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Thanks iX Cameras www.ix-cameras.com/ and Matt Rece almores.infovideos for helping with the high speed shots!
Giaco Whatever video: almores.info/rock/video/qKukppVfcdOErpc
A few more thoughts on the Nerf Cannon.
Yes, I know if I used a longer barrel I could get higher speeds, but I did not want to deal with a 20ft long gun. I think a 6ft barrel was enough to show what a supersonic nerf dart can do.
Davekni got a pingpong ball going 2000mph which is 2930 ft/s!! (mach 2.5). His barrel was 20ft long. It can shoot through 3/4in plywood! You can see that video here- almores.info/rock/video/m7Gl26dmn82BmrQ
I always thought the speed of sound was the limiting factor, because the flow 'chokes' at mach 1. Its a big controversy among air-gunners, and theres like a 900 post topic on it here www.gatewaytoairguns.org/GTA/index.php?topic=102604.540. Some guy got one going like 2100 ft/s which I thought was impossible. almores.info/rock/video/146hmIGDqb1lmto So it prompted me to do some research.
It turns out flow does choke at mach 1, but its only the mass flow that chokes. The gas can still expand supersonically.
Also a big thanks to Dr. Carl Knowlen from University of Washington, and u/Overunderrated, u/TheQueq, and u/InductorMan from reddit.
Here are the papers I referenced:
A COMPARISON OF DISTRIBUTED INJECTION
HYPERVELOCITY ACCELERATORS - www.researchgate.net/publication/268456817_A_comparison_of_distributed_injection_hypervelocity_accelerators
Probably the most concise and easily understood!
Numerical Evaluation of a Light-Gas Gun Facility for Impact Test
Shows different muzzle velocities for different barrel lengths
THE THEORY OF HIGH SPEED GUNS
Probably the most extensive on the subject "The reader Is assumed to be an advanced student in engineering." I hope you payed better attention in physics that I did.
Outro music by MDK, almores.info/rock/video/mJikmX6faJdjf9o
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