Boomerang or Super Wirraway

Does anyone know why, in 1942, Lawrence Wackett / CAC did not just upgrade the Wirraway airframe to a single seater with P&W R-1830 engine rather than going through the substantial redesign and new jigs/parts required to produce the CAC Boomerang? I know the Boomerang used a lot of Wirraway parts, but would it not have been far quicker just to upengine the Wirraway with the P&W Twin Wasp (+445lbs weight), delete the second seat (-100lbs?), reprofile the canopy/rear fusalage, and add more armament. The result would probably have been lighter than the Boomerang ((5375lbs empty vs the Wirraway's 3992 lbs) and would have looked a lot like the FW190 (on which data was available at the time from UK sources).

I dont know why, but i do know there was about 80% commonality between the Ca-12 and the Wirway. moreover, despite the delays, the production of this new type was processed in a very short space of time. it could have been produced even quicker, except that by the time the prototype flew, the RAFF was beginning to receive equpment from the US and Britain.

I dont thnk there is a lot of difference between what you are describing, and what was actually built.

It might be interesting to compare the Boomerang to the NA P-64 a NA-16 (about the same as a Wirraway) re-engined with a Wright Cyclone and converted to a single seat fighter. \

There are a few problems with re-engining a plane quite like you propose. The main one is center of gravity, sticking an extra 445lbs of engine in the nose and taking out 100lbs of rear seat behind the center of gravity is going to make for a rather unflyable airplane. The Wirraway's 2 bladed propeller is not going to able to transmit the power of an engine twice as powerful so you need a larger, 3 bladed propeller that is much heavier stuck on the nose. Then there is the gross weight and G limit problem. A plane is only rated at a given G rating at a certain weight. As in 6 "G"s at 6000lbs with a 50% safety margin for a 9 "G" ultimate load or what ever the buying government requires for a warplane. that gives you a 36,000lb factor. Increase the plane weight to 7,000lbs (new engine, prop, guns, ammo, fuel) and our hypothetical plane now has a 36,000/7000= 5.14 "G" limit. Assuming that all the weight is uniformly distributed throughout the airframe. Obviously some structural reinforcement is going to needed. A fighter that can't pull "G"s isn't much good. I doubt the Wirraway had either self sealing tanks or armor for the pilot.
Trying to get the P&W R-1830 into quite as tight a cowl as the FW 190 had might have been a problem too. The Twin Wasp didn't have a cooling fan and while adding one might not have been impossible it might have been more trouble and work than the Australians were willing to do.

I wonder, what other aircraft could they have chosen instead of the NA-33 (NA-16). And when in 1936 did they visit which countries?

A little off centre, but just to keep things in perspective. in 1939, Australia was not even producing its own motor vehicles. There was not even one Wiiraway operatinal. Wackett had moved heaven and earth to get his wackett trainer....a sort of monoplane tiger moth really, off the production lines.

In the lead up to war, my reading of the officieal history suggest the Australians were casting about for foreign manufacturers to set up facories in Australia. They preferred British companies to US at that time. they were not all that successful, though they did succeed in getting De Havilland to set up in Sydney. this was not enough. The governement had wanted to set up a shadow factory to produce Hurricane fighters, but had not succeeded. meanwhile the government proceeded to set up the Commonwealth aircraft corporation. my understanding is that wackett, was instrumental in getting this done, and since he had greater ties to the US aircraft industry, and the US was more accommodating in providing assistance to the fledgling Australian aero industry, we secured agreements to manufacter certain US engines in Australia (the twin wasp???) and to assemble certain aircraft from prefabricated parts (hudsons and PBYs from memory. We also secured a licence to build US trainer aircraft, modified to the Wirraway from scratch, in Australia. at the time this represented amassive jump in Australian Industria capability. In less than two years we had basically grown from nothing (or almost nothing), to building advanced trainers. Has to be an amazing engineering feat in anybodies book.

In the panic that followed the Japanese attack, Australians showed just how capable they could be when pushed. to take what was a trainer aircraft, and turn it into a viable fighter, that could have been ready for service within 3 months from its inception (in the finish it took more than 6 months) from such an embryonic industrial base has to be given due credit.

Its a great pity we have let that innovation and great start just slip away from us since the end of the war.

Hi Glenn


Thanks for the reply, which i think is better than the explanation that I gave. It prompted me to do some checking of some material when i got home, to see why we didnt produce the Taurus and adopted the P&W double wasp instead.

Australia produced in quantities three types of aero-engine - the Pratt and Whitney single and twin row Wasp radial engines and the De Havilland Gipsy Major in‑line engine - and in the latter part of the war the Rolls-Royce Merlin engines were planned for production.

The single wasp was produced from pre-war (something I did not know). they were among the first aero-engines made in Australia. they were rated at 650 h.p. were 9-cylinder single row Wasps, manufactured by the Commonwealth Aircraft Corporation under licence from the Pratt and Whitney Corporation in USA and installed in Wirraway aircraft. In all, the Company made 680 of these engines.

When the Beaufort project was launched, if was decided that facilities should be established for the production in Australia of suitable engines. It was not at that stage a question of reliability (though i concede the taurus was problematic). Rather the australian venture was held up by the british pre-war embargo on the export of aero equipment and material. It may be as you say that the airlines favoured the P&W engine, but in the end, it was the British govts embargo that decided the issue for us.

When the supply of Taurus engines (or jigs for that matter) from England became impossible because of war conditions, the aircraft was redesigned to take the more powerful twin row Wasp, and the Australian engine factory was consequently planned to produce that type. This redesign process as you know, took considerable time and effort, but as you are probably also aware, the Australian product was much superior as a result of that new engine fit

As the Commonwealth Aircraft Corporation was the only Australian organisation experienced in the manufacture of high-powered aero engines, that Company was invited by the Commonwealth Government to design, build and equip a suitable factory at Lidcombe, near Sydney, and, later, to conduct the factory as a Government annexe for the production of 14-cylinder 1,200 h.p. twin row radial air-cooled Wasp engines. The Manager of the factory was JN Kirby.

By July 1945, the programme of 870 engines had been completed, together with large quantities of spare parts both for the R.A.A.F. and the U.S. Army Air Forces. Because the capacity for the production of airframes outstripped the engine production, it was necessary to supplement Australian manufacture by the importation of more than 1,000 engines during 1942 and 1943 to enable the production schedules for Beaufort and Boomerang aircraft to be met. Like many countries, the production of engines was the major bottleneck in our aero production programme

Production of Gipsy Major engines for installation in Tiger Moth and De Havilland Dragon aircraft manufactured by De Havilland Aircraft Pty. Ltd was undertaken by General Motors-Holden's Ltd and 1,300 of these 130 h.p. four-cylinder invented in-line air-cooled engines were delivered between September 1940, and March 1944.

As Wasp engines were not required for the types of aircraft authorised for production in Australia from 1943 on - the Beaufighter with Hercules engines and the Lancaster, Mustang and Mosquito with Merlin engines it was decided that the Lidcombe engine factory would be converted from Wasp engine production to the manufacture of Rolls-Royce Merlin engines.

It was planned that the first Merlin engines would be delivered from the Lidcombe factory before the end of 1946. I am unsure if that ever did occur, or if Australia simply relied on imported engines after the end of hostilities. Still it is an ample illustraion of the growing skill and expertise that existed in the Australian aircraft industry at that time. An impressive progression, from nothing, to resdying to produce one of the most advanced engines in the world in just 6 years

Interesting info - thanks.

So, it would seem that a different airframe is possible, but still with a US engine. The 'twin-wasp' grew in power over time - it was for example I believe used to power the P-35. Hence, in a less powerful form could have been utilized earlier.
As a comparison in engine diameter sizes - Mercury 51.5in., Taurus 46in., Hercules 55in., and R-1830 48in.

I dont think the the version of the twin wasp produced in australia ever really changed. It remained at about 1200hp throughout. The single wasp was rated at about 650hp and was used to power the wirraway.

Judging by the entry of service of the Australian Beaforts (circa october 1941), australia may have been able to begin development of a fighter version of wirraway (either a super wirra or a boomerang) from about that time. If the development had been completed in say 4 months, we could have begun receiving the type in small numbers from about february 1942.

i personally think the fitting of 20mm cannon to the boomerang was a bit of a waste. I think if 4 x browning 0.303 had been accepted, the speed of the type may have risen to around 315 mph or so. That may have been a better traddeoff, given the speed and agility of the A6Ms and Ki-43s they would have been flying against

parsifal said:

I dont think the the version of the twin wasp produced in australia ever really changed. It remained at about 1200hp throughout. The single wasp was rated at about 650hp and was used to power the wirraway.

Click to expand...

Yes, but if they had chosen a different aircraft, and wished to put an earlier 'twin-wasp' in it; I would've thought P W would agree. Or are you implying that their search was restricted by wanting something that they could put the single Wasp engine in!?

Hi merlin

Not exactly certain what you are getting at there, but i will try anyway. I dont think the restriction with the most impact was so much to do with what the Australians were allowed to build, as what they could build, from a technical stanpoint I mean.

Remember, the wirraway was the first modern type with any combat capability before that there was nothing. There were only three engines produced in Australia during the war, with a fourth, and possibly a fifth (the merlin and the griffon respectively) at least considered. Moreover the overwhelming constraint affecting Australian aircraft production was the shortages of engines....there simply were not enough engines to match airframe production, any messing about with engine supplies would have had catastrophic impacts on aircraft production, and the provision of spares.

Moreover, as a general rule, the more complex the engine, the less there were of them. On the assumption that the Single Wasp was easier to build than the Double Wasp, it made sense to marry the wirraway airframe to the simplest engine possible. If the wirraway was in some way upgraded to taking the double wasp, that needed to be done on the understanding that every wirraway airframe completed to that standard was at least one less aircraft of another type like the Boomerang and the Beafort that could not be built. Was it worth i to utilise these scarce engines building what may be an infereior type, when for no great loss of time or output, the RAFF could have Boomerangs and/or Beauforts instead. My opinion is that a superwirra might not be worth that sort of cost.

Apologies to Glenn, but Parsifal my 'posts' were not aimed at a post Wirraway position, but pre-Wirraway ----

That is (as I wrote earlier) when the fact finding mission went to Europe the US searching for a Hawker Demon replacement - they might have chosen a different aircraft, with either a British or US engine!?
Curiously, around that time, the Fokker D.XXI (although with only the 645 hp Mercury) had already flown, and could have been a candidate. Then there's the Gloster F.5/34 - with the impetus of Australian interest could've flown earlier - with the latter, I can't see the Boomerang being needed.
There's also the bizarre thought that the 'mission' may have watched a demo of the Stuka!
But with an earlier need (i.e. before the decision on the Beaufort) for a bigger engine than the 'Wasp' mean the Mercury, Taurus, or earlier lower powered Twin-Wasp is produced in Australia??

Glenn,
in essence, from the design point of view the Boomerang is exactly as you have described, it's a Wirraway airframe with a more powerful engine, no rear seat, modified rear canopy / rear fuselage and increased armament. In addition to this it has shorter wings (faster roll rate) and a shorter tail moment (faster pitch rate) for fighter manouverability, armour protection for the pilot and an oxygen system to operate at higher altitude.

But as soon as you make these modifications, many design complications creep in:

• the more powerful engine is heavier and has a different carburettor intake location... so you need a new (shorter) engine mount and different cowling;

• the more powerful engine needs more fuel and oil capacity (or you would lose range)... so you need an extra fuel tank (a good location would be where the 2nd seat used to be);

• the heavier engine and higher g-forces from fighter operations need a stronger airframe... so you have to modify some of the fuselage framework and the wing centre-section;

• and the shorter outer wings have to be designed from scratch, with the right aerodynamic sections and strong enough to carry the extra armament.

This is what was proposed by CAC to the RAAF in Fred David's proposal on December 30, 1941 (titled "Interceptor Project - Wirraway Conversion"). His proposal showed an empty weight of 4,920lb. Then the proposal went through many reviews by the RAAF (amongst others) and was finally translated into an official specification against which CAC could build and supply aircraft.

One of the key steps in the process was a meeting at CAC on February 11th 1942 to review the RAAF requirements before the first aircraft was completed. Click here to see the minutes from this meeting. These requirements eventually became written up as "Developmental Specification 1/42 for Wackett Interceptor", according to which the first CA.12 was finally developed.