Theory recognizes that supersonic drag coefficients depend on both Mach number andReynolds number, which includes an implicit dependence of drag coefficient on airdensity. However, many modern approaches to computing trajectories for artillery andsmall arms treat drag coefficients as a function of Mach number and assume nodependence on Reynolds number. If drag force is strictly proportional to air density forsupersonic projectiles, the drag coefficient should be independent of air density over arange of Mach numbers. Experimental data to test this assumption are not widelyavailable. This experiment determined drag on a 2.59 g projectile from M1.2 to M2.9 attwo atmospheric densities (0.93 kg/m3 and 1.15 kg/m3) using optical chronographs tomeasure initial and final velocities over a separation of 91.44 m. The results supporteddirect proportionality of aerodynamic drag to air density from M1.2 to M2.9 within theexperimental error of 1%-2%.
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