RAAF A94 Commonwealth Aircraft Corporation CA-26/CA-27 Sabre Mk.30/31/32
Rod Farquhar beside the open Gun Bay of A94-974
A BRIEF HISTORY OF THE CAC AVON
FIGHTER AND GUN DESIGN
Towards the end of the Second World War Germany had a significant lead on the Allies with regard to weapons and aircraft design.
Two of these the Messerschmitt Me-262 and its primary armament the Mauser MG 213C 30mm cannon would go on to have a far reaching effect on the Sabre for RAAF service.
German engineers had a good understanding of the benefits of swept wings for high speed aircraft, they also knew of the low speed stability problems that it created, by wars end they were working on a swept wing for the Me-262 with drop out leading edge slats to combat the stability problem.
After the war teams of specialists scoured Germany for anything that might be of use, the swept wing design was taken up by the Americans and the Russians.
The Americans refined the slats concept and went on to produce the F-86A, using an almost identical wing to that designed by the Germans.
The Russians came up with the MiG 15, both these aircraft were to become mortal enemies in the skies over Korea.
The Mauser MG 213C was redeveloped by the British as the ADEN 30mm cannon, this gun was to become the armament for most British fighters for many years.
France produced the DEFA 552A, of similar design but less costly to manufacture. Used in the Mirage family of aircraft it was the main armament of Australia’s Mirage IIIO/IIID.
Towards the end of 1949 the RAAF recognized that it’s first jet aircraft, the Vampire, would need to be replaced by a more modern design. The American F-86 Sabre was an obvious choice but events in Korea meant that no Sabres could be spared for Australia. As a result Meteors were purchased from the UK and almost immediately went into service with 77Sqn in Korea.
The Government of the day had very strong leanings towards the UK, and wanted an aircraft design from there to be license built by CAC in Australia, many proposals were put forward including the Hunter but development and lead times were far too long for the RAAF.
Fortunately a visionary in CAC Lawrence Wackett could see great promise in marrying the F-86 airframe to the more powerful Rolls Royce Avon axial flow turbojet.
Finally in 1951 the Government relented and design and development got underway, the design was to be based on the F-86F with a slatted wing. The use of the shorter but larger diameter Avon meant that the fuselage needed deepening at the front to increase the intake airflow, and moving the engine mounting further aft to maintain center of gravity. The final design had only a superficial resemblance to the original.
The first prototype, designated CA-26, was delivered in
August of 1953
Fitted with early type Aden gun port, compare with later type pictured below
Deliveries of production aircraft, designated CA-27 Mk-30, commenced one year later. In all 22 Mk-30s were built.
The next version, the Mk-31, started deliveries in July 1955 with 20 being delivered by September 1956. A significant change in this model was the replacement of the original wing with a new design. Called the 6/3 wing it deleted the drop out slats which had shown a tendency to asymmetrically deploy whilst rolling at high altitude and increased the wing cord by 6 inches at the root and 3 inches at the tip, it also incorporated wing fences. Again this was as a result of experience in Korea, the new wing giving better performance at high altitude/high mach numbers. Later versions also having increased fuel capacity in the leading edge itself. The remaining Mk-30s were upgraded to Mk-31 as they became due for major servicing.
The last and definitive version was the Mk-32, with
first deliveries in September 1956, they were
produced in three separate batches totaling 69 aircraft, the final
delivery by the end of 1961. These aircraft
had an updated version of the 6/3 wing, having two hard points under
each wing for stores carriage (the original had only one). This
meant it could now carry a bomb load and long
range tanks .
During test firing of early aircraft an inherent weakness of the Avon RA7 came to light, the muzzle blast of the guns interfered with engine airflow causing severe surging. An extensive test programme was undertaken both by CAC in Australia and Rolls Royce in UK. This testing resulted in a change to the design of the blast panels to incorporate baffles, redesign of the engine with better internal flow and, the fitting of a fuel dipper to reduce fuel supply to the engine during firing .
ARMAMENT AND STORES
Experience gained in Korea proved that the six .50
machine guns in the F-86 were inadequate
(the MiG 15 had one 37mm and two 23mm
cannons) The high closing rate of modern
fighters meant that firing windows were very brief,
one or two hits
would have to be sufficient to knock out the
opponent. The initial choice was four 20mm Hispano cannon (as
per the Meteor) but two of the new 30mm
ADENs with a rate of fire
of 1200/1400 rounds per minute was the
eventual choice. For the ground attack role the aircraft could carry two
drop tanks either
100 gallon or
167 gallon and two bombs of up to
1,000lb each, there was also a provision for the carriage of either
twenty four High Velocity Aerial Rockets depending on the
warhead size. For training purposes practice bombs or rockets with inert
warheads could be used, later Sidewinders with inert motors and
heads would become available.
photo of 79 Squadron RAAF at Royal Thai Air Force Base Ubon, August 1968
Although installation and flight tests had been
performed in 1958/59 with the British designed
Firestreak ( Blue Jay ) missile further development was not carried out.
The installation required significant changes
to the airframe and wiring and could not be justified. The
AIM 9B Sidewinder on the other hand was practically a
bolt on installation, ARDU’s A94-946 being
the first Sabre to be fitted with this missile
Note later design gun muzzle housing.
The twin store wing of the Mk 32s meant that for ferry
purposes two drop tanks could be fitted to
each wing, 100 gallon inboard and 167 gallon outboard.
A recent email from Gp Capt K N Pyke (ret) an ex Sabre
pilot has informed me that the extra drag of the four tanks would negate
any increase in range that the extra fuel might provide.
This aircraft has undoubtedly become the most widely recognized Sabre in Australia.
As well as serving at various bases in Australia the Avon Sabre saw active service at Butterworth Malaya during the “Emergency”, “Confrontation” and at Ubon Thailand during the Vietnam War.
the two Sabre squadrons at Butterworth flew with their distinctive
colour schemes, 3 Squadron making a change in 1962
Between 1969 and 1972 a total of 18 ex RAAF Sabres were donated to the Royal Malaysian Air Force operating as No.11 Sqn TUDM.Butterworth 1974. Photo Kurt Finger
From 1973 to 1975 a further 23
Sabres were donated to the
Air Force, five of these being ex Malaysian
aircraft, they comprised No 14 Sqn TNI-AU.
Information sources are.
My own records
Meteor, Sabre and Mirage in RAAF service
Pictorial History of the RAAF
Military Aircraft of Australia
Updated 16th November 2014
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