In April of 1940 the RAAF issued Specification no.241 based on Wackett’s proposal. This called for an aircraft suitable for reconnaissance, level-and-dive bombing, as well as the ability to act as a torpedo bomber.

In June that year the Australian government, no doubt alarmed by the collapsing situation in Europe, allotted funding, and the CA-4, which carried the name of “The Wackett Bomber”, began full development. A mock-up was completed later that year, followed by the building of the prototype which first took to the air on 19th September 1941 – an impressively fast achievement.
Construction
The aircraft used a mixed construction that borrowed design elements from the company’s previous Wirraway aircraft. Like that, the fuselage was composed of a welded steel tube frame with a fabric covered plywood skin.

The nose and cockpit were metal skinned, while the low-mounted wing was of stressed skin construction and, in a first for the new Australian aero industry, had the fuel tanks as an integral part of the centre section wing construction.

Powerplant was made up of two Pratt & Whitney Twin Wasp radials that produced 1,200 hp each, and the nacelles that housed them had some extremely interesting features. Firstly, they acted as internal bomb bays, capable of carrying a couple of 250lb bombs each. On top of that the rear of each nacelle also housed a remote-controlled barbette, both of which held twin .303 Browning machine guns.

These were controlled by the wireless operator/rear gunner who sat at the back of the long, glazed canopy.

Additional intended armament was substantial, especially by the standards of the time.

The pilot would have four .303 Browning mounted in the nose in fixed positions, while the navigator/bomb aimer, who sat in the centre of the aircraft and had two large triangular windows on either side of the fuselage to assist him in his duties, was to have a single Vickers K in a ventral position to protect the rear lower portion of the aircraft.

On top of the four internal bombs, the Wackett Bomber was able to carry externally up to four 500 lb bombs or two torpedoes.

These could also be replaced by two external fuel tanks, boosting the aircrafts potential range even further: an important consideration for fighting in the Pacific.

Flight trials demonstrated that the aircraft had comparable performance to contemporary aircraft, with a maximum speed of around 280mph (450 kph). But as testing proceeded problems began to be identified.

The CA-4 had problems with overheating engines, as well as a dangerous tendency for the elevator to lose effectiveness, particularly during landing or sharp manoeuvres. This would also be accompanied by vibrations in the aircraft.

Performance on the ground was also poor, with the brakes being rather ineffective.

By this point it was December 1941 and Japan had attacked Pearl Harbor. Australia was at war with Japan and invasion was a very real possibility. RAAF pilots joined the testing regime and, throwing the aircraft around in the sort of manoeuvres expected in combat, uncovered additional issues with directional instability.

In early 1942, whilst performing a demonstration for several VIPs, including the Australian Prime Minister, the aircraft demonstrated itself to be remarkably tough. After takeoff, the pilot discovered a fault in his landing gear, preventing the left wheel from descending.

Unable to free the stuck wheel, the pilot decided the only option was a wheels-up landing.


Here the decision by Wackett to build the engine nacelles in a low-slung fashion meant that the aircraft was able to make a comparatively simple emergency landing that resulted in only minor damage which was bent propellers and dented engine cowlings.

In two days, the aircraft was repaired and flying again. Naturally, Wackett said that this was a deliberate design feature.

But what was alarming was that the crash report stated that the cause of the landing gear fault was due to large amounts of swarf being placed into the hydraulic lines. The conclusion was that the cause of the accident was sabotage!

Regardless, the aircraft was handed to the RAAF for official assessment and military trials in April, which actually occurred after an order for 105 of an improved version was placed by the government in March. This would be the CA-11 Woomera, which is the subject for my next article.

But before that aircraft could get properly into production and despite the desperate need for aircraft due to the threat from Japan, the issues with the CA-4 had to be resolved. RAAF testing threw up more issues, principally things like problems for the rear gunner in using his remote-control barbettes and in the bomb sight.

CAC planned to make the required changes in early 1943, as well as further modifications to the flight surfaces to deal with the handling issues. Once these were approved, they could be included into the CA-11 design and full production started.

Unfortunately, this was never to be. The novel fuel tank set up, which saw the wings act as the tanks, had proven problematic. Subject to leaks, which often saw fuel run out and accumulate in the tail, they had never been satisfactory.

And this, in turn, led to disaster.

On January 15, 1943, during a normal flight as part of tests on new fixed slats to resolve some of the stall issues, Squadron Leader James Harper, who was flying the aircraft, reported a fuel leak in his port engine. He shut down the engine and attempted to feather the propellor.

Unfortunately, this seems to have sparked a catastrophic explosion.

Harper parachuted safely from the aircraft which was destroyed when it crashed 8 Klms south west of Kilmore, about 60 Klms north of Melbourne. Both Carter and Dudgeon were killed in thecrash. Carter had attempted to parachute from the aircraft but had left it too late. Dudgeon'sbody was found inside the wreckage of the Woomera.














CA-11 Woomera
However, the RAAF had been sufficiently impressed with the design and ordered 105 of the updated version of the aircraft, the CA-11.

Plans were made for production to begin with a delivery rate of 20 aircraft per month.
Sqn. Ldr. Cuming of 1 Aircraft Performance Unit (A.P.U) was brought in to test the CA-11 as he had flown the original CA-4. On one test flight, the pilot who flew chase in a Boomerang, noticed that the tailplane tips were vibrating through an arc of 6 inches, and that the whole of the fuselage rear of the navigator’s position was vibrating torsionally. This was obviously an aerodynamic problem, but it had not shown up in wind tunnel tests. It was finally traced to the disturbance of airflow caused by the turrets on the rear of the engine nacelles striking the underside of the tailplane. The fin and rudder were then completely redesigned and the tailplane was given 12 degrees of dihedral which rectified the problem.

The updated CA-11 aircraft differed in detail from the prototype CA-4. The canopy was extended and the gunner sat in a moulded perspex sighting turret to operate the remotely- controlled rear nacelle guns. Forward armament consisted of two 20 mm cannons and two 0.303 guns, whilst a flexible-mounted Vickers G/O gun (G/O = gas operated) was installed below the fuselage. It had a maximum speed of 435 km/h (235kt) a range of 3218 km (1,725nm) (with torpedoes); Initial climb 579 m (1,900 ft)/min; absolute ceiling, 22,000 ft (6,705
m). Initially the CA-11 was powered by two 1,200 hp Pratt and Whitney R1830 Wasps, but was later fitted with two 1,300 hp Pratt and Whitney R2000 Wasps and re-designed CA-11A.

After exhaustive CAC trials, the CA-11A was transferred to the RAAF on 22 November 1944, but by this time American bombers were in plentiful supply and further production of the Woomera was discontinued instead, the factory started to gear up to manufacture the Mustang
fighter. Finally, on 16 January 1946, approval was granted for A23-1 to be converted to components.















General characteristics
Crew: 3
Length: 39 ft 7 in (12.07 m)
Wingspan: 59 ft 2.5 in (18.047 m)
Height: 18 ft 2 in (5.54 m)
Wing area: 440 sq ft (41 m2)
Airfoil: root: NACA 2218.5; tip: NACA 2209
Empty weight: 12,765 lb (5,790 kg)
Max takeoff weight: 22,885 lb (10,380 kg)
Powerplant: 2 × Pratt & Whitney R-1830-S3C3-G Twin Wasp 14 cylinder air-cooled radial piston engines, 1,200 hp (890 kW) each
Propellers: 3-bladed constant-speed propellers
Performance
Maximum speed: 282 mph (454 km/h, 245 kn)
Cruise speed: 184 mph (296 km/h, 160 kn)
Range: 2,225 mi (3,581 km, 1,933 nmi) (with external tank and one torpedo)
Service ceiling: 23,500 ft (7,200 m)
Rate of climb: 2,090 ft/min (10.6 m/s)
Armament
2 × .303in (7.7 mm) Browning machine guns in the nose
2 × 20 mm Hispano Mk II cannon in the nose
4 × .303 Browning machine guns in two rear-firing remotely controlled barbettes
1 x .303 Vickers K machine gun in a ventral position

Bombs:

4× 250 lb (113 kg) bombs internally in engine nacelle bays
and 4× 500 lb (224 kg) bombs
or 2× 45 cm Mk XII, Mk XV or 57 cm Mk 13 aerial torpedoes mounted under the fuselage
or 1× torpedo and 1× 293 imp gal (1,330 L; 352 US gal) external fuel tank mounted under the fuselage