"EDR" wrote in message
...
Interesting that many have not defined the origin of the placement of
the "red line" on the tachometer.

I don't know where to look it up, but I suspect it has something to do
with prop tip speed (as one poster mentioned).


It can have something to do with it, but the same engine in different
airplanes will have a different redline. The thing that changes is TBO. The
propeller chosen for that installation will be consistent with the engine
service life desired.