Nomex vs. Baffle vs. Piston?

[jaymeister99]

What are some of the pros/cons of nomex, baffle, and piston?

I know a few of the nomex and baffle, but haven't really heard much about the pistons.

[GregGleason]

Piston design is, IMHO, the least developed of the three. I have some things in my mind to develop them, but have yet to put it on paper, let alone test them.

That said, they work. But, they work best at mechanically forcing the recovery gear out, not necessarily at protecting the recovery gear from heat (it does attenuate the heat some, though). But the mechanical push is why I use it, to have a better likelihood that the laundry comes out at the prescribed deployment event. There are designs that work better than others.

http://www.deltavrocketry.com/piston.htm

Greg

[jpummil]

I've never used the pistons, but I tend to favor the nomex over the baffles just because of a couple of bad experiences where the baffle was damaged and I was forced to cut out the obstruction and go to nomex anyway...

HOWEVER, one of the guys on here (old_dude maybe, or qquake2k) makes his own baffles all the time using a piece of round plywood cut in half (into 2ea D shapes) one glued at top, the other at bottom forcing the gases to follow an "S" trail thru the baffle. If I ever DO go back to baffles, I'll follow this model

[fyrwrxz]

My two cents- I'm scrapping out a very old (25+?) 54mm Black Brant. The piston siezes 3/4 of the way down and I've tried to clean the gunk out to no avail. I'm cutting off the fincan and splicing on some new tubing with a coupler and going to nomex. I' haven't decided on a baffle system yet, but want to hold the laundry up for my Cg concerns. I'm sure motors and deployment charges have gotten better over the years and maybe this bird just suffered neglect at my hands. I do like piston ejection-esp. for larger diameters and this is only motor eject-no DD. It's been a simple 'shove a motor in it and fly' kinda bird-maybe why it's so crudded up.

[JStitz]

I had to sand my airframe out after every piston use,but then again I may have been using too much 4444F.
The pistons always seemed to be trashing the tubing ends or airframe...and got shattered themselves in the 2 PML kits I used them in.
I started using the Nomex underwear. BUT...I don't like my recovery harness looking like grannies laundry line either.

[New Ocean]

I would actually go with D.) Wadding. I like the full brunt of the ejection charge being used to eject the nosecone and parachute without anything else getting in the way. Pistons scare the crap out of me. Baffle worries me because it will degrade over time and get really dirty. What if it gets clogged and you can't tell?

For $10, the cost of a nomex pad, you can get enough cellulose wadding to last years. I am still using a bag from about 10 years ago, but I don't fly that often or big. Only a small amount is needed to get the job done, an inch or two in most cases, and nothing gets particularly dirty.

Nomex strikes me as a good compromise between piston and wadding - but you still have to clean it etc.

[jaymeister99]

I would actually go with D.) Wadding.

I forgot to add that one! I haven't done the barf wadding yet. I think any smaller rockets I get in the future will use some of this stuff (as soon as I run out of my bag of Estes wadding).

I found out the hard way I need to use some wadding along with the baffle I put into my Big Bertha.

[JStitz]

When airframes get away from 4" dog barf gets iffy..I have seen 7.5 inch rockets impact with the overload of loose barf they put in there,

That brings to the point...how do YOU pack your Dog barf..Loose?..or slightly packed?

[New Ocean]

When airframes get away from 4" dog barf gets iffy..I have seen 7.5 inch rockets impact with the overload of loose barf they put in there,

That brings to the point...how do YOU pack your Dog barf..Loose?..or slightly packed?

Loose, just enough to stop the ballistic particles of burning material. Usually there is some left on recovery, I dump it on the ground. It is only there to protect the parachute, it should not hinder the ejection charge. In smaller rockets (as in beginner and educational) I go with wadding sheets instead. But if the rocket can use nomex or pistons, it is large enough for dog barf. I have never flown more than 4 inch rockets so I bet nomex or a deployment bag is better in level 3 rockets. Pistons of any size really scare me! Just to restate that. Just one more thing to snag inside the rocket at the worst time.

[Rokitman88]

My experience with pistons is, while they work quite well in ejection and protecting the chute, I also have had damage to the airframe and pistons. After a few flights the pistons tend to get brittle and break very easily and they are a pain to replace so I am replacing them with nomex as they break and any new rocket I build will use nomex.

[jaymeister99]

Ok,

Sounds like pistons are out. So make that Nomex vs. Baffle vs. Wadding.

Hows nomex on smaller rockets?

[New Ocean]

Ok,

Sounds like pistons are out. So make that Nomex vs. Baffle vs. Wadding.

Hows nomex on smaller rockets?

Nomex works for reasonably small rockets, say down to 24mm. I would not go lower than that. I used it on a 24mm kit called Machbuster, it was fine! But that rocket had F or G motors with big ejection charges and I wanted the nomex to provide good protection. On a D, paper wadding would have been fine.

You can try baffles like this one: http://www.amazon.com/Sunward-Model-.../dp/B00390YSO2

[cwbullet]

I have used all 4 methods.

1) Pistons work well if you keep them clean. If you do not, the stick. I like them for large rockets to reduce the amount of black powder needed. 4 to 6 inch rockets.

2) Nomex is my preferred method. I use it with and without dog barf.

3) Dog barf is cheap and works well in just about all rockets.

4) Baffles work, but they can get dirty and foul. I like them in small rockets.

5) One not mentioned is CO2 canisters. They work well, but are expensive. I plan to use them in a high flying bird to avoid issues with black powder not igniting.

[H_Rocket]

Each one works well if properly done. I do disagree with Greg on how a piston does with respect to protecting the laundry. Personally I think it is the best there is for that purpose. And as Chuck mentioned, they can work to drastically reduce the amount of BP you need.

That said,they have to me maintained or they will fail. The most common problem is in PML kits where a phenolic piston is used with a Quantum Tube air frame. In very cold weather, the coefficient of expansion for QT and Phenolic is different enough that the airfram will bind a piston that works perfectly at higher temperatures.

[cobra1336]

LPR wadding or barf would be my choice. MPR barf, nomax or piston 2.5in. I like pistons but like stated you need to inspect and replace them often, if the pre flight inspection shows the piston working properly they are great, have extras in my box because the piston can zipper. Had a motor fly thru my rocket on the pad, piston pushed everything out with no damage. Not sure that would of happened with barf / nomax. HPR, large diameter, nomax.

[GregGleason]

Each one works well if properly done. I do disagree with Greg on how a piston does with respect to protecting the laundry. Personally I think it is the best there is for that purpose...

That is true for pistons made with very close tolerances to the airframe. I have had some pistons where there was a lot a slop and have had chutes get a little scorched. But if you have a tight fit that won't bind, it's potentially the better solution. It may help airframes that use pistons to let laminating epoxy soak inside the airframe and then coat it with high-temp release wax. Also, a piston that can be removed from the recovery train for maintenance or replacement would be a big help.

Greg

[H_Rocket]

...Also, a piston that can be removed from the recovery train for maintenance or replacement would be a big help.

Yes, I actually redid all my pistons so they had a very short (6"-10") strap that I connecct to the shock cord with a quick link. Then I can remove it for maintenance.

[New Ocean]

CO2 They work well, but are expensive. I plan to use them in a high flying bird to avoid issues with black powder not igniting.

Not to derail, but don't CO2 charges still use some kind of small pyrotechnic charge? I never understood why this is deemed better than a straight pyrotechnic system designed for altitude like surgical tubing.

One interesting thing is that, with a bunch of kevlar line, I think my 38mm diameter rocket could fly without anything. The kevlar just packs first and protects everything else. Maybe the wadding helps to protect the kevlar.

[GregGleason]

Yes, I actually redid all my pistons so they had a very short (6"-10") strap that I connecct to the shock cord with a quick link. Then I can remove it for maintenance.

Would you be so kind to post pics? I can't recall seeing pics of a removeable piston.

Greg

[New Ocean]

Sounds similar to the PML piston. I found it could potentially bind up and stopped using it in my stretched Io.

[Quaranta]

I'm building a PML Pit Bull currently. I'm choosing to not install the Piston. I'm worried of the piston binding. And then there is the decay over time issue as well.

I use kevlar cord,... nomex blanket,... and put a little wadding in the engine tube.

[fyrwrxz]

Core sampled my last 3.0 " piston bird yesterday. Even added .2 gms to I-161 to get positive deploy. Nose cone came out and saved it. Evidence shows nice sedimentary layering and recent off-road activity. Done with pistons.

[grouch]

I have only tried nomex and baffles. I like how well the baffle works but I worry about the long term with it. I have also had my chute get bunched up in the nomex a couple of times resulting in the ever dreaded parawad. I think from here on out I am just going to make each of my rockets relatively simple, probably mostly relying on some barf. Less crap is just less crap to go wrong.

[MarkII]

A baffle is by far the simplest device to use. Once it is installed, you don't have to even think about chute protection, because it's built-in. Just fold your chute, bundle up your shock cord, insert both and go. In contrast to both pistons and, when you think about it, Nomex, is that there are no moving parts that can get jammed. With a baffle, the ejection charge doesn't need to push out the protection along with the recovery device, because the recovery system protection is part of the rocket. Baffles don't last forever, but properly constructed, they can last a long time. You'll probably lose the rocket before you'll wear out the baffle. "Cold air"-style baffles don't clog or become blocked. (I don't like filter-style baffles because they carry that potential.) They all gradually collect tiny bits of debris, though; after awhile, your rocket will sound a little bit like one of those "rain sticks" when you shake it.

Baffles work best in a certain range of tube sizes. These are generally the sizes associated with mid power rockets, from 1.25" to 3". Less than that size, you can do just as well with dog barf or wadding. Above that, you should really be wrapping your parachute up in Nomex or Kevlar (or be using a deployment bag). Baffles have an additional benefit: they keep your recovery device in the upper portion of the airframe, which helps with stability.

Nomex blankets/shields can be used in smaller diameters too. They get harder to stuff in when the tube gets small, but I have used 3" x 3" Nomex squares from Sunward in BT-50 airframes. In large airframes you wrap up the parachute in the Nomex like a package and slide it in. In this arrangement, the Nomex is acting like a blanket or wrap for your parachute.

In small airframes you place the square of Nomex over the open end of the tube and push down in the center to make a "cup." You place your folded recovery device into the cup and then push it down into the tube. Used in this way, the material acts as a shield between the ejection charge gases and debris and the recovery device.

Nomex works very well and is very popular, but especially when it is used in the shield configuration, it can eventually burn through in spots. You'll get advance warning of that, though, when you inspect the cloth before use and note areas where it is beginning to get thin. (I haven't worn any of mine out yet, though.) Shields made from Kevlar can last longer, but they are often stiffer and a bit harder to use as a result. (I have one.) But they generally last for a very long time. Unlike baffles, Nomex cloth and Kevlar fabric can be washed out!

The biggest problem with Nomex in my experience is that the squares need to be matched in size to the airframes; a given size will only work in a small range of diameters. In large airframes, they need to be matched to the size of the parachute. So you need to keep a range of sizes on hand, and usually a few of each size if you prep more than one rocket at a time. A square of Nomex has about the weight and density of denim or heavyweight twill, so it adds a little bit more mass than either wadding or dog barf; in some situations that can be a potential issue. And of course, you have to remember to use it!

[Highpowerrocketyahoo]

Nomex, love it, easy simple, cheap

Kevlar, even better, not as cheap

Baffle, if built and installed properly, very reliable permanent solution. Still use some dog barf for insurance, chutes aren't cheap.

Piston, love pistons but they require maintenance and when they fault it's not pretty.

Deployment bag, awesome.....

[o1d_dude]

I recently bought an octagonal shaped nomex blanket from Fruitychutes and plan to buy a few more. It seems like the non-square shape works much better than the customary square blankets I've used in the past.

This is the one I bought: 11" Nomex Blanket for 3" Tube

A bit more expensive than the typical square blankets by top quality.

I have no financial interest in Fruity Chutes, just like the product.