http://www.eaa.org/education/fuel/cessna_study.html
The above site may be of interest
John, A230
----- Original Message -----
From: Nigel Charles <72016.3721@compuserve.com>
Subject: Re: Europa-Fuel contents
> Message text written by "LTS"
> >Advantages:
> Inexpensive
> Very low current draw
> Not susceptible to fuel density changes (like a capacitance device)
> Does not break if in contact with water
> Very well damped
> Readings are very consistent
> Very reliable
> Currently used by four of Europe's leading A/C manufacturers (soon to be
4)
>
> Capacitance gauges may appear more accurate because they have better than
> 1/8th resolution but because of the variations in fuel make up they are
> often less accurate. The difference being with our gauge if it indicates
20
> litres you have at least 20 litres. Whereas with a capacitance gauge if it
> says you have 22.5 litres may have 22.5 litres then again you may not.
> <
>
> I would say that the reliability is the main advantage. I have a double
> probe capacitance system and will report back if I lose accuracy. The very
> low current draw is not an issue as no gauging systems use significant
> amounts of current anyway. I would suggest that, looking at the percentage
> accuracy we are talking about, fuel density is not a significant issue
> either. Even if there is a difference in fuel density between Avgas and
> unleaded it is unlikely to amount to much (does anyone have any figures on
> this?). In fact one of the reasons for large aircraft using capacitance
> systems is that fuel weight is more important than fuel volume as energy
is
> proportional to weight not volume. Water is without doubt the main enemy
> to the capacitance system. Keeping moist air out of the tank and filtering
> the water out of the fuel in the first place is important. Damping can be
> achieved in any electrical gauging system by using the appropriate level
of
> capacitance. Without doubt the magnetic system will be consistent
> particularly if the fuel quantity is measured at each switch changeover
> point.
>
> I still feel an accurately set up integrator system using a fuel flow
> sender is likely to give the best results. It still needs a tank gauging
> system to act as a cross check to guard against misinformation due to
leaks
> and must be updated during refuelling. It doesn't need to make allowances
> for tank shape and senders are typically calibrated to 2 - 3% which is
> likely to be much better than any existing gauging system. With large
> aircraft, where large amounts of fuel in several different tanks over
large
> periods of time have to be measured, we find that the guages are often
only
> more accurate at full and empty. In between the linear accuracy of the
> integrator system proves to be more consistent.
>
> However we measure the fuel quantity, having a final warning in the form
> of a reserve is a useful measure to ensure a landing is achieved before
> fuel exhaustion.
>
> Nigel Charles
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