Design and Testing of a Rotor for Autonomous Autorotation

The design of an autonomous fixed pitch rotor that is released at an altitude and then autorotates to support a payload in vertical descent is addressed. The challenge is one of designing a rotor that starts from rest and enters a state of autorotative descent without any pilot inputs. Based on the results of wind tunnel tests performed on a model rotor, a hingeless hub design incorporating a ƍ3 hinge and a negative pre-cone is evolved. An analysis based on blade element-momentum theory is developed to predict the variation, with time, of the rotational velocity and thrust of a rotor that is initially non-rotating. Results are presented for the rotor in steady descent and for the spin-up of the rotor at different descent conditions. The theoretical predictions are validated by wind tunnel tests, and the results of a parametric study showing the influence of various design variables on the performance of a vehicle that is released from a height is presented.