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Vehicle work, Pilot harness

Milled brackets

January 7 and 11, 2003 Meeting notes


Vehicle Work


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 access panel.


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.  Joseph’s Bobcat is fine for our drop tests, but it can’t 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 didn’t approve of our $50 polyethylene / PVC siphon pump, so I had to spend a few thousand dollars on a Teflon solution.



Pilot Harness


We installed and tested the pilot’s 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 G’s of acceleration will obviously be less comfortable…


Test fit:



Final position:



Phil got us a supply of foam beads wholesale, so we don’t 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.




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