Stuffer tubes can get stuffy

[Veracity]

To all,

I've been flying a 3 ft long BT80 D powered home built rocket for several years now. After the first launch or so, the BT50 stuffer tube sort of caved in on itself. Not completely thank goodness, but it happened just the same.

I put a few vent holes here and there...and it continues to work beautifully.


I think it happened because, for the first few launches, I did not remove the engine after recovery. It stayed in there...baking away.

I'm designing an E powered BT80 type rocket with a BT50 stuffer tube. This time, vent holes will be incorporated into the design from the beginning.

Has anyone ever had this happen? If so, what did you do? Weep uncontrollably? Take immediate action?

Thoughts?

[K.M.Knox]

Ya know, my old Estes Shadow has a stuffer tube to about 10" from the top and I have not had any problems with it at all. Not sure what you mean by "caved in on itself"? Are there vent holes between centering rings so internal sections become pressurized in which case crush the tube? I would guess that is not the case but your tube condition is new to me. Of course I only have a couple of rockets with stuffer tubes so I am not all that experienced with them.

[Intruder]

My dad has a BT-80 Goblin upscale that has the BT-50 motor mount crushed, but it was from the foam that he injected into the space between the centering rings to give the main tube some rigidity. He's remedy for the problem is to simple give it a run through with a rod a couple of times. You'll have to talk to him get some better detail.

[barone]

My stuffer tubes first appeared to be crushed but were actually burned from the ejection charges. I've started using the foiled lined stuffer tubes from BMS now. Don't know how well they work since I haven't gotten a flight off yet. But I figure they got to work better than the unprotected BT50 stuffer tube...

[tbzep]

Yep....don't ever use canned foam. Use the two part stuff. The canned stuff never completely cures. It will expand slightly over a very long period of time. Heat from the motors still cause it to expand to this day, a good 15 years after it was built. I force a 1/2" dowel rod through the stuffer tube to make sure that the ejection gases have a clear passage.

As for burn damage from ejections, the only time I've had trouble with burn through was when I was using Aerotech single use motors. Estes/Quest motors have never caused it to happen, except with a cato.

IMHO, the best plan for burn through prevention is to build lots of rockets so you don't have to fly the same one every weekend. :D

[Doug Sams]

I've been flying a 3 ft long BT80 D powered home built rocket for several years now. After the first launch or so, the BT50 stuffer tube sort of caved in on itself. Not completely thank goodness, but it happened just the same.
There are several factors in this. First and foremost, plain old BT-50 is really not thick - durable - enough for this (IMHO).

Second, one theory I heard - and that I buy into - is that the cooling that occurs after the hot ejection charges results in condensation in the stuffer tubes which contributes to the problem.

Lastly, if the rocket is already built and it's too late to put in a beefier tube, the best suggestion I've seen is to install disposable ablative shields ahead of the motor when prepping for flight. This amounts to using a piece of card stock rolled up and inserted ahead of the motor. At ejection, it will bear the brunt of the damage thereby prolonging the life of the tube.

Doug

[Doug Sams]

My stuffer tubes first appeared to be crushed but were actually burned from the ejection charges. I've started using the foiled lined stuffer tubes from BMS now. Don't know how well they work since I haven't gotten a flight off yet. But I figure they got to work better than the unprotected BT50 stuffer tube...I've used the foil lined tubes from Totally Tubular, and, IMHO, the foil is of dubious benefit. But the thicker nature of the tube is indeed beneficial. With the rockets I've built using it, the foil tends to curl up and delaiminate ahead of the motor after only one or two flights. So, while it's conceptually appealing, in reality it's not very durable. But, as I said, the thicker wall is helpful. Thus, I've since just used the thicker walled 24mm tubes (eg, LOC, BMS) while foregoing the foil.


Doug

[barone]

I've used the foil lined tubes from Totally Tubular, and, IMHO, the foil is of dubious benefit. But the thicker nature of the tube is indeed beneficial. With the rockets I've built using it, the foil tends to curl up and delaiminate ahead of the motor after only one or two flights. So, while it's conceptually appealing, in reality it's not very durable. But, as I said, the thicker wall is helpful. Thus, I've since just used the thicker walled 24mm tubes (eg, LOC, BMS) while foregoing the foil.


Doug
Something else I've tried along the lines of thicker tubes, I've used the coupler stock from BMS to make a thicker tube. Have used that and haven't experienced any problems. Of course, it does add some weight but with the impulse I'm flying, it doesn't matter.

[Veracity]

There are several factors in this. First and foremost, plain old BT-50 is really not thick - durable - enough for this (IMHO).

Second, one theory I heard - and that I buy into - is that the cooling that occurs after the hot ejection charges results in condensation in the stuffer tubes which contributes to the problem.

Lastly, if the rocket is already built and it's too late to put in a beefier tube, the best suggestion I've seen is to install disposable ablative shields ahead of the motor when prepping for flight. This amounts to using a piece of card stock rolled up and inserted ahead of the motor. At ejection, it will bear the brunt of the damage thereby prolonging the life of the tube.

Doug

Ok, now we're on to something!

Please explain this disposable ablative shield stuff to me. The rocket I've been writing about--my ten year old one--has the goofy "the tube is burnt or caving in" look to it. Although it has not been flown a lot, it does have that look. It got that way the first day I launched it.

I love it and don't want it to "lawn dart" on me because the ejection charge leaked out.

That suggestion of yours could be its salvation.

Do tell!

[Doug Sams]

Please explain this disposable ablative shield stuff to me. This is basically just a rolled up piece of paper or card stock. You roll it tight enough to slide into the motor mount to just ahead of where the motor stops. It will unroll itself a bit to fit the tube, and when it does, make sure it's open enough to not interfere with the ejection charge. As for length, my swag is to make it as least a few inches long, and perhaps long enough to span to the forward end of the stuffer.

As for your already deteriorating tube, here's what I'd try. If you can, as suggested elsewhere in the thread, use a stick (with a smooth end) to open the collapsed tube without further damage, and the tube is otherwise sturdy enough to bear the thrust of the motor, then simply insert the paper roll and you should be good to go.

That said, I've never had one with this problem (yet, knock wood), so my advice is 2nd hand. I've had several others tell me about the paper rolls, especially in the context of SU composite motors where "afterburn" of the delay grain is known to cook motor tubes. The rest of it is my seat-of-the-pants engineering, which usually serves me pretty well but is not infallible :)

Doug