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April 1, 2009

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Originally posted by onefunzr2:
"Bullet velocities were measured with advanced Doppler Radar."



That was the first sign to me that the article was bogus.

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Originally posted by Ozzie:
You might want to check the date on the report.

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Originally posted by Roll-Crimp:

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Originally posted by onefunzr2:
"Bullet velocities were measured with advanced Doppler Radar."



That was the first sign to me that the article was bogus.

Really?
Back in the mid 70's Fairchild (the A-10 guys) did some R&D with mobile radar systems in an attempt to distinguish small arms projectiles by radar signature with microwaves. I believe one of those projects was called SCORE for Spatial Correlation something Radar something else... ?
Too many Fourier Integrals in that line of research to wrap my head around.
So why is doppler, 35 years later such a stretch?

Combined with a heavy foot, Doppler radar is what probably got you your last speeding ticket.

Can Doppler radar accurately track bullet projectile velocity? Absolutely! But don't take my word for it, there is plenty of reference material that is easy to get to.

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So, why dimples? Why not use another method to achieve the same affect? The critical Reynolds number, Recr, holds the answer to this question. As you recall, Recr is the Reynolds number at which the flow transitions from a laminar to a turbulent state. For a smooth sphere, Recr is much larger than the average Reynolds number experienced by a golf ball. For a sand roughened golf ball, the reduction in drag at Recr is greater than that of the dimpled golf ball. However, as the Reyn olds number continues to increase, the drag increases. The dimpled ball, on the other hand, has a lower Recr, and the drag is fairly constant for Reynolds numbers greater than Recr.

Therefore, the dimples cause Recr to decrease which implies that the flow becomes turbulent at a lower velocity than on a smooth sphere. This in turn causes the flow to remain attached longer on a dimpled golf ball which implies a reduction in drag. As the speed of the dimpled golf ball is increased, the drag doesn't change much. This is a good property in a sport like golf.

Although round dimples were accepted as the standard, a variety of other shapes were experimented with as well. Among these were squares, rectangles, and hexagons. The hexagons actually result in a lower drag than the round dimples. Perhaps in the future we will see golf balls with hexagonal dimples.