August 31, 2003 Notes
We received four drums of 50% concentration rocket grade
peroxide from FMC. It came with the
restrictions that we cant concentrate it or use it for flight tests, but it
will allow us to rule out catalyst poisoning due to the food grade peroxide in
our mixed monoprop tests. If our
problems go away with the better peroxide (and we cant attribute it to any of
the other changes we are making), we will have to negotiate with FMC about flight
testing, or have Don Stark run commercial peroxide through his deionizer for
The FMC propulsion grade 50% registered 5 ppm on the TDS
meter, compared to 18 ppm for the Solvay food grade 50%, and 232 ppm fpr the
FMC technical grade.
We also got 20 gallons of lab grade methanol to use in place
of the industrial methanol we have been using.
Both read 0 on the TDS meter, but the lab grade may have less
non-mineral contaminants. It is one
less question for us in the future testing.
Unfortunately, all our new catalyst still hasnt arrived. It should be here any day now.
Don Stark has reported that he has finally gotten some 90%
peroxide generated that passes the minimum TDS levels required for the
mil-spec, so it looks like we will finally be getting some 90% soon as
well. The small vehicle should be in
the air within two weeks of 90% arriving, barring unforeseen problems.
There was a noteworthy little incident while we were drawing
a peroxide sample this week. We use a
peristaltic (tubing) pump to pump from the drums into five-gallon HDPE
carboys. When we first got the pump, I
set it up with the extra soft PVC tubing hose only inside the pump, coupled to
normal clear flexible PVC tubing on the inlet and outlet sides with double hose
barbs. After we have pumped as much out
as we want, we lift the suction hose above the pump to let it suck down the
last few drops of liquid. When we did
that this time, the hose barb coupling broke right off. Nothing was spilled, but when we
disassembled everything, we found that both hose barbs had become very brittle,
and the high vibration environment right next to the pump probably wasnt
helping things. Concentrated peroxide
does tend to embrittle many plastics, and we have been using this pump for
about a year and a half, which probably left small amounts of peroxide trapped
at the hose / barb intersections for extended periods, so this shouldnt have
been too unexpected. I replaced the
entire inlet / pump / outlet hose assembly with a single long piece of
peristaltic PVC tubing, which wont have any place to trap peroxide. It probably wouldnt be a bad idea to always
flush distilled water through the pump after transferring peroxide. This is also a good reminder that it is
probably time to replace all of the carboys.
We put together a drogue spring cannon as a possible
alternate to pneumatic ejection. We
arent sure how we want to go with this, so we built a proof-of-concept to feel
out the issues. Pneumatic requires a
tank and a big solenoid of some kind, and requires a good piston seal. Spring ejection requires a longer tube to
hold the compressed spring, and requires a Sea-Catch to release the
spring. The spring system feels more
robust, because the Sea-Catch can also be released with a manual cable as well
as electronic actuation, and when it is released, the drogue is absolutely,
positively coming out. We have had
pneumatic pistons fail to eject the drogue if there was some blow by, and tank
leakage is also a possible worry (we could auto-abort on a minimum level, so it
probably isnt a fatal worry).
I got a few big industrial springs from www.centuryspring.com , and milled a
few plates to weld onto some of our big aluminum pipe. On Saturday, Russ welded everything together,
and everything worked exactly as designed.
We bolt a loading flange onto the end with a big threaded stud through
it, crank that down to compress the spring, catch a shackle hung beneath the
piston in the sea catch, add a safety interlock, uncrank the stud to releve the
pressure, unbolt the loading flange, then stuff the drogue into the pipe.
Works great. Matt
was out of town this weekend, so no pictures yet. The only thing we want to change in the future is to use an ACME threaded
stuff with a bronze nut, instead of the stainless hardware we had on hand. Even with anti-seize, the thread is
obviously suffering after a half dozen tests.
The downside is that we still dont have a high speed
electric actuator for the Sea Catch.
The one we built from KZCO valve actuators takes several seconds to release,
even when overdriven with higher voltage.
We arent able to get any faster gearing for it, so we are probably
going to have to look elsewhere. We can
always use squibs or CAD thrusters to actuate the Sea Catch, but we want our
vehicle to be completely pyro free for various reasons. We may cobble something together with the
guts of a cordless drill motor, which pops it off very rapidly.
We had a discussion about how we want to anchor down the big
vehicle for captive hover tests. It
will be suspended off the ground by a crane, but we want to avoid the
possibility of a 1500 pound vehicle flying into the crane, or flying 30 above
it before plummeting back to the ground.
The engines will probably only be producing 1000 lbf net maximum, but there
may be a really big jerk as it comes up against the restraints, and we are
afraid that it would just pull a big hunk out of our test side concrete pad,
which was laid down without rebar reinforcement.
What we decided on was to take one of our 63 diameter steel
tank ends that we got for mocking up the cabin a while ago, weld a 5 long pipe
or I-Beam in the center of the concave side, and bury it. A rocket anchor. J
We still want some kind of big shock absorber inline with
the restraint chain, but I dont know exactly what we want to use. It is going to get pretty damn hot sitting
15 or so below the rocket engines, which is a constraint. It seems likely that there is some kind of
standard line / chain shock absorber used in industrial rigging. Anyone have suggestions? In hover test trim, the vehicle will weigh
at most 1500 pounds, and it will have about 15 of maximum flight before
jouncing the chains.
Russ welded over the big vehicle distribution manifold that
was leaking, but I made a test flange so we could pressure test it without
pressurizing the 850 gallon tank, and it is still leaking quite a bit. We may need to make a brand new one.
I also finally got Russ to show me how to operate our TIG
welder. It was rather frustrating, but
Ill keep at it until I can do some of my own welding while I am fabricating