Tumble Recovery Booster Stages

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timothyterpsalot

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Does anyone know of any "rules" for tumble recovery boosters? Is there any online literature on this subject? I am designing a two stage rocket and I am wondering how to design the booster stage to fall without damage. Thanks!
 

WillMarchant

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Have the CG at or behind the CP for the separated booster stage. The Estes TR-2 on multi-staging talks about this a bit. You can find it in the "classic collection" at https://modelrockets.us/model_rocket_educational_resources.php

Tumbling booster stages in mid-power rockets might get a bit scary. What's the booster motor? How heavy will the stage be? You may want a parachute or streamer on it. Or make the fins big enough that it will glide...
 

timothyterpsalot

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Good point. The booster stage will weight a little over 1.5 lbs. The motor is a G339N (I'm certified). The CP will be ahead of the CG or the booster after burn out. The fins are pretty big on this stage.
I guess I can put a chute in it. It is a 4" dia tube and would probably only need an 18" chute. It would probably get knocked out after seperation. There wouldn't be an ejection charge on the G339N.
 

WillMarchant

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I guess it depends upon how large the fins are. I'm not sure how you'd go about calculating the descent speed of a tumbling booster.

You could probably use RockSim (or whatever) to do the worst case by manually adjusting the CG in the simulation. The "streamline" case should work fairly well to give you a terminal velocity when the CG is moved forward.

Maybe you could model the "sideways" case as exceedingly short "pods"? Or maybe you need to forget RockSim and try to treat sideways fins as flat surfaces and just calculate the drag manually...

It might be worth looking through back years of NARAM science presentations to see if somebody has done this one...
 

TheAviator

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Good point. The booster stage will weight a little over 1.5 lbs. The motor is a G339N (I'm certified). The CP will be ahead of the CG or the booster after burn out. The fins are pretty big on this stage.
I guess I can put a chute in it. It is a 4" dia tube and would probably only need an 18" chute. It would probably get knocked out after seperation. There wouldn't be an ejection charge on the G339N.
Personally, if I were an RSO at the launch, I don't think I'd be comfortable with a 1.5 pound stage tumbling back to Earth. Also, depending on the aerodynamics, the booster stage could be stable in the opposite direction (tail-first) on decent.

My suggestion is this: use electronics to deploy a recovery device on the booster stage.
 
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