Carl,
One possibility is that one or both of the seals on your filler cap is not
effective.
The fuel gauge symptoms you describe are the same as leaving the fuel cap
off altogether, whereupon the relatively low pressure in the vicinity of the
fuel filler cap in flight immediately sucks the sight gauge to zero.
Duncan McF.
----- Original Message -----
From: "Carl Pattinson" <carl@flyers.freeserve.co.uk>
Sent: Saturday, September 08, 2007 2:48 PM
Subject: Europa-List: The Factory Fuel Sight Gauge
> <carl@flyers.freeserve.co.uk>
>
> Many builders avoided this nightmare and fitted a capaticance or other
> similar gauge.
>
> We originally figured that fitting a fuel flow meter would be sufficient
> along with the factory sight gauge. Our reasoning was that as long as the
> rear wheel was raised such that the aircraft was level (we use a spirit
> level to check this) the sight gauge ought to be reasonably accurate - for
> refuelling purposes only.
>
> Last weekend we fuelled the aircraft with 40 litres of fuel on top of the
> 15 already in the tank (15 l is our minimum safety level - ie: 11 in the
> reserve plus 4). The sight gauge indicated 15 l beforewe refuelled and 55
> l after which is what we expected. The estimated flight time was just
> over 2 hrs excluding arrival and departure.
>
> As soon as we took off the sight gauge indicated the tank to be virtually
> empty which caused a degree of worry (you can never be certain there isnt
> a leak !!!). This lack of fuel continued throughout the flight and on the
> return. Before we put the plane to bed we re checked the levels and as
> expected there were 20 litres remaining (having used 35l according to the
> Fuel Flow meter). So far so good !!!
>
> Yesterday we planned for a similar trip and started to refuell with 2x 20
> litre cans. About halfway through the second can the fller tube filled up
> and we ended with fuel everywhere. Assuming this was nothing more than an
> airlock we lifted the tailplane to shoulder height (it is a momowheel) in
> the belief that this would clear the blockage - IT DIDNT !. The tank
> appeared to be full whatever we did.
>
> So we drained off 20 litres through the drain valve and rechecked the
> levels - guess what - 45 litres !!! The tank holds at least 75 litres (it
> is one of the originals). 75-20 should be 55 litres. So we put back all 20
> litres without any problem.
>
> Then as soon as we took off the gauge indicated empty!
>
> We should point out that as part of our refuelling check we first blow
> through the vent pipe (that enters at the top of the tank) to clear it and
> then we blow back the fuel down the sight gauge till air bubbles into the
> tank to clear any possible airlocks. In theory this should ensure an
> accurate reading.
>
> The problem seems to be that the filler pipe has what is in effect a U
> bend which fills up with fuel and it seems that the breather pipe is prone
> to a similar problem - despite blowing through both to clear them.
>
> If this theory is true then as soon as the fuel pumps start delivering
> fuel to the engine this will create a partial vacuum in the tank which
> would explain the low sight gauge reading.
>
> Has anyone else had a similar problem or are we the only ones using the
> old style gauge. We are aware that some of the sight gauges are fitted to
> the seat backs but according to the above reasoning this problem would
> still exist.
>
> Any suggestions ? (other than retrofitting another type of gauge). We have
> enough on our hands with mod 74 !
>
> One thing we were considering is replacing the filler pipe with clear
> plastic fuel tube (it is available) - at least it would be easier to
> diagnose the problem.
>
> Carl & Dot
> G-LABS
>
>
>
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