Brown Shock Cords

[chronister]

Hey guys. Do you know which years Estes was using the brown shock cords in their kits? I'm building an Astron Delta (2 stage launch vehicle for Camroc) clone and was wondering what color the shock cord would have been. Would they likely have used both colors at one time or another during the years this kit was being made, 1965-1973? Thanks!

Nathan

[Rocket Doctor]

Hey guys. Do you know which years Estes was using the brown shock cords in their kits? I'm building an Astron Delta (2 stage launch vehicle for Camroc) clone and was wondering what color the shock cord would have been. Would they likely have used both colors at one time or another during the years this kit was being made, 1965-1973? Thanks!

Nathan

Nathan

The "brown" shock cord are the original rubber ones, when they turn brown, they are old, and, usually brittle.

The current rubber shock cords being used in Estes kits would be a close clone of the originals.

I just may have an "original" shock cord, I will have to look.

[Mark II]

Hey guys. Do you know which years Estes was using the brown shock cords in their kits? I'm building an Astron Delta (2 stage launch vehicle for Camroc) clone and was wondering what color the shock cord would have been. Would they likely have used both colors at one time or another during the years this kit was being made, 1965-1973? Thanks!

Nathan
The shock cords in the Estes kits that I bought between 1967 and 1970 were all made of gray rubber (most likely, natural rubber, although it could have been some type of synthetic; I remember that it did smell like natural rubber, though), about 1/8" wide x 1/16" thick. It was very similar in appearance to the rubber used in wind-up free flight gliders from that period. Although the material was quite pliable, it was stiffer than either a typical rubber band or elastic and it took a firmer pull than either of them to stretch. It did stretch like a rubber band, though. I did not put in a large number of flights in any of my rockets from that time, so I cannot say what the long-term durability of these shock cords would be. In all of mine, the shock cords would get covered with soot from the ejection charge (which mostly just wiped off), but otherwise it remained pliable and seemingly undamaged. I never had any that burned-through or broke. I just assumed that they must have been made from some high heat-tolerant type of rubber, or else that their manner of installation helped to protect them from being burned by ejection charges. Today I just scratch my head; I am completely at a loss to explain why those old rubber shock cords held up so well.

I am not sure if these are the shock cords that you are referring to. It is quite possible that the brown shock cords you asked about are these same gray ones, and that they have acquired a brown patina over the years from oxidation of the rubber. I have heard that rubber never really stops vulcanizing - the process continues indefinitely but at a dramatically slower rate following the conventional vulcanization treatment.

For your vintage Astron Delta clone, I would recommend that you make the shock cord out of some durable gray rubber with the right dimensions (width = 1/8", thickness = 1/16", length = about the same length as the sustainer's body tube or just a tad shorter; Estes Industries kept the shock cords short even back then), obtained from a model aviation vendor or an industrial supplier. You can get an idea of the appropriate length by looking for shock cords in the component pages of catalogs from that period and in the 1973 Custom Parts catalog. Keep in mind that although the shock cord length seems to be rather short by today's standards, it was meant to be anchored near the top of the body tube, so that almost all of the length would extend out the top of the body tube when it was deployed.

Hope this helps.

Mark \\.

[SEL]

Hey guys. Do you know which years Estes was using the brown shock cords in their kits? I'm building an Astron Delta (2 stage launch vehicle for Camroc) clone and was wondering what color the shock cord would have been. Would they likely have used both colors at one time or another during the years this kit was being made, 1965-1973? Thanks!

Nathan

The brown shock cords in my old kits, both in the bag and built-ups, have all held up very well. In fact (and I know this may be blaspheme in to some in this group :p ) I abandoned the white braided elastic and kevlar 7 or 8 years ago and have gone back to Sig contest rubber. It's more of a tan color now, but in my opinion holds up much better to the ejection charges. The only exception is that I use round braided elastic cord for my FSI clones. No real reason 'cept a fondness for staying true to the FSI designs - and it also seems to hold up better than the flat braided elastic.

Just my 2 pence.

S.

[Royatl]

Hey guys. Do you know which years Estes was using the brown shock cords in their kits? I'm building an Astron Delta (2 stage launch vehicle for Camroc) clone and was wondering what color the shock cord would have been. Would they likely have used both colors at one time or another during the years this kit was being made, 1965-1973? Thanks!

Nathan

The brown rubber was "contest" rubber, used in rubber-powered free-flight airplanes. It was readily available back then, and used in Estes kits from the beginning until around 1968-69. At that point they started using the white vinyl rubber that they used until about 15 years ago and which they started again to use about four years ago.

The contest rubber was meant to be coated occasionally with glycerine to keep it supple. I know some free-flight guys who sometimes managed to make their "engines" last for more than five years. Of course, in the harsher environment of a model rocket, that stuff did not last nearly as long. The white stuff did last a little longer, but it too would eventually dry out. One difference was that with the brown rubber, the outside would dry out long before the inside did, and you'd know it was about to go, but you might could get an extra couple of flights out of it before it did. The white stuff would just simply break cleanly, sometimes with no warning!

[mojo1986]

I still have my original Delta from the first year the kit came out. Definitely a brown shock cord. But the shock cord in the later blue skill level 3 kit was white.

Joe

[chronister]

Here's a photo that I saved from an ebay auction I was watching a few years ago. It shows the Delta kit with one white and one brown shock cord. This one must have been transitional. It seems to indicate that the white shock cords came out before they got rid of the checkered parachutes.

I have some of the new contest rubber that they use in model airplanes. It has a light tan color, much different from what's in the photo. Is this due to age, or was it actually brown when they first made it?

[Royatl]

Pretty sure just age. Of course, one batch or manufacturer might have a slightly different color than another.

The two types were intermingled for awhile, just as there were checked and striped chutes intermingled for awhile as supplies changed.

[ghrocketman]

I know for a fact that the Astron Delta that had the blue "skill level" header card used the off white/extremely light grey "modern" shock cord and not a brown one as I still have my original Astron Delta, which was the first 2-stage kit I built, way back in 1977.

[Mikus]

I abandoned the white braided elastic and kevlar 7 or 8 years ago and have gone back to Sig contest rubber.



Hey that's this stuff right?

SIG Rubber? (http://www.sigmfg.com/IndexText/SIGSR014.html)

I was wondering how well this worked just the other day. About how long do you usually make your shock cords when you use this stuff? I'm thinking about another solution after watching the braided elastic cord break and the airframe come whistling in on my vintage Stealth's 1st freaking flight a couple of weeks ago.

[snuggles]

SIG rubber works GREAT!!!!!
My pack lasted quite a few years. Hmmmm, maybe it's time for another pack.
HTH
Mark T

[scigs30]

Sunward sells the same elastic rubber that Estes sells. They currently offer the 1/4 version in long lengths. I am trying to get them to order 1/8 rubber, right now they only offer the 1/4.

[Royatl]

Rubber is ok, but it is definitely not needed, and it contributes to what is known as the "Estes dent," where the nose cone snaps back against the body or the fins after being projected out to the end of the cord.

starting around 1970 or so (and exemplified in the MPC kits), G. Harry started recommending against elastic shock cords in favor of plain cotton twine in lengths longer than the prevailing elastic. His rationale: you don't need the elasticity, it is heat resistant enough, you can tell when it is about to fail, and it is cheap and easy to replace.

Centuri, on the other hand, started using cotton-based elastic. The best of both worlds. Elasticity and some heat resistance. Unfortunately, cloth and notions manufacturers switched rather quickly to synthetics for most elastic in the 70's.

BAR's of the 80's and 90's fondly remembered the Centuri stuff of the early 70's, and Estes started replacing the vinyl rubber with elastic about 15 years ago. But since the elastic of the 90's was synthetic, it couldn't stand up to the abuse that the Centuri elastic did, and a few years ago, Estes went back to the white vinyl.

around 1990, some people started using kevlar thread, for a few reasons: you could tie it directly to the motor mount (because it was even more heat and flame resistant), and it was extremely strong. The big disadvantage was that it tends to cut through tubes like butter. Not to mention that it is heavier, stiffer, and harder to cut.

[Bob H]

My Astron Delta from the late 60's had the brown contest rubber shock cords. Actually it still does because I never changed them.

[chronister]

The contest rubber probably costs a lot more than the white stuff, and I'm guessing that's the main reason why Estes doesn't use it in their kits. But the contest rubber may have some disadvantages other than cost. It degrades if you leave it exposed to light. The white rubber might be better in this regard. Also, the contest rubber returns most of the energy you put in when you stretch it. That's an advantage for rubber-powered airplanes, but it means the nose cone will snap back harder after the ejection charge, whereas a lower quality rubber would actually absorb a good bit of the energy.

Most hobby shops sell contest rubber in various widths. Sometimes it is kept behind the counter and you have to ask for it. The sizes range from 1/32 inch to 1/4 inch. You can order the 1/8 inch rubber from my online store:

http://www.flyabird.com/ffsup.info.html

[Rocket Doctor]

The "brown " shock cord were the same stuff used on model airplanes from that era. It's the same rubber offered by SIG, which was disgussed in a previous thread.

As far as length, you can have s hock cord as long as you like, as long as you have enough room in the body toube to store it.

The rule of thumb is, at least 1 1/2 times the length of the body tube the shock cord should be, for example, if the body tube is 20 inches, then the shock cord should be a minimum of 30 inches.

The longer, the better, as long as you can stuff everything into the body tube without "jamming" it inside.

Don't forget the wadding...........

[SEL]

Hey that's this stuff right?

SIG Rubber? (http://www.sigmfg.com/IndexText/SIGSR014.html)

I was wondering how well this worked just the other day. About how long do you usually make your shock cords when you use this stuff? I'm thinking about another solution after watching the braided elastic cord break and the airframe come whistling in on my vintage Stealth's 1st freaking flight a couple of weeks ago.

That's the stuff. As far as length, it depends on whether you've got a payload section or just a nose cone. I tend to go long - at least 1-1/2 the length of the rocket up to 2 , 2-1/2 or 3 times the length. If its just a bt20 TFNC, I might go w/ just kevlar (it's easier to stuff into the tube. In any case, I use the old FSI method of attachment (see attached.)

S.