October 29 and November 2, 2002 Meeting Notes
Neil spent a couple days in DC working on regulatory issues
for Armadillo. He attended the COMSTAC
meeting, but didnt find it to be a very good venue for Armadillo, being
dominated by the big Aerospace firms moaning about the launch calendar. We will probably start participating in the
RLV forum, though.
The meeting at AST was set up specifically for Armadillo,
and was attended by all the top brass.
It went very well, and we now have a three person team at AST assigned
to help us through the regulatory course.
They strongly advised that we begin working on our environmental impact
study immediately, because that is a requirement that is outside their control,
and will likely be the pacing item. We
have been hoping to piggyback on OSIDAs EIS work, but that wont be complete
Neil has a lot of work cut out for him on the regulatory
side over the next year. We are aiming
to put something to space (100km) by the end of 2003.
We did a lot more investigation on why the new 6 engine
isnt working well.
We tested the catalyst activity, and found it to not be as
good as the previous engine. We had
washed all the silver screens in the ultrasonic cleaner with alcohol, but
previously we had done an initial wash with hot water and Tide. We repeated that, and the activity was
indeed increased. We also tried a more
aggressive cleaning rinsing the screens in 50% nitric acid. This cleaned them extremely well, making all
the silver look completely fresh and white.
The activity was extremely good, with the reaction being fast enough to
make drops of peroxide skate around on a film of gas. One thing of note was that when we cleaned the pack, there were
some red fumes given off (red fuming nitric acid?), which we were careful not
to breath. That may have been from the
stainless screens, rather than the silver.
We also noticed that the anti-channel rings were not fitting
very tightly. We usually see this after
running an engine, but we decided to try and do something about it today. We use Smalley spiral retaining rings as
anti-channel rings, because they come in a wide range of sizes, and can be
sized to have an initial outward preload when you first install them. The spiral nature may have been allowing
them to take a permanent shrunken set after thermal cycling, so Russ welded a
few of the rings together into single units that wont slide over
themselves. We learned something interest
here. Russ did the welding by putting a
ring in a spare catalyst pack to hold the exact size, so it was an exact fit in
there. When we moved them to the engine
we had been firing, they dropped right in without any resistance, and could
even be wiggled around a bit. The fired
engine has stretched a visible amount.
We compared some of the already-fired anti channel rings with fresh
ones, and found that the rings had still shrunk as we had originally thought,
so there are two factors effecting channeling ring shrinkage after thermal
cycling (the rings heat up faster than the chamber wall), and engine stretch.
With the combination of the cleaned silver and new
anti-channel rings, we did some additional test firings.
Without any orifice at 250 psi tank pressure, it made 300 lbf,
+/- 3%, with an odd sharp upward spike in thrust at the end. Still very cloudy.
We tried even running it with the small orifice designed for
the fuel side of our big biprop, which cut the thrust down to 150 lbf, but it
was still cloudy.
We decided to test the old engine, so we hauled the lander
out for a short test hop. The main
engine did make a big cloud initially, but it did clear up after a few warmup
pulses. The flight was entirely
nominal, but it clouded up a bit as it was setting back down.
On Saturday, we decided to take a drastic step to eliminate
channeling we completely welded the anti-channel rings to the catalyst pack,
so they positively cant be leaked past.
This was a bit challenging in a 5.5 ID catalyst pack, but Russ was
getting the hang of it by the time he was done. We couldnt press down on pack while welding, so the pack doesnt
have the same compression characteristics as normal. We used the same pack that we ran on Tuesday, so it was
pre-compressed a fair amount, which may be relevant data when we make another
one like this from scratch. The exact
packing order was:
Two non-welded rings to just act as spacers at the top of
the engine to let the peroxide spread out.
10 stainless screens to act as an inert spreading zone
A welded ring
10 stainless / 20 silver screens alternated
A welded ring
10 stainless / 20 silver screens alternated
A welded ring
10 stainless / 10 silver screens alternated
A welded ring
10 stainless / 10 silver screens alternated
A welded ring with the last stainless screen brazed to the
ring, in lieu of a perforated metal retaining plate
Before inserting each ring, the pack was compressed with
10,000 lbf, but there was some spring-back before the welding. We were a little concerned that this would
break loose the earlier rings, but they held up to it with no problem. Skipping the retaining plate was another
idea to save weight and reduce flow losses.
We had run a 2 engine without a plate supporting the screens, and we
expected that the welded rings would keep all but the last set of screen
pressure drop off of the retaining screen, so it should probably work out. It may not scale to 12 engines, but we
I finally bought a new data acquisition system that can
handle a lot more channels. We have
been using various Dataq starter kits for two years, measuring only thrust and
tank pressure, but now that we are looking at optimizing some larger engines,
we need to start getting a lot more data.
I bought one of the larger Dataq systems, which are sort of a rip-off
price, but the familiarity with the product line had some value.
For measuring chamber pressure, we just ran a stainless
steel line with a bend in it right up the engine nozzle. You wouldnt be able to get away with that
on a biprop, but with monoprop it works fine.
It is possible that we have some velocity effects on the reading,
depending on the exact orientation of the line end, which may cause an
underestimation of chamber pressure.
We ran about a gallon and a half through the engine, and it
made 308 lbf steady, then sharply (but smoothly) increasing to 500 lbf over the
last second of the run. It was still
This was the smoothest large engine run we have ever seen,
it only had +/- 1% thrust roughness.
The welded rings probably prevent the entire pack from getting into
oscillations, trapping them in a smaller region. The thrust was not significantly higher than the Tuesday runs,
even though there were less screens with less compression, and no retaining
plate. Chamber pressure was only
reading 74 psi in the stead part, going to 110 psi at the peak thrust, at which
point the tank pressure was 234 psi.
That is about par for what we saw last time we measured chamber
pressure. The pressure drop across all
those screens is very significant. The
old foam packs had far less pressure drop, but crummy lifespans.
I finally realized what the very repeatable, large upswing
in thrust at the end of all these runs was:
we had a very long braided hose running from the peroxide tank on the
trailer, over to the valve on the vertical test stand. The line was a good sized 10 hose, but it
was 24 long. As the line emptied out,
the fluid pressure loss decreased.
There was a repeatable 40% drop in thrust due to the long hose. To prove this, we strapped the tank directly
to the side of the test stand, so there were only two 3 lines in the circuit
(tank to valve, valve to engine). There
is still a 90 degree fitting right at the engine, which certainly hurts, but
the thrust still went up to 360 lbf. On
the flight vehicle, the engine is directly inline with the valve, directly
connected to the tank, so I think we can count on 450 lbf at 250 psi in that
configuration, which is adequate for our needs.
The runs are still cloudy, but we noticed several things: It
is clear right underneath the engine, with the clouds only showing up when it
hits the ground. The clouds arent
really clouds of peroxide you can take a whiff of them without burning your
nose. We didnt precisely measure Isp,
but it definitely isnt far off from where it should be. When we flew the lander with the old engine,
it did clear nearly all the way when it was warmed up repeatedly right off the
ground (engine 3 from concrete), but when it lifted off and came back down in
a slightly different spot, there were clouds again.
At this point, we think the clouds are just clouds of water
vapor, coming from the fact that it has been cold and wet all week, and we were
actually doing our testing in a light drizzle this Saturday. Firing vertically onto cold, wet concrete
gives the exhaust plenty of excuse to condense. If it is fired long enough at one spot at short range, it
probably dries the area out enough to diminish the effect. I suspect that if it dries out and warms up
a bit, the current welded engine will be a flawless performer.
Tube is Done
We still need to do more parachute pull tests and a hover
test, but all elements are in place for a flight to moderate altitude of the
tube vehicle. Dry flight weight is just
under 300 pounds.
The main propellant tank is a 2 diameter polyethylene lined
fiberglass tank from Structural, directly bonded to a 60 degree included angle
tail cone, nose cone, and some filament wound pipe from Beetle Plastic. The tank has 60 gallons capacity, so we
could load it with a truly huge amount of peroxide, even with blowdown ullage,
but our initial flights will be with five gallons of peroxide. The body is very tough, and we are pretty
confident that it will survive landing shocks, unlike the first version we
built with the airfoil section fins.
The main engine and servo valve attach directly to the
bottom of the tank. The tank closure is
4 in diameter, so we are able to mount three other fittings directly to it
without needing a manifold. If it was a
bit larger, we wouldnt even need to T for each pair of attitude engines. The peroxide fill fitting on the tank bottom
is welded to a 3 long length of stainless pipe that goes high into the tank,
so as the peroxide is pressure fed in, it fountains up and cant flow back
out. This is better than using a check
valve, because it allows us to vent pressure from the top of the tank if desired,
and keeps the disconnect lines completely dry after some pressurizing gas has
been blown through. We pressurize the
tank at 250 to 300 psi.
The base structure is of welded aluminum. The four attitude control jets are canted
for roll control, and tilted on another axis to maximize the lever arm to the
vehicle CG. We are currently running
0.100 jets to get reasonable thrust at the low tank pressure. We have had some roughness problems with the
2 engines at that jet size on the lander, but they seem to be running ok here,
possibly due to the lower pressure (although that is the opposite effect that
lower pressure should have, cat packs complicate the behavior). There are Enidine wire rope isolators at
each mounting corner, of a softer rate than we used on the manned lander. Each isolator has a polyethylene brick
mounted to the bottom to raise the vehicle up enough to allow them to compress,
and to allow it to slide sideways on landing.
The bricks make a very large difference in how easy it is to scoot the
We have a bulkhead plate on the side of the base for the
loading quick connect, and a pressure gauge mounted above it. This is a very nice fill arrangement.
The test last Saturday, where it didnt lift off from the
ground, produced some thermal issues in the base cone. The heat-shrink tubing around the motor
valve wiring was melted, several tie wraps were effected, and the motor valve
connector is getting a bit crispy.
The Tefzel wiring wasnt fazed in the slightest. We wrapped the motor valve wiring in Nomex
for now, but in the future we may run Tefzel all the way inside the motor
We have a rather tacky bunch of wires running up from the
base (attitude engine control and main servo valve) along the side of the
rocket, currently just covered in duct tape.
The next vehicle will have a proper sheet metal conduit.
The main support for the parachute loads is carried by a
5/8 thick Kevlar rope that loops all the way under the tank and up to the
parachute harness. The rope along the
sides (rocket suspenders) looks a little odd, but this is probably the most
robust arrangement for now. We may
crack some of the fiberglass where the rope feeds through when we deploy. The next vehicle will rely on the bond
strength of the main airframe, and attach the parachute at the top.
We have the tank pressure transducer mounted on the top
closure, underneath the computer bulkhead.
This was one of those circumstances where we really wished we had added
two more inches to the tube height above the tank, because the transducer
wouldnt fit under the computer in any of the obvious positions. I wound up hanging it down by the deeper
domed section of the tank end, and connecting it to the tank with stiff
stainless hard line.
The parachute is a lo-po 350 (low porosity canopy) from
Butler Parachutes. It is packed into a
deployment bag, which is pulled out from the rocket by two Pro-38 three grain
motors mounted on a tower above the nose.
The actual nose cap that pulls away is cut from a jet engine spinner cap
that Phil had lying around, because the main fiberglass cone didnt come to a
complete point. Packing the parachute
into the bag is a real pain, exacerbated by the fact that we stuff the normally
8 diameter bag into a 7.5 diameter coupler that guides the nose away from the
body. We are going to want to improve
that in some way in the future.
We will be doing hover tests and parachute tests next week,
but we still havent heard from our local FAA office about our flight waiver, so
we may need to drive to Oklahoma to do the first flight at Burns Flat.