Wire Rope Part of Shock Cord

[teepot]

A couple of years ago I was using wire rope as a leader. Would wrap it around the motor tube and crimp it. I would use about 6" of wire. Would crimp a loop on the other end. The Kevlar tangled with the cable and the chute didn't come out. Now it's just Kevlar.

 

[sharkbait]

A couple of years ago I was using wire rope as a leader. Would wrap it around the motor tube and crimp it. I would use about 6" of wire. Would crimp a loop on the other end. The Kevlar tangled with the cable and the chute didn't come out. Now it's just Kevlar.

All the really, really old school guys that were in our club used steel leaders, don’t see much of anyone using them anymore here. Kevlar leads are fine or protected nylon. One trick that I use to protect the harness is using a small party balloon that I pack with dog barf, slip over the charge well and secure with a wrap of tape. This catches the brunt of the blast of hot gases and burning particles of BP and you don’t need to take up a bunch of space with a huge pile of dog barf in the airframe of which most doesn’t provide any protection. I use nylon with fiberglass sleeves from McMaster-Carr on the bottom 2’ or so and a chute blanket also. My recovery gear is also washed in the washing machine at the end of each season, all looks pretty much like brand new

 

[Dave S.]

I have not flown this rocket yet, but I am confident this will be fine. After I made the first loop/crimp, I slid on two heat shrink tubes, then made the second loop/crimp. After using the heat gun on the tubing, I attached the shock cord and put heat shrink on that.

These pics should be self explanatory:

 

[Dave S.]

It doesn't show it in the pictures, but afterwards I plugged the two holes for the wire rope and that slot in the centering ring w/ epoxy. I did that to prevent gas from the ejection charge from leaking thru & reducing the pressure that would pop out the chute. This is a 4" diameter rocket, and the smaller the volume, the higher the pressure from that charge going off.

 

[lakeroadster]

It doesn't show it in the pictures, but afterwards I plugged the two holes for the wire rope and that slot in the centering ring w/ epoxy. I did that to prevent gas from the ejection charge from leaking thru & reducing the pressure that would pop out the chute. This is a 4" diameter rocket, and the smaller the volume, the higher the pressure from that charge going off.

Dave,

Does the cable wrap around the tube under the ring where we can't see it?

 

[Dave S.]

lakeroadster - I didn't wrap the wire rope around the MMT tube like in your image.

If the motor itself was not long enough to go thru that section on the MMT tube where the wire rope was wrapped around, then its possible the tube would get crushed when the shock cord gets yanked when the charge goes off.

My pictures are from a 4" diameter HPR kit under construction.

 

[lakeroadster]

lakeroadster - I didn't wrap the wire rope around the MMT tube like in your image.

If the motor itself was not long enough to go thru that section on the MMT tube where the wire rope was wrapped around, then its possible the tube would get crushed when the shock cord gets yanked when the charge goes off.

My pictures are from a 4" diameter HPR kit under construction.

Aren't you worried about the cable ripping out of the centering ring? I "wood" be. Seems like the weak link.

 

[Dave S.]

That area is strengthened by epoxy. The epoxy holding the ring in place is generous. I basically copied the idea from previous kits I have built.

 

[Rocketjunkie]

... the cable and end fittings are magnetic.

All 300 series stainless steels are non-magnetic and can only be hardened by cold working. 400 series are magnetic and can be heat treated. I don't know of any cables made from 400 series stainless. It has to do with the micro structure. 300 series contain chromium and nickel and are austantic. 400 series only contain chromium and are martensitic. If magnetic, you probably have galvanized steel. The cable shown in my pictures is 1/8" diameter steel. It has lasted the 75 flights of this rocket and is still usable.