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Re: Bulkhead assembly / piston

After having lost another shock cord, I thought of using a bulkhead

> assembly, not glued into the tube, as a piston - attached to the motor mount > w/ mtl cable &/or nomex cord long enough to let it eject from the tube, and > attached on the opposite side to the chute - nose cone, etc. > > I can't have been the first person to have thought of this, so I was > wondering if anyone else does this, how well it works, or doesn't work. Any > help is appreciated - Thanks, > Chris > >

Do a google on piston ejection... I know Public Missles, Ltd. has a model or few with this feature.

~Duane Phillips.

Reply to
Duane Phillips
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I have had some success with a hybrid baffle piston. The piston slides on the shockcord that is quicklinked to an eyebolt on the motor bulkhead (easier to change out than the PLM glued in design). It could be mounted at a fixed point on the cord or at a joint between lengths of cord. The baffle uses 3 plates with offset holes and the top is covered with a small kevlar chute protector to keep things cleaner. I have had it both stop inside the tube and come all the way out, with laundry still launching in both cases. It may be working more as a floating baffle than a piston, but this might be controlled by using a more restictive flow path (scrubber pad). I have been toying with the idea of mounting a protected G-Wiz inside with the charge mounted on the bottom (the pressure line for a barometric unit would be a bit of a challenge).

Reply to
Eric Pederson

Haven't done a 3"; my largest so far is a 2.6" (BT-80) model/MPR. You can generate substantial forces on the piston as the diameter goes up. The internal ejection gas pressure decreases, but the piston area is also going up. My 2.6" model uses a plywood bulkhead recessed below a

1/8" "holding" ring in a piston skirt of rolled cardboard. I glassed the inside of the skirt as it was a little flimsy. Don't know if it was necessary, but it does protect the skirt from straight-shot ejection gases and hot particles.
Reply to
Gary

Be VERY careful with fine steel cable like fishing leader or control line cable. It DOES burn after exposure to ejection charge. may not happent he first time, but it will fail. And any kink or bend in the cable creates a weak point that can break.

The heavier cable used in HPR models doesn't seem to have these problems, but the small stuff sure does.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Reply to
Bob Kaplow

Thanks, Bob. Haven't had a failure with the 30# or 50# leaders yet but I'll keep on eye on them.

Tried picture hanging cable in a BT-80 cluster model. Worked fine once, then zippered down to the motor mount on a very short delay (after I carefully finished the darn thing, of course).

Which reminds me, I need a new thread...

Reply to
Gary

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