Jan 02, 2001 meeting notes
Jan 02 meeting notes:
Location: Long Range Systems
Next meeting on Thursday at 6:15 for more engine tests!
The X-L peroxide finally came in today. The freight charge was $175.
Because it is 31 degrees here right now, the stabilizing water was frozen around
the peroxide jugs.
The five gallon sample jugs have spigots on them, which makes dispensing test
samples very convenient, although it does drip a bit after closing. We
were expecting to have to make a vacuum pump to siphon it out, but this works
great. The lead time on this order was pretty long, but there were some
issues with X-L dropping support for 90% during the processing of our order (we
changed it to 98%), so I hope the next batch goes through faster.
I was concerned about the very cold peroxide, but as Michael warned us, it does
heat up noticeable when you mix distilled water into it, so it wasnt a
problem. I would like to hear an explanation for this heating behavior, if
anyone has any ideas.
We made three test firings with 85% mixtures: The first one was at 200 psi
with the .040 jet, the second one was at 400 psi with the .040 jet, and
the third one was at 400 psi without any jet at all and twice the peroxide
(200ml total). The results are available in Excel format at media.armadilloaerospace.com/misc/jan02.xls.
The jetted flow was definitely less than last time, due to the far denser
catalyst pack in the current motor.
We saw excellent catalytic reaction on all of them, with the exhaust turning
completely transparent after the first half-second or so. We took video of
it, but there isnt much to see with it working well
There are two factors that changed since our last test runs: we are using
X-L peroxide instead of our self distilled, and the catalyst pack is compressed
to 3x the density instead of loosely packed. We didnt intend to change
two factors, but Russs still cracked in the cold weather before we could try
the compressed pack with our stuff.
When we disassembled the motor, the nozzle side of the pack was pristine, so we
dont seem to be washing the catalyst off, either.
The only problem is that we only got about half the thrust we wanted.
Removing the metering jet only made minor differences in the flow through the
engine, even though it makes a huge change when water testing without chamber
We are limited right now by the nozzle size. Russ is going to drill out
the nozzle tomorrow, and we will test again on Thursday. The current
nozzle might be roughly appropriate for an AP motor, but for monoprop peroxide,
it has both too small of a throat and too large of an expansion ration.
Juans specs for the 100lb motor are:
300 psi chamber pressure
0.245 in2 throat area (0.56 diameter)
0.895 in2 exit area (1.07 diameter)
Scaling down to something in the 15lb thrust range would give:
0.036 in2 throat area (0.22 diameter)
0.134 in2 exit area (0.41 diameter)
Russ: measure the current size exactly for our records before cutting it out.
You should also measure your big motor.
I am guessing that the pulsation at the end of the third run is caused by the
chamber pressure being very close to the supply pressure, instead of having a
healthy drop across the pack.
We might also want to add some more foam disks at the nozzle side of the pack,
even if they arent silver plated, just to reduce the open gap at the
injection point. Our 200 msec warm up pulses werent even enough to get
it solidly pushed into the pack in the current form. Both the slightly
shorter pack and the longer feed hose contributed.
I brought a bunch of chemistry glassware for dealing with the peroxide. We
still need to get a better washing facility than the sink on the other side of
The new 3 hose, 90 degree fittings, and 45 degree hose ends for the VTVL
platform are here.
The magnetometer got shipped off today from JP Aerospace, and I also ordered a
different one from http://www.precisionnavigation.com/
as a backup.
Bob said that the remaining tubing for the VTVL platform will be in on Thursday,
so we should have the framework assembled next Tuesday.
I got the price quote from WinSystems for the single board computer I want for
the flight computer: In small quantities:
$200 (3A capacity, 9-36VDC input, 12V nominal)
That sounds reasonable to me, so I am going to order it after I get a little
clarification on the flash disk subsystems.
The software is nearly ready to go for the ground station and flight computer.
It is nicely configurable between running the simulator, connecting to a remote
simulator, or connecting to real remote hardware. I did wind up running
into a problem with my current control law when I added some latency to the
communication link. It is currently going into increasing oscillations, so
I have a bit more work to do there.
Stuff to do soon:
Get the water to the garage sink at LRS turned on again.
Get some of the metal foam off to the silver plater. Get the process
parameters they use for our records.
Make a vent hose for the vacuum pump, so we dont need to worry about
accidents when it is pressurized. We can tie the hose down to the other
end of the fill cart.
Pick up another compressor, in case the current pump dies.
We might want to have another N2 bottle handy, because at 400psi, we go through
it pretty fast.
Vise grips. Eventually, Russ needs to cut flats on the little engine for
Metal pipe clamps for the engines to test stand.