Re: Seatback sight tube

[Nigel Charles <72016.3721@compuserve.com>]

Message text written by "Miles McCallum"
>I've put one down the back of the fuel compartment on the pilot's side -
purely as a visual check before launching - and will use an Avilek
capacitance type (and a flowmeter, and time) for in flight.<

As most fuel gauging systems have either reliability or accuracy problems
it is important to have at least one backup for fuel quantity. The most
accurate and reliable system I have come across is the fuel flow integrator
method. When I test the accuracy by refilling the tank it comes out to be
within the stated accuracy for the sender (2-3%). To achieve this it needs
several refills to set the calibration number in the equipment. As this
doesn't actually measure level it is more important than ever to back it up
with an alternative system. I use a twin probe capacitance system with a
twin needle gauge. As these needles should show the same reading down to
the saddle level each provides a check for reliabilty for the other. More
recently the factory has offered a stepped magnetic/microswitch gauge. This
should prove to be more reliable than the capacitance system but its
accuracy is limited by the limited number of  microswitches. If used in
conjunction with a fuel flow integrator system it probably provides the
best overall compromise. The Europa has the advantage of having a reserve
tank as a final warning of low fuel and as a final gross error check time
based on an assumed fuel flow can be used. Some GPS sets will do this
calculation for you if you give it an assumed fuel flow.

Whilst there is no substitute for seeing the fuel level before flight a
combination of the above systems provides a suitable alternative to the
sight gauge. Finally it is always a good idea to start with a full tank.
Assuming the capacity has been measured accurately in the first place this
is the one time you are absolutely sure of the contents. In humid
conditions it is always a good idea to refuel after flight to prevent
condensation build up.

Nigel Charles