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Fuel leaning above 18000 feet AGL?

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I noticed that the chieftain gets right at it's limits with throttle and fuel leaning at around 18,000 feet AGL. I'm pretty sure this bird can get to higher altitudes, but throttles are maxed and any additional leaning causes the engines to cut out completely. Has anyone else noticed this?

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I had a look at he performance tables and was able to achieve near enough the figures there. Took the aircraft to FL240, about 23 minutes. Take-off using full throttle (MAP 43), full rpm. Climb - I backed off the throttle to MAP 40 and rpm to 2400. I leaned mixture, and as you say, things get a little tight at high altitudes.  MAP began to fall above 17000 feet so adjusted up to 40. But by FL200 it had fallen to 35 at full throttle travel, and at FL240 it was 30.5.Referring to the tables I used 2300rpm and MAP29 and leaned the mixture to get a fuel flow of about 32GPH. EGT was about 1225°F. This gives me about 136KIAS/197KTAS.


32GPH is only slightly high compared to the tables, but leaning is a few % "Lean of lean", with a tooltips indication of 12% on the mixture levers. If I go rich of lean, the mixture levers are at 16% and EGT at 1275°F. Airspeed is at 138KIAS/200KTAS and fuel flow is now 38GPH total.

Best Regards,

Philip M Wafer


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