Shock Cords

Oh, ok... sorry, I was zipping through the messages and I mis-read it...
Thanks.
~ Duane Phillips.


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Jerry Irvine, Box 1242, Claremont, California 91711 USA
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It's working and you ROCK.
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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Art, It's nice to use 2in for the first few feet of harness where it attaches in the airframe so you have a two inch strap pressing against the airframe opening, then transition to something smaller. This helps to avoid zippers.
I also like to z-fold the cord and tape it together.
If you make the cord too long the sections can accelerate to higher than the deployment forces before being stopped by the chute, so be carefull.
Sometimes I like to make a harness a few feet long out of Kevlar that attaches to the bulk plate and the harness attaches to this, this can handle higher heat. But if you use 2in TN it will be fine. Just sew loops in the end and wrap with duct tape to protect the thread.
RDH8

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Anti-zipper ball... neva thought of that. There are some reasons to be in this forum while one is enjoying "lone ranger rocketry".
~ Duane Phillips.

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you can see the "Fireball", a patent pending commercialized version at
Giant Leap Rocketry http://www.giantleaprocketry.com
high power -> (top frame) products -> (left frame) recovery
- iz
Duane Phillips wrote:

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I guess we'd have to see the patent claim, but this seems to be "prior art" to me...
    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
Save Model Rocketry from the HSA! http://www.space-rockets.com/congress.html
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Static URL's are superior.
Jerry

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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the problem is that in dynamically generated websites that use frames, the frame URL does not reproduce the actual context
but here's your link to the frame
http://www.giantleaprocketry.com/products_recovery.asp
- iz
Jerry Irvine wrote:

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Um, I know. That's the point.

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Jerry Irvine, Box 1242, Claremont, California 91711 USA
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wrote:

You should think about rocket mass more than airframe diameter for shock cord sizing. The shock cord has to dissipate the force of the two rocket parts separating from each other by way of ejection charge. Therefore, the mass of the rocket pieces on each end of the cord and the force (size) of the ejection charge will determine the force (momentum) that must be absorbed / dissipated by the shock cord under normal deployment. Using longer shock cords will allow the pieces to slow down due to friction with the air before the cord goes taught. rubber bands or tape as others have mentioned also help.
"blow it out or blow it up" may help gaurantee 'chute ejection, but it increases the force on your shock cord, so be carefull.
There are also other ways to deploy chutes to minimize the forces on your shock cords.
I have a 7.5" X 8.5 ft rocket that weighs about 30lbs on the pad. It has all 9/16" tubular nylon shock cords. BUT... This rocket deploys at apogee in the following manner. The charge blows the nosecone off which pulls a 36" Skyangle chute into the airstream. As that chute fills, it pulls a deployment bag housing the main (Skyangle Cert3 Large) out of the rocket. As the nosecone and rocket body separate, the main shock cord is pulled taught and then the shroud lines for the main are pulled out of the loops sewn on the outside of the deployment bag. All of this dissipates energy from the ejection charge. Finally, the bag is pulled off of the main. The main then fills and brings the rocket down. The nosecone descends independently on the 36" chute. That looks like a lot when written out in words, but it is really very simple and I have absolutely no fear of overstressing the 9/16" tubular nylon.
-- Eric Benner TRA # 8975 L2 NAR # 79398
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OK , here is what I want to do. the 7.5 : rocket is like a bruiser exp with a 4" motor mount. it will travel to about 7-9k so dual deploy is needed.
All the laundry will be in the payload bay.
The primary apogee charge cannon will blow the nose cone off and the nose will pull a sky angle drogue chute out held to the payload bay with a ring link held to an ARRD, say 25 feet of 3/4" cord. The secondary apogee charge cannon will seperate the booster from the payload bay. say 35 feet of 1" cord.
If the primary charges fails to fire, the seconday charge will end up seperating the nose from the payload (no shear pins) in the standard inertia mode that causes so many main deploy at the top situations. If the seconday charge fails, then the seperation of the booster and payload will take place with the drogue becomes taught.
at 800 feet, then the main match fires the arrd, and at 700 feet the secondary match fires the arrd weather it needed to or not.
That realeases the ring on the arrd, and lets the droge pull the main and it's deployment bag out and do all that stuff.
I've got to be missing something, so let me know if I did.
ohh, the harnesses have the "car polishing towel" wrapped in ducktape anti-zipper ball on them.
anyway, my 5.5 rockets just do the drougeless two step and so far have been fine, crossing streams, no that's fingers.
/ArtU

all
the
As
taught
the
really
tubular
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with
charge
That sounds OK.

inertia
seconday
place
Personally, I wouldn't feel comfortable relying on inertia for a backup plan. With my luck, the parts will stick at the wrong time.

That sounds OK. I have a project coming up which will require an ARRD or some similar device. I would like to use another as a backup instead of just a backup match in one ARRD.

been
Drogueless dual deploy is my most common high power rocket recovery method. Works great and usually brings everything close to the pad.
Eric B.
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the ARRD works in reverse, so if two are used, and only one fires, you don't have deployment ? I can't see how two of them does anything good ?

nose
ring
and
just
method.
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ArtU wrote: <snip> I would like to use another as a backup instead of just a backup match in one ARRD.
the ARRD works in reverse, so if two are used, and only one fires, you don't have deployment ? I can't see how two of them does anything good ?
Why not two in series. That way if one does not fire or separate hopefully the other one will. Bill Richardson
Drogue less dual deploy is my most common high power rocket recovery method. Works great and usually brings everything close to the pad.
Eric B.
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Exactly.
-- Eric Benner TRA # 8975 L2 NAR # 79398
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Still lost here.
The ARRD holds a deploymen bad to the bulkhead by holding the hook.
two in series or paralle still do the same thing.
Unless they both fire, your deployment bag is still held to the bulkhead ?
Confused
/ArtU
I will gladly pay you tuesday for a motor on the flying field today.
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