Yellow RPM range

[N73087]

Can anyone shed some light on the caution range for engine speed? Why is it there? Is there a time limit? What happens when you disregard it?
Dave

[zero.one.victor]

I assume that you're referring to the 2450-2700 yellow band on the tach. As far as I know,the C-145/O-300 can be run at 2700 rpm all day long. In fact,I know a guy who owned a C-145 powered Swift whose Swifter buddies all had big engines. He tiold me that he firewalled the thing for takeoff,and never pulled it back until he was ready to land. Ran it for over a thousand hours like that,no problem.
With some engine/propeller combinations,there is an rpm restriction,usually something like "no continuous operation between 2000 and 2200 rpm",some kind of harmonics thing. I don't know if there is any restriction of this type on the C-145/O-300,there may be one on the Lycoming conversions.

Eric

[Mike Smith]

I had the same kind of question. It doesn't say that we can't run cruise over 2450rpm, but it does say the recommended cruise setting is 2450. The times I have checked the speed at 2500-2550 it seemed that the speed increase was about 3-5 knots for the extra 50 to 100 rpm.

Mike Smith
1950 C-170A

[N1277D]

The C145 should not be idled for extended periods at less than 800 rpm. This was due to the design of the oil system. The low rpms do not provide for adequate lubrication and cooling of some engine components. If I remember correctly this was due to the splash oil cooling/lubrication used for those engine components.