Mach Diamonds =advanced=

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Well-Known Member
Jun 18, 2003
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One of the mysteries of Rocketry; What are mach diamonds? What causes them to form? Do different types of propellant (ie blackjack, white lighting etc) increase the amount produced?
Ya know, I was looking for a good easy to understand explanation and actually found one on EMRR:

The exhaust flow of a rocket motor is supersonic, but the pressure may not be matched to the ambient atmospheric pressure (this is especially true as it rises in altitude), creating a pressure boundary between the plume and the atmosphere. The diamonds are shocks reflected off that boundary, and the angle of the shocks depends on the Mach number. I'm not sure if my explanation improves on EMRR's or not.

Regarding the last question, I'm not clear on what you mean by the "amount" produced. But the Mach diamonds are more a result of nozzle design than propellant. It may just be that certain propellants produce a more transparent exhaust that makes them more visible.
There was a detailed article in HPR Mag, July 2002 (the mag date, it prolly was received in 2003) that schematically explains how these form and propagate. Too detailed to repeat here and I can't sumarize it any better. They depend on the nozzle design and the process changes slightly for under and over expanded nozzles. Other aspects of the motor design should have an effect too, shouldn't they? Such as chamber pressure.
Chamber pressure will affect the mass flow rate, but the Mach number at the exit of the nozzle is a property of the nozzle itself. That Mach number and the exit pressure vs. ambient pressure is what will determine the characteristics of the Mach least to first order.
This is exactly the material in the mag. The only difference is the mag uses a series of highlighted diagrams instead of one with keys.
Let's also keep in mind that Mach diamonds are not a phenomenon that is strictly observed in rocketry only. They are also visible behind many supersonic fighter aircraft as well.

I used to work at a complany that did plasma torches, and material depostion though said plasma torches. The plasma oplume, with it's helium rushing out at about 2 mach produced some nioce diamonds. I guess teh atomized chome particles & plasma plume jsut added to it.

And what a racket!! talk about loud!! when this thing was running, it was litterally a jet talking off. And this is in a sound porrf chamber with extra dark welder's glass!!

I did my best, I'm only a drafter! but was deepely impressed by teh technology they did!
I've heard the term "shock diamonds" is this the same thing?
Personally, I think LOKI's pix is the best. However one could also give that first place in a lawn dart contest.;)
WOW Jeff, is that Super Polish Rojo?

Very nice, and the casing it fired in is awesome too.
Video grab of said Mach Diamonds from preceeding T-bird take off......I'm starting to thaw a bit in this forum....just credit my pics and we'lll all get along just fine.

Originally posted by Hospital_Rocket
Personally, I think LOKI's pix is the best. However one could also give that first place in a lawn dart contest.;)

I like the one with the most countable mach diamonds and the most altitude per pound of propellant.

Originally posted by powderburner
I'll credit your pix if you'll credit my airplane . .

Sure, which airplane is yours? The only one I posted belongs to Sammy and his people. ;-)
The F-16 (like the one in the T-birds picture you posted) is one of several thousand that we built here in Fort Worth. I take (partial) credit---- I actually designed a few parts. Anyway, I was only facetiously claiming ownership. But they ARE kinda mine . .
Well, I have a better understanding of the subject now. Some very cool "Mach Diamond" pictures....... Maybe we should have a photo contest for the best "Mach Diamond" picture...........
Hybrid Mach diamonds...


38/400 PVC fuel
Chuck Pierce photo


38/580 PVC fuel
Jamie Black photo


38/580 PVC fuel
Jamie Black photo
Originally posted by Larry
Here is a good photo of shock diamonds. This is an SR-71 Blackbird on takeoff. I've seen lots of pictures of Blackbirds with shock diamonds in the exhaust. A couple I took at Oshkosh in 1989.

You take very nice photographs! :) Any explanation for the snakeage of the right side engine? Wind shear? Zero wind with a 'knuckleball' effect? One is so straight the other is wobbly.