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Will,
Your sight gauge woes are common. Attached is a visual of what the
problem is. Essentially any fuel trapped in the vent side of your sight
system above the fuel tank fuel level adversely affects the fuel level
in the clear sight tube.
Not to insult intelligence of anyone, but the only way to keep the sight
tube vent side clear is to run it uphill all the way to the vent. I
personally don't like the overhead vent because the low pressure area
over the top of the aircraft creates changes in the sight tube level
also. To remove some of that problem, I prefer folks to put a tee in
the fill neck to allow the tank and the sight tube to be the same air
pressure. That said, running the sight tube vent side so that fuel can
never be trapped in the line on a mono or trigear is very difficult. At
times for a tail dragger, it is impossible. I have a sight gauge in my
trigear that works flawlessly. But it runs above the tank, downhill
---From the top of the fill tube. But it still can get fuel in my vent
side. I know mono owners that have very accurate sight tubes but took
great care not to trap fuel in their upper line. Following Chapter 30
of the build manual, it shows a method to run the foot mounted sight
tube and it works well normally at cruise speed.
Most government regulations on aircraft require some means to visually
determine the amount of fuel in the fuel tanks by the pilot during
preflight because electronic gauges and senders are prone to their own
inaccuracies. I have a sight gauge, a fuel quantity gauge, a fuel
totalizer, and a wrist watch and knowledge of my engine's fuel usage per
hour. I also carry a small piece of tubing which inserts into the
inside of the fuel neck on to the tee to blow out any trapped fuel that
some line boy fueling my aircraft injected into my sight gauge line.
Talk about the department of redundant redundancy.
In the analysis from years of tinkering on quite a few aircraft: The
Europa electric fuel gauge works pretty well for a resistance unit. The
capacitance types work OK unless you change fuel from 100LL to auto fuel
as the capacitance is different leading to inaccuracies. Fuel flow
senders work generally well.
On my 914 I have a JPI. If I set the fuel on the totalizer accurately,
it is dead on accurate. The Grand Rapids dual flow are OK but require a
bit of setup tinkering then are quite good. The 912 and 912S do not use
a return flow meter and are OK but no system on these engines works
perfect, but it is close. Dynon newer systems like the Skyview use dual
fuel senders and seem OK, but all the older units can only use one
sender and are fairly accurate on the 912 series engines. Sight gauges
are a necessity to assure you that you have sufficient fuel to complete
a mission unless you always top off before any flight and land well
before a fuel low situation. I just never find myself in those
circumstances...
Regards,
Bud Yerly
Tech Support
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----- Original Message -----
From: William Bliss<mailto:william@wbliss.co.uk>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Tuesday, December 18, 2012 5:58 PM
Subject: Europa-List: Fuel sight tube
<william@wbliss.co.uk<mailto:william@wbliss.co.uk>>
Dear All
My fuel sight tube is about to be renewed. It does not seem to be very
accurate. Is there a more reliable installation position than the
pilot
footwell?
Will Bliss G-WUFF
-----
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