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FMC visit, poisoned catalyst, vehicle work

June 15, 2003 notes

June 15, 2003 notes


FMC meeting


We had an all day meeting on Tuesday with three FMC representatives, who we are still trying to convince to sell 90% peroxide to us.  We showed them our shop and test site, and went over everything we are doing.  We also learned a few interesting bits from them:


Buffalo Electro Chemical Corp (BECCO) is mentioned in a lot of early literature on peroxide from the 50’s.  I didn’t know that FMC had actually acquired them in the early days.


FMC’s dislike for polyethylene containers for 90% peroxide is mostly due to what can happen in a fire – molten PE can go into solution with peroxide and detonate.  In normal operation, there is some danger of embrittlement in long term storage, but there isn’t any actual incompatibility.  There was an incident where a train containing a tank car of 70% peroxide followed by a car full of PE pellets derailed.  After some fires started and some PE melted, it went boom.


They went over the specifics of what it takes to make 98% peroxide detonate – it has to be contained in a very strong container with no ullage space at all, then initiated with a blasting cap.


Propulsion grade peroxide is basically equivalent to the lowest grade of semiconductor peroxide.  In the early days, semiconductor grade was made by diluting propulsion grade, but they now have a separate process for it.  The two highest grades of semiconductor peroxide are even more pure than propulsion grade.


We had built a drain in the center of our storage shed that led to an external pit that would be filled with gravel.  We were a little surprised that FMC preferred that we close off the drain and just let any spills stay contained inside the concrete building.


We hope to hear something from them soon, but we have another source of 90% peroxide coming on line this weekend, so we expect to get the little vehicle in the air soon, no matter what.


Poisoned Catalyst


We set out to do a series of tests to improve the smoothness of the 50% / methonal combination on Saturday.  We made a spacer plate to fit between the catalyst chamber and the nozzle, which would allow us to try adding more screens or foam above the monolith as a flow straightner, or allow us to try sealing the monolith with an o-ring at the top.


First, we pulled the catalyst and looked at how water flow exited the spreading plate with the existing plumbing.  Not surprisingly, the tiny flow from the cavitating venturi we were using just sort of flowed along the plate and streamed down the sides.  We changed up to –6 plumbing, which flows enough for a proper showerhead distribution.


For the first test, we tried heating the catalyst pack with a hot air gun.  We made an extension tube with a piece of metal conduit and a sheet metal cone held to the gun with hose clamps, which worked out well.  The gun heated air to about 1100 F, and it should have circulated through the entire pack very evenly (up in the center, then back down around the sides), but when we ran the propellant, it pretty much just gushed out.


For the second test, we went back to heating the catalyst with a propane torch up the nozzle.  This time, we got thrust from the engine (about 75 pounds), and minimal liquid, but it was just a cloud of vapor without a flame.


We added a 1/8” restrictor to the feed line and tried again.  This made a flame at the very beginning, but was then extinguished and behaved as the previous test, but with only 60 pounds of thrust.


For the fourth test, we swapped the nozzle for the water cooled biprop chamber, which gives a large post-catalyst space for any delayed combustion to occur.  We had to make an extension for the propane torch to allow us to heat the catalyst pack through the long combustion chamber, but (somewhat to my surprise) that worked pretty nicely.  The throat on this chamber is much larger than the nozzle we were using (2” vs 1.25”), so at the same feed pressure it didn’t even reach sonic choking pressure, and generated basically no thrust.  There was a little bit of external burning, but it still wasn’t working worth a damn.


At this point, we believed that the catalyst had been poisoned.  We pulled the catalyst out and did eye-dropper tests with peroxide, and it was clearly greatly reduced in reactivity from the original.  It still looks the same, so we assume it is a deposition problem, rather than a stripping problem.  We had hoped that platinum based catalysts would be less susceptible to poisoning than silver based catalysts, but it doesn’t look like that is true.  We were running technical grade peroxide, but it looks like we will need to go to food or semiconductor grade.


We didn’t have any nitric acid on hand for catalyst cleaning, but we had heard from someone at Space Access that vinegar could be used to clean catalysts, so we gave that a try.  It didn’t seem to work.


We have several new pieces coming from Catalytic Products:  a 6” square by 2” thick block of catalyst, a 6” square by 4” thick block of catalyst, and a 6” square by 2” thick block of uncoated ceramic monolith that we can use for flow straighteners.  We will cut the blocks to round ourselves, so we can save the corner scraps for control tests on poisoning.


We have a bunch of weld-on flanges coming from Dyna-Turn any day now, so we will be able to fabricate multiple different length chamber extensions to fit between the catalyst pack and the nozzle, as well as allowing 4” thick catalyst chambers.  It isn’t clear if this arrangement needs additional combustion volume at all, but we will try a back-to-back comparison and find out.


Vehicle Work


Strong Enterprises recently finished a set of drop tests on the new canopy we are going to use for the big vehicle, and they are going to refurbish their test article for us, so we should have the big parachute system in hand within two weeks.


In discussing the parachute system for the big vehicle, we decided to re-rig the drogue ejection system on the small vehicle.  Previously, the drogue cannon piston was attached to its own cable, which was attached to an eye bolt inside the ejection tube.  This made fitting the piston a little difficult, because the cable had to coil inside it, and it allowed the piston to swing around on its cable and bash into things while the drogue was being deployed.  We changed it so that the piston is now connected at the point where the drogue suspension lines connect to the riser cable, so the piston will stay away from the vehicle after deployment.  It tested out fine, and seems to be a positive improvement.  The big vehicle will have the drogue ejected perpendicular to the vehicle to get it in the airstream rapidly, but the small vehicle just fires directly backwards.


I had bought some high alloy chain to use for rigging the helicopter drop test, but it turned out to be a mistake – the 2700 lb rated alloy chain is quite a bit smaller than even our 800 lb rated chain, so none of our quick links or shackles that can fit it have anywhere near the rated strength.  Back to cheap, heavy chain in the future. 


I am almost done with the data collection electronics we are going to use for the helicopter drop tests. 


We have worked out a nice engine mounting scheme for the big vehicle.  We will probably have that completed by the time we do the helicopter drop test.  We will be doing our initial flights with four 2” throat engines, but the X-Prize flights will need four 5” throat engines to fly with a full load of propellant.




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