It *MAY* work. The burnout is pretty violent, and can rupture even epoxy
plugs! As the Internats folks discovered when they tried this.
It definitely violates the NAR and TRA safety codes, and the laws of any
NFPA 1122 state.
I've tried non permanent (i.e. legal) methods of converting booster motors
to plugged motors. The results were unsuccessful unless your goal was to
make the worlds most powerful cork Pop-gun!
Why does your boost glider need a plugged motor? Every BG and RG I can
recall needs an ejection motor to do something to transition from boost to
glide, with the exception of RC models.
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
I think I'm going to have to disagree with you or at least take issue with
the violation of NAR/TRA Safety Codes and /or NFPA 1122.
1st of all, a C6-x motor is a model rocket motor covered only by NFPA 1122
(and 1125 if you happen to be manufacturer) and since NFPA 1127 is the TRA
Safety Code that ONLY applies to HPR NOT Model Rocket motors, the TRA Safety
Code does not apply here.
The only NFPA 1122 code that may be applicable is:
4.19.2 No person shall dismantle, reload, or alter a single-use model rocket
The "operative word here is "alter". Does adding a permannet modification to
an motor with an epoxy plug constitute an alteration? Probbaly, but what if
the person instead, uses a hardwood dowel type of plug?
Chapter 5 Prohibited Activities
5.1 Prohibited Activities. The following activities shall be prohibited by
(4) Tampering with any model rocket motor or motor reloading kit or
component in any manner or to any degree that is contrary to the purpose for
which the model rocket motor, motor reloading kit, or component is designed
and intended to be used
Does adding an epoxy plug to a C6-0 motor constitute "tampering" Is it
contrary to the purpose that a C6-0 is designed and how it is inteneded to
be used? Possibly. For an interpretation of "tampering" you would have to
approach your local or state Fire Marshall and ask them. DO you really want
to do this?
SO we are left with the NAR Safety Code. The NAR Safety Code ONLY applies to
those individuals that happen to be 1. NAR members 2. Doing NAR model
rocketry on NAR Model rocket time.
anyway the operative NARSC part is 2. 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.
Again I guess it depends on what the word "tamper" means . Unfortunately
NFPA 1122 does not define alter nor tamper. For enforcement of the NFPA 1122
code, is the responsibility of your local or state Fire Marshall authority.
I suppose you could approach them and ask them if adding an epoxy plug is an
alteration, or you could ask the NAR if adding an epoxy plug is tampering.
But this leads to my infamous question about whether or not there is any
real "self-regualtion" (which implies self-policing or self-enforcement) in
model rocktry .My question is this: if a tree falls in the forest and nobody
is there to see or hear it fall, did it really fall? If you add an epoxy
plug to a c6-0 motor on your own time , and tell no one, did it really
My point being this: ONLY your local or state fire marshall person can
interpret and enforce NFPA1122. Most Fire Marshall's don' even realize that
NFPA 1122 exists in their states, much less, know what it says or have any
idea on the interpretation of it. SO the interpretation is left to YOU, the
individual. SO the regulation, policing and enforcement is left up to YOU,
the individual, hence Self-regulation.. I mean think about it: lets say you
mod a C6-0 by adding an epoxy plug. What is the maximum possible penalty for
this violation? See, thats why NFPA codes as far as model and HPR are
concerned are meaningless: There is no penalty , hence there is no
That was an awful lot of typing when you should simply contact the
manufacturer to find out if what you intend to do is considered altering or
a use that is not intended.
That is why "tandem" motors are not legal. They were asked and they said
"NO". They had reasons which included the burnthrough of the casing wall.
For modified boosters, they may be concerned with average Americans not
being able to safely install a plug on their own.
You are not a lawyer and you are not a manufacturer. Please do not offer
pseudo legal advice to others when you should simply advise them to contact
the manufacturer. Or you can just ignore me.
Exactly my point: my psuedo-legal advise/interprtation is as valid or
invalid as anybody elses psuedo-legal advice/interpretation on RMR.
And I disagree it as simply a matter of asking the manufacturer. The
manufacturerers have no say so, its nfpa 1122 and the individual states fire
marshalls that have the duty and responsibility for interpretation and
enforcement for nfpa1122; the manufacturers have no such authority, just as
the NAR has no such authority to interpret NFPA 11xx. As Mark Bundick told
me , If I want an interpretation as to what a specific NFPA 11xx code
segment means, hire an lawyer and find out for yourself. Its not the duty
nor responsibility of the NAR to provide such. Which if you think about it
is a suspect stance considering the fact that the NAR does sit on the NFPA
PYRO-AAA committee that actuallyhelps to make the NFPA codes. You woudl
think that since the NAR sits on that committee nd helsp to make the NFPA
codes, they would be in the best position to interpret such, but they don't
and won't. The NAR takes the psotion that its up to the individual state
fire marshalls to interpret the NFPA codes: this of course leads to the
posibility that the Kentucky state fire marshall may interpret a specific
NFPA 1122 code segment one way, while the local Lexington,Ky fire marshall
could interpret another way,while the CA state fire marshll may interpret it
in a completely different way. I suppose we could end up with a minimum of
50 different interpretations, depending on where you live. I also suppose we
could get hundred's of potential interpretations, as most cities have local
fire marshalls.... Thats why I make the point that the NFPA codes are
really irrelevant in todays world.
and why would I ignore you? when I value your input?
What is a tandem motor? I've never heard of this term used in conjunction
with rocket motors before. We aren't talking about CHAD staging are we? Or
the process of inserting the end of a C type sustainer into the end of a D
type booster for more positive ignition? What's up Fred, I'm all ears.
It's sort of the latter. But instead of just inserting the 18mm
sustainer into forward end of the 24mm booster, you GLUE it in. When the
18mm sustainer lights the 24mm combustion chamber continues to be used.
This is not what the manufacturer intended, and possibly not within the
design limits. So you'll probably get a much higher rate of burnthrough,
nozzle loss or other CATOs.
... at least in theory. The known fact here is the manufacturer was
asked and said "NO", thus tandem motor means unsupported motor
(What you described, Reece, is legitimate use of the motors.)
(replace "spambait" with "merlinus" to respond directly to me)
Thanks for the info. Been in rocketry since the very late 60s and never even
thought of gluing the motors together. As to using epoxy in the C6-0...I've
done it many times in the A10-0. It was the only way I could get motors to
fly my Lil Wild Thing on for a long time. Legal...no. Does it work? So far.
Do I recommend it? Hmmm, tricky question. Since I never recommend illegal
activities I guess for consistency sake I won't recommend this
either...wink, nod, wink, wink, nod, nudge.
Inserting a smaller motor into the top of a larger motor would not be
good. Reason: Nozzle on smaller motor is smaller than the nozzle on the
larger motor, so you would not get a properly choked nozzle and you
would get less thrust and less total impulse.
The point of tandem motors was to take two identically nozzled motors
and epoxy them end to end with a reinforcement sleeve epoxied over the
outside (like a C6-0 with a C6-7 on top). The sleeve was typically a
CMR RB74 and the airframe then had to be RB77.
The firing of the booster motor produced normal results but when the
upper stage ignited the thrust curve was 10% higher. Why (when the
nozzles are identical)? Because the firing of the upper motor into the
lower casing would scour away the inside of the lower casing nozzle.
This additional mass being accelerated out the lower nozzle produced
more thrust. F=m*a
Of course, it also resulted in lots of motor failures (remember
Challenger?) where the lower casing burned through the sidewall.
-Fred Shecter NAR 20117
back in the mid-70's and even prior to that, people would take 13mm motors
and glue them into the tops of 18mm or take 18mm and glue them into the top
of 24mm motors or even just glue (2) 13 or (2) 18 or (2) 24mm motors
together with an outer body tube sleeve: hence "tandem" motors. In some
combinations you would actually get more nt-sec in total impulse then if you
used them as typical staged motors. hence they were popular for maybe 2
years for competition. In mid to late 1978, I guess Estes determined that
this was NOT a manufacturers suggested or recommended use and the practice
Tandem motors worked great. Many used them in competition even, that is of
course what drove their design.
Some didn't like them. Once in a while, they might have gotten a burn thru,
but for the most part worked great.
The NAR Model Racketeer published a nice report on their use and benefits in
I'll post this article scanned sometime in the next 7 days for those who are
interested, as I still have it.
The manufacture knew and looked the other way, it didn't bother them.
Someone(s) around 1977(?) who didn't like tandems finally asked estes if
they had Estes' permission to make tadem motors.
Estes of course has to say no for liability reasons, and hence they got
banned from competition, which was what a few had wanted.
You guys takl about the "code" too much. Heres what you do. I have a
rocket that clusters 3 D12-3's and I remove the charge for every
flight. Take an exacto knife, scratch off all the gray stuff on top of
the motor, under the gray stuff, you will find black stuff, this is the
election charge. Get rid of the black stuff until you see more gray
stuff, you now have a "code violating" plugged motor that wont CATO, I
gaurantee that if you do this right, it will work.
I suppose an argument could be made that you are just "gluing" a glue plug
to the casing:
And NO a -0 motor does not have an integral ejection charge: it does have a
little more pressed BP in the motor so it will have the same total impulse
characteristics as a C6- with delay and ejection charge. The additional BP
in the motor is of course to prevent premature blowthru..... I don't
consider that and nor do the manufacturers "ejection charge"....
SO whats your point?
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