Nomex and baffles?

[jf_reinhard]

Can anyone give me some information about Nomex and baffles? It looks like Nomex is used to wrap around parachutes/streamers to protect them from heat. Baffles are apparently to eliminate the need for wadding.

That's about all I could find. Not having to use wadding would be great, especially for larger rockets.

Can I install a baffle after I've built a rocket or is it something that needs to be installed during the build?

As for Nomex, how do you use it, what kind and how much do I need, etc?

I found both of these things at Uncle Mike's, haven't looked anywhere else.

Thanks,
Jim

 

[Mikus]

Can anyone give me some information about Nomex and baffles? It looks like Nomex is used to wrap around parachutes/streamers to protect them from heat. Baffles are apparently to eliminate the need for wadding.

That's about all I could find. Not having to use wadding would be great, especially for larger rockets.

Can I install a baffle after I've built a rocket or is it something that needs to be installed during the build?

As for Nomex, how do you use it, what kind and how much do I need, etc?

I found both of these things at Uncle Mike's, haven't looked anywhere else.

Thanks,
Jim

Baffles should be built into the rocket initially. The rocket should separate at the baffle as it will need to be cleaned of ejection residue occasionally or it could become clogged - leading to ejection problems and an eventual ballistic recovery. The upper end of the baffle is a good place to attach the shockcord if the upper baffle plate is sturdy.

Nomex is also good for eliminating the need for wadding and indeed is wrapped around the recovery system to protect it from the ejection charge. You need a 3 to 1 (round up) ratio of blanket size to body tube diameter - a 1" tube needs a 3"x3" blanket. It too needs to be cleaned occasionally but you can take it out and wash it in a washing machine (but NOT the wife's washing machine, unless you're brave) to get the residue off. :shock:

I prefer Nomex over baffles for ease of maintenance and lower weight. It also can help some with visual tracking if you use a bright color.

But I also like "barf" too, which is just fire-retardant treated shredded newspaper used as ceiling insulation. It's cheap and a bale of insulation will last you a very, very long time. It's also better for the environment than wadding and the ejection charge pounding it into dust also helps visual tracking with a bigger "puff cloud" at ejection. The drawback is it is tougher to get a feel for the right amount of barf to use.

Hope this helped.

 

[shreadvector]

Info on Nomex (and relation to tube sizes):

https://www.pratthobbies.com/products.asp?cat=1


Googling "rocket baffle" will prodcue masive amouonts of info. Here are only a few of the sites:

https://www.google.com/search?hl=en&q=rocket baffle&btnG=Google+Search

https://www.fliskits.com/products/components/misc.htm

https://www.semroc.com/Store/scripts/prodList.asp?idCategory=68

https://www.rocketarium.com/baffles.html

 

[privateer]

I just bought a bale of ceiling insulation. I haven't used it yet, but I figured a column as long as 2-3 times tube diameter ought to be about right. I figure it will compress but not enough to "flip" and let the ejection gases by. Is it trickier than that?

I just used a nomex protector for the first time at the last launch for a Gauchito, where the chute is quite close to the engine. It worked well.

 

[bobkrech]

There are 5 standard way to protect you recovery gear from being burned by hot particles from the ejection charges: wadding or "dog barf" aka blow-in cellulose building insulation; Nomex(R) blanket; baffle; piston; or deployment bag.

1.) The simplest and cheapest method is wadding or "dog barf". This is ok for model rockets, especially in smaller diameters, however as the diameter gets larger, you need more wadding or "dog barf" or the hot particles simply go around it and burn your chute. For 3" or larger diameter rockets you may need ~6" of loose "dog barf" or more to protect your chute, so that's a reason why folks use the next 4 method in bigger rockets.

2.) A Nomex(R) blanket parachute can be easily added to most rockets and is preferred over wadding in larger rockets because particles won't go through it unless it's right on the ejection charge. https://quickburst.net/9_chuteprot.htm They work well in 1.6" air frames and larger. The larger the airframe the larger the chute protector.

3.) Baffles are built into the rocket and prevent burning black powder articles from hitting the parachutes. They are usually a set of 2 or more perforated disk that do not allow a straight-line-of-sight path for the burning power particles to hit your parachute. https://www.info-central.org/?article=133

A special type of baffle for large rocket is an anti-zipper baffle. It has several advantages in large rockets. https://www.info-central.org/?article=132

An additional advantage of a baffle is that it prevents the parachute from sliding down into the airframe on acceleration. The moves the CG rearward and decrease the rocket stability. If the body tube is long and you don't have a baffle, you chute may not fully eject from the airframe if it slides all the way down into the airframe.

4.) A piston is simply (or should be) a cup containing the parachute made from a solid bulkhead and a coupler tube that is pushed out of the airframe by the ejection charge. The bulkhead should located at the aft end of the coupler facing the motor ejection charge with the parachute in the cup. (This is contrary to how most folks set them up, but pistons made in the manner are stable and will not jam.) https://www.publicmissiles.com sells rockets with pistons but uses them backwards.

5.) Deployment bags are used in large rocket (4" or larger) to insure that large parachutes are ejected and open quickly. They are essentially an Nomex(R) "zipper" bag parachute protector employing a pilot chute to assist in deployment. https://quickburst.net/ndb_4.htm

Hope this helps.

Bob