Curtiss P-36 to P-42
The first fighter with the new Allison inline engine was the XP-37, actually the original Hawk 75 airframe rebuilt with the liquid-cooled YV-1710-7 in its streamlined nose, side scoops for the radiator and intercooler inside the fuselage, and the pilotís cockpit moved back behind the fuel tank. With an external exhaust-driven F-10 turbosupercharger by General Electric under the engine, 1,000 hp was developed at 20,000 feet, enabling the XP-37 to reach 340-mph at that altitude.
Work began on the prototype, known as Curtiss Model 75, on November 1, 1934. Seeing that engines are the pacing element in aircraft design and development, he planned from the beginning an aircraft large enough in size and wing area for growth in power plants. Berlin wanted to ďprovide the ultimate in performance, stability, maneuverability, controllability and maintenance, and ... a structure which would lend itself to quantity production.Ē
Purchased from Curtiss on February 16, 1937, the XP-37 was damaged when flown to Wright Field on April 20 and had to be repaired and redelivered for its official first flight on July 23. After another accident in 1938, the aircraft was reworked with an 1,150-hp V-1710-11 and B-1 (F-13) supercharger, and again in January 1939 to test the engine arrangement of the YP-37.
Thirteen Curtiss YP-37s were ordered on December 11, 1937, and the first two were delivered on April 29, 1939, to service test their Allison V-1710-21 engine and B-2 supercharger. Ten more were accepted in November and the last was received on December 5, 1939. They could be distinguished by the lengthened fuselage behind the cockpit, a small air scoop on the left side for the intercooler, and a larger scoop on the right side for the engine radiator.
Ten served the 8th Pursuit Group at Langley, which had experience with the supercharged PB-2A, and the 36th Group in 1940. Pilot visibility was poor during landings and the superchargers constantly gave trouble. Since these turbosuperchargers were an American development unequaled in Europe, it was tempting to see them as a kind of magic for high-altitude speed, and the devices were not allowed to be exported before 1941.
But they did have important disadvantages. Turbo≠super≠chargers were heavy, had to be placed outside of the engine cowling to obtain enough cooling, and generated so much heat and pressure that explosions of their rotor blades and in-flight fires were frequent. Prewar models lacked an automatic regulator, so their control was a distraction for already preoccupied fighter pilots. With such problems, designers preferred the simpler gear-driven internal supercharger unless high-altitude speed was absolutely demanded.
Curtiss also tried to improve the air-cooled versions with the Hawk 75R, a private-venture P-36 modification, whose R-1830-19 Wasp had a two-stage internal supercharger and added an auxiliary gear-driven supercharger with external coolers behind the radial. First flown on December 13, 1938, and delivered to Wright Field on January 20, 1939, the complicated power plant proved unsatisfactory and the 75R was returned to the company for further work.
The fourth P-36A returned to Wright Field on March 5, 1939, modified as the XP-42. Reflecting an attempt to give the radial engine the streamlining associated with inline power plants, the XP-42ís R-1830-31 Wasp had an extended propeller shaft enclosed behind a large spinner with an intake for air cooling underneath and paired carburetor air intakes on top. Maximum speed was only 315 mph at first, but a large variety of cowl forms were tested at Langley Field, and by August 1941, 343 mph had been achieved with a short-cowled configuration.
Air Corps concern with its inadequate fighter armament was reflected in an August 23, 1939, contract that produced two P-36A conversions: an XP-36D with two .50-caliber guns in the nose and four .30-caliber wing guns, along with the XP-36E, which had eight .30-caliber guns in the wings, like British fighters. Both were at Wright Field by October, and after tests at the Eglin proving ground, the XP-36Dís armament was chosen for the future XP-46 and P-40B types.
Four Danish 23-mm Madsen guns had been ordered by the Army on May 18, 1937, but tests in 1938 displayed poor reliability and a slow rate of fire. Nevertheless, a September 6, 1939, order converted a P-36A to the XP-36F, which appeared in December with an imported Madsen with 50 rpg attached below each wing, as well as the usual .50-caliber and .30-caliber guns on the cowl.
A sample of the 20-mm Hispano Type 404 gun had been ordered from France on July 27, 1937, and Army tests begun June 21, 1938, demonstrated twice the Madsenís rate of fire. Another 33 were ordered December 14, 1939, and after the first arrived from France in February 1940, a pair replaced the Madsens on the XP-36F. Since their height with the 60-round ammunition drum prevented installation within the wings, large fairings were required. After successful firing tests in July, these 20-mm weapons were ≠chosen for Air Corps production by Bendix in September 1940, but in 1941, this gun was limited to the roomy noses of the P-38 and export models of the P-39.
The 27th Squadronís P-36Cs at Selfridge were transferred to the 1st Pursuit Squadron at the Eglin Field Proving Ground in September 1939. By 1940, the P-36A was being replaced by the P-40. The 8th Pursuit Group passed its P-36As and YP-37s to the 36th Group in 1940 and to the 56th Group in 1941, while the 20th Groupís P-36As went to the 35th at Hamilton Field and then to the 51st at March Field.
Overseas squadrons still used old Boeings until September 1939, when 30 P-36As were flown to the 16th Group in the Panama Canal. Three were lost on that ferry flight. Overseas deployment sent 20 P-36As to Hawaii in October 1939, followed by 31 more flown off the carrier Enterprise on February 21, 1941, a preview of wartime fighter deliveries. There were 39 left at Wheeler Field, with 20 in commission, on December 7, 1941
Twenty P-36As went to Anchorage, Alaska, with the 18th Pursuit Squadron on February 20, 1941. By November 30, 1941, 15 P-36As remained in the Canal Zone with the 16th Group and Puerto Ricoís 36th Group had 16.
Only once did the P-36A fight while carrying U.S. markings. On the morning of December 7, 1941, 14 P-36A and 11 P-40B sorties were flown during the surprise attack on Pearl Harbor. The older Hawks were credited with at least two victories, for one loss to enemy fighters and one to American anti-aircraft fire.
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