P-40D Soon after P-40 production started, Curtiss began development of its intended successor, the
XP-46. This aircraft was based on the P-40, but was an almost entirely different aircraft. While retaining the rear
fuselage of the P-40, the XP-46 had a new wing with wider track landing gear. The nose was redesigned too, as it housed a new 1,150 hp (860 kW) V-1710-39 engine. This "F-series" engine differed from the "C-series" engine of the Model 81 in having a more compact external spur gear-type
reduction gear box. The production version of the P-46 was to have four .30 MGs in each wing and two .50 MGs in the nose for a total of ten guns. This would have been the heaviest armament for a US fighter at the time. Both the USAAF and RAF placed orders for this aircraft, with the latter naming it "Kittyhawk". Due to delays in the P-46 program, the USAAF asked Curtiss to prioritize development of an improved P-40. Curtiss did so, and reworked the P-40 to accommodate the V-1710-39 of the XP-46. The resulting
P-40D (Model 87A) had a shorter nose with a larger radiator, four .50 Brownings in place of the .30 units, a revised windscreen, and provisions for two
20 mm cannons (one in each wing, never used). The nose guns were deleted as there wasn't room for them in the final design. Another problem was that engine and trim management were both somewhat complex and taxing with earlier P-40's required strong rudder pressure to offset engine torque and frequent trim adjustments were needed during rapid speed changes. Both these problems were remedied sometime late in production by enlarging the
vertical stabilizer and changing how the ammunition was stored. P-40's were more a powerful, faster-flying aircraft than the primary and advanced trainers most pre-war and early-war Allied pilots were familiar with, and transition training was often inadequate or neglected altogether in the early years of the war. The landing gear was also more narrow and not as strong as in fixed gear aircraft (like the Gladiator) or on some other retractable gear fighters such as the Hurricane. As a result, novice pilots had a hard time adjusting to the new fighter and there were many accidents on landing and takeoff in the early years of the war, with both Tomahawk and Kittyhawk types. Therefore, two P-40Es were fitted with a second seat to be used as
trainer aircraft under the designation
P-40ES. With these aircraft and improved training techniques these problems subsided.
Sub-variants and modifications •
Prototype P-40E, the second P-40D fitted with a six-gun wing. •
P-40E, 820 aircraft built. Somewhere along the production line flared "fishtail" exhaust stacks appeared, and an unknown number of late production aircraft had larger vertical stabilizers. •
P-40ES, two aircraft modified into two-seat
trainer aircraft. •
P-40EF, a number of P-40Es and Ks modified by the
Soviet Air Force as two seat photo reconnaissance aircraft.
P-40F Another solution to the high altitude performance problem was to fit the P-40 with a supercharged
Rolls-Royce Merlin engine. This idea came from the British, as they noticed that their Allison powered Kittyhawks and
Mustangs had poor performance at high altitudes, while their own Merlin powered
Hurricanes and
Spitfires did not have the same problems. Curtiss fitted the second P-40D with a 1,300 hp (969 kW) Merlin 28. Production aircraft had the American-made 1,390 hp (1,040 kW)
Packard V-1650-1 Merlin. The resulting
P-40F (Model 87B) was the first variant to carry the "Warhawk" name. Along with the added power of the Merlin engine came a decrease in directional stability. Curtiss attempted to fix this by fitting a dorsal fillet to the tail of a single P-40F; however, this was not adopted into production. Starting with the P-40F-5, the tail was lengthened by about 20 in. Although the P-40F was superior to the Allison powered P-40s, there was a shortage of Merlin engines due to the vast number of aircraft that used them. Parts for these engines were becoming scarce, and maintenance became an issue. As a result, at least 70 P-40Fs were re-engined with V-1710-81s of 1,360 hp. with a cooling grill forward of the exhaust stubs. The
P-40M was supposed to be a purely export variant of the K, although many ended up in USAAF units. In RAF service the aircraft was named
Kittyhawk Mk.III, the same as the P-40K, which can cause some confusion.
Sub-variants and modifications •
P-40M-1, the first 60 aircraft. •
P-40M-5, 260 aircraft with carburetor air filter and aileron improvements. •
P-40M-10, 280 aircraft with changes to the fuel system and undercarriage warning system. •
TP-40M, a small number of aircraft converted to two-seat trainers. •
Kittyhawk Mk.III, 466 aircraft built for the RAF,
RAAF, and
RNZAF. However, another source states that the XP-40N was converted from a P-40K-1 and later converted into the second XP-40Q, but this is unlikely as photographic evidence shows that the XP-40N had the long tail that first appeared on the P-40K-10. •
Hawk 87V and
87W, export versions, 586 built for the RAF as
Kittyhawk Mk.IVs. Some were diverted to other allies.
P-40P The
P-40P was a planned variant of the P-40N with a Merlin engine. The project was cancelled due to a shortage of Merlins and the aircraft were delivered as P-40Ns.
P-40Q In 1944, Curtiss attempted to bring the Warhawk to the standards of more modern fighters such as the
North American P-51 Mustang. To do so, Curtiss installed a 1,425 hp
water injected V-1710-121 into the Hawk 87 airframe. The resulting aircraft became the fastest P-40 model at 422 mph. Even with these modifications, the
P-40Q (Model 87X) was still inferior to modern fighters and the project was cancelled.
XP-40Q-1, originally a P-40K-10, this prototype bore a resemblance to the XP-40K, having similar wing root radiators. Apart from this, the aircraft had a lengthened nose and four-bladed propeller. == Twin P-40 ==