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FMC, dissolving check valve, metal spinning, parachute tests


July 11 and 20, 2002 Meeting Notes


In attendance:


John Carmack

Russ Blink

Phil Eaton (Saturday)


Russ, Phil, and Neil were at LDRS last week, so we missed a couple meetings.


The web site will be down for a few days next week as it is changed over to a new format.





Because we are going to run out of the peroxide we bought from X-L Space Systems (now no longer in business) by the end of the year, we are working through the issues involved in getting FMC to sell to us.  The price is reasonable, at $3.38 / lb for 30 gallon drums, and $2.65 / lb in large quantities, but they are a lot pickier about which facilities they will sell to, and they have to do a site inspection before any sale.  I am working through their checklist to make our site acceptable.  They also have a very limited number of the special drums they use, so they start hitting you with a $15/day rental fee after the first month, which means we are probably going to have to buy a storage tank of some kind.


We always have lots of water available, but they want specific eye wash stations and a safety shower, so we are putting those in.


The most annoying restriction is that they want to see no plastics (polyethylene, polypropylene, PVC, etc) used with the peroxide.  Only stainless steel, high purity aluminum, and Teflon are acceptable.  We use high density PE for many things at the moment – our peroxide came in drums lined with it, we use HDPE carboys for intermediate storage, and a HDPE graduated cylinder for test run measurements.  Our drum pump is PE and PVC, and our vacuum loading hose is PVC.  I am replacing our test stand loading hose with some braided Teflon and a length of aluminum tubing, and I am shopping for an all-Teflon diaphragm pump for the drum, but I am having a difficult time finding either Teflon or stainless steel carboys and graduated cylinders.  I found one place that listed 20 liter Teflon carboys and 2 liter graduated cylinders (just what we want), but they wanted $3725 for the carboy, and it turns out they aren’t in stock anywhere, and would have to be fabricated.  FMC actually suggests glassware, but I hate having breakable glassware filled with peroxide in the shop.


Anyone have suggestions?


Dissolving Check Valve


Last session, we were having a very hard time doing biprop testing due to inconsistent flow through our solenoids.


On Tuesday, we built new, high amp switch boxes, installed a stainless line filter from www.normanfilters.com (overpriced at >$600, but in stock), and flushed out our plumbing.  We put a manual ball valve on the test stand hose, and tanked it up with a couple gallons of water.  When you cracked open the ball valve, water would spray out rapidly, but when fully opened, the water would cut back to a relatively small stream, and the behavior changed when you tried it again.


This was highly bizarre.


We suspected we might have a collapsed hose, but when we disconnected the hose from the bottom of the tank, a ball, a spring, and a couple chunks of white plastic fell right out of the tank.


We disassembled some things, and found that one of our regulated pressurization check valves was now a straight through tube.  This is positively where the little plastic bit on the valve seat came from, and now that I think back on it, we may have had this check valve in line with the solenoid way back when we saw the plastic on the valve seat before.


This was an all stainless steel and Teflon check valve, but the Teflon had gotten rather hard and crumbly, and eventually fallen apart.  This was one of our very early purchases, so it had been exposed to peroxide over a year ago, and may have been slowly deteriorating since then, even though it hasn't been in peroxide flow service with much of any regularity at all.  Mark Henry (ex Beal propulsion engineer) had mentioned to us once that not all Teflon is completely peroxide compatible, and this seems to be an example of that.  Unfortunately, industrial suppliers don't make a distinction.


After capping off where the check valve used to be, we reloaded the tank with water, and everything flowed the way it should.  We put the solenoid back that we had cleaned out, and it also flowed fine, although it seems to have picked up a tiny leak, probably from getting a dent in the valve seat.


On Saturday, we replaced the check valve with another one we had around, but it had a serious amount of back leakage.  We manually checked a second check valve with a nitrogen tank, and found that it also had a slight amount of leakage. We opened up a brand new check valve, and while it was a lot better, you could still detect a small amount of flow coming through it if you closed off the outlet with a wet finger. 


When we examined the leaky check valve, we found another piece of plastic jamming the ball open.  It isn’t clear if it was like that when we installed it, or if it happened in the system today.  If it was today, the only place I can see where this could have come from was the nitrogen bottle, so we probably need to add another filter there.


We also saw another interesting effect today – when the kerosene tank is drained at a moderately high flow rate, the liquid in the sight glass is pulled out due to the venturi effect, which then starts pulling some gas from the top of the tank.  I plumbed the sight glass up with a 1/4" T at the bottom of the tank, which involves enough speed to drop the pressure.  I am going to re-plumb it with 3/4" fittings, which will keep the flow velocities much lower.


Metal Spinning


Tooling for metal spinning turns out to be a lot more expensive than I expected.  Apparently, it is necessary to make several intermediate forms when you are spinning something down to anything other than a shallow angle, so large items can require literally tons of tooling to be fabricated.  The tooling quote for a 2’ diameter nosecone / upper fairing was $9000.  I was given a reference to another company (www.gcmetalspinning.com ) that already has tooling for some nosecones, but their closest fit is 22.5”, so we will have to make a step adapter.


I am going to get quotes from filament winders for nose cones and base flares.  This should be a lot cheaper, because they only need to make one low strength piece of tooling.


Tooling for spinning the 12” motor was also almost $9000, with units then costing $3300 each.  We investigated rolling and welding the nozzle from plate, but apparently standard equipment can’t roll quarter inch plate to a 4” throat diameter.  I got one quote for fabricating the catalyst chamber out of welded plate and 12” ID tube, but it was more expensive than the spinning due to the labor and inspection costs.  It is looking like it is going to be cheaper to machine the entire thing down from a 600 pound block of stainless, which seems unfortunate.  This makes it much cheaper to use four six inch diameter engines instead of a single twelve inch diameter engine, which may push us back towards a differentially throttled design like our original little lander, instead of the central engine and attitude thrusters we are currently using.  That would also make our potential control authority issue completely go away.


Parachute Tests


We did three rocket drawn parachute firings, with mixed results.  Even trying to insulate the rocket motor, we burned a hole in the chute when it came back down on it.  It doesn’t take much heat at all to melt the thin nylon canopy.  When we tried to give the rocket a long enough cable so it could fall outside the canopy, we broke the cable.


It looks like we are going to have to put the chute in a free bag, and let the rocket pull the bag completely away, and come down by itself.  I wanted to have everything come down in a single unit, but it looks like that imposes too many risks for the canopy.  We are probably going to mount the rocket like an “escape tower” on the top of the big vehicle nose cone, and let it pull the cap away underneath it, which will serve as a deflector for the parachute bag that it will drag out below it.   Testing for this will have to be done in a big open area, because the nose cap will fly a couple hundred feet away from the test site.  The free-bag will function as a fine streamer for it, so it should recover without any trouble, it is just another step I would have liked to avoid.


We used Pro-38 motors today, which were a joy to use compared to Aerotech motors.  We are going to buy a couple dozen for future testing.




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