Ben Jackson wrote:

In article ,
C J Campbell wrote:

The tach should almost always run slower than the Hobbs. The Hobbs is a
clock, but the tach is connected directly to the engine and should only
click off one tach hour when the engine has turned 60 x max rpm.


But it's not "max rpm". In my Comanche (260hp IO-540, redline 2700RPM)
it's 1:1 at 2300RPM. I think the "definition" of tach time is 1:1 at
cruise.


This sounds like it would be appropriate for a CS prop because you can
always load the prop up at these low RPMs and still get 65% even at 8000
ft. For example the C-172RG also with an O-360 180HP Lycoming will put
out 68% power at 8000 ft 2300 RPM and 22MP.

I would think that the Archer fixed pitch prop would be calibrated
differently. To get 65% on a standard day at 8000 ft requires ~2480 RPM.

John Roncallo