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Anyone know where I can buy 1/8" wide, flat elastic shock cords for LPR? Odd'l Rockets used to carry a flame resistant variety but don't anymore, and online searches haven't turned up anything.
YES! That's the stuff.
Sure hope you meant "elastic" and not electric.I would not recommend electric cords. They are better in underwear and not rockets. Use nylon or Kevlar.
Ok. I have never found it needed but that is better than the Old LOC and Estes Midpower cords.Sure hope you meant "elastic" and not electric.
Anyway, I use the elastic as a kind of "bungee cord" to absorb the shock of the ejection charge. I attach it between two points on the kevlar shock cord, leaving a length of loose kevlar between the elastic. Works really well to dampen the force of the ejection charge and drastically reduce snapped shock cords (I use it on my BG rear-eject system, which typically doesn't have as long a shock cord as the traditional front-eject motor pods).
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Elastic works well in LPR and smaller MPR stuff. I don’t get the hate for it.I would not recommend electric cords. They are better in underwear and not rockets. Use nylon or Kevlar.
Another easy way to get some shock absorption on the fly is to bundle sections of kevlar strap (Z-folded) then wrap in a rubber band (or 2 or 3). The rubber band absorbs opening force as it is stretched and broken/flies off. Plus it helps to organize recovery train as you are packing the airframe. I use small, short rubber bands horse people use for horse manes.Sure hope you meant "elastic" and not electric.
Anyway, I use the elastic as a kind of "bungee cord" to absorb the shock of the ejection charge. I attach it between two points on the kevlar shock cord, leaving a length of loose kevlar between the elastic. Works really well to dampen the force of the ejection charge and drastically reduce snapped shock cords (I use it on my BG rear-eject system, which typically doesn't have as long a shock cord as the traditional front-eject motor pods).
View attachment 562569
No hate. It may work well for you but for me, it just wears out to quickly, and I hate replacing it.Elastic works well in LPR and smaller MPR stuff. I don’t get the hate for it.
That's a really intriguing approach. I'm definitely going to try that technique on my latest build.Another easy way to get some shock absorption on the fly is to bundle sections of kevlar strap (Z-folded) then wrap in a rubber band (or 2 or 3). The rubber band absorbs opening force as it is stretched and broken/flies off. Plus it helps to organize recovery train as you are packing the airframe. I use small, short rubber bands horse people use for horse manes.
Thanks for all the research and info!Fabric covered shock cord is more heat resistant than bare material. If you can find cotton covered elastic, that adds a level of heat resistance over the usual nylon or polyester. This material is typically called swimsuit elastic. The only supplier of cotton clad swimsuit elastic I could find on Amazon was Dritz. I emailed them about their elastomer and they confirmed it was latex.
The stuff you want is cotton wrapped neoprene. The neoprene is more heat resistant than natural rubber and will hold up better for the long haul, unlike latex which gets brittle with age.
The only internet source of cotton swimsuit elastic where I have been able to verify the elastomer as neoprene is Sewsassy.com. Unfortunately, unless you want to buy wholesale, minimum order is 10 yards at about $0.53/yd and they add an extra $1.00 for orders totaling less than $15.00. Plus shipping, of course.
The absolute ideal would be cotton wrapped silicone rubber, which I am not sure anyone makes. The closest I have found is silicone rubber bungee material for collapsible tent poles, made by MSR. The wrapping is either nylon or polyester and the diameter is about 3.5 - 4 millimeters. Stretch-wise, this is about equivalent to 1/2” flat material. The silicone is heat resistant to 600 degrees F, is resistant to chlorine, oil, and solvents, and does not oxidize and break down with age.
Even with reliable materials, you should consider the elastic a replaceable item. Attach to a kevlar loop, inspect often, keep clean, and replace as needed.
If anyone knows of a reliable source of flat silicone rubber cotton-covered elastic in 1/8””, 3/16”, 1/4” or 3/8” sizes, please let me know.
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