Yeoman Cropmaster

Yeoman Cropmaster YA-1
Role	agricultural aircraft
Manufacturer	Yeoman Aviation
Designer	C. W. (Bill) Smith
First flight	15 January 1960
Introduction	1960
Produced	1960-1966
Number built	21
Unit cost	£9,425
Developed from	Kingsford Smith Cropmaster

The Yeoman Cropmaster was an Australian agricultural aircraft developed from the CAC Wackett trainer of World War II.

The type was developed by Yeoman Aviation, a company set up by Kingsford Smith Aviation Services Pty. Ltd. (KSA) at Bankstown Airport to engage in agricultural aircraft production. KSA had obtained a number of Wacketts following the type's retirement from Royal Australian Air Force service and had converted four for agricultural use as KS-3 Cropmasters in the second half of the 1950s. The conversion involved little more than the installation of a hopper located in the rear cockpit of the Wackett, the cutting of a hole in the centre section of the Wackett's wooden wing to allow the dispersal of the chemical load, and re-routing controls to bypass the hopper.

By contrast the YA-1 Cropmaster involved major modifications to the Wackett airframe. The Wackett fuselage structure of steel tube was retained but had a 23 cubic ft. (650 litre) capacity hopper in lieu of the Wackett's rear cockpit and different external panels of metal and fibreglass (the Wackett fuselage was fabric covered); the Wackett's wooden wing was replaced by a new metal wing. The first five aircraft retained the Wackett's wooden tail, but subsequent aircraft had a metal tail that featured a stabilator, a swept-back fin and larger rudder. The Wackett's fixed tailwheel undercarriage was retained. The Warner Scarab radial engine of the Wackett was replaced by a horizontally-opposed engine, the YA-1 250 being fitted with a Lycoming O-540 engine of 250hp driving a Hartzell Propeller, while the YA-1 250R was fitted with a Continental IO-470 also developing 250 hp (190 kW), driving a Hartzell or McCauley propeller.

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