George;

Let me first set a misunderstanding that keeps bouncing back and forth
between you and Mike Collier:
Mike COSMAN of Rhyolite Aviation (Father & Son team) are the designers and
builders of the 20B powered Big Husky Boys aircraft.
www.microcosman.com/aircraft

Musings/Clarifications/Suggestions/Questions:

-The sharp corner at the shoulder of the of the Engine Bkt's surface's "Shear
Stop" should DEFINITELY be avoided.. ..A cutter with a 3/16 radius (minimum),
must be used so it can be machined in SIMULTANEOUSLY. What this implies is
the cutter itself must have the 3/16 radius ground on, and cut in the same
operation while cleaning up the complete mounting surface.....Which leads me
to:

-Are the Mounting Bkt. surfaces going to be machined perpendicular to the
Psru's mounting surface??......Or are you planning to just "Machine Clean"
the existing angular "Draft" surface??.......Or am I missing something??

-Since Tracy's Psru mounting bolts are through mounted with locknuts & flat
washers, the .250 dia holes MUST be "Face Spotted" with a c'bored on the
inside of the Bellhousing PERPENDICULAR to the Psru's front mounting surface.
This step can be easily performed on a decent drill press with a Pilot
C'bore.
THIS PROCEDURE IS VITAL IN PREVENTING A BENDING LOAD AT THE WEAKEST POINT OF
ANY BOLT (Root thread) AND AT THE WORST PLACE OF THE JOINT (Between the
nut/washer bottom surface and the irregular top surface of the casting) at
initial torquing of the bolts.....This, in my book of experience is NON
NEGOTIABLE....So George if your Bellhousing is not compliant to this, as far
as I'm concerned it won't even make a good "Boat Anchor" as it will be much
too LIGHT ;-)
....Tracy's plate has parallel sides so he didn't have to worry about this.

-George I must clarify the following item for the record and future
production units....In early transmissions I voted for having the Psru
Mounting Hub net excess (Hub minus Housing thickness) on the FRONT SURFACE of
the Bellhousing.....The counter argument ranged around the fact that it would
extend the Psru forward....My point was/is that when the front surface is
partially machined (Sans the Hub) stress concentrations can be created at the
juncture of the machined surface and virgin surface, especially if it's an
under-cut like in our case. This is certainly NOT a good place for this
phenomena to be allowed to reside in. However this can be easily avoided by
providing some kind of protrusion in the front surface of at least 3/16th of
an inch prior to machining, and simply do away with the phenomena
alltogether. The way I see it, is....If anybodys aircraft/installation is
that critical to dimensional tolerance & CG variation of 1/8 of an Inch, that
plane should not be flying and instead be anchored to the ground for birdies
to do their daily doody deposit on :-)

Looking at the bright side,...Gentleman/Ladies, we are already talking future
production here :)
So bring on the next dificulty, (Hate the word "PROBLEM") ;)

                                                     Butch

The stresses in this area are low Butch. Not to worry.

George, here is a quick and dirty way to test the strength (not the deflection).
Feel free to jump up and down on it.

Paul Lamar

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