1/2A6, A8, B4 are identical and take yellow plugs.
B6 and C6 are identical and take purple plugs.
The fascinating things occur in the 24mm diameter motors. Some have
identical nozzles but
the centerbore of the propellant can be slightly different depth. So
two motors may use
the same plugs but they have different peak thrusts and slightly
C11 and E9 use black plugs.
D11 and D12 use White plugs.
Compare the thrust curves. Look on the NAR website.
-Fred Shecter NAR 20117
don't forget that as far as BP motors are concerned, they also have "molded"
(actually pressure pressed during assembly) combustion chambers above the
nozzles...... the igniter plugs are slightly oversize and they squeeze the
igniter up against and into this small combustion cavity......It is this
small combustion cavity that results in the characteristic "intial spike" of
thrust......pretty spiffy huh?
The spike is a motor design feature. The plug does not add appreciably
to the spike.
Compare Estes C6 and D12 thrust curves from NAR from before and after
the plug era.
The plugs are really great BTW.
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: email@example.com>
I did not say the igniter plug had anything to do with the spike. I said
that the igniter plug held the igniter in place not only in the nozzle but
also up in that small combustion cavity... And yes the spike is a motor
design feature, but that's what I said.. and this combustion cavity does
result in that characteristic spike as after the combustion cavity is
consumed you have a neutral burning end burning motor....
and for those of you who would like more information about the design and
function of combustion cavities see: Volume #5, Summer 1997 issue of
Journal of Pyrotechnuics and the report entitled, " Model Rocket Motors,
Theory and Design " heres the abstract:
"A semi-empirical theory is presented for the design of model rocket motors
that use Black Powder for fuel. By choosing the values of a few adjustable
parameters, a hobbyist can construct motors that perform satisfactorily
without extensive or dangerous trial and error. Formulas are given for
calcualting the nozzle diameter,the combustion cavity height,and such
performance descriptors as specific impulse and average thrust for any size
of model rocket motor"
I might add that Ed Brown, the Estes BP motor guru reviewed the report
It is the roughly hemispherical grain face formed when the initial cavity
has regressed to the case walls that causes the spike, which then tapers off
again into end burn as the walls burn out. But yes as I think you are
saying, the geometry of that part of the burn is dependent on the initial
geometry of course. Luckily it all happens quickly due to the rapid low
pressure burn rate and combustion stability of BP, otherwise they'd wheeze
off the pad then kick in full bore far too late.
Did you know that the old B14 cores were drilled, after the regular pressing
process? That was apparently too hazardous (no, really?) and labor intensive
an operation for continued mass production, thus the demise of the motor. If
there were any other reasons I don't know what they were, this is what I was
told. There were a couple of guys in the Toronto crowd back in the 70's that
used to core out C's and D's for fun, and seemed to have working parameters
for doing so.
thanks for that info Mike.....
if they use some form of mandrel to get the small combustion cavities, why
not use one for the cored motors as well instead of dangerous drilling and
the associated labor costs...would that be possible? I mean if you look at
amateur rocketry books, they use this technique.
Essentially that's what they did with the B8 and C5. the mandrel was just a
bit deeper than the other ones.
The B14 drilling probably took place right after pressing, while the
propellant was still a bit damp, which probably made it safe enough. But the
labor costs were probably getting to be prohibitive. (how many times can I
use "probably" in this msg?)
Or ask him at NARCON...
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD"
>>> To reply, remove the TRABoD! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/LeadingEdge/Phantom4000.pdf
www.encompasserve.org/~kaplow_r/ www.nira-rocketry.org www.nar.org
We must have faith in our democratic system and our Constitution,
and in our ability to protect at the same time both the freedom and
the security of all Americans.
On Thu, 27 Jan 2005 12:57:15 -0500, "shockwaveriderz"
From what I know about pressing BP motors (mostly picked up from
reading posts here, on Arocket, and in David Sleeter's book), as the
mandrel size gets smaller, the odds of successfully pulling it out of
the core get worse. The very thin core in the B14 motors might be too
small to be able to reliably extract a mandrel without damaging the
Estes doesn't just have to worry about making motors; they have to
worry about making motors *consistently*, and with a high confidence
in them working as designed. "Iffy" production steps, like removing
tiny mandrels from motors, just don't make economic sense.
- Rick "On a one-off basis, however..." Dickinson
"The radio business is a cruel and shallow money trench, a long plastic
hallway where thieves and pimps run free, and good men die like dogs.
Yes, I believe that is why they went from the B14 to the B8 - to use a
die to form the core instead of drilling - I'm sure I'll be corrected
if that's wrong. But even the shorter, thicker core of the B8 gave them
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