This blog covers the day to day progress of water rocket development by the Air Command Water Rockets team. It is also a facility for people to provide feedback and ask questions.

Monday, July 28, 2008

Testing, testing and more testing

With the NSWRA launch day being postponed this weekend due to unfavorable weather conditions, we spent more time in the workshop testing all sorts of things and building a new two stage rocket that will use the Mk2 Stager.

First we pressure tested the new 3.35L sustainer to 120psi. It is using a new bottle we have not used before so we were curious to see how well it would hold up. Then we pressure tested the reinforced FTC to 180 psi. 180 psi will be the first launch pressure of this rocket. This is the actual FTC pressure vessel we will be using for our first FTC flights. The nozzle and end-cap are already attached and the entire length of the FTC has a single wrap of glass strapping tape.

After some recent great discussions on the Yahoo water rocket forum, about thermal properties of bottles, we spent some time doing thermal tests on how warm the air gets inside a rocket during pressurisation. This is important as high temperatures can weaken a bottle. The glass transition temperature for PET depends on a number of factors but can be as low as 69 degrees C.
Wikipedia lists this temperature as 75C.

"The glass transition temperature, Tg, is the temperature at which an amorphous solid, such as glass or a polymer, becomes brittle on cooling, or soft on heating. "

We are in the process of collating the information and we will try to publish it sometime this week.



Anonymous said...

Hi Geroge
If you fill your rocket slower with AIR? wouldnt that make the bottle less brital an less chance of stretching?

George Katz said...

Yes, the idea is to fill slowly so the compressed air has enough time to cool as the pressure grows. There are other factors that affect the temperature of the air and the temperature of the bottle walls.