George,
I have attached jpg files from the FEA test. I did do several versions of
this design to come up with one that had minimum stress as well as low
weight. Incorporating the front spacer of Tracy's drive ended up being key
to making this part really strong. It made the outer stiffening ribs much
deeper and they transmit the loads to the outer area of the bell very well.
This design ended with far less deflection than the original design.
The loads applied are 600 foot pounds of positive G load (6G's on a 100 lb
prop, or 12G's on a 50 lb prop), 250 pounds of thrust and 20 pounds of
asymmetric thrust (decending blade theory). The thrust load has nearly zero
impact on the stress loads. The factor of safety on the material is at 1.9
and then only in the upper corner fillets of the stiffening ribs. The total
deflection at the prop hub at this load is 0.011 inches. Stresses are low
with virtually no additional stress from the cutout (see stress distribution
plot).

And have a very Merry Christmas down under!
Larry

I appreciate those FEA's Larry - a picture speaks a thousand words.
I am in no way being critical in anything your doing just inquisitive as
I've done a couple of BH designs with Butch. Mind you we incorporated engine
mounts as well, so the strength of the sides had to be stronger.

My first BH had deep flanges - this did create some degree of difficulty in
makes the  pattern, as I had to keep the long flanges very straight and well
tapered. You don't have those 'hand-made' problems - lucky you!!

The other problem I had was depth, the deeper you make the face flange, the
bigger the flange has to be because of the necessary taper and the thinner
the end of the taper the more difficult it is to flow in the aluminium. You
have a good foundry so those problems are minimal.

Just a brief glance of the face of the BH convinces me how strong the face
is - it's super strong and it's duel purpose as it replaces the back part of
Tracy's PSRU housing. I just don't think you could get any better than this
for strength.

I notice that the flanges over the 'cut-out' don't appear to have any stress
(at all) - is this because the stresses are transferred through the face?

I did have a concern about the stresses around the mount points, but the FEA
shows no serious stresses there. It could be the shorter more rounded bell
shape compensates for this. My BH had less curvature and smaller radius (
from side to face transition). This created more room for the flex-plate/
damper, but isn't as strong as your design.

Keep up the good work Larry
And have a Merry Festive Season to all you chaps - up over.

George (down under)


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