The P-1 Hawk (Curtiss Model 34) was a 1920s open-cockpit biplane fighter aircraft of the United States Army Air Corps. An earlier variant of the same aircraft had been designated PW-8 prior to 1925.[1]
The Curtiss P-1 Hawk was the first US Army Air Service aircraft to be assigned the "P" (Pursuit) designation which replaced seven designations for pursuit aircraft, including "PW" (for "Pursuit, Water-cooled engine"). The P-1 was the production version of the Curtiss XPW-8B, an improved variant of the PW-8, 25 of which were operational with the Air Service's 17th Pursuit Squadron
In September 1923, the Army ordered production of the PW-8. The PW-8 (Curtiss Model 33) had been developed from the R-6 racer and was acquired by the Air Service after a competition with the Boeing Model 15, designated the PW-9, to replace the existing Army fighter, the Boeing MB-3A. Although the PW-8 was faster than the PW-9 (both having top speeds in excess of 165 mph), it was otherwise outperformed by the Boeing plane, and its surface radiator cooling system, mounted on the upper and lower surfaces of the top wing for streamlining, was more difficult to maintain and vulnerable in combat. However, the Assistant Chief of the Air Service, Brigadier General Billy Mitchell, agreed to purchase 25 PW-8s in return for assistance by Curtiss in making the Dawn-to-dusk transcontinental flight across the United States.
The prototype of the P-1, the XPW-8B, came about when the Air Service, which had selected the Boeing PW-9 over the PW-8 as its main production fighter, asked Curtiss to modify the last of its three original XPW-8 prototypes with wings resembling those of the PW-9. Curtiss designated the modified aircraft its Model 34A and returned it to the Air Service for evaluation, from which the service ordered it into production as the P-1. The first production P-1, serial number 25-410, was delivered on August 17, 1925, and was followed in successive years by the P-1B and P-1C variants with improved engines. The newest P-1 variants remained in operational service until 1930.
The March 7, 1925 order for the P-1 also requested five aircraft with the more powerful 500 hp (373 kW) Curtiss V-1400 engine installed. These were completed in January 1926. The first (SN 25-420) was then modified with a turbocharger mounted on the right side of the fuselage nose, and whose turbine was driven by engine exhaust; the craft was designated XP-2.[2]
However, the Curtiss V-1400 engine did not perform up to expectations, with or without the supercharger, and so after a year in service, three of the standard P-2 Hawks had their engines replaced with the Curtiss D-12 and were consequently redesignated as P-1s. The fifth machine (25-243) received a Curtiss V-1570 Conqueror engine and became the XP-6.[2]
93 production P-1s were brought into service in the P-1, P-1A, P-1B, and P-1C variants. 52 other P-1s, variants P-1D, P-1E, and P-1F, were made by conversion of other Hawk variants, primarily AT-4 and AT-5 trainers.
The P-3 Hawk was similar to the P-1 Hawk but with a radial R-1340-3 Wasp radial engine. The first of the type, designated XP-3A, was the last P-1A (serial 26-300). Originally intended to be powered by a 390 hp (291 kW) Curtiss R-1454, the engine was deemed unsatisfactory and the 410 hp (306 kW) Pratt & Whitney R-1340 engine substituted. A second XP-3A (serial 28-189) included a cowling and spinner to reduce the drag due to the radial engine; entered in the National Air Races of 1929, its speed of 186.84 mph (300.69 km/h) gave it second place in the Thompson Trophy race.[2]
The remaining four aircraft were production P-3As, but primarily used to service test the Pratt & Whitney Wasp engine. In addition to the significant increase in drag, the radial engine also interfered with the pilot's view. Addition of a Townend ring cowling worsened the visibility problem, and had only a limited effect on speed.[2] It was also tested with various types of deep-chord NACA cowls.
Two of the XP-3A aircraft were re-engined in 1929 and 1930 with the Pratt & Whitney R-985-1 Wasp Junior engine. This aircraft was redesignated the XP-21. Tests were run with this aircraft, but it was never developed into a production aircraft, despite the designation.
Five P-5 Superhawks, similar to the P-1C but with a turbocharged Curtiss D-12F engine, were delivered in 1928. They had a top speed of 166 mph (267 km/h) at 25,000 ft (7,620 m), considerably higher than the maximum ceiling of the P-1A, but their low-level performance was inferior[3]
Two single-seat advanced trainer variants were placed into production, the AT-4 and AT-5A, using Wright-Hisso E / Wright-Hisso V-720 V-8 engines. The resulting performance degradation from these lower powered engines resulted in them being deemed dangerous to fly, even for experienced pilots. All were re-engined with Curtiss D-12D engines and returned to use as fighters, designated P-1D and P-1F respectively. Five AT-4/XAT-5 test variants were re-classified as P-1E.
A total of 202 PW-8, P-1, P-2, P-3, P-4, P-5, AT-4, and AT-5 airplanes were delivered.
On June 23, 1924, taking off at 3:58 A.M., Army test pilot First Lieutenant Russell Maughan left Mitchel Field, New York, in PW-8 24-204, modified with additional fuel and oil tanks, made a dawn-to-dusk transcontinental flight across the US.[4] Refueling five times, he landed at Crissy Field, San Francisco, California, at 9:46 p.m., one minute before dusk, covering 2,670 mi (4,297 km) in 20 hours and 48 minutes. His flight time included four planned 30-minute stops at McCook Field, Ohio; Saint Joseph, Missouri; Cheyenne, Wyoming; and Salduro Siding, Utah; and an unplanned stop in North Platte, Nebraska for additional fuel when a muddy field in Missouri did not permit him to take on a full load.[5] He also lost an hour at McCook to repair a broken fuel valve after an over-eager mechanic had over-torqued the valve, damaging it.
The original fifteen P-1s served in the 27th and 94th Pursuit Squadrons, 1st Pursuit Group, Selfridge Field, Michigan. The first Hawk to serve with the Air Corps in quantity was the P-1A (17th, 27th, and 94th Pursuit Squadrons) beginning in 1925. In October 1928 the largest order of 33 P-1s was made. These were delivered by April 1929 as P-1Cs.
The AT-4 and AT-5 trainer variants served with the 43rd Pursuit Squadron (School) at Kelly Field, Texas.
While a total of 202 Hawks were built in the basic variants PW-8, P-1, P-2, P-3, P-5, AT-4 and AT-5, conversions resulted in 148 having a P-1 designation.
All variants increased in weight with each succeeding model, resulting in slight reductions in performance with each.