Rocket explosions

[chriswaterrockets]

Yesterday we had a family reunion and I was asked to launch few rockets. So we went down into the fields, set everything up, pressurized the rocket and...BOOM!
One splice failed at about 8.5 bar (123 psi). That was the first explosion I had...
Anyway, my question is how many launches can a spliced pair take? Do you have any experience? I know it depends a lot on how the splice is made, the glue used, launch pressure and so on.
I tested this pair to 10 bar (145 psi) and I used it maybe 15-20 times. So actually it's not surprising that sooner or later it fails.
The damage was minor. I had one of my aluminium guide rails bent and the splice of course, but the chute section and altimeter were fine.

So, how do you do it? Do you use a splice like 10 times and then throw it away or do you use until it blows up?

[dongfang]

Hi,

Can you post some pictures of the failure? Which bottles were that?

In my experience (with PU Max = polyurethane), the strength of a splice does not change over time. I just fly them until they get too much parachute-failed crash damage; something that happens often here

I have had many rockets made of 2 liter bottles fail in test, at about 6.5 .. 8 bar. Looking closer at it, it appears that they always started failing next to the splice, not in the splice: Where I had roughened the bottle wall for glueing, but not covered by the other bottle.

Next time I build them, I will leave the first 1/5 or so of the splice smooth, roughen the next 3/5 and leave the last 1/5 smooth again.. or something like that.

Regards
Soren

[chriswaterrockets]

Hi Soren,
Unfortunately I don't have any pictures, sorry. I'll take some next time around...
Thanks for the info anyway. Your idea about the sanding sounds good, I think I'll do that too.

[team-helder]

boom

[U.S. Water Rockets1]

It's amusing to see these scenes play out where the rocket explodes and then the crowd that gathered around starts clapping and cheering because they assumed that was that was supposed to happen.