Replacing shock cords

[sjlee]

Hi all,

New member here. I was into rocketry back in middle school (30+ years ago) and still have all my old stuff jncluding a few rockets. My son has shown an interest, so I am hoping to launch some of these old ones to show him what a launch looks like.

All the shock cords need replacing as they are all brittle. I removed as much of the old cords but was wondering how to remove the mount... if at all. I apparently did a decent job gluing them in because they are not loose at all.

I have tried peeling them off but the glue is holding firm. I don't want to try prying them off as I may damage the tube. Can I just glue a new mount over it or maybe glue the new one opposite the old one?

Thanks in advance for any help.

 

[Conway Stevens]

If you can get something downing to where the old one mounts and cut it that would work better then trying to peel it off. A razor blade with long reach needle nose plyers would work or something similar. Then just add a new one across from the old one. You didn't mention what size the rocket is? There are other attachment methods possible depending on the the rocket and motor set up.

 

[sjlee]

Thanks for the reply. This is for the original Estes Black Brant II. It takes a D12 engine. I actually never launched it. I built it over the summer and ended up moving so I never got a chance.

The parachute and shroud lines all seem in good shape.

That mount is really on there. I will try using a razor, but any issues with simply leaving it?

 

[o1d_dude]

I don’t see leaving it there to be an issue. Assuming you’re using the standard Estes glue-and-fold method just mount the new shock cord wherever there’s room...as long as it doesn’t interfere with the nosecone.

 

[sjlee]

Thank you for the help. I used a blade to get as much as I could off then just glued a new mount across from it. Worked like a charm because I was able to launch it twice this afternoon. Parachute needs to be replaced now... as it got a little melted. Next time use more wadding I guess.

 

[mtnmanak]

Thank you for the help. I used a blade to get as much as I could off then just glued a new mount across from it. Worked like a charm because I was able to launch it twice this afternoon. Parachute needs to be replaced now... as it got a little melted. Next time use more wadding I guess.

When (not if ) you need to need replace those old estes elastic cords, I recommend cutting off as much as you can like you did, then, if you can reach it, I use a dremel on slow speed to sand it down carefully. It doesn't need to be perfect, just smooth enough so nothing catches on it.

then, I personally like to forego the estes three-fold paper mount altogether. For a new build, I would use some kevlar string (appropriate size for the build) wrapped around the motor mount. I like to use a length of string just long enough to reach the end of the body tube and make a loop there (to prevent zippering. Attach the elastic shock cord to that. The kevlar string will last a long time and you greatly reduce the risk of something getting snagged in the body tube at ejection.

For a retro-fit on an older bird. I drill a hole just fore of the motor mount and feed the kevlar string in that way. On the outside of the rocket, I glue the string down the base of a fin and re-fillet. Easy to paint over it (or, just leave it if the build is really old) and no one is the wiser.

The pics below are of an old Estes Ventris my son and I made years ago. We were digging it out for a launch a few weeks ago and found the shock cord and parachute were unusable. We replaced everything as per above, including a swivel for the parachute and a nomex blanket to shield the cord and parachute from getting fried. It was an ugly fix on the outside, but we didn't care about looks for this rocket, we just wanted to fly it.

 

[mtnmanak]

Thank you for the help. I used a blade to get as much as I could off then just glued a new mount across from it. Worked like a charm because I was able to launch it twice this afternoon. Parachute needs to be replaced now... as it got a little melted. Next time use more wadding I guess.

Highly recommend switching from wadding to "dog barf". Dog barf is the cellulose insulation you can get in bales at any home depot/lowes. By law, it must be fire proof and, these days, it is all pretty much bio-degradable, so it is way more environmentally friendly than the Estes wadding. And, it works better. Just dump a loose handful in the tube, and you're good. Just about any club that launches on a working farm these days will not allow the Estes wadding - just dog barf. I even use it in my high power rockets as additional protection (in addition to a nomex blanket, etc). For about $15, you can get enough dog barf to last you years.

 

[BABAR]

Two issues either replacing an old tripod mount,

First, if you can’t get all the old mount off successfully, you leave an effective thorn or hook which may impinge on the smooth exit of the current chute. One method is to get off as much of the mount as you can, use a dremel sand drum to get as far down the tube WITHOUT damaging the tube. You can cover the any residual rough edges with a piece of cardstock with white glue, blow up a ballon inside to really force it to lay down smooth against the curve. Pop or otherwise deflate the balloon when done

Second, placement of a new cord.

Obviously put in new trifold mount.

If looks aren’t an issue, drill a hole in the rocket somewhere above the forward centering ring, run the cord through the hole, wrap a loop OUTSIDE THE ROCKET AND KNOT IT (you can feed the not through the hole), and put a wrap of vinyl or Mylar tape around the outside loop. Can use colored tape if you want to get fancy.

A third, more aesthetic but challenging approach, is to use a long drill bit to put a hole drilled from back to front through the rear and forward centering rings. This allows you to place a new shock cord that can easily be inspected and replaced if requires, and does not mar the interior of the smooth surface of the rocket in a way that may interfere with chut deployment.

Basically a retrofit following @hcmbanjo ‘s method here

https://www.apogeerockets.com/education/downloads/Newsletter338.pdf

 

[jrap330]

Thank you for the help. I used a blade to get as much as I could off then just glued a new mount across from it. Worked like a charm because I was able to launch it twice this afternoon. Parachute needs to be replaced now... as it got a little melted. Next time use more wadding I guess.

BBII. Guaranteed to lose it on D12...buy the 18>24mm red convertors and launch on 18 mm...try a B6 and C6. Of course you could just add another mount...little harder since BBII is skinny...but you did it. Not sure about drilling thru cardboard centering rings for Kevlar like Babar suggested. Read the Handbook of Model Rocketry along with your kid