Headlines > News > Armadillo Aerospace News: SFF '04, Vehicle base, LOX engine work

Armadillo Aerospace News: SFF '04, Vehicle base, LOX engine work

Published by Sigurd De Keyser on Mon Oct 18, 2004 12:11 pm
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chabot imageSFF ‘04

No update last week because most of us were at the Space Frontier Foundation ’04 conference. We debuted a new Armadillo video, which is now linked off of the Armadillo home page. The high point was a long talk with Burt Rutan the day we left

Vehicle Base

The new vehicle base is almost completely assembled. We still have to add braces between the shock mounts, fabricate insulated housings for the vane actuator motors, and do final welds, but it should be ready for initial operational testing soon.

http://media.armadilloaerospace.com/2004_10_17/baseAssembly.jpg (jet vanes not installed)

The new differential pressure transducer finally works, so we will have a fuel gauge for the next flight.
The total set of plumbing on the vehicle is:

On the gas tube:
loading vacuum port / manual pressure vent
piloted solenoid for drogue ejection / computer pressure vent
pressure guage
pressure transducer
low pressure side of differential pressure transducer
possibly the gas source for engine bubbling if we need it for stability

On the liquid tube:
engine valve o-ringed slide seal
propellant loading check valve
propellant drain valve

Directly on the manway cover:
high pressure side of the differential pressure transducer (not on the liquid tube to avoid velocity effects)

On top flange:
pressure relief valve

LOX Engine Work

We finished the multi part welded cooled engine assembly, which is getting hardcoated. The CNC mill I bought two years ago had a fourth axis rotary chuck, but we had pulled it off the table to free up space early on. We finally hefted it back up to mill channel slots on the motor, but it turned out to have a huge 0.090” runout. I couldn’t figure out any way to adjust it, so I wound up actually milling the jaws until they were concentric, which seemed to work out ok. I designed for 20 ft/sec coolant flow at 500 lbf, but the next one I make I am going to use less channels and make them deeper so any remaining runout error in depth is less critical.

We tried putting a turbine flow meter on our LOX line, but it seems to freeze up basically as soon as the line gets chilled down. We may try drawing a vacuum on it to see if the problem is atmospheric moisture.

We did some firings with the small throat uncooled chamber, and our theory about subsonic exit from the lox vaporizer does seem to be correct – when the chamber pressure was high enough to keep the vaporizer exit flow subsonic, combustion seemed much better, melting the throat out in seconds. As the throat got bigger, chamber pressure decreased and the vaporizer exit went sonic again. Interestingly, even with the chamber pressure dropping significantly as the throat widened, thrust stayed almost perfectly constant due to the flow relationship.

All of our lox engine firings so far have used separate cylinders of compressed oxygen and ethane to fuel the vaporizer. This was convenient and safe for experimentation, but we certainly wouldn’t want to have two additional consumables on an operational vehicle.

The first step was to T off the lox line before the main valve and make a coil of thin tubing to let atmospheric heat vaporize a small amount of lox for the burner. This worked fine.

http://media.armadilloaerospace.com/2004_10_17/loxCoil.jpg

The next step is to construct a burner that runs on liquid methanol instead of gaseous ethane. The smallest spray nozzle I had on hand was a 0.040” hole Bete “P” nozzle, which flows a good deal more than we need for the burner, at least with full operating pressure behind it. We made a number of burner tube firings with the methanol burner, but we had to take the methanol pressure all the way down to 50 psi and increase the gox jet size before we got something that looked near the right mixture ratio. More work is needed. Our concentric tube burner arrangement also left a lot of trapped methanol volume behind the spray nozzle on shutdown, so we need to either add a nitrogen purge or redesign to minimize the volume.

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