Wednesday, April 23, 2008

10 Points for Damien

Recently, I've been working on integrating my test setup onto a trailer so that I'm not constrained by working in the garage. I haven't had any complaints but I felt that doing 60-90 second burns might be pushing my luck in the future.

Last night was the first attempt at using the trailer to test and I was very pleased with how it all turned out. It took almost exactly 1 hour from the time I arrived home from work to the first test. During that time, we loaded the van, drove to the test location (about 10 minutes), and setup the electronics on-site. There were no issues with the test stand and everything worked correctly the first time.

If only the rocket motor were so easy ...

video

The light sequence is very reliable. I actually had two lights that are not shown in the video - for the day, the motor was 5 for 5 on light attempts. Unfortunately, there is still a fairly high pressure spike at ignition that was triggering a redline on chamber pressure. I had lowered the chamber pressure redline to just a tiny margin above the design maximum - the startup spike is around ~25% higher than that. On the first two tests of the day (not shown in the video), the software redlined at engine start and aborted the test. For the the first two tests in the video, I raised the redline limit and the motor started fine and executed a scripted throttle profile. On the last test, I knew that there was probably a damaged seal in the throttle valve but I decided to initiate a test anyway (the venting between the second and third light is a result of the damaged seal). The end result of that test is obvious - another blown gasket.

I'm not sure yet what the exact cause of the blowout was - the data did not show a pressure spike that was larger than any of the previous tests that day. I have not yet reviewed the data in detail nor have I disassembled the motor to inspect it.

So I have three problems to solve with this motor right now:

1) Pressure spikes at start up - I think I have a plumbing solution to this
2) Blown gaskets at start up - I think solving 1) should help solve this one. Maybe a new gasket material is in order.
3) Repeated failures of valve seals - More on this later

PS - Damien gets 10 points. The propane bottle can be seen in the video at the center of the screen. However, I would not call it a "torch".

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