"Dry" testing of a Hybrid motor

Morning all,

I have just about finished assembling my ground control equipment for firing Hybrid motor equipped rockets, and I was wondering about doing some "dry" test runs. By that, I mean testing the equipment and motor together with something like CO2 instead of N2O, to check for leaks, monitor the fill time/vent time, and also to possibly test the performance of the GOX/HV ignition system.

Can anyone see any potential issues with doing this? CO2 has very similar properties to N20, so should behave in a very similar fashion, with the exception of it supporting combustion.

Also, does anyone have any tips for the testing of ground equipment, such as things to avoid, things to double check, etc etc?

Cheers
Andy

What type of hybrid are you talking about?

Are the temperatures of CO2 and Nitrous the same?

One thing to consider is that if you dump cold gas down the core of the motor, you risk inducing small cracks which will cause the grain to fail on a real burn.

-Kevin

The motor I currently have is based on the skyripper 29mm hardware, but I'm going to be using my own fuel grains machined from nylon an PVC bar. Chucking a fuel grain after a dry run won't be a problem.

The temperatures and pressures involved are broadly similar to n2o, although obviously if I test the ignition, I'm not going to get many flames

Cheers Andy

With a disposable grain, testing shouldn't at all be a problem.

Just keep one grain marked for "testing" (maybe drill a hole through the side, so you can readily identify it?).

-Kevin

Why not test with N2O? It seems to be much more of a hassle to get a CO2 cylinder all setup for a test than using what you'll be using.

Edward

AlphaHybrids said:

Why not test with N2O? It seems to be much more of a hassle to get a CO2 cylinder all setup for a test than using what you'll be using.

Edward

Click to expand...

CO2 won't ignite if he does an ignition test, which i think is required since the grain breaks the seal to the fuel tank? (is that right, i've never even seen a disassembled hybrid motor :O)

Perhaps the main reason for wanting to test with CO2, is because I have a 16lkb bottle of it in my workshop, that is destined to become my N20 transport bottle, just as soon as it is emptied. I figured rather than just venting the contents off, I could put them to good use? I've already used as much as I can for all the welding jobs that I needed to do

The motor I have uses a central nylon tube to fill the N20 (or CO2 in the test case) that is severed on ignition, allowing the N20 to flow through the central bore in the grain. I'm keen to optimise the ignition system, but not fire the motor whilst doing so....

Andy