Aviation Historical Society of Australia
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Aviation Historical Society OF Australia Registered in Australia for transmission by post as a periodical Moy - June 1968. ' A H,S * A,. Journal May-June 1968 The Conmonw'ealth Aircraft Corporation CA-15« By David Eyre The CA-15 vms the second single seat fighter designed and built in Australia for service in the Pacific Theatre of Operations^ the Boomerang being the firsto During the war^ a liAAF specification was in existence for a long-range^ medium altitude^ high performance fighter^ and the original intention was to develop the Boomerang by fitting a higher powered engine than the 1,200 hp Pratt and Whitney. However it was found that the basic. Boomerang fuselage would not take the extra weight of the larger engine without a considerable amount of redesign, and so this idea was discarded. A number of conferences were held between officials of the R/\iiF and CAC daring 1943 and 1944, and in 1945 the design of the CA=-15 was accepted to fill the above mentioned specificatioiio Work on the prototype coiumenced that year and the aircraft was rolled out earl57' in 1946, taxying tests commencing on February 12tho When seen at a distance, the average spotter might have confused the GA-^15 with the North American Mustang, wiiich was being built under licence by CAC as the CA-17. Compared with the Mustang, the GA-15 had a smaller wing span and increased lengtho One of the most obvious differences was the nine degree dihedral setting of the tailplane, and another being the airscoop for the chest position radiator. The installation of a Rolls Royce Griffon engine in place of the Packard built Merlin of the Mustang involved a coraplete redesign of the cowling. This gave improved vision over the nose and employed a deeper radiator beneath the fuselage. The Pratt and Whitney Ro2800 Double Wasp eighteen cylinder air cooled radial engine rated at 2,300 hp was originally specified for the CA-15o This was to follow the pattern of CAC in using Pratt and Whitney engines. However a change of policy - occurred when this engine became unavailable late in 1945, and as an interim measure pending the availability of the Griffon with a three speed supercharger, it was decided to fit a Griffon Mark 61, with a two-stage two-speed blower. The instal lation of the Griffon enabled a much better performance to be obtained than had been originally estimated. A feature of the original layout with the Pratt and Whitney engine was the gain in thrust from the cooling fan and exhaust gasses, which ?/ere to be ejected from a nozzle below the fuselage. There were several innovations amongst the engine accessories of the Griffon. One was the then new liquid cooled "heat exchanger" system for the oil supply, fitted instead of the normal air coolingo The cooling system located below the fuselage comprised one Morris type single row main intercooler followed by a Morris type three-row radiator with a matrix area of 5.8 sq. ft. The ex;it duct was varied by a hinged door thermostatically controlled by the temperature of the engine coolant. A cartridge starter system was fitted in place of the convential electric motoro The latter was decided upon because a battery with sufficient capacity for reliable and repeated use of an electric starter for a large engine, could not be obtained without the penalty of undue battery weight. The cartridge system was simple, light and efficient and its use did av\ray with the dependance on a small battery that was fitted to so.me fighters, or battery carts out in the field. The accessories such as the Generator, hydraulic pumps and air compressor were grouped around a shaft driven auxiliary gear box instead of being fitted on the rear of the engine. One problem, encountered was the installation of the armament. Various combin ations of 20 mm cannons and 0.50 in. machine guns were considered before it was finally decided to install six 0.50 in. raachine guns with 280 rounds per gurio Provision was also made for ten rocket projectiles under the wings. Fuel capacity of the aircraft was two 110 gallon tanlcs in the wings and one 40 gallon tank in the fuselage. Two 200 gallon drop tanks could be fitted beneath ' the wings, thus making a total of 660 gallonso This was considered to be e.xception- ally high for a single seat fighter at the time as this gave the aircraft a range of A.H.S.A. Journal -52- May-June 1968 2540 miles at 5,000 feet at 1,600 rpm. Designed specifically for long range operations in the Pacific theatre, the CA~15 was too late to see operational service inWorld War Two, The first flight of the prototype took place on March 4th 1946, and the pilot was Jim Schofield* Tests were continued by GAG until the latter part of JunCo On June 2nd, the aircraft was allocated to the PvAAF with the serial number A62»«1001, and was delivered to lOo 1 Aircraft Performance Unit at Laverton, Yic*, on June 27th, Familiarisation flights were commenced with APII pilots including, 'Wing Gomman- ders JJIo, Harper, and G.D* Marshall^ Squadron Leaders D.Rc Guming, G^Go Brunner, CJh Stark and G-^Ho Shields^ and Flight Lieut^ J^A, Archer* The colour scheme of the GA^15 at this time was natural metal over all, a matt black anti dazzle patch on the cowling in front of the cockpit, EAAF Pacific area blue and white roundels on each side of the fuselage and in all four ?/ing positions^ blue and white fin flashes on the tail and the letter 'P* in a circle for Prototype on each side of the fuselage forward of the roundel. This was in yellow, the same type of marking as used on British prototype aircrafto Testing continued until the aircraft made a crash landing due to a hydraulic failure on December 10th 1946* It was extensively damaged and was returned to GAG for repairs in June 1947* By this time jet aircraft were entering service with various air forces throughout the world and plans were under way in Australia to replace the current fighters- Mustangs- with jet aircraft* Piston engines fighters were losing favour to jet aircraft and the GA-15 project naturally lost its priority* A62-1001, the only GA-15 aircraft built, was eventually returned to the RAAF on May 19th 1948, A limited test flying progranmie then continued until 1950 when further development was cancellede Special fittings in the aircraft for the programme included a torque meter on the control column, a a quick release fitting on the fin for the use of a tail parachute if release of this became necessary during spinning tests* Also fitted was a complete duplicate set of instruments, electrically illum inated in a metal case, set in front of a 35 mm robot camera* The pilot had manual control of the shutter release and cocking lever of the camera, He could take photo graphs at will during flight manoeuvers and enabled him to concentrate on flying instead of making notes on a knee pad with a pencil. Pilots reported that they were delighted with the orderly and rational manner in which cockpit instruments and controls were installed. The cockpit itself appeared to be narrower than in some fighters, but the space available was said to be adequate* The windscreen had three large flat sections giving very good for?\rard visibility, and the bubble was ^free blown^ in manufacture, no moulds being used. It ¥/as claimed that this method gave superior optical properties. In an emergency, a lever jettisoned the enclosure, together with the head rest and rear armour plating, thus enabling the pilot to leave the aircraft vTithout too much difficulty. It is reported that the pilots found the GA-15 ^*a pleasant uncomplicated air craft to fly with no apparent vices”. Due to the wide wheel track (14 ft.), the GA-15 was exceptionally stable even while taxying over excessively rough ground. GAG test pilot Jim Schofield is reported as saying that the GA-15 could be landed normally on three points without any tendency to swing or bounce* The only advice he considered that he needed to give the average fighter pilot about the GA-15 was the tendency to svring on, takeoff. This was because the propeller ran left handed and most pilots were accustomed to a right hand rotation* This tendency to swing was easily checked and fully controllable* On May 1st 1950 the prototype was transferred from ARDU to No. 1 A.Do for conversion to components. The GA-15 was unofficially known as the Kangaroo. It is considered by some people that had the War been prolonged and the GA-15 been placed in production, it would have proved itself to be one of the best fighters in the Pacific theatre. AJi.S.A. Jouriial -53-= May-June 1968 A press release stated that the CA-15 attained a speed of 502o2 mph on May 25th 1948., lioweYer the aircraft was not put into production and another promising Australian design did not get past the prototype stage. Specifications. Type. Single seat^ long range^ medium altitude fighter. Wings. Cantilever low-wing nionoplanec Low drag laminar flow aerofoil section derived from NACA066 series. Maximum thickness at 45% chordo All metal structure in two main sections joined at fuselage centreline. Formed sheet metal spars and ribs, flush riveted metal skin. All metal Frise type differentially controlled ailerons extending 48% of the span.