How to reattach shock cord to Estes PSII rocket?

[billdz]

Hi,

On the last flight of my Estes Mammoth, the shock cord broke free of the rocket. The kit came with the 2-piece plastic shock cord holder, and it appears one piece of the holder broke off and the shock cord slipped free. Any thoughts on the best way to get the shock cord securely reattached?

Thanks,
Bill

 

[neil_w]

Is that a pure Kevlar shock cord (i.e. no elastic)? If so, that's potentially a lot of shock being applied to that plastic shock cord mount. Although maybe if it's pretty long it's not an issue, dunno.

Regrettably I have no good suggestion to offer you on how to reattach it, hopefully someone else will.

 

[K'Tesh]

If you can, you could drill a small hole in the CRs between two of the fins. Then, using a straw to act as a guide, fish a Kevlar line into it after tying a loop on both ends. Attach another shock cord to the internal loop. The outer loop is looped over the engine retainer.

 

[billdz]

Is that a pure Kevlar shock cord (i.e. no elastic)? If so, that's potentially a lot of shock being applied to that plastic shock cord mount. Although maybe if it's pretty long it's not an issue, dunno.

Regrettably I have no good suggestion to offer you on how to reattach it, hopefully someone else will.

The original elastic cord was attached to the plastic mount, and I added some kevlar to make the cord longer.

 

[neil_w]

The original elastic cord was attached to the plastic mount, and I added some kevlar to make the cord longer.

Ah, OK.

 

[billdz]

If you can, you could drill a small hole in the CRs between two of the fins. Then, using a straw to act as a guide, fish a Kevlar line into it after tying a loop on both ends. Attach another shock cord to the internal loop. The outer loop is looped over the engine retainer.

Thanks, that may be my only choice, although it won't be easy on this long, thin rocket. Is it necessary to glue up the holes to prevent the ejection force from leaking through?

 

[kuririn]

KISS
Method 1.
Cut a rectangular piece of scrap heavy wall tubing.
Tie a knot on the end of the shock cord.
Epoxy the rectangular piece to the rocket body with the shock cord in between and the knot exposed at the other end.
When dry epoxy a film coat to smooth any exposed edges that can snag the recovery gear (especially the knot).

Method 2.
Get a length of nylon string and tie knots at both ends.
Embed the ends of the string in an epoxy bed inside the body tube.
When dry do a film coat as in method 1.
This will form a nylon loop to which you can attach your shock cord.
This is the method LOC uses for some of their mid power kits.

I'm too lazy to go hunting for pictures, but let me know if you need them, I'll get them.

 

[dr wogz]

+1 on Kuririn's 2nd method, but I cover my 'epoxy globs' with masking tape. Seems to make a more smoother 'blob' inside the tube.

You can also drill a small hole (1/8" dia) thru the body tube, about 3 or 4 " down from the top of the tube. Insert a stick, a chopstick, thru the holes, and glob epoxy on the stick / wall joint. sand the stick smooth to the BT on the outside (not really a great method, but can work)

 

[K'Tesh]

Thanks, that may be my only choice, although it won't be easy on this long, thin rocket. Is it necessary to glue up the holes to prevent the ejection force from leaking through?

If your holes are not much larger than the Kevlar, then no. The cord should be enough of a plug.

 

[BEC]

Others will consider this sacrilege but.... you could simply make a large Estes tri-fold style mount out of light cardstock, and in this case perhaps install it with epoxy rather than wood glue. Clean the tube of ejection residue off the inside of the tube where it will go with a stiff old toothbrush or a bit of sandpaper wrapped around a dowel first.

The first series of builders’ PSII kits (Leviathan, Ventris, Mega DRM, etc.) used this method and it works just fine as long as one doesn’t ”improve” the rocket with a bunch of extra weight.

If you want to retain the Kevlar leader, maybe tie a knot in the end so that the knot is well inside the tri-fold might be worthwhile.

I’ve just finished a LOC Weasel and used the knotted nylon string/epoxy method as directed by the kit’s instructions (per Kuririn’s post) but I haven’t flown it yet so don’t know how well it will hold up or how much it will be in the way of ejecting the ‘chute.

 

[jrap330]

Everyone uses Kevlar but since Estes does not provide Kevlar w/kit, I still used Estes tri-fold method or G. Harry Stine's index card or card stock, cut two slot and weave cord in and out thru the slots like a belt. Glue that into tube. Much easier the fishing down the tube and trying to attach to the centering ring. Guys sometimes simple is the best.

 

[jbuscaglia]

Others will consider this sacrilege but.... you could simply make a large Estes tri-fold style mount out of light cardstock.

That's what I did when I first built my Mammoth. That plastic mount just looked like a bad idea to me. No problems so far in about half a dozen flights with BP Fs.

 

[billdz]

Thanks for the replies. Several good suggestions, I'm not sure which one to use. I've never tried the Stine method, looks interesting.

 

[jrap330]

Simpler.....no folding paper, using index card or card stock which is stronger and since it is flat vs tri-fold., .if you have worries about chute catching....there are no worries. Just cut 2 slits and weave the cord in/out..just like some belt buckles. Sometimes I tied a knot at end shock , so it can not slip out to ease my mind.

 

[kuririn]

Simpler.....no folding paper, using index card or card stock which is stronger and since it is flat vs tri-fold., .if you have worries about chute catching....there are no worries. Just cut 2 slits and weave the cord in/out..just like some belt buckles. Sometimes I tied a knot at end shock , so it can not slip out to ease my mind.

That is the same as the Stine method.