The flame is 18.5 long. On other photos, nine discrete Mach diamonds can be seen in the plume.
The sound was incredible, deep, and loud… louder than any rocket I have heard. I was hanging out at the far pads and was quite close to this one (this was only a 170mm zoom vs. 400mm for most of the other BALLS shots)
Spectacular capture! Very interesting and well shot.
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We would love this pic in the Dust pool
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Awesome shot… one of the best I’ve seen!
A note to the poster, however: The term "Mach Diamond" having anything to do with the speed of a motor’s exit gases is actually a misnomer. 😮
Mach diamonds, as great as they look, are telling you that you have not expanded the combustion products at the nozzle exit to the exact surrounding ambient pressure. Theoretically (but usually not really so) if the conditions were absolutely correct you would have no mach diamonds.
Imagine the exhaust as a hollow column – the walls of the column are reflective to pressure waves. As these waves cross back and forth they create the zones of differing densities and termperature we call mach diamonds. The pressure waves come from the gas in the column trying to match the surrounding pressure.
So you really cannot tell much by counting mach diamonds…certainly not thrust or exhaust velocity.
The general volume of the plume is relatable to thrust when compared to exactly the same propellant operating at the same pressure at the same ambient pressure, but with a different nozzle and thrust level.
Just FYI. 😉
Awesome site, makes me wish I got to observe this in person. Thanks for sharing!
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Just happened on this photo — yea the "rule of thumb" ain’t exactly right 🙂 Check out the isentropic flow relations (as posted previously), particularly the one for A/A* — that gives expansion ratio as a function of exit Mach number and gamma value for the exhaust. Typical solid propellant exhaust has a gamma of ~1.2, so plug that into the relation with M = 9 and you’ll get A/A* = 12,383, meaning the exit cone would have to expand to 12,383 times the throat area to get that flow velocity. If that weren’t enough, the pressure at that point (given by the P/Pt equation) would be 1.76e-6 that of the chamber pressure; that’s impossible to have in a rocket operating in the atmosphere, due to flow separation in the nozzle. (At that pressure ratio, for the flow not to separate, the chamber pressure would have to be ~3 million psi!)
Neat pic, though. I heard Gene scrubbed this year — too bad. Balls should still be great though, as always; see you on the playa!
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