A bed mount with the rubber bushings under the
engine CG is a much lighter way to go.

Paul Lamar

'splain... what is reasoning? (not a challenge, just want more info) 
We are looking at all the possibilities
...Chrissi

Very hard to design a front cover that will take the bending stresses
of a Lycoming type cantilevered design.

Two pieces of 3/4 OD .049 tube 25 inches long  weigh only
.86 pounds each. Four pieces of 5/8 OD .049 tubing 25 inches long
weigh  .72 pounds for a total motor mount tubing weight of
about 4.6 pounds.  Add another three pounds for a larger
motor mount/PSRU  plate and you have a total motor mount  
weight of 7.4 pounds. The loads then are straight down on
the apex of the tripod through the two rubber bushings in pure 
compression during a six G pull up. This leaves the back side
of the engine (front in your case) totally unobstructed for 
accessory drives and water pump plumbing.

In the case of the cantilever mount you are looking at 
a moment around the rubber mounts of about 300 pound times
6 G times the length to the CG of the engine or about 12 inches.
That moment is 1800 foot pounds. If your four rubber bushings
are spaced one foot apart the upper two will see a tensile load
of 900 pounds each and the lower two a compressive load of 900
pounds each. This means any bracket or plate bolted to the 
engine back there will see this bending moment.

Assume for the moment the plate or bracket is made from
1/2 thick aluminum 14 inches by 14 inches it will weigh 9.8 pounds
alone.  I and Mecanair both believe 1/2 inch plate is
marginal for this application judging by the looks of the beefy 
casting of what they are using. If you cut any lightening holes 
in it it will becomes less strong and stiff. 

This does not include the 
weight of a Lycoming type steel tube mount between this
plate/bracket  and the firewall. I estimate that will weigh
additionally at least three pounds and maybe five pounds.
the total mount weight for this approach will then
be about 13 to 15 pounds roughly. You then still must get 
all the accessory drives dealt with on the back side (or front
side in your case).

The loads on the firewall are the same for both type mounts.

See the ACRE NL web site below for more info.

Paul Lamar
 
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