the fat lady sang (response from Bell) I would either crow about being right or, I would eat crow. This afternoon I received a call form the senior aerodynamicist at Bell. We had a long conversation and I expounded on my views. He gave me a bit of support in stating that there is a variation in generated lift when the blade becomes aligned with the longitudinal axis but that was not the cause of the 2-per rev bounce. He told me that the 2-per rev bounce is generated when the blades are aligned with the lateral axis of the helicopter and it was due to the lift differential across the disc. Now this sounds reasonable but after a bit of thought I became confused. I had always believed that as the advancing blade was moving into the relative wind the pitch had decreased and the opposite was true for the retreating blade as it had higher pitch and was moving with the relative wind. With this scenario in place I was lead to believe that the disc loading was the same on both sides.
I was lead to believe that if there was differential of lift across the disc, the excess lifting forces generated by the advancing blade would result in a perturbing force and through gyroscopic action would result in a flap back (blow back) as this is what happens when you have retreating blade stall. Would you care to comment? Please don’t sprain you arm patting yourself on the back.
I can’t get my money back from the school of engineering as I was an Industrial Design Major.
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The Cat