Searching for wadding advice

I went through several phases with wadding before I settled on "dog barf" or cellulose insulation as it is more correctly called. I bought a life-time supply of it for $5.99 and have been using it since 1997 or so. It's cheap, works perfectly and best of all, it is 100% biodegradable and doesn't mess up the desert. I give it two thumbs up.

Only problem is you have an open bag of the stuff lying around for years. Crepe paper is a little more expensive, but it's fire proof too, you keep only a little of it, and... it's prettier. :-)

It's probably less complicated than that. Wadding, to do its job, must accomplish two things: stop the burning particles that are blown out by the ejection charge, and keep the superheated air from reaching the parachute. This is accomplished best by a very loosely-packed wad that fills as much space as you have available. The layers closest to the motor trap the particles, and the remainder simply serves to encapsulate a quantity of cool air.

Wadding is generally porous and the pressure rise in the body tube passes right through it (unless you are using an actual piston arrangement as some HPR kits do) so that the pressure pushes the nose cone off and the 'chute is as much pulled out as pushed out. While the burning particles will penetrate an air space, the bubble of hot air will generally push the bubble of cool air that is contained in the wadding ahead of it for the brief instant that the tube is pressurized.

Usually the burst of heat from the ejection charge is dissipated too quickly to do more than superficial damage to the body tube. If the wadding is packed too tightly, the heat may be trapped there in front of the motor long enough (say, a half-second) to penetrate into the paper surface and do real damage. In a few applications, where space is very limited, a tight wad is the only choice, but usually it's unwise to pack it.

The shredded cellulose insulation mentioned above is at least as good as the commercial wadding. I, too, have read about flameproofing TP with boric acid, but have never done it. Another approach, which works well in limited-space situations, is a "parachute protector" which may be a Nomex cloth patch attached to the shock cord for re-use, a pouch arrangement often used in HPR, or a card-stock arrangement invented in the 1970's. In most larger rockets you can also route the hot gas through a labyrinth arrangement that both traps the flying particles and keeps the hot gas from mixing with the cool air ahead of it.

I've recently started re-using Teflon tape pom-poms for LPR ejection wadding. I built permanent wadding pom-poms for several rockets now and each has performed perfectly. To see more about this technique check out The Rocketry Forum and do a search on Teflon Pom poms.

They are just Teflon thread sealant cut into strips and tied loosely together in a pom-pom with light Kevlar thread. The other end of the thread is tied to the recovery harness near the main body tube. The wadding is totally reusable. I would suggest NOT skipping the Kevlar because it holds it together despite the flames. If this stuff got loose it would not be biodegradable litter. (Bad for small animals and birds.)

Teflon tape is fairly inexpensive. I bought 2 rolls at a dollar store for a buck each and made enough pom-poms for 4 rockets. I've made wadding this way for BT20, BT50, and BT55 tubes. Anything larger than BT60 would be much harder to use unless you had some really large Teflon tape. In that instance I still just use party streamer material which is flame proofed and cheap.

Kevlar (90#) is available from online vendors.

Layne

THAT IS A "BAD THING", BUT ONE SOLUTION IS TO BREAK IT DOWN INTO POLY BAGS (LIKE KITS COME IN) OR SMALL BOXES SO IT REMAINS MOSTLY SEALED FOR STORAGE AND GRABBABLE FOR A LAUNCH. AT LEAST WITH DOG BARF (YES THAT IS A TECHNICAL TERM) YOU ALWAYS WANT TO SHARE AND NEVER NEED TO SKIMP!

Caps off.

Kurt,

You could try using a baffle. We (Fliskits.com) sell a variety of them for BT-50, 55, 60 & 70 tubes.

The way they work is to break up any clear path for the burning particles, preventing them from reaching the parachute. It also helps to cool the gasses coming from the ejection charge, but the main culprit to burning parachutes are the particles.

you can find out more on our baffle page at:

Good reasons :-)

Have you considered using a permanent nomex flame shield. I've used nomex in rockets as small as BT-55 (33.7mm) without any trouble. My 'ETV2' cluster rocket has been through 10 flights and 50 motors, and while the 'ejection' side is a bit dirty, the nomex shield is doing very well.

I tend to put in a couple of sheets of crumpled Estes wadding right at the bottom of the tube to keep the recovery system away from the really hot stuff. They also help catch all the ejection debris and keep the nomex cleaner.

"jflis" wrote in news: snipped-for-privacy@g14g2000cwa.googlegroups.com:

Sure. I'm trending towards that idea nowdays. My other favorite new trend is the "zipperless baffle" design.

Centuri had been using baffles since the 70's and USR since 1980. Not exactly new.

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The nifty 'S'-baffle, which serves the smaller tube sizes, might be more recent. I'm experimenting with them on BT-5 and BT-20 designs.

Dwayne Surdu-Miller SAROS #1

I've gone back to a simple and always available product - Lettuce ! It brings wetness to the party and is biodegradeable

Since I started buying Estes bulk-packs with the 50% coupon for Michael's I have a rather large supply of their wadding. I also use the dog-barf insulation for wadding in my HP rockets. I bought a bale of the stuff for $4 about ten yerars ago and have used up about half of it, including the stuff I have given away to friends.

I don't like golf either.

Bill Sullivan "The first thing we do, let's kill all the lawyers."

- Henry VI, Act IV, Scene 2

I have not seen the particular implementation you refer to, but if you refer to a disc with a segment removed from one side, and a second disc "flipped", USR North did that.

Jerry

Hi,

Thanks for all the kind advice. Had a 70F day on Sunday that caught me off guard. Actually too windy to fly but painted two models and and shot primer on two more. They were the result of the building season. Most proud of the Estes Mean Machine and the Dyna-Star Rising Star. I went ahead and used fiberglass resin (without the the fiberglass) and impregnated the body tubes with three coats. Actually used Bondo. I sanded like crazy between coats. Was actually hard to do as you get orange peal and an uneven surfaces after applying the resin. Had to sand like heck in between the coats. Re-engined the Mean Machine to take any sized 24mm motor and felt that re-enforcing would help. Only mistake I made was I put bigger fins on the thing and I think it will weathercock more. This was before I got Rock Sim and was more enlightened by all that has been written out there. Thanks again for the advice on the "dog barf" insulation.

Kurt Savegnago

I don't know if any of you have seen the UK Scrapheap Challenge 'rocket' episode. It was either lettuce or cabbage that was used for wadding, and the results showed the importance of not letting an Army Colonel ram it into the rocket as if it was the barrel of a gun!

I can see why it would be good, just make sure you clean it all out. I wouldn't fancy finding mouldy lettuce in my rocket!

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Yes, that's the one. I am curious, what is or was USR North?

Dwayne Surdu-Miller SAROS #1

Posed a picture last night of my Teflon Pompom Maker on abmr.

I sold USR some years ago. They were located in NoCal and did some mods to some parts. That method works really well BTW.

To a kit maker it doubles the parts count however :-(

Jerry