Design and testing of an autorotative payload delivery system

The design, testing, and analysis of an autonomous autorotative payload delivery system called the Autobody is presented. The Autobody must be capable of passively deploying a payload from a conventional aircraft, by means of an autorotative rotor. Operational requirements specify the Autobody to have a four bladed rotor with a diameter of four feet, a total mass of 2.27 kg (5 lb) and a maximum steady state descent velocity of 4.57 m/s (15 ft/s). A novel rotor hub design incorporating negative pitch-flap coupling in conjunction with negative blade pitch and a negative precone is implemented to passively achieve the transition to steady autorotation. An analysis is developed to predict the steady state behavior of the Autobody. Only vertical autorotation is considered as it will result in a conservative design and is the simplest state to analyze. Wind tunnel tests were performed on a scaled model rotor to validate the analysis and to investigate the effect of different rotor parameters. The analysis was then used to perform a parametric study of the effect of several rotor variables on the system performance, from which an optimum full scale configuration is identified. An instrumented full scale prototype was flight tested by dropping it from a hot air balloon. For an Autobody of mass 2.27 kg, with a -41 degrees pitch-flap coupling angle, a -10 degrees fixed collective pitch, and a -4 degrees precone, a steady state descent velocity of 4.11 m/s (13.5 ft/s) was observed. Based on the predictions and the flight tests, it was concluded that the proposed Autobody design satisfactorily meets all operational requirements.