World War 2 In Review: 03/09/25

Northrop Delta I, U.S. Coast Guard RT-1 (382).

The Northrop Delta was an American single-engined passenger transport aircraft of the 1930s. Closely related to Northrop's Gamma mail plane, 13 were produced by the Northrop Corporation, followed by 19 aircraft built under license by Canadian Vickers Limited.

Development and Design

When Jack Northrop set up the Northrop Corporation as a joint venture with the Douglas Aircraft Company in 1932, he set out to design two closely related single-engined aircraft as the new company's first products: a mailplane/record-breaking aircraft, which was designated the Gamma, and a passenger transport, the Delta. The Delta was a low-winged monoplane, with a fixed tailwheel undercarriage. It was of all-metal, stressed-skin construction, with streamlining spats covering the main landing gear. While the Delta's wings were common with those of the Gamma, it had a new, wider fuselage, which seated the pilot in an enclosed cockpit immediately behind the engine, and had accommodation for eight passengers in a cabin behind the pilot.

The first Delta was flown in May 1933, and received an airworthiness certificate in August that year.

Role: Transport aircraft

Manufacturer: Northrop Corporation

Designer: Jack Northrop

First flight: May 1933

Introduction: 1933

Primary user: Royal Canadian Air Force

Number built: 32

Developed from: Northrop Gamma

Operational History

Although it was intended that the Delta would be sold in both airliner and executive transport (initially named "Victoria") versions, a change to the regulations governing commercial air transport in the United States in October 1934, prohibiting the use of single-engined aircraft to carry passengers at night or over rough terrain which would prevent a forced landing, stopped the market for single-engined airliners in the United States, and only three aircraft, all ordered before the passing of this regulation, were built as airliners. These consisted of the prototype, leased to Trans World Airlines for use to carry airmail, which crashed on 10 November 1933, one sold to Pan-Am for use by its Mexican subsidiary, destroyed by a fire in May 1934 and one sold to AB Aerotransport of Sweden, delivered in April 1934. AB Aerotransport purchased a second Delta, but this was a dedicated mailplane which more closely resembled the Gamma, with a slim fuselage carrying its cargo in a compartment ahead of the cockpit.

A single aircraft was built for the United States Coast Guard. Designated the Northrop RT-1, this was used as the personal transport of Henry Morgenthau Jr., the Secretary of the Treasury and as a staff transport. Seven more aircraft were built as executive transports for private owners. Of these, three were purchased by the Spanish Republicans for use in the Spanish Civil War. Two of these aircraft were captured by the Nationalists when the ship carrying them (along with four Vultee V-1s, a Fairchild 91 and a Lockheed Electra) was captured at sea. These two Deltas were used as Transports by Franco's forces, while the third Delta was used by the Republican airline Lineas Aéreas Postales Españolas (LAPE) until the end of the civil war when it was handed over to Franco's air force.

In 1935, Canada selected the Delta for use as a photographic survey aircraft for use by the Royal Canadian Air Force (RCAF), to be built by Canadian Vickers under license. One aircraft, the last Delta built by Northrop, was supplied as a part assembled pattern to Canadian Vickers, first flying on 16 August 1936 and being delivered to the RCAF on 1 September that year. It was followed by a further 19 aircraft built wholly by Canadian Vickers, production continuing until October 1940. The Northrop Delta was the first completely all-metal, stressed-skin aircraft built in Canada, however it was closely preceded by the Fairchild Super 71, whose stressed skin construction was limited to the fuselage and not the flying surfaces.

The Deltas, which were capable of being operated from wheeled, ski or float undercarriages, proved capable survey aircraft, well suited to operations in the north of Canada, but in August 1939, when the outbreak of the Second World War loomed, Canada found itself short of coastal patrol aircraft, and the Deltas were diverted to this role, being fitted with floats and carrying out long anti-submarine missions. The Deltas were less successful as patrol floatplanes, as they were damaged by ocean swell and by salt water corrosion, and they were forced to revert to landplane use after two months. The Delta was withdrawn from operations in late 1941, then being used as instructional airframes in training schools.

Variants

Delta 1A: Prototype. Powered by 710 hp (530 kW) Wright SR-1820-F3 Cyclone radial engine. One built.

Delta 1B: Passenger airliner for Pan-Am. Powered by 660 hp (490 kW) Pratt & Whitney Hornet. One built.

Delta 1C: Passenger airliner for AN Aerotransport. Powered by 700 hp (520 kW) Hornet.

Delta 1D: Executive aircraft, powered by Cyclone or Hornet engines. Eight built, including one Northrop RT-1, powered by 735 hp (548 kW) Cyclone for United States Coast Guard.

Crew: 1

Capacity: 8 Passengers (passenger variants)

Length: 33 ft 1 in (10.08 m)

Wingspan: 47 ft 9 in (14.55 m)

Height: 10 ft 1 in (3.07 m)

Wing area: 363 sq ft (33.7 m2)

Empty weight: 4,504 lb (2,059 kg)

Gross weight: 7,350 lb (3,334 kg)

Powerplant: 1 × Wright SR-1820-F2 Nine-cylinder air-cooled radial engine, 735 hp (548 kW)

Maximum speed: 190 kn (219 mph, 352 km/h) at 6,300 ft (1,920 m)

Cruise speed: 174 kn (200 mph, 332 km/h)

Range: 1,435 nmi (1,650 mi, 2,655 km)

Service ceiling: 20,000 ft (6,095 m)

Rate of climb: 1,200 ft/min (6.1 m/s)

Wing loading: 20.2 lb/sq ft (98.9 kg/m2)

Power/mass: 0.10 hp/lb (0.16 kW/kg)

Delta 1E: Airmail carrier for AB Aerotransport. One built. Powered by 660 hp (490 kW) Hornet.

Delta I: Survey aircraft for RCAF. Powered by 775 hp (578 kW) SR-1820-F52 Cyclone. Three built, including pattern aircraft and two license built. Based on the 1D-8.

Delta IA: Partial modification to Mk.II standards, with bomb racks fitted.

Delta II: Revised version with provision for armament, including bombs, a dorsal turret mounting a .30 in Browning machine gun (later removed) and two wing mounted machine guns. Nine built.

Delta III: Unofficial designation for Mk.II fitted with enlarged tail surfaces to counter tail buffeting from turret. Eight built.

RT-1: United States Coast Guard designation for its sole Delta 1D-7, which was named "Golden Goose".

Military Operators

Australia

Royal Australian Air Force – Operated one impressed Delta from December 1942 to September 1943.

Canada

Royal Canadian Air Force

No. 8 Squadron RCAF

No. 119 Squadron RCAF

No. 120 Squadron RCAF

Spain

Spanish Republican Air Force – ex-Swedish Northrop 1C Delta with LAPE

Nationalist Air Force - Northrop 1D Delta captured on Mar Cantabrico

United States

United States Coast Guard

Civil Operators

Australia

Civil Aviation Authority of Australia

Mexico

Aerovias Centrales SA (a Pan-Am Subsidiary)

Sweden

AB Aerotransport (now part of SAS)

United States

Trans World Airlines (aka TWA)

Honeywell (executive aircraft)

Richfield (executive aircraft)

Bibliography

"The Latest Northrops: The "Victoria" and "Delta" Models". Flight, 8 February 1934. pp. 123–124.

Francillon, René J. McDonnell Douglas Aircraft since 1920. London: Putnam, 1979. ISBN 0-370-00050-1.

Green, William. War Planes of The Second World War: Volume Seven – Bombers and Reconnaissance Aircraft. London: Macdonald, 1967.

Northrop Delta 1D (NC13777), Alhambra, California.

Northrop Delta 1D, Spanish Nationalist service (43-5), having been captured aboard the Mar Cantabrico which was attempting to run the Nationalist blockade.

Northrop D.1 Delta, ‘VH-ADR,’ in service with the RAAF (A61-1).

Delta A61-1 with RAAF 35 Squadron, Pearce, Western Australia. Both were taken on 2 April 1943 at Maylands Aerodrome, Perth, where 35 Squadron deployed their aircraft. Lower sections of the undercarriage fairings are removed, probably for use on rough dirt strips.

Photograph taken on 22 April 1944 at RAAF Richmond, where the damaged Delta was held by No. 2 Aircraft Depot pending a decision in its fate. On 30 September 1943, aircraft swung on takeoff, due to tailwheel strut collapsing causing significant damage.

Photograph taken on 22 April 1944 at RAAF Richmond, where the damaged Delta was held by 2AD pending a decision in its fate. In October 1943, RAAF determined that the Delta could not be repaired due inability to source airframe spare parts. On July 25, 1944, aircraft was sent to No. 2 Central Recovery Depot, Richmond for conversion to components and later broken up for parts at RAAF Richmond.

Northrop Delta, RCAF (667).

Northrop Delta Mk. II, RCAF (670), No. 120 (Bomber Reconnaissance) Squadron based at RCAF Station Patricia Bay. The squadron, part of Northwest Air Command, was commanded by Wing Commander R.A. Delhaye DFC. The aircraft behind the Delta is a Junkers W 33/34 with Canadian Airways Limited.

Northrop Delta II, RCAF (670), written off after accident at Discovery Passage, British Columbia, 8 August 1942.

Northrop Delta, RCAF (669).

Northrop Delta, RCAF (683).

Northrop Delta Ia, No. 8 Squadron, RCAF (667).

Northrop Delta seaplane, RCAF (667).

Northrop Delta Mk. I, RCAF (667).

Northrop Delta I cockpit, RCAF.

Northrop Delta Mk. II, RCAF cockpit, 12 Apr 1937.

Northrop Delta I instrument panel, RCAF.

Northrop Delta interior with Very Pistol and shell storage behind the cockpit seats. Note the window under the cockpit for a prone bombardier.

Delta cockpit in action.

Northrop Delta I, RCAF.

Northrop Delta II, RCAF (675).

Northrop Delta I, RCAF.

Northrop Delta II, RCAF (684).

Northrop Delta II, RCAF (688) delivered 14 August 1940, assigned to No. 120 (Bomber Reconnaissance) Squadron, RCAF Station Patricia Bay, British Columbia, written off 10 October 1940 due to engine failure.

Northrop Delta, RCAF (667), first Canadian built Delta, 1936.

Northrop Delta I, RCAF.

Northrop Delta II, RCAF (676).

Northrop Delta II, RCAF.

Northrop Delta II, RCAF (670).

Northrop Delta, RCAF (682).

RCAF Canadian Vickers-built Northrop Delta Mk.I.

Canadian Vickers (Northrop) Delta Mk. I, RCAF (675), Vancouver, British Columbia, ca 1939.

Northrop Delta Mk. Is on floats, No. 120 (Bomber Reconnaissance) Squadron, RCAF, based at RCAF Station Patricia Bay, British Columbia, 1940.

Three RCAF Northrop Delta Mk. Is (668, 670 and 673) and a Noorduyn Norseman, in the Ottawa River at Rockcliffe, Ontario.

Northrop Delta, RCAF (675), initially posted to No. 8 Squadron, Rockcliffe, Ontario, in 1938. 675 later flew with No. 120 Squadron from RCAF Stations Sea Island and Patricia Bay, British Columbia, from May 1940 to July 1941, coded MX-C. It served with No. 13 (OT) Squadron, RCAF Station Patricia Bay, BC, 1941.

Northrop Delta Mk. I (668), 17 Aug 1937. The Delta often flew on floats during RCAF service. This photo illustrates the waterline on the floats of a fully-loaded aircraft. The floats were designed specifically for the Delta by Canadian Vickers.

Northrop Delta Mk. I, RCAF (667), No. 8 (BR) Squadron, East Coast, ca. 1941.

Northrop Delta Mk. IIs, RCAF (677 and 675), Noorduyn Norseman Mk. IV, RCAF (678), No. 8 Squadron, Aug 1939.

Northrop Delta Mk. II, RCAF (675).

Northrop Delta Mk. II, RCAF (671) on skis, 2 Feb 1938.

Northrop Delta Mk. II, RCAF (676), from No. 8 Squadron. It is shown being prepared for a flight from RCAF Station Rockcliffe, Ontario, to Sydney, Nova Scotia, on 26 Aug 1939. RCAF Marine Launch No. ML171 is being used to assist.

Northrop Delta Mk. II, RCAF (676), from No. 8 Squadron on the water.

Northrop Delta Mk. II, RCAF (671), Aug 1939.

Northrop Delta Mk. II, RCAF (673) on skis, Apr 1939.

During the winter of 1938, four Deltas were operated on skis. Operation of the Delta on skis was never completely satisfactory, as trimming problems during flight could not be overcome. The two bomb aimers windows of differing shapes under the cockpit are also of note.

Northrop Delta Mk. II, RCAF (673) on skis, Apr 1939.

Northrop Delta Mk. II, RCAF (673) on skis, undergoes testing with bomb racks under the center and outer wing sections, RCAF Station Rockcliffe, Ontario, ca. Apr 1939.

The under fuselage bomb racks with a bomb fitted.

A close up look at the under wing light stores carriers.

A view of the cockpit from the rear cabin.

A Lewis gun could be fitted in the rear fuselage of the Delta though the fuselage camera port.

A view of a Delta with the wing removed and the crew hatch open.

Northrop Delta Mk. II, RCAF (673) on skis, Apr 1939.

Canadian Vickers (Northrop) Delta Mk. I, RCAF (675), with a Hawker Hurricane, Vancouver, British Columbia, ca. 1939. Delta 675 was assigned to 1 (F) Squadron to assist the pilots with transition training to their new Hawker Hurricanes. In the end the performance was found lacking and a Harvard replaced the Delta.