September 6, 2003 notes
I am going to start putting a link to each Armadillo update
at Frontier Files Online, a Slashdot-like message board system run by the Al
Differ of JP Aerospace and the Space Frontier Foundation. I get a lot of useful suggestions from
people by email, but it will probably be interesting to let everyone publicly
discuss Armadillo technical issues, and my replies to specific comments will
probably be of interest to more people than just the comment author.
We had a pretty light week, because delivery of our big
catalyst order was delayed again. They
are now projecting a ship date of next Friday, but I am trying to get them to
ship three 5.5 rolls earlier so we can do engine testing next Saturday. Engineering designs certainly do benefit
from using standard parts that are available for next-day shipping from
McMaster-Carr, but there are a few specialty items that we just need to deal
with longer lead time suppliers on.
Don Stark is reporting that he has the first five gallons of
concentrated 90% peroxide ready for us, but I told him we dont really want to
start using it until we have at least 20 gallons on hand, enough for us to
ground test, hover test, and flight test the small vehicle, barring
problems. We have contracted for five
hundred gallons of peroxide from him, which will be enough to do all the tests
we want with the small vehicle, and fly the big vehicle a couple times with
silver screen based engines if the mixed monoprop engines wind up not working
out. If the mixed monoprop engines do
work out, we will wind up sitting on most of the 90% peroxide until we get back
to working on biprop engines for upper stages.
We had an interesting experience looking for replacement
zippers for our space suit the seamstress that we had given it to was looking
all over the DFW area for appropriate heavy-duty zippers, and finally found
some at a tent / awning fabrication shop.
It turns out that the owner was actually involved in making the original
space suits for the monkeys way back in the early 60s US space program. He knows exactly what to do, so we just
turned the project over to him.
Several readers suggested mooring line snubbers for line shock
absorbing for our big hover tests. They
were cheap, so I bought a couple of each size, but it turns out that they
arent nearly strong enough for us. The
thickest snubbers, designed for 1 diameter lines, broke with only about 900
pounds of force. This is probably still
a good direction to investigate, they must have larger snubbers of some kind
for ocean going ships of various kinds.
It still seems to me like there should be some arrangement used with
steel cable that operates on the same principles as wire rope isolators, which
would allow us to use them without insulation.
We have matching press plates for both the 5.5 and 12
diameter engines now. The next engine
we build will have the pack plates welded in with the assembly under moderate
pressure to prevent any warping. We
should have laser cut pack plates from Global Stencil for both engine sizes
We finished up the preheat system for the full size
vehicle. Four quick connect lines go to
each engine and meet at a manifold on the ground, which is connected to 50 of
line leading to the propane and air tanks.
We plan on using compressed air tanks instead of an air compressor in
the field, because an air compressor capable of supplying 16 cfm sustained is
very large. Because the air tanks will
be significantly emptied during the preheat, I bought a dual stage regulator to
minimize the pressure drop. If the air
flow dropped off, the fuel mixture would go closer to stoichemetric, and we
would start melting screens in the engine.
I am still a little concerned that even if the air flow stays constant
in CFM, the density will be increasing due to the reduced temperature as the
bottle empties. The flow meters we are
using are not temperature insensitive, so there is some self-correction, but it
may still be a factor. We changed to a
larger flow meter on the air side, so we can measure enough to preheat four
engines at once. Small check valves in
our preheat system limited us to flowing 14 cfm, so we will have to replumb
some of those to ½ to get the flow to our desired 16 cmf. At 14 cfm, one air bottle ran four a bit
over 4 minutes, which is borderline for a full preheat, so we will probably
take two bottles.
We changed the compression thread on the spring cannon over
to a 1 diameter acme thread with a bronze nut and added a big T handle, which
makes the compression a lot smoother.
We noticed that our retention cable that keeps the spring and piston
from flying out of the cannon is fraying a bit. At first, we thought this was from the shock, but it turns out
that it gets pinched by one of the shackles during compression. We tried another mounting point, but it
didnt fix the problem. When we build a
6 ID cannon, we will have a lot more room to give it a separate mounting
We built some simple strap clamps to allow us to bolt the
hatch on the vehicle without requiring air pressure to push it in place.
We prepped five 1 KZCO valves for the big engine
development and deployment. Our prep
work consists of venting the ball valves, bridging over the thermal cutoff control
(if we are flying, we would rather have a valve motor die trying to operate
than cut off when it gets a little hot), and soldering some terminals on the
The welded distribution manifold still leaks, so we started
working on a replacement that would be configured with two ports on two sides,
instead of one port on four sides, which will avoid the need for a big 90
degree fitting. I was boring the main
3.75 deep by 1.8 wide hole on the mill using helical interpolation with a 1
diameter end mill, but half way down it grabbed and broke the bottom cutting
edge off the bit. It would have been
faster to just bore it manually on the lathe, but I tend to prefer building
parts on the CNC mill, because it makes building the part a second (or third)
time a lot easier.