Designed by Theodore Paul Wright and Al Wedburg, the Curtiss Model 55 Kingbird was a twin-engine airliner with a fuselage derived from the single-engine Curtiss Thrush. The Kingbird had two engine nacelles mounted on the struts on either side of the fuselage that braced the wing and the outrigger undercarriage. A distinctive design feature was the aircraft’s blunt nose, located behind the propeller arcs. This allowed the engines to be mounted closer to each other and to the aircraft’s centerline, therefore minimising asymmetrical thrust in case of an engine failure. For the same reason, the Thrush’s single tailfin was replaced by twin tails on the Kingbird, and the main production model, the D-2 fitted a second horizontal stabilizer and elevator between these fins.

The prototype Kingbird C performed the first flight in May 1929 with two Curtiss Challenger motors with 185 hp each.

The prototype was followed by two Kingbird D-1s with Wright Whirlwind J-6-7 motors of 225 hp. Airline “Eastern Air Transport” ordered a series Kingbird D-2; two D-1 modified in D-2.

The only Kingbird D-3 took off in the summer of 1931 with two 330-horsepower Whirlwind J-6-9 engines.

Modernization was carried out before the first three Kingbird were assembled. Kingbird C became Kingbird J-1 with Whirlwind J-6-7 motors with 240 hp; the first Kingbird D-1-Kingbird J-2 with Whirlwind J-6-7 motors; the second Kingbird D-1 turned into a Kingbird J-3 with 300-hp Whirlwind J-6-9 motors, which was used to transport mail.

Selling for $25,555 each, Eastern Air Transport was to be the Kingbird’s main operator, flying 14 of them for a few years. The United States Marine Corps also purchased an example in 1931, first designating it JC-1, then RC-1 and using it as an air ambulance. Apart from some improvements to their requirements, it was the usual eight-seater Kingbird D-2. Others were operated by Turkish Airlines (under former official name: State Airlines Administration).

First flying in 1929, 19 were built in total.

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Variants:

Kingbird C
Prototype powered by 185 hp (138 kW six-cylinder Curtiss R-600 Challenger engines. One built, but found to be underpowered. Later converted to Kingbird J-1.

Kingbird D-1
Second and third prototypes (previously Kingbird J-3 and J-2) powered by 225 hp nine-cylinder Wright Whirlwind J-6-7 radial engines. Later converted to D-2 standard.

Kingbird D-2
Production aircraft with two 300 hp (224 kW) Whirlwind J-6-9 engines. 14 built plus two converted from D-1s.

Kingbird D-3
One-off Curtiss executive transport. Two 330 hp (246 kW) Whirlwind J-6-9 engines. Seats for five passengers.

Kingbird J-1
First prototype after re-engined with Whirlwind engines.

Kingbird J-2
Third prototype, J-6-7 engines.

Kingbird J-3
Second prototype, J-6-9 engines.

RC-1
Single Kingbird D-2 for US Navy, originally ordered as JC-1 (J for utility), but delivered as RC-1 (R for transport).

Specifications:

D-2
Engines: 2 × Wright J-6-9 Whirlwind, 300 hp (224 kW) each
Wingspan: 54 ft 6 in (16.61 m)
Wing area: 405 ft2 (37.6 m2)
Length: 34 ft 10 in (10.59 m)
Height: 10 ft in (3.04 m)
Empty weight: 3,442 lb (1,561 kg)
Gross weight: 5,202 lb (2,360 kg)
Maximum speed: 142 mph (229 km/h)
Cruise speed: 112 mph (180 km/h)
Landing Speed: 54 mph / 86-8 km/hr
Range: 415 miles (668 km)
Service ceiling: 16,000 ft (4,880 m)
Rate of climb: 850 ft/min (4 m/s)
Crew: one, pilot
Capacity: seven passengers

In 1934, Curtiss began work on a brand new twin-engined attack aircraft, which received the designation Model 76 and the name “Shrike”. Originally built as an in-house venture as the Curtiss Model 76, the 76 was of all-metal construction with an oval section semi-monocoque fuselage, described as “pencil slim” with a fabric covering of ailerons, rudder and stabilizers. The main landing gear retracted into the engine nacelles, the rear wheel also retractable

First flying on 17 July 1935, with the civil registration NX15314, the first multi-engine attack aircraft tested by the United States Army Air Corps at the Wright Field air base in Ohio, but in the fall it was returned to the company for improvements. Carrying a crew of two, it was as fast as the standard pursuit aircraft in service at the time.

The XA-14 was extensively tested, at one stage being fitted with a 37 mm (1.46 in) nose cannon. Powered by two experimental Wright XR-1510 radial engines, flight testing was sufficiently impressive that after the USAAC appraisal the Model 76 was returned to Curtiss and fitted with two 775 hp (578 kW) Wright R-1670-5 Cyclone engines with two-blade constant-speed propellers. This configuration was accepted by the Army with the designation XA-14 given to the sole example. It had standard Army markings with the serial number 36-146.

The Great Depression of 1929-1932 severely curtailed military allocations. The price of a single Wright engine was then $ 90,000, which was considered excessively expensive for mass construction.

On 23 July 1936, 13 pre-production versions, re-engined with two Wright R-1820-47 Cyclone twin-row radials with three-blade propellers, were ordered into production as the Y1A-18.

The only prototype XA-14 was initially planned to be used to set aviation records, but instead in June 1936 this aircraft was tested with a new 37-mm cannon (sometimes it was called YA-14). At the end of the year, it was dismantled for scrap after 158 hours of flight time.

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Engines: 2 × Wright R-1670-5 Whirlwind, 775 hp (578 kW) each
Wingspan: 59 ft 5 in (18.11 m)
Length: 40 ft 3 in (12.27 m)
Height: 10 ft 9 in (3.2.7 m)
Empty Weight: 3680 kg
Max takeoff weight: 11,750 lb (5,330 kg)
Maximum speed: 254 mph (221 kn, 409 km/h)
Cruising speed: 340 km / h
Range: 825 mi (717 nmi, 1,328 km)
Service ceiling: 27,100 ft (8,260 m)
Crew: two
Armament:
4 × .30 in (7.62 mm) M1919 Browning machine guns forward-firing
1 × .30 in (7.62 mm) machine gun aft-firing
650 lb (295 kg) bombs in internal bay