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12.3 I've heard that Copperhead igniters are 'unreliable' for igniting HPR motors. Is that true?




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This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.

12.3 I've heard that Copperhead igniters are 'unreliable' for igniting HPR motors. Is that true?

Many HPR flyers do not like the Copperhead igniter, prefering alternatives
when they can be found. It is certain that Copperhead igniters are not
a good choice for igniting clusters. However, some have found the
Copperhead to be a reliable igniter for single-motor HPR rockets.

From: dcrcep@mizzou1.missouri.edu (Elmer M. Price)
Hi Folks: I have a comment on the reliability of Copperhead ignitors.
Our small group has had no problems with these, once we figured out the
best way to use them. So, in spite of all the negative comments, we
actually really like these things. We have launched composites up to and
including I-sized motors with great reliability. For example, two weeks
ago, two of us (at the excellent St. Louis launch), launched two I284
birds, one I161, one I211, two H123 and a few F's and G's. We had 100%
ignitor success.

O.K. So what do we do to achieve such reliability? First, open the
reload pack and assemble the motor in the usual manner. Second, find the
Copperhead that came with the reload kit and THROW IT AWAY. What we use
are Copperheads which we purchase separately. These arrive from the
dealer (like Magnum) in a nice package and the ignitors are not all beat
up and crimped and bent to heck like the ones which are provided in the
reload kit. We feel this is an important point. Second, since the H and
I (and larger) motors are a bit more difficult to light, we modify the
new Copperhead as follows (this idea came from RMR): take a slug of
white lightning propellant (we use the slug from a D9) and cut a very
small sliver (and I mean small, about 1/16 inch square and about 1/2 inch
long). Tape this sliver (Fred from our group optimized this point) to
the Copperhead by overlapping the bottom half of the pyrogen on the
Copperhead with the top half of the sliver. Use a small strip of masking
tape to attach the sliver to the copper below the pyrogen. The point
here is to ensure the tape is below the area where the pyrogen and the
sliver overlap. This is important because if the tape is higher up the
ignitor, the sliver may fall off of the Copperhead and lead to a chuff
(ignition too far aft).

This modification is not necessary for G and smaller motors, since the
pyrogen is in close proximity (or touching) the propellant.

And this was added by: bday@fly.HiWAAY.net (Brian Day)
I've also gotten *MUCH* better reliability from Copperheads by not using
the red plastic cap over the nozzle, and just using a small piece of
masking tape to hold the igniter in place. This technique doesn't crimp
the Copperhead like the plastic cap does. Since doing this, I've gone
from roughly 50% reliability to darned near 100%.

Oh yeah, someone else on rmr recently suggested clipping off the pyrogen
part of an old, crummy Copperhead and using it to augment another one,
like you do with your sliver of propellant. Beats throwing it away...

Finally, regarding the red caps provided with Aerotech motors for holding
in the igniters,

From: Bob Kunz (bkunz@boi.hp.com)
You do know that one is supposed to provide a vent in the red cap? I would
presume this is to allow some leakage of pressure but enough to get the
white/blue/black propellant to ignite. Typically, I find that the red cap
is blown through when I recover the rocket. Only once was it blown off at
the launch pad. So far in about a dozen launches on RMS 24/80, I've had no
failures. But sure those are small grains compared to some of the 54mm
stuff.

From: curcio@telerama.lm.com (Larry Curico)
Copper Head igniters have acquired reputations for unreliability. I'm
wondering if the problem is in the igniters or in the red nozzle
caps, which blow off during most Copper Head failures. IMHO, it's the
sudden release in pressure that makes ignition fail - by disrupting the
newly forming flame. When I use a piece of masking tape instead of a cap,
I don't seem to have the problem.

Editor's note (jjirvine@cyberg8t.com):
As of 11-96 Aerotech has made some efforts to eliminate the microshort
problem which is an artifact of the Coppercrap manufacturing process.
They have tried making versions with thicker insulator layers.
While they are more fragile and subject to peeling, they are more
reliable than before. Time will tell.

 

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