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080519-001 - FTC Burst tests
Date 19th May 2008
Tested by PK and GK.
Location Sydney, Australia
Test Procedure Burst Test
References http://www.aircommandrockets.com/day60.htm

Aim

  • To test the failure pressure of regular T8 FTC.
  • To test the failure pressure of glass strapping tape reinforced T8 FTC.

Experiment Setup

The standard hydrostatic burst test procedure was used to carry out these tests. (See above)

The FTC used for these tests only has an average wall thickness of 0.36mm. We made an end-cap out of some PVC we had on hand and the nozzle is based on a 15 mm Gardena nozzle. The one we bought from the local hardware store came with an outside thread. We machined an adaptor with a matching thread that fits snugly inside the FTC. We then epoxied the nozzle inside the adaptor. The seal for the end-cap and nozzle is provided by an o-ring that sits against the FTC. Just behind the o-ring is a groove that allows us to shrink the FTC into it to hold the end-cap and nozzle in place. We copied this technique from Urie's water rockets.

To secure the end-cap and nozzle we wrapped a couple of loops of thin fencing wire around the FTC just over the groove. We then apply heat from a heat gun to the FTC while applying tensile stress to the wire. This allows the wire to deform the FTC into the groove. We then let it cool down and twist the wire closed. For the first test we used a 1 foot length of the FTC and secured the end-cap and nozzle at either end.

Results

Test #1

FTC just after the 190psi burst test.
Detail showing where the wire sits in the groove at the nozzle end.
Burst location.

We hydrostatically tested the FTC to 190 psi before the FTC split. The end-cap and nozzle held and that there were no leaks.

Test #2

We hydrostatically tested a 1 foot length of FTC wrapped with one layer of fiber glass strapping tape. We also added a number of extra wraps of the tape around each end right near the o-rings to help with the seal.

FTC test with glass fiber strapping tape reinforcement.
At 230psi the end cap came out. The flare at the end of the FTC was due to the heating process and normally would be removed for a real rocket.

As we reached 230 psi the end-cap flew out of the FTC. It looks like the groove in the end-cap was not deep enough and the wire probably loosened where it was twisted.  This allowed the end-cap to slide past the wire. There was no damage done. The single layer of tape added 7grams to the 1 foot length of FTC. 



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