Abstract
Abstract : Tests were made on 42- and 51-in. diameter rotorchutes with either 2 or 4 untapered and untwisted blades with airfoil section. The rotorchute which is an autorotating propeller was suggested for use instead of a parachute to decrease the descent velocity of free-falling loads. In vertical descent and proper autorotation tor rotorchutes had a drag coefficient referred to the rotor-disk area of 1.0 to 1.3 and a tip speed ratio (circumferential speed to sinking speed) of 4.4 to 9.3. The maximum drag coefficient remained essentially constant between the largest blade incidence at which proper autorotation was possible and a blade incidence of about 6 deg less. When the blade incidence was decreased through this range the tip speed ratio increased about 40%. Changing from 4 blades (with a solidity of 18%) to 2 blades of the same chord caused a slight increase in drag coefficient and a substantial increase in tip speed ratio. The optimum solidity for obtaining a high drag coefficient appears to lie between 0.06 and 0.09. Blade offset forward seemed to cause slight increases in the drag coefficient. Blade sweep produced no significant effects on the drag coefficient. Blade sweep forward and blade offset forward improved the starting of autorotation.
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