Airspeed Oxford

Description
Unlike its contemporary the Anson, the Airspeed Oxford was designed from the outset as a trainer, though it too had a civil predecessor, in this case the Envoy, which was well tried and tested, over 50 being built for successful use at home and overseas for feeder-liner and charter work, A development, the ASI8 Viceroy had taken part in the l936 air race to Iohannesburg, and the South African Air Force had been supplied with several Convertible Envoys fitted with a removable upper gun turret, so that they could be quickly changed from passenger transport to a light bomber or reconnaissance aircraft.

During the expansion period of the mid~l930s, Airspeeds were handicapped in official eyes by a link with the Dutch firm of Fokker, founded by the young designer whose aircraft has been the scourge of the Royal Flying Corps in the First World War. Nevertheless, Airspeeds had already proved their ability to design and manufacture modern aircraft, and in late 1935 the Air Ministry made preliminary enquiries about the cost of converting the Envoy into a trainer,

Some months later came an invitation to tender to Specification T23/36 for a now urgently needed twin-engined advanced trainer This had obviously been written around the Envoy design, no other manufacturer being invited to tender, and in the autumn of 1936, despite the frowned on Fokker connection, 136 machines were ordered straight from the drawing board,

Despite its origins, the machine which finally emerged was a virtual redesign, very little of the original Envoy having survived, The initial production aircraft, L4534, made its first ﬂight in lune l937, powered by two Armstrong Siddeley Cheetah X engines Fitted with retractable undercarriage, flaps, and other modern equipment, it was a versatile machine, which could be used for training in bombing, navigation, air gunnery, radio or aerial photography, L4534 was subjected to tests at Martlesham Heath, and the resulting report was generally favourable, It was found to have a good field of view, the instrumentation was satisfactory, the engine controls were well placed, and the flap controls were convenient and easy to operate. The cockpit was also satisfactory, though space between the controls and the seats was limited, nor was there much elbow room in the left-hand seat, Headroom was normally ample, but difficulties could be encountered when the blind ﬂying hood was in use, as the head of a tall pilot would touch it even when he had his seat fully down. The safety belt fitment also caused criticism, as it left the pilot vulnerable to head injuries in the event of a crash, Its handling qualities were designed to match those of the larger aircraft which most pupils would go on to fly, There was a tendency to swing on take~off, and it became tail heavy with an increase in engine power, but for normal cruising conditions the change of trim could be easily held with the elevators, which were moderately light but effective and quick in response. When trimmed the aircraft could be flown feet-off at all speeds, On approach there was effective warning of stall by a marked vibration throughout the structure, but the stall could be easily controlled, In such conditions the wing which dropped suddenly, could be raised immediately by the ailerons alone, provided the control column was not brought further back, in which case the aircraft could develop a vicious stall.

The design had a pleasing appearance, with a neatly streamlined fuselage, and engines mounted above the wings, The latter were in three sections, the centre of which was attached to the lower fuselage and accommodated both the engines and a retractable undercarriage‘ Four bolts and locking nuts were used to attach the outer sections to this. Split trailing-edge flaps were fitted inboard of the ailerons. For ease of construction, the wooden semi-monocoque fuselage was built in two sections, one including the cockpit and cabin, and the other the rear fuselage with its integrated fin, It had a cantilever tail unit, the wooden frame being plywood covered, apart from the movable surfaces, which had fabric covering. The tailwheel was of the fixed variety.

The fuselage was designed for a variety of training purposes. ln addition to the pilot, it had provision for either a second pilot or a navigator, The third crew member could be a gunner. radio operator, camera operator or air bomber, The cabin, which was fitted with full dual control, had a full range of instruments, including a Sperry panel in the centre of the first pilot‘s dashboard, and for the second pilot a duplicate altimeter, airspeed indicator and turn and bank indicators. The height of the first p1lot’s seat was fully adjustable in flight, by use of a lever on his left, but the second pilot could only make such an adjustment on the ground, and was limited to three possible positions,

The Mark I, equipped with Cheetah Xs, was an allepurpose aircrew trainer fitted with an Armstrong Whitworth dorsal gun turret, a bomb bay and various ancillary equipment. The Mark ll version, however, being intended for navigation and radio training, had the turret omitted, but there were no other significant differences and very little change in the handling qualities. Both versions were built in large numbers, total production exceeding 8,500. Many were ﬂown in Australia, Canada, New Zealand, South Africa and Southern Rhodesia. ln practise, the crew training role largely fell to the Anson, and the Oxfords were mostly used for pilot training, the turrets being removed from Mkls. Many of the Oxfords used in Canada and Rhodesia had Pratt and Whitney Wasp junior engines, and in this specification were designated Mark V.

Neither the Mklll nor the Ml<lV versions had gone into production, these being fitted respectively with Cheetah XVs and experimental Gipsy Queen Ivs. Much of the production was sub-contracted to Percival and Standard. and a test report in April l94l commented that one of the latter (V3868) compared favourably in performance and general handling qualities with those built by the parent firm. Much the same comment was made in October 1942 on the first production MkV (EB424), whose engines, cowling, exhaust ring and muff had been adapted from the equipment of the Vultee BT13.

Colloguially known as the ‘Ox-box’, the Oxford entered service in late 1937, and was soon in use by the Central Flying School and the expanding number of Flying Training Schools. lt continued to serve throughout the war. mostly with Service Flying Training Schools or their successors, the (Pilot) Advanced Flying Units. Both aerobatics and spinning were prohibited, being a twin-engined machine, though it was not unknown for an Oxford to be rolled or looped.

Recovery from an unintended spin was deemed not difficult, however, normal procedures in such a situation being effective, the inner motor being opened up to help rudder action. On occasion, however. an Oxford would spin unaccountably, and be difficult or impossible to recover, and consequently Flying Training Schools banned this manoeuvre. Investigation eventually found the aircraft susceptible to misalignment between the wing root fillets and the engine cowlings. Fitting a leather seal improved matters somewhat, but a hoped for cure to the problem by fitting twin fins and rudders on N632? proved unsuccessful.

The Oxford was much more demanding of the pilot than the Anson. and consequently those that survived their training course attained flying skills of a relatively high standard. On takeeoff extreme care was necessary with the throttles and controls. if the aircraft was not to swing smartly to starboard, resulting in either an Seshaped take-off or a ground loop. Single-engined ﬂying could be tiring as the rudder proved inadequate in this situation despite its size. The good field of view was an asset in landing, which was not usually difficult, except for attempts at threeapointers in cross-winds, when the rudder became blanketed. causing the aircraft to wander offacourse.

In Canada. the Oxford was very prone to moisture problems. Having wooden wings, the damp climate affected the glue in the ioints. which gradually filled up the drain holes. Consequently when the aircraft went in for repair or inspection. several gallons of water would pour out. It was not uncommon for dry-rot to develop in these conditions.

The wooden construction also gave trouble in the tropics. in humid conditions. the casein-based adhesive used in construction developed a fungoid growth, particularly in the toints. Experimentation led to production of a resin-based adhesive, and this was used for later production aircraft. entirely curing the problem.

As with the Anson, aircrew experienced difficulty adiusting to the normal British weather after learning to fly in clear overseas skies, and a number of (Pilot) Advanced Flying Units were set up, mainly equipped with Oxfords. to overcome this problem. In addition. several dozen Oxford-equipped Beam Approach Training Flights were set up, their aircraft being distinguished by large yellow triangles painted on the fuselage sides and under the wings. Attached to both Advanced Flying Units and Heavy Conversion Units, these units provided tuition in the Standard Beam Approach system for bringing in operational aircraft safely in conditions of poor visibility.

Production ended in ]uly 1945. and the Oxford was largely superseded after the war. though a number were retained. mainly for communications duties, or attached to Fighter Command to help single-engine pilots to adjust to the Hornet and Meteor. They were also issued to reformed reserve squadrons. some of which were equipped with Mosquitoes, being used for conversion and instrument training. When the Korean war and other factors led later to an expansion in flying training, many surviving Oxfords were brought out of storage and issued to Advanced Flying Training Schools. where they were used to train National Service pilots until the last of these closed in 1954. A number were also sold for civil use, some after being reworked as small airliners by Airspeed. in which guise they were rechristened Consuls.