Quote:
Originally Posted by SteveC  I'm not yet convinced of your contention that 1" = 100 RPM. Do you have more charts available that support your thesis? |
Here are two charts that I adapted from "Theory of Flight" by Richard von Mises. I left the numbers off because they would only clutter the chart. I calculated the slope of each line. The rule of thumb that shdw is proposing is derived from the ratio of the two slopes. The slope of the left chart is the torque of the engine, which is relatively constant as you reduce RPM, keeping the manifold pressure the same.
The slope of the right chart is determined (I think) by the rate at which the mean effective pressure (MEP) in the cylinder changes with changes in manifold pressure.
The numbers support shdw's thesis, on an engine very different from the ones in the airplanes he flies. I don't consider the issue proven, though, unless you can make an argument as to why the slopes of the two graphs should always bear the same relationship to each other.
Steve, as for the "O-320" chart you posted a link to (the actual chart says "O-360"), it really doesn't have the range of data to make a comparison to the IO-360 chart you posted; rounding errors could easily throw the data into the same range as the numbers shdw and I generated.