G SERIES PILOT’S GUIDE .
INSIGHT
INSTRUMENT CORPORATION BOX 122, FORT ERIE, ONTARIO, L2A 5M6
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Another observable characteristic is that the required fuel flow is dependent on altitude under conditions of constant rpm
and manifold pressure. It may seem reasonable that the optimum mixture for a given power setting should remain constant.
However, when the turbo compresses the induction air it also increases its temperature and reduces its density.
Although the manifold pressure is restored, the oxygen content of the induction air is reduced because it is a function of air
density. It should be remembered that the exact nature of this complex and confusing issue is dependent on the engine and
installation. For this reason it is difficult to make generalizations about the leaning characteristics of turbocharged engines,
but one thing can be said with certainty: a generous enrichment of the mixture from peak will prolong the life of exhaust
valves, the wastegate and the turbocharger itself.
Special Considerations for Twins
Some twin engine aircraft exhibit an unusual mixture control reversal characteristic. We speculatively attribute this to the
long flexible cable used to link the cockpit controls with the engine. The phenomenon is easily observed in aircraft with fuel
flow gauges. When the pilot pulls back on the mixture controls to lean the engines, fuel flow is reduced and the EGT rises
as expected. But when the mixture controls are pushed forward to enrich the mixture, the fuel flow continues to drop and the
EGT drops on the lean side of peak. Even though the mixture control is moved in the rich direction, leaning continues.
It would appear that the function of the mixture control has temporarily reversed! Continued movement of the mixture control
picks up the slack and normal mixture function resumes. The magnitude of this phenomenon varies from aircraft to aircraft,
but we have observed transitions of up to 1.5 gph past peak before the fuel flow began to increase.
Monitor the fuel flow gauge to identify this phenomenon in your G3-4
