The CA-31 – the best little jet trainer that never was.

A while ago now, the HushKit Blog posted a list about the Top Ten Best Looking Australian Aircraft to ever fly. After going through the list, I felt a little blighted by history – Australia has designed some amazing-looking aircraft.

The sad reality is we never built them.

The best example of this now lives in a shed in suburban Melbourne. In the Australian National Aviation Museum at Moorabbin Airport in Victoria, there lies the mock-up of the best-looking aircraft ever designed by an Australian.

It’s the CAC CA-31 jet trainer.

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You could probably build your own with a trip to Bunnings and a spare Saturday afternoon.

There’s not a whole lot you can tell from the above, so here’s an artist’s impression.

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Courtesy of Frank Munger, Flight Magazine, 1967

If you think the CA-31 owes a lot of its design to the Dassault Mirage III, you’d be right. Its origins go back to the early 1960s, when the RAAF hierarchy perceived a coming problem with its pilot training model. Ab initio pilots joining the RAAF would train on the CA-25 Winjeel before progressing to the DH115 Vampire, and for a lucky few, to either the CA-27 Sabre or Canberra B.2. In 1963, the RAAF ordered the F-111C strike bomber, and was already preparing itself to receive the Mirage III fighter. Both types possessed a blistering performance that would require a modern training pipeline to produce qualified pilots to fly them.

To meet its training needs, the RAAF ordered the Aermacchi MB326 to replace the Vampire and the Winjeel. The intent was for the Macchi to be an ‘all-through’ jet trainer. Ab initio candidates would conduct their training entirely on the the Macchi before converting to their operational type. That leap from the Macchi to fast jets led the RAAF to believe a Lead-In Fighter was needed – an aircraft that would take young pilots from the straight-wing subsonic Macchi towards a mach-two delta like the Mirage or F-111C.

The answer from the Commonwealth Aircraft Corporation in 1967 was the CA-31. It was optimised to be small, light and cheap – but at the same time, offer high performance that could prepare pilots for the world of fast jets.

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Here, the numbers get a little fuzzy:
It had an empty weight of 6080lbs (just shy of three tonnes), and gross weight of 8500lbs. The designers went for the Rolls-Royce Adour turbofan (at time, being built for the Sepecat Jaguar, and today, powering the BAe Hawk) which promised 4600lbs of dry thust and 6900lbs with reheat. Top speed for the CA-31 was intended to be Mach 1.5.

Now, bear those figures in mind when you consider how small the CA-31 was. Total length: 37ft, 8.5in. Height: 10ft, 9.5in. The span on the delta wing? 21ft, neat.

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I believe these plans come from the CAC CA-31 Manual – but if anyone can confirm this, please contact me.

Let’s compare – the A-4 Skyhawk had a 26ft wingspan and was 40ft long; had an empty weight of 10,000lbs and a 9300lb non-afterburning turbojet. For the Anglophiles, the Folland Gnat had a wingspan of 22ft; length of 28ft, and an empty weight of 4800lbs. The Gnat was powered by a Bristol Siddeley Orpheus producing 4700lbs of thrust. Both the Skyhawk and Gnat could get up to just below Mach 1.0, and both those jets carried an internal cannon (or two).

While the CA-31 was intended to be a Lead-In Fighter trainer, any guns would have had to have been carried externally. The designers proposed a number of wing/fuselage pylons, which also would have allowed it to carry an external bombload or fuel tanks. Online forums have waxed lyrical about Sidewinders or even Sparrows being under the wings to make a CA-31 air-defence variant – which assumes you could have built build the world’s smallest airborne intercept radar for 1967.

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Better get Q onto that.

On the plus side, the CA-31 would have been relatively inexpensive to maintain and operate. I can’t vouch for any of the CA-31’s aerodynamic qualities, but the chines on the nose (blending into the wing’s leading edge) may have offered some degree of maneuverability, and in air combat maneuvers, the CA-31’s small dimensions would make it extremely difficult to get a bead on it.

On the other hand – and again, I stress that I am not an aerodynamicist – something about the CA-31’s layout and size just screams out “issues”. I don’t know what the internal structure would have been like, but it would have needed to be strong if it was to sustain a high-G dogfight and mach-one flight. Spin recovery would have posed some ultimate tests for young pilots. If building a high-performance jet the size of a family sedan was such a good idea, someone probably would have done it already.

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Or lost face trying.

There’s not a whole lot else we know about the CA-31 (it was only a plywood mock-up, after all). Landing speed was intended to be 120kts and range up to a 1000nm. Take off distance was little over a thousand feet, and landing distance twice that number. The location of the engine intakes would have made FOD an issue at some airfields, and its location relative to the nose landing gear could have made operating from wet airstrips risky.

The CA-31 offered little forward visibility for an instructor in the backseat. Judging from the mockup, cockpit ergonomics would have left a lot to be desired – there wasn’t a terrible lot of space on the dash for controls and instruments, much less elbow room in the rest of the cockpit for the pilots. Poking my head into the mockup, tall fellas like myself would have hard a hard time easing themselves into the front seat of this.

Had the little jet come to life (and assuming it was not a complete aerodynamic dog), it could have carved quite a niche for itself – and not just on its looks alone. Based on the assumption of the RAAF operating a conversion unit and a fighter training squadron (like it does today), Australia would conceivably have had a requirement for at least 24 CA-31s, and perhaps more if it was a worthwhile performer.

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The resin kit of the CA-31 in 1/72nd scale, from the Uncle Les kit, built by Peter Hobbins.

Noting Australia’s subsequent export history with second-hand CA-27 Sabres along with the GAF Nomad, it wouldn’t be hard to imagine a few CA-31s finding service with Indonesia, Malaysia, Thailand, and maybe even Singapore. The CA-31 was intended to be a cheap and inexpensive means of training pilots for advanced aircraft types, which could have made it an attractive option for Air Forces seeking a jet trainer/strike aircraft. That being said, there’s few existing contemporaries for the CA-31 to suggest a dedicated supersonic Lead-In Fighter trainer was a good idea – the jet trainer/strike jet market has been largely dominated by more traditional designs like the Hawk, Alpha Jet, and numerous generations of Macchis.

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The idea of an Australian warbird community with a handful of ex-RAAF CA-31s is enough to make you salivate.

The closest contemporary is perhaps the supersonic Northrop T-38, which remained largely wedded to the F-5 fighter in its design and performance. Likewise today, the KAI T-50 owes no small part of its design to the F-16. By comparison, the CA-31 held little commonality to the Mirage III aside from its planform. There are numerous examples of Air Forces operating different types of jet trainer/strike aircraft alongside one another. Provided the CA-31 could have been built, owned and operated cheaply, price might have been its greatest attribute on the foreign market.

But alas, the CA-31 was not to be. The all-through jet training model was abandoned after two courses, and the CA-25 Winjeel was reinstated as the ab initio trainer. The Macchi remained as an advanced trainer, and also found service with fighter training units in the RAAF and Royal Australian Navy. In 1975, the Winjeel was replaced by the CT-4A Airtrainer (affectionately known as the ‘Parrot’ in Australian service), a New Zealand-built aircraft based on the Australian Victa Airtourer – effectively marking the last ‘Australian’ type that RAAF pilots would train on.

At the ‘sharp end’ of the spear, the introduction of the F-111C to Australian service was significantly delayed until 1973 (although the F-4E served as an interim from 1971). Perhaps the biggest stake in the CA-31’s heard was the introduction of the Mirage IIID, a two-seat conversion trainer variant of the single seat Mirage IIIO. The Macchi, it was deemed, was a suitable Lead-In Fighter trainer for the F-111C and Mirage (and later F/A-18) until 2000 when it was replaced by the Hawk Mk.127.

There were a couple of attempts by Australia to build an ‘advanced’ trainer for the RAAF, but even in the late 1960s, Australia’s military aircraft manufacturing industry was becoming more deeply rooted in licence production. In 1969, CAC was in collusion with the British Aircraft Corporation for the AA-107, a variable-geometry trainer which appeared like a Alpha Jet mated with a Tornado. In the 1980s, what was left of Australia’s military aircraft manufacturing industry teamed up to create the A20 Wamira, a two-seat turboprop trainer, which reached the unflown prototype stage before being cancelled in 1986.

Special thanks to the Secret Projects UK Forum; What-If Modelers; and the Australian National Aviation Museum at Moorabbin Airport, Victoria. If there’s anything you wish to add/correct, contact me on Twitter.

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About eamonh

Air Mobility enthusiast and Star Wars fancier. All writings my own opinions and not those of my employers or associates.
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2 Responses to The CA-31 – the best little jet trainer that never was.

  1. Pingback: 1/72 CA31 – CAC’s little advanced trainer proposal of the ’60s | Uncle Les

    • eamonh says:

      Thanks for this post, and building the kit in the first place! Let me know if/when I can ever get a hold of an unbuilt one.

      Would love to post about the CAC CA-23 if I ever had more information on it.

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