CAC Wirraway Technical Details

Development

The Wirraway is an Australian-built version of the North American Aviation NA-16-2K advanced trainer, the design of which was licensed from NAA for production in Australia. The Wirraway is a "cousin" to the well-known T-6 Texan trainer and the Harvard trainer, as all three aircraft were developed from the same "ancestor" - the NA-16 basic trainer which first flew in 1935.

Commonwealth Aircraft Corporation licensed the design of the NA-16-1A (North American "charge number" NA-32) and the design of the NA-16-2K ("charge number" NA-33) and ordered one of each of these designs from North American. The NA-16-1A aircraft carried the North American manufacturer's serial number 32-387 and the NA-16-2K carried the serial number 33-338. The license deal signed on March 10th 1937 included a fee of $100,000 for the two designs, $30,000 for the specifications and manufacturing data, a $1,000 royalty for each of the first 25 aircraft produced and $600 for each of the subsequent 75 aircraft produced.

At the time of the Wirraway's introduction, the NA-16-1A (charge number NA-32) was commonly known in the press as the NA-16 and the NA-16-2K (charge number NA-33) was commonly known as the NA-33.

Modifications to the NA-16-2K design which resulted in the first production Wirraway (A20-3) included the following:

• Flare tubes in the rear fuselage for releasing parachute flares;
• The addition of a second forward-firing machine gun in front of the pilot (earlier versions of the NA-16 family - such as the NA-18 of 1935 - already featured two forward-firing machine guns). The guns were changed from US-built Browning models to Vickers 0.303" calibre Mark V.
• Modifications to the rear gun-mount
• Changes to the exhaust system (two outlets instead of 1)
• Modifications to the oil cooler air intake
• Changes to the drawings to use BA engineering standard fittings rather than US standards

It has also been noted elsewhere that the design was strengthened to allow for dive-bombing, but evidence supporting this suggestion is not apparent. The structural design of the fuselage framework and wing spars appears identical to earlier NA-16 variants.

Variants

The Wirraway was built in 3 distinct versions (Mk I, Mk II and Mk III) and orders were placed in 7 different batches (contract numbers CA-1, 3, 5, 7, 8, 9 and 16). A total of 755 Wirraways were produced by Commonwealth Aircraft Corporation at Fisheman's Bend in Melbourne, with deliveries between July 1939 and June 1946. The correspondence between versions and CAC contract numbers is listed in the table below:

Dimensions

The drawing below shows the general dimensions for the CAC Wirraway.

This drawing is scanned from the Wirraway spare parts manual issued in 1941. It shows a very basic general arrangement drawing of the Wirraway Mk I with major dimensions shown. Click on the thumbnail at the left to view a larger image.

This cutaway drawing of the Wirraway was drawn by F.D. Rogers in 1944. It shows the internal structure and layout of the major equipment, and appears to be the Mk III or CA-16 model with "dive bomber" wings (with airbrakes above the flaps) and no armament. The quality is not very good, due to the blueprint reproduction process, but this interesting drawing shows the technology of aircraft design in the late 1930's when the Wirraway was designed. Click on the thumbnail at the left to view a larger image.

Engine

CAC-built Pratt & Whitney Wasp R-1340 S1H1-G engine:

The Wasp was the first engine produced by Pratt & Whitney Aircraft Co. following the establishment of the company in 1925. Fred Rentschler and George Mead left the Wright Aeronautical Corporation to form the company with Clayton Burt (President of Pratt & Whitney Company, a machine-tool company originally established in 1860).

The first Wasp engine to be developed was fired into life on Christmas eve of 1925. It was a 9-cylinder air-cooled radial engine with a displacement of 1,340 in³ (hence the designation of R-1340) and it developed 425hp by it's third test run. Many developments and versions of this basic engine followed, and the S1H1-G model which powers the Wirraway produces 600hp and features a 10:1 supercharger and a 3:2 geared propeller drive shaft (the propeller spins slower than the engine - at 66.7% of the crankshaft speed).

	Detailed photos of the CAC-built Pratt & Whitney R-1340 S1H1-G engine on display at the Australian National Aviation Museum in Moorabbin, Australia. Click the thumbnail at the left to view the photos on Flikr.
	Clearance index chart from the engine overhaul manual (sheet 1 of 2). This drawing shows an interesting cross-section view of the engine. The numbers on the drawing correspond to clearances for the listed dimensions, which are described on a separate chart (not shown). Click on the thumbnail at the left to see the full-sized image.
	Clearance index chart from the engine overhaul manual (sheet 2 of 2). This drawing shows a view of the rear of the engine where the accessories (starter motor, magnetos, carburettor, oil pump, oil filter, etc) are mounted. Click on the thumbnail at the left to see the full-sized image.

Stromberg NA-Y9E carburettor:

Schematic diagram showing all parts labelled. Click on the thumbnail at the left to see the full-sized image.

Bendix-Scintilla SB9RN magnetos:

	Schematic diagram showing electric and magnetic circuits. Click on the thumbnail at the left to see the full-sized image.
	Service chart showing maintenance and installation instructions. Click on the thumbnail at the left to see the full-sized image.

Propeller

The Wirraway was fitted with a 10 foot diameter De Havilland ADH2 constant speed propeller. The design for this propeller was licensed from Hamilton Standard, and the version fitted to the Wirraway corresponds to the Hamilton Standard 3D40 constant speed hub with 6101A-3 forged aluminium blades. The part numbers for these items provide the following descriptions:

3D40 hub description:
3 = 3 blades
D = Blade shank size "D"
40 = SAE #40 prop shaft spline size
Pitch range of this hub = 20°
High pitch setting = 39°
Low pitch setting = 19°

6101A-3 blade description:
6101 = basic blade design
A = the blade is an Assembly (including the blade itself, bearing assembly, chafing ring, bushing, bushing drive-pins, bushing drive-pin screws, and balancing-plug assembly)
-3 = the length of each blade is reduced from the basic design to achieve a 3 inch reduction in the overall diameter

	Exploded view of the De Havilland ADH2 propeller hub, which was a licensed version of the Hamilton Standard 3D40 hub. This image was scanned from a 1942 monthly technical bulletin issued by De Havilland in Australia. Click on the thumbnail at the left to see the full-sized image.
	Exploded view of the Hamilton Standard 3D40 constant speed hub showing all parts labelled. This drawing is reproduced from the Hamilton Standard maintenance manual. Click on the thumbnail at the left to see the full-sized image.
	Blade form curves for the basic Hamilton Standard 6101 blade design. These curves show the following ratios at different locations along the radius of the blade: p/D = pitch / Diameter (shown at 4 different pitch settings) b/D = chord / Diameter h/B = airfoil thickness / airfoil chord (the 6101 blade design uses the Clark Y airfoil section) Click on the thumbnail at the left to see the full-sized image.

Manuals

	The Wirraway Overhaul and Repair Manual RAAF Publication No. 76 Issued by the Engineering Department, Aircraft Division of Commonwealth Aircraft Corporation Pty Ltd, November 1940 This manual covers all the information required for servicing and repairing the Wirraway aircraft. The manual is divided into 3 parts: Part I covers Service and Maintenance; Part II covers Inspections; and Part III covers Repairs. You can order an electronic copy in PDF format from Mach One Manuals.
	Pilot's Notes for the Wirraway Aircraft RAAF Publication No. 109 This manual covers all the information required for operating the Wirraway aircraft. This includes notes for pilots and descriptions of operating all the aircraft equipment and controls. You can sometimes find copies available on eBay, or order an electronic copy in PDF format from Mach One Manuals.
	CAC Wasp Operating Instructions RAAF Publication No. 71

Additional information sources

You can find more information regarding the Wirraway on these websites:

• ADF Serials website entry for Wirraway (this website includes the service history of all Wirraways produced)
• Australian National Aviation Museum details for Wirraway A20-10 on display at the museum in Moorabbin, Victoria
• The Australian War Memorial archive has many images of Wirraways in service and during production. Click here to see search results for "Wirraway".
• Queensland Air Museum details for Wirraway A20-652 on display at the museum in Caloundra, Queensland
• RAAF Museum website entry for A20 series Wirraway
• Wikipedia entry for CAC Wirraway

Bibliography

A selection of books, magazine articles and newspaper articles related to the Wirraway:

• Caruana, Richard J. The Commonwealth Aircraft Company Wirraway. Scale Aviation Modeller International magazine. Volume 9 Issue 11, November 2003
• Davis, Larry. T-6 Texan In Action. Aircraft Number 94, Squadron/Signal Publications, 1115 Crowley Drive Carrollton Texas, 1989 (includes a chapter on the Wirraway)
• Gillison, Douglas (1962), Royal Australian Air Force 1939-1942.Australia in the War of 1939–1945. Series 3, Volume 26 – Air. Canberra: Australian War Memorial. Retrieved 29 December 2010
• Green, William. War Planes of the Second World War, Bombers, Volume Seven. London, Macdonald, 1967. ISBN 0-356-01477-0
• Justo, Craig. Together Again... Aeroplane Monthly magazine March 1997
• Owers, Colin. Wirraway Australia's Warlike Trainer Air Enthusiast No. 50, May - July 1993. Key Publications, Stamford, Lincolnshire, United Kingdom. ISSN 0143 5450
• Pentland, Geoffrey. Wirraway and Boomerang Markings. Dandenong VIC, Australia, Kookaburra Technical Publications, 1970
• Profile Publications Research Staff. The Commonwealth Wirraway, Aircraft in Profile no.154. Leatherhead, Surrey, UK, 1967
• Rolland, Derrick. Aerial Agriculture in Australia: a history of the use of aircraft in agriculture and forestry. Aerial Agricultural Association of Australia Ltd. 1996. ISBN 0 646 24840 5
• Smith, Peter Charles. T-6: The Harvard, Texan & Wirraway - A Pictorial Record. North Branch, MN: Speciality Press, 1995. ISBN 0-7603-0191-3
• Wilson, Stewart. Wirraway, Boomerang & CA-15 in Australian Service. Sydney, Aerospace, 1991. ISBN 0-958797-88-9
• Vella, Joe. Aircraft Described No. 219 C.A.-1 Wirraway. Aeromodeller magazine. January 1973.
• Vella, Joe. From Fisherman's Bend - The Aircraft of the Commonwealth Aircraft Corporation, Air Enthusiast magazine, No. 61 January/February 1996
• Zbiegniewski, Andre R. and Nowicki, Jacek. CAC Boomerang & CAC Wirraway, Wydawnicto Militaria 43 (in Polish). Warszawa, Wydawnicto Militaria, 1997. ISBN 83-86209-57-7

Survivors

A number of Wirraways are preserved in museum collections, and several have been restored to air-worthy condition. Here is a list of remaining Wirraways (I'm sure this list is far from complete, so let me know if you can provide any additions or updates):

Picture courtesy of ANAM	A20-10 (CAC construction number 8, Mk I produced under contract CA-1) The earliest Wirraway still surviving (the eighth production aircraft), 10 is held in the collection of the Australian National Aviation Museum in Moorabbin, Victoria. A20-10 was produced as a Mk I aircraft, in the first contract order CA-1 for 40 aircraft. During it's service life the carburetor and oil cooler air intake were upgraded to Mk III standard. Click here to visit the museum web page describing this aircraft.
	A20-81 (CAC construction number 79, Mk II produced under contract CA-3, displayed as A20-176) A20-81 has been restored to air-worthy condition in the markings of A20-176, registered as VH-WWY. It is operated by a syndicate out of Caboolture. Click here for photos of A20-81 on JetPhotos
	A20-99 (CAC construction number 97, Mk II produced under contract CA-3) A20-99 is currently being restored by a team headed by Bill Smith at the Historical Aircraft Restoration Society at Illawarra Regional airport in New South Wales. The aircraft is owned by Eric Lundberg and it is intended to restore the aircraft to airworthy condition. The civil registration VH-JML has been reserved for this aircraft. Click here for HARS blog posts about the progress of the restoration.
	A20-103 (CAC construction number 101, Mk II produced under contract CA-5) A20-103 is held in the collection of the Australian War Memorial in Canberra. It may be the best-known Wirraway, having achieved the only air-to-air victory by a Wirraway during the Second World War, while piloted by Flt-Lt John Archer and Sgt Les Coulston. Click here to see details of the encounter by Archer and Coulston from the Australian War Memorial collection.
	A20-502 (CAC construction number 703, Mk II produced under contract CA-9) A20-502 BF-O is held in the collection of the Ballarat Air Museum in Victoria.
Picture © Doug McPhail, used with permission	A20-651 651 is held in the collection of the Fleet Air Arm Museum in Nowra, New South Wales. Click here to visit the museum's web page.
	A20-652 652 is held in the collection of the Queensland Air Museum in Caloundra, Queensland. It was restored to airworthy condition by Vin Thomas and returned to the air in September 1986, registered as VH-WIR. In 2006 it was sold on eBay to Peter Smythe (resulting in a much publicised dispute). In 2010 it was purchased by QAM, funded by a donation from The John Villiers Trust. It is now on display in Caloundra. Click here to visit the museum web page describing this aircraft.
	A20-653 653 was the first Wirraway restored to airworthy condition, returning to the skies in 1975. This aircraft was also the first ex-military aircraft permitted to fly on the civil aircraft register, starting the "Warbird" movement in Australia. It was restored by Richard Hourigan while in the collection of Malcolm Long. It was purchased by David Lowy and donated to Temora Aviation Museum in Temora, New South Wales. 653 is displayed as it appeared during its service in 5 Squadron, RAAF based in Bougainville, Papua New Guinea. It's civil registration (VH-BFF) corresponds to the squadron markings of 5 Squadron (whose squadron code was "BF") Click here to visit the museum web page describing this aircraft.
	A20-685 685 is held in the collection of Camden Aviation Museum in Camden, New South Wales. Click here to visit the museum web page describing this aircraft.
Picture from RAAF Museum website	A20-687 (displayed as A20-561) 687 is held in the collection of the RAAF Museum in Point Cook, Victoria. Produced under the CA-16 contract, 687 went into storage at Tocumwal. It was restored over an 8-year period from 1968 to 1977 by Richard Hourigan and Pat Capron to the specifications of the CA-9 production contract and painted to represent A20-561 of 4 Squadron. Click here to visit the museum web page describing this aircraft.
	A20-688 688 is held in the collection of the RAAF Association Museum in Bull Creek, Western Australia. 688 was incorrectly labelled as 668 by the museum sign-writer. Click here to visit the Aviation Association of Western Australia web page describing this aircraft.
	A20-695 695 resides at the Caboolture Warplanes Museum in Caboolture, Queensland. It was purchased from CAC by Pearce Dunn and stored in Mildura. 695 then moved to Point Cook and finally Caboolture where it was restored to airworthy condition flying again in July 1997 registered as VH-MFW. Click here for photos of A20-695 on JetPhotos.
	A20-704 (displayed as A20-436) 704 is owned by Murray Griffiths. It was part of Joe Drage's Air World collection in Wangaratta, Victoria and was restored to airworthy condition, flying again in June 1997. 704 has been painted to represent A20-436 BF-B of No. 5 Service Flying Training School, and is registered VH-BFO. Click here for photos of A20-704 on JetPhotos.
	A20-719 (was displayed as A20-458) 719 was restored to airworthy condition by a syndicate led by Rob Greinert, the third Wirraway to be returned to the air. 719 was painted to represent A20-458 of No. 5 Service Flying Training School, and was registered VH-WRX. Sadly it crashed during an airshow handling display at Nowra, New South Wales in May 1999. The pilot Owen O'Mally (a World-War II veteran) and observer Phil Lloyd were both killed in the crash. Click here for a website commemorating Owen O'Malley and Phil Lloyd.
	A20-722 722 has been restored to airworthy condition by Borg Sorenson. It returned to the air in June 2002, registered as VH-CAC. Click here for photos of A20-722 on JetPhotos.