If not piston deployment, then what???

I've heard a few people say they don't like piston deployment, but I've never heard why.
Is there a 'Better' way
Peter

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snipped-for-privacy@jci.com wrote:

I just used piston deployment for the first time in my Level 1 certification flight last weekend. Here are my comments:
1. I don't think I'd 'trust' the standard elastic that is/was supplied for use with the piston on the engine side. I replaced mine with heavy-duty Kevlar. 2. It is/was 'difficult' to sand the piston to be 'just right'. By that I mean that I wanted it 'snug', but not 'too snug', which meant a few passes with the sandpaper, then re-testing it. And it makes a difference what temperature you fly it at, so you might need to 'touch it up' for the first few flights. 3. There's a bit of grit on the inside of the tube after launching, which means you need to clean the tube out so that the piston works well for subsequent flights. Not a big deal, but it's something you need to be mindful of.
That having been said, I don't think there's a better way to completely protect the chute -- the chute looks like I just took it out of the bag.
David Erbas-White
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The only real problems with piston recovery i've seen is when you use a phenolic piston with quantum tubing AKA drainpipe.
With the expansion rates of the two materials being different they have the nasty habit of jaming in cold or damp weather.
Damian
--
Damian Burrin
UKRA 1159 Level 2 RSO
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On Wed, 30 Mar 2005 08:28:43 GMT, "Damian Burrin"

Which is why you should check it before flight. Every rocket should have some things checked before each flight - it's no biggie.
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Phil Stein wrote:

use a

have the

ok I checked it ..it's too tight.... ,, simply checking something does not fix it.
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I appologize for assuming that you read the directions in the kit or for assuming that your smart enough to know you should fix it.
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I think for almost all of us, the verb "check" is a shorthand for "check and adjust if necessary, or delay the flight if whatever you checked can't be fixed." Though I'll grant you that NASA has, on occasion, used "check" as you seem to, as in "the temperature was checked just before the Challenger launch."
--
Joseph J. Pfeiffer, Jr., Ph.D. Phone -- (505) 646-1605
Department of Computer Science FAX -- (505) 646-1002
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Not for Phil Stein.
For him it means post a personal attack on rmr.
Jerry
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Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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wrote:

Jerry - in your case, I'm always willing to provide a personal attack but as often as you prove yourself to be an asshole, I don't think my confirming it means much.
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Turn the piston over the other way. Have the ejection charge hit the flat end of the piston as it is done in a car engine. The piston remains stable and doesn't rattle on the way out. It has been tested.
wrote:

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I add another bulkhead to the base of my pistons with another U-bolt for symmetry/cosmetic reasons. Not really necessary and adds extra weight.....
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I saw those videos as well so I built one of my pistons following the manufacturers directions and built the other with the bulkhead halfway up. I couldn't tell the difference in performance, they both worked is all I knew.
Andrew
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snipped-for-privacy@jci.com wrote:

Advantages:
1. A piston pushes the recovery system out of the rocket. The other option is to hope the nose cone drags it out.
2. A piston protects the recovery system from fire and heat. The fire and heat is on one side of the piston. The nylon parachute is on the other side. I have a great video that illustrates this. An ejection charge was test fired in an unpainted fiberglass tube. Carefull examination shows the piston sliding and pushing the chute out, and you see a big fireball.
If done right a piston is great. But, just like assembling a motor incorrectly, if it isn't done right then you've probably created a worse problem.
If the fuselage is plain cardboard then I cannot recommend a piston. Plain cardboard is soft and absorbs crap that is difficult to impossible to remove.
The piston needs rigid walls that cannot bend, fold or otherwise deform. A deformed piston can jam. Imagine what would happen in your car if a piston deformed.
I start with a phenolic coupler tube. Plain cardboard is too soft and absorbs crap that is difficult to impossile to remove.
Fill the coupler tube with two-part foam to make it non-deformable. After the foam has cured, cut to size (about 1/2 the fuselage's diameter). Coat the exposed foam on the ends with epoxy to protect the foam from the BP blast. I cut a hole in the center for the TN to slide through. (Coat the hole with epoxy, too, otherwise the foam will tear apart.)
My pistons slide on the tubular nylon cord. The pistons are not fixed to a point. They don't snap to a stop and rip something apart. Sometimes one will slide several feet along the TN before drag and gravity stop it.
If the tube is 30" long then place at least 30" of TN (covered with Nomex) under the piston. The piston should be able to clear the fuselage before it needs to slide on the TN (or Kevlar or whatever you use).
A piston should freely slide in the fuselage. Hold the fuselage tube vertical and the piston should freely slide to the bottom. I needed to remove a layer of paper from the (flex phenolic) piston for it to slide freely, in part because the fuselage wasn't perfectly round.

Sabot?
There isn't a single recovery methodology that is perfect for all rockets. What size rocket and what recovery scheme (single deployment, dual deploy, etc.) are you using? What is the fuselage material? What is the diameter?
Dean
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snipped-for-privacy@jci.com writes:

Piston deployment has a possibility of the piston getting sticky, or getting cocked in the body and stuck, or getting a shroud line or something caught between the piston and the body (thus getting stuck once again).

Well... I like pistons a lot. People who don't prefer things like Aerotech-style baffles or putting the chute in a kevlar bag.
--
Joseph J. Pfeiffer, Jr., Ph.D. Phone -- (505) 646-1605
Department of Computer Science FAX -- (505) 646-1002
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Piston deployment is the best method to ensure safe ejection of your recovery system. Wadding, Baffles, Nomex or Kevlar pads are also viable options, but there is a better protective seal between the motor and chute when using the piston. And as stated in another comment, with the piston, after deployment, you cant even tell that the chute was subjected to the ejection gases.
-- Jeffrey L. Miller Anchor Parachutes www.anchorparachutes.com

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says...

Opinion? Fact? Strongly stated opinion = fact?
How about: Piston deployment is the best method to ensure occasional lawndarts due to complete failure of the recovery system to deploy?
--
Tweak

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On Wed, 30 Mar 2005 11:27:30 -0500, Tweak

I like pistons. I've never had a failure caused by them. Although I build rockets larger that 4". I've never used a piston on one larger than that. It doesn't mean that you couldn't.
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snipped-for-privacy@ArielSystems.spamsks.net says...

Ahh, but you clearly state an opinion based on empirical evidence, not an opinion presented as fact.
My (somewhat snarky) comment was not meant to be a serious response.
--
Tweak

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On Wed, 30 Mar 2005 16:31:16 -0500, Tweak

Are you trying to imitate Jerry or something? 8-)
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For you, EVERYTHING is about Jerry.
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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