leaning

Tom-D

Tom-D

Taxi to Parking
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Feb 23, 2005
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Tom-D
using these numbers,

INTRODUCTION CESSNA MODEL 172S
PERFORMANCE - SPECIFICATIONS
*SPEED:
MaximumatSeaLevel ......................... 126KNOTS Cruise, 75% Power at 8500 Feet. ................. 124 KNOTS

If you were to climb to cruise altitude, level off, trim up, and pull mixture until you see 124k

what power setting would have ? 75% ?
 
I think the performance charts also note 1) at gross, 2) 8500 is density altitude, and that the whole chart uses RPM + temperature setting to get the 75% BHP. But, it makes me wonder, if you consistently tool around at 77% because perhaps the tach is off, are you going to shorten the engine life that much?
 
What makes you think you'll shorten the life at all?
 
Tom-D said:
using these numbers,

INTRODUCTION CESSNA MODEL 172S
PERFORMANCE - SPECIFICATIONS
*SPEED:
MaximumatSeaLevel ......................... 126KNOTS Cruise, 75% Power at 8500 Feet. ................. 124 KNOTS

If you were to climb to cruise altitude, level off, trim up, and pull mixture until you see 124k

what power setting would have ? 75% ?
Click to expand...

If you could do that, yes it would be 75% power. But that 8500 is density altitude, and the airspeed is TRUE. Not sure if a 172S has a TAS indicator (but it probably does somewhere deep in the bowels of the G1000).

Not all engines can make 75% power at book RPM. Especially if TBO is approaching.

Fixed pitch, it's a whole lot easier to lean to peak RPM than to do so by airspeed. You can "feel" a right mixture in the seat of the pants, at least roughly, but your butt isn't a precision instrument.
 
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