What is the best replacement for elastic shock cord

[traveler]

What would be the best upgrade from a 1/4" elastic shock cord?

Kevlar only? Nylon only? Combination of kevlar and nylon? Woven? Tube?

What would be the best length?


:confused:

[pantherjon]

If for replacing the 'rubber band' shock cord found in Estes kits I use threaded nylon cords..You can get them in various widths(1/8" up to 5/8") at WalMart in the crafting section. A package will have usually 6 to 9 yards for about a buck.

The best length? As much as you can fit in the rocket! ;) But, generally, the rule of thumb is 1.5 to 3 times the length of the rocket..

[ghrocketman]

For anything above BT-60 sized rockets, I like to use about 5+ feet of black tubular elastic cord that Semroc sells, along with a braided kevlar strap of the appropriate length. BT-60 and BT-55 I like about 4 feet of the same. Less than BT-55 I use the old style flat elastic cord. I never use that "rubber band like" guff. Good for nothing but eventual breakage.

[mycrofte]

When getting back into rocketry, I ordered a shock cord just to see what it was (being used to rubber bands). When I got it in the mail, it was exactly what you will find in the sewing section at Wal-Mart...

[blackshire]

For smaller rockets using up to 18 mm motors (especially minimum-diameter rockets), elastic cords aren't necessary. Using 20" to 24" of Kevlar cord or cotton twine is sufficient.

[traveler]

Thank you everyone for the replies.


When getting back into rocketry, I ordered a shock cord just to see what it was (being used to rubber bands). When I got it in the mail, it was exactly what you will find in the sewing section at Wal-Mart...


After checking at walmart and a few fabric stores, all I found were elastics made out of rubber and polyester. Research says to get rubber and cotton for use as a shock cord in a rocket (polyester melts; cotton does not). But I can't find elastic cord made out of rubber and cotton. Asking for cotton only brings blank stares from the sales people.

Where can I get elastic material made out of rubber and cotton? Or is that why it's so cheap to buy it at a local store instead of from a rocket supply source?




:cool:

[blackshire]

In an admittedly very brief online search, I found this Rhode Island Textile 1/4" wide and 3/8" wide flat cotton/rubber elastic cord (see: http://www.createforless.com/Rhode+Island+Elastic+Cotton+Swim+Roll+1/4+150yd+Natural/pid36743.aspx and http://www.createforless.com/Rhode+Island+Elastic+Cotton+Swim+Roll+3/8+100yd+Natural/pid37695.aspx?utm_source=googlebase&utm_medium=cse ). Rhode Island Textile's South Carolina Elastic Division (see: http://www.scelastic.com/ ) makes their elastic cords, and they may also make 1/8" wide flat cords and round elastic cords. Below are the product descriptions from the vendor web site.

1/4" cotton/rubber elastic cord description: "Unaffected by chlorine and salt water, this elastic is great for swimwear, and other wash and wear garments. 1/4" 150yd Natural - 76% cotton, 24% rubber"

3/8" cotton/rubber elastic cord description: "Unaffected by chlorine and salt water, this elastic is great for swimwear, and other wash and wear garments. 3/8" 100yd Natural - 65% cotton, 35% rubber"

I just e-mailed the Rhode Island Textile home office and their South Carolina Elastic Division for information on 1/8" wide (flat), 1/4" wide (flat), 1/32" diameter (round), and 1/16" diameter (round) cotton/elastic cord, and I will post their reply when it arrives.

[traveler]

Thank you blackshire for your find and the links.

Checking into it....

A minimum order of 150 yards is required for an order of the 1/4" cotton-elastic. Including shipping ... it comes out to about $42. The local stores have packages of 10 yards of the polyester-elastic for $2 to $3 dollars. A 10 yard package of the cotton-elastic should be about the same cost (if one could find it). 10 yards should be enough for a half dozen rockets. That leaves $39 of material (from the 150 yard roll) sitting on the shelf for a long time. Not cost effective.

Seems like the only place to get 10 yards of the proper 1/4" elastic material might just be only from a rocket supply center these days. :(


:cool:

[UMRS]

You might find what you need here :)

Shock Cord Material (http://www.unclemikesrocketshack.com/Recovery_Devices/Cords/Cords.html)

[luke strawwalker]

Yes, polyester can melt, but I can tell you for a fact, cotton covered elastic shock cords will get some nasty burns from BP particles landing on them as well... Cotton won't melt, but it WILL burn, and it will eventually give out anyway as the fiber frays...

I just go with the regular polyester sewing elastic and replace it when the cord gets gnarly...

Cheap and effective... OL JR :)

[blackshire]

It may be possible to fireproof the cotton using a fireproofing solution that a July 1961 "Popular Science" article (about tissue paper model hot air balloons) recommended for fireproofing the tissue. Here is the recipe:

4 ounces of water
60 grains of borax
28 grains of boric acid
3 or 4 drops of white glue

The article said to just saturate the paper by flowing the solution over it. A cotton/rubber elastic shock cord could be soaked in the fireproofing solution and then be hung up to dry.

[blackshire]

Here is another shock cord option--Hans Michielssen's "How to Build Model Rockets" web site (main page: www.howtobuildmodelrockets.20m.com/index.html ) describes an interesting, very strong, and cheap shock cord material on the "Budget Rocketry Part 2" page (see: www.howtobuildmodelrockets.20m.com/BudgetRocketryPart2Page9.html ): Hemp! (Uh--no, not *that* kind of hemp...) :-) As he wrote:

"ORGANIC" KEVLAR - HEMP!

I read of this on a internet Rocketry Forum. I bought my corded hemp at the craft section at WalMart. It's the same hemp that crafter's use to string glass beads. I was amazed at how strong the hemp was. I couldn't break the cord with my hands!

Contrary to what some may think, Kevlar will burn. An ejection charge shoots through the rocket body very quickly. So fast that it doesn't have time catch fire to the inside cardboard body tube and Kevlar.

Try to burn through a scrap piece of Kevlar cord with a match sometime. Hemp burns also, but a light coating of white glue will protect it from the flame and heat of an ejection charge. The white glue coating also holds down the few loose strands of hemp fiber. [A light coating of white glue should also protect a cotton/rubber elastic shock cord from ejection charges *and* prevent its cotton strands from fraying. -- Black Shire] Hemp may be thicker than a Kevlar cord and may not be as pretty, but using hemp in the place of Kevlar will save you money!

[Mark II]

Just make sure that you "tar" the hemp cord before using it. Hemp cord has a reputation for developing rot from the inside out; you won't see the rot until your cord suddenly breaks.

http://en.wikipedia.org/wiki/Tarring_%28rope%29

Hemp rope is no more resistant to heat than is cotton or other natural fibers. For model rocketry, the break strength of the shock cord is less important that its resistance to degradation from heat. Hemp cord has many virtues, but I won't use it for shock cord material, even though I have a spool of it.

Kevlar doesn't burn, but it does sublimate when it is exposed to temperatures above 450°C (842°F). It will also lose strength if it is exposed to high temperatures, but the exposure must be continuous and prolonged. For instance, Kevlar will lose 50% of its strength when it is exposed to 500°F for 70 hours. Kevlar that is used for shock cords is rarely exposed to high temperatures for more than a couple of seconds at the most, and so it takes many thousands of exposures in order for motor ejection charges to have any real effect on the strength of Kevlar shock cords. If you expect to fly the same model rocket 5,000 times, then perhaps you might want to consider using another material, such as nylon-coated stainless steel cable, for your shock cord.

Anecdotal accounts come up periodically about broken or "burnt-through" Kevlar shock cords. These almost always involve Kevlar cords used in low-power model rockets; on rare occasions, an account might be circulated about a "burnt" Kevlar cord in a mid-powered rocket. It is interesting, though, that you never hear of high power rocket fliers discussing incidents in which their Kevlar shock cords "burned through" and broke. I suspect that nearly all of the incidents of broken Kevlar shock cords in LPR or not due to heat exposure but rather are due to using very thin cord with a low break strength. In my own admittedly limited experience, the only time that I have ever experienced broken Kevlar shock cords was with hair thin sub-30 lb. test weight strands. I use microbraided tubular Kevlar cord exclusively now; this method of ropemaking produces a cord that is exceptionally strong and wear-resistant, yet much more flexible and kink-resistant than twisted cord. There has been a flurry of talk about Kevlar "burn through" and breakage on the various rocketry forums lately, but I think that the issue has been greatly exaggerated.

Still, if you really feel a need to stay away from Kevlar, there is one very good alternative: the nylon-coated braided stainless steel microcable that I mentioned earlier. Sportsmen know this as fishing leader. Although it is highly resistant to heat, it does not have nearly as much break strength as Kevlar of an equivalent diameter. You won't see large quantities of it being used in high power rockets, for instance, because a shock cord made entirely of stainless steel cable that has an appropriate length and break strength for that application would be excessively heavy. Fortunately for low and mid power applications, you can get steel leader that is sufficiently strong and yet will not strain the lifting power of black powder A-C motors. If you are shopping for it, you should get cable with the highest strand count that you can find. You can usually find it in 7, 19 and 49 strand versions. The 49-strand leader is preferred, because it is by far the most flexible; 19-strand is also quite flexible, and 7-strand is moderately flexible. Anything with a lower strand count will be akin to picture hanging wire, and you will not want to use that. Also, make sure that the metal is stainless steel and not regular alloy steel. Black powder residue will quickly corrode alloy steel; stainless steel is much more corrosion-resistant. Finally, look for cable or leader that is coated with nylon. Not only does this add to the corrosion resistance, but it also makes the cable more slick and slinky, so that it is much less likely to develop kinks. The 49- and the 19-strand varieties and most of the 7-strand nylon-coated cable can be tied using the same knots that are used for monofilament line.

MarkII

[blackshire]

Other than the occasional problem of tube zippering (which is easily preventable by applying two rectangles of masking tape to a Kevlar shock cord at the point where it emerges from the body tube), I have never had any problems with Kevlar shock cords. (I only posted Hans Michielssen's description of hemp shock cords as another option.)

With dual Kevlar-polyester/rubber elastic shock cords, I have had good results with prolonging the elastic portion's service life by adding an additional square or two of wadding just below the Kevlar/elastic knot, after packing the Kevlar portion of the shock cord into the rocket's body tube.

[Mark II]

Other than the occasional problem of tube zippering (which is easily preventable by applying two rectangles of masking tape to a Kevlar shock cord at the point where it emerges from the body tube), I have never had any problems with Kevlar shock cords. (I only posted Hans Michielssen's description of hemp shock cords as another option.)

With dual Kevlar-polyester/rubber elastic shock cords, I have had good results with prolonging the elastic portion's service life by adding an additional square or two of wadding just below the Kevlar/elastic knot, after packing the Kevlar portion of the shock cord into the rocket's body tube.OK, I guess that I misread your post. I have been reading plenty of posts in various places over the past year that have condemned Kevlar, implying or saying outright that it is not all that it is cracked up to be. And that hasn't been my experience at all. I do understand what you are saying.

An interesting material that I have started using is paracord. It is kind of like small diameter tubular polyester. I have found it at K-Mart and at Joanne's Fabrics. It is similar to Venetian blind cord in weight, has a soft hand and is quite flexible but strong. For my mid power rockets, I have used it in combination with other materials for the shock cords. What I typically do is use tubular Kevlar from the mounting point up to just below the lip of the tube, then a foot or so of 1/4" or 3/8" flat elastic, and then paracord for the remaining 90% or so of the shock cord. The short length of elastic is enough to provide the entire three-part cord with some give, but is not long enough to create a problem with snap-back. Mounting this wide piece of elastic down where it spans the lip of the tube helps to cut way down on the zipper potential, and any snap-back that it does impart will be when the nose cone is far away. The maximum amount of stretch that the short length of elastic will achieve will not be enough to bring the nose cone back to the airframe. I have only made a handful of flights with this configuration so far, but the deployments have all gone well.

MarkII

[Pem Tech]

BAH!
Ditch the elastic....
Go with 150lb to 300lb Kevlar twine, yarn or cord. It never needs replacing and will hold up to almost anything but a motor CATO/Burn-Through/Blowtorch or whatever you wish to call that type of event.

Make sure the Shock cord is ~2 to 3x the length of the rocket to allow the NC to deccelerate and prevent snap-back. The smaller diameter twine will need a wrap or three of tape where it contacts the edge of the BT to prevent zippering, but has seldom been a problem.

Her is our newest Sci-Fi kit, the Arcturus, undergoing flight tests using an 18" chute and 300 lb KEVLAR twine.

Ejection
http://pembertontechnologies.com/images/MSRS_Arcturus_0185.jpg

And a successful recovery.
http://pembertontechnologies.com/images/MSRS_Acturus_0193.jpg

And here is the Sorta Saturn 7 Gemini recovering on the same type of shockcord and on the same chute.
http://pembertontechnologies.com/images/MSRS_Saturn7Gemini_0215.jpg


We include a full 60" of Kevlar twine with every LPR rocket kit we sell. The reason? Because that is what I would want to find in the kits I buy.
I'll never use elastic again...

[traveler]

You might find what you need here :)

Shock Cord Material (http://www.unclemikesrocketshack.com/Recovery_Devices/Cords/Cords.html)


Interesting that the elastic shock cords that they, a rocket supplies company, carry are made of polyester-rubber.


:cool:

[Mark II]

Interesting that the elastic shock cords that they, a rocket supplies company, carry are made of polyester-rubber.


:cool:I don't know what you are getting at here. Is there any kind of elastic that is not made from a combination of rubber and another material?

Even if the elastic was made from a combination of rubber and woven titanium, it would still be vulnerable to heat.

MarkII

[traveler]

I don't know what you are getting at here. Is there any kind of elastic that is not made from a combination of rubber and another material?

Even if the elastic was made from a combination of rubber and woven titanium, it would still be vulnerable to heat.

MarkII
"I don't know what you are getting at here."


My point is: . . . When there is a choice between polyester-rubber and cotton-rubber then cotton is the one to choose.

Carrying the point: ... A rocket supply company has the choice to make and the bulk inventory to keep. It makes no sense to stock in bulk the polyester-rubber elastic shockcord material when every Walmart store has 10 yard packages of it for a couple bucks as do many other stores. Within hours anyone can purchase this material locally. No need to mail order it. But cotton-rubber elastic shockcord material on the other hand is not easy to find. I can't find it at all in my local, can you?

Tim Van Milligan in his book "Model Rocket Design and Construction" (Copyright 2008) must have had a reason to say the use of cotton is preferable to polyester for shockcords.


:cool:

[AFlyingMonkey]

I'm actually thinking of weaving some 50lb test strength into a finger cuff configuration then having it compress and stretch like the cuffs when the ejection charge goes off. at least that way it takes out some of the energy of the ejection charge. At least that way it doesn't have the tendancy to twist. And if you really wanted to you could throw in some rubber in the middle to take even more of the energy out of it. Granted it would be thick, but would be good for larger models, like a bt-60 size or bigger model. Just a thought....

[Mark II]

"I don't know what you are getting at here."


My point is: . . . When there is a choice between polyester-rubber and cotton-rubber then cotton is the one to choose.

Carrying the point: ... A rocket supply company has the choice to make and the bulk inventory to keep. It makes no sense to stock in bulk the polyester-rubber elastic shockcord material when every Walmart store has 10 yard packages of it for a couple bucks as do many other stores. Within hours anyone can purchase this material locally. No need to mail order it. But cotton-rubber elastic shockcord material on the other hand is not easy to find. I can't find it at all in my local, can you?

Tim Van Milligan in his book "Model Rocket Design and Construction" (Copyright 2008) must have had a reason to say the use of cotton is preferable to polyester for shockcords.


:cool:I'll have to look that up in my copy. As someone mentioned before, cotton burns. By using a Kevlar or steel leader for the portion that remains inside the tube, I have avoided having any of my elastic cords melt or break. (As long as I use 1/4" wide or above. The 1/8" elastic just doesn't seem to hold up very well.) There is a reason why this method has been so widely adopted over the past couple of decades. But you are right that cotton/rubber elastic is hard to find; in fact, I can't recall ever seeing any in a store. I purchase most of my elastic from Joanne's Fabrics*, because they have such a wide selection of it, and you can buy it there by the foot.

As I indicated in my hypothetical woven titanium/rubber example, the fabric is only part of the issue. The rubber component will make the elastic vulnerable to melting, regardless of what it is combined with. And without the rubber component, it's not what we commonly refer to as "elastic." The woven Ti/rubber elastic will be just as vulnerable to melting and breaking as one made with polyester and rubber.

What is usually used for the covering of bungee cord? It seems to me that the way that this cord is constructed makes it much more heat tolerant and less vulnerable to melting than flat elastic. In fact, FSI used to advertise that their bungee cord shock cords were fire-resistant. You can get genuine bungee cord in as small as 1/16" diameter. I have used 3/32" diameter bungee in a couple of my FSI clones, more for the sake of historical accuracy than anything, but they have worked fine.

Just using a length of tubular or twisted Kevlar for the entire shock cord, as Layne advocates, is a very viable but somewhat more expensive option. Aside from the increased cost, the other reason that I don't just go with Kevlar all the way is because most of my clone builds have used relatively thin-walled low power tubing, and I am very concerned about zippering. If I was using more heavy-walled MPR tubing like Layne uses in his kits, that might not be such an issue. But honestly, my biggest concern is simply the expense, along with the lack of local sources for it. I can't just buy a little bit at a time, like I can with other materials. And buying a spool of it would be a major purchase.

(* A U.S.-based textile and crafts store chain, for the information of those forum members who are not in the US.)

MarkII

[Mark II]

I'm actually thinking of weaving some 50lb test strength into a finger cuff configuration then having it compress and stretch like the cuffs when the ejection charge goes off. at least that way it takes out some of the energy of the ejection charge. At least that way it doesn't have the tendancy to twist. And if you really wanted to you could throw in some rubber in the middle to take even more of the energy out of it. Granted it would be thick, but would be good for larger models, like a bt-60 size or bigger model. Just a thought....Are you talking about doing that with Kevlar? It sounds like an interesting idea, but unless you have a weaving machine, it would be a lot of work. Plus you would go through a great deal of Kevlar, too, many times the amount that you would use for a simple shock cord. The rubber content, if you added it, would still be vulnerable to melting unless you completely encased it in a couple of layers of Kevlar or Nomex, and it doesn't sound like that is what you plan to do.

Bungee cord, I believe, is made up of many thin individual strands of rubber that are twisted around a material that allows them to slide past each other without binding. The bundle is then spiral-wrapped with some kind of thin, strong fabric and then finally encased in a woven tubular sheath that is capable of being stretched a great deal without breaking or unraveling, and yet will return to its original form when it is relaxed. (That last part sounds like a marvel of engineering just by itself.) The many thin strands of rubber are collectively stronger than a solid strand of rubber that is the same thickness as the bundle (no doubt due in part to the fact that the strands can slide past each other), and if a strand or two breaks, the cord is still usable. The spiral covering and the woven sheath add even more strength. I'm not sure, but I think that bungee cord somewhat resembles skeletal muscle in its construction. (Except, of course, that it is not self-repairing.)

MarkII

[AFlyingMonkey]

Mark II,

Even if its not a full cover weave, if its done right it might work better than doing just kevlar alone, and with a wider impact area it might do a better job of preventing zippers. I've see zippers done with elastic as much as with kevlar. To me its more about the diameter of the substance more than what the substance is made of that causes the zipper.

Personally I like the idea of having the light weave covering. Yes it maybe more expensive, yes it may take up more room but if it proves to be better stuff then why not do it?

Its at least something I'll try once. Who knows it could be stronger and more durrable than anything else we have out there.

Monkey

[luke strawwalker]

It may be possible to fireproof the cotton using a fireproofing solution that a July 1961 "Popular Science" article (about tissue paper model hot air balloons) recommended for fireproofing the tissue. Here is the recipe:

4 ounces of water
60 grains of borax
28 grains of boric acid
3 or 4 drops of white glue

The article said to just saturate the paper by flowing the solution over it. A cotton/rubber elastic shock cord could be soaked in the fireproofing solution and then be hung up to dry.

That just makes it FLAME RESISTANT (not likely to support combustion, self extinguishing) not FLAME PROOF (inert and incapable of burning, or capable of resisting much higher temperatures than it's likely to be exposed to). Glass, kevlar (to a certain temperature anyway) and asbestos are flame PROOF, pretty much everything else we commonly use is at best flame RESISTANT...

Look at used sheet wadding-- the stuff WILL have substantial burns on it and through it from particles of BP and slag from the engine (contaminants in the BP, bits of superheated ceramic, etc) and that DESPITE the 'flameproofing' solution... I've even found Estes wadding still smoking, even smoldering (still burning around the edges of the burn hole) but not 'flaming up' enough to start a grass fire...

It might help SLIGHTLY, but the cotton shock cord damage I've seen looks identical to wadding 'smolder burns' from particles burning through it. I recovered one rocket and it was LITERALLY hanging by a pair of threads-- the rubber and the rest of the cotton jacket of the shock cord had burned away and/or snapped under the load of the chute deploy... the cord didn't 'flame up' because the burn only involved the edges of the spot, and you could kinda tell when you laid the shock cord out that it basically had caught a chunk of burning BP or slag that burned through the material in about a 1/8 inch "hole" through the shock cord.

SO, it might help but I wouldn't count on it... OL JR :)

[traveler]

[snip]

Still, if you really feel a need to stay away from Kevlar, there is one very good alternative: the nylon-coated braided stainless steel microcable that I mentioned earlier. Sportsmen know this as fishing leader. Although it is highly resistant to heat, it does not have nearly as much break strength as Kevlar of an equivalent diameter. You won't see large quantities of it being used in high power rockets, for instance, because a shock cord made entirely of stainless steel cable that has an appropriate length and break strength for that application would be excessively heavy. Fortunately for low and mid power applications, you can get steel leader that is sufficiently strong and yet will not strain the lifting power of black powder A-C motors. If you are shopping for it, you should get cable with the highest strand count that you can find. You can usually find it in 7, 19 and 49 strand versions. The 49-strand leader is preferred, because it is by far the most flexible; 19-strand is also quite flexible, and 7-strand is moderately flexible. Anything with a lower strand count will be akin to picture hanging wire, and you will not want to use that. Also, make sure that the metal is stainless steel and not regular alloy steel. Black powder residue will quickly corrode alloy steel; stainless steel is much more corrosion-resistant. Finally, look for cable or leader that is coated with nylon. Not only does this add to the corrosion resistance, but it also makes the cable more slick and slinky, so that it is much less likely to develop kinks. The 49- and the 19-strand varieties and most of the 7-strand nylon-coated cable can be tied using the same knots that are used for monofilament line.

MarkII

I just "bumped" into the 49 strand nylon coated stainless steel cord in the bead section of a craft store.

I bought a roll of the .024 thickness cord, the thickest one they had. (also available was .015 and .018) Looks like good stuff; seems very strong; but I wish I knew it's breaking strength. I'll use it as the shockcord anchor in the sustainer of my Oracle and as a parachute mount for the point on the nosecone for the camara payload on the Oracle.


:cool:

[Mark II]

I just "bumped" into the 49 strand nylon coated stainless steel cord in the bead section of a craft store.

I bought a roll of the .024 thickness cord, the thickest one they had. (also available was .015 and .018) Looks like good stuff; seems very strong; but I wish I knew it's breaking strength. I'll use it as the shockcord anchor in the sustainer of my Oracle and as a parachute mount for the point on the nosecone for the camara payload on the Oracle.


:cool:I have some of that, too. Is it Beadalon? It should state the break strength somewhere on the label. According to the Beadalon web site, the 0.024" diameter bead stringing wire (http://www.beadalon.com/49standard.asp) has a break strength of 40 lbs. I recently got some of this leader (http://www.cabelas.com/cabelas/en/templates/product/standard-item.jsp?_DARGS=/cabelas/en/common/catalog/item-link.jsp_A&_DAV=MainCatcat20166-cat20180-cat20204_TGP&id=0011246314955a&navCount=18&podId=0011246&parentId=cat20204&masterpathid=&navAction=push&catalogCode=IK&rid=&parentType=index&indexId=cat601233&hasJS=true) from Cabela's Online (http://www.cabelas.com/cabelas/en/templates/home/home.jsp?cm_re=store*topnav*CabelasLogo):

[/url]http://images.cabelas.com/is/image/cabelas/s7_314955_imageset_01?$main-Medium$

It is 7x7 strand (49 total strands), but I bought the 90 lb. test version. The 90 lb. is thicker (0.036") than any of the weights of bead stringing wire that I have used in the past and is also slightly stiffer, but it is still quite limp and knottable. It is interesting to note that the 90 lb. test AFW Surflon Micro Supreme leader is the same diameter as Beadalon's 90 lb. bead stringing wire.

When I use Beadalon, I use crimp beads to connect and close loops. When I ordered the Surflon, I also ordered a pack of these [url="http://www.cabelas.com/cabelas/en/templates/product/standard-item.jsp?id=0011430316147a&navCount=25&podId=0011430&parentId=cat20204&masterpathid=&navAction=push&cmCat=MainCatcat20166-cat20180-cat20204_TGP&catalogCode=IK&rid=&parentType=index&indexId=cat20204&hasJS=true"]double-barrel sleeves (http://images.cabelas.com/is/image/cabelas/s7_314955_imageset_01?$main-Medium$). I believe I ordered the Size 7 sleeves.

If 90 lb. test isn't strong enough, AFW also makes 7-strand Surflon (http://www.cabelas.com/cabelas/en/templates/product/standard-item.jsp?id=0011429317460a&navCount=77&podId=0011429&parentId=cat260004&masterpathid=&navAction=jump&cmCat=MainCatcat20431-cat20439-cat260004&catalogCode=IK&rid=&parentType=index&indexId=cat260004&hasJS=true) in 135 lb. test weight.

If you want the ultimate in flexibility and the utter coolness factor of titanium (and don't mind paying for it), you can also get this product (http://www.cabelas.com/cabelas/en/templates/product/standard-item.jsp?id=0017977316703a&navCount=75&podId=0017977&parentId=cat604280&masterpathid=&navAction=jump&cmCat=MainCatcat20431-cat20439-cat604280&catalogCode=IK&rid=&parentType=index&indexId=cat604280&hasJS=true) in 30 lb. to 100 lb. test weights.

MarkII

[blackshire]

That just makes it FLAME RESISTANT (not likely to support combustion, self extinguishing) not FLAME PROOF (inert and incapable of burning, or capable of resisting much higher temperatures than it's likely to be exposed to). Glass, kevlar (to a certain temperature anyway) and asbestos are flame PROOF, pretty much everything else we commonly use is at best flame RESISTANT...

Look at used sheet wadding-- the stuff WILL have substantial burns on it and through it from particles of BP and slag from the engine (contaminants in the BP, bits of superheated ceramic, etc) and that DESPITE the 'flameproofing' solution... I've even found Estes wadding still smoking, even smoldering (still burning around the edges of the burn hole) but not 'flaming up' enough to start a grass fire...

It might help SLIGHTLY, but the cotton shock cord damage I've seen looks identical to wadding 'smolder burns' from particles burning through it. I recovered one rocket and it was LITERALLY hanging by a pair of threads-- the rubber and the rest of the cotton jacket of the shock cord had burned away and/or snapped under the load of the chute deploy... the cord didn't 'flame up' because the burn only involved the edges of the spot, and you could kinda tell when you laid the shock cord out that it basically had caught a chunk of burning BP or slag that burned through the material in about a 1/8 inch "hole" through the shock cord.

SO, it might help but I wouldn't count on it... OL JR :)

I was quoting the term, "fireproofing solution," that was used in the July 1961 "Popular Science" article. From my experience, model hot air balloons that are made of tissue that has been so treated will not burn.

I have tried to burn samples of the tissue with matches and cigarette lighters, and the tissue merely turns brown or black while creating no flame of its own. The treated tissue takes long enough to char that a brief "lick" of flame from the balloon's burner or the ground-based heat source usually doesn't darken it. Since the duration of a model rocket motor's ejection charge firing is so brief, a cotton/elastic shock cord treated with the water/borax/boric acid/white glue solution may be fireproof for all practical purposes in this application.