Lockheed P-38 Lightning
The Lockheed P-38 Lightning is an American single-seat, twin-engined fighter aircraft that was used during World War II. Developed for the United States Army Air Corps by the Lockheed Corporation, the P-38 incorporated a distinctive twin-boom design with a central nacelle containing the cockpit and armament. Along with its use as a general fighter, the P-38 was used in various aerial combat roles, including as a highly effective fighter-bomber, a night fighter, and a long-range escort fighter when equipped with drop tanks. The P-38 was also used as a bomber-pathfinder, guiding streams of medium and heavy bombers, or even other P-38s equipped with bombs, to their targets. Some 1,200 Lightnings, about 1 of every 9, were assigned to aerial reconnaissance, with cameras replacing weapons to become the F-4 or F-5 model; in this role it was one of the most prolific recon airplanes in the war. Although it was not designated a heavy fighter or a bomber destroyer by the USAAC, the P-38 filled those roles and more; unlike German heavy fighters crewed by two or three airmen, the P-38, with its lone pilot, was nimble enough to compete with single-engined fighters.
The P-38 was used most successfully in the Pacific and the China-Burma-India theaters of operations as the aircraft of America's top aces, Richard Bong, Thomas McGuire, and Charles H. MacDonald. In the South West Pacific theater, the P-38 was the primary long-range fighter of United States Army Air Forces until the introduction of large numbers of P-51D Mustangs toward the end of the war. Unusually for an early-war fighter design, both engines were supplemented by turbosuperchargers, making it one of the earliest Allied fighters capable of performing well at high altitudes. The turbosuperchargers also muffled the exhaust, making the P-38's operation relatively quiet. The Lightning was extremely forgiving in flight and could be mishandled without incident in many ways, but the initial rate of roll in early versions was low relative to other contemporary fighters; this was addressed in later variants with the introduction of hydraulically boosted ailerons. The smaller and more streamlined P-51 was significantly faster in a dive, which led to the P-51 replacing the P-38 in most European fighter groups by mid-1944. The P-38 was the only American fighter aircraft in large-scale production throughout American involvement in the war, from the Attack on Pearl Harbor to Victory over Japan Day.
Design and development
The Lockheed Corporation designed the P-38 in response to a February 1937 specification from the United States Army Air Corps. Circular Proposal X-608 was a set of aircraft performance goals authored by First Lieutenants Benjamin S. Kelsey and Gordon P. Saville for a twin-engined, high-altitude "interceptor" having "the tactical mission of interception and attack of hostile aircraft at high altitude." Forty years later, Kelsey explained that Saville and he drew up the specification using the word "interceptor" as a way to bypass the inflexible Army Air Corps requirement for pursuit aircraft to carry no more than of armament including ammunition, and to bypass the USAAC restriction of single-seat aircraft to one engine. Kelsey was looking for a minimum of of armament. Kelsey and Saville aimed to get a more capable fighter, better at dog fighting and at high-altitude combat. Specifications called for a maximum airspeed of at least at altitude, and a climb to within six minutes, the toughest set of specifications USAAC had ever presented. The unbuilt Vultee XP1015 design was offered to fill this requirement, but was not advanced enough to merit further investigation. A similar proposal for a single-engined fighter was issued at the same time, Circular Proposal X-609, in response to which the Bell P-39 Airacobra was designed. Both proposals required liquid-cooled Allison V-1710 engines with turbosuperchargers and gave extra points for tricycle landing gear.Lockheed formed a secretive engineering team to implement the project apart from the main factory; this approach later became known as Skunk Works. The Lockheed design team, under the direction of Hall Hibbard and Clarence "Kelly" Johnson, considered a range of twin-engined configurations, including both engines in a central fuselage with push–pull propellers.
The eventual configuration was rare in contemporary production fighter aircraft design, with the Dutch Fokker G.I heavy fighter, and the later Northrop P-61 Black Widow night fighter and Swedish SAAB 21 having a similar planform. The Lockheed team chose twin booms to accommodate the tail assembly, engines, and turbosuperchargers, with a central nacelle for the pilot and armament. The XP-38 gondola mockup was designed to mount two.50-caliber M2 Browning machine guns with 200 rounds per gun, two.30-caliber Brownings with 500 rpg, and a United States Army Ordnance Department prototype T1 23 mm autocannon with a rotary magazine as a substitute for the nonexistent 25 mm Hotchkiss aircraft autocannon specified by Kelsey and Saville. In the prototype YP-38s, an Army Ordnance Department T9 37 mm autocannon with 15 rounds replaced the 23 mm T1. The 15 rounds were in three, five-round clips, an unsatisfactory arrangement according to Kelsey, and the T9/M4 did not perform reliably in flight. Further armament experiments from March to June 1941 resulted in the P-38E combat configuration of four M2 Browning machine guns, and one Hispano 20 mm autocannon with 150 rounds.
Clustering all the armament in the nose was unusual in U.S. aircraft, which typically used wing-mounted guns with trajectories set up to crisscross at one or more points in a convergence zone. The P-38 cannon used heavier 20 mm rounds, creating a different trajectory, so it was inclined upward slightly more than the four machine guns such that the trajectories of the cannon rounds and.50-caliber bullets came together between 350 and 400 yards/meters. Nose-mounted guns did not suffer as much from having their useful ranges limited by pattern convergence, meaning that good pilots could shoot much farther. A Lightning could reliably hit targets at any range up to, whereas the wing guns of other fighters were optimized for a specific range. The rate of fire was about 650 rounds per minute for the 20×110 mm cannon round at a muzzle velocity of about, and for the.50-caliber machine guns, about 850 rpm at velocity. Combined rate of fire was over 4,000 rpm with roughly every sixth projectile a 20 mm shell. The duration of sustained firing for the 20 mm cannon was about 14 seconds, while the.50-caliber machine guns worked for 35 seconds if each magazine were fully loaded with 500 rounds, or for 21 seconds if 300 rounds were loaded to save weight for long-distance flying.
The Lockheed design incorporated tricycle undercarriage and a bubble canopy, and featured two turbosupercharged 12-cylinder Allison V-1710 engines fitted with counter-rotating propellers to eliminate the effect of engine torque, with the turbochargers positioned behind the engines, the exhaust side of the units exposed along the dorsal surfaces of the booms. Counter-rotation was achieved by the use of "handed" engines; the crankshafts of the engines turned in opposite directions, a relatively easy task for the V-1710 modular-design aircraft powerplant.
The P-38 was the first American fighter to make extensive use of stainless steel and smooth, flush-riveted, butt-jointed aluminum skin panels. It was also the first military airplane to fly faster than in level flight.
XP-38 and YP-38 prototypes
Lockheed won the competition on 23 June 1937 with its Model 22, and was contracted to build a prototype XP-38 for US$163,000, though Lockheed's own costs on the prototype would add up to $761,000. Construction began in July 1938 in an old bourbon distillery purchased by Lockheed to house expanding operations. This secure and remote site was later identified by Johnson as the first of five Lockheed Skunk Works locations. The XP-38 first flew on 27 January 1939 at the hands of Ben Kelsey.Kelsey then proposed a speed dash to Wright Field on 11 February 1939 to relocate the aircraft for further testing. General Henry "Hap" Arnold, commander of the USAAC, approved of the record attempt and recommended a cross-country flight to New York. The flight set a speed record by flying from California to New York in seven hours and two minutes, not counting two refueling stops. Kelsey flew conservatively for most of the way, working the engines gently, even throttling back during descent to remove the associated speed advantage. Bundled up against the cold, Arnold congratulated Kelsey at Wright Field during his final refueling stop, and said, "don't spare the horses" on the next leg. After climbing out of Wright Field and reaching altitude, Kelsey pushed the XP-38 to. Nearing his destination, Kelsey was ordered by Mitchel Field tower into a slow landing pattern behind other aircraft. Carburetor icing caused it to be brought down short of the Mitchel runway, and it was wrecked. On the basis of the record flight, though, the USAAC ordered 13 YP-38s on 27 April 1939 for US$134,284 each. Lockheed's chief test pilot, Tony LeVier, angrily characterized the accident as an unnecessary publicity stunt, but according to Kelsey, the loss of the prototype, rather than hampering the program, sped the process by cutting short the initial test series. The success of the aircraft design contributed to Kelsey's promotion to captain in May 1939.
Manufacture of YP-38s fell behind schedule, at least partly because of changes to meet the need for mass production, making them substantially different in construction from the prototype. Another factor was the sudden required expansion of Lockheed's facility in Burbank, taking it from a specialized civilian firm dealing with small orders to a large government defense contractor making Venturas, Harpoons, Lodestars, and Hudsons, and designing the Constellation for TWA. The first YP-38 was not completed until September 1940, with its maiden flight on 17 September. The 13th and final YP-38 was delivered to the USAAC in June 1941; 12 aircraft were retained for flight testing and one for destructive stress testing. The YPs were substantially redesigned and differed greatly in detail from the hand-built XP-38. They were lighter and included changes in engine fit. The propeller rotation was reversed, with the blades spinning outward at the top of their arc, rather than inward as before. This improved the aircraft's stability as a gunnery platform.