In 1943, the Australian government arranged for the Commonwealth Aircraft Corporation (CAC) to manufacture the Mustang Mk IV (P-51D) under licence from North American Aviation. The RAAF urgently needed a new fighter, and so the first CAC Mustangs were built mainly from imported semi-finished parts. A prototype Mustang, A68-1001, was used for development trials and the first Australian production Mustang, A68-1, flew on 29 April 1945. This aircraft was handed over to the RAAF on 4 June 1945 and was used for trials by No 1 Aircraft Performance Unit until October 1946. It was placed in storage until 1953 when it was delivered to the Department of Supply at Woomera.

CAC Mustang Article

The first 80 Mustang 20s (A68-1/80) were delivered with Packard Merlin V-1650-3 engines, under the CA-17 designation. A second contract called for 170 improved Mustangs, but only 120 were completed. Known as CA-18, the first 40 were built as Mustang 21s (A68-81/120) with Packard Merlin V-1650-7 engines. The remaining CA-18s comprised 14 Mustang 22s (A68-187/200) with Packard Merlin V-1650-7 engines. A CA-21 contract for a further 250 Mustangs was cancelled and, in lieu of the remaining CA-18s and CA-21s, 298 lend-lease P-51Ds and Ks were taken on strength (A68-500/583 and A68-600/813). In addition, the RAAF also accepted Mustangs for the Netherlands East Indies Air Force (N3-600/640).

Produced too late for World War II, RAAF Mustangs were assigned to Japan for occupation duties and, early in 1946, Nos 76, 77 and 82 Squadrons flew into Iwakuni. In 1949 Nos 76 and 82 Squadrons withdrew to Australian and the Mustangs of No 77 Squadron remained to take part in the Korean War from June 1950 until April 1951, when they were replaced by Gloster Meteors.
In Australia, Mustangs remained in service with Citizen’s Air Force Squadrons until they were withdrawn from service in 1959.

CAC CA 18 Mustang Mk 21
Engine: One Packard Merlin V1650-7, 1490 hp at sea level, 1720 hp at 6300ft & 1565 hp at 17250 ft.
Propellor: Hamilton Standard 4 Bladed Constant Speed
Propellor diameter: 11ft 2in (3·4m).
Span 11.28 m (37 ft)
Length 9,83 m (32 ft 3 in)
Height: 3.71 m (12 ft 2 in).
Empty weight: 3567 kg (7863 lb)
Maximum Take Off Weight: 10,500 pounds or 4763kg.
Internal Fuel Capacity 224 Imp Gallons / 1018 litres
External drop tanks of 75 US Gals (284 litres) & 110 US Gals (416 litres).
Max IAS/Mach all altitudes: 438 kts IAS/Mach 0.77
Vne at 9,000ft: 500 kts TAS / 925 km/h
Max speed straight and level 10,000ft: 348kts TAS / 643 km/h
Max speed straight and level 25,000ft: 380kts TAS / 703 km/h
Maximum Rate of Climb: 3475ft/min at 5000ft
Service ceiling: 41900 ft / 12771 metres.
Time to 20000ft: 7·3 mins
Time to 30000ft: 12·6 mins.
Maximum Range 25000 ft internal fuel: 840 nm / 1530 km.
Maximum Range 25000 ft external fuel: 1435 nm / 2655 km.
Armament: Six 0.50 in Colt Browning machine guns; two 454 kg (1000 lb) bombs or up to 10 rockets
Inboard guns contained 400 rounds per gun & the rest – 270 rounds per gun.
Underwing hardpoints for six, 5 inch rockets or two 500lb (227kg) bombs.

The Wirraway had been the first product of the Commonwealth Aircraft Corporation formed in 1936 by several of the largest industrial concerns in Australia. To gain manufacturing experience, it had been decided to acquire a licence to produce an aircraft suitable for advanced training and as a replacement for RAAF Hawker Demons.
An Australian Air Board Technical Commission visited the USA and evaluated the North American NA-16, ordered into production for the USAAC as the BT-9 (NA-19) basic trainer.

CAC Wirraway Article

At the time of the Australian Commission’s visit, North American was working on a development of the BT-9 with a 600 hp Pratt & Whitney R-1340, retractable undercarriage and armament provision as a basic combat trainer. Designated NA-26, this aircraft fulfilled the Australian requirements, although there was disagreement over the need for retractable undercarriage. As a result, two versions of the A-26 were offered to the Australians, the NA-32 (NA-16-1A) with fixed undercarriage, and the NA-33 (NA-16-2K) with a retractable undercarriage, and in 1937, negotiations for manufacturing rights in both the NA-32 and NA-33 were completed, and an order placed for one of each.

The NA-32 was completed in July 1937, although it was not taken on charge by the RAAF until 8 November 1938, and by that time, the NA-33, which had been completed in September 1937 and taken on charge by the RAAF on 2 February 1938, had already been selected for Australian production. With minor changes to suit it more closely to RAAF requirements and Australian operating conditions, the NA-33 was ordered into production for the RAAF as the A20, the Commonwealth Aircraft Corporation applying the designation CA-1 to the type, and the name Wirraway being adopted.

The NA-16-2K changes including a reinforced sub-structure consistent with the rigors of the bombing role and improved offensive/defensive capabilities by the inclusion of 2 x 7.7mm machine guns as opposed to the NA-16’s sole gun.

Production of the initial aircraft was handled out of the Commonwealth Aircraft Corporation (CAC) facility at Fisherman’s Bend in Victoria.

CAC designations for Wirraway orders included CA-1, -3, -5, -7, -8, -9, -10 (a bomber version which was cancelled), -10A (dive bomber), and -16. The designation CA-20 covered the conversion of Wirraways for the RAN.

The Wirraway was a low-wing monoplane assemblies with sweep back and curved wingtips, mounted well forward of amidships. Wings were attached to the oblong, rounded airframe. The engine was held in the forward most compartment and was of an air-fed radial type. The cockpit was held aft of the wings with adequate views from under the heavily framed “greenhouse-style canopy. The empennage was conventional and tapered off to form the base of the rounded vertical tail fin. Horizontal tailplanes were situated at the forward base of this single vertical fin. The undercarriage was of the “tail-dragging” arrangement dominated by the two single-wheeled main landing gear legs. While these twin assemblies retracted into the aircraft, the diminutive single-wheeled tail wheel did not and remained exposed whilst the aircraft was in flight. Crew accommodations amounted to two personnel made up of the pilot and an observer.

The Wirraway’s structure comprised a welded chrome-molybdenum steel-tube fuselage with light metal-covered decking and underside, the sides having fabric covered light-alloy frames; a single-spar wing with spaced ribs and metal stressed-skin covering, and fabric-covered dynamically-balanced ailerons and split trailing-edge flaps, and a tail assembly consisting of metal-covered fixed surfaces and fabric covered moveable surfaces.

All fuel was housed in two 46 Imp.gal tanks in the wing centre section. The main undercarriage members were hydraulically operated, retracting into wells forming extensions of the leading-edge roots. The tandem cockpits were enclosed by sliding canopies, full dual controls were installed, the rear seat could be folded and rotated, and a prone bombing position was provided in the floor. Racks beneath the wing centre section could carry 8.5 lb or 11.5 lb bombs and marker flares, and provision was made for mounting two 0.303-in Vickers Mk.V machine guns in the forward upper decking, the pilot being provided with a ring-and-bead sight, and a Vickers Mk.1 0.303-in could be mounted in the rear cockpit.

Early Wirraways were powered by imported Wasp S1H1-G engines, but this engine was subsequently licence-built by CAC (680 single row Wasps eventually being produced), and the three-bladed Curtiss electric controllable pitch airscrews were produced from 1940 by de Havilland Aircraft at Alexandria, NSW.

Top speed was roughly 220 miles per hour with a cruise speed of just 155 miles per hour. Fuel was limited to 116-US gallons in wing fuel tanks with a pair of 11-US gallon reserve fuel tanks. Dimensionally, the aircraft sported a wingspan of 43-feet even with a length of 27 feet, 10 inches. Her height was 8 feet, 8 3/4 inches. When empty, the Wirraway displaced at 3,992 lbs and 6,595lbs for a maximum take-off weight.

The Wirraway was produced in seven major marks beginning with the CA-1. The initial contract called for 40 CA-1 Wirraways (A20-3 to -42) powered by the Wasp R-1340 S1H1-G of 600 hp, and the first aircraft of this contract (A20-3) was flown on 27 March 1939 at Fisherman’s Bend by Flt.Lt. L.H. ‘Boss’ Walker. Production of the initial aircraft was handled out of the Commonwealth Aircraft Corporation (CAC) facility at Fisherman’s Bend in Melbourne, Victoria. The first three RAAF Wirraways were accepted in July 1939. By December 1940, seven aircraft were being delivered weekly, and by September 1941, 45 Wirraways per month were coming off the production line.

The initial contract had been supplemented by the spring of 1940 by orders for 60 CA-3 Wirraways (A20-43 to -102) which differed externally from the CA-1 in having an enlarged oil cooler beneath the engine. The CA-3 was wholly similar to the CA-1, just assigned a different designation due to the nature of the Australian government production contract. This mark numbered 60 examples in all. In fact, the CA-5, CA-7, CA-8 and CA-9 were all also similar in scope to the original CA-1. The CA-5 was produced in a further 32 examples (A20-103 to -143) embodying minor instrumentation and equipment changes.

The CA-7, CA-8 and CA-9 marks were produced in totals numbering 100 (A20-135 to -234), 200 and 188 examples respectively. CA-7 Wirraway production attaining a rate of seven per week by the end of 1940. By this time further orders had been placed with the CAC calling for 200 CA-8 Wirraways (A20-436 to – 635) and 188 CA-9 Wirraways (A20-636 to -823), these each introducing small changes, such a the repositioning of the carburettor air intake, additional wing racks, etc. The CA-10A was an uncompleted bomber proposal, fitted with dive bomber wings but the CA-3, CA-5, CA-7 and CA-9 models were ultimately modified with such wings to become the CA-20 mark. CA-16, the last production Wirraway, was built to the tune of 135 examples before the last rolled off of the Commonwealth assembly lines and these represented the largest modification since the inception of the CA-1.

The initial orders for 620 aircraft, production rate attaining 45 aircraft per month in September 1941, and was completed by June 1942, but limited production continued until 1946 when the 755th Wirraway, A20-757, was delivered. The exigencies of the times had resulted in an order for a further 150 Wirraways of the modified CA-16 version (A20-1075 to -1224) intended for the dve-bombing role, although only 135 of these were to be delivered to the RAAF.

Earlier proposals for dive-bombing versins of the Wirraway, the CA-10 and CA-10A, had been cancelled, and the CA-16 differed from the standard Wirraway primarily in making provision for larger external bomb loads, racks being fitted immediately outboard of the wing centre section for two 500 lb and two 250 lb bombs which could be carried in addition to the six 8.5 lb or 11.5 lb anti-personnel bombs and eight target-markers. The 1500 lb increase in offensive load necessitated a conmitant reduction in weight elsewhere, and the twin Vickers guns in the forward fuselage decking and the flexible rear-firing gun were removed, and the aircraft was normally flown as a single-seater when maximum bomb load was carried, although the second seat was retained. The CA-16 fitted a pair of dive brakes for dive bombing sorties. The last was delivered on 30 November 1953.

Australia maintained the largest collection of Wirraways and these served with the Australian Air Force squadrons No.4, No.5, No.12, No.21, No.22, No.23, No.24 and No.25. The Australian Navy Fleet Air Arm utilized 17 of the type with squadrons No.723 and No.724. The RAN first aircraft was delivered on 24 November 1948. The United Kingdom’s Royal Air Force fielded one squadron (Y Squadron) of Wirraways in Malaya from 1941 to 1942, this being formerly the No.21 Squadron of the RAAF. The United States operated the Wirraway in limited numbers and only for a brief time with its HQ Flight as part of the 5th Air Force.

In 1940-41, camouflaged Wirraways were deployed to forward bases in Malaya (No 21 Squadron) Rabaul (No 24 Squadron), and Darwin (No 12 Squadron). On 6 January 1942, Flight Lieutenant B. Anderson of No 24 Squadron became the first RAAF pilot to engage in air-to-air combat in the South-West Pacific, when his Wirraway intercepted a Kawanishi (Mavis) flying-boat over Rabaul on January 6th, 1942 with no confirmed kill.
Two weeks later, on 20 January 1942, the Rabaul Wirraways achieved fame when eight aircraft, including A20-177, piloted by Sergeant W. Hewett, engaged a force of over 100 Japanese fighters and bombers. Although hopelessly outclassed by enemy aircraft, the Wirraway remained in the front line as a stop-gap fighter, and on 26 December 1942, Wirraway history was made when Pilot Officer J. Archer, in A20-103, succeeded in shooting down a Mitsubishi A6M Zero fighter near Gona.
Additional actions placed Wirraways over the skies of New Guinea but these were primarily used as ground attack platforms in support of ground forces in the region. The Wirraway continued in this respect until Curtiss P-40 Warhawks could be delivered in sufficient numbers from America and CAC could bring online its “Boomerang” dedicated fighter platform.
A Wirraway was used in 1947-48 by No 81 Wing while on duty with the British Commonwealth Occupation Forces in Japan.
The total production run was 755 and despite her early-war origins, the Wirraway continued on in the post-war world, primarily back in form with her dedicated trainer roots. The Royal Australian Navy would retire their Wirraways in 1957, replaced by the jet-powered de Havilland Vampires from Britain, while the Royal Australian Air Force continued Wirraway use up until 1958 – her last flight being formally recognized on April 27th, 1959.

After WW2 a number of Wirraways were converted to agricultural use, leading to development of the CA-28 Ceres agricultural aircraft.

Gallery

CAC CA-16 Wirraway
Engine: One 600 hp (448 kW) Pratt & Whitney R-1340-S1H1-G Wasp 9-cylinder radial
Weight loaded: 2991 kg / 6,595 lb
Propeller: Hamilton Standard Constant Speed, All metal, three blade
Fuel: Aviation Gasoline 100 Octane
Wing Span: 13.11 m / 43 ft 0 in
Wing Area: 255.75 sq. ft / 23.76 sq. m
Length: 8.48 m / 27 ft 10 in
Height: 2.66 m / 8 ft 8 in
Empty weight: 3,992 lb / 1,811 kg
Maximum Takeoff weight: 6,595 lb / 2,991 kg
Wing Tank Capacity: 97 Imp Gal / 441 Ltr / 116 U.S. Gallons
Reserve Tank Capacity (2): 9 Imp Gal / 41 Litres / 11 U.S. Gallons
Initial Rate of Climb: 1,950 ft per minute
Max. speed: 354 km/h / 220 mph / 191 knots
Cruise Speed: 135 knots / 155 mph / 250 km/h
Ceiling: 7010 m / 23000 ft
Range: 1159 km / 720 miles
Armament: 2 x 0.303 Vickers machine guns, 2 x 500 lbs and 2 x 250 lbs if no observer carried
Crew 2
Hardpoints: 2

Wirraway 3
Engine: CAC-Pratt & Whitney R-1340-S1H1-G Wasp, 600 hp
Wingspan: 43 ft
Length: 27 ft 9 in
Wing area: 255.75 sq.ft
Empty weight: 3980 lb
Loaded weight: 6353 lb
Max speed: 210 mph
Cruise: 186 mph
ROC: 1350 fpm
Range: 735 mi

During the war with Japan in 1941 Australia decided to produce an emergency fighter based on the Wirraway trainer. Designed and built in 16 weeks during 1942, the CA-12 prototype used the wings, landing gear, and tail unit of the trainer married to a new fuselage and a more powerful 1,200 hp Pratt & Whitney R-1830-S3C4G Twin Wasp 14 cylinder twin row radial engine from the DC-3.

CAC Boomerang Article

No actual prototype was produced. The first five production aircraft were already under construction before the first aircraft flew on 29 May 1942 (Test pilot Ken Frewin flew A46-1).
The first Boomerang Mk 1 fighters entered service in October 1942.
Following the flight of the first Boomerang, a further 249 Boomerangs were constructed under four separate contracts between 1942 and 1945. As production progressed, many improvements and modifications were incorporated, and the various standard versions were grouped under three CAC designations: CA-12, CA-13 and CA-19. The last 39 CA-19 Boomerang Mk II were completed as recconnaissance fighters.

A high performance prototype, the CA-14 A46-1001 was built with a turbo-supercharger. This same aircraft was later streamlined and fitted with a square-cut tail assembly and became the CA-14A.
The RAAF accepted the first Boomerang, A46-1, on 15 July 1942, and the last aircraft, A46-249, was delivered on 1 February 1945. Initial pilot conversion was carried out with No 2 Operational Training Unit at Mildura, and these pilots formed the first operational units, Nos 83, 84 and 85 Squadrons.
The first enemy contact was made on 16 May 1943, when Boomerangs from No 84 Squadron intercepted and drove off three Betty bombers. For many months, the Boomerangs successfully carried out many similar sorties until replaced by Kittyhawks and Spitfires.
Relegated to the army co-operation role with Nos 4 and 5 Squadron, the Boomerangs soon established a strong reputation for effective strikes throughout New Guinea, the Solomon Islands, and Borneo; particularly so in co-ordinated operations with RNZAF Corsairs.
A Boomerang at No 1 Aircraft Performance Unit was modified to take two seats; the second position was placed inside the fuselage behind the pilot and was used by an observer to record instrument and performance data.
Altogether, 250 Boomerangs were built and the various versions included 105 CA-12s, (A46-1/105), 95 CA-13s (A46-106/200), 49 CA-19s (A46-201/249), whilst the sole CA-14/CA-14A was numbered in the prototype range as A46-1001.

The standard production CA-12/13/19 Boomerang’s Pratt & Whitney R-1830 Twin Wasp power plant was not supercharged sufficiently to permit adequate high-altitude operations. Full-throttle height, in high blower at military power, being only 13,500 feet. To overcome this deficiency, a turbo-supercharger installation was engineered and fitted into A46-1001, the suffix – 1001 allotted to all Australian military prototypes.

Initial layout, under the name, ‘Turbo Boomerang Interceptor’, was shown on a GA drawing dated 8 January 1942, so that early thought was being given to the altitude deficiency inherent in the use of the standard Twin Wasp. A CA-13 airframe was taken off the assembly line at an early stage of production and converted to suit the installation, (attempting to fit the supercharger and ancillaries to a completed aircraft being too demanding).

Engineering commenced in July 1942 with Ian Ring, Ian Fleming, and Alan Bolton working on it. Under Tom Air, Bolton was Project Engineer for the design with CSIR doing the research work on the ducting. A mock-up was built in the No.2 Hangar of the Aircraft Factory. A CAC-built R-1830 S1C3G single-stage Twin Wasp on a longer engine mount, with General Electric B2 exhaust driven supercharger and ancillary equipment from a Boeing B-17E, were made available by the USAAF. Their fitment into the aircraft necessitated considerable redesign.

A Harrison intercooler was fitted into the fuselage behind the cockpit, and an intake for engine and intercooler air was positioned on the fuselage port side. Intercooler air was exhausted over the top of the fuselage through a temperature-controlled shutter behind the cockpit. The supercharger was mounted in the starboard fuselage, the normal exhaust tailpipe being extended down the fuselage to feed the turbine. The standard down-draught carburetor air intake was dispensed with giving it a cleaner top cowl line, while high-altitude magnetos were also fitted. A panel of test instruments was mounted in the rear fuselage, with a 35mm remotely-controlled camera to record in-flight data.

As in production of the Boomerang, compromises had to be tolerated, due to lack of optimum equipment. The best propeller available was a three-blade, eleven-foot Curtiss Electric, with a blade activity factor of 87, which limited climb performance and was 50 pounds heavier than that on the standard Boomerang. The B2 supercharger (as the only one obtainable) had a diffuser design which limited critical altitude by 4,000 to 5,000 feet when used with the R-1830 engine, and a further 500 feet in critical altitude was lost because of a 0.50 in-Hg greater pressure drop across the intercooler, compared with an Airesearch cooler which became available after first flights.

Rate of climb was also restricted because of the necessary use of large opening, conventional cowl gills to induce sufficient cooling flow, and resultant large increase in drag.

While the project was being developed, CAC design engineers had the use of the six RAAF Republic P-43 Lancers at Fishermans Bend for study and evaluation, examination of which was of material assistance.

Through October, work progressed and target date for completion was set at the end of the year. Some trouble was experienced with rudder and elevator control-cable runs which had to be duplicated to meet revised AP970 requirements; bends in the system to clear the ducting compounded this modification.

Although Lawrence Wackett requested Air Board approval, on 4 January 1943, for test pilot Jim Carter to be given some flying in an RAAF P-43B Lancer before flying the CA-14, it was advised that there was not one ‘conveniently available’. Instead, Flt Lt John Holden, the RTO at CAC, who had both Lancer and Boomerang experience, was nominated. (six P-43B reconnaissance fighters were allotted for Australian use, as PRU aircraft).

Ian Ring wrote, on 29 November 1986, ‘I was responsible for the turbo-supercharger installation in the CA-14A. I seem to recall seeing an American installation, but I do not remember getting any significant help from it, other than a general picture. Our installation and turbine performance data came from Pratt & Whitney. The problem was mainly one of accommodating the turbine in the appropriate position in the exhaust system, with suitable heat and fire isolation, and designing the inlet manifolds. The result was a spectacular rate of climb.’

The initial CA-14 flight was made on 13 January 1943 by Holden (promoted to Squadron Leader in that period). He not only proved the turbo installation, but also carried out comprehensive performance trials, and was commended by Aircraft-Superintendent Hugh Francis in a letter to Wackett, then in the US.

Even if Carter was to have taken over the further test work, as would have been the norm, it was not to be, as he was killed in the CA-4 Woomera crash on 15 January. Subsequently the new company test pilot, Greg Board, who arrived on 10 March, took over the task, and in the letter to Wackett, Francis told of Board’s appointment, stating that he had so far flown at very high pressure, and had been satisfactory in every way.

Precedence was given to assessing the engine installation and aircraft performance, and, with approximately 17 hours of flying by 29 March, the only other aspects noted were that ground handling, take-off, and the stall, were similar to the Boomerang, with better forward visibility resulting from removal of the carburetor air intake on top of the cowl.

At that time, engine overheating was occurring with the use of continuous climb outlet to 20,000 feet, but it was felt that fan cooling, then being planned, would cure this. Turbine exhaust temperature was at 780C, 35C below the maximum permissible, while turbine cooling and lubrication were satisfactory. Initial intercooling deficiency was overcome by removing the two lower cowl gills on the port side, thereby obviating engine cooling efflux inflow to the intercooler. Ignition breakdown at high altitude was overcome by replacing the Scintilla magnetos with Bosch high-altitude types. Further flights revealed that the aircraft was neutral stable in the lateral plane, directionally unstable, and rudder-trim changes with speed were excessive.

To overcome these latter two faults, the fin area was increased and redesigned, while lateral stability was improved by sweeping the wing tips up, as had been done on the Boomerangs. The supercharger installation was considered to be very satisfactory, but, due to the restricted climb, a cable was sent to Wackett on 15 April recommending that he obtain a four-blade eleven-foot propeller for the aircraft, similar to that fitted to the P-51B.

Performance and handling tests, at which time it was fitted with a large spinner, were completed by CAC (including flying to 35,000 feet) and it was delivered to the RAAF in April. On its return from Laverton in May, a new fin and rudder were fitted to further increase vertical area, and these improved the aircraft’s handling qualities as reported by the company test pilot.

It was returned to the RAAF for further evaluation. Board had flown it to 41,000 feet, its upper limit, and found that controllability was then almost non-existent, and that it fell away out of control very easily, (as was to be expected). From the lessons learnt with the CA-14, the same aircraft was developed into the CA-14A, still as A46-1001. Design calculations showed it to have a better all-round performance than the Thunderbolt and the Spitfire VC, comparative operational ceilings (at which rate of climb falls below 1,000fpm) were 34,400 feet, 32,000 feet, and 29,700 feet respectively. With 30 hours of CAC test flying and ten hours of RAAF evaluation on the CA-14, the conversion was carried out through June and July, with the following changes and new equipment scheduled for incorporation.

1) CAC-built R-2000 Twin Wasp replacing the R-1830. (not achieved.)

2) A B9 turbo-supercharger (actually a B13 was fitted).

3) The four-blade 11 foot Hamilton Standard propeller with blade-activity-factor of 113.5.

4) Ten-bladed cooling fan mounted behind the propeller, and driven through the reduction gearing at three times propeller speed.

5) Sliding cowl gills in place of the conventional hinged type.

6) Retractable tail wheel (not achieved).

7) The intake for the intercooler and engine air was fed from directly behind the fan, gaining considerably from ram effect, and also further increasing critical altitude. The ducting was set nearer the fuselage centre line and did not protrude as far out from the fuselage as it did on the CA-14.

8) The Airesearch intercooler. (40 pounds lighter than the Harrison)

9) A bulkhead in the rear fuselage (not achieved, it is believed, unless the auto observer panel was so described).

10) Changes in the oil-cooler installation and ducting.

With the original hinged gills opened, there was a tremendous increase in drag and buffeting and a reduction in controllability and forward vision. To overcome these liabilities, sliding gills were developed on A46-157 and a variable exit orifice, which was capable of controlling the cooling airflow within laid-down limits, was achieved. Operated hydraulically, as were the standard hinged gills, these slid backwards and forwards along a series of rails to alter the exit.

For some reason, the hinged gills were reinstated at some later stage, and were still on the aircraft when it was eventually broken-up. (It has not been possible to find detail of the changes in item 10, necessary because the exit ducting from the oil-coolers could not be allowed to feed the exhausted air into the extended intercooler/engine intake in the CA-14A, on thermodynamic grounds, and so as not to detract from maximum power).

The first graduate from the Sydney University Aeronautical Engineering Course, completed in 1941, was Alan Bolton, who went straight to CAC on Boomerang stressing, and then worked on the CA-14/14A design – he was able to advise in January 1994 that, to the best of his recollection, the outlet had been relocated to the starboard side into the duct which carried the exhaust tailpipe.

However, it is not known how oil-temperature control was effected in such a position, seemingly without the pilot-controlled exit flap, which had been on the port-side of the CA-14 and all production Boomerangs. During the conversion, a further increase in fin area was added, and the centre-section leading edges were straightened and swept forward, thus cutting out the wheel well fairings. During high-speed dive tests, up to 400 mph IAS, on A46-27, shock waves at the fuselage wheel-well junction occurred at about 360 mph by obviating this junction, wind-tunnel tests, showed the shock waves disappeared unti1 420mph was reached.

A limiting dive speed of 410mph was then placed on the CA-14A. Weight increase with these modifications was 100 pounds, making the all-up weight 8,132 pounds. Wackett wrote to DAP Secretary Letcher on 29 June 1943 to recommend production of the CA-14A before CA-17 manufacture could be started. With almost all of the detail parts for the 200 Boomerangs completed, various departments would be out of work within the next two months, and the assembly task would be completed in October.

With at least six months to the start of detail work on the CA-17, dependent on the arrival of information from the USA, and manufacture of the necessary tooling to begin fabrication, at least 200 more Boomerangs could be built, and such was necessary to keep the organisation intact, pending the start of CA-17 work. As there was need for
an urgent decision, for either standard Boomerangs or the CA-14A development, he recommended the latter.

It used fully 75% of the tooling for the standard Boomerang, and it was therefore possible to issue production orders for much of the detail parts immediately, while producing tooling for the new parts necessary to suit the supercharger installation. He summarised the project and company hopes in a report which contained the following key points:
The CA-14A’s performance would better the Spitfire Vc:

• it is sound reasoning to produce a version which can continue until the CA-17 becomes available;
• installation of the CA-14A’s turbo-supercharger has been carried out successfully;
• the 2000 cubic inch conversion of the 1830 engine, conducted locally on a Lidcombe built engine, has much promise;
• after a long series of trials the 40-degree propeller with wooden blades functions perfectly in flight;
• the development of the geared cooling fan is sufficiently advanced to enable this feature to be incorporated in the CA-14A. The success of the Focke Wulf 190 is largely due to this feature;
• the CA-14A will incorporate a larger fin and rudder and an improved fairing at the leading edge of the centre section. Both of these features have proved advantageous;
• the U.S. Army Air Force in Australia has hundreds of superchargers in store, and it should be possible to make a strong case for favourable consideration that sufficient of these be allotted for CA-14A production.

At the 5 July 1943 meeting of the AAC, Wackett emphasised that it was necessary to give immediate consideration to the production to be carried out between the thencurrent Boomerang contracts and the beginning of the Mustang, re-iterating the points made in his letter to DAP, and pointing out that the CA-14A was definitely the best possible aircraft to build until the CA-17 was under way.

Production of 120 further Boomerangs out of a DAP proposed 325 was recommended by the Minister for Aircraft Production on 8 July, with these to have the R-2000 and turbo-supercharger installed as soon as it could be done. However, the War Cabinet authorised only 50; this was not considered worth the extra effort involved for such a small number, and accordingly the CA-14A proposal was dropped. These 50 were built as standard Boomerangs, under the CA-19 contract. The CA-14A was actually completed and flown on about 26 July with the R-1830 sans fan, and a three-blade Hamilton Standard propeller. The R-2000 engine had suffered from bearing failure on test, and was not ready. Although the necessary enquiries had been made overseas for a suitable four-blade propeller, none was procured in time.

This would have resulted in much greater efficiency at climbing speed at all heights above about 15,000 feet, and at maximum speed. A letter from CSIR to Dept of Air (dated 20 August 1943), stated that the CA-14A incorporated many experimental features, in the design of which the CSIR had been actively concerned, and for this reason the RAAF was requested to carry out further detailed tests beyond the Type Trials.

These were to cover intercooler flows and temperatures, engine cooling, fuel consumption,
duct pressures, etc, in order to confirm the theoretical figures arrived at. Gp Capt Walter Armstrong (DTS) answered on 27 August, by saying that, although the CA-14A was of great technical interest, alterations in policy and pressure of other work placed further testing of the aircraft in a low-priority bracket. Turbo-supercharging for fighter aircraft had fallen out of favour here and overseas, mainly because of the slow response to throttle opening, and consequent lack of acceleration during combat.

However, if opportunity occurred, tests on the CA-14A were to continue. Both the CA-14A and A46-157 (and A46-27?) were used by CAC as test beds for the prototypes of a CAC-designed-and-built four-blade propeller with high-density wooden blades, a 38 degrees pitch range and 130 pounds lighter than similar metal propellers. Although developed with some success, and intended for, among others, the Mustang, it did not go into production.

A forced landing was made by A46-157 on 5 November 1943, believed to be due to the loss of about six inches off the tip of a blade, the resultant vibration loosened all but one tailplane attachment bolt before the landing could be effected. Just one week later, the CA-14A made a forced landing at Geelong when a bolt on the spinner backplate fractured.

Both of these aircraft were finally handed over to the RAAF in June 1944, fitted respectively with the first production fan and the first experimental one. The original allotment for the CA-14 project was £15,000 and the actual costs incurred until final delivery totalled £16,418/11/5, the engineering hours expended on it amounting to 15,160. The CA-14A was scrapped at the surplus aircraft park at Laverton during 1947 however, its mainplanes were used by ARL in its structural-fatigue research program.

A Boomerang was modified for use in the Australian film “Smithy” but afterwards was parked in a backyard at Blacktown, NSW, Australia.

Gallery

Commonwealth CA 12 Boomerang Mk.I
Engine: Pratt & Whitney R 1830 S3C4G Twin Wasp, 1184 hp
Wingspan: 10.97 m (36 ft 3 in)
Length: 7.77 m (25 ft 6 in)
Height: 3.5 m (11 ft 6 in)
Wing area: 230.35 sqft / 21.4 sq.m
Weight empty: 5455.2 lb / 2474.0 kg
Max take off weight: 7007.5 lb / 3178.0 kg
Max. speed: 256 kts / 474 km/h / 296 mph
Cruising speed: 226 kts / 418 km/h
Service ceiling: 29019 ft / 8845 m
Range at 190mph/304kph: 930 mi / 1490 km
Wing load: 30.55 lb/sq.ft / 149.00 kg/sq.m
Crew : 1
Armament : 2x MK 20mm, 4x MG 7,7mm

CA-13 Boomerang Mk II
Engine: one 1,200-hp (895-kW) Pratt & Whitney R- I 830-S3C4-G Twin Wasp radial piston
Propeller: Hamilton Standard 3E50 Constant Speed three-blade
Diameter: 11′ 0″ (3.35 m)
Fuel: Aviation Gasoline 87 Octane
Maximum speed 305 mph (491 km/h; 265kts) at 15,500 ft (4,725 m)
Initial climb rate 2,940 ft (896 m) per minute
Service ceiling 34,000 ft (10,365 m)
Range 1,600 miles (2,575 km)
Weight empty 5,373 lb (2,437 kg)
Maximum take-off 8,249 lb (3,742 kg).
Wing span 36 ft 0 in (10.97 m)
Length 25 ft 6 in (7.77 m)
Height 9 ft 7 in (2.92 m)
Wing area 225.0 sq ft (20.90 sq.m)
Armament: Two 20mm Hispano or CAC manufactured cannons, Four 0.303in Browning machine guns
Fuel capacity Wing Centre Section (2): 45 Imp Gal / 204 Litres / 54 US Gallons
Fuel capacity Fuselage Tank: 70 Imp Gal / 318 Litres / 84 US Gallons
Fuel capacity jetisonable: 70 Imperial Gallons (318 Lt)
Accommodation: 1

CA-19 Boomerang
Engine: Pratt & Whitney R1830 Twin Wasp.