Well, the airplane RPM range is just around where the lightest bearing
loads are found. There was a chart on the other list about that. For the loads
you might see, the bearing area is huge. The first bearing failure anyone would
be likely to see is a rotor bearing, and if it still has oil pressure, that just
will not happen below 9,000 RPM. (Thus the need to lighten the rotors for
long term use above 9,000 RPM.)The rather high weight of the iron rotor is
enough to load up the bearing to a point where the film strength of the oil is
becoming important. Even then, the wedge oil temp is the culprit. The soft metal
overlay on the bearing has a very low melting temperature, and starts to migrate
away from the loaded area when over heated. This makes razor thin flakes along
the bearing edges. The bearing face will be bright and shiny rather than a dull
flat appearance of a new bearing. So those people who scream the
engine all of the time, machine off the overlay and run on the copper. The extra
.0015" is just fine for additional oil flow and the copper is a great bearing
surface. It is however, far less tolerant of dirt bits in the oil.
The bottom line is: You cannot hurt it. Cool the oil, keep the oil pressure
at 71.5 (stock) pounds or better.
Run an air filter, and it will outlive you. Check for apex seal groove
wear at 100 hours, (through the exhaust ports) then after each 100 hours.
(annual).
Tracy should have a thought on the oil type if anything special is needed
for gear box support.
The Farm and Fleet store or, Tractor supply used to have Alnico magnets
that they feed to cows to collect scrap metal that cows eat all of the time. It
keeps the scrap in their first stomach where it dissolves. Put in a course
screen so the magnet cannot block the flow.
Lynn E. Hanover
In a message dated 3/25/2008 5:32:33 A.M. Eastern Daylight Time,
msteitle@gmail.com writes:
Lynn,
Thanks for the great summary on oil. I guess I should have
provided a bit more information on my first posting. This is a 3-rotor
with a 2.85:1.0 RD2-C gearbox and an electric c/s prop. Normal engine
operating range is between 5200 and 7000 rpm with the vast majority of time
spent in the 5000 - 6000 range. I may briefly hit 7200-7300 rpm on
takeoff roll, but that's only for a few seconds until the prop bites.
Mark S.