X-Mozilla-Keys:                                                                                 
Mike Wills wrote:

At 07:03 AM 11/2/1999 -0800, you wrote:

This is more what Mike had in mind. He wanted to use
channel instead of a 1/2 inch plate for the back bulkhead.
I prefer 1/2 plate with a large hole as it is stable
in shear. The channel system relies on the bolts
to stabilize the bulkhead in shear resulting in somewhat
higher stress in the bolt hole area.

 Much closer to what I had in mind. I see your point regarding the
torsional rigidity. Don't the gussets also add to the torsional rigidity of
the assembly? Its my thinking that the channel handles the bending loads
much better than the plate and also weighs considerably less.

Mike Wills

Yes the gussets are essential. Everything is a compromise with this
design. You need to calculate the volume of material. Aluminum weighs
about 0.1 pounds per cubic inch. Don't forget the weight
of the nuts, bolts and washers. One thing that could put a mount
like this on the map is an NC mill. With that device you could
pocket out material where is is not needed and save a lot of 
weight.

I think this whole situation is very instructive. It make me 
appreciate the genius of Jim Griswold when he designed the
very inovative Questair Venture type motor mount. Yes he messed up 
on the nose gear but he did so many other things so very 
right indeed. 

Moving the rubber motor mounts outboard reduces
the torque loads on the mounts and moves the main motor mount
tubing tripods out away from the engine giving plenty of
room for accessories and room to perform maintenance.
It also reduces the loads in the motor mount tubes
due to prop torque. It also reduces the heat
applied to the motor mount rubbers.

IMHO Jim's design is hard to beat.

Paul Lamar
 
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