September 13, 2003 notes
Much to our dismay, our big order of platinum catalyst has
been delayed again, so we didn’t get to do any engine testing this week. They say it is due to ship next Thursday
now. Also no update on our 90% peroxide
supply.
I spent Thursday at White Sands Missile Range discussing our
flight operations. WSMR is a
spectacular location for flying rockets, but they are a military facility, and
they aren’t really sure they want to be involved with commercial manned rocket ships. We have some good supporters there, but they
consider flying something before the end of 2004 a “very aggressive schedule”
just to get all the paperwork done.
Cost may also be an issue – a test taking full advantage of all the
range facilities, like tracking, telemetry, flight termination, and other
services, can cost $180,000 per test flight.
That is a lot more than our entire vehicle costs, so we clearly aren’t
interested at that level. Our position
is that all we want from them is a clear range, and we will handle everything
else. We need to convince them that our
vehicle absolutely, positively cannot leave the range boundaries under any
failure condition, so we can fly without real time monitoring and a flight
termination system. Somewhat
surprisingly, the dominant factor by far is drift under the main parachute if a
series of failures causes the vehicle to apogee at 100,000’ and deploy the main
parachute there. High winds can cause
it to drift a long way by the time it gets to the ground.
I think I finally found The Right Thing for absorbing shock
loads on the hover test of our big vehicle.
They are called “snatch straps”, and are used for recovering stuck off
road vehicles. Unlike a normal tow
strap, where you bring the line up taught and slowly apply load, these are
designed to actually have the pulling vehicle take a run at it with a slack
strap, building up a lot of energy.
Normal nylon straps stretch about 10% at their breaking point. Snatch straps are woven so they stretch 20%
at half their breaking point, and are designed to do that many times. We are going to use these for both the
hanging and ground restraint strap on the big vehicle hover test. The ground restraint will be enclosed in a
tubular woven ceramic insulation sleeve to protect it from engine heat. Really cheap, too – a JC Whitney item.
We have started using ¼” stainless cable for some things
recently, like the lines going through the top of the cabin wall to connect to
the snatch strap shackle, and the line to the drogue on the bottom of the big
vehicle. This is as big as we can go
without needing a hydraulic crimper, and gives us 5700 to 9000 pounds of
strength, depending on the cable configuration. Working with chain and shackles is usually a lot more convenient
than wire rope, but the wire rope is a lot lighter for a given amount of
strength. When we fly the big vehicle
with the big engines, we are going to need significantly more strength in the
drogue line, so we may wind up going to an insulated synthetic (spectra / Kevlar
/ etc) rope to save weight over a huge stainless cable. We did figure out that if you cut the cable
with a welder and bead the end a bit, it is a lot easier to work with than if
you manually cut it.
Our big piloted solenoid valve, a ¾” 6242 series from Snap
Tite, arrived this week, and we built a big pneumatic drogue launch tube to test
it. Results were better than
expected. The valve is more compact
than I thought it would be, and it has nice positive opening and closing. Our previous experience with piloted
solenoids from a different manufacturer was not so good, but I like this
model. Our small vehicle uses the giant
30 amp direct acting NOS solenoid to dump a 600 psi tank into its small drogue
tube. We had found that a good O-ringed
piston was necessary to get this kicked out.
With the big piloted solenoid (that only draws 1.5 amps), we were able
to punt our big parachute all the way across the room even without an O-ringed
piston, at only 250 psi tank pressure.
We had some difficulty dealing with 50’ of ¼” stainless cable connected
to the drogue, though. It can’t coil in
the 4” diameter drogue tube, and various methods of external coiling are
difficult to both guarantee deployment when you want, but not do anything bad
under high flight wind loads before deployment. We may wind up just using a larger diameter tube.
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We did some more work on our Russian space suit now that the
blown zipper has been repaired. We got
an excellent book on the topic: http://www.amazon.com/exec/obidos/tg/detail/-/185233732X/qid=1063573608/sr=8-1/ref=sr_8_1/002-0650100-0153661?v=glance&s=books&n=507846
which gave us some important information.
The likely reason we blew the bad zipper was that there was a restraint
strap missing on our suit, which put a lot more stress on the zippers than they
should have held. We fabricated our own
clasp, which seems to work well. We
closed up two more notable leaks through various fittings on the suit, and it
is holding air a lot better, although it takes more than 2 scfm of flow to get
up to operating pressure. It looks like
a couple of the other zippers were weakened when we popped the bad one, so we
are going to get them all replaced before taking it back up to 5 psi.
http://media.armadilloaerospace.com/2003_09_13/repairedSuit.jpg
We built another big welded aluminum main distribution manifold,
and were very frustrated to find that it has pinhole leaks as well. We went over it a second time with a bit of
vacuum drawn in the manifold, in hopes of having it suck weld into the
pinholes, but it still had problems. We
don’t seem to have any problems making pressure tight welds in stainless, but aluminum
is giving us problems. We are using
6061 for the machined parts, but I don’t know what alloy the Earl’s –16 AN
fittings we cut off for the hose connections are. We did good surface prep, and the welds looked good, but there
was still pinhole porosity. We are
considering going to SAE straight thread fittings with O-rings for the
manifold, but we might just wind up with 1” NPT, although we would really like
to avoid big pipe taped connections.
Our big wire rope isolators arrived. They are just giant versions of the ones we
have used on the manned lander and the tail flare vehicle, big enough to absorb
landing shock for a 2400+ lb vehicle. Powered
landing instead of parachute landing is still where we want to go in the
future, and we will probably do some testing with it on the current
vehicle. This is somewhat higher in
priority than it used to be, because getting flight clearance for 100km turns
out to be a lot easier if we don’t have to worry about parachute drift. The downside is that it would be a lot scarier
for the pilot.
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Joseph built shelves to allow us to install all of our base
station equipment in the back of Phil’s suburban, so we won’t need to have any
set up time for flight operations. The equipment
we use is: laptop, joystick, Esteem wireless Ethernet, ATV receiver, TV/VCR
combo, 2m/80cm mobile transceiver (not pictured), and a big inverter to run it
all from the truck battery. There will
be three yagi antennas mounted on top of the vehicle. We will get everything bolted down in place next week.
http://media.armadilloaerospace.com/2003_09_13/baseStation.jpg
We got a hopper spray gun from Home Depot to test spray
application of our Fastblock insulation.
We had hand packed it on the engines for the small vehicle, but we need
to get some idea what the spray coverage on the big vehicle is going to
be. We added some water to it and
sprayed it on a test panel, but we are going to need to get a mixing system to
remove all the lumps in the future.
http://media.armadilloaerospace.com/2003_09_13/sprayGun.jpg
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