Consequences of staging and sustainer light < and > mach

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kclo4

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Calling Jim Jarvis and other high performance wizards. I am planning a very high performance 2 stage flight in future land and looking for discussion on the consequences and challenges associated with staging above mach. I am also interested in the challenges, advantages, and disadvantages with lighting the sustainer above and below mach.

First, staging, this would naturally occur exactly at booster burnout ideally. If the rocket is above mach when this happens what issues are there with making sure staging happens smoothly? This will be a 54mm to a 3" rocket so the booster would be more draggy which should help.

Second, is there any advantage in letting the sustainer slow to less than mach then break mach again after sustainer light?
There is lots of turbulence and extra forces in the mach transition, but if the rocket handles it well once, is it a problem to do it twice?

It seems like you could gain some extra altitude into lower density air for the sustainer by waiting having less time at mach 2+ in thick air which would be easier on composite fins and nosecones. In addition the max speed would be less.

Are these advantaged outweighed by problems in the mach transition?

Sorry if this is came up, haven't seen a lot of in depth discussion on these specific topics.
 
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JimJarvis50

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My high altitude flights all go above mach on the booster burn. I let the sustainer drop below mach before lighting it - typically around 700 ft/s or so is the goal. This speed is high enough so that the rocket is not starting to arc over. The reason for this is to reduce the top speed of the rocket to the extent possible, since that's where failures typically occur. This can result in a pretty long delay - as much as 20 seconds on some flights. Keeping the rocket vertical during that coast is another issue, which I try to address by other means. I have not seen any issues going through mach. I had a three stage where the sustainer went through mach six times. Ho hum. About the only thing I have noticed going through mach is that the direction of spin sometimes changes.

Don't assume that having a booster and sustainer of different sizes increases the tendency to drag separate. That's not necessarily the case.

Jim
 

kclo4

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Thanks for jumping in on this Jim!
I was kind of under the impression that most folks try to keep things above mach once it breaks it the first time, but your reasoning is as I thought, try to keep the top speed as low as is reasonable.

Not planning on a 3 stage at this point, but you mentioned keeping things vertical is a challenge. Do you rely on spin stabilization via canted fins?

As far as the actual staging, do you use some sort of piston in the interstage area with a pyro charge to force separation?
 

JimJarvis50

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Not planning on a 3 stage at this point, but you mentioned keeping things vertical is a challenge. Do you rely on spin stabilization via canted fins?

As far as the actual staging, do you use some sort of piston in the interstage area with a pyro charge to force separation?
I'm using vertical stabilization between the stages. It's possible that some day, it might work! You can read about it here, although it looks like an update might be needed before too long.

https://www.rocketryforum.com/showthread.php?122042-I-could-use-just-a-little-guidance

Generally, I use a separation charge, which is between a bulkhead of some sort on the bottom and the next motor in line on the top. There isn't much space there, so it's sort of acting like a piston, with the motor as the piston. I usually cover the nozzle opening in some manner.

Jim
 
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