X-Mozilla-Keys:
Bulent Aliev wrote:
It will have to be thickened up with another layer of 1/4 inch ply on
both
sides about three inches diameter minimum. This is necessary so the
rubber
is working against the proper area. The shear and torque loads from
the engine is taken by this area of the rubber in the mounts.
The wood in the plywood donut hole should be coated with epoxy.
This is a good idea. I'm nervous myself with the 1/4" plywood myself but is holding the
L O-360 without problems.
An alternative is a 1/2 inch plywood three inch diameter donut bonded
to the back of the firewall. The aluminum is un-needed and will
probably get in the way.
I think the aluminum was there to take the compression loads of the bolt. Plywood will
compress too much.
The lower mounting points can not be lowered more than per plans. There is no space.
The upper ones if you lift them higher, they will have to move closer inward, since the
firewall curves inward.
Bulent
With the Barry rubber mounts there is a steel spacer that takes the bolt
loads. The rubber transmitts all the compressive, shear and tension
loads
into the firewall directly. This distributes the loads over a large
area of plywood and fiberglass. Ideal in this application.
The 3/4 inch bolt and aproximately one inch diameter steel spacer are
subject to moderately high bending loads in a hard landing. At $6.98
each you can afford to check these mounts for bending
after a hard landing and replace if necessary:-)
Moving the mounts closer inboard is no problem. There are very few
side loads on an aircraft motor mount compared to the verticle loads.
Keep the mounts as close to the fuselage skin as possible.
As you can see from the last drawing with the stock vertical spacing
the loads are rather high on the rubber bushings. This is the only
drawback to this type of motor mount.
Paul Lamar
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