Shock cord question

[rocketgroupmike]

Hi, all. I've been lurking around here for a couple of months, and this is my first post. I'm another BAR, having flown Estes kits in the early 70's, and I now have a PML Sudden Rush spread out on my workspace. My question is this: Should I replace the 3/4" by 1/16" nylon shock cords with Kevlar or is there some treatment I can apply to the nylon to make it more heat resistant? Or should I not worry about it? Thanks in advance.

Regards,
Mike

 

[Karl]

The Nylon strap should hold fine! I have seen incidents where it has burnt through at ejection , but this is rare! If you want to reassure your self , replace the Nylon with Kevlar.
-Karl

 

[als57]

Originally posted by rocketgroupmike
Hi, all. I've been lurking around here for a couple of months, and this is my first post. I'm another BAR, having flown Estes kits in the early 70's, and I now have a PML Sudden Rush spread out on my workspace. My question is this: Should I replace the 3/4" by 1/16" nylon shock cords with Kevlar or is there some treatment I can apply to the nylon to make it more heat resistant? Or should I not worry about it? Thanks in advance.

Regards,
Mike

Mike:

If your building it with the piston ; I replace the strap on the motor mount side with kevlar. Found the 5/8" tubular kevlar Magum sells is a good replacement.


Al

 

[Todd Knight]

My Sudden Rush probably has 6-7 flights on it and the nylon strap is a little crispy but still solid. Doing it again, I would use Kevlar.

Flys great on I-211s and 4-grain Pro 38s.

 

[Hospital_Rocket]

I'm simutaneously building a Sudden Rush CP3K and a Endeavor

If I replace the Nylon with Kevlar, is there a sizing factor? is 1/2" Kevlar as Strong as 1/" Nylon? should the Kevlar be thicker or thinner for the same strength of similar sized Nylon?

 

[Todd Knight]

Originally posted by Hospital_Rocket
O'm simutaneously building a Sudden Rush CP3K and a Endeavor

If I replace the Nylon with Kevlar, is there a sizing factor? is 1/2" Kevlar as Strong as 1/" Nylon? should the Kevlar be thicker or thinner for the same strength of similar sized Nylon?

The 1/2" Kevlar is plenty strong. Only use it between the ejection charge and the piston. Use the supplied Nylon forward of the piston. If you don't, you may run into space issues in the drogue compartment (Kevlar will not pack as tight as the nylon). The only issue would be the possibility of a zipper with the smaller tether but these rockets are light enough to not cause a problem.


Also, hook up with somebody who is familiar with the CPR3K to help you set it up the first time. It can leak into the electronics if you are not careful. Make sure you check the O-rings before every flight and fill the extra space where the e-matches pass thru the charge bulkhead (I use some Estes wadding jammed in with a small screwdriver.

 

[rocketgroupmike]

Thanks, all, I've ordered the 1/2" flat kevlar from Magnum for the piston straps only. I will use the stock tubular nylon for the rest of the recovery harness. Happy flying!