Perhaps I could add some of my observations to this discussion. I have
recently done some checks at various altitudes and can report the
following :-
All results were done on the same flight and are at 5,500 rpm, at full
throttle and the heights are pressure altitudes. The engine is a 912S
and I have the data to prove that my fuel flow meter is accurate.
2,500 ft, OAT = 13 degC, 6.6 US gal/hr.
5,000 ft, OAT = 9.5 degC, 6.2 US gal/hr.
10,000 ft, OAT = 7 degC, 5.5 US gal/hr.
I did not note the EGTs but will check these next time out.
I do not have any technical info on the Bing carb but it appears to me
that the fuel flow rate is certainly being adjusted with altitude. This
is consistent with my understanding of how the similar SU carburettor
works with the free floating piston and tapered needle being positioned
according to the pressure in the carburettor throat. If the absolute
pressure in the throat at full throttle is lower due to increased
altitude/reduced density, the tapered needle will be lower in the jet
and the fuel rate will decrease accordingly.
Cheers, John
N262WF, mono XS, 912S, Whirl Wind C/S prop, 220 hours
Mooresville, North Carolina
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