Into the separate thrust needle bearing. Same as the Ross.
Paul Lamar
I am now enlightened. for the thrust bearing I would still like to
see one using the tapered rollers to prevent skidding and scoring of
the thrust bearing at low lube levels. I'll see if I can find a bearing
number we could use. Thanks Bill Jepson
That would up the cost.
Also you have a preload and differential heat expansion problem with
tapered roller bearings. Here is an earlier concept using the light weight
tapered
roller bearings with part numbers. It is better to use bearing lock
and replace hardened sleeves for the needle bearings if you are worried
about that. As far as I know nobody has worn out a Ross shaft yet.
It would probably be as easy to replace the whole shaft as the planet
pinion
shafts are also welded to the main four inch prop shaft. They wear too.
Note also going just one inch larger on the shaft eliminates the
the steel prop flange and places the load directly into the prop
drive dowel pins. Also the bolts on the inner end are eliminated by
welding the planet pinion shafts to the prop shaft.
BTW I need to redo the 3D based on this dwg. I over estimated the prop
drive dowel pin circle diameter. Its looking better and better the more I
get
into it.
Paul Lamar
Paul,
OK I can't hold it in any longer. I hate to be the skunk at the garden
party, but maybe we can do even better. While I agree with the overall
approach, I have serious misgivings about the bearing design.What speed are
you asking those needles to spin at? Is it a reasonable surface speed to
prevent skidding? 3 in OD shaft and .25 in needles at 2500 rpm is asking
them to spin at 30000 rpm. What about peening from vibration or imbalance?
Designing rolling element bearings is not as simple as it looks. There are
people who do this thing for a living and that is all they do.
The Torrington catalog I have has extensive life calculations Monty.
I have scanned them in and uploaded them below. Been there done that.
If you are going to design this thing on a limited budget with limited
resources then you need to pick a design that has a low risk. There are too
many variables in a needle bearing design, having to do with surface finish,
material hardness, dimensions etc, etc etc. Sure if you are Bell helicopter
with their resources and experience and the ability to test all the
materials and dimensions on every part etc. But I think Tracy is right, you
are not going to be able to build this and have an aircraft quality part
without spending a lot more money on inspections: both material and
dimensional. The wonderful thing about store bought bearings is, all the
engineering testing, quality control etc is already done for you. If you
feel you can compete with Timken and actually can, then I guess you will
succeed, but the odds are not good.
A much lower risk more forgiving design would use pressure fed journal
bearings. Pressure-fed bearings are: light, compact, inexpensive, and
forgiving in the tolerance dpt. They tend to damp vibration, there is no
chance of peening. Failure modes are benign if you design it properly. There
are less parts and less critical dimensions. You have an engine with a large
enough oil pump, and filter system, so the weight penalty has already been
paid, why not use it? If the oil pump fails you are toast anyway. You might
even be able to find off the shelf bearing shells from a large engine that
will work. Any good Mechanical design text will have plenty of EMPERICAL
(not bogus theory) design data. You should be able to figure out the
tolerances required, flow of oil required, even how much the oil temp will
rise, given rpm, dia, and oil type and viscosity.
Monty
I thought of this Monty but the rotor bearings are three inches in diameter
and these would be four inches in diameter. My guess is it would
take an oil pump twice the current size to adequately feed
journal bearings in the psru. Everett Hatch had a large diameter
journal bearing in his original psru and it failed. It could
have been too narrow or it could have been fed from an inadequate
supply. I notice that Power Sport did away with it and went to
ball or roller bearings. Needle bearings have held up well
in the Ross.
Paul Lamar
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