The Aeroelastically Conformable Rotor Concept

An analytic Investigation was conducted to determine the feasibility of improving helicopter performance and reducing flight loads by passive control of blade torsional response. Distributions of time-varying blade elastic twist that improve performance and decrease blade stress are identified. Blade design features producing the desired twisting are then sought through examination of model and full-scale torsional response data and through an analytic evaluation of significant parameters. Results indicate a significant potential for inducing 1P and 2P elastic twisting. Tip sweep on a blade of reduced torsional stiffness improves performance and reduces control loads and blade stress by inducing a 1P torsional response which decreases advancing-blade twist and increases retreating-blade twist. The dynamic twist produced by negative airfoil camber is shown to reduce blade stress but generally degrade performance. Control of the spanwise distribution of aerodynamic center--center-of-gravity axis offset is shown to be effective in producing 2P elastic twist, which improves forward-flight performance. The potential for improving hover performance by inducing large negative elastic twist is also demonstrated.