BC... — Our GA Drag Model/ Drag Coefficient

[JungleShooter]

Our GA Drag Model/ Drag Coefficient

Strelok Pro has an option to enter custom drag profiles, and when going to that function the user can choose to "email" the data — and in reality it is a "share" option.

The content of the text file (.txt) that Strelok gives me is listed below — and No, it does not make sense to me — so please, ballisticians, chime in!!   

The first number in each line is the drag coefficient (Cd), the second the mach number (though when entering this data in Strelok manually these are switched around).
Why would there be velocities beyond mach 1?
Do these number look right?   

Matthias


CFM, GA, 0.0, 0.0, 0.00000, StrelokPro, 0.000, 0.000, 0.000, 0.0
Chairgun GA retardation table for Diabolo Airgun Pellet
0.250   0.000
0.235   0.100
0.221   0.200
0.207   0.300
0.196   0.400
0.189   0.500
0.189   0.600
0.202   0.700
0.241   0.800
0.329   0.900
0.488   1.000
0.597   1.100
0.649   1.200
0.669   1.300
0.672   1.400
0.667   1.500
0.657   1.600
0.644   1.700
0.630   1.800
0.616   1.900
0.602   2.000
0.589   2.100
0.577   2.200
0.566   2.300
0.556   2.400
0.548   2.500
0.540   2.600
0.534   2.700
0.529   2.800
0.524   2.900
0.521   3.000
0.521   3.100
0.517   3.200
0.514   3.300
0.510   3.400
0.507   3.500
0.503   3.600

[rsterne]

That is indeed the GA Drag Model, although I have not seen the numbers past Mach 2.... It is nearly the same as the G1 Drag Model, except slightly lower drag between Mach 0.2-0.7 and slightly higher drag at Mach 0.9 and over.... The two curves intersect at Mach 0.8 (900 fps)…. You are correct, we don't care what the numbers are in the Supersonic (over Mach 1.2), and I suspect that for many airgun pellets the drag is greater than shown in the Transonic.... There are many different Drag Models, here are some of them....



I only plotted up to 1500 fps to expand the scale to make it easier to understand.... Note that all projectiles have a huge increase in drag in the Transonic range (Mach 0.8-1.2)….

Bob

[anti-squirrel]

Mathias, thank you.

I suspect I might not be the only person who find value is just knowing this information is available as a reference, despite not really using it day-to-day.

LOL, I can only imagine what would happen with a wadcutter pellet at mach 3.5...

[rsterne]

Good example of a mismatch between the pellet and the drag model.... Wadcutters show their increase in Transonic drag much sooner (ie at a lower velocity) than do round-nosed pellets.... and their drag when Supersonic will be much higher....

Bob

[JungleShooter]

Thank you for confirming this. 

And yes, I think we really need CDMs (custom drag models) for long range shooting...!

Matthias

[rsterne]

After I retire, I will be purchasing a LabRadar…. The plan is to try and develop one or more drag models for airgun pellets.... I will start by working on the popular JSB Exact series to see if I can come up with a single drag model that will be suitable for most or all of them.... If that works, I hope to do a similar drag model for wadcutters.... Most likely a third drag model in between would provide ballistics modelling close enough for any Diabolo pellet by choosing one of the three.... At least that is the plan.... 

Bob