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Vehicle modifications and tests, New engine test

November 22, 2003 notes

November 22, 2003 notes


Vehicle modifications and tests


Because the new engines have the mounting flange on top, and hang down a lot lower, we had to raise the vehicle up a fair amount and relocate the engines.  We moved the engine mount points inboard, and made an extension to mount the wire rope isolators directly under the support struts.  We chopped off the old extension brackets we had previously used for the isolators (hurray for the plasma cutter…), so this was actually a small net savings in weight.  If we started over, we would just have longer side panels and angle braces and avoid the extension.




Useful tip: we were using a carbide hole saw to cut the opening for the new engine plumbing into the bulkhead plates, and it was very problematic after the first ¼” or so of aluminum depth.  On the second hole, we discovered by accident that if there was already a hole drilled through the plate somewhere on the perimeter of the circle being cut, it goes dramatically easier because it can clear chips and get a good bite.  The remaining holes went much faster.


For the new engine mountings, I made full milled rings for the 3 degree roll cant for the engine mounts.  Previously we have used separate little angled blocks, but with the flat engine top it is nice to make a single piece with the exact angle.  We still use separate blocks on the opposite side of the bulkhead plate, but if I make new bulkhead plates I will mill the angles directly into pockets around the bolt holes.





We filled the 850 gallon tank all the way up with water, which took nearly three hours, and started pressurizing it from our fill trailer.  These style tanks always make some distressing snap and pop sounds the first time they are pressurized, but this one is ten times the volume of the smaller ones we use, so everyone was a bit on edge.  We took it to 450 psi without incident.  We were a bit concerned about the support leg bonds and the cabin bond possibly having problems as the tank stretched, but none of them seem any worse for the experience.


We did six landing drop tests on the wire rope isolator landing gear.  We did 6”, 12”, and 18”, then added 50 gallons of water to the tank and did 6”, 12” and 18” again.  There is a bit of a bounce, but everything held up fine.  We were concerned about the aluminum channels we had used as spacers, but there wasn’t any sign of bending.  The isolators do take a set after they have been hit a few times, especially in the shearing-over-the-coils direction, and they were rather resistant to just prying back into shape, so we may need to make some jigs to allow us to push on them with a hydraulic press to square them back up.




We took delivery of a liquid nitrogen dewar, which we plan to use for pressurizing the big vehicle tank for flight operations.  Filling the entire tank to 300 psi takes almost six big nitrogen bottles, but a single dewar holds enough nitrogen to allow three flight tests.  It can only put out 250 psi nitrogen, so we may still need a couple bottles when we want to go to higher pressures.




The last aluminum distribution manifold we made was leak free at the welds, but we were having some problems sealing at a nicked AN cone, so we tried to just weld up a stainless steel manifold without any custom milled parts.  This turned out to go surprisingly well – we chopped off the threads of some –16 AN fittings on the band saw, ground them by hand to a somewhat circular face profile, cut a section of 2” pipe, plasma cut a circle to weld on the end, used the carbide hole saws to cut side holes in the pipe, and welded it all to one of the flanges that came with the 2” KZCO valve.  It probably took less time to do this than it took to do the precision helical boring for the aluminum ones on the mill, and the extra length on the pipe gave us a lot more room for things.





New engine test


We got our new catalyst order in, so we welded up what we hoped would be a production engine.  The 600 cells-per-square-inch catalyst was only slightly heavier than the 400 cpsi – 324 grams vs 275 grams.


We built the engine with three separated catalyst blocks in the hot section:




Note that the stack is upside down compared to the engine, the screens go at the inlet side.  The blue caps are just indicators of open space where the glow plug ignition chamber goes.


When we put it on the test stand, we had high hopes.  The engine preheated much faster than previous engines, likely due to the denser cold catalyst doing a better job at decomposing the 50% peroxide before the glow plug chamber.  The catalyst all got evenly orange hot from the preheat, and the run was perfectly smooth and clear.  However, it still didn’t make the nozzle glow with the first run, and there were cooler spots in the catalyst at the end of the run.


We doubled the amount of propellant and let it run for 12 seconds, which it did perfectly, but only a couple patches on the chamber heated to red hot, and there were some dark areas in the catalyst at the end of the run.  Measured Isp was still low, as we saw on the previous monlith-only engines.




We are going to make a few changes in the next engine we build, because we aren’t confident that this won’t quench on longer runs, and we don’t want to risk the vehicle.



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