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end of motor 2" inside body tube - can this be right?

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billdz

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Please have a look at the 2 attached pics, can this be right? Both are from The Launch Pad, one is a Martel and the other is a Bullpup. In both, the end of the motor mount is 2" from the end of the paper body tube. Isn't this dangerous, with the body tube possibly catching on fire when the motor ignites? In any event, what is the purpose of this type of mount? I got these in a box of rockets I purchased. The instructions for the Martel indicate the motor mount is supposed to be this way, in fact there is supposed to be a paper tail cone attached to the bottom of the body tube. The instructions for the Bullpup do not call for this type of mount, there is supposed to be a plastic tail cone and the end of the motor mount is supposed to be 2" from the end of the tail cone.

Martel motor mount.jpg


Amraam motor mount.jpg
 

timbucktoo

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No - it should be fine. I had an Aerotech Sumo and the MMT was about 3-4" inside the air frame. 29mm MMT & 4" air frame.
 

AfterBurners

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Tim is right I had a SUMO too, but you could always coat the tubes with epoxy or JB Weld if it concerns you. As far as the SUMO I think it looks cleaner with aft ring flush against the end of the mmt
 

Incongruent

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It'll probably be okay, but use a clothespin to elevate the end from the blast deflector.
 

kclo4

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The purpose of having the motor tube recessed in the body tube is to shift the CG forward so the rocket needs less nose weight to be stable. For that size of rocket you should only need a protective coat of paint(maybe black grill paint if you are worried) to keep the body tube from getting scorched. There is more of a concern with bigger longer burning high power motors of course.
 

rstaff3

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As long as the recess is no more than one BT diameter up you are fine. The motor on my TLP Rapier is similarly recessed and after dozens of flights the inside of the body tube is just sooty.
 

Flyfalcons

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The Estes Saturn V is like this as well. Works okay.
 

Bat-mite

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Note how thin the flame is on a mid-power motor (this is an Aertoech G-something-or-other). Not much risk of fire.

IMG_0063.jpg
 

samb

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Please have a look at the 2 attached pics, can this be right? Both are from The Launch Pad, one is a Martel and the other is a Bullpup. In both, the end of the motor mount is 2" from the end of the paper body tube. Isn't this dangerous, with the body tube possibly catching on fire when the motor ignites? In any event, what is the purpose of this type of mount? I got these in a box of rockets I purchased. The instructions for the Martel indicate the motor mount is supposed to be this way, in fact there is supposed to be a paper tail cone attached to the bottom of the body tube. The instructions for the Bullpup do not call for this type of mount, there is supposed to be a plastic tail cone and the end of the motor mount is supposed to be 2" from the end of the tail cone.
Recessed motor mounts and paper tailcones and paper nose cone caps are design features of many TLP kits. A little different flavor than most. I didn't know that either the 12B or the 12C model had a plastic tail piece. Perhaps the builder did make an error on the placement of the motor mount in your Bullpub, not taking the length of the tailcone into account. Here is an old build thread of the 12B by the one-n-only sodmeister that may help you: https://www.rocketryforum.com/showthread.php?18321-TLP-BullPup-12B-Build&p=162423#post162423

His solution to possible charring of the inside of the tail - a slice of a soda can. Genius !
 

AfterBurners

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Recessed motor mounts and paper tailcones and paper nose cone caps are design features of many TLP kits. A little different flavor than most. I didn't know that either the 12B or the 12C model had a plastic tail piece. Perhaps the builder did make an error on the placement of the motor mount in your Bullpub, not taking the length of the tailcone into account. Here is an old build thread of the 12B by the one-n-only sodmeister that may help you: https://www.rocketryforum.com/showthread.php?18321-TLP-BullPup-12B-Build&p=162423#post162423

His solution to possible charring of the inside of the tail - a slice of a soda can. Genius !
this makes sense
 

KarlS

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If you want, you can go to a "big box" hardware store and get "aluminum" tape and put that inside the body tube. It works very well.
 

timbucktoo

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I mixed up some epoxy and thinned it with alcohol and applied with an acid paint brush along the inside of airframe. Soot wipes right off.
 
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