May 23, 2001 Meeting Notes
Servo operated ½ ball valve
Larger electronics box
New 12v battery and charger for electronics box
More Tefzel wire
3 KVH Fiber Optic Gyros
Two liter flasks
-10 hose and fittings for test stand
Another pressure transducer
NPT temperature transducer
1.125-12 UNF to ½ NPT adapters
for NGV tank (size 216 teflon O-ring)
Three more Super Pro Shot
Inverter for remote test stand
Plastic 55 gallon drums for
water and as heavier tether anchors
Dolly for moving drums
We are going to hop the VTVL again
on Saturday, probably starting work around 3:00.
We did engine testing on the small motor today with very
We are planning on using roughly 50 pound thrust engines
four the four attitude control engines on the manned vehicle, mostly because
that is about the flow limit of the NOS Super Pro Shot solenoids as determined
by firing it on Juans 100 pound thrust motor.
The Super Big Shot flows more, but we want to avoid using those 30 amp
solenoids if possible.
The small test engine makes about 13 pounds of thrust in its
last tested configuration, with a 0.25 diameter throat. We wanted to see if the same size motors
could still be used with a 0.5 diameter throat, which should give us about the
thrust we want. That would defiantly be
pushing it, because the inside diameter of the motors is only 1.1 diameter,
and going below a 4x area ratio between combustion chamber and throat starts
bringing in losses.
The question was if we were going to be able to fully
catalyze four times the flow we normally use.
We started by loading the engine with one of our old catalyst packs that
was about four times what we wound up eventually cutting them down to.
Russ drilled the nozzle out to 0.375 where it still had a
tiny expansion lip, and we loaded it with 250 ml of peroxide. It catalyzed perfectly, but it only made
about 16 pounds of thrust, which was a bit less than we expected even without
the nozzle, and it had a buzz in the thrust curve.
We then drilled it out to 0.5, which is now just a hole in
the end of the motor.
(we are using the 30 amp Super Big Shot solenoid on the test
stand it is probably twice as heavy as the engine
Phil didnt think it was going to make much more thrust,
theorizing that it was flow limited through the catalyst pack. He was right it didnt make any more
thrust, and it still had the buzz.
We then cut the catalyst pack in half, and run it
again. We ran out of nitrogen during
the pressurization, so we only got 375 psi (instead of 430), but the run still
made 23 pounds. The buzz was also gone,
but we couldnt tell if that was due to the lower pressure or the change it
catalyst back pressure.
Rather than cutting the pack down some more, we tried out
what we have theorized a bit about in the past: we took four of the unplated nickel foam discs, compressed them
four to one, and put that on top of fifteen (the same number we have been using
in the VTVL engines) completely uncompressed silver plated foam discs. The idea is that the highly compressed nickel
discs will spread the peroxide and decouple the pressure feed system from the
catalytic activity, then the peroxide can flow freely through the rest of the
It worked strikingly well.
It made 40 pounds of thrust, and ran smooth.
Getting a 3 to 1 expansion exit cone on the nozzle should
give a coefficient of thrust around 1.35, which should give us right around 50
pounds of thrust (we will drop a bit with the one size smaller solenoids).
It is interesting to note that the only changes between the
last three runs are catalyst pack changes, giving 2.5x more thrust and getting
rid of the buzz.
Russ is going to make four completely new nozzles with 0.5
throat and 3x expansion ratio, which we will be able to just screw on the
existing engines. With the current
plumbing, they will probably only make about 25 pounds of thrust, but that will
still give the VTVL the ability to accelerate at more than 1G straight up. When we replace the plumbing with the same
stuff we will use on the bigger vehicle, it should be able to pull 3Gs.
Once we get gyros that arent G sensitive, we will install
some fins and parachutes on the VTVL and really let it fly. Eventually we will want to do a complete
powered landing, but it is going to be extremely cool just to lift it off the
ground and hover for a second, then tear off at 3Gs
Other Propulsion Issues
The small plastic solenoid we were testing at 150 psi turned
out to have a nitrile seal, which is another form of Buna-N, which is nor
peroxide compatible. I am still
interested in looking at 150 psi valves for some applications, but I need to
find a good (C)PVC valve with Teflon or Viton seals.
Neil brought a 32 liter NGV tank that we are considering for
the manned vehicle. It is fiber
wrapped, but mostly it is a heavy hunk of aluminum. It weighs 60 pounds, and is rated for 3000 psi, which is huge
overkill for us, but the extra mass still wont be as dominant as the pilots
mass. We need to get it well cleaned,
and I need to buy some adapters to plumb it up.
Having ports on both the top and bottom is going to be a nice
improvement for us. We can load
peroxide with a normal pump (or just a funnel) instead of drawing a vacuum in
the tank, and we wont have to blow the nitrogen up through the peroxide when
pressurizing. We will also be able to
monitor gas temperature and pressure, allowing us to make a fairly accurate
The kzco servo ball valve seems to be a pretty nice
unit. It was $395 for a stainless/Teflon
½ ball valve with servo motor and potentiometer feedback. It masses 1.7 kg, but that will hardly
register on the next vehicle. Ball
valves up to one inch can use the same servo system, and they have larger ones
for valves up to several inches. We are
probably going to have to use four solid state relays to allow switching the
current direction for forward / backwards, and I am going to need to write some
potentiometer closed loop control code to run it from the remote joystick.
The main lifting engine will probably have about a 1.75
diameter throat (Russ: note that I increased this), which should give something
over 500 pounds of thrust. The ½ servo
ball valve is probably good for about 2000 pounds of thrust if we ever max it
I wrote some graphing software for our flight logs, and
gathered together the first three sets of tests:
I have updated the 3D flight simulator to model blow down
pressure changes (but not temperature changes) and use roughly the correct
values for the current vehicle. I need
to get the updated version put on the web site.
As soon as we get higher bandwidth gyros, changing to a
continuously variable attitude control system should give us large benefits in
stability, control authority, and response time.
The specs on the WatsonGyro 3 axis unit are:
ARS-E332-2A is $3408.
This triaxial gyro vibration survival 10G rms (20 to 2Khz.
Delivery 3 weeks ARO.
>The AQRS rate sensor is available in two variations,
-104 and -109. The
>only difference between these two units is unit price
>performance vs. temperature. Budgetary pricing for
the AQRS rate sensor
>in quantities of one to three units is $600 for the -104
>$300 for the -109 variation. A mating connector is
included with each
>shipped unit. Please note that SDID is currently
only manufacturing the
>AQRS in the 75 deg./sec. full range.
The specifications can be found here:
I also got some more info from BAE systems, but they didnt
provide a price.
I decided to order the KVH fiber optic gyros, at $1500 /
axis. We are going to have to make up a
fairly precise set of perpendicular mounting plates for them. Having a full 100hz bandwidth and no shock,
G, or cross axis sensitivity at all will be very nice.
I recently talked to a few of the people that worked on
DC-X, which was interesting.
DC-X used a Honeywell radar altimeter from a helicopter, but
it was blended as one of several inputs into their guidance system. Bogus data from it at one point was the
cause of the harder-than-expected landing on one of the DC-X flights.
The radar unit was pretty bulky, and I was urged to purse a
GPS / inertial based solution.
I will probably start working some on this in the next week
or two. I dont plan on going all the
way to a Kalman filter for blending, but instead plan on just buffering
accelerometer data, and back-correcting to the point of the GPS second pulse
after all the GPS data has been read in over the serial line. I will probably just use Z axis
acceleration, because inside of one second, in the attitudes we will be landing
at, the cosine variability wont be very large.
Tim Nolan volunteered to build a rangefinder for us to
try. The initial one will be
ultrasound, which I am rather dubious of working next to the rocket engines,
but he has also found some low cost radar parts. I still have a preference for a direct reading type of sensor
like this, but we will see how the GPS + accelerometer works out.
It looks like our project will probably be the first to
demonstrate vertical landing with an engine restart after ballistic flight,
which is still an often sited problem with VTVL. The DC-X, and I presume the Japanese VTVL project, dont have
easily restarted engines, so they have been constant thrust only.
Manned Vehicle Design Issues
Relief valve vs burst disk
Piloted solenoid vs servo ball valve for purge valve. Probably need a ball valve for high flow,
and because it might be called upon to operate at over 1000 psi if the tank is
Do we need check valves in front of engines? The half inch check valve will be a LOT more
restrictive than the half inch ball valve, and it may prevent us from hitting
our thrust targets. I did realize that
the only valid place for the check valves is between the controlling valves and
the engines, because any other location would leave trapped peroxide in the
system in the event of a purge.
We probably need another servo ball valve for the master
cutoff valve, although in the event of an emergency, purging might be almost as
My wife is closing on 100 acres of land in Rockwall next
month, so we should have plenty of room for a noisy static test stand and some
moderate altitude flights.
We are going to have Armadillo Aerospace shirts soon.