10/31/2010. Remarks by Walter van Tilborg: "This twin tail boom pusher engine homebuilt aircraft was an original design two-seater featuring an all-composite material construction, designed by William A. Shaw, with assistance of the well-known designer Martin Hollman. The first prototype was built by Progress Aero Research & Development, Inc. of Monterey, California and registered N81D (c/n 101) it was first flown in 1991, powered by an 112 hp Lycoming O-235 four-cylinder horizontally-opposed piston engine. Later the aircraft received a similar 160 hp Lycoming O-320 engine, but subsequently it was damaged during parachute-assisted recovery from an uncontrollable flat spin during flight testing on July 2, 1989.
The pictured projected production model, to be available in kit form for amateur construction, was fitted with a similar 180 hp Lycoming O-360-A1D engine, hence it was also known as the Discovery 360. This second aircraft was flown for the first time in 1990 and differed mainly in lacking the small additional cabin windows of the first aircraft. Development of the Discovery was halted and reportedly only N81D and N360F were completed.
During 2004, development was restarted by FreeBird Sport Aviation Company (Freebird Sport Aircraft) under the name FreeBird Xtreme. The new company had acquired the original Discovery aircraft N81D as a static demonstrator for the planned production of various models as the Xtreme LSA meeting the Light Sport Aircraf rules and the Xtreme Experimental homebuilt. However, no additional aircraft were built and again later Aero Concepts, LLC acquired the rights and re-introduced the name Discovery. The company planned Experimental and E-LSA versions to be available in kit form, but no additional aircraft were completed."