Rolf,

Unlike the discussion above I will fix the ring gear and take power
out of
the planetary cluster. The cluster would be attached on the prop shaft
and
be supported front and back on bearings.  How would I calculate the
load the
planetary gears will be seeing?  Total torque divided by the total tooth
contact area?   My engine will be putting out over 200 ft/lbs of
torque at
max rpm. With a supported prop shaft  I believe the loads on the bearings
will be from torque transmission and the centrifugal force of the planets
themselves, right?

Also if I understand it correctly the gear line velocity is circumference
times rpm.   Calculating it from  the Bell sun gear in feet that is
377mm /
304.8mm = 1.24 ft.  1.24' X 8200 rpm = 10,168 ft per min?

Mistral's unit  at a 8000 designed redline with a slightly larger sun
gear
would not be far off this figure.  You mentioned maximum line speeds of
5,000 ft/ min.  Is that figure for light duty gearboxes?

Thanks

Doug,



You have a fixed ring gear and rotating planets. Give me the dimensions
of all the gears, DP and pitch diameter and we can calculate it
together. As already mentioned, it is pitch diameter times pi times rpm
/12. Pitch diameter in inches, pitch line velocity in fpm.


Since the pitch line velocity of all gears is the same, one need to
calculate just one. Best is the ring gear and the output speed or
propeller speed. The gear ratio is thereby irrelevant. The torque load
is also the same on all gears. The load per tooth is divided by the
number of planets.


The bearing loads are essentially torque divided by radius. The
centrifugal force of the planets only need be considered on the planet
bearings, for the output shaft they cancel each other out through equal
spacing around the circumference.

Rolf

The centrifugal load of the rotating planet assemble is
contained by the ring gear and the separating tooth forces.

Paul Lamar ...No rotor no motor.

Hi Rolf,

Here is the info again on the Bell 47 gear sets.

*Diameter is measured at gear tooth contact point. All measurements in mm.

Name    teeth number    diameter    gear width

Sun         46             120      27
Planet      23              57      22
Ring mm     92             234      25.4

Proposed input max rpm =  8200
Proposed max hp  343Hp
Proposed max input torque 220 ft/lbs

The planet gears  tooth dimensions from the valley to the top of the 2mm
wide flat top is 5.9mm.  The teeth are 4.6mm at their widest root.

In application Bell used the inner part of the hardened gears as the bearing
race.  A hardened collar (sleeve?) was placed over the gear shaft to become
the inner race.  This was 1950's technology and designed for low rolling
speeds but great torque.  Keeping them center in the race where thick
washers on the outside and a fiber cage on the inside.  TBO on the whole
craft was 1200hrs.  The fiber cages lasted about 300 hours. Perhaps on later
models Bell improved the bearings cages.

The inner hardened roller race that fits on the gear shaft is 23 mm in
diameter.  The outer part of the bearings (actually the inner part of the
gear itself) is 39mm.  The recess axially dimension to the central inner rib
is 9 mm.  Therefore the central rib must be 4mm wide.  22 - (2X9).


Calculations  of bearing loadings:

Please check I am on the right track here.

The sun gear has to transfer a maximum of 220 ft/lbs  torque at full chat.
Most likely less.  The torque output to the prop shaft with the 3:1 ratio
would increase to about 660 ft/lbs.  Each of the six planetary gears would
see 110 ft lbs. on what is basically a 2.5mm x 22mm (or 55 square mm) one
tooth contact area.  The bearing is seeing 110 ft/lbs divided by the gear
28.5mm radius which works out to 3.85 lbs distributed over a line 18mm long
contact line.

In conclusion. I believe I will have to have new planetary gears made and
ground with different internal bore specs to accept a standard high speed
sleeved roller bearing. Perhaps to increase bearing contact surface area 22%
the internal gear rib will have to be eliminated.  If gear deflection
strength becomes an issue the bore can be reduced in diameter slightly.
Depending on the design of the gear case the gear also can be widened a bit
more thus giving even more bearing surface area. Presently the hand inserted
roller bearings are held in place by two 3.2mm (one on each side) thick
spacer washers.
The housing has several ports to direct a stream of oil at the planetary set
and at the front bearing.  Since this design unit was meant to fly on a
helicopter I would like to find a way to introduce pressurized oil through
the sun gear.

For pressurized oil into the prop shaft the Bell unit offers several
possible locations.  The easiest manner would be to feed it into a  slightly
thicker outer collar that contained the proper shaft seals. This would be a
'two birds killed with one stone' possibility. The present collar is about
25mm thick.

All in the all the unit is rugged, compact and the case designed to take the
large lateral transient loads placed on it which I believe my plane will
require.


Doug Fir


And too big to run at 8200 RPM.