Bill, youshould make an entry in your log book, saying that you have incorporated the zenith upgrade modification of the wings and center wing spar supports on this date ddmmyyyy. If you incorporate the aileron balance arm as well another entry specificaly pertaining to that mod needs to be entered as well.
Definitely no 337 forms for experimental. If you are experimental, amatuer built, reference your operating limitations. I called my FSDO rep on this, just be to be sure and he confirmed the following. To paraphrase, my limitations say that if I incorporate a major change as describred in FAR 21.93, then I must make a detailed logbook entry describing the change, fly 5 hours in an approved flight test area, then make a log book entry that looks just like the one we all filled out after our 40 hour flight test was completed. No contact need be made with the FAA, unless you need to have a flight test area established. I am still based in my original flight test area, so I am OK. If I had moved outside my local area, then I would have to contact the responsible FSDO and have one established. That's pretty much it.
As far is this being considered a major change per 21.93, structural change is specifically mentioned, so I am considering it so.
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