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Staging: Why Cover Joint With Engine Tube?
When building a multi-stage rocket, why do we typically cover the joint between the upper and lower stage engines with engine tube?
The biggest problem I have with staging rockets is that the fatness caused by the cellophane tape on the sustainer engine will cause the booster stage to stick to the sustainer engine and the booster engine gets blown out of the booster stage. Then the exhaust from the sustainer engine flows down through the booster engine tube during the whole flight. Upon recovery, I have a burnt out booster tube. (Burned out the engine tube in a SuperNova booster this weekend.) Now, I know, one is meant to wrap the booster engine with enough tape so that it doesn't get blown out of the booster stage. But if you make a really tight fit, then you can't slide the booster stage over the engine stack. But if you use too little tape, then you get a burned/toasted booster stage. If there were no engine tube around the joint between the engines, then this could not happen. There'd be no way (short of a stuck stage coupler) for the booster to stick to the sustainer after sustainer engine ignition. So why not just make the engine tubes 1/4" - 1/2" shorter and leave the joint exposed inside the body tubes? I was thinking this would only apply to rockets with a larger body tube than engine tube, but minimum diameter staged rockets could do the same. It might not look as good, if the booster body/engine tube stops 1/2" short of the sustainer, but there would be no possibility of the sticking and burning problem. I think I'll rebuild my Midget and make the booster stage tube out of BT-5+ (slips over BT-5). Then I'll put a couple of small rings of BT-5 inside to hold the booster engine centered, but the sustainer engine will not be fat enough to stick to the BT-5+. I've rebuilt the booster of the Midget lots of times because of getting the wrong balance between tight booster engine tape and being able to slide the booster stage over the engine stack. |
#2
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Jeff, when I staged my clustered/staged model you see in the pics below, I had NO tubing covering the engine joints. Just used cellophane tape wrapped very, very tight and it did the job with no problems. Flew this about a half dozen times, all success....
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Dave, NAR # 21853 SR. |
#3
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Quote:
Very nice. I can't quite tell. Is that a two or three engine cluster? Okay, I'm going to go forth and build all my boosters so they do not cover the engine junction with engine tube any more. I may do some creative work with BT-5+ and BT-20+ though. |
#4
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Four engine cluster.....
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Dave, NAR # 21853 SR. |
#5
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Never have done a staged rocket, I can only guess the tape is supposed to burn through and release the boost stage!?!
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#6
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When the hot gases of the 1st & 2nd stage combine, it burns or melts the cellophane tape and that releases the booster/upperstage. I think Vern Estes was the first to discover this (hence, his famous Technical Report on Staging, still classic after all these years!!).....
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Dave, NAR # 21853 SR. |
#7
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I use gap staging whenever possible. Both motors are retained in their respective stages with motor hooks. A stage coupler does the job of keeping the stages together. No taping necessary.
In my Mini-Brute Midget (a clone), the fit of the BT-5 booster stage over the exposed end of the sustainer motor is so tight that taping the motors together is not necessary, or even possible. Yet it stages just fine. The original K-40 Midget had a low-profile engine block in the aft end of the booster stage. The booster motor absolutely could not be blown out of the back end of the booster at staging. Thus the booster motor did not need to be firmly friction-fitted into its stage. The two motors were taped together, and the sustainer motor was friction-fitted into its stage. The booster stage was then just slipped over the exposed booster motor, with only enough friction-fitting to insure that it stayed on during the first-stage boost. The ignition of the sustainer motor reliably separated the stages. MarkII
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Mark S. Kulka NAR #86134 L1,_ASTRE #471_Adirondack Mountains, NY
Opinions Unfettered by Logic • Advice Unsullied by Erudition • Rocketry Without Pity
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#8
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Without knowing any better, I was wondering why Jeff's booster stage didn't have anything like a engine block or motor hook!
I learned a lot here about staging just from a few messages... |
#9
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Quote:
If you tape the motors together for staging, an engine block or hook would get in the way. For classic Vern Estes style staging, you tape both motors together and friction fit the sustainer engine in the rocket. You then slide the booster stage airframe over the booster motor. When you slide it on, make sure the booster motor fits moderately snug in the booster stage so that it doesn't get kicked out of the booster stage by sustainer ignition and leave it attached to the rocket to get fried. Edit: Oops. I reread your post and realized you have already learned about it and weren't asking a question. I tried to delete the post and it won't let me.
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I love sanding. |
#10
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Well, I guess that is standard for Estes then. So, I learned something.
In that case an engine block would help since a hook would interfere. |
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