The XP-31 or Curtiss Shrike of 1932-3 was an all-metal, low wing, strut-braced fighter design which drew heavily upon the characteristics of the manufacturer’s A-8 Shrike (enclosed cockpit, trailing edge flaps and leading-edge slots), but failed to attain the A-8’s production status. The sole prototype XP-31, at first designated XP-934, arrived on the scene just when the comparable Boeing P-26 ‘Peashooter’ had already proven itself superior in most aspects of performance.
First flown in July 1932 with a 522kW Wright R-1820-4 Cyclone engine, the XP-31 was immediately found to be underpowered. Though the purpose seems unclear, the sole airframe was re-engined with a 447kW Curtiss V-1570 Conqueror powerplant which, in 1933 flight tests, offered no improvement of any kind. Slower than the P-26, and with a 595km range, the XP-31 helped Curtiss to upgrade its design and structural thinking at a time when the monoplane was clearly the aircraft of the future. Its non-retractable landing gear and drag-inducing wing struts were the last to appear on a USAAC fighter, but the XP-31, although very small by comparison with other pursuit ships of its day, was unduly heavy. The XP-31 was rigorously tested and underwent various minor modifications in the early 1930s, but it was not chosen for production and did not, directly, lead to any later designs. The existing XP-31 is understood to have been scrapped in 1935.
Engine: 522kW Wright R-1820-4 Cyclone Take-off weight: 1879 kg / 4143 lb Empty weight: 1512 kg / 3333 lb Wingspan: 10.97 m / 35 ft 12 in Length: 8.00 m / 26 ft 3 in Height: 2.36 m / 7 ft 9 in Wing area: 18.86 sq.m / 203.01 sq ft Max. speed: 334 km/h / 208 mph Ceiling: 7430 m / 24400 ft Range: 595 km / 370 miles Armament: 4 x 7.62mm machine-guns
Ordered in July 1931, the Curtiss XP-23 was the last biplane in the pursuit series, altered on the production line from the final airframe of the 45 ordered as Y1P-22 but redesignated P-6E. With fabric-covered metal wings of standard P-6 planform and a new metal skinned fuselage and initially powered by a 447kW Curtiss GIV-1570C Conqueror with a turbo-charger and three-blade propeller, the YP-23 was delivered 16 April 1932. Evaluated by operational fighter pilots at Wright Field with turbo-charger removed, two-blade propeller retrofitted, and its designation changed to YP-23, the YP-23 seems to have performed very well, subject only to the limitations of the biplane configuration. Some reports that the XP-23 was excessively heavy, with maximum take-off weight as high as 1950kg appear to be based on an erroneous interpretation of Curtiss documents from the period. The XP-23 was denied a production contract, competing not with other biplanes but with the monoplane Boeing P-26 ‘Peashooter’. Ultimately, the YP-23 was deleted from Army inventory and turned back to Curtiss, where its wings were retained for use on the prototype US Navy XF11C-1 shipboard fighter.
XP 23 Engine: Curtiss V 1570 23 Conqueror, 447kW Wingspan: 9.60 m / 31 ft 6 in Length: 7.26 m / 23 ft 10 in Height: 2.90 m / 9 ft 6 in Wing area: 23.23 sq.m / 250.05 sq ft Take-off weight: 1542 kg / 3400 lb Empty weight: 1315 kg / 2899 lb Top speed: 354 km/h / 220 mph at 4570 m / 15 000 ft Initial climb, 1,370 ft/min (6,96 m/sec) Ceiling: 7925 m / 26000 ft Range: 700 km / 435 miles Armament: 1 x 12.7mm + 1 x 7.62mm fixed machine-guns, 227kg of bombs
Perhaps the most unusual single-seat fighter developed by Curtiss was the Model 70, which was designed from the outset to be flown either as a monoplane or as a biplane with the minimum of structural change. A metal semi-monocoque aircraft with fabric-covered wings, it was ordered on 23 November 1932 as the XF13C powered by a Wright SGR-1510-2 two-row radial rated at 600hp at 3050m. The designation XF13C-1 was assigned to it for test in monoplane form and XF13C-2 in biplane (or more strictly, sesquiplane) form. It was initially flown in December 1933 as a biplane, flying in monoplane form on 7 January 1934, and being delivered to the US Navy as the XF13C-1 on the following 10 February. Featuring a manually-operated retractable undercarriage, an enclosed cockpit, retractable upper wing leading-edge slats and trailingedge flaps, the XF13C-1 did not revert to biplane standard, but, in February 1935, was returned to Curtiss for various modifications, including installation of an XR-1510-12 engine affording 700hp at 2135m. With these changes it was redesignated XF13C-3. In biplane configuration, the XF13C was 30km/h slower than as a monoplane, but possessed a shorter take-off run and better low-speed characteristics. Trials were terminated in October 1935, primarily owing to lack of engine spares.
XF13C-3 Engine: Wright SGR-1510-2 two-row radial, 600hp at 3050m Take-off weight: 2142 kg / 4722 lb Wingspan: 10.67 m / 35 ft 0 in Length: 7.86 m / 25 ft 9 in Height: 3.88 m / 12 ft 9 in Wing area: 19.04 sq.m / 204.94 sq ft Max. speed: 373 km/h / 232 mph
Based on a US Navy Bureau of Aeronautics design for a two-seat fighter, the XF12C-1 all-metal parasol monoplane, ordered on 30 June 1932, featured aft-folding wings with leading-edge slats and trailing-edge flaps, and manually-operated retractable main undercarriage members. Flown in July 1933, the XF12C-1 was initially powered by a Wright R-1510-92 two-row radial rated at 625hp at 1830m. By the time the XF12C-1 was tested by the US Navy in October 1933, the Twin Whirlwind engine had been replaced by a Wright SR-1820-80 Cyclone single-row radial. With the discarding of the two-seat fighter category it was redesignated XS4C-1 in December 1933 and the XSBC-1 in January 1934 as a scout-bomber. Among the evaluations of the Model 73 XF12C-1 was a dive bombing test on 14 June 1934 that resulted in a failure of the parasol monoplane wing assembly. Though the pilot and machine were wholly spared, the prototype was nonetheless heavily damaged. Testing had shown that the parasol wing assembly was generally unfit for the stresses of what the new aircraft would be called upon to achieve. As a result, the US Navy ordered a new prototype to fall in line with stricter requirements. Curtiss once again delivered an answer, this time the Model 77, to which the US Navy affixed the designation of XSBC-2.
XF12C-1 Engine: Wright R-1510-92 Whirlwind two-row radial, 625hp at 1830m Wright SR-1820-80 Cyclone single-row radial Empty weight: 1 762 kg Wingspan: 12.65 m / 41 ft 6 in Length: 8.86 m / 29 ft 1 in Height: 3.94 m / 12 ft 11 in Wing area: 25.27 sq.m / 272.00 sq ft Max. speed: 349 km/h / 217 mph Range: 1188 km / 738 miles
During 1928 Curtiss was assigned the task of mating the 600hp Curtiss H-1640 Chieftain 12-cylinder air-cooled radial engine to the P-6 airframe. A USAAC contract was placed for three aircraft which were designated P-11s. In the event, the Chieftain proved unsatisfactory and the P-11 was abandoned (together with the projected Curtiss XP-14 that had been designed around this engine). Two of the airframes that had been ordered in January 1929 were completed as P-6Ds and the third, which was fitted with a 575hp Wright R-1820-9 Cyclone, was assigned the designation YP-20 on delivery in October 1930. It was later fitted with the V-1570 engine of the XP-22, complete with cowling, the cantilever main undercarriage members and three-blade propeller of this aircraft to become the XP-6E.
YP 20 575 hp Wright R 1820 9 Cyclone radial Take-off weight: 1466 kg / 3232 lb Empty weight: 1124 kg / 2478 lb Wingspan: 9.60 m / 31 ft 6 in Length: 7.24 m / 23 ft 9 in Height: 2.79 m / 9 ft 2 in Wing area: 23.41 sq.m / 251.98 sq ft Max. speed: 301 km/h / 187 mph tailwheel
The XP-17 comprised the airframe of the first P-1 mated to the new 480hp Wright V-1460-3 Tornado inverted inline air-cooled engine, and was intended primarily to test the power plant rather than extend the service life of the P-1 design. The conversion was undertaken by the US Army and flight testing was initiated in June 1930.
Engine: 480hp Wright V-1460-3 Tornado Wingspan: 9.63 m / 31 ft 7 in Length: 6.96 m / 22 ft 10 in Height: 2.62 m / 8 ft 7 in Wing area: 23.41 sq.m / 251.98 sq ft Take-off weight: 1358 kg / 2994 lb Empty weight: 1000 kg / 2205 lb Max. speed: 265 km/h / 165 mph
On 18 June 1928, the USAAC placed a contract with Curtiss for one prototype of the XP-10 single-seat fighter powered by a 600hp V-1570-17 Conqueror engine. Of mixed construction with fabric-covered steel-tube fuselage and plywood-covered wooden wings, the XP-10 placed emphasis on aerodynamic cleanliness and utilised surface evaporation wing radiators and a gulled upper wing. Delivered in August 1928, the XP-10 was tested until October 1930, but continuous problems with the cooling system prevented further development.
Engine: 600hp V-1570-17 Conqueror Take-off weight: 1803 kg / 3975 lb Empty weight: 1379 kg / 3040 lb Wingspan: 10.06 m / 33 ft 0 in Length: 7.47 m / 24 ft 6 in Height: 2.64 m / 8 ft 8 in Max. speed: 307 km/h / 191 mph Range: 742 km / 461 miles
In 1931, the third production P-6 (which had been converted to P-6A standard) was withdrawn from service and returned to Curtiss for extensive modification as the XP-22. Retaining the V-1570-23 engine, the XP-22 was cleaned up aero¬dynamically and featured cantilever main undercarriage legs and wheel spats, plus a redesigned engine cowling with, initially, an annular radiator. The radiator was subsequently returned to a position beneath the rear of the engine. On 30 June 1931, the XP-22 demonstrated a level speed of 202.4 mph (326 km/h) and on 10 July a USAAC contract was placed for 45 Y1 P-22s. These were subsequently redesignated as P-6Cs, but prior to the start of production deliveries the designation was to be changed once more to P-6E. By this time the engine of the XP-22, complete with cowling and three-blade propeller, plus the main undercarriage members, had been grafted on to the YP-20 which had thus become the XP-6E while the XP-22 was returned to P-6A configuration.
XP 22 Engine: Curtiss V-1570-23 Conqueror Span, 31 ft 6 in (9,60 m) Length, 23 ft 7 in (7,19 m) Height, 8 ft 10 in (2,69 m). Wing area, 252 sq ft (23,41 sq.m) Empty weight, 2,597 lb (1178 kg) Loaded weight, 3,354 lb (1 521 kg) Max speed, 202 mph (325 km/h) at sea level Max speed: 195 mph (314 km/h) at 10,000 ft (3050 m) Initial climb, 2,400 ft/min (12,19 m/sec)
Installation of the new 600hp Curtiss V-1570-1 Conqueror engine in a P-2 airframe for participation in the September 1927 National Air Race at Spokane led to the application of the designation XP-6 (Curtiss Model 35). The prototype placed second averaging 189 mph. A similarly-powered aircraft utilising a P-1A fuselage, untapered XPW-8A wings and surface radiators in both the top and bottom mainplanes became the XP-6A. A third Conqueror-powered conversion of a P-1C airframe for a New York-Alaska flight, in July 1929, was assigned the designation XP-6B. Although these aircraft were intended purely to prove the Conqueror engine, the success of this power plant prompted a USAAC order for 18 P-6s (as YP 6s) on 3 October 1928, these being powered by the 600hp water-cooled V-1570-17Conqueror.
Although generally similar to the P-1 in construction, they embodied extensively revised fuselage contours, a deeper fuselage, and were aerodynamically cleaner. Deliveries commenced in October 1929, but with the 11th aircraft Prestone (ethylene glycol) cooling was introduced, the designation changing to P-6A. The V-1570-23 engine in the P-6A had a similar rating to that of the -17 that it supplanted; armament remained unchanged at two 7.62mm guns. In service, eight of the Army Air Corps P-6s were brought up to P-6A standards. Eight additional P-6s were delivered to the Netherlands East Indies and one to Japan under the export designation Hawk I. Subsequent to being converted as a P-6A, the first production P-6 was fitted with a side-mounted turbo-supercharger on its V-1570-23 engine as the XP-6D, and, in 1932, 10 P-6As were fitted with F-2F superchargers as P-6Ds. In addition, two aircraft originally ordered as P-11s (P-6 airframes with the unsatisfactory 600hp Curtiss H-1640 Chieftain engine) were completed as P-6Ds. The P-6D was 122kg heavier than the P-6A and featured a three-bladed propeller, and its performance included max speeds of 306km/h at 3050m and 317km/h at 3960m, service ceiling being 9755m.
Of three P 11s ordered, two were completed as P 6s as the intended engine (Curtiss Chieftain) was found unsuitable; the third became the YP 20 with a 575 hp Wright R 1820 9 Cyclone radial engine. Modifica-tions to all three included a new control system, a tailwheel instead of a skid, spats on the main wheels, and more fin and less rudder area. The XP 22 was a P 6A, retaining the Conqueror engine but having a modified nose and radiator, single strut main undercarriage legs and revised tail unit. Forty six of these, ordered as YIP 22s, were completed as P-6Es; 45 were delivered in late 1931/early 1932, the remaining aircraft becoming the XP 23.
P-6E Hawk
The Army Hawks engendered a bewilder¬ing assortment of experimental conversions, reconversions and redesignations, but the mainstream production models were the P 1, P 2, P 3, P 5 and P 6 fighter series. When the V-1570-23 engine of the XP-22, complete with three-blade propeller and the cowling, plus the cantilever main undercarriage members of the XP-22 were grafted on the YP¬20 airframe in the autumn of 1931, the result was designated XP-6E. The 45 Y1P-22s ordered during the previous July and which were briefly to be referred to as P-6Cs, being designated as P-6Es by the time deliveries began on 2 December 1931. Powered by the same 600 hp Curtiss V-1570-23 Conqueror engine, the P-6E carried an armament of two 03-in (7,62-mm) Browning machine guns and 17 surviving examples were eventually assigned to ground schools during the summer of 1939. In the spring of 1932, the XP-6E was returned to Curtiss for a turbo-supercharged V¬1570-55 engine of 675 hp, a fully-enclosed cockpit with aft¬sliding canopy being fitted at the same time and the designation being changed to XP-6F. This attained 225 mph (362 km h) at 18,000 ft (5485 m) during tests. One P-6E was temporarily assigned the designation XP-6G while being used as a test-bed for the V-1570-51 (F-series) engine, while the first production P-6E was also fitted with this engine and experimental wing armament as the XP-6H. The wing armament comprised two 0.3-in (7,62-mm) guns in both the upper and lower wings, these firing outside the propeller disc and augmenting the twin synchronised fuselage guns. Armament on all biplane Hawks was the same: two 0.30 in (7.62 mm) Browning machine guns in the decking above the engine. (The only exception was the XP 6H, to which were added two 0.30 in (7.62 mm) guns in the upper wing and two in the lower wings.) Provision existed for the carriage of bombs beneath the fuselage Total Hawk production for the USAAC was 243 aircraft; in addition, eight P 6s were sold to the Dutch East Indies and one P 6, for evaluation, to Mitsubishi in Japan. Also exported were several ‘Cuban Hawks’, powered by 450 hp Pratt & Whitney R 1340 radial engines.
P-6 Engine: 600hp Curtiss V-1570-17 Conqueror Armament: two 7.62mm guns
P-6A Engine: Curtiss V-1570-23 Conqueror Wingspan: 9.60 m / 31 ft 6 in Length: 7.19 m / 23 ft 7 in Height: 2.62 m / 8 ft 7 in Wing area: 23.41 sq.m / 251.98 sq ft Take-off weight: 1439 kg / 3172 lb Empty weight: 1083 kg / 2388 lb Max. speed: 286 km/h / 178 mph Armament: two 7.62mm guns.
P-6D Engine: Curtiss V-1570-23 Conqueror F-2F supercharged Propeller: three-blade Wingspan: 9.60 m / 31 ft 6 in Length: 7.19 m / 23 ft 7 in Height: 2.62 m / 8 ft 7 in Wing area: 23.41 sq.m / 251.98 sq ft Max speed: 306km/h at 3050m Max speed: 317km/h at 3960m Service ceiling: 9755m Armament: two 7.62mm guns.
P-6E Engine: one 600 hp (447 kW) Curtiss V-1570-23 Conqueror Span: 31 ft 6 in (9,60 m). Length: 23 ft 2 in (7,06 m). Height: 8 ft 10 in (2,69 m). Wing area: 252 sq ft (23,41 sq.m) Empty weight: 2,699 lb (1 224 kg). Loaded weight: 3,436 lb (1 558 kg). Max speed: 193 mph (311 km/h) at sea level Max speed: 180 mph (290 km h) at 15,000 ft (4570 m) Cruising speed: 145 kts / 269 kph Service ceiling: 26263 ft / 8005 m Initial climb: 2,460 ft/min (12,49 m sec) Normal range: 285 mls (458 km). Armament: 2x MG .30 cal. (7,5mm) Crew: 1
The fourth production F11C-2 Goshawk was completed with manually-operated retractable main undercarriage members accommodated by a deepened forward fuselage. It was powered by an R-1820-80 Cyclone rated at 700hp at 2440m, and was delivered to the US Navy on 27 May 1933 as the XF11C-3. Twenty-seven production models were ordered as F11C-3s with raised aft turtle decks, partial canopies and the metal wings that had proved satisfactory on the XF11C-1. Prior to the commencement of deliveries on 7 October 1934, the designation was changed to BF2C-1. The BF2C-1 carried an armament of two 7.62mm Brownings and made provision for a single 215kg bomb or up to four 53kg bombs. An R-1820-04 Cyclone rated at 770hp for takeoff was fitted. At cruising rpm the Cyclone set up a sympathetic vibration with the metal wing structure, the aircraft shaking dramatically in this regime, and, the problem never being satisfactorily resolved, the BF2C-1s were withdrawn within a few months.
Hawk III
The export version of the BF2C-1, the Hawk III, differed from the US Navy fighter-bomber in reverting to the wooden wing structure of the F11C-2 (spruce beams with plywood webs and spruce ribs) and in having a Wright SR-1820F-53 Cyclone offering 785hp for take-off and 745hp at 2925m. Gun armament comprised two synchronised 7.62mm weapons. The first export of the Hawk III was a single example to Turkey delivered in April 1935, supply of 24 to Thailand following from August 1935. In early 1935 an order was placed by Thailand for 24 Hawk III and a manufacturing licence was also purchased. The first 12 were shipped in August and the remaining 12 in late 1935. They were locally designated ‘fighter Type 10’. In March 1936, the first of a total of 102 Hawk IIIs was delivered to China, 90 of these being assembled by the Central Aircraft Manufacturing Company (CAMCO) at Hangchow. One other purchaser of the Hawk III was Argentina, which took delivery of 10 from May 1936. Argentina also purchased the sole example of the Hawk IV in July 1936, this using a Hawk III airframe with a full sliding cockpit canopy, carburettor heating and an exhaust collector ring for the SR-1820F-56 Cyclone, which delivered its maximum 745hp at 3810m. The Hawk IV attained 399km/h at 3810m and 390km/h at 5000m.
Hawk IV
BF2C-1 / F11C-3 Engine: Wright R-1820-80 Cyclone, 700hp at 2440m Take-off weight: 2066 kg Empty weight: 1529 kg / 3371 lb Wingspan: 9.60 m / 31 ft 6 in Length: 7.01 m / 22 ft 12 in Height: 3.30 m / 10 ft 10 in Wing area: 24.34 sq.m / 261.99 sq ft Max. speed: 362 km/h / 225 mph Range: 917 km / 570 miles
Hawk III Engine: Wright SR-1820F-56 Cyclone, 745hp at 3810m Take-off weight: 1958 kg Empty weight: 1457 kg / 3212 lb Wingspan: 9.60 m / 31 ft 6 in Length: 7.14 m / 23 ft 5 in Height: 2.98 m / 9 ft 9 in Wing area: 24.34 sq.m / 261.99 sq ft Max. speed: 325 km/h / 202 mph Range: 925 km / 575 miles
Hawk IV Engine: Wright SR-1820F-56 Cyclone, 745hp at 3810m Wingspan: 9.60 m / 31 ft 6 in Length: 7.14 m / 23 ft 5 in Height: 2.98 m / 9 ft 9 in Wing area: 24.34 sq.m / 261.99 sq ft Max speed 3810m: 399km/h Max speed 5000m: 390km/h
