Planetaries have been used in aircraft engines from
the get go as that results in the lowest weight design.
Many were bevel plantaries as in this Zepplin engine.

Spur gears have only been used in inline engines (mostly V12s)
to raise the thrust line (P51) or to allow a cannon to shoot
through the hollow prop shaft (ME109).

Paul Lamar

Or the P-39/P-63 Aircobra/ King Cobra, Virg

Paul, the Lycoming shells are not large enough in diameter for a hollow
prop shaft. They do not have a thrust surface on the wide front bearing
behind the prop. I propose using the automotive thrust face as only a
backup for the roller thrust bearings, however it also acts as an oil
slinger taking the pressure load off the front case seal. A plain
surface thrust bearing continuously loaded seems to be hard to keep
lubrication on and carry heat away from. Wear rate would be no better
than an aircraft engine where a roller thrust bearing endplay stays
constant.

These automotive bearings are used in top fuel engines which
can make 8,400HP in a Chrysler Hemi  "V" configuration engine. In a
planetary drive which is self centering with minimal side loads they
would be indestructable. These bearings are steel backed with copper
faceing and a tin running surface (tri-metal) construction. I don't have
a problem with babbit bearings in my 1940 chevrolet but can't see 1930's
technology in a 21st century composite/4rotor aiecraft.
I also have a problem with buying a prop governor which costs
more than my airframe. Then when you ask about BETA on the prop well
lets not even go there.

george grimes7

I doubt seriously the Lycoming Bearings are babbit :)

Aircraft engines being 1930 tech is largely a myth. They are
generally made with the finest material and manufacturing methods
available. I do know the A/C bearing shells are tri metal
construction with steel backing.

http://www.sacskyranch.com/eng219.htm

An excellent book on certified aircraft engines is the
    
Sky Ranch Engineering Manual

http://www.sacskyranch.com/index.html
I am not against roller thrust bearings as long as the RPM
is no higher than 3000. The Ross used them for prop thrust
for 30 years. Perry Mick ran a direct drive ducted fan
for 650 hours at roughly 4000 RPM before the roller clutch thrust
bearing went out in his 2nd gen 13B. In the 3rd gen they
increased the size.

If the RPM is over 3000 you can stack them 2 or 3 deep
as Tracy is now doing for the helical sun gear thrust.
An idea Ross pioneered after he discovered the thrust
bearing in the Mazda was not up to continuous helical
gear thrust thrust.

The side load on these bearing comes from gyro bending
loads when the rudder is kicked or the aircraft stalls
and pitches down at a one radian per second rate.
Page 436 Sky Ranch Engineering Manual.
It is called a gyroscopic couple.

Paul Lamar


Automotive bearings have an upper and lower shell. The upper shells are
drilled for the oil to get in and grooved to supply oil 180 degrees around for
oil to the conn rod bearings. Some performance sets have the grooves extended
into the lower shell to increase the time oil is supplied to the rod journals.
If the grooves is made all around the bearing, you loose surface area on the
lower shell.

For this application, you will need to put the plain (lower) shells in the
place the gyroscopic loads are the highest or buy two sets of bearings and
only use the lower shells from each. You can use two of the upper shells in
the location that lets the governor oil get into the shaft to supply the CS
prop mechanism. That way you have even oil without pulsing.

Dale Davies

The gyro loads are applied to both upper and lower shells in different
maneuvers. A quick pull out will reverse the loads I think.
Just copy the Lycoming shell grooves. As I recall rapid yaws
will affect the top and bottom of the shells while
rapid pitch will affect the sides of the shells.

BTW this is not much of a problem with wood or carbon
fiber props due to much lower weights. It mostly applies
to heavy, constant speed, metal propellers.

Paul Lamar