Lockheed P-38 Lightning XP-38

The XP-38 grew out of Circular Proposal X-608, issued by the US Army Air Corps in February 1937. Its authors were First Lieutenants Benjamin S. Kelsey, then in charge of fighter development, and Gordon P. Saville. They framed it as a high-altitude "interceptor" precisely to get round two Air Corps rules: one capped a pursuit aircraft's armament, ammunition included, at about 500 lb (230 kg), the other confined single-seaters to one engine. Kelsey wanted at least 1,000 lb (450 kg) of armament and two engines. The proposal called for at least 360 mph (580 km/h) at altitude and a climb to 20,000 ft (6,100 m) in six minutes, required turbosupercharged liquid-cooled Allison V-1710 engines and gave extra credit for a tricycle undercarriage. It went to Boeing, North American, Bell, Grumman and Lockheed, while its single-engined twin, X-609, produced the Bell P-39.

At Lockheed a team led by Hall Hibbard, with Clarence "Kelly" Johnson, weighed several twin-engined layouts, including one with both engines buried in a central fuselage driving push-pull propellers, before settling on the most striking answer: two booms carrying the engines, turbosuperchargers, radiators and tail, with a central nacelle for the pilot and guns. Lockheed called it the Model 22, and it won the competition on 23 June 1937. The contract covered a single prototype, the XP-38, for US$163,000, although the company's own costs would reach $761,000. The nacelle mock-up was laid out for two .50-calibre and two .30-calibre machine guns plus an experimental T1 23 mm cannon, but the prototype itself flew without weapons.

Construction, under constructor's number 022-2201 and Army serial 37-457, began in July 1938 in an old bourbon distillery next to the Burbank airfield, bought to absorb the factory's expansion; Johnson later named it the first of five Skunk Works locations. The airframe used butt-jointed, flush-riveted aluminium skin to cut drag, and a tricycle undercarriage with the nose leg retracting into the nacelle and the main legs into the booms. Power came from two experimental C-series Allisons of opposite rotation, the V-1710-11 to port and the V-1710-15 to starboard. Through a 2:1 reduction gear they drove 3.353 m three-bladed Curtiss Electric propellers that turned inward to cancel torque; the YP-38s and production P-38s would reverse the direction. Each engine was rated at 1,000 hp continuous and 1,150 hp for take-off, and a gear-driven supercharger working with a General Electric B-1 turbosupercharger held that power up to 25,000 ft (7,620 m). The prototype was 11.532 m long with a 15.850 m span; it weighed 5,219.5 kg empty and 6,992 kg at maximum take-off weight, and was credited with a top speed of 664 km/h at 6,096 m and a service ceiling of 11,582 m.

On the night of 31 December 1938 to 1 January 1939 the aircraft was dismantled, wrapped in canvas and moved in a convoy of three trucks to March Field, Riverside, where Lockheed technicians reassembled it under tight security. The first taxi trials exposed overheating brakes: during one run at 95 km/h the aircraft failed to stop at the end of the runway and ended up in a ditch. A new brake supplier and an added hydraulic pump cured the problem.

Kelsey took the XP-38 up for the first time on 27 January 1939. Straight after take-off it began to shake violently; the pilot of a chase aircraft could see the flaps flailing in the slipstream. Kelsey raised them, the vibration stopped and he carried on, but he had to land flapless, fast and nose-high, so that the bottoms of the fins scraped the runway. Inspection showed that three of the four aluminium flap control rods, undersized for the loads, had failed; heavier steel rods replaced them and the fault never returned. Time magazine reported that General Henry "Hap" Arnold, Chief of the Air Corps, told the press the new fighter opened up levels of performance that nations relying only on single engines might never reach, while Kelsey said he had exceeded 350 mph and believed the aircraft had more than 400 in it.

By early February the XP-38 had logged only about five hours, yet the Air Corps decided to move it to Wright Field, Ohio, for official testing. Turning the ferry flight into a record attempt was Kelsey's idea. Lockheed objected because the aircraft was barely tested, but Arnold, alive to the value of good publicity, approved it and suggested pressing on to New York. The target was Howard Hughes's mark of 19 January 1937, when his H-1 racer had flown non-stop from Burbank to Newark in 7 hours 28 minutes.

On 11 February 1939 Kelsey left March Field at 6:32 a.m. Pacific time. He refuelled at Amarillo, Texas, in a 22-minute stop, and landed at Wright Field at 3:10 p.m. Eastern time, 5 hours 43 minutes after departure. Arnold, bundled up against the cold, met him there, agreed to continue and sent him off with the words "don't spare the horses". Kelsey had flown conservatively so far, nursing the engines; on the final leg, once at altitude, he pushed the aircraft to about 420 mph (676 km/h). At 4:55 p.m. he was over Mitchel Field on Long Island.

The tower put him into a slow landing pattern behind several training aircraft. Kelsey throttled back to stay behind them, and when he tried to open up again the carburettors had iced and the engines would not respond, remaining at idle; the prototype had no anti-icing system. The Associated Press reported that one engine seemed to choke and swung the aircraft into a steep turn. Without power the XP-38 clipped the trees bordering the field, caught its undercarriage in one of them and came down in a sand bunker on the Cold Stream Golf Course at Hempstead, some 2,000 feet short of the runway. It lost its right wing and was left with mangled propellers and a twisted nacelle. Kelsey escaped with cuts to one eye and one hand and was released after a hospital check; the field commander, Colonel James Chaney, convened a board of inquiry at once while a fifty-man guard surrounded the wreck. A low approach, flown to touch down as early as possible and spare the brakes, was later cited as a contributing factor.

The National Aeronautic Association's official timing gave a total elapsed time of 7 hours 45 minutes 36 seconds, with 7 hours 36 seconds in the air and an average of 340 mph (547 km/h). It was not enough: Hughes stayed ahead by 17 minutes 11 seconds according to This Day in Aviation, or by 16 minutes 35 seconds according to the AP report filed that night, even though his H-1 had flown non-stop and the XP-38 had made two fuel stops. The distance was officially estimated at about 2,400 miles.

The aircraft was beyond repair, but its showing outweighed its loss. On 27 April 1939 the Air Corps ordered 13 YP-38 service-test aircraft at US$134,284 apiece. Lockheed's chief test pilot, Tony LeVier, dismissed the flight as a needless publicity stunt; Kelsey argued instead that losing the prototype had speeded the programme by cutting short the initial test series, and he was promoted to captain in May 1939. The YP-38s were substantially redesigned for mass production: lighter than the hand-built XP-38, with revised engines and outward-turning propellers that made them steadier gun platforms. On 20 September 1939, before any YP-38 had flown, the Air Corps ordered the first 66 production P-38s.