Jim Beckman wrote:

With the addition of the "red" struts, all being in tension under
right-side-up flight, the owner could remove that lower tube which is
the one dangerously in compression, I think.  It does serve to reduce
the compression force of the main rectangular tubing beam against the
vertical (parallel to the firewall) part of the mount at the firewall,
but maybe not appreciably.  Removing it will not alter the loads at
the firewall hard points, only way the rearward force against the
rear vertical tube is distributed.  Is removing 12 oz worth it (there
was one on the other side, too, correct? - 24 oz)?  Will the vertical
rect. tubing take the bending moment of the main beam against it at
X g's?

While I agree with your assessment, I'd recommend leaving them for the
following reasons:
+ it's less work (none required to leave them).
+ two less operations where you *might* foul up the whole mount
  (oops! I didn't mean to cut that off...)
+ they provide some lateral stabilization to the motor mounts
  (though I don't know if its adequate)
+ if removed, then the diagonal cross brace under the oil pan will
  definitely be required, and I'm hoping to keep that space clear
  in case the radiator is relocated, and also because the diagonal
  cross brace may make it harder to drain the oil. 'Course the
  radiator might make changing the oil a *real* challenge...

Paul Lamar wrote:

I should do a 3D if I had time showing all the loads.

Absolutely.

Paul continues:

I'll say one thing for the builder... he sure crammed a quart
into a pint pot. The original builder, Jim Wilhauer, is a
professional welder.

"When the only tool you have is a hammer, every problem looks like a
nail." (Unknown)

Russell Kent


RE:  The lateral stability:  I don't get that any cross or diagonal bracing
is required at all.  Isn't that engine a solid block?  Its four-point
attachment to that mount assembly provides the diagonal stability, +/- the
little flex of the motor mounts.  Are the two horizontal mount rails, or
beams, too slender to take the bending moment at the rear mount when the
engine mass pushes to one side or the other?  What am I missing?

How many G's do we design for in sideways direction?

And I think leaving the lower compression tubes installed is best to
distribute the load lower in the assembly and not have it (the rearward
force) all directed into that back vertical piece so many inches above the
assembly's attachment to the airplane.

Jim Beckman
Austin


I rarely if ever exceeds one G but it is hard to insure
it is just strong enough. Most designs exceed that
but what the hey. Better be safe than sorry.

You don't want the engine/mm vibrating laterally
applying bending loads to the tubes where they are
bolted to the firewall and possibly fatiguing them.

Kicking the rudder will apply a lateral bending load
due to engine inertia but I have never calculated it.
If I were to calculate it I would use the same angular
acceleration as used in calculationg the the gyro torque
load on the prop flange. Namely 60 degrees per second
per second. I think that was the downfall of the
Airbus that had the composite rudder fall off over Long Island.
I could be wrong. I know the FAA applied guide lines
for kicking the rudder.

Paul Lamar ...No rotor no motor.

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