Most agricultural aircraft before 1949 were converted military aircraft and it was in that year that
Fred Weick, based at
Texas A&M University, designed a dedicated agricultural aircraft: the
AG-1. The AG-1 first flew on 1 December 1950. During 1953, Fred Weick was approached by Piper to become a consultant on the agricultural version of the
PA-18, the PA-18A, in particular to design and test a distributor for dust and seeds. The aircraft's flying tests were successful and, in 1957, Weick was invited to join Piper at Vero Beach, and the AG-3 was renamed the PA-25 Pawnee. The engine was upgraded to a 150 hp Lycoming O-320-A1A engine. In 1974, the Pawnee D was introduced, with the fuel tanks moved from the fuselage to the wings; the 260 hp variant was also available with either a fixed pitch or constant-speed propeller. On April 15, 1988, Piper Aircraft, Inc. officially sold the PA-25 series aircraft to Latino Americana de Aviación S.A in Argentina. The sale included all drawings, engineering data, parts inventory, tools, catalogs, and manuals. All support of any nature became the responsibility of the new owners. In 2019, Australia's
Civil Aviation Safety Authority formally approved the issuing to eTugs of Certificates of Airworthiness in the Limited category for the purpose of glider towing. An etug is a PA-25 where the Lycoming engine has been replaced with a General Motors
LS automotive engine. The advantages for glider towing, compared to a Lycoming powered PA-25, include a greater rate of climb, reduced fuel consumption, the elimination of
shock cooling (since the LS is water-cooled rather than air-cooled) and a less costly maintenance regime. ==Variants==