Heat-PROOF engine mount tubing?

I've been experimenting with a no-wadding chute packing/deployment method and run into a snag.
What I've done is to run a stuffer tube all the way up to the nosecone,
then pack the shock cord and chute around the stuffer. The nosecone has a plug attached to the center that mates to the stuffer. So the ejection gases pop off the nose, and it pulls the chute out after itself. The shroudlines are wrapped around the chute so that it gets completely out of the body before opening.
This scheme has worked nicely, with one problem: I'm using Estes BT20 for the stuffer, and it burns completely through after 4 or 5 flights. Apparently the BP is hanging around too long and frying the tube. I still get a recovery under 'chute, but the bird has to be rebuilt to fly again. This puzzles me, since I have other models with stuffer tubes (albeit not all the way to the nose) and they don't burn through even after dozens of flights :-/
I coated the stuffer with CA on the first rebuild but that burned through also. So I guess I need a stuffer tube made out of something that just plain doesn't burn. Or some way to get the hot stuff out before it starts burning the stuffer. It seems to me this problem must have come up with baffle designs also, so there should be some useful wisdom out there.
Suggestions?
--
Gordon S. Hlavenka http://www.crashelectronics.com
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Gordon S. Hlavenka wrote:

Could you take tubular kevlar, form it around a mandrel(dowel), coat it in some very high temp epoxy to make a kevlar tube? Or maybe just take the BT-20 and coat it in high-temp epoxy (JB Weld?) There are also high temp paints you could use (engine block paints) to coat the inside of a BT-20.
The baffle designs I've seen don't trap the hot gases for very long and any burning particles get trapped into a metal mesh or onto something like plywood. Since you only need the gas pressure to pop the nose, why not build a baffle into the lower section of the stuffer tube (two plywood bulkheads with holes in them, seperated by a few inches with the holes offset from each other)
I'm just rattling ideas off the top of my head.
-Aaron
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The ejection charge is not roasting the stuffer tube - the delay afterburn is roasting it. bad on all motors but worst on special composite motors. Also the most vulnerable tubes are those with thin walls like standard Estes BT-5, 20 and 50. BT-55 thickness is a bit more. MRC tubes were the thinnest ever.
Google Hibachi Effect.
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLR,GGLR:2005-41,GGLR:en&q=hibachi+effect
http://www.apogeerockets.com/education/newsletter28.asp
-Fred Shecter NAR 20117 http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQfsooZ1QQfsopZ1QQsassZshreadvector
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I thought this applied only to drilled out delays like those on composite motors. In a pressed BP motor (or an undrilled composite), there's no left over delay column to continue burning after ejection.
--
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
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Bob Kaplow wrote: > I thought [Hibachi Effect] applied only to drilled out delays like > those on composite motors. In a pressed BP motor (or an undrilled > composite), there's no left over delay column to continue burning > after ejection.
The delay breaks through shortly before it would have burned through, due to the motor chamber pressure. The delay remnants keep burning for a bit.
Drilled delays are the main culprit, though.
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Steve Humphrey
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http://www.aerotech-rocketry.com/customersite/resource_library/Instructions/RDK_Instructions/rms_delay_mod_inst.pdf
Adjusted/drilled RMS delays have the cavity toward the combustion chamber to reduce the afterburn effect.
Apogee motors have the drilled cavity toward the ejection charge end resulting in way more afterburn of the delay.
End burning Estes black powder motors have plenty of afterburn since they burn in a domed shape.
-Fred Shecter
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You misunderstand, Phred.
At makes motors like the old B7 and E6 and similar motors with long delays. Then after manufacturing, they drill the ejection hole through the epoxy. They drill shallow for a long delay, and long for a short delay. So a B7-4 has a delay that still burns a bit after ejection, creating the Hibachi effect.
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Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
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I do not misunderstand. I posted longer messages than you snipped/quoted. I posted links to the apogee article that displays the long non-standard motors with the drilling on the ejection charge end.
I pointed out the apogee type motors are drilled on the ejection charge end, yet the RMS drilling/adjustment instructions tell you to drill on the opposite end: the combustion chamber or aft end.
The apogee type motors will have severe afterburn of the delay. More severe than Estes BP motors and more severe than RMS and more severe than "normal" modern Aerotech motors (with the screwed and secured plastic delay/ejection housings).
I do not snip so that people can see all the words that I'm responding to, AND I top post so those with a functioning memory do not have to scroll through 45 feet of message to get to a short response.
that oughta send you off in a tangent.
;)
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What's Holverson got to do with this?
--
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
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BURMA!
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-Fred Shecter
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Fred Shecter wrote:

Hey! No panicking in my thread.
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Gordon S. Hlavenka http://www.crashelectronics.com
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Yes there is. The motor burns in a domed shape and there is delay left against the casing walls.
I've static tested HUNDREDS of BP motors and the delay afterburn seen up close (through a quartz window) will scare the $#!+ out of you.
-Fred Shecter NAR 20117
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Got any video? Not that I doubt you, I just wanna see.....its the 8 year old in me comming out. :)
-Aaron
Fred Shecter wrote:

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Aaron wrote:

Run a "static test" of an Estes motor taped to a rod driven into the ground. You'll see a very nice fireball an instant after the ejection charge fires. (Not one of those Hollywood fireballs, but a translucent orange ball of heat.)
I don't think it would scare the $#!+ out of you ... it's not THAT big. But seeing it at ground level is educational.
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The fireball is the ejection charge. After that, a highway flare like afterburn flame continues to come out of the top of the motor.
Again: I am talking about the delay afterburn and not the very fast burning and very fast gone ejection charge.
I have no video. I static tested hundreds of motors at MIT in the late 1970's and into 1980.
You can also do a series of experiments and watch (and video):
1) static test Estes motors.
2) put an Aerotech ejection charge from an RMS inside an Estes spent motor casing and install in a body tube. Fire it electrically and observe the effect.
3) Do the same with an Aerotech RMS delay train.
4) Static test full Estes motors installed in body tube normally.
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Bob Kaplow wrote:

I noticed the same thing. But the "Hibachi Effect" was not something I'd thought of before, so it's good information to have in any case. Using JB Weld to stick in a piece of a Coke can will work regardless of whether the problem is leftover ejection BP or delay grain. Hopefully the aluminum will last a good long time.

I think there might be, even in an undrilled grain. Mightn't the grain burn a bit more slowly near the casing, due to heat soaking away? In which case there would be a slightly convex burn front; the center would break through first and fire the ejection BP, then the remaining ring of delay would burn out: Hibachi.
But the above is just handwaving; any composite motors _I_ buy are flying! I don't have the budget to do pure science :-)
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Gordon S. Hlavenka wrote: > I've been experimenting with a no-wadding chute packing/deployment > method and run into a snag. > > What I've done is to run a stuffer tube all the way up to the > nosecone, > ... > This scheme has worked nicely, with one problem: I'm using Estes BT20 > for the stuffer, and it burns completely through after 4 or 5 flights.
What motors are you using? Larger motors have a larger ejection charge since the manufacturers assume the rocket has a larger volume to evacuate. Confining that ejection charge to a BT-20 means the heat doesn't dissipate as fast as designed.
If you can afford it, buy plenty of BT-20's and (re)build the rocket so that the stuffer tube is easily replaced.
Or, buy a full-length BT-20 coupler (or a bunch of regular couplers) to line the BT-20 to prolong its life. Use epoxy to glue the coupler(s) in place, thereby adding another layer of protection. Or buy a T-20+ (Totally Tubular) or T-20Q (BMS) to slip over the outside of the BT-20 to increase the lifespan of the stuffer tube.
Or get some Nomex paper (Totally Tubular) to line the stuffer tube. Here's how I do this: Use the thinnest paper, long enough to reach past where you've observed the charring of the burnt tubes. Wrap it into a cylinder and tape it to the end of the motor. Then insert the motor as usual, slipping the paper up into the stuffer tube first.
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Steve Humphrey
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gordon:
I use epoxy glue to glue in a sleeve of aluminum can about 3-4" in length right at the top where the ejection charge gases would be the hottest. I have also experimented with using pipe screeens to allow the gases through but not the hot particles...
you could combine both of the above ideas into a baffle.....inside the small stuffer tube....
terry dean nar 16158
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"Gordon S. Hlavenka" < snipped-for-privacy@crashelex.com> wrote in message
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I've been doing the Coke can thing for years and it works well. Just cut a rectangle of aluminum from a can, coil it up, and stuff it in the tube. It makes an effective heat shield, weighs practically nothing, and is very easy to do.
Chuck W Sharc, NAR Section 613 www.flysharc.org
Sharc, we fly rockets so you don't have to!
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Gordon S. Hlavenka wrote:
<edited for brevity - snip>

For Estes BP motors only...
I paint the inside of baffle tubes with epoxy. Not a cure, but seems to help. I use a type of Kaplow baffle and spreading the hot ejection gas/residue over larger internal volumes also helps, ie, a ported baffle vents into a larger airframe which is also epoxy painted, or lined with a layer of split body tube. I have found CA soaked paper tubes to be more susceptible to heat damage than plain tubes. I "think" the CA structural polymer has a fairly low melting point which causes the tubes to delaminate upon heating.
My baffles catch so much particulate matter that I have to regularly clean them out with a test tube brush. They are fairly new models, but a few have 10+ flights on them without a burn through. And my min diameter BT-20 models do not exhibit that kind of burn through rate, either.
Are you using a particular brand of BT-20 for all the stuffer tubes so far?
--

Gary

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