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.
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.
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.
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.
On 14-Dec-2006, email@example.com wrote:
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).
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.
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...
Vertical, facing nozzle down. It's also important to have
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
do. The certification testing is only one snapshot of the motor's
based on the temperature and procedures done by the certifying group.
someone questions the performance using their own fill equipment and
fill tank temperature controls and the local launch temperature, they
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
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
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
idea than ruining a load cell!
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 www.back2bed.com/rockets/static2.wmv showing
Skyripper G69 motors.
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