One thought: It seems to me that holes in the upper spar cap would most likely be a problem when pulling negative g's, wouldn't they? Or, during extreme vibration (i.e. flutter)? I wouldn't think normal flying loads within the normal positive g limits would strain the upper spar cap.
But, then, I'm not an engineer of any kind. Are there appropriate non-destructive diagnostic means to inspect for cracks in the spar cap? Dye penetrant? Portable x-ray? Do we have any aeronautical engineers here? Ed Ed Burkhead http://edburkhead.com/Ercoupe/index.htm ed -at- edbur???khead.yyy change -at- to @, remove the ??? and change yyy to com
