I have examined the "Shertz Beam" Motor mount on "the other" Mail List.

Searched and did not find a comment on this list.

Other than it is recomended by "The Other" list, is there anything wrong
with it?

I am looking for solid/semi solid engineering critique.  I really dont want
to talk about "feelings" or "preferance".

Thans for your time.

I prefer the straight stuff too so to get right to the core of it:

1.  Shertz Beam -  Which incantation do you mean?  There is no single definition.  I have seen at least 6 versions.  In it's original incantation, a SINGLE 6mm bolt in tension absorbed ALL of the torsion forces (prop torque and vibration loads).  This was unacceptable.  I have seen a few attempts to fix this, some good some not.

2.  The beam is NOT at the CG, contrary to claims otherwise.  There are significant loads on the rear mount which is not even a part of the Shertz beam design.  It has been proposed that the rear of the engine be hung from a central point off the engine front housing from an assembly made from 2 rod ends.  The other end is supposedly attached to a hard point near the center of the firewall.  On most aircraft, there IS NO HARD POINT at this location.  In addition, on an aerobatic plane where negative loads can occur, the "hanging rod" in compression is 'less than ideal'. 

3.  This mount more or less assumes that the rad is going to be mounted under the engine.  This rad location and the Shertz beam makes more sense on a composite canard design but on a tractor, the mount ends up taking up space in the wrong places.  The most popular and successful cooling scheme so far use two heat exchangers in a location that interfears with this mount.   It would also not work with what I plan to do on my -8 with a single rad.

Tracy Crook