Lockheed P-38G & L Lightning

The Lockheed P-38 Lightning racked up an impressive series of "firsts"--it was the first Lockheed-designed military aircraft to go into series production, it was the first twin-engined interceptor to serve with the USAAC, it was the first production fighter powered by the Allison V-1710 in-line engine, it was the first modern fighter equipped with a tricycle landing gear, it was the first American plane to use butt-jointed flush riveted external surfaces, it was the first to make extensive use of stainless steel, it was the first fighter to use a bubble canopy right from the start, it was the first fighter with speeds over 400 mph, it was the first US twin-boom fighter to go into production, it was the first USAAF fighter to shoot down a German aircraft, it was the first USAAF fighter to carry out an escort mission to Berlin, it was the first USAAF plane to land in Japan after that country had surrendered, it was the heaviest US single-seat fighter of WWII, it was the only American fighter in production at the time of Pearl Harbor to be still in production at the war's end, and it accounted for more Japanese aircraft destroyed in combat than any other US fighter.

In 1937 Lockheed was invited along with Boeing, Consolidated, Curtiss, Douglas, and Vultee to take part in a USAAC design competition X-608 for a twin-engined high-altitude interceptor. The specification called for a maximum speed of at least 360 mph at 20,000 feet and 290 mph at sea level, an endurance at full throttle of one hour at 20,000 feet, and the ability to take off and land over a 50-foot obstacle within 2200 feet.

The Lockheed design staff was headed by Hall L. Hibbard. Working with Hibbard was the soon-to-be famous Clarence L. "Kelly" Johnson. After studying a lot of different designs, Hibbard and Johnson finally settled on a twin-boom design with each boom extending aft of the engine and the pilot sitting in an enclosed cockpit in a central nacelle. Each boom was to house one of the new 1150 hp Allison V-1710C twelve-cylinder liquid-cooled engine with an exhaust-driven turbosupercharger. The Allison engine at that time had just completed a 150-hour type approval test at 1000 hp. The central nacelle contained a forward-firing armament of one cannon and four 0.50-in machine guns. This armament was quite heavy for its time, the standard USAAC armament of the day being one 0.30-in and one 0.50-in machine guns. One advantage of the twin-boom layout was the possibility of installing the armament in the central nacelle, unhampered by synchronizing gear and allowing sighting of the parallel streams of fire up to the maximum range of 1000 yards. Tail surfaces consisted of a fin and rudder at the end of each boom and a horizontal tailplane and elevator between the booms. It was anticipated that the twin fin-and-rudder tail assembly would increase the effective aspect ratio of the tailplane by the endplate effect, thereby providing stability over a large c.g. range. At 14,800 pounds, the XP-38 weighed more than a bombed-up Bristol Blenheim I, at that time the standard British medium bomber. Fowler flaps were fitted between the ailerons and the booms and between the booms beneath the trailing edge of the wing center section.

The project was given the company designation Model 22-64-01. Lockheed promised a maximum speed of over 400 mph. Although the USAAC was somewhat skeptical about so radical a design, the Model 22 won Design Competition X-608 and on June 23, 1937, Lockheed was awarded a contract for one XP-38 prototype. Construction began in July 1938. Construction proceeded rather rapidly despite the radical features that it embodied. Few problems were presented by the installation of the Allison V-1710-11/15 (C9) engines, which developed 960 hp at 10,000 feet and 1090 hp at 13,200 feet. Each engine had a General Electric B-1 turbosupercharger. To combat torque, the propellers rotated in opposite directions, a special version of the Allison engine being produced with a left-hand rotating propeller shaft. The engines had inwardly-rotating propellers. No armament was installed on the XP-38. The XP-38 aircraft was completed in December of 1938.

On the last day of the year, the completed XP-38 was stripped down, covered with canvas, and loaded onto three trucks. In great secrecy, the convoy of trucks was escorted by police to March Field, near Riverside, California, where Air Corps Project Officer Lt. Benjamin S. Kelsey was to began the flight testing. However, on the very first ground run, the wheel brakes failed and the XP-38 ended up in a ditch. Lt. Kelsey finally took the XP-38 into the air for the first time on January 27, 1939. The early test flights turned up some problems with the wheel brakes and with vibrations of the flaps, requiring that some modifications be made to the prototype. Reaction to the first few test flights was highly favorable. And in spite of the problems encountered on those first few flights, it was decided to attempt a record transcontinental flight before delivering the XP-38 to the Army at Wright Field. At daybreak on February 11, 1939, Ben Kelsey left March Field destined for Mitchell Field, New York with refuelling stops at Amarillo, Texas and Wright Field, Ohio. On the final leg of the flight, the XP-38 lost power as Kelsey was coming in for a landing at Mitchell Field and crashed on a golf course just short of the runway. Fortunately, Lt. Kelsey was unhurt, but the XP-38 was a total loss. In spite of the loss of the XP-38, the Lightning had shown its true potential and on April 27, 1939 a Limited Procurement Order for thirteen YP-38 service test aircraft was issued. The company designation for the planes was Model 122-62-02.

The YP-38 was redesigned for production and had a pair of 1150 hp Allison V-1710-27 and -29 (F2R and F2L) engines equipped with B-2 turbosuperchargers. These engines were equipped with spur reduction gearing rather than the former epicyclic type of gearing. This caused the engine's thrust line to be raised upward. The propellers were outward-rotating rather than inward-rotating as on the XP-38 (that is, the port propeller turned counterclockwise when seen from the rear and the starboard propeller turned clockwise). The chin-mounted lip intake under the propeller spinner was replaced by a pair of cooling intakes. Enlarged coolant radiators were adopted on both sides of the tail booms. Armament was revised to substitute two 0.30-in machine guns for two of the four 0.50-in machine guns, and a 37-mm Browning M9 cannon with 15 rounds was substituted for the 20-mm weapon. The 0.50 inch guns carried 200 rounds per gun and the 0.30 inch guns carried 500 rounds per gun. All the guns were mounted in the nose, with the 0.50 inch guns mounted above the 0.30-inch guns. One or two YP-38s were seen with prominent gun enclosure tubes protecting the two 0.50-inch machine guns, with flush plates covering the other gun ports. In reality, most YP-38s were flown without guns installed. At 14,348 lbs, the YP-38 was lighter than the overweight XP-38 due to structural redesign.

The first YP-38 flew on September 16, 1940 with Marshall Headle at the controls. In March 1940, the Army received its first YP-38 for service trials. Production lagged seriously behind schedule, and all thirteen YP-38s had not been completed until June of 1941. During trials, the YP-38s ran into a problem in which the tail began to buffet severely during high speed dives, making it difficult to pull out. On November 4, 1941, the tail booms of a YP-38 came off during a high speed dive over Glendale, California. Test pilot Ralph Virden was killed. This was initially falsely diagnosed as elevator flutter, and a set of external mass balances were added above and below the elevator. This problem was later solved by adding large wing-root fillets at the points where the wings joined the fuselage. This filleting had to be done very carefully, since failure to ensure a tight fit could severely impair the flight characteristics.

Even before the YP-38s had been built and delivered, on September 20, 1939 the Army placed an order for 66 P-38 fighters. Twenty-nine of these were delivered as P-38-LO (company Model 222-62-02). The P-38 had the same powerplants as the YP-38, but armament was changed to one 37-mm cannon and four 0.50-in machine guns. Armor plate and bulletproof glass were added for pilot protection, and fluorescent instrument lighting was provided for night flying. One of these P-38s was later modified to study the effects on flight crews of asymmetric cockpit location. The turbosuperchargers were taken off the modified airplane, and the unit in the port boom was replaced by a cockpit for a flight surgeon.

The P-38G model of the Lightning began to roll off the production lines in June of 1942. It was powered by the Allison V-1710-51/55 (F10) engine with increased boost ratings and offering 1325 hp for takeoff. However, the engine was limited to 1150 hp at 27,000 feet due to inadequate cooling. In addition, the P-38G carried a SCR-274N radio and A-9 oxygen equipment. The P-38G was the most widely-built version of the early Lightnings. 1082 P-38Gs had been delivered by March of 1943.

The P-38L was the final production version of the Lightning and was numerically the most important of all the Lightning versions. Lockheed built 3810 P-38Ls and Consolidated-Vultee at Nashville built 113 more. The P-38L was powered by 1475 hp Allison V-1710-111/113 engines with a war emergency rating of 1600 hp at 28,700 feet and a military rating of 1475 hp at 30,000 feet. After the unsatisfactory testing fourteen five-inch HVAR on zero-length launchers beneath the P-38L's 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. The P-38L could also be fitted with either a glazed bombardier station or bombing radar in the nose.

P-38s were involved in what is regarded as one of the most significant missions in the Pacific. After U.S. cryptographers broke the Japanese navy's secret code in the spring of 1943, they learned the travel itinerary for Admiral lsoruku Yamamoto, a brilliant strategist and architect of Japan's attack on Pearl Harbor. Sixteen P-38s made the 1,000-mile round trip from Guadalcanal to Bougainville in the Solomon Islands. In a perfectly timed aerial ambush, two Mitsubishi Betty bombers - one of which contained Yamamoto - and five Zeros were shot down. (Controversy continues to this day over which attacking pilot deserves credit for destroying Yamamoto's plane.) A total of 10,037 Lockheed Lightnings were built.

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