Novermber 28, 2004 Notes
We got one of the main computer boards in, but it has some
issues, and the motor drive board still isnt done. We didnt find out until this week that some of the PC board
mount CPC connectors we had specified werent available, and of the few
connectors that they actually got installed, one was the wrong polarity, and
another was missing hold down screws.
In any case, we are finally bringing up the board, with Russ
making hand soldered changes as necessary.
We have already found a few things we would like to revise in the
future, but Im certainly not going to wait on another rev of the board before
flying the vehicle.
We upsized the hose from our LOX dewar to the test stand,
but our flow didnt increase at all, so we are limited by the dewar dip tube
and globe valve. We are probably going
to have a custom tank made with 1 or larger plumbing.
We built and tested another all-aluminum preburner that uses
a large central burner chamber instead of expecting some of the burning to take
place in the radial pancake sections.
This design also tried a significant simplification instead of having
an external LOX vaporizer to feed GOX to a control solenoid for the burner, we
just drilled three 1/16 holes from the LOX manifold into the burner area. The idea is that the aluminum facing the
burner will be hot enough to vaporize the small amount of lox flowing through
the little holes, and since we start the lox flow first anyway, everything
should just work. The spark plug is
also positioned on top, instead of on the side.
We made several extended length runs with it (without a
chamber below), and everything worked out well. The first spark plug we used had too much reach and burned off
the top, but when we switched to a shorter one, it showed no signs of damage at
all. The internal lox vaporizer worked
great, all starts were instant. We did
notice that at least the top of the burner was frosted over after the long
runs, and there was a slow drop in the main gox temperature as the runs
stretched towards a minute, so we think it is likely that at thermal
equilibrium there is actual LOX getting through the holes to the burner, which
messes up the mixture ratio a bit, but it doesnt seem to be hurting the burner
operation other than slightly reducing the total output temperature.
We are probably going to try pulse width modulating a
solenoid to demonstrate throttling with the preburner, because the flow is far
too small (0.022 injector orifice) for any of our proportioning valves. Were not sure how that will work out, but
we will find out
We are still running
all the valves with manual control switches right now (we dont have any of the
tight timing issues that most liquids have, because we bring the lox vaporizer
up all by itself to start), but when we get our spare flight computer
electronics boards, I plan on using that to bring all the engine actuators
under closed loop control. At that
point we should finally be able to demonstrate the smooth biprop deep
throttling that we have been developing the engine for.
We have built a new channel wall cooled chamber that has the
external contour follow the nozzle contour to increase the cooling. As an experiment, I actually used the CNC
mill to cut the external contour. It
was nice to be able to cut the contour and the cooling channels without
changing the setup, but it took 14 hours on the mill to cut (it did fine
completely unattended), and even with 3 degree steps, there is a pretty
noticeable scalloping on the slopes.
We filled the channels with pressed in slivers of wax, which
turned out to be much more labor intensive than expected pressing them in was
pretty easy, but cleaning all the wax off the area in between the channels,
especially at the nozzle, took several hours.
We had intended to wrap epoxy impregnated fiberglass pipe repair tape around
everything, then melt the wax out, but we couldnt get the tape to follow the
nozzle contour worth a damn, so we aborted that operation, and we are going to
instead try to wrap epoxy impregnated fiberglass cord around the chamber on
We are going to try making a gun-drilled chamber /
hyperboloid nozzle sometime soon, which we have reason to believe may be the best
way to go, but likely has a minimum reasonable size a couple times bigger than
what we are doing now.
Im going to be lazy and just dump up all the pictures Matt
took for the last several weeks, you can try and match them up with the last
two updates yourselves