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Old 09-13-2017, 08:20 PM
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flytoboat flytoboat is offline
Join Date: Dec 2006
Location: Collinsville, IL
Posts: 599

Originally Posted by scsmith View Post
The Lycoming performance charts in the Operating Manual show HP at various RPM and MAP combinations. At lower RPMs (below 2400), the power curves stop at various MAP, with a notation of "max pressure for continuous operation", presumably because Lycoming does not recommend operating at that low an RPM and high MAP. Its kind of like lugging your car in too high a gear. For reference, the chart for my IO-360-A1A shows 28 in. Hg limit at 2300 RPM. (figure 3-24 in my Operations Manual).

That being said, you make a good point about fixed pitch prop operation. The thing is, you open the throttle and start your ground roll, and although static RPM might be 2300, the RPM very quickly increases. And of course engine power increases with the increasing RPM, so by take-off, you are getting much higher RPM and close to max engine power. This takeoff transient is not what would be considered 'continuous operation.'

That is quite different from doing a go-around with a constant speed prop set at 2300 RM, where full throttle and 2300 RPM will be maintained for an acceleration and climb to some particular altitude where you may consider it safe to change engine settings, presumably either pushing the prop forward or closing the throttle some.

Of course, all this only has significance near sea level where there is enough pressure to be an issue.
Note also that the notion of "over-square" being a problem itself is disproved by the performance charts. The charts define the max MAP for each RPM and the boundary is WAY beyond the fake limit of 'square'.
My full throttle climb at 115Kts yields 2350RPM at 10.4GPH. I don't have my Manifold pressure sensor installed yet.
VAF #1100, EAA864
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