May 5 and 10, 2001 Meeting Notes
Next meeting Saturday at LRS around 7:00
150 psi ASME composite tank
220 psi pvc tubing
100 psi plastic solenoid
Tefzel mil-spec hookup wire
Super big shot NOS solenoid (the 30 amp one)
Super pro shot NOS solenoid
1/2" 110 VAC solenoid for the test stand
More stainless fittings
Plastic hose barbs
Five sets of hearing protection.
Four XL disposable protective suits
Five rolls of mil-spec teflon pipe tape
2 40 amp DC solid state relays
2 40 amp AC solid state relays
5 4 amp DC solid state relays (for low cost, low pressure
3 NOS blow off valves
10 -6 hose ends that turned out to be the wrong kind.
5 8" foam cubes for landing gear
Rubber anti-vibration mounting pads
The correct 6 hose ends
Swivel ¼ inch to 4 fitting for fill cart
½ inch check valves
More plastic solenoids
Spill tray to put under our peroxide container
More distilled water
Contact cement for the foam pads
Extra hose clamps for the engine mounts
Some kind of shims for positioning the clamped engines
Some extra ¼ male to 1/8 male fittings
Various AN straight size adapters
On Saturday, we did some testing with a tiny (and cheap)
little plastic solenoid (McMaster 7877K25)..
We are seriously considering doing some work with low pressure
rockets. The Isp will suffer, but being
able to use plastic fittings and valves completely removes the peroxide
corrosion problems, and you can flow more through a low pressure solenoid for a
given amount of actuation force. It is
also safer and cheaper.
I wanted to try McMaster 7876K28, which is listed as twice
the flow, but Delrin is on the severe reaction list with peroxide.
Tip: the 220 psi tubing was incredibly difficult to get on
the hose barb, but a little time in front of a heat gun softened it so it slid
on a lot easier.
We did some water flow tests on the solenoid:
1000 msec at 100 psi: 59 ml
1000 msec at 150 psi: 75 ml
That is nearly as good as the small nitrous solenoid, which
flowed 33 ml in 500 msec at 100 psi.
The valve would not open at 200 psi. The valve was rated for 100 psi, but a 24vdc
version is rated for 150 psi.
We fired the 100lb thrust motor with the tiny little valve
and made a steady 10lb of thrust with it at 150 psi supply pressure. A more reasonable nozzle to prevent huge
overexpansion would have helped a bit.
That valve had a listed Cv of 0.17, but the pressure drop was quite high
with the big nozzle, so with a more reasonable chamber pressure it would flow less.
When we went to do a second run, the solenoid was dead. The coil had fused internally. We are going to try again with the coil that
is actually rated for 150psi.
We also tested a big stainless solenoid that Bob had lying
around at his shop. It appeared to be
the same style as the NOS valves, but rated for a lower pressure (400psi vs
1500 psi), so we expected it to flow better.
Surprisingly, it flowed worse than the tiny little plastic valve.
We were planning on firing the motor with the ½ manual ball
valve, allowing it to reach its full 100lb thrust, but we ran out of Teflon pipe
tape. We tried just tightening it up
until the water tests didnt leak, but we would up galling the threads. Lesson learned never ever assemble
stainless fittings without Teflon.
We probably wont be able to use the ASME composite tank I
ordered (I bought it from McMaster, but it is manufactured by Amalga
Composites), because it has brass threads on the fittings. We may still do some water tests with it to
evaluate the advantages of working with tanks with both top and bottom
ports. Getting away from our current
vacuum loading and pressurizing through a single port would eliminate some
check valves and avoid dissolving nitrogen in the peroxide while pressurizing. Also, while I had seen one reference that
epoxy was an acceptable short term material for peroxide, we heard from one of
the Beal people that it should be avoided.
I talked with a rep from Structural Composites about some of
their 150 psi pressure tanks. They
offer polyethylene lined tanks, but their internal material compatibility chart
only showed that to be good for 10% hydrogen peroxide. I think they are just mistaken, because we
got our original 98% sample in a PE jug, and it hasnt given us any problems at
all. They wouldnt give me any direct price
quotes, but I got the number of a distributor to contact.
On Thursday, we had four firings of the big motor, and we
began assembly of version 2.0 of the VTVL.
The new lander design is using foam blocks for landing gear:
The much lower center of gravity should make it harder to
top over, replacing the springy legs with foam will keep the liftoff jerk down,
and the electronics box is soft mounted, which will help the gyros. We may fly it this Saturday.
We now have four different sized solenoids out of the NOS
line that we test with. I wish they
gave the Cv ratings for their valves, but the only thing the rate them with is
the potential horsepower gain for auto applications.
175 hp 8.6 amps, 1/8 to
1/8 Super power shot
250 hp 10 amps, ¼ to
350 hp 10 amps, ¼ to
1/8 Pro shot
400 hp 8.6 amps, ¼ to
1/8 Super Pro Shot
450 hp 8.6 amps, ¼ to
1/8 bottom discharge Pro race
600 hp 30 amps, ¼ to ¼ Super
The question is if the top of the line is barely large
enough to let us squeak by with a single solenoid for the manned vehicle.
All of the firings were at the max pressure of our
regulator, about 435 psi, with 500 ml of 90% except for the last..
The first firing was with the Super big shot solenoid, no
check valve, and a 4 feed line.
63 pounds peak thrust.
The second firing was with the 110vac piloted solenoid, no
check valve, and a 4 feed line.
The first thing we noticed was that the piloted solenoid
wouldnt hold a vacuum, so we had to manually close the tank while loading, then
open it before pressurizing.
When we fired it, the 200 msec warmup pulse emptied a third
of the peroxide! The piloted solenoid apparently
closes very slowly. Pulsing is obviously
out of the question.
72 pounds peak thrust (from the warmup pulse!)
The third firing was with the 110vac piloted solenoid, no
check valve, and a 6 feed line.
I cut the warmup pulse to 100 msec, and it didnt fire anything
during the warmup segment. From looking
at the data, it looks like valve requires about 100 msec before anything at all
flows through, and around a quarter second before it is near full flow.
88 pounds peak thrust.
The fourth firing was the same as the third, but with 800 ml
of peroxide, and a tiny bit more peroxide concentration due to rounding off the
mixing numbers. This is about as much
as we can vacuum load into our little test stand tank (the lander tank is 2.5
times as large).
91 pounds peak thrust.
The small tank on the test stand has a very noticeable pressure
blow down effect with the large motors.
It looks like Juans analysis was just about spot-on in the
motor design. If we had a regulated 450
psi of feed pressure, it would probably be right at 100 lb of thrust.
This is interesting, because we originally sized our 15 lb
thrust motors by just scaling down Juans numbers, and we had to drill them out
a bit to get what we wanted. We were
only running 400 psi most of the time, but it looks like there are some additional
inefficiencies with very small (under 0.25 throat) motors.
The last run is enough data to roughly calculate our Isp: 1233
newton seconds of thrust from 1.11 kg of propellant ( 800 ml of 90% peroxide of
density 1.387 ) gives an Isp of 113 seconds.
If it was kept steady state at 450 psi, Juans number of 125 seconds is
We need to test the Super Big Shot solenoid again with a 6 hose,
because the hose made a much larger difference than just going to the big
We may have one more restriction in our test stand
plumbing: the manual bottle valve doesnt
have all that large of an orifice. Russ
is going to make us a custom manifold out of aluminum like the one on the
lander, but with a ½ port straight out the bottom, and four ¼ ports around
the side (the lander manifold has eight 1/8 ports).
We may be able to hit 80 pounds of thrust with the single
NOS solenoid on the current engine with better plumbing, but that is probably
about it. We could either increase the supply
pressure or decrease the chamber pressure (by opening the throat more) to flow
more peroxide through the valve, but to make it to 150 pounds of thrust we
would need to nearly quadruple the pressure drop, which seems unlikely.
Our propulsion options for the manned vehicle are:
Live with less thrust.
We could still lift off with four 100 pound engines if our pilot isnt
too heavy, but it wouldnt leave a lot of margin for killing velocity when
Gang two solenoids together on each engine. There would be twice as many hoses, but the
solenoids could be run out of phase, giving much smoother pulse modulation of
the thrust, and we could easily hit our 150 pound per engine target.
Keep the four engines with a single solenoid, but add a
fifth engine in the center dedicated to lifting. Just adding one more identical single-solenoid engine would give
a reasonable margin, but because it wouldnt need to pulse, a piloted valve
could be used, allowing much more flow.
This would also give a growth path to adding very high thrust central engines
for the vertical dragster.
Develop non PWM throttled valves that can flow a lot
more. A ½ straight-through ball valve
flows five times as much as the ½ 110 vac solenoid we have. I have been looking for an appropriate valve,
but I havent found exactly what I want yet.