Static testing a hybrid motor

Why would you want to test a hybrid? I mean if one is mixing APCP research motors and they want to see if they correlate to their calculations I can see the interest in testing. I think the hybrids have been characterized and unless there is something the user can do to modify the nozzle or some other parameter, what would be the use other than curiosity? Indeed I'm coming from the point of view of no experience with hybrids. I'd email the folks that do the testing at Tripoli or NAR and see how they safely set up their test stands.

Kurt

I'm not an expert but think it through, in the gas chamber there is N20 in both gas and liquid forms, the best burn comes with using the liquid which only happens with gravity working for you.

Lets see what others say...

Halam

Vertical, facing nozzle down. It's also important to have sufficient weight and/or staking to make sure you don't fly the test stand!

I think testing hybrids is a reasonable thing for some end-users to want to do. The certification testing is only one snapshot of the motor's performance, based on the temperature and procedures done by the certifying group. If someone questions the performance using their own fill equipment and fill tank temperature controls and the local launch temperature, they might want to test the motor before putting it into a high-value rocket.

Another good reason to have a hybrid-capable test stand is to work on your own motor modifications and fuel grains, under Tripoli Research rules, or as an independent amateur rocketeer.

It's less important to test a commercial solid rocket motor, unless of course you have bunch that've been around for a while and you question the performance. In that case, sticking one in a hole in the ground is a better idea than ruining a load cell!

-John D.

What John said.

Another reason to static test hybrids - familiarization with hardware and GSE, and getting an estimate of fill times for various motors. I static test every new motor system I get, just to be sure I've gotten the assembly and operation correct. Better to do so at home than at the field. Test, test... then test again.

Static stands need not be complicated. A vid of a picnic table + block of rock hybrid stand is at

Kevin O

I want to develop my own fuel. One with lots of smoke. So far the hybrid grains I have purchased have little smoke and it is hard to track them if they go very high.

Kimball

Cool Video. Looks like you are testing a cluster set up. Were you happy with the dual ignition?

KT

Yes. They lit within 1/30 second of each other on two consecutive tests. Should be just fine if I can replicate that in the field.

Kevin O

Well,

That's a good reason. I guess you saw where folks stated you have to have the motor upright. I hope you come up with something better than that picnic table and the flexing board routine. Was entertaining but if the board or weight doesn't hold, could make a mess of your motor.

Kurt

I design test stands for 500,000 lb thrust rocket motors for a living... So a little hybrid should be no trouble. However, I did enjoy the simplicity of the board and brick test stand.

KT

How might I go about getting one of those rockets that were on that test stand?

hmmmmm....

-Aaron

Bring about 8 million and a LEUP. Plus shipping.

KT

I saw this and thought of you

I wonder what the purpose was of lighting the motor off with an 8 inch gap between the slide mechanism and the button load cell? Can't get very accurate thrust loads out of that. One thing was apparent, He lit it horizontal, unless he had his camera turned 90 degrees..ha ha.

thanks for the video.

KT

I left out the word "was" in the sentance above.

Anyway, I also wanted to say that this looks like an easy test stand to build. There will be friction loss but for hobby stuff who cares. I could mount one of these vertical on the back of my pickup or on a vertical wall or post. I would want to put a spring under the motor slide assy if I hang it vertical to keep the slide assy up against the loadcell (also applys preload to the loadcell, a good thing).

kt

Maybe its to give that neat recoil jump...

You'll still have no smoke during the coast phase. I used to fly the Aerotech hybrid, including a manufacturer demo flight on an all AP fuel load that produced very heavy smoke. But at burn out the smoke is over.

My favorite way to handle this was to air start several long delay G motors at burnout of the hybrid. Makes for a cool flight that's easily tracked.

Dave

Thanks for the advice Dave. I'll have to try something like that.

Kimball