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In earlier papers, techniques have been described using optical chronographsto determine free flight drag coefficients with an accuracy of 1-2%,accomplished by measuring near and far velocities of projectiles in flight overa known distance. Until recently, Doppler radar has been prohibitivelyexpensive for many users. This paper reports results of exploring potentialapplications and accuracy using a recently available, inexpensive (< $600 US)amateur Doppler radar system to determine drag coefficients for projectiles ofvarious sizes (4.4 mm to 9 mm diameter) and speeds (M0.3 to M3.0). In manycases, drag coefficients can be determined with an accuracy of 1% or better ifsignal-to-noise ratio is sufficient and projectiles vary little between trials.It is also straightforward to design experiments for determining drag over awide range of velocities. Experimental approaches and limitations aredescribed. Overall, the amateur radar system shows greater accuracy, ease ofuse, and simplicity compared with optical chronographs. Doppler radar hasadvantages of working well with less accurate projectiles without puttingequipment at risk of projectile impact downrange. The system can also detectphenomena that optical chronographs cannot, such as projectile instabilityresulting in tumbling in flight. This technology may be useful in introductoryphysics labs, aerodynamics labs, and for accurately determining drag andballistic coefficients of projectiles used in military, law enforcement, andsporting applications. The most significant limitations are reducedsignal-to-noise with smaller projectiles (< 5 mm diameter) and inability todetect projectiles more than 100 m down range.

Accurate Measurements of Free Flight Drag Coefficients with Amateur Doppler Radar