Removing CTI Ejection Charge - Seal Hole?

[wighty44]

My next launch plan will use a P54 CTI K2045 VMAX. My rocket is DD and will use the on board altimeter for the separation events. Normally this would not be any big deal but the K2045's stock ejection delay of 15 sec. is too close to the simulation's optimum delay of 14.8 sec. So I plan to remove the ejection charge from the K2045. I've read in CTI's FAQs that it's OK to remove the charge.

My question is should I epoxy the 'touch hole" or leave it alone. It seems that it might be best to seal up the hole but I wanted to see what others have to say about it...

Thanks.

 

[tim cubbedge]

All I do is dump the BP, fill cavity with dog barf and tape it up. Never experienced any burn through.

 

[rharshberger]

The delay grain burns with much less pressure than the motor, by the time the delay/smoke grain burns out the pressure has dropped off in the motor casing. Just putting putting dog barf in the powder well and taping over will stop any possible forward flame.

 

[Handeman]

I haven't tried it with CTI, but I've been flying DD with AT motors and no powder for 10 years now. I've never bothered plugging the hole with dog barf or anything else. I've never had a problem.

Of course, that doesn't mean I won't, but I'll go with my experience. Take it for what it's worth.

 

[noffie79]

I haven't tried it with CTI, but I've been flying DD with AT motors and no powder for 10 years now. I've never bothered plugging the hole with dog barf or anything else. I've never had a problem.

Of course, that doesn't mean I won't, but I'll go with my experience. Take it for what it's worth.

I'll second this. I just leave the well empty. No problems here.

 

[wighty44]

Thank you all for the feedback. It seems a minimalist approach works fine.

 

[JimJarvis50]

I had a rocket almost destroyed by fire coming out of the ejection charge hole, and I have seen this happen to others. If I am not using the charge, I remove it, put a penny in the well and epoxy it shut. If you find any rockets out there with pennies in the well, they are mine. Cheap insurance.

Jim

 

[OverTheTop]

I usually just fill the thin hole (the one that goes from inside the motor to the charge well) with whatever grease I am using, then tape up the exterior of the charge well.

 

[Bat-mite]

All I do is dump the BP, fill cavity with dog barf and tape it up. Never experienced any burn through.

Ditto. Probably, you can get away with doing nothing; however, it doesn't take much time or nearly any money to put some barf and retape.

 

[Handeman]

I had a rocket almost destroyed by fire coming out of the ejection charge hole, and I have seen this happen to others. If I am not using the charge, I remove it, put a penny in the well and epoxy it shut. If you find any rockets out there with pennies in the well, they are mine. Cheap insurance.

Jim

Sounds like you had pressurized gases during the burn get past the delay grain. I lost a rocket and two forward closures like this, but I consider that a CATO, because the delay grains don't burn with enough flame and pressure to burn up a rocket.

You did have the delay grain in place? Epoxying a penny in place sounds like trying to plug the closure so it can hold chamber pressure. IMHO that would be way overkill for just stopping a little flame from a delay grain. As other have said, a little dog barf and tape is more then enough.

 

[JimJarvis50]

Sounds like you had pressurized gases during the burn get past the delay grain. I lost a rocket and two forward closures like this, but I consider that a CATO, because the delay grains don't burn with enough flame and pressure to burn up a rocket.

You did have the delay grain in place? Epoxying a penny in place sounds like trying to plug the closure so it can hold chamber pressure. IMHO that would be way overkill for just stopping a little flame from a delay grain. As other have said, a little dog barf and tape is more then enough.

Yes, the failure mechanism of concern is flame coming out of the top of the ejection well while the motor is under pressure. It's actually happened to me twice. One is in the picture. I recall this was a Smoky Sam motor. The other was the sustainer in a two stager, and in that case, it might have been due to a long-burn motor with the delay being not that much longer than the motor burn. It burned through the top long enough to char the tube above the motor but not long enough to cause real damage. And yes, the purpose of the penny and then potting the charge well above it with epoxy is to prevent a rocket-destroying burn through. I figure any failure mechanism that has happened twice is worth stopping. So, if I am not using the ejection charge, the charge well gets filled. I'll bet I've spent a buck on this by now. Actually, it was my impression that quite a few people do this, but perhaps not.

And as long as we're on the subject of CTI 54mm motors, the other thing I do is glue the forward closure to the top of the liner (and on the bottom, too, if it is not already glued). I have seen on the order of a dozen failures where gas gets by the seal and either causes the motor tube to bulge just below the forward closure or causes a burn through. A few pics of that failure mechanism are attached as well (I have an assortment of those, including (somewhere) a picture of flame coming out the side of the rocket).

You don't have to do these things if you don't want to because most of the time the motor will work as designed. Most of the time....

Jim

 

[wighty44]

I must say I was not prepared to learn as much as I have from the issues that have happened to others after removing commercial motor ejection charges. I really appreciate those who have shared their failure mechanism experiences. I hope this topic helps others as it has has for me...

 

[blackjack2564]

And yes, the purpose of the penny and then potting the charge well above it with epoxy is to prevent a rocket-destroying burn through. Actually, it was my impression that quite a few people do this, but perhaps not.

And as long as we're on the subject of CTI 54mm motors, the other thing I do is glue the forward closure to the top of the liner (and on the bottom, too, if it is not already glued).

You don't have to do these things if you don't want to because most of the time the motor will work as designed. Most of the time....

Jim

+1 I have been doing this.....[penny in closure & glueing closure/nozzle] since day one.

 

[Banzai88]

And as long as we're on the subject of CTI 54mm motors, the other thing I do is glue the forward closure to the top of the liner (and on the bottom, too, if it is not already glued). I have seen on the order of a dozen failures where gas gets by the seal and either causes the motor tube to bulge just below the forward closure or causes a burn through. A few pics of that failure mechanism are attached as well (I have an assortment of those, including (somewhere) a picture of flame coming out the side of the rocket).

You don't have to do these things if you don't want to because most of the time the motor will work as designed. Most of the time....

Jim

What glue are you using to glue the forward closure to the liner on the CTI54s? Do you sand the inside of the liner and the outside of the closure to give the glue some tooth to hold on to?

 

[GrouchoDuke]

I just put a little bit of epoxy in the cavity.

 

[Handeman]

I must say I was not prepared to learn as much as I have from the issues that have happened to others after removing commercial motor ejection charges. I really appreciate those who have shared their failure mechanism experiences. I hope this topic helps others as it has has for me...

+1 I have been doing this.....[penny in closure & glueing closure/nozzle] since day one.

I understand the forward closure failures and burn through but I don't see where removing the charge powder would have anything to do with causing these kind of failures. It looks like these failure would happen if the ejection charge powder was in place or not since the failure is internal to the motor and not external in the charge well.

With that said, I've only flown a couple of Pro54 motors, an 6GXL and a 6G and 5G with spacers. What I learned is that you have to lube the inside of the case very well, especially near the forward end. If you don't, the forward o-ring gets very dry as the lube gets rubbed off on it's way up the long case and I would expect it could easily be damaged just getting it into the long 6GXL Pro54 cases. That could contribute to some of the case burn through/bulging issues.

Just a thought....

 

[JimJarvis50]

What glue are you using to glue the forward closure to the liner on the CTI54s? Do you sand the inside of the liner and the outside of the closure to give the glue some tooth to hold on to?

I just sand and clean (alcohol) the parts. If there is an O-ring, I just glue over it. Any epoxy including 5 minute epoxy has been used. You just want a small fillet between the inside of the liner and the closure.

Jim

 

[JimJarvis50]

I understand the forward closure failures and burn through but I don't see where removing the charge powder would have anything to do with causing these kind of failures. It looks like these failure would happen if the ejection charge powder was in place or not since the failure is internal to the motor and not external in the charge well.

With that said, I've only flown a couple of Pro54 motors, an 6GXL and a 6G and 5G with spacers. What I learned is that you have to lube the inside of the case very well, especially near the forward end. If you don't, the forward o-ring gets very dry as the lube gets rubbed off on it's way up the long case and I would expect it could easily be damaged just getting it into the long 6GXL Pro54 cases. That could contribute to some of the case burn through/bulging issues.

Just a thought....

You're correct. Removing the charge or not doesn't matter.

The case bulging issue was known to CTI and they thought it was caused by liners that were not to spec. They thought the issue had be fixed. I'm not 100% convinced of that, but the accident occurred as this was being discussed. Folks that might have followed up didn't, so I just try to re-post the "fix" to this from time to time.

Jim

 

[Banzai88]

I just sand and clean (alcohol) the parts. If there is an O-ring, I just glue over it. Any epoxy including 5 minute epoxy has been used. You just want a small fillet between the inside of the liner and the closure.

Jim

Excellent, thanks.

 

[tbonerocketeer]

I saw this failure at nsl.

 

[Bat-mite]

That's not a failure! That's a ... that's a ... that's a pipe bomb!

 

[wighty44]

Just looking at that is quite painful...

 

[wighty44]

I saw this failure at nsl. View attachment 321670

I meant to ask if this was a CTI or AeroTech motor failure, and what rocket (kit) was involved?