Perry is thinking of extending his prop shaft and adding
a ball thrust bearing. This is similar to what Charlie
Airsman did on his direct drive Soob.
Here is my first cut on the the design.
Any criticism or comments?
Paul Lamar
vjaqua wrote:
Paul - Just a few questions and comments. Is that the bearing that Charlie
used?
Why did you transition to steel? Aluminum would be structurally adequate,
and avoid the differences in thermal expansion, modulus of elasticity, and
electrochemical potential. What does the engine end look like? Are there
any provisions for torsional damping. or misalignment ? Vance
Paul wrote:
I was worried about the local bending loads due to gyro reaction of the
prop. I don't thrust aluminum for cyclical bending.
The gyro loads on the bearings themselves are real low because they are so
widely separated. The rear main is used as one and this bearing is the
other. That ball bearing is also designed for aircraft controls and as such
it is not rated for speed. It has real big static load numbers however
at 27,500 pounds radial and 12,100 pounds thrust.
"Perry J. Mick" wrote:
This is for a future project, in which I may try to turn a
50" prop to 4000 RPM with a turbocharged engine.
But I would also like the option of running up to 6000
RPM with the NA engine. So the bearing should be
capable of that speed. Paul, you mentioned the possibility
of a sealed bearing?
--
Perry Mick
Duckt N7XR
http://www.ductedfan.com
That bearing is technically not sealed but perhaps a sealed version is
now available. You will have to order a newer Fafnir catalog.
If a sealed version cannot be obtained you will have to provide oil
seals and perhaps an oil supply as suggested by Bill.
I forgot to answer Vance's question. I don't think so. As I recall
Charlie used a plain bearing pressure fed.
Paul Lamar
The bearing that you show would appear ro have too small ball diameter.
The turbo machinery designers at Rocketdyne use a DN factor relating
diameter to rpm. As you can imagine what the ball rpm would be when
the direct drive shaft is turning 5000 + (for Perry).
Unless you reduce the shaft diameter( I know! that goes against all your
instincts), you will need some cooling flow for the higher rpm applications.
His approach of a pressure fed "plain" bearing has a lot of merit,
but some compliance must be provided to keep bending loads away
from the bearing.
You are right in that I had misplaced the other picture which
showed the elastomeric drive coupling which looks very good.
I still favor aluminum for the flange. The increased section for
the same weight is much stiffer, and years of prop extensions,
some over 12 inches, have demonstrated that aluminum works
just fine - Vance
Yes on the shaft diameter. No on the big balls because they are heavy :-)
Maybe we should go to an engine oil pressure fed plain bearing?
Ok I will try to find something out of a big truck engine like about three
inches in diameter. I got email into Charlie on the bearing he used.
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/ http://www.linux.org