January 7 and 11, 2003 Meeting notes
We mounted the fill connector and did test fit-ups of the
engine plumbing. We have decided that
the computer to engine and parachute wiring harness is going to be permanently
glassed to the side of the vehicle, along with several spares, with connectors
on both ends so the computer and engine bulkhead can be removed. We probably should have made the top section
another 6 long, because we are going to be forced to put some connectors on
the bottom of the electronics bulkhead so they can be attached through an
The Esteem wireless unit has been repaired at the factory to
replace. Phil made a custom shielded
enclosure for the RF section, so we can run it without the case and save a lot
of layout space on the electronics bulkhead.
We will range test it the next time we go out to the test site.
I have the new Ampro PC104 system booting, but I am going to
try and get it to run from the built-in Compact Flash socket, instead of our
external IDE-Flash drive, because it will save a board and reduce total system
interconnects. I tried to get previous
systems working with CF, but I always got intermittent drive errors under Linux
with the Kingston CF cards. I tried
again with the new system, and the behavior is the same, so I am going to try a
different brand of CF.
We expect to do our instrumented crushable nose-cap drop
tests next Saturday.
After much debate, we have decided to do the hover tests of
the new propulsion system with the system suspended from a crane. We originally planned to hack on some temporary
landing gear and fly it like our previous vehicles, but the bottom bulkhead is
so tightly packed that it would turn into a bigger project than it is worth. Josephs Bobcat is fine for our drop tests,
but it cant get enough total height for a decent hover test. We talked about fabricating various tower and
cable arrangements, but just renting a small crane for a few hundred dollars
turns out to be much easier and cheaper.
Our Teflon diaphragm pump also arrived this week. FMC didnt approve of our $50 polyethylene /
PVC siphon pump, so I had to spend a few thousand dollars on a Teflon solution.
We installed and tested the pilots harness in our big test
cone. The harness was mounted on a 40
diameter bulkhead of 2 thick aluminum core fiberglass panels, secured with
generous filets of epoxy / flox on both sides.
The vehicle will be reentering and landing nose-down on a long,
crushable nose section, so the pilot is arranged with his back to the top
bulkhead. This means that the pilot is
launched with his back on the ceiling, basically hanging from the seat. We expect this to be a moderately
controversial decision, but there are some strong systems reasons why we want
it like this.
I milled custom seat belt mounting brackets out of a bar of 7075
aluminum. I have moved to 2 flute, high
helix end mills for aluminum, which work better then the general purpose 4
flute end mills I was using. I still
managed to break two of them on the last pass of the 1 deep by 0.25 wide
center slot of the bracket, before I figured out that I had to drop the depth
of cut down to 0.1 (from 0.25) after the pocket got over 0.75 deep to
prevent the chips from clogging up in the deep slot.
Brackets and backing plates:
Joseph hung from a single strap and bounced up and down on
it, which is a lot more force than it will take during flight (under 3G
acceleration for a 200 lb pilot divided over the four straps), and there was no
discernable flexing on the back plate.
We cut belt holes in one of the custom foamed seats, and
Russ strapped in. Adjusting the lap
straps was difficult because they were so short, but we eventually got
everything tightened down, then we had the rest of us turn the entire cone
upside down. The belt position shifted
during the rotation, leaving Russ very uncomfortable with it over his stomach
instead of his hips.
To fix things, we welded a bracket to the cone for the crotch strap, which keeps the lap belt
from moving upwards, and we put a pad between the cone side and Russ to keep
him from sliding down. The next foam
seat we make will have a lot of extra volume going up the wall to make the
supplemental pad unnecessary. We also
added a foot rest and hand rests. This
time, it was comfortable, and Russ reported that he could stay that we for a
long time without a problem. Doing it
at a couple positive Gs of acceleration will obviously be less comfortable
Phil got us a supply of foam beads wholesale, so we dont
need to butcher a bean bag the next time we make a foamed insert. We are still considering the possibility of
using memory foam / Tempur foam instead of custom foamed seats. The two pads that I got from Aircraft Spruce
were rather expensive, but the same basic material is available in mattress liners
up to 4 thick for a drastically cheaper price, so we are probably going to see
what we can do with cutting one of those up.