1) Attitude sensitivity.
Angling the tube towards the centre of the lower portion is fine for the
gauge but what about the engine ? With the outlet at the back and low fuel
level, you can only climb or the engine stops (and should be descending !).
This could be cured by taking the outlet from the side, but then you could
only roll one way, almost as bad. (The outlet should really be at the bottom
of a cone with obvious new problems).
So the bottom of the gauge tube would be best next to the tank outlet, but
this is clearly getting academic, you just mustn't get low at all. On the
main side, may climb, may survive. On the reserve side, mayday, may not
(:-))
2) Airspeed sensitivity.
If the tank vent does not produce cabin pressure, there will be a speed
dependent correction/calibration required. The size of the "rain hole" in
the vent pipe outlet will affect this, as well as the angle to the
airstream. AFAIR it is arranged for some degree of positive pressure.
Disconnecting it to vent in the rear fuselage is a non-starter as fuel often
spills out during filling, and anyway with its various apertures, it could
be below cabin pressure. I will do some manometer tests and report.
Graham C. G-EMIN
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