John Weatherly designed the Weatherly ag-airplane and began production in 1976.  His design concept was (and still is) aerodynamic, elegant, rugged, and economically optimal in its class.  A hallmark is the venerable, reliable Pratt & Whitney radial 985-R engine, which provides far more power for the money.  The airframe has evolved over the years with improved materials, precision manufacturing, and advanced ag-chemical deposition systems, but it is the same powerful albeit nimble airplane.  No new ag-airplane provides more power and profitability for the money.