Impact of Main Rotor Tip Geometry on Main Rotor/Tail Rotor Interaction in Hover

One area that has been identified as affording increased operational efficiency in future rotary wing aircraft is that of improved Main Rotor/Tail Rotor/airframe interaction in hover. Further, the question arises as to the sensitivity of some of the hover improvements to be gained by the use of advanced geometry tip configurations, when subject to operating in close proximity to a tail rotor. To assist in identifying and quantifying the impact of the tail rotor on the improvements attainable by using advanced geometry rotor tip configurations, Sikorsky Aircraft, under NASA contract NAS2-11266, conducted a series of model scale tests, in its Model Hover Test Facility. The test was conducted in two phases. The first phase consisting of main rotor only tests on 2 current technology rotors (representing a scaled UH-60A BLACK HAWK rotor and a scaled S-76 rotor) and eight different tip configurations - three on the BLACK HAWK and five on the S-76. In this phase the main rotor hover performance was acquired as a function of tip Mach number and ground effect using all eight tip configurations. From these results, four of the more advanced tip configurations were selected for the second phase. In this the main rotor performance was obtained in the presence of an operating tail rotor (configured both as a tractor and pusher tail rotor). The tip Mach number and ground effect ranges were identical for the two tests. The test results showed that overall the tail rotor effects on the advanced geometry tip configurations tested were not substantially different from the effects on conventional tips. Hence the majority of the benefits obtained from advanced tips (as identified in isolated main rotor tests or through analysis) should be retained when operating in the presence of a fuselage and tail rotor.