Back in the early 1970's Frank Christensen attempted to purchase the rights to market the Pitts S-2A as a homebuilt, but was unsuccessful.He then started an "improved" design based on the S-2A. Both the Eagle and S-2A are very similar in specs and performance. But the Eagle is much roomier and has some other aerodynamic changes.
As a side note, you could build the S-2 as a homebuilt, it was designated the S-2E. But most people built them to early S-2A standards from what I can tell.
In the 1980's Frank was eventually sucessful in purchasing the entire Pitts manufacturing facility. Integrating the Eagle kit into the product line. Later he sold it again, but the Eagle stayed. Hence, Aviat now sells Eagles along with the Pitts'.
John Smutny
Eagle N16EE