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Date: Tue, 17 Feb 2009 22:21:41 -0500
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: hauling gas
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SHIPCHIEF@aol.com wrote:
> That's an interesting antecdotal story, and I believe it's true. And a 
> cracking tower would be a lot more likely to have fuel vapor around due to the scale 
> and nature of the operation.
> But the question remains, in our application, has anyone EVER put a meter 
> between the aircraft and the fuel nozzle to see if any static voltage exists?
>   
I think the burning linemen in those military videos I've watched would 
say, "Damn the voltmeters!  Just ground the airplane."  But, heh, those 
guys weren't smart enough to stay out of a FIRE.  What do they know?

> Why is it not required for cars? Is there any significant difference? They 
> are both grounded thru the carbon black in the tires?
>   
The tires of the car are constantly grounded (unless you're one of the 
Duke boys), and the fuel pump at the gas station is tied directly to 
ground.  You've kept your airplane wheels off the ground for a while, 
and park beside the fuel truck on a concrete pad (much higher resistance 
than asphalt or dirt).  The static charge has to pass through your 
tires, the concrete and then the truck's tires to equalize.  How long 
does that take?  It's a simple RC circuit.  No problem to calculate if 
you know the capacitance of your fuel system, how much static has built 
up, and the path resistance.
> I'm not advocating unsafe operation here; I just want the facts so I know 
> where the potential danger is really coming from, not some armchair monday 
> morning quaterback, look over your shoulder whiner's dictum, like not allowing you 
> to fuel your own car in Oregon. Oregonians look just as smart as anyone else to 
> me?
>
>
>   
The danger is very real, and the USAF has the coroner's reports to prove 
it (notice the 's' at the end of report).  If you don't ground your 
plane, nothing will happen for the vast majority of the time.  But that 
last time you don't do it, may well be the last time you'll ever have to 
worry about it.

I generally think there is to much scaremongering in the aviation 
community, but this is a known problem with a bonehead simple solution.  
Its one of those situations where smart pilots use their superior 
judgement to avoid having to use their superior skills.

-- 

http://www.ernest.isa-geek.org