Investigation of increased forward flight velocities of helicopters using second harmonic control and reverse velocity rotor concept
Van Riper, Steven G.
Wood, E. Roberts
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Described is the behavior of a rotorcraft equipped with Higher Harmonic Stall Control (HHSC) and a Reverse Velocity Rotor (RVR). Current rotorcraft are limited in forward flight speed by retreating blade stall and compressibility effects on the advancing blade. Stall occurs as the blade encounters increasingly severe reverse flow. HHSC enables conventional rotor systems to fly on the forward and aft sections of the rotor disk, greatly reducing reliance on the mixed flow regions defined by the advancing and retreating blades. Employment of the RVR allows lift generation while the rotor is experiencing reverse flow. A similar type of two per revolution (2/rev) input can be tailored to deliver maximum benefit to RVR equipped rotorcraft. Modification of the Joint Army Navy Rotorcraft Analysis and Design (JANRAD) computer program allows 2/rev cyclic input, use of the RVR, and analysis using high fidelity graphical output to examine angle of attack, coefficient of lift, and air load. Computational results show performance gains in conventional helicopters and high speed flight potential for RVR equipped aircraft. The RVR is applied to the Joint Heavy Vertical Lift (JVHL) aircraft conceptual design for preliminary analysis. This conceptual design can be used as an indicator of the performance of a high speed RVR equipped aircraft.
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