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Armadillo Aerospace News: Vehicle work, Lox engine work

Published by Sigurd De Keyser on Mon Nov 1, 2004 12:08 pm
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chabot imagearmadilloaerospace.com: Vehicle Work


We welded dedicated lifting points to the tank top flanges for easy hoisting.

The drogue cannon is mounted on one of the legs. This is a standard drag race parachute, which won’t slow the vehicle down to anywhere near a soft landing, but it will point the nose to the ground, which should let the nose absorb most of the energy as a crush cone. All the base gear is really sturdy, so we expect to be able to reuse it after a drogue-crash.

With the tank on, but no crush cone or electronics, weight is up to 810 pounds.

We continue to have problems getting good seals on > 1” pipe threads, especially mating aluminum and stainless, and they usually gall up on removal. We are trying Teflon sealing paste now instead of tape. It is messier, but hopefully it will seal better.

We loaded two drums of water into the tank to test the new system. The larger diameter loading hose and the elimination of one of the check valve in the loading line should give much faster loading times, and it did. The first drum loaded in 5 minutes 45 seconds, while the second drum loaded in only 3 minutes 15 seconds more, because the vacuum continued to improve. We were a little surprised to see some water splash all the way up into the fountain tube and spit out the vacuum pump when the second drum finished loading and the rest of the vacuum sucked air through the loading line. We may have to watch out for this while loading propellant, and we might want to add some kind of a splash guard to the fountain tube.

We logged the differential pressure transducer output when we drained the water back into the drums:


You can clearly see the linear drop in level as the first drum is emptied, the pause as we switched to another drum, then the slope change as the propellant level dropped into the bottom tank dome. We will calibrate with real propellant mixture when the flight computer is reading the sensor, but this should work out just fine for us.

The custom electronics boards are due in next week, so all that will be left is mounting the electronics and making the wiring harness.

Putting the new vehicle together has taken a lot longer than I expected. We have probably diluted out focus with all the lox engine work.

Lox Engine Work

We did more regeneratively cooled runs with the lox engine on Tuesday. We added a thermocouple to the outlet of the cooling jacket to monitor temperatures. At 150 psi, methanol boils around 130 C. Now that we have both flowmeters working, we can actually tell what our mixture ratio is.

The first run was lean, and worked its way up to 100 C temperature after 20 seconds, and looks like it might have climbed a little bit more. We replaced the big fuel solenoid with a ¼” ball valve to increase fuel flow and did another run. Thrust jumped to 380 lbf, but we were now quite a bit rich. Coolant temperature stabilized early at 70 C. We should be able to throttle the fuel valve to cover a wide O:F range now.

Our chamber pressure reading keeps getting messed up with this engine, it looks like we are getting a splash of methanol clogging up the porous snubber we use to help protect the transducer. We may not even need the snubber with the length of thin pipe we stand the transducer off from the engine, but I went ahead and got some really coarse (75 micron) snubbers for our future tests.

Our combustion efficiency is still poor, even with an extra stainless steel spacer between the preburner and the cooled chamber for more volume, so the heat load will go up a fair amount when we start getting the Isp we want, but it looks like we have a fair amount of cooling margin. Now that we know the fuel cooling is going to be ok, we are starting on a new cooled chamber that will have the fuel injectors integrated directly from the cooling passages. This prevents us from doing water-cooled runs, but it cuts down on the plumbing and gives us much better fuel distribution.

We are also looking at making a “pancake preburner” that could fit directly on top of the cooled chamber instead of hanging off to the side. If that works out, it may allow us to package everything very neatly.

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