The Fork-Tailed Devil

A bright page in the history of American military aviation is turned, as production of the Lockheed Lightning tapers off.

To the Germans the P-38 was der Gabelschwanz Teufel — fork-tailed devil, The Japs call it "Two Airplanes With One Pilot." The British dubbed it Lightning — and that name stuck. It earned its reputation from the outset of the war, racking up a long row of "firsts" — the first US plane to shoot down an enemy plane after our entry into the war (a Focke-Wulf over Iceland); first over Tokyo after Doolittle's famous "Shangri-La" raid; first photo plane over Formosa; first fighter to land on Leyte and Luzon in the recent Philippine invasion, and the first land-based plane to land on Iwo Jima to provide fighter cover.

More than 6,500 Lightnings have rolled off Lockheed and Consolidated Vultee production lines. although the Lightning was an "obsolescent" airplane from the first, avoiding becoming obsolete for years because of its design versatility.

With the war against Germany ended, Lockheed is tapering off P-38 production to push production of newer models, including the jet-propelled Shooting Star Thus the Lightning is about to take its rightful place in aviation history.

The P-38 was born early in 1937. when the US Army Air Corps sent manufacturers specifications for a single-seat military airplane — specifications which set up rigid performance requirements. Lockheed had never produced military aircraft. It then was a small company with fewer than 2,000 employees, and had produced only 107 aircraft during its entire history.

Numerous designs were proposed. First sketched was a twin-engined fighter with conventional fuselage and twin rudders. Next, a pusher-tractor type with twin engines mounted fore and aft of the pilot's gondola, with twin booms reaching the now-famous twin tail. Then came a conventional fuselage design with two engines housed behind the pilot, with only the pusher blades projecting from the trailing edges of the wing, one on each side of the fuselage. This was followed by a similar proposal, but with the propellers on the leading edge of the wing. From the fifth and final drawing was evolved the basic design of the P-38.

The two-engine design, with guns mounted in a central nacelle and firing straight ahead, promised the pilot better visibility, more effective concentration of firepower and avoidance of synchronizing firepower with the speed of the propellers. Twin booms did not comprise an attempt at streamlining but stemmed from the business of solving the major problem in Lightning design — what to do with its turbosuperchargers. Placed within the fuselage, their bulk would have made streamlining impossible, so the engine nacelles were extended back of the wing to house the two superchargers. Once this was done it seemed logical to extend them still further and join them with the horizontal stabilizer.

Design specialists finally agreed that "this was it". Performance calculations, photographs of a mockup and drawings of the structure were submitted to the Army, A contract was signed in June, 1937. Where contemporary fighter planes lifted from 20 to 25 pounds with each foot of wing area, the prototype (designated XP-38) boosted wing loading to 35 pounds without sacrificing speed or maneuverability. Wing surface loss was offset by reduced drag and added power and Lockheed-Fowler flaps were grafted to the design to aid in take-off and to permit slow landing speeds. Two 980-hp Allison V-1710-C9 liquid-cooled engines provided the power. It is significant that the length and span of the P-38 has always remained constant.

In wind tunnel tests the aerodynamically new wing wanted to flop on its back. Another wing developed a flap flutter at a wind tunnel speed of 150 mph. This was cured by putting holes in the wing at a point where the flaps were attached.

Tests were run on the new and radical tricycle landing gear. A three-wheeled tow truck was constructed and pulled at high speeds, carrying the approximate gross weight of the airplane. These tests eliminated nose-wheel shimmy.

The hand-built prototype first rolled from its hangar on New Year's Eve, 1938, and trucked to March Field, near Riverside, CA, where Lieut (now Col) Benjamin F Kelsey ran ground tests for several days. On its maiden flight, on January 27, 1939, the flap link broke and developed a flutter. Kelsey retracted the flaps and landed at less than 100 mph.

On February 11, Kelsey took off from March Field for New York City, made one refueling stop en route and 7 hr 43 min later (actual flight time, 7 hr 2 min) crash-landed in a ravine bordering a golf course just short of Mitchel field, LI. Fatigued by the long test hop, Kelsey reduced throttle too much when his approach overshot the field. Reapplying power, he choked the engines and had to put the plane down in the ravine. Though he was unhurt, the plane was a total washout.

However, as a result of Kelsey's enthusiastic reports, the Army authorized building 13 YP-38s. Major changes were included, such as upping military horsepower 170 hp per engine, designing the airplane for mass production, elimination of 1,300 pounds gross weight; revolving propellers outboard at the top instead of inboard, redesigning the armament compartment for a 37-mm cannon to replace a Swedish-made 23-mm, and two of the four .50-cal machine guns with .30s.

YP-38 engineering began in April, 1939; fabrication began in August. In February, 1940, assembly work on the first plane (used for static testing) got under way. Production workers soon were calling the YP-38 Yippee, a name derived from the plane's prefix designation, YP. The first YP-38 was flown by Marshall Headle, then Lockheed's chief test pilot, on the morning of September 18, 1940. Engineering on the production P-38 model began late in 1939, with deliveries beginning in July, 1941. The basic difference in the YP-38 and the later model was its use of .30-cal machine guns rather than .50s.

The P-38D, evolved in 1940 and delivered in 1941, marked the installation of self-sealing fuel tanks and a change from a high- to a low-pressure oxygen system. In the next model the cannon was changed from 37-mm to 20-mm, which has been standard in all subsequent models except for the unarmed camera planes. This model also saw the replacement of the hollow steel propellers with Curtiss electric constant speed propellers with dural blades.

About this time the Model 322 (or Lightning I) which was designed for the British, came along. It had low-powered engines, no superchargers and did not meet performance expectations. This model further suffered from British insistence that the propellers turn in the same direction. This added torque, which had been eliminated in the American model by turning the blades in opposite directions. The contract was ultimately canceled and the handful of Model 322 planes was converted as nearly as possible to the model used by the AAF to train American pilots. So far as is known, not one of this model has been in combat.

The P-38 was slow to make itself felt in actual warfare. People began to wonder why the Army didn't use it in combat. The Army couldn't reveal that the Lightning was to make its debut in the invasion of Africa. There was a trickle of interest in the new plane when Capt (now Col) Karl Polifka was reported in Australian dispatches to have flown a P-38 photo plane over a Japanese fleet that was moving toward Australia.

News of P-38 activities blacked-out for about a year. Suddenly the reason for silence was made known — Africa was invaded. The first American planes to strike the enemy from air fields in Morocco and Algiers were P-38s that had been flown down from England. Not until a year after the feat had been accomplished did censorship allow the story of how fleets of P-38s, escorted by Flying Fortresses that served as navigational shepherds, had flown across the North Atlantic from America to England — the first fighter craft to make the crossing. Only one of these long-range Lightnings was lost at sea.

In the African campaign the P-38E also got its first taste of combat, These long-range fighters, equipped with droppable fuel tanks, struck at the enemy over great distances from fields well behind the lines. They served as tank busters at Kassarine Pass, escorted bombers in scores of raids against Axis-held Europe, bombed and strafed and photographed thousands of square miles of occupied territory and, in general, helped pave the way for invasion.

Development of P-38 camera planes began in 1941. First of its kind, the F-4 (an adaptation of the P-38E with new autosyn-type instruments) was equipped with four cameras. This model also was equipped with drop-tank brackets and was the first to be converted into the famous "piggy-back" plane for fighter pilot training — an advancement that substantially reduced the percentage of Army flight accidents in this phase of training from an index rate of 6.5 to 1.5 within two months.

In the fall of 1942 the F-5, a specially-equipped P-38F camera plane, was unveiled. It carried five cameras, had the Allison V-1710-F5 engine and was the 12th P-38 model to be released. The 13th, which was ready in May, 1943, upped engine horsepower to 1,000 normal, 1,325 war emergency for each engine.

Other modifications of the fighter craft followed rapidly, the most important being those incorporated in the P-38J. The J, First delivered in August, 1943, had more changes than had been made in total since the fifth model appeared. More horsepower was added by using Allison V-1710-F15 engines, and rate of climb increased 100 per cent at altitudes over 30,000 feet. Built-in, bulletproof tanks increased range 30 per cent, service ceiling was raised to "well above 40,000 feet," straightaway speed was boosted and single-engine speed increased to more than 300 mph. It was during production of this model that the compressibility dive flap was introduced. Not only were the flaps incorporated into the assembly of the J model, but special kits were rushed overseas so that they could be added to earlier P-38s already in service. It was not until the L model was released that both dive flaps and aileron boosters were made standard equipment.

The P-38K had the Allison V-1710-F17 engine, which put out the same horsepower as its predecessor but had a different gear ratio to turn the new 12' 6" propellers. This model had unusually high performance, but the engine manufacturers couldn't make the necessary changes quickly enough to insure quantity production. Hence production models jumped from J to L, with K written off as an experimental model.

All model changes indicated by the suffix letter are dictated by the Army. Basic major changes have been made, however, with no change in model letter. All changes are, nevertheless, recorded by Lockheed in their own identification system. From this one learns that there were actually 50 to 60 versions of the Lightning. Master records show that more than 700 changes have been made. One change as an example, was the addition of aileron boosters and dive flaps on the model J after a large number of this model had been built, but it still remained the Army's model J.

The dive flap, which is not a diving brake, proved that the buffeting encountered by the Lightning in high speed dives was caused by airflow action on the underside of the wing when it entered the compressibility shock wave. Wind tunnel experiments were conducted, and finally W W Beman, Lockheed`s chief aerodynamics engineer, proposed that a dam under the wing, well forward of the leading edge [sic] might control the flow of air in the compressibility field. A trial proved his theory correct and ended compressibility buffeting.

Model P-38L, the newest (and last) "On-To-Tokyo" P-38, is the only one factory-equipped with the hydraulic aileron booster control. The action of the boosters is automatic, enabling the pilot to roll the heavy twin-engined fighter more quickly than most lightweight fighter planes —negotiating a complete 360° wing-over in less than three seconds. A fast roll is one secret of combat efficiency in fighter craft and the P-38 can execute the maneuver on one engine. Even though the quoted terminal velocity for the P-38L is 575 mph, and its level flight speeds more than 425 mph, controls are never stiff. If boosters should be shot out by enemy action, control could still be maintained manually.

The P-38L, designed originally as an interceptor, has become more truly a fighter-bomber, carrying a bomb load of 4,000 lb — greater than that of the early Flying Fortress. It has increased its already fast rate of climb to 3,200 fpm at 3.000 rpm, using 54" Hg. In spite of its 18,000-lb gross and 21,400-lb overload, the P-38 takes off in 1,030 ft. The P-38L returned to the 11' 6" propeller, geared to Allison V-1710-F30 engines.

The Lightning was assigned to specific phases of aerial warfare because of its adaptability to certain operations. Its unique design. however. led to its consideration as a carrier-based fighter, a torpedo-bomber and a ski-equipped fighter for far-north operations. At least one P-38 with full-retracting skis was tested but never produced in quantity. Some specially-equipped models were tested as torpedo carriers, using dummy torpedoes. And while no known arrangements were made culminating in carrier tests of this plane, Lockheed engineers say such an adaptation would be feasible.

When converted to glider-towing, the P-38 theoretically became a 15-place transport plane. Tests proved that the P-38 could successfully tow a fully loaded CG-4A glider.

The Lightning is more effective for every duty assigned to it today than it was in prototype. This performance record has been established despite the addition of 3,898 pounds empty weight, 6,500 pounds gross weight, 6,190 pounds overload weight and an increase of 13 pounds in wing loading. The Lightning — the fork-tailed devil — did not grow obsolete with age — instead, it improved vastly. But progressive demands of air-craft science have pushed the P-38 to a place in history as newer and faster jet-propelled planes demand the attention of today and tomorrow.

This article was originally published in the August, 1945, issue of Flying magazine, vol 37, no 2, pp 26-28, 124, 126.
The original article includes 4 photos, 7 drawings of proposed types, and a data table (below).
Photos credited to AAF, Lockheed.

Data table:

Evolution of the Lightning

.   Engine    .HPGrossRangeTopArmamentModification
Model  Model1   NormMilWeight2in mi3Speed4  Mach
  Guns
Cannon  
XP-38V-1710-C998098011,5001,3004032: .30s
2: .50s
1: 23mm
YP-38V-1710-F21,0001,15013,5001,3004032: .50s1: 37mmHigh-pressure oxygen equipment added. Turbosuperchargers moved to top of booms.
P-38V-1710-F21,0001,15013,5001,3004034: .50s1: 37mmFirst regular production model. Same as YP-38.
P-38V-1710-F21,0001,15013,5001,3004034: .50s1: 37mmSecond production model. Armor plate, bulletproof glass added.
P-38V-1710-F21,0001,15013,5001,3004034: .50s1: 37mmImproved radio in 3rd model. New instruments, improved oxygen equipment.
P-38DV-1710-F21,0001,15014,5001,2504034: .50s1: 37mmSelf-sealing fuel tanks; new low-pressure oxygen equipment.
322V-1710-F21,0001,15014,5001,2504034: 50s1: 37mmBritish model. No superchargers. Propeller rotation in same direction.
P-38EV-1710-F21,0001,15014,4251,2504034: 50s1: 20mmNew Autosyn-type instruments.
P-38E (LR)V-1710-F21,0001,15014,4252,3004034: 50s1: 20mmLong-range bombing model. Wing shackles hold one 150-gal droppable fuel tank or one 1,000-lb bomb each.
F-4V-1710-F21,0001,15014,4252,300403nonenoneAdaptation of P-38E. Four cameras.
P-38FV-1710-F51,0001,32514,4252.3004034: 50s1: 20mmResistance-type instruments, desert equipment, battery-cart plug for field starts.
F-5V-1710-F51,0001,32514,4252.300403nonenoneAdaptation of P-38F. Five cameras.
P-38GV-1710-F101,1001,32514,4253,0504034: 50s1: 20mmAuto engine temp control, demand-type oxygen equip., heavier wing shackles.
P-38HV-1710-F151,1001,42514,4252,7004034: 50s1: 20mmNew type turbosuperchargers.
P-38JV-1710-F151,1001,42514,4252,7004034: 50s1: 20mmNew core intercoolers, engine cowling, flat panel windshield of bulletproof glass.
P-38KV-1710-F171,1001,42514,4252,7004034: 50s1: 20mmPropeller gear ration changed to accommodate new 12' 6" propellers.
P-38LV-1710-F301,1001,42518,000over 3,000over 4254: 50s1: 20mmImproved superchargers. Propellers changed back to 11' 6".
  1. All engines are Allisons.
  2. From model P-38E through P-38L, gross weight varied with duty of plane.
  3. Range is dependent upon gross load, altitude flown and whether equipped with belly- or wing-tanks.
  4. Top speed is given in mph. Figures shown are those permitted by military security and are very conservative.