Last updated 17.4.13
FROM WACKETT TO CROPMASTER
The genesis of the Yeoman YA-1 Cropmaster 250
by Geoff Goodall
Wackett Trainer, VH-ALV at Moorabbin November 1967. Photo by Geoff Goodall
Yeoman YA-1 Cropmaster 250R VH-TSD at Parafield March 1963. Photo by Geoff Goodall
The transition of the two-seater Commonwealth Aircraft Corporation CA-6 Wackett Trainer into the all-metal single seat agricultural Yeoman YA-1 Cropmaster 250 series is outlined in these topics in this series:
- CA-6 WACKETT TRAINER
- YEOMAN YA-1 CROPMASTER
This paper details the steps and lists the Wackett Trainers modified along the way.
By 1956 Kingsford Smith Aviation Service Pty Ltd at Bankstown Airport, Sydney still held a considerable number of RAAF disposals CA-6 Wackett Trainers in storage in hangars at Bankstown Airport, Sydney. Company founder John T. Brown OBE had purchased 91 Wacketts from RAAF disposals and established KSAS in 1946. His son, wartime pilot Peter Brown DFC, who was also a foundation director of KSAS, along with KSAS engineer C.W. (Bill) Smith were convinced the CA-6 could be modified for agricultural use, and saw this is as an effective way to utilise their stored Wacketts.
KSAS had considerable experience in modification and re-engining of various aircraft types. The company had carried out agricultural modifications to Austers and built the KSAS PL-7 Tanker designed by Luigi Pellarini.
In 1957 Bill Smith designed an arrangement for a stock CA-6 Wackett Trainer to have a hopper installed in the front cockpit area with the pilot sitting in a slightly raised position in the rear seat position. The original windscreen and overturn pylon were moved rearward. It retained the Warner Scarab radial engine and little modification of the basic airframe was involved, except some mods to reduce empty weight. It had a good performance for minimum cost and there was obvious potential for the growing Australian aerial agricultural market. KSAS development work, experimenting with position of pilot and hopper, resulted in the KS.1, KS.2 and KS.3 Wackett-Cropmaster. Five of these aircraft had been completed (VH-AJH, VH-FBD (1, FBD (2, FBE & FBF) when the Australian Department of Civil Aviation confirmed its earlier warnings to KSAS that it would not approve any more agricultural aircraft with wings of wooden glued structure.
Having proven the concept, the KSAS directors decided to form an associated company to specialise in developing the design into a modern agricultural aircraft. It would have a metal mainplane and tailplane and be powered by a current American flat-six engine: from this concept the YA-1 was designed.
The new company Yeoman Aviation Pty Ltd was established effective 8 August 1958, during a company restructure of Kingsford Smith Aviation Service Pty Ltd. The prime KSAS business had been the Australian Auster dealership, importing almost 300 new Austers from Britain. But that market had been lost to new Cessnas. New associate companies were:
- Austerserve Pty Ltd: Auster sales and service. Managing Director J.T.Brown
- Yeoman Aviation Pty Ltd: develop agricultural aircraft: Directors J.T.Brown, P.G.Brown, C.W. Smith
- Kingsford Smith Flying Service Pty Ltd, an associate company since 1951 operating a successful flying school at Bankstown
A new design single-unit metal wing duplicated the dimensions of the CA-6 Wackett's wooden mainplane but reduced the empty weight by 200 pounds. The Wackett's rounded wingtips and slots were deleted but the fabric-covered wooden ailerons were retained. The windscreen, canopy and turtledeck were of new design and extensive use was made of fibreglass, then new to aircraft construction, including engine cowlings, lower fuselage forward of the wing, front and rear turtledeck, dorsal fin and removable rounded wingtips. The new design 145 gallon hopper was also made from fibreglass.
Twenty Yeoman YA-1 Cropmasters were constructed in the Yeoman Aviation hangar at Bankstown between 1960-1966 with constructor's numbers 101 to 121 (c/n 109 was not completed). It was a new design, using a new metal making much use of fibreglass panels, using American horizontally opposed 250hp Lycoming or Continental engines. At first the basic structure was the CA-6 fuselage frame, but as Yoeman production continued the use of Wackett parts was reduced.
The initial engine chosen was the 250hp Lycoming 0-540A engine with a Hartzell constant speed propeller. The stainless steel exhaust augmenter tubes to provide engine cooling did away with the need for cowling flaps, and became a distinctive identification feature of the aircraft.
L-R Bill Baldwin, Bill Smith, Brian Wagner with the first YA-1 c/n 101. Allyn Eckford collection
Three CA-6 Wackett Trainer fuselage frames on the YA-1 production line. Allyn Eckford collection
The new metal tailplane being fitted. Allyn Eckford collection
The first YA-1 c/n 101 was test flown at Bankstown on 15 January 1960, flown by Peter Brown. Yeoman Aviation was under-capitalised which restricted their ability to develop a new metal tailplane at the same time as the metal wing was being designed and tested. DCA were persuaded to allow the early YA-1s to enter service fitted with CA-6 Wackett wooden tailplanes. A fibreglass dorsal fin disguised the shape.
When the new metal tailplane design featured a stabilator, attractive swept-back fin and large rudder. The first unit was testflown on a Wackett Trainer VH-CYB in December 1961 and January 1962, then the fuselage frame and new tailplane of that test Wackett was used to construct the next production YA-1 c/n 106 VH-CYW which first flew 13 April 1962 as the first Cropmaster 250 with the metal tailplane.
DCA had delayed full Type Approval waiting on further operational experience, and the metal tail unit. After flight tests of VH-CYW, the Type Approval Certificate was issued in June 1962. As YA-1 production continued, CA-6 components were replaced by new-build units. By 1966 the only original Wackett Trainer components remaining were the undercarriage structure, comprising only 3% of the total airframe.
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Airwork Pty Ltd KS.3 at work in WA circa 1959 with Chief pilot Bill Boulden. Ben Dannecker collection
This story is one of conflicting aims of producing a low priced agricultural aircraft, which gave better performance and payload to the DH.82 Tiger Moths then in widespread agricultural use versus DCA concern with the strength of the wooden wing and tailplane structure.
The KS.3 Cropmasters utilised the basic wooden CA-6 wing and tailplane of glued plywood and spruce box spar with glued plywood covering on its wings and empennage. In addition to DCA concern over the integrity of the glued wood 15 years after manufacture, tests had shown agricultural chemicals reacted with the glue resulting in deterioration of the joints.
KSAS founded the associate company Yeoman Aviation Pty Ltd to develop the concept to produce a more modern aircraft with metal wing and metal tailplane, powered by the latest American engines. The result was the YEOMAN CROPMASTER 250.
Twenty YA-1 Cropmaster 250s were built at Bankstown between 1960-1966. The CA-6 Wackett Trainer fuselage frame was used as the basic structure at first but gradually replaced by new-build structure. The first five YA-1s retained the Wackett wooden tailplane, mounted on a newly designed metal main plane. A schedule was implemented for delivered YA-1s to be returned to Yeoman Aviation at Bankstown to have the new metal swept-back tailplane fitted. A "metalisation program" was devised for the remaining KS.3 Cropmasters but accident losses reduced their numbers and none were fitted with the metal wings and tailplane.
The following sequence shows the steps in the development of the YA-1. It highlights the continual struggle with the Department of Civil Aviation over the airworthiness restrictions being imposed on certain wooden structure aircraft being used for agricultural flying. However frustrating it was for the regulator, DCA can be seen to be sympathetic to the struggling Yeoman Aviation, and allowed a series of dispensations to allow the KS.3 Cropmasters to continue in commercial operation while waiting to be replaced by the new metal wing YA-1 Cropmaster range. Similarly DCA gave owners dispensations against its Air Navigation Order cancelling the CofAs for the first five YA-1s with wooden empennage, because of Yeoman Aviation delays in manufacturing the new metal tailplanes.
INDEX ONE: THE FIVE KS.3 WACKETT CROPMASTERS:
VH-AJH, VH-FBD (1), VH-FBD (2), VH-FBE, VH-FBF rebuilt at Bankstown by KSAS 1957-58
KS.3 Cropmasters with Airwork Pty Ltd in WA during 1959. Geoff Goodall collection
A3-49 c/n 283 to KS.1, KS.2, KS.3 Cropmaster VH-AJH
VH-AJH at Bankstown in KS.2 Cropmaster configuration 1957. Ben Dannecker collection
Rebuilt as a KS.3, at Maylands WA with Air Culture Pty Ltd. Photo by Ern Flanders
Jandakot December 1973, waiting collection by AFA museum. Photo by Roger McDonald
Queensland Air Museum, Caloundra December 2009. Photo by Ron Cuskelly
A3-65 c/n 299 to KS.3 Cropmaster VH-FBD (1)
A3-176 c/n 410 to K.S.3 Cropmaster VH-FBD (2)
Airwork Pty Ltd KS.3 in WA during 1959, showing the belly crop dusting chute. Geoff Goodall collection
VH-FBD fuselage frame removed from fire drill ground, Jandakot in August 1975. Photo by Geoff Goodall
VH-FBD frame leaves Jandakot for Sydney August 1975, compiler at rear. Photo by Roger McDonald
A3-131 c/n 365 to KS.3 Cropmaster VH-FBE
VH-FBE at Beacon WA in May 1959 with Air Culture Pty Ltd, Perth. Geoff Goodall collection
A3-141 c/n 375 to KS.3 Cropmaster VH-FBF
VH-FBF at Cootamundra March 1958, during ferry to WA. Photo by Ben Dannecker
VH-FBF frame at Jandakot airport fire drill ground, January 1973. Photo by Geoff Goodall
INDEX TWO: OTHER WACKETT TRAINERS MODIFIED BY YEOMAN AVIATION
A3-40 c/n 274 VH-AJB
Bankstown August 1958, parked outside the KSAS hangar. Photo by Dave Eyre.
A3-129 c/n 363 VH-AMA
Bankstown c1958 with modified canopy for hopper in the back seat position. Allyn Eckford collection
A3-23 c/n 257 to Yeoman 175 VH-AIV, (VH-CYB)
Yeoman 175 VH-CYB at Bankstown in December 1961. Photo by Eric Allen
VH-CYB registration was painted on the wings only. Photo by Greg Banfield
A3-172 c/n 406 VH-AKF (2)
Bankstown in May 1963, parked outside the Yeoman Aviation hangar. Photo by Geoff Goodall
Bankstown January 1964, retired after YA-1 cockpit section was installed. Photo by Geoff Goodall
- Australian Civil Aircraft Register - Department of Civil Aviation and its successors
- Flypast A Record of Aviation in Australia, Neville Parnell & Trevor Boughton, CAA 1988
- Annual Survey of Accidents, DCA publications 1960-1968 editions
- National Library of Australia, Trove website, newspaper archive search
- DCA aircraft registration files, WA Region, National Archives of Australia, Perth WA
- DCA Airwork Licence files: Airwork and Air Culture, National Archives of Australia, Perth WA
- Cropmaster, Allyn Eckford, AHSA Aviation Heritage, June 2004
- Allyn Eckford, Brisbane: interviews and correspondence with Yeoman founders and YA-1 operators
- KSAS workshop records for KS.3 conversions, via Allyn Eckford
- Peter Brown’s pilot log book, courtesy Allyn Eckford
- Airframe log book VH-AJH, transcribed by compiler
- Aerial Agriculture in Australia, Derrick Rolland, Aerial Agricultural Assoc of Australia, 1996
- Wackett CA-6 Aircraft - Use for Agricultural Operations, DCA Central office file 1957-58,
National Archives of Australia, accession MP726 reference 16/11/141