Plugged motors question.

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Astro-Baby

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Quick question on plugged motors.

If I have a D12-0 in a motor tube how much space should I leave at the plugged end for any gas to expand into on burn out. Can I cut right back to the motor block and just assume any surplus bang gas goes out the back end and if not how much space is sensible ?


I need to butt a motor up close to a bulkhead in something I am working on and it doesnt leave much space in front of the motor...maybe an inch at most. If it needs more space it complicates the design but its doable...would just be easier if I dont need it.
 
FYI, the D12-0 isn't a "plugged" motor. The propellant just ends with no delay smoke and no ejection (bang gas). As long as the motor is physically retained, you can block it right above the casing. The propellant will burn and all thrust will go out the nozzle end. To keep it a little cleaner, stuff the open space above the propellant with some recovery wadding. Some are going to say to fill with epoxy, but "technically" that's modifying a motor and a no-no. It's just not necessary.

There were some D motors that were plugged D11-P, I believe.
-Ken
 
Astro Baby-

The fiery gasses and stuff that come out of the front of a D12-0 are pretty intense. While not as violent as an ejection charge it is still a big pressure pulse and if the tube is plugged will either:
-Cause the unretained motor to eject, or
-If the tube is plugged and the motor is retained, cause a risk of the tube rupturing due to pressure pulse. Don't ask me how I know.

If you reinforce the inside of the short length of body tube with a coupler for its length before the bulkhead, the risk will greatly diminish and pressure will just relatively gradually vent through the nozzle.

My designs using side boosting -0 motors include either pressure vent holes or nose cones that pop off to relieve pressure.

Good luck!

Marc
 
D12-0's are not Plugged motors and can NOT be Plugged as it violates the MR Safety code by altering the intended use of the motor.

-0 motor have no delay or ejection charge. However the Burn-through & afterburn expanding gas can be very intense enough to eject any friction fit motor casing from a confined space. If you can use some sort of external retainer or clip the casing should stay installed.
That said the afterburn flame lasts up to 2 full seconds and extends as far as 4inches so reinforcing your plug is necessary to withstand this flame is very important. I usually add two layers of Stainless Steel tape to the face of my wooden bulkheads imbedded in 30minute epoxy. These have proven over time to last about 20-25 flights.
Hope This info helps.
 
This might be one of those "don't ask and don't tell" type questions. So here are a couple of experiments which may challenge some long held opinions.
(No animals were injured during the filming of these experiments.)

[video=youtube;E98rlFZmuOE]https://www.youtube.com/watch?v=E98rlFZmuOE[/video]

[video=youtube;wBO99FPxgGY]https://www.youtube.com/watch?v=wBO99FPxgGY[/video]
 
Quick question on plugged motors.

If I have a D12-0 in a motor tube how much space should I leave at the plugged end for any gas to expand into on burn out. Can I cut right back to the motor block and just assume any surplus bang gas goes out the back end and if not how much space is sensible ?


I need to butt a motor up close to a bulkhead in something I am working on and it doesnt leave much space in front of the motor...maybe an inch at most. If it needs more space it complicates the design but its doable...would just be easier if I dont need it.
What diameter is the body tube? Or is it a minimum diameter model in which the motor mount is the body tube?

One possibility if there's a reasonable difference between the body tube and motor tube diameters is to centre the motor mount, not with rings, but with strips of balsa. The entire difference between the tubes, minus said balsa strips, is then effectively a nice big vent out of the back. It also means you don't need vent holes in the body tube, which is good if this is to be a scale model. You'll still want to reinforce the bulkhead as Micromeister suggested because, although not officially an ejection charge, the forward blast from a -0 motor at burn-out is pretty strong. I have a couple of parallel stage models which rely on that blast to kick out the nose cones and streamers from the boosters.
 
This might be one of those "don't ask and don't tell" type questions. So here are a couple of experiments which may challenge some long held opinions.
(No animals were injured during the filming of these experiments.)

Both of your experiments violate the Model rocket safey code. If you were to do this at a sanctioned NAR Launch it would void your insurance and that of the sponcering org and land owner. DON'T do This Kind of Stuff! doing so puts our hobby at risk! It is a violation to attach anything to a model rocket motor which alters the "INTENDED Use" of the motor by the manufacturer. Pluging -0 motors can cause them to Split the casing. There are a few Plugged motors on the market C11-P is a manufactured Plugged 24mm motor, if you have some unexplained need for a plugged motor use ONLY manufactured units.
 
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This might be one of those "don't ask and don't tell" type questions. So here are a couple of experiments which may challenge some long held opinions.
(No animals were injured during the filming of these experiments.)

Both of your experiments violate the Model rocket safey code. If you were to do this at a sanctioned NAR Launch it would void your insurance and that of the sponcering org and land owner. DON'T do This Kind of Stuff! doing so puts our hobby at risk! It is a violation to attach anything to a model rocket motor which alters the "INTENDED Use" of the motor by the manufacturer. Pluging -0 motors can cause them to Split the casing. There are a few Plugged motors on the market C11-P is a manufactured Plugged 24mm motor, if you have some unexplained need for a plugged motor use ONLY manufactured units.

And, it would also void the manufacturer' warranties.
 
My apologies, incorrect use of the term 'plugged motor' ......I am really talking about a D12-0 with a bulkhead almost imeddiately to its forward end so thers no real space for anything in front of it to allow the gas to vent forward.


This is actually for the Soyuz boosters. The base of the boosters will hold a D12 offcentre towards the core of the rocket. Because of the layout there will be a bulkhead almost directly in front of the booster motor tube which will will be holding onto a core tube that provides rigidity to the boosters very long shallow paper cone. Its really tough to describe in words but in order to simplify construction and design I need the bulkead as close to the end of the D12 as possible.

What I could do is be smart and have the D12 vent into the lower compartment of the booster and have the gas flow out of the small vernier rocket nozzles on the edge of the booster I suppose. It might work and perhaps increase the vent space by having an outlet inboard on the booster where it cant be seen.
 
If a solid bulkhead is placed directly ahead of a booster motor and the motor is properly secured then upon burn-through all that will occur is the pressure and hot gases etc will be channeled backwards and out the nozzle just as if the motor was still burning fuel.

The bulkhead will take somewhat of a beating with repeated use but if you coat the surface exposed to the burn-through with high-temp epoxy (J.B. Weld) or epoxy a steel washer/slug to the exposed face, then the bulkhead will probably outlast the rest of the rocket.
 
With regard to my videos at post number 5 of this thread, these tests were conducted on my own property at my own risk and were in no way intended to encourage anyone to duplicate them. As this question has arisen in the past and will no doubt arise in the future, I offered it only for informative and educational purposes.

In the first video, you will notice that at the end of the burn that there was a loud pop that propelled the motor casing away from the wooden dowel which had only been friction fitted into the cavity of the motor. If you will look carefully to the left of the sawhorse near the end of the video, you can see the motor casing hit the ground. Had this experiment been conducted in a minimum diameter booster "pod" without proper venting against an immovable bulkhead within said pod, the motor would most certainly have been ejected and the pod destroyed either by rupture and/or fire.

In the second video, you will notice that at the end of the burn the propellant simply burned out because a short section of wooden dowel had been securely glued into the cavity with epoxy and allowed to fully cure.

I have not attempted a similar test using either smaller or larger black powder motors, mainly because of a lack of funds. If and when I have the funds, I may or may not conduct more experiments. YMMV
 
Try something like this:

P1010026.jpg


That's a piece of dowel approximately the same diameter as the casing i.d. with an O ring around it. The motor needs to have solid retention. It's a B6-0 in the photo but should scale up. There was a little bit of blow by around the end of the motor. As a bonus, it added about .5 Nsec of total impulse.
 
If you are not a square jawed macho man launching at a Tripoli EX launch, if you are launching at the club, and if you have not succumbed to the Dark Side, then use all of the above techniques - tube, cap and epoxy/metal tape reinforcement, wadding and vent holes; especially if you are using a D12 0 in the confined space of a booster pod very close to vacuformed plastic parts made in Germany. You will have to pay the weight penalty and the subsequent stability issues requiring even more nose weight. That penalty will not be that great given all the additional power from the lovely clustered D12's. If you are launching for fun on your own back 40 acres then you can do what you wish in a safe and efficient manner. Can you get your hands on D11-Ps across the pond?
 
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Motors. I 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.

I haven't used too many Estes type motors in the last 7 years or so, but plan on using a lot more. When I did use them often, sometimes I slit the casing and peeled off a layer of the casing to get them to fit in the MMT. Never had a problem, they worked fine. I don't know if this is still a problem or not. Rules are rules and being a member of NAR I follow them. There is a need for plugged motors, and I don't think the D11P's are even available anymore.

Years ago there was a big uproar over adjusting the delays on APCP motors. Everybody was doing it before the rules where changed. It used to be wrong now it's OK. Now some guys are gluing fins on a HPR single use motor putting a nosecone on top of it with no recovery other than tumble for which the weight is way to high for and calling it a rocket. That is OK?

Plugging a booster motor is probably the safest alternative to the others posted here to solve the problem. That is unless you want to degrade the integrity of your rocket over time or add substantial metal parts. I say plug away!!
 
I have in hand a 2005 Estes Catalog which lists an A10-PT, a D11-P and an E9-P as "plugged" engines for that year. I believe there was at one time a C11-P motor. There may have been others through the years. Currently, only the A10-PT is still being produced.

https://www.estesrockets.com/rockets/engines/plugged-engines

My guess is that Estes stopped producing these because of a lack of broad consumer interest and not as a result of safety issues. They have already proven that this variation can be safely produced and used. Perhaps one day they will again. Who knew that they would ever produce a 29 mm black powder motor?
 
Plugging a booster motor is probably the safest alternative to the others posted here to solve the problem. That is unless you want to degrade the integrity of your rocket over time or add substantial metal parts. I say plug away!!

Put a little wadding in front of the booster motor to protect the airframe...then everyone's satisfied, no?

Similar topic came up in my club...kinda funny how gluing something to a motor is against the rules, but tape the sucker in place and it's ok...oh well. Rules are among mankind's crudest inventions.
 
Just be careful. Black label D11 Ps can be just as addictive as Black Label Jack Daniels Ole #7. They are once again available in the States in limited quantities and a little pricey for the average junkie, especially when you see the pile of unsold and discounted D12 0's at the local Hobby Lobby. That little Satan can easily pop up on your shoulder reminding you of those partially used tubes of JB weld in the cupboard. Hummmm, could it be? Maybe its SATAN!
 
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Are you doing the Noris Soyuz? Highly modifying a kit that is a bit dodgy to begin with! Very Naughty! Very Nice! I just took a look at mine and what I would do on a cluster. My face began to prematurely wrinkle and sparks starting coming out the ends of my fingers, I couldn't find the black robe fast enough. To make this work well you must stay away from the Republic and have an escort of storm troopers at all times while launching on the outer rim. A shield wall protecting the construction site is also a good idea. It took the Empire a while to iron out most of the bugs on the first Death Star, modifying the Noris Soyuz to fully operational status will be much the same. I would place the motovators as high as possible and keep the weight on the hind end to the bare minimum. Recovery system needs a custom touch. Bulkheads need to be penetrated. The full set of plans can only be revealed to Rebel spies after completion. They are sure to find fault. It might be wise to plan for a second if the first is destroyed by a pure young Jedi.
 
OKis - heres the plan. I am using the cardstock soyuz as a base to build from but pretty much only using it for rough diemsioning. I am finding it a pig to put together to be honest with some of the transitions not fitting properly (though in fairness that could be my poor paper modelling technique). In any event its only being used to extrct some workable dimensions from. So its pretty much a non flying prototype.

The final build, once i have all the parameters worked out will be based pretty much on standard tube sizing but the boosters appear to be problematic. Because I dont like the idea of a D12 pushing againts paper and card the booster bases and motor tube suppor rings will be balsa or possibly a thin ply (I want to run some mock up to see what the weight strength trade off will be. Inside the base of the boosters will be the D12 motor tube and a bulkead just ahead of the paper cone of the booster. As you know a Soyuz will have a very long paper transition to a cone. On my design whats inside the cone is a small tube (sizing TBC) which will lead to a balsa nose cone point. The tube will run the length of the booster back to the bulkead in front of the motor and will be held down by a concealed 'fin' that connects to the core rockets tube. So whats in effect flying is 5 tubes tied to gether with some struts while the rocket 'body' and boosters are merely trim - ie they have no structural requirement.

THe embuggerment is that the base of the boosters is too shallow to get much of a tube in being only a tiny bit (about 1cm) longer than a D12 casing.

The solution I was initially happy with was to have the motor tube offset and connected to the long tube up the booster thereby giving around an 8" space for the motor to vent into but going this way makes construction very hellish so I am moving towards the washer idea on the bulkhead with a small vent area in front of the motor and a concealed vent plus the two vernier rocket nozzles being used to vent any excess gases.

It may be possible later on to work the extended tube up the booster into the plan - I have to run up a test rig I think for this and maybe even build a booster for testing. ie just fly the booster on its own and see what happens :)


As soon as I get some plans drawn up I'll post up and see what you guys think.

Daddyisbar - no its not the Noris kit - I considered it but decided it would be a lot of work and I may as well semi scratch plus the cardstock rocket as a base gives a Soyuz closer to the size I wanted to build at - around 46" long as opposed to 36". The really rough tacked together one is currently close to the height of a TLP Perseus II but the Soyuz will be a lot lighter as its most tubes and fibre rings and no large wooden fins etc.
 
Ah - thought I would post an update. As things turned out when I started designing with pen, pencil and protractor this problem appeared to vanish - All it takes is ze vill you see.

I still have to build a prototype booster and see where we go but I looking now at the motoor being able to vent up almost a foot of pipe with a baffle in it to try and mute down any flash from the motor doing anything nasty to the immaculately made paper cone that makes up the booster body. I reckon with some vent space I should be ok on this.

The back up plan is to friction fit the motors and just let any remaining bang powder just kick the motors out of the boosters. I have to say thats not a preference as I don't like littering up the countryside with spent black powder motors plus I am always nevrous about stuff like that in case one of them fell out and based someone on the head.

THe Soyuz plans are all systems go right now so as soon I order up some parts I will start posting a build thread. I have to say a Soyuz is a real pain - from a casual look it all seemed so easy. Its actually a bit of a mare to make but we shall see.
 
The back up plan is to friction fit the motors and just let any remaining bang powder just kick the motors out of the boosters. I have to say thats not a preference as I don't like littering up the countryside with spent black powder motors plus I am always nevrous about stuff like that in case one of them fell out and bas[h]ed someone on the head.
One of our club members was out to our field this past week with the UMASS USLI team. He found a C6 motor casing on an area the snow had melted off of. The wound paper tube was deformed and starting to delaminate due to the moisture. The clay nozzle was mostly gone, back to nature. No doubt we will find more casing like this from last year once we start flying with larger crews next month. Given time, the materials will degrade enough they won't have an impact on the environment.

I do appreciate your concern for not dropping the spent casings out of the sky. I was starting to take down our launch equipment at the end of the day when one of the last flights went up. It had a D12-something pushing it and popped the motor at ejection. My collar bone just happened to be in the same spot as the casing as it fell to Earth. It didn't break anything but I was bruised and it hurt for a few days.

If you can, post a picture of the new sketch.
 
The back up plan is to friction fit the motors and just let any remaining bang powder just kick the motors out of the boosters. I have to say thats not a preference as I don't like littering up the countryside with spent black powder motors plus I am always nevrous about stuff like that in case one of them fell out and based someone on the head.

Tape a piece of streamer to the motor. There should enough room in a Soyuz booster to hide it. It will slow the spent casing down a little and it will give the people shouting "heads up!" something to point to. It should also make it easier to find and retrieve at the end of the day.
 
Does a D12-0 really have any "bang powder?" Is there an ejection charge at all? My understanding has always been that it does not have an exploding ejection charge --- all it has is a single fuel grain that provides thrust and burns through at the end, allowing hot gas forward. There isn't an explosion, just a burn through with a couple seconds of flame and pressure. It seems like if the zero motor were secured tightly against a flame-proof bulkhead, that would be adequate. You would NOT want to retain a motor with an ejection charge against a bulkhead! BAM! But I think a zero-delay booster motor would work fine that way. The pressure would continue to vent out the nozzle, just like before the burn through.
 
I'm interested in seeing the solution and how it works. I'd like to build some cluster rockets with outboard pods, and I've been wondering how to handle this same issue.
 
There is no ejection charge, it is just casing with clay nozzle and propellant.


HOWEVER when the motor burns it burns like a cigarette, from the bottom to the top. Inside is tremendous pressure. When the flame reaches a point NEAR the upper end of the propellant grain, the pressure causes it to rupture. This sends the extremely high pressure and flame upward, since the nozzle is much smaller AND the amount of propellant surface area burning and the resulting pressure and heat goes up EXTREMELY since the entire upper surface is now also burning along with the fragments exposed when the forward end ruptured.

The resulting flame and pressure on a D12-0 is absolutely hellish. There is video from NARAM R&D showing what happens when a D12-0 booster motor burns and sends that flaming jet of hot gas forward.

[video=youtube;1Nhe5Y78PRQ]https://www.youtube.com/watch?v=1Nhe5Y78PRQ[/video]



Does a D12-0 really have any "bang powder?" Is there an ejection charge at all? My understanding has always been that it does not have an exploding ejection charge --- all it has is a single fuel grain that provides thrust and burns through at the end, allowing hot gas forward. There isn't an explosion, just a burn through with a couple seconds of flame and pressure. It seems like if the zero motor were secured tightly against a flame-proof bulkhead, that would be adequate. You would NOT want to retain a motor with an ejection charge against a bulkhead! BAM! But I think a zero-delay booster motor would work fine that way. The pressure would continue to vent out the nozzle, just like before the burn through.
 
Ah - thought I would post an update. As things turned out when I started designing with pen, pencil and protractor this problem appeared to vanish - All it takes is ze vill you see.

I still have to build a prototype booster and see where we go but I looking now at the motoor being able to vent up almost a foot of pipe with a baffle in it to try and mute down any flash from the motor doing anything nasty to the immaculately made paper cone that makes up the booster body. I reckon with some vent space I should be ok on this.

The back up plan is to friction fit the motors and just let any remaining bang powder just kick the motors out of the boosters. I have to say thats not a preference as I don't like littering up the countryside with spent black powder motors plus I am always nevrous about stuff like that in case one of them fell out and based someone on the head.

THe Soyuz plans are all systems go right now so as soon I order up some parts I will start posting a build thread. I have to say a Soyuz is a real pain - from a casual look it all seemed so easy. Its actually a bit of a mare to make but we shall see.

They always seem so easy at first glance and then a few troubles set in. There are guys at the club who have been scratch building one rocket for years. When I ask about progress I can get all kinds of excuses. . ."Oh, the old war wound is acting up again and I just can't get that jet pack Barbie finished." Or "I can't have the fire department at my house for the third time." No excuses! This is a results based forum!
 
Yup - I appreciate theres no ejection charge but the burn through was about what I thought. Dang....looks like I may end up going for just the burn through pushing the motor out the back.
The original plan was to have a long tube mated to the motor mount with a baffle in it to try and reduce the pressure and flame effect. If I can get the design right it may just work out with very rigid tubs and flame retardant material inside to mitigate the heat effects. Past the baffle there will be vent holes but its starting to look like an awful lot of pressure and I am not sure it would accommodate the ferocious heat and blast shown in that video.

Pushing the spent casing out the back might be the best alternative. I will have to wait till the parts arrive and see whats feasible on this one I think.

As soon as I get some solid drawings I will post up - thanks as ever for all your input guys.

Mel
 
I'm interested in seeing the solution and how it works. I'd like to build some cluster rockets with outboard pods, and I've been wondering how to handle this same issue.

+1 on that. I'm too new to even consider experimenting with this stuff, and I wouldn't modify a motor, but I have looked a little bit for plugged motors, only to find they're rare.

I read that the Cluster Duck uses -0 motors for the ring of mounts around the central mount. I've wondered how they handle that.
 
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