December 1, 2001 Meeting Notes
New Manned Vehicle
We did a full up test fit of the new vehicle frame today,
installing all the plumbing we could without the two tanks that arent here
We did a drop test from a foot off the ground with Russ
seated in the vehicle, and it bent a bit at one of the braces, so Bob is going
to add some more strengthening to the frame before we fly it. We also turned it upside down in all
possible landing positions with Russ seated inside it:
Landing this way would be bad news all around, but there is
a lot more protection for the pilot than in the previous vehicle.
Ready to go, but for the tanks:
The electronics box has had a couple minor changes. The last time we flew, we accidentally left
the electronics box on, so when I looked at it days later, the battery had been
completely drained down and ruined. I
replaced the main electronics battery with one nearly twice the size, which we
had needed to do since we added the standalone 802.11b module and more pc104
boards. Our current draw is right at
two amps with everything on, so we should have about two and a half hours of
life with the new battery. The solenoid
/ motor battery is 3.3 amp hours, which never gets even a fraction discharged,
but it still needs to be pretty beefy to source the nearly 20 amps that the
actuators need. To make sure we dont
run it down again, I put a big, bright power light on the box top.
We have argued the cases for different ablative / cooled /
exotic material nozzles for our hybrid motors for a long time, but I am looking
into another potential option now.
Molybdenum is a step down the exotic materials list from the
iridium - rhenium nozzles that we have talked about, but it may still be useful
for us. Moly alloys can retain good
strength to 3000 deg F, which while a lot lower than rhenium, may still be good
enough for us. The combustion
temperature of a peroxide polyethylene hybrid is around 4000 deg F, but if
you run the grain all the way down to the nozzle instead of leaving a
post-combustion chamber, then you get a lot of film cooling, which may keep the
nozzle under 3000.
Moly is reported to be a pain to work with, but you can still
turn it on a lathe, and there are welding methods for it, which makes it a lot
nicer than rhenium. Like rhenium, it
does oxidize at elevated temperatures, so it will need to have a protective coating
applied. I believe that any of the
platinum group metals would do, but I have found some definite references to ruthenium
plating on molybdenum. www.artisanplating.com offers plating
of many PGM for consumer uses.
I have requested a quote for some bar stock from www.csm-moly.com , which we will make some test
nozzles out of, and some information on larger scale fabrication options.
We have started pursuing a new direction in conjunction with
our current work. It originally came
out of nailing down all the difficulties in doing parachute recovery from
outside the atmosphere once you start talking about putting controllable dive
brakes on a vehicle, it is worth considering some other mechanical additions to
the vehicle. The original HMX Roton
has a lot going for it, and while Rotarys SSTO design was extremely ambitious,
it seems that there are dramatic simplifications that can be made by
sacrificing flexibility and performance down to the suborbital level.
We are basically looking at making a tiny monoprop roton.
There are three key advantages that we see:
It may be possible to fly to 100 km using only monoprop
peroxide with a rotary design, which would be a big win in development and
test. You get significant atmospheric
augmentation up through 50,000 or so, and after that you get extremely high chamber
pressure on the lifting rockets even with light tanks. I dont know enough yet about prop drag to
properly simulate this, but it sounds in the right ballpark. Jeff Greason of XCOR mentioned to us that
there is a significant EPA marker at 5000 pounds of peroxide, so that becomes
one of the gating design factors for us.
We would almost certainly not undertake development of a biprop roton,
which would be significantly more challenging.
A rotor can help solve the suborbital recovery in several
different ways. At the least, it can
act as an already deployed drag break to orient and slow the vehicle down to
subsonic speeds for a normal parachute descent, even if the blades are
completely stalled. If the pitch is
adjustable, autorotation can get you down to a pretty reasonable rate of
descent (30-60 fps straight down, slower if you have ground speed), and you may
be able to flare for a soft touchdown.
A small amount of reserve propellant could allow a powered soft landing
It may be easier to deal with the FAA if you have a vehicle
that gets its lift from a rotor instead of a rocket. This may turn out to be an important consideration.
Im sure we can make one fly, because there are at least two
existence proofs of peroxide powered helicopters the Rotary Rocket ATV, and
the Firebird: www.intora-firebird.com
. It is much more debatable if you can
fly straight up at over 500 mph with one, then transition to supersonic ascent,
then reenter at mach 4 or so. The
fastest helicopters only climb around 60 mph, but prop planes can exceed 500
mph (horizontally), so that part seems reasonable with an appropriate power to
weight ratio, but everything after that would be unknown territory.
There are tons of design choices rotor at top or bottom, fixed
or adjustable pitch blade, powered landing or parachute landing or flared
autorotate landing, rotating shaft or rotating hub, swiveling tip engines or separate
rotate / lift engines, engines on props or separate extensions, etc. I believe that it is possible to get
attitude control by pulsing the engines as they rotate, sort of like an
in-plane helicopter style cyclic, but our first vehicle will use our existing
attitude control engines, with the drive prop just replacing the main lifting
We have a bunch of shafts, bearings, clamps, motors, and
gears now, and we have started assembling some different configurations. The old stand-up lander frame is getting turned
into our rotary test stand, which we will probably have something spinning around
under in a month or so. Once we have
that going well, we will attach a prop to it and get some lift measurements,
then fly it in a vehicle.