February 12 and 16, 2002 Meeting notes
Joseph LaGrave (Tuesday)
Regulated Test Stand
On Tuesday, we did a lot of work modifying our test stand to
allow pressure regulated biprop work. I
got more AN swivel fittings, so we moved the jetting around so that the
kerosene jet is right at the engine for high speed injection, and the peroxide
jet is now also a flare jet instead of the hand-made NPT union jets we were
using before. I didnt want to spend
time making a lot of little flare jets, so I went looking to see if nitrous
jets went up to the larger sizes we would like. I was pleasantly surprised to find that Edelbrock offered a huge
set of AN flare jets from 0.018 to 0.130, and they are made of stainless steel
instead of brass like the NOS jets. I
bought the master tuner jet kit, which has eight of each size. We are probably going to add jets on all the
lander attitude engines the next time we test.
With the new plumbing arrangement, we can change jets on the test stand in
under a minute without even depressurizing our tanks.
We were a little concerned that the spare regulator we had
wouldnt flow enough to hold a constant pressure, but I logged ullage pressure
today, and the runs only dropped one or two psi when they started, and held
Here is the new fuel injector ring that I made, which allows
us to change nozzles and cat packs independently, and will allow us to swap a
hybrid grain section in place of the fuel injector section. We test fired it with water, and with the
jet right at the injection port, the water slams against the other side at very
high velocity, atomizing well. An
impinging jet injector would be almost impossible to align with tapped holes
and held jets, and at our fuel flow rates, the required jet sizes would be
smaller than we can get or make, so we will stick with single point injection
for a while.
Russ managed to get a water jacketed combustion chamber made
this week. The internal chamber is 1
diameter and 2.75 long, which gives us well over the recommended L*. We hook one end up to a garden hose, and the
other end up to some tubing that ejects in front of the test stand so we can
see if we ever get any steam.
Here is the test stand before we connected the nitrogen
Matt, our camera guy, was out of town today.
Unchanged monoprop from last Saturday, except the NPT 0.060
jet on the peroxide was changed to a 0.060" AN flare jet.
The pure silver screen pack warmed up on the very first
pulse from stone cold, and continued to catalyze perfectly.
Still running rough, as it was last week.
We removed the check valve from the peroxide side,
theorizing that the check ball gave pressure pulsations more leverage.
This run was rougher than the last.
Still with the check valve out, reduce to a 0.040 peroxide
Less thrust, a little smoother, but still not very good.
Change back to 0.060 jet, swap ball valve for solenoid, replace
First hot fire of the regulated biprop. 0.024 fuel, 0.060 peroxide, 150 psi.
Did not light. Not
unexpected, as our previous tests were with a higher peroxide tank pressure to
compensate for the cat pack drop, so this was much richer.
0.040 peroxide, 0.018 fuel
Still did not light.
The 0.018 fuel jet is as small as we have, so increased the
peroxide side to 0.050. Pressure
increased to 200 psi.
It lit instantly on each press of the fuel button, and made
lots of mach diamonds in a beautiful exhaust jet!
The roughness was worse in the hot firing sections.
same jets, 250psi pressure
We tried to record this on my little camera, but the battery
died literally two seconds before we hit the hot fire button.
We made a new cat pack in the second 1 by 2 body that I
made. The formula is currently: five
layers of: ten each alternated 80 mesh silver screen and 20 mesh stainless
screen with a gapless retaining ring ahead of each block for a total of fifty
silver screens, fifty stainless screens, and five retaining rings. The remainder of the pack space is taken up
with the retaining plate and a 0.25 spacer, and about 0.2 is compressed down
during the tightening of the pack chamber onto the fuel injector. There is no spreading plate at the top.
The run was smooth, like the first 80 mesh pack when we
first started running it, but not quite the absolute-dead-smooth of the (slow
warming) 20 mesh pack we made a couple weeks ago that later crapped out on us
(before we were using the gapless retaining rings). It will be interesting to see if this pack also gets rough after
a dozen runs.
The hot fire sections were also smooth.
We see a bit of smoke above the plume, and there is soot in
the engine, so we believe it is still running rich. Increase the peroxide jet to 0.060.
Still a bit of smoke, but still smooth on both monoprop and
hot periods. There was ten seconds of almost
continuous hot fire with only a brief pause with the fuel off.
Increased peroxide jet to 0.070.
This was still smooth on the monoprop periods, but rough on
the hot periods.
back to 0.060 peroxide, exactly as test 10.
Still rough on the hot periods. Strange.
Increase fuel jet to 0.020.
Still rough on hot period, obviously richer.
We still dont have a handle on the rough monoprop running. About our only theory is that the 80 mesh
screen may be interacting with the gas flow in some way. Our big loads of catalyst still arent here,
but if we need to, we still have an engines worth of 20 mesh silver screen
that we can reuse for tests.
We have a theory about the rough hot fire sections. Because we are using the smallest fuel jet, our
thinking is that we dont have sufficient pressure drop across it. The two runs where it was smooth may have
had a more restricted jet due to soot or a foreign particle. Tiny nitrous jets are well known for getting
clogged up. We cant go up much on feed pressure because of the rating on the fuel
tank, so Russ is going to bore out the nozzle from 0.25 to 0.40, which will
increase our total mass flow enough to hopefully choke the small fuel jet. That will also reduce our L*, but there is a
bit more meat that can be bored out of the chamber to compensate.
It is definitely possible to be to rich to light, even with
a big chamber and good atomization, which places a limit on how much cooler you
could get an engine to run overjetting.
At optimum mixture ratios, peroxide / kerosene is hot enough to melt
TZM, so if we want a completely passively cooled engine, we will need to do
something to lower the chamber temperature (and give up some Isp).
The water cooling seems to work fine. After a hot fire, the exiting cooling water
is only slightly warm. We might try
taking the cooling exhaust out to where a person can monitor the temperature
The current cat pack formula seems very solid from a
Leaving fuel in the tank between runs is extremely
convenient. However, when we tried to
spray the remainder at the end of the day back into the kerosene can, we wound
up making a mess after the last of the kerosene came out of the tank and the
nitrogen started blowing by. Next time,
we are probably going to leave the kerosene in the tank and just vent off the
We improved both the injector and the chamber volume over
the runs last weekend, but we could tell that the chamber volume was the more
important factor, because on some of the runs we got spatters of combustion
after the fuel valve was closed, probably a result of it sucking the remaining
little bit of fuel left between the check valve and the jet into the
chamber. Even the non-atomized spatters
had mach diamonds.
After we actually get some good video of the biprop running,
we will probably take the test stand out to the 100 acres and see if the biprop
can run steady state for 60+ seconds with water cooling (we will have to use
another pressure vessel for the water, there isnt city water out there). If that works out fine, we may try making a
regeneratively cooled engine, possibly out of aluminum.
The Oklahoma Space Industry Development Authority (OSIDA) meetings
are continuing to go well. I have been
driving up to Oklahoma City for the meetings, and we should be signing a
memorandum of understanding soon. It is
looking good for getting airspace for manned supersonic work late this year,
working towards 100km shots next year.
The ethane arrived, but we need to get a special CGA fitting
for it before we can try it out. We
seem to be getting good combustion with liquid kerosene, but when we try
building bigger biprops, we will probably want to start with gaseous ethane
because it removes the requirement of getting good atomization and
distribution. The metering will also be
a lot more positive with a gaseous fuel, because the orifice will be larger,
and it will be choked sonic flow.
The Laser Atlanta Advantage rangefinder arrived, and I have
it configured as we will use it on the vehicle. It gives 240 samples a second, with an accuracy of a couple
inches, and a range of 2000 without a reflector (20,000 with a
reflector). We will be logging this
data on the next lander flight, but we wont be using it for auto-hover and
auto-land until later tests. Mounting
it is going to be a bit of a trick.
Joseph will soon have a 1000 square foot concrete pad poured
for lander operations and high speed rotor testing at my 100 acre lot.
Our airplane parachute is supposed to be here on Tuesday.