Svein,
I basically agree with what you wrote. However my proposed schematic
is very close to the one recommanded (and optionally supplied) by
Rotax in the 912 Install Manual (see attached). This arrangement works
on most LSAs so I do not see why it would not work with the addition
of the fuel flow sensor as propsed.
Regards
Remi Guerner
<<<<<<At first sight, your proposal may look like the obvious
solution. With
respect, however, I think it is not to be recommended for 912ULS
installations (I do not know enough about 914 to comment on that
engine).
Contrary to what seems to be a common assumption, the return flow
through
the restrictor is not insignificant - it is roughly 10 litres per hour
(i.e.
roughly half of the net cruise consumption, or roughly 1/3 of the fuel
going
to the engine is flowing back to the tank). The reason for this
relatively
high surplus circulation is of course to reduce the time the fuel is
exposed
to heat before it reaches the carbs, by increasing the flow velocity
through
the fuel line. According to the build manual, the return line
branches off
at the point farthest from the pump, just before the left side carb
(assuming the fuel line goes from the pump to the right side of the
engine
with a short branch off to the right carb, and from there across the
back of
the engine to the left carb).
Moving the return line branch-off upstream (closer to the pump)
increases
the risk of vapour forming in the fuel lines downstream from this
branch-off
point. By how much, I do not know, but maybe it is critical under
unfavourable circumstances. "Maybe's" under the cowling are not nice
- - -
- - .>>>>>>>>>
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