The drag coefficient of Slug darts

Posted on 2010-06-29 00:23:10

Filed under fang4

Back in July 2009 my brother and I did a limited amount of testing with typical Slug darts that I made to determine their approximate drag coefficient. The drag coefficient of a 2 inch long Slug dart is about 0.34 with the reference area being as is convention in the exterior ballistics community. The 95% confidence interval is 0.28 to 0.40 (n = 9). One outlier was removed from the data set.

These darts were not of the best quality. Your results may vary. This data may be useful for rough estimations.

This drag coefficient is lower than tested values for cylinders in axial flow. However, I hypothesize that the surface of the cylinders in the earlier tests was far smoother than that of these darts. The roughness of the surface could make the boundary layer turbulent, preventing the flow from separating.

I will not detail basic fluid mechanics here. I suggest reading a very accessible book titled Shape and Flow: The Fluid Dynamics of Drag by Ascher H. Shapiro for a good introduction.

The raw data and a list of equipment used is listed below. The data is at full precision. In a future blog post I'll detail how to use this data to predict ranges.

Equipment used

Chrony
Scale
A tape measurer

Raw data

Dart mass (g)	Range (ft)	Muzzle velocity (ft/s)
1.05	84	186.4
1.09	74	170.0
1.08	81	180.5
1.01	88	200.0
1.11	88	184.8
1.15	104	186.9
1.11	79	183.8
1.05	83	195.9
1.00	80	203.8
1.00	81	205.6