A joint United States Army‐NASA‐Bell experimental investigation has shown that rotor operation at advancing tip Mach numbers above 1.0 is possible and, with special treatment at the blade tip, practical for certain applications. Tests were conducted in the NASA‐Ames
40‐ × 80‐Foot Wind Tunnel with production UH‐1D (NACA 0012 profile) blades and with experimental blades incorporating reduced thickness at the tips. The production blades were evaluated at advancing tip Mach numbers up to .95 and the thin tip blades to Mach 1.025.
The production and thin tip blades are compared. The results show that compressibility effects are delayed and that at the higher tip Mach numbers, significant reductions in both power and loads are obtained with the thin tip blades. Additionally, the state of the art of calculating rotorcraft
performance at low advance ratios (μ = .3) and at Mach numbers above 0.8 is reviewed and limited experimental data, from special boundary layer instrumentation, are also presented.
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Document Type: Research Article
Bell Helicopter Company, Ft. Worth, Texas
Publication date: 1968-04-01
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