Jul 10, 2001 Meeting Notes
In attendance:
John Carmack
Phil Eaton
Russ Blink
Some pictures of the manned frame at Bob’s shop last week:
media.armadilloaerospace.com/2001_07_10/MannedFrame.jpg
media.armadilloaerospace.com/2001_07_10/AttitudeEngine.jpg
media.armadilloaerospace.com/2001_07_10/Platform.jpg
We tested a small sample of powder coated steel for peroxide
compatibility, and it seemed to be ok, so we are probably going to get the
entire thing powder coated so it doesn’t pick up rust spots as quickly as the
little demonstrator.
I found a supplier for a twist grip throttle that we can use
on the manned vehicle. 4QD Products
sells the Magura GTH-103, which is used on electric mopeds and scooters.
Phil has ordered the big blocks of closed cell foam we are
going to use for landing gear on the manned vehicle. They should be adequate floatation to allow water launch as well.
Because we ran down the battery during flight tests on
Saturday, I added a voltage divider so I could log battery voltage on the
flight computer and give some warnings when it is looking marginal. We still need to qualify what number “marginal”
turns out to be.
I also added a logged pressure transducer signal, and I am
just about done adding an RTD temperature probe.
I converted the A/D board back to 16 single ended channels
instead of 8 differential channels, because I was about to run out (3 gyros, 3
accelerometers, voltage, pressure, temperature, and soon throttle valve
feedback). There is supposed to be a
slight decrease in accuracy using the gyros single ended, but our other noise
sources are swamping that small issue.
I am going to do some experiments with different cable
lengths, types, and shielding methods this week to try and learn some more
about our noise sources.
Russ is going to cut the current lander engines down so they
don’t require the spacer plates. This
may also give us a slight improvement in engine response time to the flight
controls.
Russ is also going to tap out the port on the lander distribution
manifold that we used to use for the AN fill hose so we can plumb in either a
pressure or temperature sensor for the next flight test.
Bob needed the 5lb nitrous bottle that we have had on the
test stand back, so we swapped it out for a 10lb bottle. We did all the cleaning and passivation
today, which went smoothly.
We fired a quick experimental hybrid motor today. It was constructed with a heavy copper heat
sink nozzle, so it should be able to run uncooled for several seconds.
media.armadilloaerospace.com/2001_07_10/HybridTest.jpg
We were very cautious with the test, setting up some blocks
to catch the nozzle if it ejected, and getting everyone on the other side of
the wall before firing. We had the
video camera and a mirror set up for viewing.
media.armadilloaerospace.com/2001_07_10/jul10_2001.xls
( hybrid, 100psi, 200psi, 400psi, note the five pound bias
in the scale baseline)
The hybrid grain didn’t light at all, and only showed a tiny
amount of erosion after the test. The
run was extremely ragged, and we aren’t sure if that was just because the
catalyst pack was bad, or if it was an interaction with the hybrid grain. The next time we try it, we are going to
have a much smaller nozzle, because this motor had a nozzle nearly as large as
the grain ID. We should also run it
without the grain at all, so we know that it makes smooth power as a monoprop.
After that, we set out to test the manned vehicle attitude
engines at a range of pressures, because I have been curious to see how they
behave going from 100psi up to 600psi.
We have fired this motor on Jun 26 at 450 psi and 600
psi. The runs were predictable, but somewhat
ragged, which we attribute to not having enough pressure drop across the
perforated steel injector plate. I have
another grade of perforated steel coming with a smaller open percentage that
should be here tomorrow. Note that now
that we have a tank twice as big on the test stand, we won’t see the runs
tailing off as obviously due to blow down pressure changes.
We have decided to change our standard peroxide mix
percentage from 85/15 to 80/20, which drops us from 89% to 85% peroxide
concentration. It is easier to measure,
and gives us a little extra margin. We
have seen some occasional silver stripping when an 85/15 run got fudged a
little more concentrated than it should have.
We can always go back up if we need a touch more performance. We are still interested in trying some 98%
runs if we get a better catalyst.
The current packs have been reacting so quickly that we
decided to remove the warm up pulses from the control file for these runs. After today, we may put them back, because
they serve to effectively “burp” the plumbing, even if the cat pack doesn’t
need to be preheated.
The 400 psi run was about what we expected at around 50
pounds of thrust, slightly down from the 450 psi run at higher concentration on
the 26th. There was a big
hose kick at the start of the run.
Amusingly, the exhaust knocked over the concrete blocks we
had set up five feet away from the nozzle.before the hybrid test.
The 100 psi run only made about 10 pounds of thrust, but
interestingly, it was a bit less ragged than the 400 psi run, which is contrary
to what I would expect, with a lower pressure resulting in a lower pressure
drop across the injector.
Our solenoid started giving us some trouble, staying in a
stuck-open position. We checked the
computer and solid state relay, but it was definitely the solenoid itself. We got it to close, but it gave us trouble
for the rest of the tests. This is
worrisome.
The 200 psi run was similar to the 100 psi run, making s bit
over 20 pounds of thrust, with less noise than the high pressure runs. There was a big hose kick at the start of
the run.
We were preparing to do a final 300 psi test, but the
nitrogen tank only had enough to get it to 225. We made a mistake here by trying to get the very last bit of
pressure out of the nitrogen tank. We
were pulling the tank out to swap it, and we found that some peroxide had been
forced back into our fill manifold. Our
feed line goes over the test stand tank, so it will never drain back at an
equilibrium pressure, but it looks like it is possible to develop a temporary
positive pressure in the test tank if you pull the nitrogen tank all the way
down, probably due to relative heating and cooling issues. We got a little puddle of peroxide under the
fill cart and on the regulator, so we decided to just blow out what we had and
clean up.
We should put a check valve between the nitrogen solenoid
and the fill cart manifold.
We are planning on flying the VTVL again on Saturday,
hopefully to do some nice translational maneuvers. We have about enough peroxide left at Long Range for two full
length hops, then we need to go pick more up.
Need to pick up more nitrogen.
I’ll pick up more distilled water.
Cut the engines down if there is time, otherwise just fix
the threads on the problem engine.
Tap the manifold if there is time.
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