Tetroon Drag Coefficients from Experimental Free-Flight Data

Drag coefficients were determined for a 152-cm (60-inch) tetrahedral Mylar plastic balloon in free flight as functions of Reynolds numbers ranging from 104 to 3.3 × 105. Vertical relative air speeds ranged from 9 to 270 cm sec−1. Most drag coefficients derived from the 186 tests lay between 0.7 and 0.8. The average drag coefficient was 0.73 for point-first motion and 0.72 for broadside-first motion. For relative speeds ≤100 cm sec−1, the range of interest of the Air Resources Laboratories, the average drag coefficient was 0.74 for both point- and broadside-first motions. Five force (free lift) category observations were duplicated on different days giving generally good repeatability of drag coefficients.