Wendell Voto wrote:

I am trying to decide which motor mount bushing to purchase (using a bottom plate mounting method).  Should I get the Barry mounts rated at 130lb. or 240lb? What radial load will these bushing see? I intend to use one bushing in each corner of the plate.
Wendell

The two front ones will see the vast majority of the vertical load
due to the fact they are close to the CG of engine/psru/prop.
All four will take the radial load and all four will probably share
the torque load. Each front bushing will see about 750 pounds vertical
load down in a six G landing or pull up. That is no real problem as the
rubber mounts can take that bottomed out without failing. Each front 
bushing will see about 125 pounds static load down due to the weight of 
the engine alone. The trust load is roughly 350 pounds at 200 MPH  so 
the radial load is about 90 pounds each on all four. This would be higher 
at lower speeds with a variable pitch prop.
 
The torque is about 400 ft pounds at the prop and if the distance between 
the mounts is 1.2 feet or about 14.4 inches the vertical load due to torque 
is about plus 160 pounds each on one side and minus 160 pounds each on 
the other side. That means one side of the engine on the front mounts 
will see about 300 pounds vertical load down on average and the other 
will see about 40 pounds up on average.

The peak torque pulse is about twice the average torque mentioned above 
and  is the main vibration source in a rotary so minimizing rubber mount 
static deflection improves torque vibration isolation by minimizing bottoming 
on that one highly loaded rubber bushing.

That is why I like to spread the mounts out to about 30 inches center
to center with the mounts located on the psru/motor plate.

Paul Lamar
 
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