Lockheed P-49 Lightning

Introduction

The Lockheed P-49 was a progressive development of the P-38 Lightning, powered by two radial engines. It became the major production variant of the Lightning family from the end of 1943 onwards and undertook most of the long-range escort missions. Since the end of the Second World War, supporters of the liquid-cooled engine P-38 and the radial P-49 have been locked in mortal combat over which of the two aircraft was superior. The issue had not been resolved.

Early Development.

On March 11, 1939, the USAAC Materiel Division called for a new type of twin-engined, high-performance interceptor fighter. The successful entry was, however, to derive as many design features as possible from already existing aircraft. The Lockheed entry was a progressive development of the P-38 Lightning, and was given the company designation of Model 222. The Model 222 had the same general arrangement as the P-38, but featured a pressure cabin and was powered by a pair of turbosupercharged twenty-four cylinder Pratt & Whitney X-1800-SA2-G (military designation XH-2600) liquid-cooled engines which were supposed to develop somewhere between 2000 and 2200 horsepower. Lockheed proposed to replace these engines by a pair of 2300 hp Wright R-2160 Tornado turbosupercharged radials in production aircraft. Armament was to be a pair of 20-mm cannon and four 0.50-inch machine guns. Total fuel capacity was to be 300 US gallons, as compared to 230 US gallons for the early production P-38. The Model 222 was rather optimistically estimated to have a top speed of 473 mph at 20,000 feet when powered by the Pratt & Whitney XH-2600s, and a speed of no less than 500 mph at the same altitude when powered by the Wright Tornadoes.

A contract for a single XP-49 prototype was officially issued on January 8, 1940. Because the Lockheed company was preoccupied with the P-38 Lightning, work on the XP-49 proceeded quite slowly during the early months of 1940. Both the USAAC and Lockheed soon came to realize that with either the Pratt & Whitney XH-2600 or the Wright R-2160 engines, the XP-49 would be seriously overpowered.

On January 1, 1943, the XP-49 was damaged during an emergency landing at Muroc AAB after a simultaneous inflight failure of both the hydraulic and the electrical systems.. By that time, the Army had lost all interest in the XP-49, since the performance was actually inferior to that of the standard P-38G which was already in service. In addition, the questionable future of the troublesome Continental engine caused the Army to abandon any further consideration of quantity production of the XP-49.

However, things changed quickly at that point. As combat experience with the P-38 in Russia grew, calls were mounting for the troublesome liquid-cooled engine installation to be replaced by a radial engine. This would ease operations from the crude Russian airfields as well as reducing maintenance. Initially, Lockheed examined installing a pair of Wright R-2600-12 Cyclones rated at 1,700 horsepower but those engines proved to be unsuited to turbocharging. The alternative was to use a pair of Pratt & Whitney R-2800-9 Double Wasp engines rated at 2,000 horsepower. This was the option selected.

The problem was that, while the depth of the R-2800 was compatible with the existing boom structure, the engine’s width was 20 inches greater and that could not be easily accommodated. At that point, somebody remembered the XP-49 sitting out on an airfield somewhere. The booms there had been designed to accommodate much larger engines and could be modified to include the R-2800.

The result was the XP-49A, an aircraft that was effectively a hybrid of the proposed XP-38H and the XP-49. The weight of the XP-49 was reduced by deletion of the pressurized cockpit and the elaborate cooling system used for the liquid-cooled engines. The XP-49A proved to have sparkling flying capabilities, exhibiting a clear improvement over the P-38, able to "fly rings around the Lightning" in the words of one pilot. The only problem was an outbreak of minor but troublesome fuel leakage problems that were eventually solved. At that point the XP-49A was ordered into production.

Variants

Lockheed P-49B Lightning

The P-49B was virtually identical to the P-49A except for the installation of a low-pressure oxygen system. Production deliveries started to US-based units in October 1943 with the type reaching the Russian Front in January 1944.

Specifications of the P-49B Lightning

Maximum speed of 426 mph at 15,000 feet, 384 mph at 10,000 feet, and 347 mph at sea level. Initial climb rate was 3,300 feet per minute, and the P-49B could climb to 20,000 feet in 8.7 minutes. Normal range was 679 miles, and maximum range was 1800 miles. Service ceiling was 37,500 feet. Weights were 15,410 pounds empty and 18,750 pounds loaded. Wingspan was 52 feet 0 inches, length was 40 feet 1 inch, height was 9 feet 9 1/2 inches and wing area was 327.5 square feet. Armament was 2 20-mm cannon with 170 rpg and four 0.50-inch machine guns with 300 rpg

Lockheed P-49C Lightning

The P-49C was fitted with automatic oil radiator. An M-2C cannon took the place of the M-1, and two underwing racks capable of carrying 1,600 pounds each were installed. The first of 226 P-49C-5-Los went into service in May 1944. They were followed 375 P-49C-15-LOs were fitted with B-33 instead of B-13 turbosuperchargers which gave improved high-altitude performance.

Lockheed P-49D Lightning

When earlier Lightnings went into a high speed dive, their controls would suddenly lock up when a certain speed was reached and the nose would begin to tuck under, making recovery from the dive very difficult. The problem would begin at Mach 0.65 to 0.68, accompanied by vigorous buffeting and a strong nose-down pitch. As speed increased, it became progressively more and more difficult to recover from the dive, larger and larger stick forces being required for a pullout. At Mach 0.72, dive recovery became for all practical purposes impossible, and runaway dives that got this far out of hand usually had fatal results. The onset of severe buffeting would, of course, usually provide adequate warning for a pilot in a diving Lightning that he was about to encounter a problem, but it is easy to get distracted while in the stress of combat. This dive recovery problem was so severe that the Lightnings found it very difficult to follow German fighters in a dive, allowing many Luftwaffe fighters to escape unscathed.

The problem was eventually traced to a shock wave that formed over the wings as the Lightning entered the transonic regime, the shock wave preventing the elevators from operating. In order to counteract this problem, the P-49D was equipped with a small electrically-operated dive flap underneath each wing outboard of the engine nacelles and hinged to the main spar. These dive flaps would change the characteristics of the airflow over the wing, offsetting the formation of the shock wave and permitting the elevators to operate properly. This innovation largely solved the problems encountered by diving P-49s.

Lockheed P-49E Lightning

The P-49E introduced power-boosted ailerons. These consisted of ailerons that were operated by a hydraulically-actuated bell-crank and push-pull rod, making it easier for the pilot to maneuver the airplane at high airspeeds. This boosting system was one of the first applications of powered controls to any fighter, and required only 17 percent of the previous stick forces. The hydraulic aileron booster system vastly improved the roll rate and thereby increased the effectiveness of the P-49 in combat. P-49Es with power-boosted ailerons proved to have the highest roll-rates of any fighter.

Lockheed P-49F Lightning

The P-49F model introduced the R-2800-59 engine rated at 2,300 horsepower (2,850 with water injection) that brought about a major boost in performance. The aircraft also had submerged fuel pumps and, after the unsatisfactory testing fourteen five-inch HVAR on zero-length launchers beneath the wing outer panel, underwing rocket "trees" for ten five-inch rockets were mounted. The racks underneath the wing center sections were strengthened to enable either 2000-lb bombs or 300-US gallon drop tanks to be carried.

Specifications of the P-49F Lightning

Maximum speed of 446 mph at 15,000 feet, 390 mph at 10,000 feet, and 360 mph at sea level. Initial climb rate was 3,700 feet per minute, and the P-49B could climb to 20,000 feet in 7.3 minutes. Normal range was 679 miles, and maximum range was 2,200 miles. Service ceiling was 39,500 feet. Weights were 15,410 pounds empty and 18,750 pounds loaded. Wingspan was 52 feet 0 inches, length was 40 feet 1 inch, height was 10 feet 5 1/4 inches, and wing area was 327.5 square feet. Armament was 2 20-mm cannon with 170 rpg and four 0.50-inch machine guns with 300 rpg

Lockheed P-49G Lightning

Early in 1944, at least two unidentified P-49Bs were modified in the field by the Fifth Air Force as single-seat night fighters by fitting an SCR540 radar with yagi antennae on the nose on both sides of the central nacelle, and above and below the wings. In order to make room for the radar, two of the 0.50-inch machine guns and their ammunition boxes had to be removed forward. Three P-49Cs were also modified in the field as experimental night fighters. However, these modifications were all single seaters, and it was found that the flying of the plane and the operation of the radar was too much of a job for just one person.

The results were interesting enough to induce Lockheed to adapt the P-49F as a two-seat night fighter. In 1945, Lockheed converted a P-49F with the radar operator sitting aft of the pilot under a raised section of the canopy. The aircraft was fitted with an AN/APS-6 radar in an external radome underneath the nose, relocated radio equipment and anti-flash gun muzzles. This modification was successful, and provided the USAF with a night fighter having a top speed of 426 mph at 15,000 feet as compared to only 369 mph at 20,000 feet for the Northrop P-61A Black Widow.

Consequently, the Air Force issued a contract change calling for the Lockheed Modification Center in Dallas to convert 280 additional P-49Fs into P-49G twin-seat night fighters. They were painted glossy black overall and entered service in 1946, seeing much operational service in over the Russian Front. It was an effective night fighter with very little performance penalty over the standard single-seat Lightning. Experiments were conducted with the object of shielding the turbosupercharger exhaust, but the entire exhaust system was so hot that it glowed at night, making the small reduction of visibility possible with the shielding of the actual efflux relatively pointless. Consequently, no modifications of the exhaust system were undertaken on "production" P-49Gs. Initial climb rate was 3075 feet per minute, and an altitude of 20,000 feet could be attained in 8.7 minutes.

Lockheed XP-49H Lightning.

An experimental high-altitude version of the P-49, the EP-49H would have had lengthened wings and a high-altitude optimized turbocharged for its R-2800s. The idea was not proceeded with, being dropped in favor of a modified version of the P-58 Chain Lightning


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