10mm Engines
 

We started refitting "Mabellette" to produce 10mm engines just before we left for NARAM. Over the last few weeks we have been able to finish the tooling and make adjustments to the machine and program. Mabellette works great and the engines look very good. There is just one small problem...

At between 3 and 5 seconds into the delay, the casing burns through on many of the engines. We had never noticed before that the first 1/8" of the inner (beginning) wrap does not have any glue. The failure always occurs at the unglued seam just above the nozzle. It does not matter if the delay is a fast burning (10sec/inch) or slow burning (30sec/inch) type. It is still around 5-7 seconds of total time since ignition. Replacing the delay with BP gives a 2+ second burn with no case weakness.

This is disheartning. We were trying to get about a thousand ready to give to the FAI team at the Capital Cup next month to use as practice engines over the next year. I am sorry for the SAM members that were anticipating the 10mm engines. :(

Perhaps this is a manufactuing flaw or it may be a problem just associated with very small tubes. They were made by New England Paper Tube, the original engine tube company for Estes and others. The 18mm casings made at the same time do not have the problem. I will be following up with NE this week.

Bruce said the upside is that we have B14's quicker and 18mm engines work in most of our current kits. I still hope we can make the 10mm work.

Sounds like the delay grain burns a bit hotter than the propellant grain. If replacing the delay with BP doesn't cause a burn-through, then it must be a temperature issue. Are there any delay grains that burn at a lower temperature?

Even though I'm not a likely customer for the 10mm motors, I'm sorry to hear this.

And....I hope you and yours are not too wet from the storm. Obviously you have power you you wouldn't be posting right now. Do take care!

It is hard to see since there is so much ash, but when the 1/8" flap moves away slightly from the tube, it appears that it causes a swirl or vortex at the joint where the glue starts.

The slow delay generates much less heat and gas, so it seems to be a time issue.

Yeah, the 10mm are definately a specialty engine. I know the market is very small, but we have really wanted to do something to help the FAI team be more competitive.

The only thing I picked up in this whole thread was "B14"

Ya, me too. It was like, "Asdg dfgdfg f hf hfhfdhfg hfxg h fgh fgh f hfg hfgj B14 dfh fgfsg hfg hgh fg jfggdhj." ;) :D :chuckle:

I would buy them for sport flying. They are something different. They would sent my BT-4 micro rockets into the stratosphere. :D Especially if I could stage them. :cool:

Carl,
Good to hear that you got through Irene alright. My daughter lives outside of D.C. and seemed disappointed...

Have you tried to make a few motors after running a swab with either CA or white glue down to tubes to verify that the loose flap is indeed the problem? I can appreciate that this might be a lot of work to verify the problem, but it would add some verification when you talk with the tube manufacturer.
Just a thought from a non-engineer missile technician.

Chas

Good thinking. I had thought of that briefly and since you did too, maybe it is time to try it. I just have not figured out the best way of doing it. The tab is tight against the tube. It would have to be very viscous to seep under the edge. First attempt will be CA using an insulin needle from one end. If it runs out the other end, it will probably be a good check.

I am not ready to give up yet and appreciate any more suggestions.