In an effort to do the job as inexpensively as possible agricultural aviation has relied for some time on retired military aircraft or other general aviation aircraft modified for the task of spraying. Boeing PT 17 Stearman were the most common, but Avengers and even Dauntless torpedo planes have been used. Cessna took their basic wind design and turned the 185 into a low wing aircraft and Piper put its Pawnee and Brave machines together largely from their other lines of planes.

The design of a dedicated "for agriculture" aircraft is limited to only a few designs and this is one of those. A Texas spray pilot named Leland Snow designed an earlier version of this machine and began marketing his S1 in the early fifties. His designs improved as the market grew and evolved into the design you see here which was bought by Rockwell Commander and marketed as the Thrush. Later, the design was sold to Ayres, who currently still develops and build the Thrush as Ayres Turbo Thrush.

After selling the design to Rockwell and the production having been moved to Alabama, Leland Snow decided to go back into the business and began producing the Air Tractor from an airfield plant in Olney Texas. The majority are like this one, powered by a growling 600 hp Pratt and Whitney radial engine with a life of just over 1,000 hours. In above picture you can see the air conditioner compressor mounted to the right of the propeller. Extra air conditioner belts are tied to the engine so should one wear out it can be replaced without dismounting the prop. Air Tractor and Aryes both build aircraft similar to this fitted with Pratt and Whitney PT 6 turbo jets or AiReasrch turbo jet engines. These turbine powered machines can handle even larger application tanks than this 400 US gallon monster.

The exhaust system. Mounted on the back of the huge engine are its two magneto's, an alternator and a carburetor.