>I had this idea quite some time ago but have not had
 >time to knock it out in Rhino. I think you
 >will find this much easier to fab than my original idea
 >of the aluminum spacers and rolled 3/16 sheet aluminum
 >tig welded to the spacers. You can weld this up anyway
 >you wish. It uses 1/2" 4130 .035 wall tubing bent using
 >a plywood form. The radius is about 7 inches. Heat the tubing,
 >clamp one end and pull it around the plywood form.
 >Not all diagonals will be needed to be bent to clear the
 >starter ring gear.
 >
 >I have never been entirely comfortable with the aluminum
 >block configuration for several reasons. High weight among
 >them. I like this idea a lot better.
 >
 >Paul Lamar

 Paul, is  there anything to be gained by completing the circle across
 the bottom?  Also,  is  is permissible  to form the right hand
 diagonal to clear the starter?    Jerry

I think the bottom is best done using this idea. I don't consider
it necessary but it makes certain builders more comfortable.
This too should be pocketed out if you can afford it as making it
out of solid plate is rather inefficient use of material.
I suppose I could do a casting if we achieved some sort of
unanimity :)

I don't understand this comment. My question referred to extending
the truss spacer across the bottom.  You don't show this in the rhino
rendering.

I think the bulge in the starter pinion holder would cause too much
of a bend in the tube. I could be wrong. You might want to mock it
up and take a picture. Bent tubes are not ideal compression and
tension resisting devices. Only the local bending stiffness of the
tube shape makes them marginally effective when used in space frames.
It is best to keep all tubes as straight as possible.

It might be possible to make a piece that circles the starter

Of course is it widely done in successful Lycoming and Continental
motor mounts and for roll cages in racing cars. Any time something
like this is designed it should be inspected for cracks on a regular
basis until years of experience have been accumulated to insure there
are no problems. This in fact is what has been achieved by the current
crop of certified aircraft bent tube engine motor mounts. Lacking that
a computer FEA of the proposed bent tube motor mount design could be
done to gain confidence.

Last, may I use 1/2" sq tubing for the diagonals.  Would look very
good.   Jerry

Sure. That was actually my first choice as it has somewhat higher bending
stiffness than round. The big problem is cost per foot. Last time
I checked it was $3 a foot and heading north. Of course you only
need six feet of square and two feet of round so that is not so bad.
I was also not sure how it would bend to a seven inch radius.

Paul Lamar
 
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