bodytube inner surface and ejection charge - heat protection

[nils]

Parachute ejection charge burns a bit my fibreglass bodytube inner surface each time. What would be a good material or a good coat to protect fibreglass inner surface?

[SpaceManMat]

Interesting observation, I've not seen that. I take it you are using electronic deployment? Are your charge well pointed sidewise?

Anyway I would use a thin epoxy to coat the inside of the tube in the area of damage such as Wests.

[OverTheTop]

I have not observed any damage to my fiberglass from ejection charges.

As has been said, a coating of epoxy would be a reasonable fix.

[nils]

That's what I suspected. I used polyester resin. So I will try to find epoxy for my next rockets.

[OverTheTop]

Not sure if polyester was a bad choice. I have no experience with it. Anyone else experienced problems with polyester resin being damaged by ejection gases?

[SpaceManMat]

I would think that would not be a good idea. It’s polyester cloths that are known to be very dangerous if they catch fire.

Not sure how much the resin varies but obviuosly from your previous report it’s not holding up too well. I’d recommend retiring it, if it does catch fire during deployment it could burn all the way down and start a grass fire.

[nils]

One more bad thing I discovered about polyester resin - it becomes sticky when hot. Rocket motor must be very well isolated, otherwise rear ejection does not work.

[nils]

One question about switching from polyester to epoxy:
Polyester does not stick to cooking paper so I can use it as release agent when rolling tubes. Would cooking paper work with epoxy as well or do I absolutely have to switch to some special release agent?

[OverTheTop]

Use Glad Bake (accept no substitute) as the cooking paper and you will have no problems. I use it all the time.

There are numerous threads here where people have, to their detriment, used other brands during builds.

[Kryten]

I would think that would not be a good idea. It’s polyester cloths that are known to be very dangerous if they catch fire.

It's the first time I've heard this. Can you provide a link to the source of this information?

Not sure how much the resin varies but obviuosly from your previous report it’s not holding up too well. I’d recommend retiring it, if it does catch fire during deployment it could burn all the way down and start a grass fire.

I suspect it's just charring, rather than catching fire - unless the resin is severely under-cured, in which case it may be a good idea to chuck it out

[SpaceManMat]

https://firescienceblog.com/tag/fabric-flammability/

When scanning the internet, I came across a great article in the Fall 2011 edition of On Track! magazine, which you may have some familiarity with. The article is titled, “Safe Batting Choices for Baby and Invalid Quilts,” by Beth Kurzava. The article does a great job of demonstrating how easy or hard it is to spread flame over different batting materials. Cotton, wool, silk, cotton-poly blends, polyester, bamboo-cotton blends, cotton-corn blends, and fire retardant cotton fabrics were all tested following an ad hoc procedure based on the code of federal regulations (CFR) clothing fabric flammability test. The test was simple, expose an 8” square of each fabric on a 45 degree incline to a three second fire exposure at the corner of the sample, then sit back and observe the fire spread. Pictures were provided in the article and show that wool and fire resistant cotton are the best performers and polyester is the worst performer. These results are very consistent with the science of fabric flammability. Natural fibers will burn or smolder, but are naturally resistant to rapid fire spread over a surface. Polyester, on the other hand, is a petroleum-based, plastic synthetic fiber. Like all petroleum-based plastic products, it tends to melt and liquefy upon heating, but once ignition has occurred, it will sustain vigorous flame spread over a surface.

To make things worse the cloths stick to your skin making them difficult to remove.

[kopius]

That's what I suspected. I used polyester resin. So I will try to find epoxy for my next rockets.

As others have mentioned, I have not seen the fibreglass tubes burnt from an ejection charge, rather just residue/marks. So just for clarity, are you saying that you made your own tubes using polyester resin and that is what is burning?

[nils]

Yes, I made my own bodytube with polyester resin.
Here is a picture of my rocket before the first flight and before 2 successful flights:


An area above engine block has turned from half transparent to milky. I made the second picture after washing the rocket.
The other white area is just white glue for bonding cord.

[Kryten]

https://firescienceblog.com/tag/fabric-flammability/

When scanning the internet, I came across a great article in the Fall 2011 edition of On Track! magazine, which you may have some familiarity with. The article is titled, “Safe Batting Choices for Baby and Invalid Quilts,” by Beth Kurzava. The article does a great job of demonstrating how easy or hard it is to spread flame over different batting materials. Cotton, wool, silk, cotton-poly blends, polyester, bamboo-cotton blends, cotton-corn blends, and fire retardant cotton fabrics were all tested following an ad hoc procedure based on the code of federal regulations (CFR) clothing fabric flammability test. The test was simple, expose an 8” square of each fabric on a 45 degree incline to a three second fire exposure at the corner of the sample, then sit back and observe the fire spread. Pictures were provided in the article and show that wool and fire resistant cotton are the best performers and polyester is the worst performer. These results are very consistent with the science of fabric flammability. Natural fibers will burn or smolder, but are naturally resistant to rapid fire spread over a surface. Polyester, on the other hand, is a petroleum-based, plastic synthetic fiber. Like all petroleum-based plastic products, it tends to melt and liquefy upon heating, but once ignition has occurred, it will sustain vigorous flame spread over a surface.

To make things worse the cloths stick to your skin making them difficult to remove.

Trying not to hijack this thread, but polyester thread/fabric, and fibreglass using unsaturated polyester resin, are completely different.
The information in the article would only be applicable to rocketry if you were wondering if other fabrics could be used for chute protection

[Kryten]

Back on topic:
I suspect the discoloration/charring may be related to undercure of the resin.
Your comment that it gets sticky when hot supports this.
Since it's already had 2 successful flights, and you're only using low power motors, it looks like you'll probably get away with it.
If the apparent discoloration detracts from its appearance, you can always paint it.
BTW, "white glue" would not be the preferred adhesive for bonding to fiberglass