Experimental and analytical investigations were conducted to evaluate a bearingless heli¬copter rotor concept (CBR) made possible through the use of the specialized nonisotropic properties of composite materials. The investigation was focused on four principal areas which were expected to answer important questions regarding the feasibility of this concept. First, an examination of material properties was made to establish moduli, ultimate strength, and fatigue characteristics of unidirec¬tional graphite/epoxy, the composite material selected for this application. The results confirmed the high bending modulus and strengths and low shear modulus expected of this material, and demonstrated fatigue properties in torsion which make this material ideally suited for the CBR application. Second, a dynamically scaled model was fabricated and tested in the low speed wind tunnel to explore the aero-elastic characteristic of the CBR and to explore various concepts relative to the method of blade pitch control. Two basic control configurations were tested, one in which pitch-flap coupling could occur and another which eliminated all coupling. It was found that both systems could be operated success¬fully at simulated speeds of 180 knots;however, the configuration with coupling present revealed a potential for undesirable aeroelastic responses. The uncoupled configuration behaved generally as a conventional hingeless rotor and was stable for all conditions tested. Another decoupled rotor con¬figuration was extensively analyzed, but was not tested due to scaling difficulties. Third, a pre¬liminary design of a full-scale rotor was conducted to establish full-scale requirements and to show that no significant problems would be encountered in the manufacture of a CBR blade. Finally, an aeroelastic computer program was developed to simulate the unique CBR blade structure and operating environment. This analysis was then employed to examine the stability characteristics of a full-scale design under various flight conditions and under conditions where material properties were degraded due to possible flaws in fabrication or partial failures in operation. This study revealed no dynamic problems for the conditions investigated, has confirmed that significant reductions in rotor system complexity and weight can be achieved with the CBR, and further, that graphite/epoxy is idea by suited for the special requirements of the CBR.
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