Our solid propellant rocket, on test, produces sonic boom. Right after, the plume of exhaust tilts sideways. This will definitely have a gimbal effect during flight. The propellant chamber has one hole in the center to increase the burn surface area. I am assuming that the shock produced that shakes the propellant chamber crumbles the unburnt fuel inside. This affects the fuel burn and mass flow resulting in the tilting of the plume at the nozzle.

We have fixed fins and the nozzle cannot be gimballed to correct the direction. Is there a way to correct this situation?Tilted Plume after sonic boom

  • $\begingroup$ Sonic boom or just BOOM ? $\endgroup$
    – AJN
    Oct 3, 2021 at 13:21
  • $\begingroup$ Hello@AJN, I am not sure how to differentiate between the two. My effective exhaust velocity is 1264 m/s(Mach 4) so I assumed it was sonic boom. $\endgroup$ Oct 3, 2021 at 14:35
  • $\begingroup$ I was referring to the nozzle failure in the answer posted. $\endgroup$
    – AJN
    Oct 3, 2021 at 15:34
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    $\begingroup$ Hello @0xDBFB7, Is there another forum you could refer me where I can ask more of rocket questions without worrying about the restrictions. We are a student led team preparing to compete in Spaceport cup America 2022 and need as much help as possible.Sadly, we don't have an active advisor and looking for one. $\endgroup$ Oct 4, 2021 at 2:50
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    $\begingroup$ It looks like there are some good high-powered rocketry forums on the net, though I'm not familiar with any of them. $\endgroup$
    – 0xDBFB7
    Oct 4, 2021 at 3:38

1 Answer 1


What is the condition of the nozzle after burnout? is it asymmetrically eroded? That points to nozzle failure.

If it is spitting chunky sparks, then your fuel grain is fracturing and you are operating not a rocket motor but a malfunctioning bomb. It is absolutely vital that your fuel grain remain mechanically intact and adhered to the sidewalls of the motor during firing, or really bad things can happen. Is your motor sidewall possibly not rigid enough?

  • $\begingroup$ The nozzle is in fine condition. No erosion that I noticed. Initially, there is smooth burn for about 3 sec, then the boom happens. You are also correct about the the combustion chamber not being properly harnessed. It had been moving/shifting around from t = 2 sec. We will get it supported better next time. Thank you. That was helpful. $\endgroup$ Oct 3, 2021 at 16:10
  • $\begingroup$ When you say 'chunky sparks', is it like the ones in the pic above? $\endgroup$ Oct 3, 2021 at 16:47
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    $\begingroup$ @RocketHack Pretty much so, yes. Those sparks, if not part of your ignition system, are definitely something that is not normal exhaust. They seem to be particulate, do not follow the roughly aerodynamic flow of the main exhaust, and seem to be larger and much fewer in number. It points to either erosion of something, or fragmented fuel being spit out in largely unburned state.(or possibly just photo artifact from the exhaust impinging on a deflecting baffle. One fuzzy photo is not very clear) $\endgroup$ Oct 3, 2021 at 16:51

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