Commonwealth Aircraft Corporation Boomerang Restoration

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CAC Boomerang - Exploring the myths and facts.

Much has been written by various authors about the Boomerang aircraft that has introduced, developed, and extended myths over the years. This hopes to answer some of those myths. The greater majority of this information was verified or provided in conversations with Alan Bolton, Boomerang Design Engineer, CAC Board minutes, CSIRO reports on the Boomerang, Australian National Archive reports, and extensive restoration knowledge of Matthew Denning and Greg Batts.

The Boomerang was a super Wirraway. Wrong, it was a new design.

Lawrence Wackett designed the Boomerang. Wrong, there was a design team set up following preliminary design drawing by Alan Bolton and Fred David, at the instigation of Fred David. According to Alan Bolton, Wackett was unaware of this design work until 3 weeks after it was commenced, when most of the preliminary sketching had been done. The design team was:

Bill Air	Chief Engineer	Responsible for project reporting direct to General Manager
Fred David	Chief Design Engineer	Head of project team
Alan Bolton	Boomerang Design Engineer	Overall design and stressing. Detail of outer wings, tail surfaces, tail wheel, engine mount, turbo � supercharger installation and ducting, intercooler installation. Structural testing
Morrie Lodge	Project Engineer	Aircraft Manufacture Control
Ernie Jones	Chief Draftsman	Control of all drafting aspects
Joe Solvey	Engineer	Detail wing aerodynamics
Lionel Stern	Engineer	Design and production of 20mm cannon (Hispano)
Ian Flemming	Engineer	Flight Testing and aerodynamics
Col Belwood	Engineer	CA14 engine mod, fan, spinner, and cowling design
Lawrence Wackett	General Manager	Government Liaison, Board Manager, overall responsibility for CAC operations

The Boomerang used many Wirraway parts to speed up the build of the aircraft. Wrong. Let's look at the aircraft structure.

Boomerang has a spinner, Wirraway doesn't.
Boomerang has a twin row 2 stage supercharged 14 cylinder 1200HP radial engine, the Wirraway has a single row single stage 7 cylinder 600HP radial engine.
Boomerang engine cowling is different to accommodate larger engine.
Boomerang propeller larger to accommodate bigger HP engine.
Boomerang engine mount larger and stronger to handle the bigger engine.
Boomerang has 2 oil coolers to Wirraway's one.
Boomerang has a 14 gal oil tank to the Wirraway's 7 gal tank.
Boomerang cockpit tubular frame different construction and much heavier tubes to Wirraway, and shorter by 14 inches to the Wirraway.
Boomerang windscreen of stainless steel construction to Wirraway's aluminium.
Boomerang canopy of stainless steel construction to Wirraway's aluminium.
Boomerang has a 70 gal fuel tank and radio shack in the position where the Wirraway had a second seat arrangement.
Boomerang has a stronger/thicker tubular rear frame than a Wirraway does.
Boomerang has a full wooden fuselage covering with cloth over, versus the Wirraway's aluminium framework with cloth covering.
Boomerang instrument panels are different to Wirraway.
Boomerang saddle fillet is larger than Wirraway's.
Boomerang fin built in same jig as Wirraway's but includes additional castings/ stiffener plates/ attachment lugs/ provision for a servo unit/ changed top cap and flush rivets.
Boomerang has a 3 start acme thread servo unit in fin driving a different shaped rudder trim tab, whilst the Wirraway has a trim drum in the rudder torque tube centre casting.
Boomerang rudder built in the same jigs as Wirraway, but has different top ribs and cap, and different centre casting/ lower rudder horn and trim tab, to Wirraway.
Boomerang stabilisers built in the same jigs as Wirraway but feature much strengthened spars/ additional stiffening doublers/ provision for a servo unit in starboard unit/ flush rivets.
Boomerang has a 2 start acme thread servo unit in starboard stabiliser driving the elevator trim tab, whilst the Wirraway has a trim drum in the elevator torque tube centre casting.
Boomerang elevators built in same jig as Wirraway with starboard elevator accommodating servo rod.
Boomerang tail wheel dog leg different to Wirraway.
Boomerang wing centre section built in same jig as Wirraway, but highly strengthened. Has thicker skins/ stronger corrugation stiffening/ larger fuel lines/ different fuel selector arrangement/ changed fuselage pickups at front/ modified leading edge to accommodate wheels retracting � inch higher into wheel bay.
Boomerang has different upper undercarriage door to Wirraway and has a lower door which the Wirraway doesn't.
Boomerang has larger wheel wells to accommodate the wheels retracting higher into the fuselage and for streamlining airflow.
Boomerang has same oleo as Wirraway, but a stronger lower dog leg assembly than Wirraway.
Boomerang carries 160 gals fuel internally to Wirraway's 90 gallons.
Boomerang outer wings are a complete new design, not cut down Wirraway wings.
Wings are much stronger and shorter than Wirraway.
Boomerang has 12 � Degree sweepback to Wirraway 12 � Degree.
Boomerang dihedral is 5 � degrees to Wirraway 5 degrees.
Boomerang incidence 2 degree at root twisting to 1 � degree at Sta 133 then to � degree at tip. Wirraway incidence is 2 degree at root twisting over length to zero degree at tip.
Boomerang flush rivets all over. Aerofoil changes shape as it progresses outboard, NACA 2215 at centre section root end, (to theoretical laminar flow at tip NACA 2206) while Wirraway NACA 2215 at root end progressing to NACA 2209 at tip.
Boomerang has 2 � 20 mm Hispano or CAC cannons and 4 � 0.303" Browning machine guns, whilst Wirraway has 2 � 0.303" Vickers Mk V machine guns synchronised to fire through the propeller arc and 1 � 0.303" Vickers GO gun on a revolving mount in the rear cockpit.
Boomerang has approximately 60,000 components of which less than 2% are Wirraway compatible parts.

Fred David was a German Jew that worked on the Mitsubishi Zero. Wrong, Mr. David was an Austrian Jew who had worked for Heinkel AG in Germany and when the Nazi's came to power, Ernst Heinkel obtained a position for him in Japan working for Aichi Tokei Denko KK on the D3A dive bomber. When Japan joined the Axis power, Mr Davis moved to Australia to take up the position of Chief Designer at CAC reporting to the local police station each week as an enemy alien.
Later ailerons were aluminium clad. Wrong, ailerons were always an aluminium frame with cloth over. From A46-106 (first CA-13) on, wooden wingtips were introduced with a more pronounced upsweep to the lower surface. A new aileron (but of standard construction mentioned above) was produced with a profile to match to the wooden wingtip (a matching set). Metal tips could still be used on the wing in place of the wooden tips, but had to have their matching aileron applied.
The Boomerang was going to be fitted with the Wright R2600hp engine. Wrong, a complete new design was worked on that created a new fuselage and wing centre section. There were plans under way to delete the centre section and have two laminar flow wings joined at the centre similar to P40/P51, but never proceeded. This may have led to the future design of the CA-15 wing. Tail and outer wings were to remain the same. CAC board papers show that the widened centre section was completed (11' 10" wide), but from there on it is no longer mentioned. Design drawings are held showing a deepened fuselage to accommodate the larger diameter R2600, and the introduction of a 4 blade wooden propeller, and the wider centre section. One of the reasons this project may have terminated was the inability to obtain supply of engines from the USA. What is known from CAC papers is that the Turbo CA-14 and the CA-15 were in mock up at the same time, (substantiated by factory photos) and it could be that the CA-15 became the greater prospect. As for the Boomerang, plans were underway for the CA-14 to have an R2000 engine (1,425HP) with cooling fan installed. CSIRO documents held show this engine and fan under test, but it was never installed due to problems with valves. The CA-14 always operated with the R1830-90B engine installed. What is known from CAC papers is that CAC had established that the standard R1830 engine Boomerang with Turbo Supercharger would perform better than the new Wright engine aircraft with 1700HP engine only.
The CA-14 had a 10 bladed cooling fan behind the propeller. True, but the design by CAC originally only had 5 blades. According to CAC papers, Defence personnel required the number of blades increased to 10 by installing an extra blade between the existing blades. Interestingly CSIRO reports held show from their testing that they believed that the 5 blade configuration proved to be the better application. Some publications have stated this fan was a copy of the FW190 cooling fan. Wrong, the FW190 fan is driven by a shaft protruding out of the front of the reduction case. The CA-14 fan is operated by epicyclical gearing, the propeller shaft being extended 3.5 inches to accommodate the fan assembly.
The prototype first flight was on the 29 May 1942. True, but it wasn't a prototype. The contract required the production of 105 aircraft with the first 5 aircraft to be completed as quickly as possible for evaluation and training, so the first aircraft was a production aircraft. A46-1 was actually delivered to the RAAF 4 times, each time being returned to CAC for some correction.
First issue 16/07/42
Second issue 24/12/42
Third issue 04/01/43
Fourth issue 02/02/43
Of the 105 CA-12 aircraft ordered, all of them had been delivered by 24/06/43. From a conceptual idea by Fred David and Alan Bolton on the morning of 8 December 1941 to 105 aircraft delivered was a remarkable achievement, just 314 days from No. 1 delivery to the 105th delivery.
The Boomerang was later fitted with a wooden pilot seat. Wrong, there is no evidence to date that this occurred. It could be confusion with the later fitting of the wooden wingtips.
The Boomerang jacking points were removed from the aircraft. Wrong, they are in fact able to be unscrewed and were secured into stowage clips inside the wing behind an inspection panel next to the jacking point mount.
Cannons were able to be cocked from a lever in the cockpit. True, early Boomerangs were fitted with a hydraulic cocking valve on the left side of the lower sub panel in the cockpit, however this was found to be troublesome, and the lever/valve was removed from aircraft and the cocking of cannons was done on the ground by armourers.
Each of the 4 machine guns was able to be cocked from a lever in the cockpit. True, early Boomerangs were fitted with mechanical cocking handles on the lower right hand side in the cockpit, but again, this was found to be troublesome, and the mechanisms were removed from aircraft and the cocking was done on the ground by armourers.
The engine cooling fan and square fin/rudder were only on the CA-14 derivatives. Basically correct, however they were trialled on other Boomerangs. The square fin/rudder was trialled on A46-47 and the cooling fan on A46-157. Sliding gills were also developed on A46-157 capable of controlling the cooling airflow. Operated hydraulically, as were the standard hinged gills, these slid backwards and forwards along a series of rails to alter the exit flow. These never eventuated in production.

LAST UPDATE: JUNE 2014

This will be updated from time to time.