Airspeed AS.5 Courier

During 1931, as work on the three-engined Ferry airliner was winding down, Airspeed co-founder Hessell Tiltman was eager to get the next project moving. The design team had been passing around rough sketches of an aircraft for private owners that would beat what was then on sale: more useful, more spacious and able to carry five or six people. Tiltman put the early drafts to the board, which approved further work in November 1931. Capital was tight at the young company, though, and a prototype would have to wait for a customer willing to fund it.

Tiltman saw the aircraft as fast and advanced for its class, and as something that could double as a medium-sized transport rather than just a private machine. The centrepiece of that ambition was a main undercarriage that folded away in flight. The aviation historian H. A. Taylor suggests that the idea of a hydraulically retracting gear may have come from the similarly sized but manually operated Lockheed Orion, while cautioning that the story could be apocryphal. Nevil Shute, Airspeed's other co-founder, repeated it in his autobiography Slide Rule and believed the Courier's to be the first hydraulically retracting undercarriage.

The project happened to meet the needs of Sir Alan Cobham, one of the leading figures of interwar British aviation. Cobham was planning a non-stop flight to India to showcase his methods of air-to-air refuelling and was looking for a suitable aircraft. By April 1932 talks were under way between Airspeed, Cobham and his sponsor Lord Wakefield, and on 6 May 1932 a provisional contract was issued for a single machine.

Cobham and his backers were prepared to pay £10,000 for that first aircraft, Armstrong Siddeley Lynx engine included, but they set a tight schedule: delivery by 6 April 1933 at the latest, backed by stiff penalty clauses if the work fell behind.

Not everyone liked the retracting gear. Some in British aviation circles doubted that the extra complexity of raising and lowering the wheels would pay its way, and on Airspeed's own board Lord Grimthorpe was pessimistic, reportedly swayed by outside critics. Tiltman argued hard for the feature, several directors backed him, and it stayed.

The arrangements with Cobham were finalised in August 1932 and construction of the prototype started the following month at York, even though the design was not frozen until October. The aircraft was built at a brisk pace so that it could reach Cobham quickly. The undercarriage in particular had to be made almost entirely in-house, because suitable parts simply could not be bought.

In March 1933 Airspeed moved from York to Portsmouth, where the city council offered generous terms for a factory at the municipal aerodrome. The prototype travelled by road to the new site, was reassembled and, registered G-ABXN, made its first flight in April 1933 in the hands of George Stainforth of the Royal Aircraft Establishment. Sources disagree on the exact day: English Wikipedia and Aeropedia give 10 April, while the Delta encyclopedia, German Wikipedia, Aviastar and the Nevil Shute Foundation timeline give 11 April.

The first flights were made with the 240 hp Lynx IVC uncowled, yet the aircraft came close to the performance predicted for the finished design; a Townend ring was fitted later. The trials attracted so much interest that engineers from rival manufacturers came to watch. The prototype suffered two minor mishaps during testing, in April 1933 at Portsmouth and in June at Martlesham Heath, and was repaired quickly on both occasions.

The Courier was a cantilever low-wing cabin monoplane built mainly of wood. The wing centre section was integral with the fuselage; the outer panels were built around two spruce box spars linked by plywood ribs, and the wing was fabric-covered except at the leading edge. The fuselage had a plywood skin. The tailplane, with a cantilever fin, could be trimmed by a screw jack.

The real novelty was the retracting main gear, developed and patented by Airspeed, which later earned royalties when the system was used on other types such as the Oxford. The pilot worked it with a hand-operated hydraulic pump. The mechanism added around 30 lb, in exchange for roughly 20 mph more cruising speed thanks to lower drag. A practical touch made it forgiving: with the gear up the wheels still protruded slightly below the wing, so a landing with the undercarriage forgotten usually cost no more than a bent propeller. The aviation press of the day gave the arrangement a great deal of attention.

Airspeed offered the aircraft for short or long stages, with two fuel arrangements: 28 gallons in a centre-section tank, or 66 gallons split between two centre-section tanks and a header tank. Cobham's prototype carried far more, 275 gallons, about 1,250 litres, a load it could not lift off the ground with because it would be badly overweight. That capacity only made sense if it was filled in flight.

Several engines were offered as well. The Lynx was promoted for use at home, while the Armstrong Siddeley Cheetah radial went into many of the aircraft. By December 1933 Airspeed was offering two basic versions: one for the home market, the AS.5A with the Lynx IVC, and a colonial model for the territories of the British Empire, the AS.5B with the Cheetah V.

Encouraged by the prototype's trouble-free trials, Airspeed decided in the summer of 1933 to put the Courier into production. On 4 September 1933 it delivered the first of an initial batch of three to its distributor, Aircraft Exchange and Mart, which promptly flew it to Scotland on a demonstration tour and on further sales trips. Between 1933 and 1934 the Portsmouth works turned out 15 production aircraft, giving 16 Couriers in all with the prototype.

The main version was the AS.5A, with the Lynx IVC and a five-passenger cabin, of which 11 were built according to the French and German Wikipedias. The AS.5B used the more powerful Cheetah V, and two were made. The AS.5C was a single aircraft, G-ACNZ, bought by Napier to develop its Napier Rapier IV, a 16-cylinder H engine driving a four-bladed wooden propeller; it later reverted to a Lynx. There was also an AS.5J, G-ACVG, intended for India, which was brought to AS.5A standard before delivery as VT-AFY. Airspeed even studied an all-metal AS.11 Courier for Canada, which stayed on paper.

With the Lynx IVC the Courier spanned 14.33 m, was 8.69 m long and 2.67 m high, with about 23 m² of wing area. It weighed 1,063 kg empty and up to 1,769 kg loaded, reached 246 km/h, cruised at 212 km/h, had a range of about 1,022 km and a service ceiling of 4,115 m.

The prototype missed the 6 April 1933 deadline, but Cobham was not ready for his long-distance attempt either. For about a year he practised refuelling in the air, much of it from Martlesham Heath, using Handley Page W.10 biplanes as tankers. Nevil Shute took part in some of these trials and later described in Slide Rule how he stood half out of the Courier trying to grab the hose trailing from the Handley Page as the two aircraft flew in formation.

On 24 September 1934 Cobham took off from Portsmouth for India and successfully took on fuel from a W.10 along the way. A broken throttle then forced him to land in Malta. The non-stop link to India was not achieved, but the method had been shown to work, and Cobham went on refining it in the years that followed.

Production Couriers went to civil customers, who used them as small airliners and air taxis. Several companies tried out early scheduled routes with them, among them London, Scottish & Provincial Airways, North Eastern Airways, Cobham Air Routes, Channel Airways and Air Taxis Ltd, while Portsmouth, Southsea & Isle of Wight Aviation operated five over a number of years. On 29 September 1934 G-ACSY of London, Scottish & Provincial crashed at Shoreham, killing all four on board and injuring two people on the ground.

The type also made its name in air racing. The first production aircraft, G-ACJL, entered the MacRobertson race from Mildenhall to Melbourne in October 1934, flown by Squadron Leader D. E. Stodart and K. G. Stodart. It was one of 11 aircraft out of 20 starters to reach Australia and finished sixth; Aeropedia places it fourth in the handicap section with a time of 100 hours 24 minutes. It stayed in Australia afterwards and was registered there as VH-UUF.

Its advanced aerodynamics turned two Couriers into research aircraft. In 1934 the Air Ministry bought an AS.5A, serial K4047, which went to the Royal Aircraft Establishment at Farnborough. According to the Delta encyclopedia it went back to Airspeed in 1935 to be fitted with lift and drag devices, since the Courier was hard to slow down and put back on the ground: Handley Page slotted flaps on the trailing edges of the outer wings, air brakes on the centre section next to the fuselage and drooping ailerons, together with modified controls. Later re-engined with a Cheetah IX, it remained in use until a fatal accident on 14 July 1943. The second test aircraft was Napier's AS.5C, used to develop the Rapier engine.

Shute recalls in Slide Rule that six Couriers came back to the company when their operator suspended services, and that the outbreak of the Spanish Civil War let Airspeed sell them at once to intermediaries for more than their original price, after which they made their way to Spain by roundabout routes. In 1936 an arms-trading concern, the Union Founders' Trust, bought five Couriers for resale to the Republican side, but protests from the non-intervention lobby in Britain halted delivery.

Two Airspeed employees sympathetic to the Republic then tried to take G-ACVE themselves. It crashed on take-off from Portsmouth on 20 August 1936; Arthur Gargett was killed and Joseph Smith was jailed for four months.

When the Second World War broke out, most Couriers still flying were impressed into the Royal Air Force. French Wikipedia counts nine AS.5As, first assigned to the National Air Communication Unit and then spread among various communication flights; with K4047 the RAF had ten Couriers in service, while Aeropedia speaks of eight impressed. They also flew with the Air Transport Auxiliary and No. 3 Ferry Pilots Pool on transport and liaison duties. Cobham's own prototype was among those called up.

Only one, G-ACVF, survived the war. Delta records its return to the civil register on 15 January 1946; it spent a short spell giving pleasure flights at Southend-on-Sea and, according to most sources, was scrapped in December 1947, although Aeropedia dates its end to 1949 for lack of spares. No example survives.

The Courier was built in small numbers, but it opened a path. It proved in Britain that a retracting undercarriage could be reliable and worthwhile on a commercial aircraft, and it gave Airspeed a patent the company went on to exploit. Its formula passed to the twin-engined AS.6 Envoy, which appeared in 1934 as a development of the Courier, and from the Envoy came the Oxford, the twin-engined trainer the RAF used in thousands during the war. Through its flight towards India, the Courier also remains linked to the beginnings of air-to-air refuelling, the technique Cobham would make his life's work.