October 25, 2004 notes:
I was traveling on Sunday, and had trouble finding the time
to do the update
The X-Prize forum moved a little while ago, the new location
I still check the Official Armadillo Q&A Thread
regularly, and this is the place to ask any questions that may have general
interest, rather than sending me email.
All the fabrication for the base is done, but we ran out of
argon before some of the final welds were completed.
The base with the engine and shocks is 293 pounds, and the
manway with all the plumbing is 67 pounds, for a total of 360 pounds. We probably threw away all our weight
savings by making the landing gear framework out of stainless instead of
aluminum, but it is much sturdier.
We are milling pocketed backing boards for the new
electronics boards, so they will be supported extremely well.
Regen Lox Engine
The new cooled chamber is back from the hardcoating shop,
and we did several runs with it, including our first fuel cooled run.
We did some long run tests on various lox vaporizer coils,
and learned some interesting things.
All tests were with an NOS pro race solenoid with a 0.11 (about)
orifice. The little coil we had would
flow gox for twenty seconds or so, but after that it would be all frosted over
and lox would be coming out. We went to
a longer 10 coil of 3/16 OD aluminum tubing wrapped around a 2 aluminum
pipe. This ran longer, but still
eventually failed to vaporize. We went
to total overkill with 40 of 3/16 tubing, and it ran for several minutes, but
the frost slowly crept up the tube, and even this eventually started spitting
lox. The flow rate was also way down
from frictional losses.
It is arguable that we may not care if lox reaches the
preburner after it has been running a long time, because it should still burn
fine, just at a leaner ratio. However,
we decided to try to keep it vaporized by wrapping 10 of tubing around the
chamber (outside the cooling jacket) and using a metal filled epoxy to give it
good heat transfer to the chamber. Even
with just the vaporizer running, the chamber gets quite a bit of heat thrown
into it, so it will never cool down to lox temperatures. This seems to work fine. We will probably make an external channel
wall jacket for this at some point in the future.
We got a brand new methanol preburner fully operational, so
we now dont need any consumables other than the main propellants. We used a normal spark plug instead of our
concentric tube arrangement, and we used a tiny Bete spray nozzle directly on
the bottom of a solenoid to minimize trapped volume. We had to go all the way down to a 0.018 jet on the methanol to
keep the preburner from getting too hot with methanol pressure at 400 psi and
lox pressure at 300 psi. One of these
solenoids can flow enough methanol to vaporize lox for a 10,000 lbf engine.
We got the lox turbine flowmeter working by drawing a vacuum
on the lox plumbing to pull out all the atmospheric moisture. It has been working fine ever since. At 300 psi, saturated lox is at 134k and
0.87 g/cc density, while methanol is 0.79 g/cc density. We want to run somewhere between 1.25 : 1
and 1 : 1 O : F by mass, so we basically want to flow roughly equal volume of
lox and methanol.