10mm Engines

[Carl@Semroc]

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.

[CPMcGraw]

We started refitting "Mabellette" to produce 10mm engines ... one small problem...

At between 3 and 5 seconds into the delay, the casing burns through on many of the engines ... 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...

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?

[BEC]

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!

[Carl@Semroc]

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?
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.

[Carl@Semroc]

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!
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.

[STRMan]

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

[Ltvscout]

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:

[Mark II]

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:

[Chas Russell]

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

[Carl@Semroc]

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.

[Ltvscout]

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.
Thin CA should wick under it just fine.

[blackshire]

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.Chas' idea sounds sensible. A modification of his idea from a non-rocket engineer (and I am a living example of Richard Feynman's quote: "You can't teach calculus to a horse!") is this: If you soaked a small sponge or a ball of fabric in white glue (that might be thinned with water) and pulled it through the motor tubes using a string (while rotating the tubes to "lay down" the tabs), the film of dried glue would provide a protective layer inside the tube. This method might lend itself to production quantities of motors. The unknowns are [1] Will the clay nozzle bond sufficiently strongly to the glue film, and [2] will the propellant, delay charge, ejection charge, and clay ejection charge cap also bond sufficiently strongly to the glue film?

[ghrocketman]

HIP HIP HOORAY !!!!!
I KNEW Carl would come through with a B14 when NOBODY else would and I will be happy to give him ALL my B engine business !!!!

So much for baloney excuses why it could not happen.....

[blackshire]

HIP HIP HOORAY !!!!!
I KNEW Carl would come through with a B14 when NOBODY else would and I will be happy to give him ALL my B engine business !!!!

So much for baloney excuses why it could not happen.....You've just inspired an idea: Since these motors (Carl, are you planning to call them "modules" as you did before?) aren't approved for sale & shipping yet, maybe those of us who happen to be traveling through the vicinity of Knightdale, NC could..."drop by" to evaluate their motors (perhaps in exchange for appropriate "donations" if their selling them even for on-premises use is verboten)?

[STRMan]

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:


EXACTLY!!!!!!! :chuckle:

[Carl@Semroc]

You've just inspired an idea: Since these motors (Carl, are you planning to call them "modules" as you did before?) aren't approved for sale & shipping yet, maybe those of us who happen to be traveling through the vicinity of Knightdale, NC could..."drop by" to evaluate their motors (perhaps in exchange for appropriate "donations" if their selling them even for on-premises use is verboten)?
We always welcome friends!

[blackshire]

We always welcome friends!Good! While I'm not in a position to engage in such travels, others who are could post their reviews and photos here.

[Chas Russell]

My suggestion for gluing down the flap was just for a few test motors. I can't imagine doing it for a thousand motors!
I have some cotton swabs on sticks that I use and I "believe" at least one SEMROC kit included one for gluing. If it is successful in preventing a burn-through, at least it is a data point for the tube manufacturer to find a correction (and the old casings becoming collector items...).
Carl, any approximation of the burn-through rate on your test motors? Was it prevalent past a certain delay time? Is a three second delay good and five or more a problem?

Oh, and Bruce is right. B14's!

Chas

[Gus]

Carl, thank you so much for working on this. Emma and I really need 10 mm booster motors to practice staging, so the difficulty with the delays would not cause us a problem. Thanks again for spending so much time on this,

Steve and Emma

[Quixote]

WOW!

Just caught this thread today, I wish you every success in fixing the burn through problem. I would echo Mr. Russell's suggestion re sealing the inner tube with CA, many of us already use thin viscocity CA to prevent fraying of our body tubes, so it should work well due to its wicking ability with the motor case. When you get this problem licked, please contact Taras Tataryn to check on Canadian importation as there are several of us CAR members that have been playing with FAI competition and to have motors equivalent (or better) than the Europeans would be a real boon.

Also B14's .....Yes!

Garth Illerbrun
SAM 20
CAR S04

[Carl@Semroc]

Using CA to glue the flap did fix the burn-through problem at the nozzle. However, further tests had blistering at the delay section at 5-7 seconds and burn through at 10+ seconds. We would never have a delay that long, but it does show a potential problem with external case heating.

In cutting open many of the casings, I noticed that the layers are not glued as well as the 18mm casings made at the same time. I suspect NEPT has problems with tubes that small.

We have refiitted to 18mm and will put the 10mm on hold until we have more resources (time, money) to continue trying to make them work.

Thanks to all for the suggestions!

[Ltvscout]

We have refiitted to 18mm and will put the 10mm on hold until we have more resources (time, money) to continue trying to make them work.
B14's, here we come! ;)

[ghrocketman]

Mmm Yummy !
B14's !!!!
Hopefully we can get them in -0,3,5, and 7 flavors.
I would think the -0 then -5 would get the most use, with the -3 and -7 about equal to each other.
Forget the -6 delay; that one NEVER made any sense and it always seemed like they missed the boat by NOT having a -3

I had an Astron Avenger I really liked to launch on an A8-0 to B14-5 combo.
It would launch and stage low and slow then take off like a bullet once the B14 kicked in.

An Astron Farside or Arrow 300 on an 1/2A6-0 or A8-0 to B14-0 to 1/2A6-4 makes for a wacky interesting flight too.

[Doug Sams]

Hopefully we can get them in -0,3,5, and 7 flavors.
I would think the -0 then -5 would get the most use, with the -3 and -7 about equal to each other.

Forget the -6 delay; that one NEVER made any sense and it always seemed like they missed the boat by NOT having a -3I agree, the -6 seems pretty pointless between the -5 and -7. I wonder if they did the -6 'cause they couldn't get to a -3. Perhaps a delay that short couldn't withstand the chamber pressure and would rupture.

Doug

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[Royatl]

Using CA to glue the flap did fix the burn-through problem at the nozzle. However, further tests had blistering at the delay section at 5-7 seconds and burn through at 10+ seconds. We would never have a delay that long, but it does show a potential problem with external case heating.

In cutting open many of the casings, I noticed that the layers are not glued as well as the 18mm casings made at the same time. I suspect NEPT has problems with tubes that small.

We have refiitted to 18mm and will put the 10mm on hold until we have more resources (time, money) to continue trying to make them work.

Thanks to all for the suggestions!

The casings for Apogee's 10mm motors appeared to have something impregnated in them. I don't know if they are phenolic or not. Did you ever see any of them? Have you tried things like fish paper (as in the later Quest Micro motors)?

[ghrocketman]

I know Estes made a B8-3 for Centuri at one point, but not sure why the B14-3 never existed.
If blow-thru was a problem it would seem it would be even worse with the B14-0 and we all know that one worked for years.
The B14-6 has always had me scratching my head though...makes NO sense unless it was specific for some competition event that made the B14-6 optimum, but I have no idea what kind of event that would be.

[Doug Sams]

If blow-thru was a problem it would seem it would be even worse with the B14-0 and we all know that one worked for years. I considered that, but, keep in mind, boosters function by blow-thru.

That is, the flier would probably never notice anything unusual, as long as the staged flight was successful. But a B14-3 burning thru would be obvious since it would have a very early deployment.

Doug

.

[blackshire]

How about a B1-7 motor? In 1997, Stuart Lodge set an altitude record that still stands. At the 1st World Air Games, held at Ankara-Golbasi in Turkey, he flew a small FAI S6A Class (single-stage streamer-recovery) model to an altitude of 1,850' (569 m) on a Delta B1-7. These Czech motors are 10.5 mm in diameter. You can see some Delta motors and other foreign-made model rocket motors here: http://homepage.mac.com/georgegassaway/GRP/Galleries/EnginePics-F/Engines-F.html