Hello Kingsley,
One reason for a higher fuel flow at altitude for the same MAP and RPM is that
your engine is developing more power. Taking your example, full throttle/20"
means
you are at around 10000 ft. At this altitude, the outside temp is minus 4,5C
(standard atmosphere) This is almost 20C less than at sea level. Then your
engine is developing 7% more power (293/273). The Rotax runs richer at altitude.
Based on my experience, this over rich mixture increases the fuel consumption
about 10% at 10000ft compared to low altitude at the same power. You say your
fuel flow is 40% higher: that is surprising and I assume your flow meter is
not accurate.
I do not have any experience with the Hacman, but I have done some testing on my
912ULS with my own mixture system (using an electric pump to suck pressure out
of the carb bowl vents). The system worked fine, was fail safe, but there was
no power gain at full throttle at altitude. This was disappointing and I decided
that the possible 10% fuel saving was not worth the additional complexity.
Remi
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