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FMC 50%, Spring cannon, Misc

August 31, 2003 Notes

August 31, 2003 Notes


FMC 50%


We received four drums of 50% concentration rocket grade peroxide from FMC.  It came with the restrictions that we can’t 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 can’t 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 us.


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 hasn’t 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 wasn’t 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 shouldn’t have been too unexpected.  I replaced the entire inlet / pump / outlet hose assembly with a single long piece of peristaltic PVC tubing, which won’t have any place to trap peroxide.  It probably wouldn’t 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.


Spring Cannon


We put together a drogue spring cannon as a possible alternate to pneumatic ejection.  We aren’t 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 isn’t 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 don’t 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 aren’t 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 don’t 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 I’ll keep at it until I can do some of my own welding while I am fabricating things.






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