Infinite Mass Testing of a Scaled Parachute using a Tow Tank Facility

Abstract

The drag characteristics of a round parachute with a constructed diameter of 30.5 cm are investigated using a water tow tank facility. Force measurements on the parachute are obtained for a range of constant velocity cases during parachute deployment and steady descent. These constant velocity tests represent an infinite mass parachute drop. The peak opening force and average drag during steady descent are determined for a range of velocities between 0.2 m/s and 0.7 m/s. The corresponding Reynolds numbers (based on constructed diameter) are between 60,000 and 200,000. The parachute opening time is also documented. Two series of tests are conducted. One series examines an unconstrained parachute that is free to oscillate about its towing axis. For the second series, the parachute is constrained about its center axis by a retaining line. Results indicate that the peak opening force for a given Reynolds number is the same for both the unconstrained and constrained parachute. In addition, the average force on the constrained parachute is larger than the average force on the unconstrained parachute during steady decent. This difference in average force is attributed to the large off-axis oscillations present for the unconstrained parachute testing. Since the constrained testing does not have off-axis oscillations, the constrained testing provides the best indication of the steady drag for the round parachute canopy design. The average steady drag coefficient for the constrained parachute canopy ranged between 0.7 and 0.8.