Bottle Reinforcement

We learned from our first on pad explosion that our 1.5L Lipton Ice Tea bottles need some reinforcement. The bottom of the bottle as you can see in the pic below sinks in quite a bit, approx 10mm and this is the first section to expand when pressurized. As there are many (12 or so) crease lines in the plastic, when it expands it has many weak points, hence this is where it let go

Lipton Ice Tea Bottle (bottom)

Lipton Ice Tea Bottle (bottom)

You can also make out the panels in the side of the bottle, its not round. Not a perfect water rocket body, but its what we have available. We strapped the bottom of the bottle with plenty of duct tape that has material inlayed in it. Also the sides were strapped to provide further reinforcement.

Re-inforcement1

You can see the reinforcement yellow strapping through the nosecone

The tail section from SRT was a bit clumsy to get at the nossle, the solution to this was to just trim out the sections between the fins up higher to that it was easier to access the nossle. This still allowed the fins to be mounted further back for better stability.

The fins were also too long as the rockets weight would sit on the fins and bend them. So I just trimmed them up higher than the three bottom sections of the fin ring

Fin assembly showing the cut outs also shorter fins and section sfor the rocket to rest on

Fin assembly showing the cut outs also shorter fins and section sfor the rocket to rest on

You can see now the fins are above the bottom of the rocket and it can sit on the three sections of the fin ring to support its weight. The fin ring is secured by skewers to the main bottle.

So SRT II was ready to fly on our next outing

SRT II

SRT II

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This entry was posted on Friday, July 18th, 2008 at 8:48 am and is filed under Development. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

 
 

3 Responses to “Bottle Reinforcement”

  1. ishra 123567gre Says:

    when i use three fins the rocket does not stay stable .any idea how to prevnt this

  2. todd Says:

    Three fins are fine, what you need to do is ensure the centre of pressure is behind the centre of gravity of the rocket. Check this link for an easy way to tell where your CG and CP are on your rocket.

    http://www.info-central.org/design_cg-cp.shtml

  3. ishra 123567gre Says:

    thanks