In a message dated 10/24/2002 9:06:26 PM Eastern Daylight Time,
marv@lancaironline.net writes:

>  Lynn,
>          With your experience with oil temps and its effect on rotor brgs
as
> a
>  guide
>     what do you about the usefulness of HI temp coatings (rotor faces) as
>  advocated
>     in recent posts to reduce rotor bearing temps? I fully understand this
is not
> a
>  real
>     problem at the power and RPM levels we normally use in our aircraft.
>    
>         Kelly Troyer
>  

     That area has been getting much better in the last few years. The NASCAR
people picked up on that way back. Ceramic coated piston tops and Teflon
coating on the sides. They could run very close piston to wall clearance to
hold the ring package dead square and not worry about the piston getting too
hot and getting too big for the hole. Any energy (heat) that escapes into the
oil or water is energy wasted. The perfect engine would have an EGT the same
as the intake air. Smokey Yanuk (I hope that's right) insulated the inside of
aluminum heads so they couldn't transfer as much combustion heat into the
coolant. Same idea. Later they ceramic coated the combustion chambers. Still
less heat lost to the coolant.
     If the people doing it have experience doing Rotors, so that they mask
all the grooves off properly, it sounds like a good idea. If that ceramic
gets into anything important, the rotor is scrap. Less oil, smaller oil
radiator, lower fuel consumption and less weight. Sounds pretty good so far.
But, the coating just insulates the combustion side of each rotor face so
that it cannot absorb as much of the heat. So lower oil temps. Lower temps
overall reduces probability that an overheated bearing can occur. However,
much higher localized temps occur in the oil wedge between the bearing
surface and the crank. Just a small amount of the oil between the bearing and
the crank is superheated to some ridiculous temperatures. This is where and
why the bearings get overheated. The spent oil is forced out by fresh oil
under pressure and it mixes with oil that was not in the wedge area. So you
look at the gage and say to yourself, look, the oil is only 220 degrees on
climbout. No problem. Keep the hammer down. But what is the highest oil temp
in the bearing interface? 275? 300?
More? I don't know, but it sure isn't 220 is it? The 220 is sort of a poorly
done average of all of the oil spilled from the bearing, plus all of the
rotor cooling oil from the spray holes in the crank and the oil falling back
out of the rotor after cooling it.
While the rotor bearings will survive at 220 degrees (indicated) for a while,
how long would you want to run them that hot? The strength of the soft
bearing material is going away fast above 220. I think I would spend the
money on a bigger cooler. Better to make 180 the maximum and keep shooting
for 160 on climb out. There is more power to be had at 160 anyway.    

Lynn E. Hanover