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Date: Wed, 04 Jul 2012 13:15:21 -0400
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From: "Dan Schaefer" <dfs155@roadrunner.com>
Subject: Static discharge protection
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FWIW.

When I built my early 235 ('78 to first flight in '93) there was little talk 
in Lance's manuals or monthly mail-out about such things. Regardless, I 
decided to stuff all three tanks with the aluminum mesh "Explosafe" and 
ground the metal fuel fillers and mesh to the aircraft's ground holy point, 
where every electrical system, and the engine, is grounded with a dedicated 
return. I ran a number of bare Al wires from the fillers, thru the mesh to a 
terminal thru the inner tank wall access panel (0.062 aluminum) then with an 
insulated #20 wire to the ground point. It all cost about 2 lbs but made me 
feel safer.

Measuring the resistance from the filler cap to ground, I noted that the 
"plug" part of the cap (at least the version that came with my kit) was hard 
anodized which is a very good insulator - so originally, there was no ground 
path from the top of the cap to the aircraft ground point. To remedy this, I 
ground off a bit of the anodize on top and just under the lip of the cap and 
measured again to be sure it made good connection to the grounded filler 
ring/Explosafe-tank filler/ground holy point.

When fueling, and the pump ground clip is attached to the gear or exhaust 
pipe, I know that all my tanks are at ground potential including the caps 
and filler inlets. I was accused of a "belt and suspenders" approach but 
after almost 40 years in the aerospace business, working on the 
electrical/electronics design and production of a number of military 
aircraft, one develops some hard and fast rules about safety and I applied 
them to my Lancair - fuel tank grounding was just one. I still touch the 
fuel nozzle to the fuel cap before opening the tank but have never had a 
static discharge when doing so. After over 1100 hours, I'm still flying 
N235SP, and though I know one can't prove a negative, I think it was a good 
idea and am still happy to have done it.

One caveat: First, I don't know whether Explosafe is still available, and 
second, back in around the early 90's, there was some talk about the 
possibility that the aluminum mesh could collect moisture as a result of 
condensation on the mesh. After about 1100 hours I have never experienced 
that problem though the airplane has had to occasionally sit thru all kinds 
of temperature and humidity swings with less than full tanks. Probably 
because the Al mesh and fuel stays close to uniform temperature and not 
conducive to condensation. Can't say the same about a spam-can's alumininum 
walled tanks. (This last part about the reason for no condensation is just 
speculation but for what ever reasons, it seems to work - and after ~1100 
hours, I'm keeping my set-up).

Regards,

Dan Schaefer
LNC2     N235SP