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Formed seats, Flying unstable, Critical path

December 3 and 7, 2002 Meeting Notes

December 10 and 14, 2002 Meeting Notes


Formed seats


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 don’t 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.


Flying unstable


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 doesn’t 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 doesn’t 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 isn’t 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 don’t have to fly past a fin can at the base of the vehicle.



Critical path


In general:


Final fire department inspection

Peroxide delivery

Get the CNC mill running


For hover:


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

Watchdog computer





High dynamic range GPS integration

High power backup telemetry

Video camera integration




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