X-Mozilla-Keys:                                                                                 
Tracy Crook wrote:

Herb Sanders wrote:

Tracy, I am also apprehensive about the spacer mount engine to psru. A

bellhousing

would subject the bolts to shear and tension loads. Your 3" spacers with

small

sholder area put a bending load on the bolts and spacers repeated

thousands of

times per minute from power pulses and from asymetrical thrust from the

propeller

anytime the prop is not 90 degrees to line of flight (P factor from

climbs,

decent, aerobatics, etc). Even the slightest movement could deform the

sholder on

the alum spacer and deterioration would accelerate to possible failure.

I don't

have a mechanical engineering education, so the view is have is

intuitive - I

would appreciate a more educated opinion from those more able to give

one.

Regards, Herb Sanders

Paul Lamar wrote:

Tracy's "spacer" are really half inch thick rectangular aluminum
plates that encompass more than one bell housing bolt. As such
they provide shear material for the torque loads.

Paul's explanation is correct but the spacers are  made from 3/4 " thick
plate.  Two of them encompass two bolts each and one of them is long enough
that it had to be curved (to clear the flywheel). The other two spacers have
a single bolt. Just  an "eyeball analysis" of the force vectors was enough
to convince me that the forces would be put in tension or shear and there
would be no significant bending moment on the bolts.  I understand that
"eyeball analysis" is not good enough for some people and I have no quarrel
with that position.  I have enough math skills to calculate the bending &
shear loads but only if I had accurate figures for the loads that the prop
would generate while in-flight.  These are hard to come by and without them,
any calculation I (or anyone else) did would be meaningless.

The only forces which would tend to put a bending load on the bolts is the
torque which is transfered through the planetary gear planet carrier which
is fixed to the gear housing. (my drive uses a "fixed planet"
configuration).  The two long spacers for the mounting plate ensure that
this torque is converted to tension and shear in the mounting bolts.

 I constantly do what I call "sanity checks" when I design anything.  When I
was pondering just this point in the design,  the sanity check was this:  If
I were to put a very long lever arm attached to the planet carrier and start
putting torque on the carrier with the lever, what is going to break first?
Using the eyeball analysis tool again,  the answer was obvious.  The  12
aluminum tabs on the planet carrier which carry the torsional load would
shear off long before the mounting adapter even started to sweat.

The propeller loads are more complicated but if you look at the layout and
dimensions, you can see that there is no senario which would put a
significant bending load on the bolts even if the spacers were all small
tubular jobs that only encompassed 1 bolt each.   Here are the numbers you
need:

1.  Mazda end housing bolt pattern is about a 13"  bolt circle.
2.  The plate spacers are 3 inches long.
3.  The prop flange is 14.625" from the end housing.

No matter what force vector is imposed out at the prop hub, virtually all
stress ends up as tension at the bolts (or compression at a spacer).

I welcome any and all comments.  Let me know if I've missed something.

PS:  Bulent, thanks for the info on Todd Silver's redrive.  It looks
absolutely cannon proof but what does it weigh?

Tracy Crook
www.rotaryaviation.com

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