Check your rubber!

I bought an Estes CC Express about a year ago and built the rocket around 9 months ago. Until last weekend when I decided to fly it for my younger grandson, it had been stored indoors. I'd built it exactly in line with the instructions.

We flew it without the second stage on a C11-5 motor. I'd lowered the fin height a few millimetres to bring the calibre ratio slightly under 2.

The flight was perfect, the 2 metre streamer with "congratulations on your 3rd birthday" falling impressively to earth. Only problem was that it was attached only to the nose cone. The rocket fell quickly, alone, and apart from the cone, landing on the sun baked field. One fin damaged but easily repairable.

On inspection the elastic shock cord was perished and had broken. It wasn't visible before the flight but obvious when I pulled it easily to pieces with evidence of crumbling at the break.

I don't like elastic shock cords and rarely use them. A good idea maybe but a bit like assembling cold tagliatelle.
Anyway, my message is - check your Estes shock cord. If it breaks before it stretches, don't use it.
I'm sure this was a rogue batch of rubber and not the norm for Estes. Maybe the fault lay with the supplier in selling old stock?

Good news is that my grandson was greatly impressed and wasn't particularly worried about the minor detail of shock cord failure. The streamer is now pinned to his bedroom wall, he's convinced that it's been to the moon and back.
Hopefully another convert to rocketry in future years?

SO.

Yep, that happens. The rubber dry rots; I went through a bit of that last year when I started resurrecting my fleet from the late '80s/early '90s. I don't use the rubber chord for anything these days. Its probably not long enough anyway.

Six feet of 1/8" Kevlar is a good upgrade for any Estes LPR kit.

When getting rockets ready for the weekend, I give the shock cords a pull and look for signs of drying out or ragged edges. Replace as necessary. Rubber is cheap, works, and generally doesn't zipper.

Yup, practice safe launching...always check that your rubber is good.

I just started building an Estes Mega Der Red Max. The first thing I did was throw away the elastic shock cord.

Ever since this flight two years ago I never use elastic shock cords . . .

The white rubber has additives and colorants in it that reduce the life. For a longer lasting shock cord, ditch the Estes stuff and replace with model airplane rubber motor stock. It is tan color, much more pure and lasts a really long time by comparison. In the old days Estes actually used it. Check out www.faimodelsupply.com - they have 1/16 through 1/4" width, and it's not that expensive, 32ft of 1/8" for $3 and change. Or you can buy a 1lb box for a near lifetime supply. Or try decent sewing elastic which also has pretty good life and fails more gracefully by losing its stretch rather than abruptly breaking. Some people don't like it but I've always had good luck with it, and it will not zipper your model.

+1 on Elastic
I've used sewing elastic in 1/8" to 1/2" since early 70's.
I raided my mothers sewing draw until it was empty and then had to ask her to buy some.
This after my first scorched and broken rubber shock cord.
Takes a lot to burn through the elastic compared to the rubber.

Yep, elastic all the way here! I used to check my rubber after every launch. I even cleaned it, but I'd find holes and cracks when I'd stretch it out. A recovery failure after a couple of reuses made me rethink my rubber.

hornet driver said:

Yep, elastic all the way here! I used to check my rubber after every launch. I even cleaned it, but I'd find holes and cracks when I'd stretch it out. A recovery failure after a couple of reuses made me rethink my rubber.

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Holes in your rubber is never a good thing.

lcorinth said:

Holes in your rubber is never a good thing.

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That's what she said!

The rubber embrittles with age and exposure to ozone, UV, and certain chemicals. I replace the rubber with kevlar and sewing elastic.

RocketT.Coyote said:

The rubber embrittles with age and exposure to ozone, UV, and certain chemicals. I replace the rubber with kevlar and sewing elastic.

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I use the same recipe. I have the Kevlar end with a loop just slightly below the top of the tube, to prevent body tube zippering. The elastic cord can easily be replaced when it starts to fail. It's cheap at fabric stores like JoAnne's.