v1.1.0 / 01 aug 03 / greg goebel / public domain

* The P-38 Lightning was one of the most important American fighters of the Second World War. Although its operational record was somewhat mixed, in general the P-38 was a fast, powerful, and capable aircraft that performed well in a wide range of roles. This document provides a short history of the P-38.

* The Lockheed P-38 was designed in response to a 1937 US Army Air Corps (USAAC) specification for a high-altitude interceptor, capable of 580 KPH at an altitude of 6,100 meters (360 MPH at 20,000 feet). The Bell P-39 Airacobra and the Curtiss P-40 Warhawk were designed to meet the same request.

At that time, really powerful piston engines that could push prop-fighter performance to the limit were not available, and so the Lockheed design team, under the direction of Clarence "Kelly" Johnson, who would eventually design a string of famous aircraft up to the SR-71 Blackbird spy plane, decided to use two supercharged 12-cylinder, vee-inline, water-cooled Allison V-1710 engines. When Johnson selected it, the Allison had not been rated at even 746 kW (1,000 HP).

Johnson's initial concepts for the new fighter covered a range of configurations, but the Lockheed team finally decided on a scheme with twin booms to accommodate the engines, and with the pilot and armament in a central nacelle. The propellers would rotate in opposite directions to eliminate the effect of torque. The superchargers were positioned in the booms, behind the engines. Armament was to consist of four machine guns in the nose of the nacelle, clustered around a cannon. The design featured tricycle landing gear, making the aircraft one of the first with such a feature.

The prototype Lockheed "Model 22", later designated the "XP-38", was rolled out in December 1938 and first flew on 27 January 1939. It was powered by "handed" Allison V-1710-11 and V1710-15 engines with 716 kW (960 HP) each. The XP-38 set a cross-continental speed record by flying from California to New York on 11 February 1939, in 7 hours and 2 minutes, including two fuel stops. Unfortunately, the prototype landed short of the runway in New York and was wrecked, much to the distress of the Lockheed engineering team. They had opposed the flight, but it was done at the insistence of General Henry "Hap" Arnold, commander of the USAAC.

* The engineers regarded the loss of the aircraft as a serious setback, but it had a beneficial side effect. On the basis of the record flight, the Air Corps ordered 13 "YP-38" evaluation aircraft in April 1939. If the XP-38 had not been destroyed, orders would not have been placed until the prototype had been thoroughly evaluated.

However, manufacture of the YP-38s proved troublesome, and the first didn't roll off the production line until September 1940, with the last delivered in June 1941. Although they looked much like the custom-built XP-38, they were substantially redesigned and differed greatly in detail. They were lighter, and there were changes in engine fit, most particularly in that the direction of propeller spin was reversed, with the propellers rotating up towards the cockpit rather than down as had been the case in the XP-38.

They were powered by Allison V-1710-27/29 engines with 858 kW (1,150 HP) each. Although weapons were not fitted in most of these aircraft, they were designed to be armed with two 12.7 millimeter (0.50 caliber) Browning machine guns with 200 rounds per gun, two 7.62 millimeter (0.30 caliber) Browning machine guns with 500 rounds per gun, and an Oldsmobile 37 millimeter cannon with 15 rounds.

* Orders were already in hand from France, Britain, and the USAAC. The French and the British ordered a total of 667, with a "Model 322F" for the French and a "Model 322B" for the British. Each of these variants had unique minor equipment fits tailored for their respective air arms, such as metric measurements on the flight indicators for the French aircraft, but they both shared a major change from all other P-38 variants that were ever made: the superchargers were to be deleted, and the left-handed and right-handed engine arrangement was to be changed to twin right-handed engines.

As superchargers were a new technology, the Anglo-French purchasing commission that ordered the fighters was concerned that the superchargers might lead to delays, and felt that as the aircraft were intended for medium-altitude combat the superchargers would not be needed. The requirement for the sole use of right-handed engines was for commonality with the large numbers of Curtiss Tomahawks both nations had on order. Lockheed engineers protested strongly against this decision, and privately labeled the variant the "castrated" P-38.

After the fall of France in June 1940, the British took over the entire order. They decided that only the first 143 of the order would be delivered in the castrated format, as "Model 322 Lightning Is", with the remaining 524 to be delivered with superchargers and left and right-handed engines, as "Model 322 Lightning IIs".

The British never got that far. Three of the castrated Lightning Is were delivered to the UK in March 1942, and were promptly given a thumbs-down. They "redlined" at 480 KPH (300 MPH) and had nasty handling characteristics. The entire order was cancelled.

The remaining 140 Lightning Is were completed for the USAAF. and the rest of this batch of castrated aircraft, most of them refitted with contra-rotating engines but still minus superchargers, were relegated to US Army Air Forces (USAAF, which superseded the USAAC in June 1941) for training under the designation "RP-322".

These aircraft helped the USAAF train new pilots to fly a powerful and complex new fighter. The RP-322 was actually a fairly hot aircraft at low altitude and satisfactory in the training role. The other positive result of this fiasco was to give the aircraft its name: "Lightning". Lockheed had originally wanted to call it the "Atlanta", but the RAF name won out.

* 30 initial production "P-38 Lightnings" were delivered to the USAAF in mid-1941. Although not all these aircraft were armed, when they were they were fitted with four 12.7 millimeter machine guns, instead of the pair of 12.7 millimeter and pair of 7.62 millimeter weapons of their predecessors. The 37 millimeter cannon was retained. They also had armor glass, cockpit armor, and fluorescent cockpit controls. One was completed with a pressurized cabin on an experimental basis and designated "XP-38A".

The 30 P-38s were part of an order for 66, but in light of USAAF feedback the remaining 36 in the batch were fitted with various small improvements such as self-sealing tanks and enhanced armor protect to make them "combat capable". For some odd reason, the USAAF specified that these 36 aircraft were to be designated "P-38D". As a result, there never were any P-38Bs or P-38Cs. Early Lightning production variants are a confusing subject.

* None of these aircraft ever saw combat. Their main role in the story of the P-38 was to work out bugs and give the USAAF experience with handling the type.

Tail flutter was quickly found to be a problem. As a fix, small weights were attached to little booms in the middle of the elevator. Kelly Johnson was contemptuous of the "fix", regarding the weights as useless, and in fact the buffeting eventually proved to be due to the straight connection of the wing root to the fuselage pod. A few aerodynamic changes, most particularly the addition of a wing-root fillet, solved the problem. Nonetheless, the little weights were a feature of every P-38 built from then on.

A more serious problem was "compressibility stall", the tendency of the controls to simply lock up in a high-speed dive, leaving the pilot no option but to bail out. The tail structure also had a nasty tendency to fall apart under such circumstances, and in fact this problem killed a YP-38 test pilot, Ralph Virden, in November 1940. A USAAC major named Signa Gilkey managed to stay with a YP-38 in a compressibility lockup, riding it out until he got to denser air, where he recovered using elevator trim. This feat led to experiments that would eventually resolve the problem.

Kelly Johnson later recalled: "I broke an ulcer over compressibility on the P-38 because we flew into a speed range where no one had ever been before, and we had difficulty convincing people that it wasn't the funny-looking airplane itself, but a fundamental physical problem. We found out what happened when the Lightning shed its tail, and we worked during the whole war to get 15 more knots more speed out of the P-38. We saw compressibility as a brick wall for a long time. Then we learned how to get through it."