Mxsmanic wrote in
:

Is it normal to have throttles set to the maximum during cruise, in
small aircraft? I always set them all the way forward because that
seems to get the best speed, and the engine parameters still stay in
the green areas, but I don't know if this is actually a good idea.
Obviously it would be a bad idea in a car, but perhaps aircraft
engines are specifically designed (?) to operate mainly at full
throttle during cruise.

In other phases of flight I use other settings: always full throttle
for take-off (the manual said so), and low settings or idle to
descend. Also if I'm not in a rush I use lower throttle settings at
cruise, as long as I (or the autopilot) don't have to keep the nose
too high to maintain altitude.

So what is the deal? Is it okay to run for several hours at full
throttle?


At altitude in a normally aspirated engine, full throttle may not present
maximum engine power. As a sim guy, you probably don't need all the
details, and I'm not fully versed in the mechanics of it anyway. But
basically, as you climb, the air becomes less dense, and the amount of air
let into the system by the throttle is effectively reduced. The effective
result is that while the throttle is fully open, the amount of air getting
in is going down, as if you were very slowly closing the throttle.

From my experience with the planes that I fly, once you get up to 6500' or
so, the engine at full throttle will produce 75% power or less (less as
you go higher). Variance in temperature and pressure may have impact, but
that seems to be the "standard".

I have read that engine manufacturers actually do this on purpose because
they cannot precisely control how the air is restricted when the throttle
is partially closed, so it's best to run the engine with the throttle wide
open if possible (ie: if it will produce 75% power or less).

From what I have been taught, cruising at 75% power for an extended
period of time would be worse than partially restricting the airway with a
partiallly closed throttle, so if you're cruising at 2000', you probably
don't want the throttle wide open...