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Rex R

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so I am planning a gap staged two stager, and have a few questions.
lower stage motor mount tube extends how far forward? rocket I am planning will have a bt-60 airframe
paper punch holes in the mmt end, check. would a couple of paper punch size holes in the centering rings suffice to vent the lower stage?
all I can think of ATM...likely have more later :). thanks
Rex
 

kjohnson

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I like to extend the booster MMT to engage the upper stage motor. Hole punch holes about 1/4" down from the front of the tube.
I think 1 hole is enough in the lower CRs to let the pressure escape to prevent blow off.

kj
 

Rex R

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sounds like a plan to me, thanks. just have to adjust the design file and I'll be ready to consider building the booster :).
Rex
 

kjohnson

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Another thing I've done when the booster is pretty long, is to make the booster MMT slide out the back of the booster to deploy a streamer. There are a couple of drawings of one way to do that here: https://meatballrocketry.com/booster-recovery/
I used this on a small scale-altitude model with 13mm motor mounts using standard centering rings. It takes some thinking about how to get all the parts glued to the right place, but is fairly reliable.



kj

stagingstuff.jpg


booster.jpg
 

Rex R

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I think that I am okay with a firmly affixed tube, the booster tube is only 5" long and it will use 18mm motors.
Rex
 
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BABAR

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so I am planning a gap staged two stager, and have a few questions.
lower stage motor mount tube extends how far forward? rocket I am planning will have a bt-60 airframe
paper punch holes in the mmt end, check. would a couple of paper punch size holes in the centering rings suffice to vent the lower stage?
all I can think of ATM...likely have more later :). thanks
Rex
At least two ways to do it.
Extend your motor mount all the way up to the encase the lower say 1/4 to 1/2 inch of the sustainer (or next stage in 3+ stages.). Put a hole (punch size is fine) just below where the upper stage engine will stop when stages joined.

YOU WILL ALSO NEED EITHER A HOLE IN THE OUTER BODY TUBE (unless you are minimum diameter) OR SOME GAPS IN YOUR MOUNT CENTERING RINGS to let the the gas further vent from between motor mount and outside tube and outside of the rocket

Second option is to extend your motor mount tube to about 1/4 inch below the upper stage engine. The gap will allow the igniting hot gases to duct right to your upper stage nozzle. You will still need a vent hole in the outer body of the booster (or tail of sustainer below the lowest motor mount centering ring) to vent the gases.

I have successfully gapped up to 36" with these techniques.

Looking forward to the pics and a good flight!
 

Rex R

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going to be a bit longer before I can start building due to a hiccup in my parts order(which I am sure will be swiftly taken care of).
Rex
 

Screaminhelo

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At least two ways to do it.
Extend your motor mount all the way up to the encase the lower say 1/4 to 1/2 inch of the sustainer (or next stage in 3+ stages.). Put a hole (punch size is fine) just below where the upper stage engine will stop when stages joined.

YOU WILL ALSO NEED EITHER A HOLE IN THE OUTER BODY TUBE (unless you are minimum diameter) OR SOME GAPS IN YOUR MOUNT CENTERING RINGS to let the the gas further vent from between motor mount and outside tube and outside of the rocket

Second option is to extend your motor mount tube to about 1/4 inch below the upper stage engine. The gap will allow the igniting hot gases to duct right to your upper stage nozzle. You will still need a vent hole in the outer body of the booster (or tail of sustainer below the lowest motor mount centering ring) to vent the gases.

I have successfully gapped up to 36" with these techniques.

Looking forward to the pics and a good flight!
So a 2 stage STM-012 is feasible?
 

Rex R

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you would want some sort of recovery device for the booster, but I think it could work.
Rex
 
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Screaminhelo

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I have seen it suggested that a 2 stage STM would have a booster stage that is at the limits (maybe a bit beyond) of how long the gap can be for successful staging but it begs to be a 2 stage rocket. I will be ordering a Quark shortly and may just have to give this a try. If BABAR has done a 36" gap, this one should be fine.
 

rharshberger

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I have seen it suggested that a 2 stage STM would have a booster stage that is at the limits (maybe a bit beyond) of how long the gap can be for successful staging but it begs to be a 2 stage rocket. I will be ordering a Quark shortly and may just have to give this a try. If BABAR has done a 36" gap, this one should be fine.
It will probably stage fine, but due to the stability of the booster it will probably lawn dart (the booster not the sustainer).
 

BABAR

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Here is a gap staged EPM-010
https://www.rocketryforum.com/showthread.php?43496-epm_207&highlight=stage
Above posters are right, booster will come in ballistic without some modifications, the gap ignition itself really isn't a problem so long as you vent it right.
Modification include adding a pod wth an engine, nose cone, and streamer or small chute on the booster

Here is an example
https://www.rocketryforum.com/showt...ged-2-successful-flights!&highlight=gap+stage

Others have come up with putting a pod on the upper stage with a streamer (attached to the BOOSTER) that gets pulled out the back at staging.
 

BABAR

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On the other hand, particularly if you reinforce the tube of the booster, coming in ballistic may be an okay
From a NAR safety code standpoint, you might call it featherweight recovery. This is ballistic recovery, but the rocket is so light it is not damaging to bystanders or the rocket.
If you build otherwise light, you could launch with a B6-0, it will stage low and not fall very far.

My preference for staged rockets is to stage low, where everyone can see it, since I fly for fun and not for altitude.

So ballistic may actually work for you.
 

Screaminhelo

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This has given me food for thought. I just may have to get another STM, one for staging and one as a DD practice mule.
 

Gus

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This will help you understand why you need to vent the booster of a gap staged rocket. It also helps understand what is going on when you tape two motors together in the more common butt-staging.

[video=youtube;1Nhe5Y78PRQ]https://www.youtube.com/watch?v=1Nhe5Y78PRQ"]https://www.youtube.com/watch?v=1Nhe5Y78PRQ[/video]
 
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