manthey/ballistics

Calculate power factors for historic black powder data using external ballistics.

ballistics's Issues

Coefficient of Drag

By default, the program uses a coefficient of drag based on Reynolds and Mach numbers from Miller, 1979, with the low-speed Cd taken from Munsun, 1998. These don't match values given by Hutton, 1812 (Vol. III, p. 318), and seem like they aren't as high as they should be for lower speeds.

Specifically, Hutton gives some values with both range and time-of-flight, and the time-of-flight is longer than it should be based on the drag I am computing. Also, Helie, 1865 gives some trajectories from some data collected in Russia that also exhibit this problem. Ideally, the power factor computer for the gunpowder would be essentially the same (within expected experimental error) throughout the trajectory if the ballistics calculations match reality.

I've added a version of Miller, 1979 as converted to equations by Collins, 2016. For some comparisons, I've added a low-speed equation from Morrison, 2013, and a formula from Henderson, 1976 for a wide range of Re and Mn. Of these, Miller seems to give the closest to the experimental data, yet it still isn't right.

It would be good to find better support for the Cd, or possibly try out equations produced by Helie, Hutton, or others.