Northrop Delta
The Northrop Delta was a single-engined, all-metal passenger transport built by the Northrop Corporation as the passenger companion to the Gamma mailplane, sharing the Gamma's wing under a wider fuselage seating eight. First flown in May 1933, it was shut out of its intended American market by October 1934 rules that stopped single-engined passenger flying at night and over rough terrain, and Northrop built only 13, as airliners, executive transports and one Coast Guard staff transport. The type's substantial career came in Canada: Canadian Vickers built 19 more under licence, the first all-metal stressed-skin aircraft built in Canada, for RCAF photographic survey work, an unsuccessful spell as float-equipped anti-submarine patrol aircraft in 1939, and instructional duties until late 1941. The fuselage of one Canadian aircraft survives at the Canada Aviation and Space Museum in Ottawa.
Why It Mattered
The Delta was one of the first two products of the Northrop Corporation, set up by Jack Northrop in 1932 as a joint venture with Douglas: a passenger transport designed alongside the Gamma mailplane. It shared the Gamma's wing but carried a new, wider fuselage seating eight passengers, in all-metal stressed-skin construction. Its American airliner career was ended by regulation rather than by the design, when an October 1934 rule change stopped the market for single-engined airliners in the United States. In Canada the type found its real career, and a place in that country's industrial history: the aircraft built there under licence were the first completely all-metal, stressed-skin aircraft built in Canada. The RCAF's official history calls it the most modern aircraft in the Canadian fleet when the Second World War began.
Design Notes
The Delta was a low-wing monoplane with a fixed tailwheel undercarriage, its main legs covered by streamlining spats. The wing was the Gamma's; the fuselage was new and wider, with the pilot in an enclosed cockpit just behind the engine and a cabin for eight passengers behind him. Power came from a single radial engine, a Wright Cyclone on most variants and a Pratt & Whitney Hornet on some, among them the Pan-Am and Swedish airliners. For the RCAF the design was adapted to survey work, with camera mounts and ports fitted in the cabin, and the aircraft could be operated on wheels, skis or floats. The Canadian Mk II could carry bombs, and mounted a .30 in Browning machine gun in a dorsal turret that was later removed.
Operational History
The first Delta flew in May 1933 and received its airworthiness certificate that August. Only three were built as airliners, all ordered before the regulation passed: the prototype was leased to Trans World Airlines to carry airmail and crashed on 10 November 1933, one was sold to Pan-Am for its Mexican subsidiary, and one went to AB Aerotransport of Sweden. AB Aerotransport also bought a second aircraft, a dedicated mailplane which more closely resembled the Gamma. One Delta was built for the United States Coast Guard, designated RT-1, serving as a staff transport and as Treasury Secretary Henry Morgenthau Jr.'s personal aircraft. Seven more were built as executive transports for private owners. Three of those reached Spain during its civil war: two, captured at sea by the Nationalists, became transports for Franco's forces, and the third flew for the Republican airline LAPE until the war ended. Canada had selected the Delta in 1935 as an RCAF photographic survey aircraft, to be built by Canadian Vickers under licence; the last Delta Northrop built went north as a part-assembled pattern, first flying on 16 August 1936 and delivered to the RCAF on 1 September. Canadian Vickers built a further 19 aircraft wholly in Canada, with production continuing until October 1940. The survey aircraft proved capable in Canada's north, but in August 1939 they were diverted to anti-submarine patrols on floats, were damaged by ocean swell and salt-water corrosion, and reverted to landplane use after two months. The RCAF's history judges that the type proved entirely unsuitable for the anti-submarine job it had never been designed for. Withdrawn from operations in late 1941, the Canadian Deltas finished as instructional airframes in training schools, and Australia's air force also operated a single impressed Delta from December 1942 to September 1943.
Afterlife
The best-documented survivor is Canadian: the fuselage of RCAF Delta 673, held by the Canada Aviation and Space Museum in Ottawa. Delta 673 crashed in a low valley near Beaverbrook Lake, New Brunswick, on 14 September 1939, killing its pilot and mechanic; they were the first RCAF airmen to die in Canada in the Second World War, and the wreck was not found until 1958. A decade after the discovery, the wreckage was airlifted out for the museum at Rockcliffe, but only the fuselage arrived, the engine and everything else being lost on the way. The RCAF's account describes the fuselage as the only extant example of the Canadian Vickers-made Delta, and the wreckage is categorized as "unrestorable".