Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)
6 May 1935: At Buffalo, New York, the prototype Curtiss-Wright Model 75, X17Y, serial number 11923, made its first flight.
Donovan Reese Berlin. (Niagara Aerospace Museum)
Designed by Donovan Reese Berlin, the airplane was a modern design of all metal construction, with fabric covered control surfaces. The Model 75 was a single-seat, single-engine low-wing monoplane with retractable landing gear.
Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)
In its original configuration, the Model 75 was powered by an air-cooled, supercharged 1,666.860 cubic inch displacement (27.315 liter) Wright Aeronautical Division GR1670A1 two-row 14-cylinder radial engine. The GR1670A1 was a developmental engine with a compression ratio of 6.75:1. It was rated at 775 horsepower at 2,400 r.p.m. at Sea Level, and 830 horsepower at 2,600 horsepower for takeoff, burning 87-octane gasoline. The engine was 3 feet, 9 inches (1.143 meters) in diameter, 4 feet, 4–25/32 inches (1.341 meters) long, and weighed 1,160 pounds (526 kilograms). The GR1670A1 drove a three-bladed Curtiss Electric constant-speed propeller through a 16:11 gear reduction.
The GR1670A1 was also used in the Seversky SEV-S1, NR18Y, a record-setting experimental variant of the rival Seversky P-35.
The United States Department of Commerce, Bureau of Air Commerce, registered X17Y to the Curtiss-Wright Corporation, Kenmore & Vulcan Street, Buffalo, New York, on issued 1 June 1936. This registration was cancelled 26 April 1937.
Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)
The Curtiss-Wright Model 75 would be developed into the P-36 Hawk fighter for the U.S. Army Air Corps. France ordered it as the H75A-1, and in British service, it was known as the Mohawk Mk.I.
The tenth production P-36 was modified with a liquid-cooled Allison V-1710 V-12 engine to become the prototype XP-40.
1st Lieutenant Benjamin Scovill Kelsey in the cockpit of a Curtiss-Wright P-36A Hawk, circa 1938. (U.S. Air Force)1st Lieutenant Benjamin Scovill Kelsey, Air Corps, United States Army, with a Curtiss Wright P-36A Hawk, Air Corps serial number 38-2, at Wright Field, Ohio, circa 1938. (Ray Wagner Collection/San Diego Air & Space Museum Archives)Curtiss-Wright P-36B 38-020. (U.S. Air Force)Curtiss-Wright P-36B 38-020. (U.S. Air Force)Curtiss-Wright P-36C camouflage test, Maxwell Field, 1940. (Ray Wagner Collection, San Diego Air & Space Museum Archives)Curtiss-Wright P-40 Warhawk, 55th Pursuit Squadron, Oakland, CA, 1941 (IWM FRE11437)
Curtiss-Wright’s Chief Test Pilot, H. Lloyd Child, in the cockpit of a P-40 Warhawk, circa 1940. (Rudy Arnold Collection/NASM)
26 April 1939: The United States Army Air Corps placed an order for 524 Curtiss-Wright P-40 Warhawks. This was the largest production order for any U.S.-built fighter since World War I. The total cost was $12,872,398.¹
The order was authorized by the Air Corps Expansion Act, approved by Congress 3 April, and signed by President Roosevelt on 26 April 1939.
The Curtiss-Wright Corporation Hawk 81 (P-40 Warhawk) was a single-seat, single-engine pursuit, designed by Chief Engineer Donovan Reese Berlin. It was developed from Berlin’s radial-engine P-36 Hawk. The P-40 was a low-wing monoplane of all-metal construction and used flush riveting to reduce aerodynamic drag. It had an enclosed cockpit and retractable landing gear (including the tail wheel). Extensive wind tunnel testing at the NACA Langley laboratories refined the airplane’s design, significantly increasing the top speed.
The first production Curtiss-Wright P-40 Warhawk, 39-156. (U.S. Air Force)
The new fighter was 31 feet, 8-9/16 inches (9.666 meters) long with a wingspan of 37 feet, 3½ inches (11.366 meters) and overall height of 9 feet, 7 inches (2.921 meters). The P-40’s empty weight was 5,376 pounds (2,438.5 kilograms) and gross weight was 6,787 pounds (3,078.5 kilograms).
The P-40 was powered by a liquid-cooled, supercharged, 1,710.597-cubic-inch-displacement (28.032 liter) Allison Engineering Co. V-1710-C15 (V-1710-33). This was a single overhead cam (SOHC) 60° V-12 engine designed by Harold Caminez, Allison’s chief engineer. The V-1710-33 had a compression ratio of 6.65:1. It was rated at 930 horsepower at 2,600 r.p.m. at 12,800 feet (3,901 meters), and 1,040 horsepower at 2,800 r.p.m. for takeoff, burning 100-octane gasoline. The engine turned a three-bladed Curtiss Electric constant-speed propeller through a 2:1 gear reduction. The V-1710-33 was 8 feet, 2.54 inches (2.503 meters) long, 3 feet, 5.88 inches (1.064 meters) high, and 2 feet, 5.29 inches (0.744 meters) wide. It weighed 1,340 pounds (607.8 kilograms).
Allison Engineering Co. V-1710-33 V-12 aircraft engine at the Smithsonian Institution National Air and Space Museum Steven F. Udvar-Hazy Center. (NASM)
The cruising speed of the P-40 was 272 miles per hour (438 kilometers per hour) and the maximum speed was 357 miles per hour (575 kilometers per hour) at 15,000 feet (4,572 meters). The Warhawk had a service ceiling of 30,600 feet (9,327 meters) and the absolute ceiling was 31,600 feet (9,632 meters). The range was 950 miles (1,529 kilometers) at 250 miles per hour (402 kilometers per hour).
Captain Charles W. Stark, Jr., 35th Pursuit Squadron, 8th Pursuit Group, climbing from the cockpit of a Curtiss-Wright P-40 Warhawk, 39-188, at Langley, Field, Virginia, 1941. Note the single .30-caliber machine gun visible on the left wing. (Rudy Arnold Collection/NASM)
The fighter (at the time, the Air Corps designated this type as a “pursuit”) was armed with two air-cooled Browning AN-M2 .50-caliber machine guns on the engine cowl, synchronized to fire through the propeller, with 380 rounds of ammunition per gun. Provisions were included for one Browning M2 .30-caliber aircraft machine gun, with 500 rounds of ammunition, in each wing.
The first production P-40 Warhawk, 39-156, made its first flight 4 April 1940. The 8th Pursuit Group at Langley Field, Virginia, was the first Army Air Corps unit to be equipped with the P-40.
Curtiss-Wright P-40 Warhawks of the 8th Pursuit Group at Langley Field, Virginia, 1940. (Unattributed)
After 200 P-40s were produced for the Air Corps, production was interrupted to allow Curtiss-Wright to build 100 Hawk 85A-1 export variants for the French Armée de l’air, then engaged with the invading forces of Nazi Germany. When France surrendered 22 June 1940, none of these airplanes had been delivered. The order was then assumed by the British Royal Air Force as the Tomahawk I.
U.S. Warhawk production resumed as the improved P-40B, and the remainder of the P-40 order was cancelled.
The Curtiss-Wright XP-40 prototype, 36-10, at Langley Field in the original configuration. Compare this to the first production P-40 Warhawk in the photograph below. (NASA)Curtiss-Wright P-40 Warhawk 39-156. (U.S. Air Force)
24 April 1939: Curtiss-Wright’s prototype fighter, the XP-40 (Model 75P), was evaluated by the National Advisory Committee for Aeronautics (NACA) at the Langley Memorial Aeronautical Laboratory, Langley Field, Virginia, in March and April 1939. NACA engineers placed the XP-40 inside the Full-Scale Wind Tunnel, which was capable of accepting airplanes with wing spans of up to 40 feet (12.2 meters).
Compare this production Curtiss-Wright P-36A Hawk to the first production P-40 Warhawk in the photograph below.Curtiss Model 81, P-40 Warhawk, 39-156. (San Diego Air and Space Museum Archive)
The airplane was a production Curtiss P-36A Hawk, serial number 38-10, which had been modified by replacing its original air-cooled Pratt & Whitney Twin Wasp S1C1-G (R-1830-17) 14-cylinder radial engine with a Harold Caminez-designed, liquid-cooled, supercharged, 1,710.597-cubic-inch-displacement (28.032 liter) Allison Engineering Co. V-1710-C13 (V-1710-19).
This was a single overhead cam (SOHC) 60° V-12 engine with four valves per cylinder and a compression ration of 6.65:1. It had a Normal Power rating of 910 horsepower at 2,600 r.p.m. at Sea Level, and 1,060 horsepower at 2,950 r.p.m. for Takeoff. At 10,000 feet (3,048 meters), the V-1710-19 had Maximum Continuous Power rating of 1,000 horsepower at 2,600 r.p.m., and Military Power rating of 1,150 horsepower at 2,950 r.p.m. The engine required 100/130-octane aviation gasoline. It drove a three-bladed Curtiss Electric constant-speed propeller through a 2:1 gear reduction.
The V-1710-19 was 8 feet, 1.75 inches (2.483 meters) long, 3 feet, 4.75″ (1.035 meters) high and 2 feet, 4.94 inches (0.735 meters) wide. It weighed 1,320 pounds (599 kilograms).
Curtiss-Wright XP-40 prototype in the NACA wind tunnel at Langley Field, Virginia, 24 April 1939. The technician at the lower left of the photograph provides scale. (NASA)
The primary benefit of the engine change was the streamlined fuselage that resulted. The new airplane was capable of a speed of 366 miles per hour (589 kilometers per hour), a 53 miles per hour (85 kilometers per hour) increase over the P-36.
Over a two-month period, NACA engineers made a number of improvements. The radiator was moved forward under the engine and the oil coolers utilized the same air scoop. The exhaust manifolds were improved as were the landing gear doors.
When they had finished, Lieutenant Benjamin Scovill Kelsey flew the modified XP-40 back to Curtiss at Buffalo, New York. Its speed had been increased to 354 miles per hour (570 kilometers per hour), a 12% improvement. Other improvements were recommended which may have increased the XP-40’s speed by an additional 18 miles per hour (29 kilometers per hour). By December 1939, the airplane had been further improved and was capable of 366 miles per hour (589 kilometers per hour).
These photographs show the full-size prototype in the NACA wind tunnel at Langley, 24 April 1939. Two days later, the U.S. Army Air Corps ordered 524 airplanes as the P-40 Warhawk. By the time production ended in 1945, 13,738 Warhawks had been built.
Curtiss XP-40 in the NACA full scale wind tunnel, Langley Field, Virginia, April 1939. (NASA)
