When the XP-40 (Model 81) prototype was still undergoing trials back in 1939, a team of engineers at Curtiss-Wright Corporation, Airplane Division led by Donovan Berlin were already working on its successor – the XP-46 (Model 86) fighter design.
Although smaller than the P-40, the new aircraft was to receive a more powerful Allison V-1710 series F engine, better armament and stronger armor protection. It would also have a much improved performance compared to its predecessor. US Army Air Corps (USAAC) command showed a keen interest in the proposed design and in September 1939 placed an order for two XP-46 prototypes. In early 1940 the XP-46 project was temporarily put on the back burner due to intensive preparations for the launch of the P-40 production. As a result the Curtiss management submitted a proposal to develop an improved version of the P-40 that would incorporate only some of the XP-46 design features. That way the new aircraft would be available sooner and its production would require significantly less effort than launching a completely new design. With the war raging across Europe it was not long before the improved P-40 became a hot commodity: France and Great Britain placed orders for several hundred examples as early as May 1940. A month later USAAC also accepted Curtiss bid and terminated the XP-46 program to focus on the development of the improved P-40.
The new aircraft was officially designated Model 87. It was powered by a V-1710-39 (F3R) powerplant equipped with a single stage, single speed supercharger and delivering 1,150 hp. The engine was only 26 lb (12 kg) heavier than the C series powerplants, but it was also shorter and taller than the previous units. Additionally, the engine’s shaft ran 6 in (150 mm) higher, which meant the engine mount and cowling had to be completely redesigned. The carburetor air scoop on top of the engine was also modified: it now featured a flatter, rounded shape. The radiator air intake under the engine was enlarged and lengthened which brought its front edge closer to the propeller. The air splitters inside the intake duct were also reshaped.
The new engine left no room under the cowl for the installation of nose guns, so the aircraft’s internal armament fit consisted solely of wing-mounted weapons: a pair of Browning M-2 .50 cal (12.7 mm) machine guns installed in each wing with a supply of 615 rounds of ammunition per pair. The guns were mounted deeper inside the wing, so their barrels did not protrude from the leading edge as much as in the previous version of the fighter. Although there was a provision for additional installation of 20 mm cannons, the weapons were never installed. As some extra space became available after removal of nose-mounted guns, the oil tank was moved from its original location in the rear section of the fuselage and placed between the engine bay and the cockpit. The instrument panel also benefited from the lack of nose guns and it now featured a full, semicircular shape (unlike the inverted T-shaped panel in the previous models).
Due to extensively redesigned nose section the new aircraft was 7 in (17 cm) shorter and measured 31 ft 2 in (9.50 m) instead of 31 ft 9 in (9.67 m). The mid and rear fuselage sections also saw major redesign: the “hump” behind the cockpit was lowered and a completely new canopy design was introduced. The windshield section featured an integral armored glass panel separated by metal frames from bubble-shaped side panels. The sliding canopy section was also redesigned compared to the earlier models. The aft transparencies behind the cockpit were enlarged. The aircraft was equipped with a new N-2A gun sight, later superseded by the N-3A model. Gone was the characteristic rectangular gun sight reflector glass attached to the inside of the windshield on the previous models. Internal fuel load was reduced by as much as 32 gal. (121 l) compared to the P-40 version, but the fuel tanks featured self-sealing liners (P-40B had a similar fuel tank design). To compensate for the reduced internal fuel capacity, the aircraft had a provision for the installation of an external 52 gal. (197 l) drop tank under the fuselage. Alternatively, a 500 lb (227 kg) bomb could be carried on the centerline hardpoint, although neither drop tank pylons, nor bomb racks were provided as standard factory fit. The aircraft featured improved cockpit and pilot seat armor protection.
The redesigned fighter not only looked different (only the wing and the tail assembly remained unchanged), but also gained some weight: its empty weight was now 6,208 lb (2,816 kg) and loaded weight went up to 7,740 lb (3,511 kg). Despite a stronger powerplant the aircraft performance suffered in almost every respect – compared to the P-40 it had a lower top speed, initial climb rate, service ceiling and a shorter range.
The new fighter became an instant hit with the British, who ordered the new design right off the drawing board in May 1940. In British service the fighter would receive Kittyhawk Mk I designation (factory designation H-87A-21). Altogether 560 aircraft were built for the RAF (serial numbers AK571 to AK999 and AL100 to AL230) and delivered between August and December 1941. Only the first twenty examples (AK571 to AK590) carried four wing-mounted weapons – the remaining aircraft were armed with six machine guns. The first Kittyhawk Mk I (AK 571) was flight tested on May 22, 1941. The RAF handed over 72 Kittyhawk Mk Is to the Canadians, one ended up in Australia as a training airframe and 24 examples were delivered to Turkey.
USAAC did not order the new fighter until September 13, 1940. The aircraft received P-40D service designation (factory designation Model 87A). Initially 323 aircraft were ordered (plus one slightly modified Model 87B example), but eventually USAAF2 took delivery of only 22 machines in July 1941 (s/n 40-359 and 40-361 to 40-3813) in favor of the P-40E version. The P-40D model had a very short career in USAAF service: in October 1942 all remaining examples were withdrawn from line units and sent to training squadrons with a new RP-40D designation (the letter R stood for “restricted from combat use”).
Simultaneously with the development of Model 87A Curtiss engineers were working on its sister design, Model 87B. The principal difference between the two was the weapons fit: Model 87B features six wing-mounted .50 cal (12.7 mm) machine guns, which was to most of the RAF Kittyhawk Mk I configuration. The ammunition supply was 240 rounds for each inside gun, 291 rounds for each middle gun and 312 rounds for each outside weapon4. The installation of additional weapons meant that gun bay access panels under the wings had to be enlarged. By the same token the option for internal 20 mm cannon was no longer available. The aircraft was factory configured to accept underwing Q-2 bomb racks, each capable of carrying three light fragmentation bombs – 20 lb (9 kg) M42, or 30 lb (13.6 kg) M5. The area just behind pilot’s headrest received additional armor protection. All those modifications further inflated the aircraft’s weight (loaded weight went up to 8,280 lb [3,756 kg]) and degraded its performance in terms of service ceiling, range and rate of climb. However, production machines had slightly higher top speed performance due in part to new “fishtail” exhaust stack design.
The first example of the new version, USAAC designation P-40E (s/n 40-358), was ordered at the same time as the production P-40D aircraft. On February 18, 1941 a decision was made to deliver the remaining 300 machines from the original P-40D order upgraded to the P-40E standard (s/n 40-382 to 40-681). At the same time the USAAC ordered additional 519 P-40E models (s/n 41-5305 to 41-5744 and 41-13521 to 41-13599). Several further modifications were introduced during the production run. Beginning with s/n 40-480 a new, twin-layer windshield was installed with hot air circulation between the layers. The true self-sealing tanks (similar to the ones in the P-40C model) were installed beginning with s/n 40-584. Finally, beginning with s/n 41-5521, the original SCR-283 VHF radio was replaced with an SCR-274 or an SCR-522A unit.
Eventually 820 P-40Es (Model 87B-2) were delivered to the U.S. units. The P-40E became the first P-40 variant to be mass-produced for the USAAF. The deliveries began in August 1941 and were completed by May 1942. Only four Pursuit Squadrons received the new fighters before the U.S. entered the war: two from the Philippines-based 24th Pursuit Group (3rd PS at Iba and 17th PS at Nichols Field), 21st PS from 35th PG (also deployed to the Philippines) and 79th PS from 20th PG based at Hamilton Field, California. Two P-40E examples were later converted into trainers by adding a second cockpit with an independent sliding canopy in place of the fuselage fuel tank. The aircraft (one of them was s/n 40-582) were redesignated TP-40E5.
Once again, the British were very much interested in the acquisition of the new P-40 model and the RAF promptly placed an order for 1,500 fighters (RAF serials ET100 to ET999 and EV100 to EV699). Since the aircraft were ordered and paid for by the U.S. Government and delivered to Great Britain under the provisions of the Lend-Lease Act, they were also given USAAF serial numbers: 41-24776 to 41-25195 and 41-35874 to 41-36953. In RAF service they were known as Kittyhawk Mk IA (to distinguish them from almost identical Mk I fighters), while USAAF machines received the P-40E-16 designation (factory designation H-87A-47). The deliveries took place between December 1941 and June 1942.
Kittyhawk Mk IAs differed from American P-40Es in some configuration details: they featured a rear view mirror mounted externally on the windshield frame (left of the centerline), a provision for a traditional ring-and-bead gun sight in front of the windshield and the lack of bleed air heating installation of the carburetor air scoop assembly. U.S. Q-2 bomb racks were replaced with two British units, each capable of carrying five 25 lb (11.3 kg) fragmentation bombs. Most of the fighters delivered to Great Britain had factory-installed centerline pylon. Majority of the aircraft from the first delivery batch (s/n 41-24776 to 41-25195 and 41-35874 to 41-36353, RAF serials ET100 to ET999) retained their blue formation lights on the fuselage. Furthermore, the first 400 or so machines delivered to the RAF featured a British style pitot tube and the gun camera housed in a pod under the starboard wing (similar to the P-40D and Kittyhawk Mk I), while the remaining machines had a straight, U.S. style pitot tube and the gun camera located in the forward part of the starboard landing gear fairing (as in the P-40E). The last 200 examples of P-40E-1 (s/n 41-36754 to 41-36953, RAF serial EV500 to EV699) featured manual gun charging and a provision for an antenna mast installation. Late production P-40E-1s were additionally equipped with a slightly enlarged vertical stabilizer with a small dorsal fin at its root, a design feature common to the P-40K-1 and K-5 versions. That particular vertical stabilizer design feature was to improve lateral stability that was somewhat worse than in the P-40 and P-40B/C models.
RAF Kittyhawks saw service mainly in the MTO8, i.e. North Africa, Middle East and, later, in Italy and in the Balkans. Several Commonwealth units in the MTO also operated the type, e.g. No. 3 and 450 Sqn RAAF, or No. 2, 4, 5 and 11 Sqn SAAF. The aircraft may have been inferior to the modern fighter types flown by the Axis pilots, but they fared well in the fighter-attack role due to their sturdy design, respectable range and good armament fit. Over 1,000 P-40E/E-1 aircraft were delivered to other allied nations, both directly from the USA or through RAF: 163 examples were delivered to Australia, 62 to New Zealand, 57 to China (in fact the aircraft went to American Volunteer Group, which became 23rd Fighter Group, USAAF in July 1942), 12 to Canada, 6 to Brazil, 22 to South Africa and 691 to the Soviet Union. As an interesting side note, a dozen or so captured P-40Es were flown by the Imperial Japanese Army Air Force. After the U.S. entered the war some of the P-40E-1s earmarked for Great Britain were pressed into USAAF service.
Between 1941 and 1942 a high altitude P-40J version was briefly contemplated. The aircraft was to be a modification of a basic P-40E with a turbosupercharged engine. The idea was discarded in May 1942.
P-40D/E was a cantilevered, low wing, all metal semi-monocoque design with fabric covered control surfaces. It featured a three-spar tapered wing with rounded wingtips. The wing was equipped with conventional ailerons and split flaps. Port and starboard wing sections were mated prior to fitting to the fuselage structure. The wing featured a +6° dihedral along the span, the leading edge was swept back at 1°18’, wing incidence angle was +1°. The NACA 2215 airfoil was used at the wing root, changing to NACA 2209 at the wing tips. The maximum flap extension was 45°; the ailerons moved 18°45’ upwards and 10°30’ downwards. The trailing edge flaps had a span of 10 ft 2 in (3.1 m) and the ailerons spanned 6 ft 11 in (2.12 m). The cantilevered taiplane was of a conventional design. Vertical stabilizer was offset to the left at 1°30’ in relation to the fuselage centerline. The rudder movement was 30° each way. The rudder height was 6 ft 3 in (1.89 m). Horizontal stabilizers had an angle of incidence of +2° and spanned 12 ft 10 in (3.90 m). Elevators moved 30° up and 20° down. Rudder and elevators were equipped with trim tabs. Rudder trim tab moved 15° each way, while elevator tabs moved 30° up and 26° down.
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