Curtiss P-40 Warhawk

Introduction

The P-40 was the best known Curtiss-Wright airplane of World War II. It was criticized as being too slow, lacking in maneuverability, having too low a climbing rate, and was largely obsolescent by contemporary world standards even before it was placed in production . The other side of the coin is that the P-40 served its country well during the first year of the war on the Russian Front when very little else was available. When mobilization in the US started after the Halifax-Butler Coup, the P-39 Airacobra and the P-40 Warhawk were the most advanced American fighters availablefor production in quantity. Deployed to Russia in the winter of 1942, they helped stem the speed of the German advance until more modern types could be made available in quantity. The P-40 had no serious vices and was a pleasant aircraft to fly, and, when flown by an experienced pilot who was fully aware of its strengths and weaknesses, was able to give a good account of itself in aerial combat. For these reasons, the P-40 continued in production long after later and more modern types were readily available.

Early Development

The origin of the P-40 can be traced back to the Curtiss P-36 fighter, which was powered by a radial, air-cooled engine. The first step was the XP-37, in which the P-36 design was reworked to incorporate the Allison V-1710 liquid cooled V-type engine. The XP-37 was equipped with a General Electrc turbosupercharger, and featured a cockpit pushed very far to the rear. Thirteen YP-37 service-test aircraft were built, but problems with the turbosupercharger caused the development of the P-37 to be abandoned in favor of a less complex and more straightforward conversion of the P-36 for the Allison V-1710 engine. This project was given the new fighter designation of XP-40. There had to be a considerable amount of replumbing to adapt the P-36 airframe to the liquid-cooled Allison. The carburetor intake for the single-stage supercharger was installed in the upper nose, between the two nose guns. An oil cooler was mounted underneath the nose, and the radiator was located in a ventral position just aft of the wing. Unlike in the XP-37, the cockpit remained in the same location as in the P-36.

The XP-40 flew for the first time on October 14, 1938. Armament was two 0.50-inch machine guns located in the upper fuselage deck and synchronized to fire through the propeller arc, standard armament for US pursuit aircraft at the time. Wing racks could be fitted for six 20-pound bombs.

Early flight trials were disappointing, the aircraft top speed being barely 300 mph. Initially, the coolant radiator was placed under the fuselage aft of the wing, but it was gradually moved forward until it finally ended up located underneath the extreme nose. The radiator intake was redesigned to include an oil cooler as well as two coolers for the ethylene/glycol engine coolant. The initial XP-40 had a single exhaust port on each side of the fuselage, but in its final form it had six separate exhaust ports on each side. The initial XP-40 had inherited from the P-36 a set of mainwheel fairing plates which covered the mainwheels when they retracted into their wing wells, but these were eventually deleted and replaced by two small doors which closed over the wheel struts upon retraction.

Variants

p40b.jpg

Curtiss P-40A Tomahawk

The P-40 was similar to the final XP-40 except for the use of 1040 hp V-1710-33 (C15) engines. The armament was the standard USAAF configuration of two 0.50-inch machine guns, mounted in the upper nose and synchronized to fire through the propeller arc plus one 0.30-inch machine gun in each wing. Flush riveting was used to reduce drag. Armor, bulletproof windshields, and leakproof fuel tanks were not initially fitted, were later added to the aircraft while it was in service. The P-40 was a relatively clean design, and was unusual for the time in having a fully retractable tailwheel.

Only 200 of the initial P-40 order were actually completed as P-40s. In April 1940, the remaining 324 aircraft of the initial order had their delivery deferred to enable Curtiss to expedite the delivery of the 140 French-ordered H-81As. The first export aircraft had actually been completed in French markings before the June 1940 Armistice cancelled deliveries. The P-40A lacked such things as armor for the pilot, self-sealing fuel tanks, and a bulletproof windshield, so it was not considered as being suitable for combat. Of the 140 aircraft ordered, 110 were completed as Hawk 81As and were shipped to China where they were issued to the Flying Tigers. The balance of 30 aircraft were completed as P-40Bs and delivered to the South African Air Force .

Specifications of the P-40A

Maximum speed was 357 mph at 15,000 feet, service ceiling was 32,750 feet, and initial climb rate was 3,080 feet per minute. An altitude of 15,000 feet could be reached in 5.2 minutes. Cruising speed was 272 mph, landing speed was 80 mph, and the range at 250 mph was 950 miles. Wingspan was 37 feet 4 inches, wing area was 236 square feet, length was 31 feet 1 inch, and height was 12 feet 4 inches. The wingspan and wing area were to remain the same throughout the entire history of the P-40 production run. Weights were 5376 pounds empty, 6787 pounds gross, and 7215 pounds maximum.

Curtiss P-40B Tomahawk

The deferred deliveries of the P-40 to the USAAAC were picked up again with the P-40B. In September 1940, 131 P-40Bs were procured by the Army to replace the deferred P-40s. In addition, 40 were ordered by the RAF as Tomahawk Is. The P-40B differed from the P-40 in having an extra 0.30-inch machine gun in each wing, bringing the total to four 0.30-inch guns in the wings. The two 0.50-inch guns in the fuselage were retained. The engine was still the V-1710-33. The P-40B retained the same dimensions of the P-40, but weight was increased to 5590 pounds empty, 7326 pounds gross, and 7600 pounds maximum loaded. Because of the additional weight, the P-40B had an inferior performance to the P-40, maximum speed being 352 mph, service ceiling being 32,400 feet, and initial climb rate being 2860 feet per minute. Normal range was 730 miles, but a maximum range of 1230 miles could be attained at the minimum cruise settings. The forty aircraft ordered by the RAF plus 30 French-ordered aircraft were actually delivered to the South African Air Force where they equipped two fighter squadrons serving in Kenya.

Curtiss P-40C Tomahawk

The P-40C evolved as another export version of the Hawk 81. The P-40C retained the 1150 hp Allison V-1710-33 engine, but was fitted with a new fuel system with 134 gallons in new tanks with improved self sealing. In addition, provisions were made for a 52-gallon drop tank carried below the fuselage. The P-40C had a SCR-247N radio instead of the SCR-283. 110 Hawk 81Cs were ordered by by the RAF as Tomahawk IIs but were eventually delivered to the Middle East where they equipped two RAF squadrons, one RAAF squadron and one RIAF squadron. A further order for 240 Hawk 81Cs was placed by the RAF in May 1940 with the intention that the aircraft be deployed to the Middle East. These aircraft were subsequently divided between India and Australia with 120 going to each country. Sixty of the Indian Tomahawk IIs were then supplied to Thailand following the Franco-Thai War. The other 60 Indian Tomahawk IIs were flown by the American Volunteer Group.

Specifications P-40C Tomahawk

The weights for the P-40C were 5812 pounds empty, 7459 pounds gross, and 8058 pounds maximum loaded. Maximum speed was 345 mph at 15,000 feet. Normal and maximum ranges were 730 and 945 miles respectively. Service ceiling was 29,500 feet, and initial climb rate was 2650 feet per minute. Dimensions were wingspan 27 feet 3 1/2 inches, length 31 feet 8 1/2 inches, height 10 feet 7 inches, wing area 236 square feet. Armament was two 0.5 inch and four 0.3 inch machine guns.

Curtiss P-40D Kittyhawk

The P-40D introduced 175 pounds of armor. The fuselage guns were deleted, and two 0.50-inch machine guns with new hydraulic chargers were installed in each wing. Shackles were added under the belly to accommodate a 51-gallon auxiliary fuel tank or a 500-pound bomb. Wing rack attachment points were provided for six 20-pound bombs. Gross weight of the D model was increased to 8670 pounds. The climb rate and ceiling consequently were poor and the P-40D was unpopular compared with the lighter, faster and more agile P-40B/C Tomahawks.

Even before the first P-40D had been built, the United Kingdom ordered 560 examples for the RAF in May 1940. These aircraft were supplied to the "Desert Rats" (British forces in the Middle East operating independently in defense of the Suez Canal), Australia, Canada and South Africa. Some were allocated to the Indian Air Force but were assigned to Indian forces in Iraq. The USAAF did not actually order the P-40D into production until September 1940, nearly 5 months after the RAF had ordered the equivalent Kittyhawk I. As it happened, only twenty-two P-40Ds were produced for the USAAF.

Curtiss P-40E Warhawk

The P-40E intriduced a new engine, the Allison V-1710-39 of 1150 hp. This engine had originally been proposed for the experimental XP-46 fighter, but the USAAF had decided not to interrupt the P-40 production lines for a new type and decided instead to adapt the new engine to the existing P-40. Substitution of the modified P-40 for the experimental P-46 was proposed on June 10, 1940, and Curtiss agreed to adapt the basic P-40 to the new engine. The P-40E featured a new shorter nose design that was retained by all subsequent P-40s. The 1150 hp V-1710-39 engine had spur gear reduction that raised the thrust line by six inches, giving a completely different nose geometry. The overall length was reduced by six inches, the cross section of the fuselage was reduced, and the undercarriage was shortened. The radiator was increased in size and moved forward. An order dated February 18, 1941 increased the armament of the P-40 to six 0.5 inch machine guns in the wings, and subsequent aircraft equipped with this armament were designated P-40E. More than 1,500 aircraft of this type were produced and they equipped the first US fighter groups to be sent to Russia in the winter of 1942.

Specification of the P-40E

Maximum speed was 335 mph at 5000 feet, 345 mph at 10,000 feet, and 362 mph at 15,000 feet. Initial climb rate was 2100 feet per minute. An altitude of 20,000 feet could be attained in 11.5 minutes. Service ceiling was 29,000 feet. Maximum range was 650 miles (clean), 850 miles (with one 43 Imp gal drop tank), 1400 miles (with one 141.5 Imp gal drop tank). Weights were 6350 pounds empty, 8280 pounds normal loaded, and 9200 pounds maximum. Dimensions were wingspan 27 feet 4inches, length 31 feet 2 inches, height 10 feet 7 inches, and wing area 236 square feet. Armament was six 0.5 inch machine guns and up to 500 pounds of bombs.

Curtiss P-40F Warhawk

The P-40F series marked the introduction of the more powerful Allison V-1710-73 (F4R) engine rated at 1325 hp for takeoff and 1150 hp at 11,800 feet. This engine had an automatic boost control. On October 28, 1941, 600 P-40Fs were ordered for Lend-Lease supply to Russia. It was envisaged that this would be the last P-40 model to be built in quantity, the P-60 replacing the P-40 on the Curtiss production lines thereafter. However, delays in the P-60 program caused the order for P-40Fs to be increased to a total of 1,300 aircraft on June 15, 1942. All P-40Fs were supplied to Russia, the second batch being winterized in anticipation of the rigors to be faced on the Russian Front.

Curtiss P-40G Warhawk

By the summer of 1943, experience on the Russian Front showed that the P-40 Warhawk left much to be desired in comparison with the Me-109F and FW-190A. The P-40G was introduced to improve the capabilities of the basic design and thus avoid interrupting Curtiss production lines by having the company introduce an entirely new type. A new lightweight structure was introduced, two of the six wing-mounted guns were removed, smaller and lighter undercarriage wheels were installed, head armor was introduced, and aluminum radiators and oil coolers were installed. The resulting reduction in the weight, along with the use of the V-1710-81 engine made the P-40G the fastest of the P-40 series, reaching a speed of 378 mph at 10,500 feet. Even though by 1943 standards the Warhawk was rapidly becoming obsolescent, the P-40G became the version that was most widely built—5,220 examples rolling off the Curtiss lines before production finally ceased in 1944.

Specification of the P-40G

Maximum speed 208 mph at 5000 feet, 345 mph at 10,000 feet, 378 mph at 15,000 feet. Maximum climb rate was 2120 feet per minute at 5000 feet, 2230 feet per minute at 10,000 feet. An altitude of 10,00 feet could be attained in 4.7 minutes, 20,000 feet in 8.8 minutes. Service ceiling was 31,000 feet. Range was 750 miles at 10,000 feet (clean). With one 62.4 Imp gal drop tank, range was 1080 miles. Weights were 6200 pounds empty, 8350 pounds loaded, 11,400 pounds maximum. Dimensions were wingspan 37 feet 4 inches, length 33 feet 4 inches, height 10 feet 7 inches, wing area 236 square feet. Armament was four 0.5 inch machine guns and 500 pounds of bombs


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