Model Forum / General / Rockets / February 2004

I like to use Choreboy scrubbing pads. You can put some right in the motor
tube if it's long enough.  After several uses, you can pull out the Chorboy
pad and clean out all the debris. The ejection charge wont blow out the pad
because it's too "porous".

A baffle chamber can be made using a bulkhead with holes drilled near the
OD. (Don't drill any holes in the center) Glue it one motor diameter above
the end of the motor tube. For added protection, put some Choreboy in there
before gluing it in place. Building baffle chambers are nice but the down
side is you can't clean out the debris.

Just trying to reduce the signal to noise ratio.

--
Drake "Doc" Damerau
www.rocketmaterials.org
NEPRA President
NAR Section 614
NAR 79986 L3
www.nepra.com
Remove "My Shorts" to reply

    <edited>

I have the same goal for several models which I am using to "catch up"
on building techniques and for payload and recovery testing. The
following is what I now use in non-minimum diameter models. For minimum
diameter models, I use pistons.

The biggest threat to parachutes are the hot/burning particles from the
ejection charge, not necessarily the hot "gasses". Stopping or
deflecting those particles will prevent most chute damage. I use about a
9" motor mount tube for 18mm or 24mm motors. The forward end is plugged
with balsa or tissue-glue. The tube wall ahead of the forward centering
ring is drilled with many 1/8" holes so that the ejection gasses vent
"sideways" into the airframe. This traps most particulates within the
forward motor mount tube. A couple balsa disks are mounted in the
airframe ahead of the motor tube and are drilled/cut to prevent a
straight shot path forward as well.  I have used this baffle without
wadding and aluminized mylar chutes were undamaged, though a couple
plastic chutes developed a "heat set" and did not inflate fully.

My most successful setup uses a piston ahead of the balsa disks. The
baffled piston design offers (so far) complete chute protection and a
positive deployment.

I tried a couple "metal scrubber" filters, but did not see any
protection improvement and they are hard to clean. I do paint the inside
of the forward motor mount tube with thin epoxy to keep the burning
particulates off the paper. A test tube brush cleans out the (amazingly
large amount of) residue trapped in the forward part of the motor tube.

This is obviously much more work than is really required to protect a
chute. Nomex or fiberglass protectors and/or permanent wadding is
probably simpler, but I enjoy the building aspect almost as much as the
flying so I don't mind complicating the design to reach the same ends.

Let us know what you decide upon and how it works.

See the pointer in my .sig

    Bob Kaplow    NAR # 18L    TRA # "Impeach the TRA BoD"
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