D-12 Ejection Pressure OK to use Anti-Zipper?

D-12 Ejection Pressure OK to use Anti-Zipper?

Post by Jerry O'Sulliva » Tue, 02 Feb 1999 04:00:00



Hi all,

Just finishing a rebuild of an Estes Phoenix. I've made a baffle using 2
bulkheads w/offset cutouts epoxied to either side of a coupler. Coupler is
epoxied into the lower airframe. There's just enough room between the top of
the coupler (with eyebolt) and bottom of the nose cone shoulder to fit a
parachute and shock cord. At this point I can either glue the upper BT
(about 6") to the coupler and attach the shock cord to the nc as usual OR
not glue the upper BT and in the process make an anti-zipper affair.

Is an Estes D12 ejection charge (with this type baffle) sufficient?

I've been lucky I guess not to have yet had a problem with weak D12 ec's but
there's always a first:)).

Thanks,
Jerry

 
 
 

D-12 Ejection Pressure OK to use Anti-Zipper?

Post by AAFCf » Wed, 03 Feb 1999 04:00:00


Jerry, this may not directly answer your question, but I can give a scenario
that you might consider useful, from a real world standpoint anyhow.

I flew my LOC Grad (20 oz.) on a D12-3  once. It boosted to about 70', nosed
over and started doing a death dive. ~20' off the ground, it spewed the guts
and managed to FULLY blossom the chute just before TD.

Take into account that it's got a 12" long 38mm motor mount, leaving an
additional ~18" of 2.63 airframe to contend with, besides the oversized Nomex
protector and the laundry.

Hope I was some help...the add'l given was that I didn't have one of the dog
D12's...

 
 
 

D-12 Ejection Pressure OK to use Anti-Zipper?

Post by Hilty Information Syste » Thu, 04 Feb 1999 04:00:00


On Mon, 1 Feb 1999 13:50:37 -0500, "Jerry O'Sullivan"

Quote:

>Hi all,

Hey Jerry!

<snip>

I finished one last fall.  Cool rocket, and it flies nicely on D's.
It weathercocks massively though, so watch the wind when you fly it!
Haven't put my 24/40 RMS in it yet, but maybe when the weather gets a
little nicer.  

Quote:
>At this point I can either glue the upper BT(about 6") to the coupler
>and attach the shock cord to the nc as usual OR
>not glue the upper BT and in the process make an anti-zipper affair.

I guess I'm not clear on how you're doing this.  If you don't glue the
upper BT, are you going to glue up the nose, and basically have the
model eject "in half" to deploy the chute?  Actually, not a bad design
variation!

I built mine stock with the exception of a stainless steel lanyard
that John Cato turned me onto  (btw John, if your listening, it works
quite nicely!  Thanks!).  The cable passes all the way down through
the MM centering rings, loops around the MMT once, and passes up the
other side to form a loop.  I used a crimp connector to attach both
ends of the cable between the MMT centering rings.  I used a little
piece of shrink tubing to form the loop which is about 1" inside the
upper BT.  Standard elastic extends from the loop to the nosecone.
This way, if the rocket ends up in a zipper situation, the only stress
on the BT will be from the elastic, not the cable.  Wadding tends to
hang up in the lanyard, but I think that could be eliminated by using
"dog barf" (cellulose insulation).

Quote:
>Is an Estes D12 ejection charge (with this type baffle) sufficient?

Based on the strength of the ejections on mine, I don't see any
problems with it.  I mean gas pressure is gas pressure, so whether the
tube break is in the middle, or at the nose, it probably shouldn't
matter.  I fly mine on D's with a 24" nylon chute.  The 18"er Estes
included with the kit just didn't cut it in my mind!

Quote:
>I've been lucky I guess not to have yet had a problem with weak D12 ec's but
>there's always a first:)).

Yeah, I've only hit one thus far, and it was an Estes Python that came
in ballistic from its apogee.   Estes replaced the kit though, and now
I'm considering building a two stage Python, using the original lower
half as the booster.

Quote:
>Thanks,
>Jerry

Good Luck!

tah

Tod A. Hilty  NAR #72099    
Hilty Information Systems

"I'm going to put the wheels of the bus back on... just in case"
   - BlankReg, Max Headroom: 20 Minutes Into the Future

"I speak for myself _and_ my corporation!  Deal with it!"
   - blankreg

   - remove nospam.ever, and replace with apk for reply