The Yeoman Cropmaster was an Australian

agricultural aircraft An agricultural aircraft is an aircraft that has been built or converted for agricultural use – usually aerial application of pesticides (crop dusting) or fertilizer (aerial topdressing); in these roles they are referred to as "crop duster ...

developed from the

CAC Wackett The CAC Wackett Trainer was the first aircraft type designed in-house by the Commonwealth Aircraft Corporation of Australia. The name was derived from its designer Lawrence Wackett. "In acknowledgement of the CAC Manager's enormous contribution, ...

trainer of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

Design and development

The type was developed by Yeoman Aviation, a company set up by Kingsford Smith Aviation Services Pty. Ltd. (KSA) at

Bankstown Airport Bankstown Airport is an airport and business park located in the City of Canterbury-Bankstown, approximately from the Sydney Central Business District (CBD), Australia and west of Sydney Airport. It is situated on of land and has three paral ...

to engage in agricultural aircraft production. KSA had obtained a number of Wacketts following the type's retirement from

Royal Australian Air Force "Through Adversity to the Stars" , colours = , colours_label = , march = , mascot = , anniversaries = RAAF Anniversary Commemoration ...

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 Hopper or hoppers may refer to: Places *Hopper, Illinois * Hopper, West Virginia * Hopper, a mountain and valley in the Hunza–Nagar District of Pakistan * Hopper (crater), a crater on Mercury People with the name * Hopper (surname) * Grace H ...

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.Eyre, David. "KINGSFORD SMITH KS-3", ''The Illustrated Encyclopedia of Aircraft in Australia and New Zealand'', p.143. Sunshine Books, Hornsby NSW, 1983. Yeoman YA-1 vs CA-6 Wackett frame

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 stabilator is a fully movable aircraft horizontal stabilizer. It serves the usual functions of longitudinal stability, control and stick force requirements otherwise performed by the separate parts of a conventional horizontal stabilizer and el ...

, a swept-back fin and larger rudder. The Wackett's fixed

tailwheel undercarriage Conventional landing gear, or tailwheel-type landing gear, is an aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynami ...

was retained. The

Warner Scarab The Warner Scarab is an American seven-cylinder radial aircraft engine, that was manufactured by the Warner Aircraft Corporation of Detroit, Michigan in 1928 through to the early 1940s. In military service the engine was designated R-420. Vari ...

radial engine of the Wackett was replaced by a

horizontally-opposed engine A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, wh ...

, the YA-1 250 being fitted with a

Lycoming O-540 The Lycoming O-540 is a family of air-cooled six-cylinder, horizontally opposed fixed-wing aircraft and helicopter engines of displacement, manufactured by Lycoming Engines. The engine is a six-cylinder version of the four-cylinder Lycoming ...

engine of 250 hp driving a

Hartzell Propeller Hartzell Propeller is an American manufacturer that was founded in 1917 by Robert N. Hartzell as the Hartzell Walnut Propeller Company. It produces composite and aluminum propellers for certified, homebuilt, and ultralight aircraft. The compan ...

, while the YA-1 250R was fitted with a

Continental IO-470 The Continental O-470 engine is a family of carbureted and fuel-injected six-cylinder, horizontally opposed, air-cooled aircraft engines that was developed especially for use in light aircraft by Continental Motors. Engines designated "IO" ...

also developing , driving a Hartzell or McCauley propeller. The first Cropmaster, a YA-1 250, took to the air for the first time on 15 January 1960. Twenty further aircraft were converted before production ceased in 1966, by which time the company was known as Cropmaster Aircraft. Like its contemporary the

CAC Ceres The Commonwealth Aircraft CA-28 Ceres was a crop-duster aircraft manufactured in Australia by the Commonwealth Aircraft Corporation (CAC) between 1959 and 1963. The aircraft was a development of the Wirraway trainer of World War II. Developmen ...

the Cropmaster was unable to compete with more modern types of agricultural aircraft. Six of the twenty-one aircraft were the YA-1 250R model and the final three aircraft produced featured relocated main landing gear to counteract a tendency for the type to nose over on the ground. Six Cropmasters were exported to

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with the last registered example being returned to Australia in April 2022. Two examples (one flying) are registered in Australia.Australian civil aircraft register search, using "Yeoman" as the search parameter.
Search conducted 29 December 2008. The second is under rebuild at

Wagga Wagga Wagga Wagga (; informally called Wagga) is a major regional city in the Riverina region of New South Wales, Australia. Straddling the Murrumbidgee River, with an urban population of more than 56,000 as of June 2018, Wagga Wagga is the state's la ...

. Several other Cropmasters reportedly still exist in Australia and New Zealand.

Variants

An intermediate flying test-bed, the single Yeoman 175 was converted from CA-6 Wackett airframe C/N 257 for trials of a new all-metal empennage, and had the swept fin of later Cropmasters but retained the Warner Scarab radial engine and fabric-covered aft fuselage of the Wackett. A proposed variant with

tricycle undercarriage Tricycle gear is a type of aircraft undercarriage, or ''landing gear'', arranged in a tricycle fashion. The tricycle arrangement has a single nose wheel in the front, and two or more main wheels slightly aft of the center of gravity. Tricycle ge ...

was the YA-1B, none were built. A cut-away drawing of the YA-1B was included in a Yeoman Aviation brochure. The YA-1B design proposal also included an early version of the design for the all-metal empennage, with a more upright tail-fin than was actually produced. Another variant was the YA-1 285 with a Continental engine, sources disagree as to whether any of this variant were produced. At the time manufacture ceased, metal had been cut on the next evolution, this being the Cropmaster 300. The existing wing was to be retained with the span increased to 37 ft (11.28 m). The tail group was to remain unchanged. The tailwheel configuration was retained although new oleo legs to handle the heavier take-off weight were required. New plastic fuel tanks, still mounted between the front and rear wing spars, were of 21.5 imperial gallons capacity each, giving a total capacity of 43 gallons (195 lit.). Therefore, the practical working endurance remained at two hours or so. The fuselage was an all new design optimized for the topdressing role. The hopper remained in the same position but was of considerably increased capacity. Hopper load on topdressing would have varied between 12 and 17 cwt. (611/865 kg). The area from the hopper to the tail was to be of monocoque construction with an access hatch to permit loading of cargo/work equipment or (no doubt) the odd passenger. The cockpit section forward of the hopper was to be built on a steel tube frame and featured side by side seating for the pilot and a passenger (typically the landholder or the loader driver).

Accidents

Four pilots were killed in Cropmasters. In 1961 at Deniliquin, Ralph Dennis ran a tank dry in Marshall's VH-MSS and spun in. In 1964 John Waddell pranged VH-BAQ near Boorowa while doing low level aerobatics. In 1965 Air-Culture's VH-CXQ, with Richard Adams flying, struck a tree whilst entering a spray run at Highbury near Narrogin. Also in 1965 Bill Pearson flying Bender's VH-RPB at Kempton went in from a hundred feet or so, just after lift-off. Non-fatal misadventures included wire strike, jammed elevators after fence strike, getting trapped in a blind gully, Hartzell propeller blade failures and nose-overs.

Specifications (Yeoman YA-1 250R Cropmaster)

References

* Taylor, John W. R. ''Jane's All The World's Aircraft 1965–66''. London:Sampson Low, Marston & Company, 1965. * ''Tiger Moth, CT-4, Wackett & Winjeel in Australian Service'' Stewart Wilson. Aerospace Publications Pty. Ltd. * ''The Observer's Book of Civil Aircraft of Australia and New Zealand'' Timothy & Elizabeth Hall. Methuen of Australia Pty. Ltd. * original company documents and plans held by Fred Burke * research material compiled by Allyn Eckford

External links