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GOT: The CAC CA-4/CA-11 Woomera


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#1 Romantic Technofreak

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Posted 21 November 2004 - 01:29 AM

Oh Greg, what have you done! You make me get such bad ideas! Of course, your list is full of many of the most interesting obscure WWII types, and, of course, I have the ambition to work it down, no matter what time it takes.
I didn't find much about the CAC Woomera, especially not more than I expect you to have already, but there is the wonderful site

www.samoloty.ow.pl (sorrily disappeared already)

It's wonderful, but it is - in Polish! No English version. Then I got the worst idea and tried to find a free Polish-English translation program, and I got


Maybe you know about these automatic translators. They translate, but, at least, produce an impossible sentence construction, and they keep on ignoring the most difficult words. This one is no exception. So, translating sentence by sentence, I had to look how to get out a reasonably sounding result. Sorry - this was so difficult, that I cannot exclude omssions happened and some of Romantic Technofreak's fairy tales having crept in, I just try to claim that the point is not completely perverted. And this work really takes time, at least several hours. But, on the other hand, it's the most interesting thing I ever did for tgplanes.com!
More is to follow. But I surely cannot deliver more than one article a week - if ever so.

Now, here we go with the

Commonwealth Aircraft Corporation (CAC) CA-4/CA-11 Woomera

Beginning in the mid-30s, the Australian government took respect on its weak military strength, especially concerning aviation. With few exceptions, the Royal Australian Airforce (RAAF) was furnished with obsolete equipment of British production. A big amount of strain was needed to create an aircraft industry of her own, thus making Australia independent from supplies of foreign equipment. The most significant foundation arising from the governmental iniative was in June 1936 the establishing of the big aviational factory Commonwealth Aircraft Corporation in the suburb of Fishermen's Bend of Melbourne, over the river Yarra, gathering the fairest Australian aircraft project engineers and technicians there. The expenses amounted about 1 million Australian pounds and were raised by the Australian government as well as by private investors.

Near the end of the 30s, Wing Commander Lawrence J. Wackett, at that time both manager and project engineer of CAC , proposed to elaborate a modern two engined aircraft, able to perform bombing, torpedoing and special missions. The tactical specification was accepted on April 15th, 1940, giving it the technical Air Board no. 241.

After receiving a governmental subvention of 50.000 Australian pounds, project engineers T. W. Air (chief of the group), F. W. David, D. G. Humphries, E. F. Faggeter and I. B. Fleming started intensive work on the new aircraft. The project received the factory designation CA-4 and was informally called "Wackett bomber". The official name "Woomera" was derived from the aborigines spear thrower and appeared considerably later, together with a new version and plans for to start up production. As there was no local motor available for the all-metal cantilever construction, the aircraft had to be driven by two American license-built Pratt & Whitney Twin Wasp R-1830-S3C3-G, delivering 1.100 hp at 1.115 rpm. Wing and tailplane were adopted from the other CAC construction "Wirraway". Its proper to write down on margin, that the driving capability of three engines for the CAC was also considered! While the firm Pratt & Whitney delayed the supply of the type 1830 for Australia, the weakest by reason possible engine was considered, the Pratt & Whitney Wasp R-1340-S1H1, delivering 600 hp at 608 rpm. They were produced in Australia already, but the production capacity was much to small to deliver enough samples to equip two-engined CA-4s.

The offensive arming of the aircraft consisted of four machine guns in the aircraft's bow, initially Vickers K, then Browning Mk, as well as of special bomb rooms within the motor gondolas and bombs or torpedoes hanging on special clinches under the fuselage's center plate (the aircraft had no classical bomb bay within the hull). The bombs could be thrown also in diving, so aerodynamic speed brakes were installed over the center fuselage (??, RT) as well as in the external wing section. Most remarkable, two remote-controlled defensive turrets were installed over each wing in the extention of the motor gondolas. In the long cabin on back of the hull there was the station of the gunner/radio operator, who could also fulfill the role of a second pilot by installed remote controls. The third member of the crew was the bomb aimer and navigator in one person. He had his position in the middle fuselage behind the wings, from there also operating the motor gondola guns turrets. The machine was built with a three-point undercarriage, where two wheels sheltered retractably in the motor gondolas and one fixed in the rear part of the fuselage. For the boost of range for distinctive missions also two additional external fuel tanks could be employed, having a capacity of 1.333 litres each.

The first protototype of the CA-4, given the military designation number A23-1001, was ready in summer 1941, 17 months after the construction had started. It performed its first flight on Sept. 19th, 1941, with factory test pilot Flt. Lt. H. F. Boss-Walker on the controls. After the factory tests, on April 20th, 1942, the aircraft was transferred to the RAAF aircraft depot at Laverton for military evaluations. Lots of experimental flights, performed by several different pilots of the SDPF (Special Duties and Performance Flight) also on the remote controls, showed an exerted range of constructional defects, caused by the hastily conducted an unexperienced design team. The first problem of all was the hydraulic steering of the motor gondola gun turrets, the power to drive them was insufficient, the wheel brakes were far too week, the construction suffered by oscillation, inefficacy of helm of height and, under some conditions, flight stability problems. In the meantime on a similar destination, since May 1941 under British license the torpedo-bomber Bristol Beaufort was already produced in Australia, which completely met the requests of RAAF in that category. The computational performance of the Woomera was better than the one of the Beafort, but reality turned out the completely other.

During the probations, some slight modifications were made on the prototype, e.g. change of the hull-wing passage. Bigger changes were also considered during the tests. E.g. a change of the wing profile and outline, also about slots on the forward edge. Ultimately, after wind tunnel research, Handley-Page type slots were installed, but this immediate solution was a small improvement. The tunnel research also exerted, that the scratchy aerodynamical properties were strongly influenced by the poor form of the motor gondolas. Besides this, range tests showed the necessity of changing the station of the second pilot/gunner. By reason of the above mentioned, the project engineers came to opinion that the farthest possible development of the aircraft needed the thorough change of almost every sub-assembly.

The CA-4 prototype returned to factory in December 1942, were several internal modifications on it were intended. On 15th or 16th January 1943, a tragical case happened. Flying at a height of 300 m, the aircraft suddenly exploded, and two of three crew members perished, pilot Jim Harper and second pilot/gunner Jim Carter. The third member of crew, navigator Lionel Dudgeon managed to bail out on parachute.

During a certain time, the plant had already worked on the successor of the CA-4, which had to be stripped of the majority of defects of its precursor. The new aircraft was named CA-11, but works on it had no high priority. The RAAF already had bombers available, the British Bristol Beaufort as well as the American Douglas A-20 Havoc and North American B-25 Mitchell. The new model matched identically the aerodynamical design of the CA-4. However, it employed the soundest engines for drive, the R-1830-S3C4-G, delivering 1.200 hp start force at 1.217 rpm. The shooting armament was intensified both in the forward hull and in the remote-controlled gun turrets, which were also modified. The lifted bomb load was increased too. Besides that, modifications for vertical stability were still needed, while distinct horizontal stability was received. The wing geometry was also changed and powerful wheel brakes were employed. The extent of the hull also matched an improvementof the crew cockpit, a major postulate resulting from the probations of the CA-4. The first prototype of the CA-11, given the military identification number A23-1, was not ready before July 7th, 1944. CAC factory test pilot G. R. Board sat behind the helms. Anyway, it did not proceed without certain inconvenience in flight, forcing the auxiliary pilot on the remote controls to a luckily managed emergency landing.

The prototype tests of the Woomera remained troublesome, although the layout already was on the farthest query of development. Mentioned was e.g. oil overheating and small speed performance. Thus, the oil cooler was rebuilded. The motor gondolas were extended to the farthest, and the gun turrets received a new protection. Flaps and elevator rudders were also modified. After 19 flights, on November 21st or 22nd the aircraft was transferred for conducting military tests to the Air Performance Unit at Laverton.

In this time, the second prototype was placed, given the military identification number A23-2, employing completely new 14-cylinder radials Pratt & Whitney Twin Wasp R-2000, delivering 1.330 hp at 1.350 rpm. The same engines were provided for the coming serial version CA-11A, which were ordered in 105 copies by the optimistically RAAF on March 8th, 1942, due to the specification number 242. After the problems with the CA-4, then also with the CA-11, RAAF limited the order to 20 serial machines, but they canceled the contract officially in September 1944.
A limited number of flight tests were still undertaken with the CA-11, but already in 1945 it was transferred to the 1st Central Recovery Depot in Werribee.
According to the source you read, either on January 16th or on April 11th, 1946, after dismantling of engines and other endowment, the aircraft was scrapped. The second protototype was not finished.

The CA-4 Woomera was the first warplane independently constructed in Australia. Perhaps, if its young design group had greater experience at its disposal and the aircraft industry a better technological background, the aircraft would have turned out progressively and would manage operational readiness and accustom for serial production within reasonable time. The corrected version CA-4 appeared much too late - and even omitting the still appearing engineering problems, it did not answer contemporary demands of military aviation at that time.

Souces mentioned:

1. Letectvi + Kosmonautika nr 2/91

2. Jane's All The Worlds Aircraft, rocznik 1947

3. AirWar - letecké muzeum 2. svìtové války

End of the article. As the old hotlinked picture could not be reconstructed, I give you what pays from the very favourable Nhungdoicanh blog:










Regards, RT

#2 GregP


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Posted 21 November 2004 - 10:43 AM

Nice post RT, and thanks! I like the Australian planes, especially the CAC-15 ... but it is not a WWII craft, being completed after the cessation of hostilities. Still, it was probably among the best piston fighters ever.

The Woomera was also very interesting, and I have not seen the photo with the nacelle turret before.

Again, thanks!

#3 Corsarius


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Posted 21 November 2004 - 02:08 PM

Great post, RT.

I always loved the CA-4. I think it is very attractive, innovative, and useful for it's time. I just wish we had gone ahead and built it in quantity. *sigh*.

#4 Romantic Technofreak

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Posted 08 August 2013 - 08:29 AM

New pictures inserted in the original posting. Scroll up please!


Regards, RT

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