Dear Decision-Makers in Penrose: More Plugged Rocket Engines, Please!

[Art Upton]

Nah, it just goes out the nozzle.

Well, I had one that did not a few decades ago;

 

[Art Upton]

Back in the mid 70s the NAR Model Rocketeer ran an article on delayed staging to get higher altitude in competition. If I recall Correctly it was written by a top competitor.

You removed the clay cap , emptied the charge on like a B6-2 and used it as a booster motor.

Some complained about that and called the motor maker and after that it became a motor modification that made it a no no, per safety reasons.

 

[BABAR]

Putting an epoxy plug over an ejection charge rather than a -0 motor well, could blow your epoxy plug out like a shot gun shell wad.

I’ve wondered about this, but I haven’t tried plugging motors and I have never read of such things happening. your follow up post says you’ve seen it at least once. Anybody else have this happen?

i would guess this might be disallowed in a NAR or Tripoli club launch, and if fecal turbine action occurs it might invalidate your NAR insurance as a safety code violation.

”2. MotorsI will use only certified, commercially made model rocket motors, and will not tamper with these motors or use them for any purposes except those recommended by the manufacturer.”

some motors have very little “empty” space between the forward end of the clay cap and the forward end of the casing (C5-3 comes to mind, I think they’ve wadded all the panties they can get into that puppy.A10-3T might be tight too), so some motors may not have much room for the plug to form, or more importantly much inner luminal surface area to adhere to. On the other hand, A8-3 and probably B6-4 would likely work. Might need to keep track of epoxy weight if stability is marginal.

 

[mh9162013]

I’ve wondered about this, but I haven’t tried plugging motors and I have never read of such things happening. your follow up post says you’ve seen it at least once. Anybody else have this happen?

TVM from Apogee concurs with @Art Upton:

 

[SolarYellow]

I wonder if there is anything in an old ('60s-'70s) tech manual from Estes or Centuri that says it's OK to epoxy a -0 motor. Would be a very cool find if someone wanted to pore through all those old materials for a few nights.

 

[BABAR]

TVM from Apogee concurs with @Art Upton:

Good info.

Makes sense that a zero delay would be a better choice to plug, and likely zero delays are more available than plugged motors. Even so, still may have issues with NAR and Tripoli launches (and your NAR insurance if things go reaaaaaallly badly.)

While zero delay motors do NOT have an actual ejection charge, the "blow through" or "burn through" does generate some force (at least enough to eject a non-vented motor tube, often enough to deploy a chute or streamer, although the advisability of employing them as such is questionable---rocket is gonna be going pretty fast with no delay. Don't ask how I know this.)

For clusters with motor eject, zero delay motors are probably a good choice (assuming you WANT motor eject), as the force into a forward closed body tube should be enough to eject the casing, AND it will do so immediately on burnout, so IF the other motor(s) are still burning propellent, the mass of the ejected motors comes out earlier (and lower, so easier to FIND the casings as good rocketry citizens should at least try to do.)

maybe @kuririn or @Ronz Rocketz can post a pic of an A10-0T motor forward end. I think some zero delay motors may not have enough space forward to hold sufficent epoxy even with no ejection charge.

 

[SolarYellow]

Remember that a every black powder -0 motor currently (and that I am aware of historically) produced is an abridged version of a motor that in other specs includes a delay grain, ejection charge, and clay cap. So any -0 motor you'll find will have plenty of space for an epoxy plug.

I have previously posted the brainstorm that Estes should exploit the additional space in -0 cases by filling it with powder to make long-burn -0 or -P motors. I would very much like an "E12-P" or "E15-P"* to run with electronics. Of course, they didn't launch any products based on my brilliant idea yet.

*This nomenclature is used to clearly indicate which existing motor I'm imagining an alternate version of. If the "sustain" burn on these motors was extended, the average thrust would go down as the total impulse went up. Which would make it a little bit of a pickle for the marketers: The "smaller number" motor would actually be the one that would fly your rocket higher.

 

[jmasterj]

Well, I had one that did not a few decades ago;

Fair enough. It worked fine for me before it was made clear that is wasn't an acceptable modification, but that's just a small set of anecdotes. Tape/wadding has worked fine too, even on motors with ejection charges, to direct that out the nozzle.

 

[Azamiryou]

Not permitting an epoxy plug for this purpose is nonsense. It in no way impacts the structural integrity of the motor. Calling this a modification and prohibiting it seems like an over reach.

It seems to me that 1) plugging a booster this way is safe, 2) plugging an ejection charge this way is unsafe, and 3) there are people out there who wouldn't understand the (importance of the) difference.

Allowing it for boosters would lead to people doing it for motors with ejection charges.

 

[jmasterj]

It seems to me that 1) plugging a booster this way is safe, 2) plugging an ejection charge this way is unsafe, and 3) there are people out there who wouldn't understand the (importance of the) difference.

Allowing it for boosters would lead to people doing it for motors with ejection charges.

If I can plug a motor with an ejection charge with wadding and tape with no discernable disturbance of the tape after firing, I'm not sure why epoxy would be worse. It would make it easier to use to normal rockets vs oddrocs.

 

[bad_idea]

Tape/wadding has worked fine too, even on motors with ejection charges, to direct that out the nozzle.

I would very much like to learn how to do this. Would you mind posting the details of how you pack and tape these? Being able to do this with the C5-3 would be hugely useful to me.

 

[Alan15578]

Back in the mid 70s the NAR Model Rocketeer ran an article on delayed staging to get higher altitude in competition. If I recall Correctly it was written by a top competitor.

You removed the clay cap , emptied the charge on like a B6-2 and used it as a booster motor.

Some complained about that and called the motor maker and after that it became a motor modification that made it a no no, per safety reasons.

I don't remember that. I do remember reading about using safety fuse to effect the delay, ignited by an ordinary booster motor. This may have been in the NAR Tech Review. Back then I think motor caps were paper and would occasionally work loose in the packaging. Also, a clay capped delay motor with ejection charge can ignite an upper stage motor unmodified, but reliability is not high.

 

[Daddyisabar]

I have seen many things. Been with old dudes at park launches and Top Men at prestigious national events. From real life Steely Eyed Missle Men to oddroc scum. A glance into a range box here and there, I see the Dark Side of epoxy plugged motors afoot. A Youngling with plugged Green lables in cluster SR 71 pods... KABOOM! Nasty plugged and modified green lables with some careful scraping...OK. Know the difference between the ejection, delay and propellant pressings. These things you will not learn from the Jedi. Beware of the Restricted Section at the Hogwarts library and poopy clay kitty litter scrapings on the floor. Younglings, stay away from the crazy pyros!

So despirate to fly silly cluster rockets requiring less harm from multiple hibachi ejection charges, one may even epoxy plug a few CATO prone, red lable E12 0's. You will find pain.

Exotic ducting and venting to keep your clustered Estes SR71 totally within the rules requires huge skill, patience and knowledge of the Jedi. So admirable and gallant. Not the selfish and ease of sithy epoxy which always seems to work. Easy peasy lemon squeezy Dark Arts...yucky! Rules are meant to be followed. Be a Lawful Good Boy!

Where have all the old Black Lables gone? Those were more civilized times. Current plugging red lables with epoxy, SO UNCIVILIZED!

 

[burkefj]

Not permitting an epoxy plug for this purpose is nonsense. It in no way impacts the structural integrity of the motor. Calling this a modification and prohibiting it seems like an over reach.

Nar leaves it to the motor mfg to define what is and what is not a mfg approved motor modification, and Estes was asked specifically about epoxy plugging or removing caps and ejection charges and they said these were not approved modifications so Nar does not allow them. Aerotech on the other hand says that shortening a delay or removing ejection charges are mfg approved modifications.
Take it up with Estes and their lawyers. Nar insurance requires some criteria and uses mfgs determinations on what is allowed as part of that.

Note Tripoli does not allow non mfg approved motor mods either for BP motors nor does it support research BP motors.

Or fly on your own property with your own liability insurance coverage and do what you want.

You can talk about how stupid it is or isn't but that's beside the point, it really just comes down to insurance coverage. If you were to plug a motor that way and something was to happen and property or a person got damaged/hurt and that was discovered as part of the investigation it could void the liability coverage for you or the property owner and could result in the risk of a loss of a field and or worse so you'd have to weigh if that's a risk worth taking.

 

[BEC]

Dang! When you mentioned that approach it seemed like such a clever idea!

A -0 engine has no ejection charge or smoke charge. We are just talking about the little “pfft” when the flame burns through the top of the black powder. That can’t be that strong, can it?

Actually it is pretty strong.

There is a fellow who used to come to WAC launches at Sixty Acres who insisted on flying a Mean Machine on a D12-0. It never failed to get the 'chute out, even though it was REALLY early.

 

[Art Upton]

I don't remember that. I do remember reading about using safety fuse to effect the delay, ignited by an ordinary booster motor. This may have been in the NAR Tech Review. Back then I think motor caps were paper and would occasionally work loose in the packaging. Also, a clay capped delay motor with ejection charge can ignite an upper stage motor unmodified, but reliability is not high.

Yes, they were paper caps back then.

 

[AtlPhilip]

Not permitting an epoxy plug for this purpose is nonsense. It in no way impacts the structural integrity of the motor. Calling this a modification and prohibiting it seems like an over reach.

100% affects neither the structural integrity, the burn profile, or the safety of the motor. NAR and/or Estes are choosing CYA over actual safety.

You can stick wood in there. You can stick dog barf in there. You can fill it with sand. But you can't put glue in there. Nonsense.

You can see how this would create a slippery slope type of problem...

It seems to me that 1) plugging a booster this way is safe, 2) plugging an ejection charge this way is unsafe, and 3) there are people out there who wouldn't understand the (importance of the) difference.

Allowing it for boosters would lead to people doing it for motors with ejection charges.

Speculation about other things that people *might* do is not a valid argument. Those same people *might* use a -0 motor in a single stage rocket thereby creating a lawn dart. That is unsafe, so plugged motors are no longer permissible at NAR events. With speculation, anything is possible.

 

[SolarYellow]

If you were to plug a motor that way and something was to happen and property or a person got damaged/hurt and that was discovered as part of the investigation it could void the liability coverage for you or the property owner and could result in the risk of a loss of a field and or worse so you'd have to weigh if that's a risk worth taking.

A reasonable person might go out into the middle of a dry lake with nothing around for miles but flat, dried mud and proceed without worry.

 

[AtlPhilip]

Note Tripoli does not allow non mfg approved motor mods

That is not entirely true. TRA has an entire experimental classification where you can mod until your heart's content.

You can talk about how stupid it is or isn't but that's beside the point, it really just comes down to insurance coverage. If you were to plug a motor that way and something was to happen and property or a person got damaged/hurt and that was discovered as part of the investigation it could void the liability coverage for you or the property owner and could result in the risk of a loss of a field and or worse so you'd have to weigh if that's a risk worth taking.

What is covered is determined by what NAR considers permissible within the NAR Safety Code. NAR *chooses* to defer to the manufacturer without exception, and that choice is the point. The same is also true for Estes.

 

[Astrobuf]

Thinking outside the box, what are your field rules And conditions?

outside of competition, there is nothing in NAR rules nor the safety code that says you can’t eject a motor, and there are number of kits including the Semroc Hawk glider (which I believe is a repro of an Estes and/or Centuri kit), and the Sprite and of course the Mosquito which are motor eject.

so skip the vent holes, make sure the pod nose cone is glued in firmly or add a bulkhead, throw some JB weld or other heat protectant on the base of the cone or rear of bulkehead. Usually don’t need anything to hold the motor in place, if really “falling out” loose on pad put a loose friction fit, and let her rip.

I’ve been doing this for years with 13-24 mm motors (D12s, E motors might be pushing it) without any issues.

I look For and when found I pick up the casings if I can find them, I don’t sweat it if I can’t as they are biodegradable.

some fields have rules that disallow free falling casings, and Miiiight want to skip it if high fire danger due to dry field conditions.

there are ways to add streamers if you feel the need, even on minimum diameter. See post 20
https://www.rocketryforum.com/threads/glider-front-motor-eject-feasible.181457/#post-2476414

I built a big glider with swing wings and rear ejection back in the 70's when active in NAR competitions. The vertical stabilizer wast attached to the basswood spar comprising the fuselage, upside down from a conventional empenage. It flew very well and won several competitions. Never had an issue with the ejected motor mount (small streamer wound on it) damaging the empenage. Opened, it's wingspan was about 40", so it came down softly.

Astrobuf

 

[2-0turbo]

Maybe, maybe not. But to keep things simple, the rules/guidelines may just use a "belt and suspenders" blanket approach as to what's allowed and not allowed with motor modification.

If they allowed certain types of plugging, what about shortening rocket engines? For example, cutting an A8-3 in half as much of the motor casing is just empty space. Or how about removing some or all of the clay cap covering the ejection charge to make it less powerful (or for some other objective). You can see how this would create a slippery slope type of problem...

I agree that "shortening" motors is a modification. I would also agree that removing the delay grain on a motor to make it a booster would also be a modification (I've personally never done that and probably wouldn't.) But removing the clay cap and dumping the BP to make a plugged motor and calling this a "modification" seems like a stretch. I've done this more times than I can count. I hear everyone one on here who says they asked NAR/Estes and that is what they said, I just don't agree with what they consider to be a modification.

Rocketry is about experimentation, that is part of the reason most of us got into it. I have and fly many rockets that are clusters. I suppose I could just buy a single motor and stick in there, but what is the fun in that? Sometimes sticking 7 or 8 BP motors into a rocket requires some changes to make it work. Much like how folks on this forum calculate how much BP to put into an ejection charge and adjust/tailor the qty to their rocket or specific application.

The attached picture is a great current example. I have an Estes E12-6. While prepping a rocket, I dropped it on the floor...a laminate floor. So not a hard impact, but enough to break the clay cap and spill my ejection charge everywhere. Personally, I have no qualms about flying this motor. Could it cato because I dropped it? Perhaps. It also might cato even if I didn't. Maybe Hobby Lobby dropped it on their floor while stocking shelves? Who knows and I don't really care.

So per this discussion thread, my options are:
1) Destroy the motor (very unlikely).
2) Static fire it? (more likely than #1, but also not likely)
3) Remove the rest of the BP and pour epoxy in the top and stuff it in one of my cluster rockets since I don't really need/want 8 ejection charges going off.
4) Remove the rest of the BP and measure out 0.7 grams of 4fg, install on top of delay grain and secure with a piece of tape and fly it.

Probably either 3 or 4 is going to happen. It all depends. If something was to happen with the flight, would it be caused by me restoring the ejection charge or plugging the motor with epoxy? I really can't imagine that scenario. That is kind of like the car dealership voiding your warranty because you installed a K&N air filter--they can try to make that argument, but it doesn't hold much water. If the rocket in this case crashes, it would be because the other XX motors didn't eject my chute. Or I didn't get them all lit. Or I packed my chute wrong and the other motors ejected, but it wasn't successful. Lot's of reasons for failures.

This is just debate on the topic...we can have different opinions. When you look at why and how TRA and NAR tests motors and the criteria for approving them, option 3 and 4 above don't change the basis of the motor certification at all (burn time, delay time and tolerance, casing temperature, casing integrity, etc.) AT G77-79 motors are assembled at home with 5-min epoxy and require that epoxy to secure the primary pressure bulkhead. This is much less consequential than that.

 

[burkefj]

That is not entirely true. TRA has an entire experimental classification where you can mod until your heart's content.

True but not for BP motors, a modified composite motor is considered research but there is no research black powder as they don't support that.

 

[mh9162013]

100% affects neither the structural integrity, the burn profile, or the safety of the motor. NAR and/or Estes are choosing CYA over actual safety.

You can stick wood in there. You can stick dog barf in there. You can fill it with sand. But you can't put glue in there. Nonsense.



Speculation about other things that people *might* do is not a valid argument. Those same people *might* use a -0 motor in a single stage rocket thereby creating a lawn dart. That is unsafe, so plugged motors are no longer permissible at NAR events. With speculation, anything is possible.

Speculation isn't a valid argument? Tell that to the decades of product liability case law. What a reasonable consumer may or may not do in a hypothetical situation is 100% relevant to a company's rules, policies and warnings concerning their services/products.

It's one thing to tell someone not to do something because it could be dangerous...and they do it anyways.

It's totally different to tell someone they can do something when it's reasonably foreseeable that they will do it in a way that could cause harm to others.

For better or for worse, "the consumer lacked common sense" isn't much of a defense when it's reasonablly foreseeable they would act in a way that lacked common sense and the company could take basic steps to prevent the situation (like telling a consumer not to do something).

 

[mh9162013]

I agree that "shortening" motors is a modification. I would also agree that removing the delay grain on a motor to make it a booster would also be a modification (I've personally never done that and probably wouldn't.) But removing the clay cap and dumping the BP to make a plugged motor and calling this a "modification" seems like a stretch. I've done this more times than I can count. I hear everyone one on here who says they asked NAR/Estes and that is what they said, I just don't agree with what they consider to be a modification.

Rocketry is about experimentation, that is part of the reason most of us got into it. I have and fly many rockets that are clusters. I suppose I could just buy a single motor and stick in there, but what is the fun in that? Sometimes sticking 7 or 8 BP motors into a rocket requires some changes to make it work. Much like how folks on this forum calculate how much BP to put into an ejection charge and adjust/tailor the qty to their rocket or specific application.

The attached picture is a great current example. I have an Estes E12-6. While prepping a rocket, I dropped it on the floor...a laminate floor. So not a hard impact, but enough to break the clay cap and spill my ejection charge everywhere. Personally, I have no qualms about flying this motor. Could it cato because I dropped it? Perhaps. It also might cato even if I didn't. Maybe Hobby Lobby dropped it on their floor while stocking shelves? Who knows and I don't really care.

So per this discussion thread, my options are:
1) Destroy the motor (very unlikely).
2) Static fire it? (more likely than #1, but also not likely)
3) Remove the rest of the BP and pour epoxy in the top and stuff it in one of my cluster rockets since I don't really need/want 8 ejection charges going off.
4) Remove the rest of the BP and measure out 0.7 grams of 4fg, install on top of delay grain and secure with a piece of tape and fly it.

Probably either 3 or 4 is going to happen. It all depends. If something was to happen with the flight, would it be caused by me restoring the ejection charge or plugging the motor with epoxy? I really can't imagine that scenario. That is kind of like the car dealership voiding your warranty because you installed a K&N air filter--they can try to make that argument, but it doesn't hold much water. If the rocket in this case crashes, it would be because the other XX motors didn't eject my chute. Or I didn't get them all lit. Or I packed my chute wrong and the other motors ejected, but it wasn't successful. Lot's of reasons for failures.

This is just debate on the topic...we can have different opinions. When you look at why and how TRA and NAR tests motors and the criteria for approving them, option 3 and 4 above don't change the basis of the motor certification at all (burn time, delay time and tolerance, casing temperature, casing integrity, etc.) AT G77-79 motors are assembled at home with 5-min epoxy and require that epoxy to secure the primary pressure bulkhead. This is much less consequential than that.

I think you (and a few other(s)) are missing the point. The point isn't what's ok and what's not ok from a practical or engineering perspective. The point is what's ok and what's not ok from a legal/insurance coverage perspective.

 

[AtlPhilip]

I think you (and a few other(s)) are missing the point. The point isn't what's ok and what's not ok from a practical or engineering perspective. The point is what's ok and what's not ok from a legal/insurance coverage perspective.

I am not missing that at all, in fact I addressed it.

the company could take basic steps to prevent the situation (like telling a consumer not to do something).

Basic steps like telling them not to epoxy a motor with an ejection charge?

 

[mh9162013]

I am not missing that at all, in fact I addressed it.

But let's discuss it. What does the law, and the relevant insurance policy, say about this matter?

Don't add epoxy to the back end of certain Estes BP rocket engines or you could risk losing insurance coverage.

As for case law, that would depend on each state, but I think it's safe to assume that if your rocket harms another and the proximate cause for the harm was your decision to violate a warning or guideline from the manufacturer, you will be deemed to be at least partially at fault for the person's damage. How much you have to pay will depend on the applicable state law concerning negligence (comparative, pure comparative, contributory, etc.).

 

[jmasterj]

What is covered is determined by what NAR considers permissible within the NAR Safety Code. NAR *chooses* to defer to the manufacturer without exception, and that choice is the point. The same is also true for Estes.

As has been hit above, I would bet my motor stash that that deference is to satisfy insurers.

 

[BABAR]

I am not missing that at all, in fact I addressed it.

But let's discuss it. What does the law, and the relevant insurance policy, say about this matter?

@mh9162013 beat me to it.

I think the universally relevant "law" would be the model rocket safety code. In the event of fecal-turbine interaction that results in a lawsuit, the NAR insurance is going to use any and every means of avoiding liability. That's what insurance companies do. Any modification of a rocket motor NOT approved by the manufacturer is a violation of the model rocket safety code rule 2. (Doesn't matter how minimal the modification is, and how irrelevant YOU might think it is, insurance companies are going to go by the letter of the law, or in this case a rule.)

So I can pretty much guarantee the NAR insurers are going to try to weasel out of paying a claim when the rocket wasn't flown under NAR safety code rules, whether or not it contributed to the injury or not. I'm not trying to denigrate them, that's what insurance companies do to keep costs down. That's what I would do if I was them. Will they win in court. Dunno, juries do some crazy things. But whether WE think plugging a motor is okay IS irrelevant, I am confident that plugging a motor puts your insurance at risk.

 

[AtlPhilip]

Don't add epoxy to the back end of certain Estes BP rocket engines or you could risk losing insurance coverage.

As for case law, that would depend on each state, but I think it's safe to assume that if your rocket harms another and the proximate cause for the harm was your decision to violate a warning or guideline from the manufacturer, you will be deemed to be at least partially at fault for the person's damage. How much you have to pay will depend on the applicable state law concerning negligence (comparative, pure comparative, contributory, etc.).

Thank you for clarifying that we are discussing your opinion and not actually "what's ok and what's not ok from a legal/insurance coverage perspective." Now that we have dispensed with that facade...

It is my opinion that such a limitation is pointless from an practical or engineering perspective. It is also my opinion that NAR should modify it's safety code to permit such activity, and that doing so would keep such activities covered by insurance.

True but not for BP motors, a modified composite motor is considered research but there is no research black powder as they don't support that.

TRA doesn't allow BP motors, modified or unmodified. But they do support modification of all motors they allow.

I think the universally relevant "law" would be the model rocket safety code.

Who wrote said code? The NAR. The question on the table? Should the NAR allow...?

I am confident that plugging a motor puts your insurance at risk.

And what is the basis for your belief? The MSRC. Which brings us back to "who wrote the MRSC?" A: The NAR

 

[mh9162013]

The question on the table? Should the NAR allow...?

The answer to that question is self-evident, given the presumed (and likely) requirements and advice from the insurance companies and attorneys, ie "do it my way if you want legal and insurance protection."