I checked the motor mount loads on the RV4 for a very 
conservative nine G's. The wings would probably break
off before the engine fell off. The compressive load
in the lower tube is well within the capabilities of
a 25 inch long 3/4 by 0.049 wall 4130 chrome molly
tube. Since this is the critical tube the top tube
could be 5/8 with no problem. Make sure you gusset 
all the joints to take out minor local bending loads.

The grid around the outside can be used to make graph paper
of this drawing once you print it out. The lines are one
inch apart.

Paul Lamar
 
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