Re: running over-square

Doug wrote:
The same is true in an automobile. If you go up a hill, stay in high
gear and floor it as opposed to shifting down and NOT having to floor
it. It is not intuitive. For maximum fuel economy and least engine
wear go for the least revolutions per MILE.

The trouble is that is isn't true in either an airplane or an automobile. Jay is correct that the tach records less time, but you can't be sure that you are using either less fuel or incurring less engine wear. If you run too slow with cylinder pressures to high, you will run hotter, often much hotter in a water cooled engine that depends on the water pump speed to circulate coolant. And running way below the torque peak is not efficient fuel-wise at some point either.


It's a bit different in a plane, because you are dealing with a
constant speed prop instead of transmission with gears, but the
principles are the same.

To a degree. There is an optimum point and running too slow with cylinder pressures too high is not the most efficient at some point.


There is one other caveat, and it can be a big one. That is to run the
engine where it is smoothest. You can feel it.Vibration shakes thiings
apart, and the less the vibration the better off your aircraft is
going to be. So keep that one in mind too.

That is generally too, but there are exceptions here as well. Some frequencies of vibration are much more damaging to certain instruments and components that are others. What feels good to a human may be killing a sensitive instrument.

Matt
.

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