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Do I really need that aft centering ring?

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blackwing94

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I'm building a fiberglass Madcow (wildman) X-celerator. It's a split fin rocket. The motor mount tube that comes with the kit seems to be about a 1/4 inch to short. Or maybe I just built it wrong. Anyway, on the motor mount tube I have the top centering ring followed by 6 through the wall fiberglass fins epoxied to the motor mount. I'm left with just barely enough motor mount tube to put on an aeropack 54mm retainer. If I add in the aft centering ring, the retainer will have very little real-estate to JB weld on to. My question is, with all the fins holding the motor mount in place, do I really need the aft centering ring? Just wondering.

That would make it a Scottish rocket with the up the kilt wind blowing. Without the aft centering ring there's lotsa room to stick a camera in there.
 

K'Tesh

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As long as the forward CR is sealed to keep in the ejection gasses, and the fins are firmly attached to the motor tube (with internal fillets), the only reasons I can think of is to help align the motor tube, to have an aft CR help act as a thrust plate, and to reinforce the rear of the rocket (preventing damage on hard landings, or knocks...)

My vote... No, it's not needed.

You might want to add a short length of coupler in there to help reinforce the back end just a little, but it's optional.
 
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markkoelsch

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I think you will be fine without it. If you want a little extra get some of the PML urethane foam, and fill the space between the body, find, and motor mount.
 

MClark

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The ring keeps fire out of the tube. Look at rockets that have been launched many times the aft ring is roasted.

M
 

blackwing94

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Thanks for the replies. I have to say I never even considered that a aft centering ring might be optional in some cases. I've never questioned it.
 

jeff_j_black

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Another time the aft ring comes in handy is during landings when the motor nozzle is the first thing that comes in contact with the ground.
 

fyrwrxz

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I think you will be fine without it. If you want a little extra get some of the PML urethane foam, and fill the space between the body, find, and motor mount.
+1! (BTW- he meant 'fins') I injected foam, cured and trimmed it back and then carefully sealed the back end with JB weld AFTER I mounted the retainer. Mix up your epoxy or whatever and throw it in a sandwich bag-viola'! An ersatz icing bag making everything easier to control. Just don't cut too big a hole in the corner and everything will stay neat.
 

markkoelsch

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+1! (BTW- he meant 'fins') I injected foam, cured and trimmed it back and then carefully sealed the back end with JB weld AFTER I mounted the retainer. Mix up your epoxy or whatever and throw it in a sandwich bag-viola'! An ersatz icing bag making everything easier to control. Just don't cut too big a hole in the corner and everything will stay neat.
Yep, I meant fins. Damned spell check on phone.
 

blackwing94

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Foam sounds like a fun plan. I've never used foam before. This is a 4" rocket so I would need to fill 24 inches of body tube (minus the motor mount tube) with foam.

After I slept on the problem, I am considering making the motor mount hole in the centering ring a little bigger so it fits around the outside of the retainer. I would have to epoxy/jbweld them in at the same time.
 

Dave A

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Another option, Take the remains cr and cut into pie wedges and stick them just between the fins.
 

3stoogesrocketry

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You should be able to enlarge the ID of the rear ring to fit over the retainer.
 

blackwing94

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Problem solved. As advised, I enlarged the ID of the centering ring to include the retainer.

There are few problems in life that can't be solved by the judicious application of a Dremel. :cool:
 

manixFan

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Good solution. Having the centering ring will help reduce base drag over leaving it open.


Tony
 

Bat-mite

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The Madcow X-Celerator is from Rocketry Warehouse, not WIldman, FYI.

I had the same problem with mine, years ago before Madcow took over. I complained to RW, and they sent me a longer MMT at their expense. Might be worth a call to Mike.
 

tball7

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Use it, the ring, and spray with BBQ paint as an ablative..
 
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