Jerry Hey wrote:
Paul, I completed the deflection tests. The MMP deflected .174"
measured at 24 inches. Tracy's adaptor plate deflected .137 inches
measured at 24 inches. I'm dying to find out what this signifies.
You need not worry about the test stand deflecting at all. It was
very rigid and heavily braced. The steel plate is .375 thick with a
piece of 3" channel as stiffener from top to bottom. This was tied
into the stand frame and welded to the 3" plate. During the test we
kept bubble levels on the stand and saw no movement. The two foot
tube is 4.188 o.d. Wall thickness is .188"
Jerry
Excellent work Jerry. Thanks a bunch.
This is 600 ft pounds of torque applied to the motor plate
and 300 pounds of shear load applied to the 10 mm bolts and
3.050 long 1/2 inch thick spacers. 600 ft pounds is the gyroscopic
torque you would get from a metal prop rotating at 2500 RPM and
pitching at 60 degrees per second. A worst case scenario
as we mostly run wood or carbon fiber props.
That includes the deflection in the two foot long, 4" dia. 188 wall,
steel pipe, the steel flange and the 10 mm bolts and spacers. Not bad.
.174 in 24 inches is only an angle of .44 degrees. So Tracy's stock
plate deflected about .42 degrees or so. Hardly any difference. I think
if we tested his super light weight plate version it would probably
deflect more than our pocketed plate.
I here bye sign it off for production :-)
You might unload the 300 pounds and put the dial indicator under
the plate and reload the weight to see how much the 10 mm bolts and
spacer are deflecting due to the 300 pound shear load. We will need
to do that to prove to Tracy that our spool and our 360 degree 1/4"
plate spacer scheme is as stiff as his 1/2 plate spacers.
Paul Lamar
I hate to have to point this out, but you'll have to repeat this in 5 or 10
degree increments (rotating the engine mount plate). Not sure how you can do
this with your existing fixture.
Finn
No we won't Finn. The plate is symmetrical enough and the angle numbers
are small enough that we will not bother. As far as the shear loads are
concerned they are only in the vertical direction.
Not only that nobody runs a metal prop and the test loads are for
a metal prop. This is a conservative and severe test. The angles
would probably be half for a wood or carbon fiber prop.
In the lateral plain our motor mount/PSRU plate scheme
is far more stiff as the prop gyro torque reactions are ultimately
reacted by the motor mounts. In our case that is a direct load
path while the other configurations must go through the spacers,
into the engine and then into the motor mounts.
There is way more slop in the gears than these tiny angle numbers
we are seeing.
Besides all this one could brace the plate
with 1/2 inch square 4130 diagonal tubing to the nose of the PSRU
as in this drawing. That would allow a much thinner plate with
some real PSRU weight savings.
Paul Lamar
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