Remi,
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 - - -
- - .
Regards,
Svein
LN-SKJ
-----Opprinnelig melding-----
Fra: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] P vegne av Guerner Remi
Sendt: 22. oktober 2010 19:53
Til: Europa-List Digest Server
Emne: Europa-List: Rotax fuel flow detection
Thank you Ian for posting the LAA mod.
I have not installed a fuel flow in my aircraft but if I had to, I would use
the attached schematic which allows measuring the flow to the carbs with a
single sensor, therefore improving accuracy and reliability and reducing
cost.
The same principle can be used for the 914. In that case the single flow
sensor would be installed between the pressure regulator and the carbs.
Remi Guerner
F-PGKL
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