Early Piper cubs were built with wood spar wings. Later in production came the change to an aluminum spar wing. The later wing is built different but will mount the same as the wood spar wing. The TCDS for the J3 does not give indication as to the interchangability of the wings. According to aircraft serial #'s, it appears that during the change over period, at production, the wing that was availible at the time was what was installed on the next fuselage, (no specific change date or serial number location). Many in the cub world think it is legally acceptable to change an aircraft wing that came originally with a wood spar, to an aluminum spar wing, with a logbook entry. Some even go so far as to think it is acceptable to have a wood spar wing on one side and an aluminum spar wing on the other. It is my opinion that just because piper could use either wing (and did so as a set) at their discression during the manufacturing process, does not allow us to use that same attitude at will for MX. I think to change a wing from one type to another would be considered a major alteration and would require approved data to do so which would also require more than a logbook entry. Perhaps a field aproval would be possible useing the documents that showed the flexibility during production. Records are availible to find what plane came from the factory with what wings/spars installed. I have found no indications in parts list or any other documentation from Piper, or anywhere else that approves of the wing exchange. Your opnion and any reference that supports that opinion would be greatly appreciated.