Mon Jun 11 2007

Capacitive sender nutplates

The wire for my little compensator probe is going to be about six or eight inches away from the vent line, so I was trying to think how to route the wire. I considered using some little plastic clips like we use for tidying up wires at work. The problem is that the only plastic I know of that's really inert to fuel is polypropylene. And it has crappy structural properties. So I tried something really simple...weaving the wire through a series of holes. I prototyped the setup in a scrap piece of aluminum (actually my practice riveting sheet). I think this'll work if I goop the wire over with proseal to prevent it from moving and chafing through the insulation.

It looks even better when I squashed the wire flat.

I drilled holes for attaching the wire lug to the little senders. Since I'm only going to use one of the polypropylene washers between these angles and the stiffeners, the head of the screw would have been quite close to the stiffener, so I bent the corner over to give more clearance for the screw head.

I also drilled all the sender plates to their respective ribs and attached the nutplates. The plans show countersinking the sender plates, but the material is only .025 thick. I don't think you're supposed to countersink anything less than .032, so I dimpled the plates and countersunk the nutplates as well. Countersinking the nutplates was a real pain. Maybe I should have tried dimpling them instead.

I had to call my friend and fellow builder, Brent Owens, to find out how far the aft edge of these plates should be from the aft edge of the ribs. The plans call out dimensions for RV-4, 6, and 8 but not 7. Brent is building an 8 and verified that his tank ribs are the same as on the RV-7. So I used the dimension on the fuel sender plans that was specified for the 8.

It sounds like Brent's gonna be ready to start assembling his tanks soon. I hope he gets me involved to help out. I like working with Brent and I would also like to get some experience with proseal assembly before working on my tanks.