Curtiss P-36 to P-42
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 “provide the ultimate in performance, stability, maneuverability, controllability and maintenance, and ... a structure which would lend itself to quantity production.”
When the design was first offered to the Army on May 24, 1935, three different power plants were proposed, and the prototype actually experienced four engine changes within a year’s testing. For the generous 236-square-foot area wing, a new NACA 2300-series airfoil was chosen, with less drag than the Clark CHY profile used by Seversky. Using a unique retractable landing gear whose wheels rotated as they folded back flat within the wings, the Model 75 had a 700-hp Wright XR-1510-C5 when test pilot H. Lloyd Child made the first flight on May 13, 1935.
Top speed was estimated as a modest 253-mph at 10,000 feet, but this experimental radial engine was replaced in July by a 775-hp Wright XR-1670-5, which promised 263 mph. Neither of these power plants was accepted for Air Corps production, so another air-cooled radial, the 750-hp Pratt & Whitney R-1535 adopted by the Army for attack and observation planes, powered the Curtiss Model 75 when it appeared on August 7 for the Army competition.
The larger Wright R-1820 on Seversky’s entry gave it an advantage in speed. When Curtiss complained, the Secretary of War set back the contract competition to April 15, 1936. Don Berlin’s Hawk was flown again as Model 75B on April 4, 1936, powered by an 850-hp single-row Wright XR-1820-G5 Cyclone, and with indentations behind the cockpit to help visibility. Curtiss estimated the top speed of their Hawk as 294 mph with the Cyclone, or 297 mph if provided with a Twin Wasp, but only 285 mph was actually obtained during the tests.
Although Seversky won the Fiscal 1936 contract, Curtiss did get an order on August 7, 1936, for three Y1P-36s. The first Y1P-36, was delivered to Wright Field with a twin-row Pratt & Whitney R-1830-13 and Hamilton propeller on March 4, 1937, and was soon followed by its two service test companions. The gear-driven supercharger built into the back of the R-1830-13 yielded 1,050-hp for takeoff and 900-hp at 12,000 feet with 92-octane fuel, giving the Y1P-36 a top speed of 295 mph.
Fiscal 1938 funds would allow purchase of about 220 new pursuits, so both companies tried again with bids opened April 2, 1937. Specification 98-605 called for 300-mph and deleted the old bomb rack requirement; the Air Corps then didn’t want its fighters diverted to ground- attack work.
Seversky offered its AP-1 at $15,900 each, while Curtiss wanted $18,720 for its P-36. This time the lowest bidder lost. Curtiss won the largest fighter contract since 1918: for 210 P-36s on July 30, 1937.
The first production P-36A was flown April 20, 1938, using the same Twin Wasp as the Y1P-36, but with a Curtiss propeller, and a new cowl with cooling flaps and blast tubes for the usual two nose guns. When the fourth P-36A, 38-4, was delivered on September 12, it had a new R-1830-17 with a carburetor for 100-octane fuel. These engines were standardized, beginning with the 15th P-36A. They delivered 1,050 hp at altitude, improving performance, so the P-36A did 313 mph at 8,500 feet. (P-36A 38-4 was flown back on October 26 to Buffalo, where it would be converted to the XP-42.)
The 20th Hawk was accepted on November 4 and designated P-36B with an R-1830-25 giving 1,100-hp at takeoff and 950-hp at 14,300 feet. Top speed was 327-mph at 17,000 feet. After a decision not to produce more of this engine model, the plane reverted to the standard P-36A power plant.
Two guns in the nose had armed American single-seat fighters in 1918, and still did twenty years later. Curtiss P-36A Hawks of 1938 had a .30-caliber Browning on the left side of the engine cowl with 500 rpg and another on the right side that could be replaced by a .50-caliber gun with 200 rpg. No bomb racks were used on any Army P-36s.
Not until September 12, 1938, was the Curtiss proposal to add two .30-caliber guns in the wings accepted, and the 85th aircraft was delivered as a P-36C on December 2. These wing guns were also authorized on December 9 for the last 30 contract aircraft. Retainer boxes were added under the P-36C wing guns to prevent used cartridges from damaging other aircraft. These P-36Cs were delivered to the 27th Pursuit Squadron at Selfridge from April 4 to May 5, 1939.
The Curtiss fighter was a “much better flying plane than the P-35” wrote Colonel Charles Lindbergh in 1939, and other pilots usually agreed. Air Corps pursuit strength then consisted of the 1st Group (with one squadron each of P-35, P-36A, and P-36C fighters and a large reserve of the former), and the 8th and 20th Groups with P-36As.
At last Air Corps pilots had a plus 300-mph fighter, but this speed was surpassed abroad. In June 1936, the same month the Army ordered 77 P-35s, the Royal Air Force had ordered 600 Hurricane and 310 Spitfire fighters with eight guns. Hurricanes entered service in December 1937 with a 320-mph speed and the 362-mph Spitfire joined a squadron in August 1938. Their streamlined nose enclosing Rolls-Royce inline engines contrasted with the built-in drag of the Wasp radials.