This is the bird cage approach made with a whole bunch of 1/2
diameter .049 wall tubes. It is less complicated than  it looks.
Make a 1/4 scale balsa model to prove to yourself that it
will be rigid.

The rubber bushings are on the engine/psru/prop/
alternator/starter CG so the rear mount is trivial.
Little to no load back there.

The red tubes are the motor mount tubes proper. The green tubes
are necessary to insure the integrity of the RV4 landing gear.
If the transverse green tube is not installed the landing gear will
tend to spread the motor mount tubes. The fore and aft green
tubes feed the landing gear loads into the motor mount.

The new tandem RV's are much simpler with a bent aluminum gear.
A lot of this stuff would be unnecessary.

A custom oil pan must be made to fit inside the bird cage.

When you use a pointy cowl like this kind of motor mount that implies
The mufflers are a problem. Perhaps Mike Wills twin
side mufflers will work fine. Lets keep our fingers
crossed. Here is a picture of Mike's mufflers.

Looks like Mike's engine is a bit further forward than shown
on this sketch. His rubber mounts are aft of the engine/psru/prop/
alternator/starter CG. This picture should also help you to visualize
this motor mount design.

Paul Lamar

OPS! I forgot a tube. I also added a bit of detail because now I can :-)

BTW this mount uses the Tracy trick of the oil foam separator sandwich plate 
extended and thickened into a motor mount. We got to give credit where credit is
due. A bit heavy as it is about 144 square inches by 1/4 inch thick
at a volume of 36 cubic inches and 3.6 pounds not counting a few
little holes. It is necessary and would be about one pound in any event.
Could be welded in as part of the custom pan of course.

BTW Mike Wills mount would work well and would be simpler than this one 
IMHO if another hard point was constructed at the very top of the 
firewall to brace the rear motor mount vertically. This one on the
other hand gives a bit more clearance around the water pump plumbing.

The extreme forward PSRU/motor-mount plate type mount would also work 
with this scheme. That would give a bit more room for the front
of the pan.

Let me know if anyone wants this ACAD 12 drawing file.

Paul Lamar
 
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