December 10 and 14, 2002 Meeting Notes
We have been doing some work with seating positions and seat
forming in the full-size mockup. It is
rather interesting how some things that look like they should work on paper,
just dont quite work when you have to get into them
Cutting out a bunch of plywood and seeing where everything fits
is easy and valuable.
We are planning on using individually custom foamed seat
liners in the big vehicle. The basic
enclosure will be made of honeycomb core panels that contain a bag filled with
expanding foam that is cured around the pilot.
This is very lightweight, rigid enough for good support, but still
absorbs energy under heavy impact.
Our first test just used straight two part polyurethane foam
poured into a bag the pilot was sitting vertically in front of. It was difficult to get consistent back
support with this, so our second test started with bean-bag foam that was
wetted down with mixed polyurethane foam.
This allowed us to lay the seat frame down and push the foam filled bag
around a bit before the laid down on top of it. The foam expanded to fill up the gaps, giving a pretty good
overall structure. We will need to do a
few more experiments to get the exact proportions right, but this looks like a
pretty good arrangement.
We are going to be doing a series of drop tests with various
crushable energy absorbers, and eventually manned couch drop tests to start
giving us a good idea of just how hard a given deceleration actually is. I recently bought a 50g accelerometer for
instrumenting these tests.
We are giving strong consideration to flying the high
altitude vehicles without static stability.
The major plus is that the whole fin assembly just goes away, saving
mass, forward area, and fabrication time.
The major disadvantage is that as soon as your propellant is expended,
you are going to start spinning if you are still in the sensible atmosphere.
Our control system already deals with neutral stability
conditions in hover, but I need to do a lot of simulations to see what the
response is like with actual instability at high speeds. I am running into some interesting issues
with the control system running the four servo valves already, and the code is
getting some restructuring as a result.
The idea would be to have a drogue chute that acts like a
spin-stabilizer chute for unstable jets.
As soon as the main engine burns out, the chute would go out the back,
providing passive stability. That would
cut our coast altitude drastically, but that doesnt bother us at all. For an X-Prize vehicle, the trajectory could
be tailored to burn out at a very high altitude (not optimal, but it doesnt
hurt too much) where the drag forces would not be very severe. With a Kevlar drogue and monoprop engines,
we could even eject the drogue while the engines are still burning, so there
isnt any period at all of instability.
There is a bit of a temptation to do a flight with the
honeycomb board box fin can just to have a conservative success, but we are
leaning towards just making the next flight attempt without fins.
Another advantage is that a pilot bail-out looks a lot more
survivable if you dont have to fly past a fin can at the base of the vehicle.
Final fire department inspection
Get the CNC mill running
Finish quad motor driver board
Silver for four engines
Milled aluminum engine mount bulkhead
Finish quad engine flight control code
Some kind of temporary landing gear baseplate
For high altitude flight:
New PC104 (with soldered ram) configuration
Fix Esteem antenna connection
Install rigid nose cone
Turn and install nose bulkhead
Test crushable nose sections
Drogue ejection control
Main parachute release control
High dynamic range GPS integration
High power backup telemetry
Video camera integration