Design Analysis No 8
The Lockheed P-38

By Hall L Hibbard
Vice-President and Chief Engineer, Lockheed Aircraft Corp.

One of the world's outstanding triple-duty warplanes — which serves as long-range high or low altitude fighter, bomber, or photo reconnaissance craft — presented in Aviation's unmatched style. Revealed here are details of the daring pioneering design features which have made it one of the most controversial as well as successful combat planes.

The Lockheed P-38 Lightning fighter has been quite appropriately called the most controversial airplane ever adopted by the U.S. armed services. In thousands of sorties and hundreds of combat victories many of the points of controversy have been resolved, but. there still persists much that is either erroneous or due to misunderstanding.

Perhaps some of the derogatory items in the P-38 legends are traceable to the superlative requirements contained in the Army's specifications. To meet or surpass those requirements, and more recently to modify the P-38 as war experience and developments required, it has been necessary to do considerable pioneering. Particularly is that true in the higher speed ranges. And for such pioneering, the Lightning has had to accept the penalties of popular misunderstanding and the criticisms most pioneers undergo.

The P-38 was the first modern fighter equipped with tricycle landing gear; the first to use the Allison engine; the first equipped with a turbosupercharger; first in the "above 400 mph" class; first successful twin-boom design; first twin-engine "interceptor" fighter ; first American airplane to have flush or butt joined external surfaces; first fighter of its weight; first to mount its guns ahead of the pilot where they fire straight ahead, rather than in a "cone"; first to make extensive use of stainless steel; first to be delivered under its own power to bases overseas; first fighter to carry and launch torpedoes: and first fighter to tow gliders.

The list could be continued, particularly in the field of combat versatility. however, these "firsts" illustrate many of the sources of P-38 legends especially those partially or entirely inaccurate. In pioneering high altitudes and speeds. for example, the Lightning has had to temporarily take the blame for operational peculiarities later proven common to all airplanes at such speeds and altitudes.

Versatility now credited to the P-38 is a pure byproduct, rather than designed intent. We designed a superlatively fast, rapid climbing, hard hitting, high altitude fighter. That fact required the ultimate in clean design and great horsepower, which in turn established the plane s other specifications. These in turn have made possible the carrying of bombs and droppable fuel tanks for long range operation. The high speed has made possible the photographic version. And the concentrated firepower has been found excellent for ground strafing missions.

The current P-38J is the 36th development, including several designs which were never built, of the original Lockheed Model 22, and represents seven basic model variations. This evolution has resulted in the airplane now credited with being the fastest, most maneuverable, hardest hitting fighter. with the greatest ceiling, longest range and fastest sustained climb of any now in combat operation.

Dimensionally the Lightning is big for a fighter, having a wing span of 52', an over-all length of 37' 10", and a maximum height from the static ground line to upper tip of the empennage of 9' 9-11/16". Its weight empty is 12,700 lb and its normal useful load is 2,000 lb. However, one specification alternate provides for a gross weight of approximately 18,000 lb.

Every design feature of the P-38, as in most successful airplanes, was originated by necessity. The distinguishing twin-booms, for example, were not selected because they would be different. Neither was the twin-boom design originated by Lockheed. Some previous planes of this design, it is true, had not been too successful but for reasons other than the booms. In the Lightning they evolved as a logical development of engine nacelles made long to house the engine oil cooler turbosupercharger, Prestone radiators, and landing gear, Because of the greater nacelle length it was logical to extend them into booms to carry the empennage. Engineering-wise they add nothing or subtract nothing that could not have been achieved in other ways.

Necessity was truly the mother of invention in the evolution of the Lightning design. The Army specifications, laid down in 1937, were such that power requirements were greater than could be obtained from any single engine then available. Superior speed, rapid climb, high ceiling, and great firepower were the principal objectives demanded by the Army. To them we added placement of firepower where it would be most effective — ahead of the pilot and below his line of vision to provide unexcelled visibility and a distinct advantage in shooting. The pilot can pick up his target quicker and need not get it at the precise apex of a cone of fire such as is necessary when the guns are mounted in the wings.

The P-38 is now credited with speeds above 425 mph. This high speed, plus great maneuverability due to new booster-type aileron control, plus added dive control obtained by specially designed wing flaps, result in a tremendous combat advantage now being demonstrated daily all over the world.

An all-metal, mid-wing, single seater fighter, the P-38's wing is of full cantilever design, constructed in five components: center section, outer panels and tips. The center section, forward booms, and gondola-type fuselage are jig mated and bolted together. Main structural members of the center section are a main beam, located at 35 percent chord, front and rear shear beams, tied together with corrugated and flat 24ST to form a box section in which space is provided for fuel cells.

The main beam is double web, box type in the center section, and a single web, modified Wagner type in the outer wing, the two sections being joined together by means of bolts. A partial front shear web extends from the side of the fuselage to the engine nacelle and in combination with the continuous full-span rear shear beam, completes the torsion structure of the wing.

Upper and lower center section main beam caps are 24ST extrusions connected with sheet metal shear webs. The rear face of the beam is strengthened with 18 extruded stiffeners spaced about 6" apart, and seven bulkheads along the span act as additional stiffeners. Front face of the main beam is truss or open construction for the center 30", which allows for accessibility and for location of pulleys and other connections to the cockpit.

Thickness of the beam caps tapers from the center toward the outboard ends to save weight where less strength is required. This taper ranges from 7/16" thickness at the inboard end to 7/8" at the edge of the fuselage and back to almost 7/16" again at the outboard ends. The inboard end is thinner to permit bending of cap extrusions for the required dihedral.

The main beam varies from a depth of 19" at Station 0 at its inboard end, which is the center line of the airplane, to 13½" at the point of attachment of the outer panel.

The box beam is composed of the main beam, rear shear beam, and upper and lower surface — flat and corrugated — structures. Spanwise corrugations stiffen the skin and help carry bending and air loads on the wing. Webs of the main beam are 5½" apart and .040 ST Alclad aluminum. Corrugations in the center wing section are .064 SRT and .032 SRT Alclad. The upper and lower skin is .040 ST aluminum with lower skin strengthened with an .040 doubler extending inboard from the outboard end to a diagonal line approximately half way to the center line.

The rear shear beam is a single-web, modified Wagner type, constructed of extruded Ts and sheet stock.

Wing fittings which attach to the upper and lower caps of the main beam are of 14ST forgings and are formed multi-fingered, pin joined. For con­nection of the outer wing main beam the fittings on the outer wing are multi-fingered steel forgings, to reduce their size and increase the faces carrying shear loads.

Rear shear beam of the outer wing joint is a simple shear fitting, steel pin connection at the upper and lower caps. Corrugations of the surface structure are spliced at the outer wing joint by means of aluminum alloy forgings and tension bolts.

The box structure and leading edge section forward of the main beam extend from the fuselage to the engine nacelles and form a two-cell torsion box which carries torsional loads to the fuselage. The surface structure through the center section is stabilized for a portion of its length from the center line outboard to the edge of the fuselage with ribs built up with sheet metal stampings. The surface structure is unsupported from that line to approximately where the booms attach to provide room for fuel tanks in the box beams and leading edge sections. The leading edge sections have chord-wise formers in both upper and lower surfaces instead of ribs extending from the main beam to the front shear beam. The front beam is interrupted at the fuselage and nacelles and the loads are taken across by the box beam between the main and rear spars.

In the gas tank area .025 ST inner skin is riveted to the corrugated stiffener by means of flush rivets. Due to the inaccessibility it was necessary for Lockheed tooling engineers to develop a magnetic bucking bar for this operation, which was typical of the many manufacturing problems posed by the pioneering done in the P-38.

Trailing edge of the center section consists of sheet metal ribs and intercostal stiffeners which support the upper skin, and Lockheed's design of Fowler flaps. Flaps consist of a main spar formed with a sheet metal web and formed sheet metal caps, sheet metal ribs and stringers. They are carried on forged 14ST arms guided on tracks machined from 14ST forgings. They extend from either side of the fuselage outboard to the inner end of the aileron, a distance of approximately 180", with the exception of a section approximately 43" wide, omitted at each boom.

Having a total area of approximately 40 sq ft, the flaps are secured to the wing by means of eight carriages supported in tracks attached to the flap supporting ribs and providing for tension aft in line with the flight path so that, in extended position, the flap leading edge corresponds approximately to the trailing edge of the wing. The flap is actuated by an irreversible screw driving a guided push-pull tube, which runs outboard from the fuselage through each wing and to which the flap carriages are connected by means of a system of 1/8" extra flexible, preformed tinned carbon steel cables.

All pulleys and other rotating parts of the flap actuating system are mounted on anti-friction type bearings. This mechanism permits the flap to be extended to its optimum setting or held in any intermediate position desired without loading the driving mechanism. The irreversible screw is hydraulically operated, with activation by means of controls in the pilot's cockpit. An auxiliary hydraulic hand pump provides operating power in case of failure or damage to the engine-driven hydraulic pump.

Outer wing panels consist of main beam, rear shear beam, and upper and lower stressed skin, forming a box beam, and hydro-pressed sheet 24ST ribs spaced at 12-in centers. Outer skin and corrugated stiffener are 24ST Alclad. The leading edge has no ribs and is made up of formed inner skin and shallow chordwise corrugations of 24ST. These are built up of upper and lower halves, joined at the leading edge with piano hinge fittings, and are removable. In earlier models the inter-coolers were housed in the leading edge of the wing, which now carries fuel cells.

A flush type leading edge light is incorporated in the left side. The skin, of .040 gauge, 24ST Alclad, is flush riveted and butt jointed.

Main beam of the outer wing panel consists of upper and lower beam caps which are 24ST aluminum alloy extrusions, tapering out from the center until a heavier, reinforcing section disappears and the extrusion becomes a plain angle of sheet metal. The lower cap tapers faster than the upper and is finally replaced by a pair of sheet metal angles.

One of the interesting new cases of P-38 pioneering is the use of recently added dive flaps to offset compressibility effect which shifted center of lift from fore to aft portions of wing. Due to the unusually high speeds attained by the heavy P-38 in power dives, shifting of the center of lift caused loss of normal control above the "hydrodynamic" speeds — where air reacts much like water — with a resulting tendency of the plane to go into an outside loop. Since installation of the flaps this characteristic has been overcome.

The flaps are fabricated of three layers of aluminum alloy sheet, flush riveted. They attach, by means of a piano-type hinge, along the same line at which the leading edge of the wing is joined to the outer panel. Actuation is electrical, with a high speed electric motor driving actuating screw mechanisms connected to a curved arm hinged to a fitting on the brace or rearmost of the two panels of the flap assembly. When lowered, the flap stands at an angle of 40° from the lower skin surface line, and at its farthest point is 5½" from the wing to the piano hinge by which it is attached to the brace panel. Two actuating mechanisms, side by side at the center, operate each flap, the actuating arms swinging downward through an opening in the wing skin. The flap and brace panels have a combined chord of 15½", divided 8½" to the flap itself and 7" to the brace. Length is 58". The mechanism is bolted to a heavy casting anchored to the lower skin structure and two wing ribs between which it is located.

The wing tips are made up of smooth outer skins spotwelded to beaded inner skins and reinforced with two small spanwise beams each. Attachment is made to the wing by screws. A streamlined formation light is contained in both upper and lower surfaces of these structures.

One of the performance characteristics of the Lightning — for which the tail surfaces and virtually all other parts of the airplane have taken quite a beating from critics — was its apparent inability to roll as rapidly as fighter tactics required. Here again the high speed with its resultant pressure on the ailerons, necessitated another first, the aileron booster.

This system uses the main hydraulic pressure to supplement the pilot's pressure on the aileron control surfaces. Operation is such that the pilot maintains the feel of the control but supplies only 17% of the force required to actuate the ailerons, servo action supplying the remainder.

A shut-off valve in the hydraulic pressure line, controllable from the cockpit, is provided for the system.

Metal-covered ailerons are of standard design, and have a total area of 24.44 sq ft, an angular movement of 25° up and 20° down, a differential movement of 2.3 to 1, and the distance from the plane of symmetry to centroid of the aileron area is 230.4". They are statically and dynamically balanced and are attached to the wing by stainless steel piano-type hinges.

Engine nacelles extend forward from the main beam of the wing and join the booms at the firewall, the latter being merely a bulkhead and not a structural member. The nacelles consist of an engine mount with two 14ST side truss forgings and steel tubular members with forged end fittings welded to them, and support bay forgings. The tubular members attach to ribs in the leading edge of the wing and the support bay attaches to the forward boom structure, giving the mount lateral support. The combined forgings and tubes form a truss providing vertical and lateral support. The mount attaches by means of four nickel steel bolts.

Cowling consists of mild steel lower nacelle, and quickly removable aluminum panels, attached by means of flush-type fasteners to supporting framework of pressed aluminum alloy and steel attached to the engine itself and to the mount. Bottom skin of the cowling and sections around the exhaust manifolds are of steel. Intercoolers are below the engines and housed within the engine, cowling.

Booms begin at the firewall and extend aft to support the empennage, tapering from 47-3/8 in in height and 38.63 in in width at their deepest section just aft of the trailing edge of the wing, to an ellipse, 13 in high and 10 in wide at the point where the empen­nage booms join. They are built in two sections — forward and aft. The turbosuperchargers are within the forward booms, in the upper section just aft of the junction with the wing. In the lower portions are main landing gear and the wells.

In the forward ends of the aft booms are the engine coolant radiators, with their air scoops attached outside of the booms themselves. Also included in the left boom is a battery compartment and balancing it in the right boom is a luggage compartment.

Boom structures are of 24ST rolled sheet of .040 gauge in the forward boom, and .032 gauge in the aft boom, and extruded bulb angles, stiffened by bulkheads of hydro-press formed 24ST Al-clad spaced approximately 15 in apart in the forward boom and about 10 in apart in the aft boom. Forward and aft booms are joined around their top and sides through a butt joint and heavy doubler and at the bottom by means of a pin and forged fitting in the ends of heavy channel sections of 24ST hydro-pressed parts which form the lower edge of the wheel well and to which the landing gear doors attach. The semi-monocoque construction of the booms gives required strength and is reinforced at the edges of the gear recess.

Considerable stainless steel is used in the booms, in the areas around the superchargers and it was to fabricate this that the manufacturing divisions were forced to do considerable research and other pioneering.

The empennage consists of two booms — forming the tail cone — two vertical stabilizers, two rudders and tabs, one horizontal stabilizer and one elevator and tab. Outboard the aft empennage boom supports the rear portions of the stabilizer tips and is attached to the forward empennage boom by screws and plate nuts. The forward empennage boom is a formed skin reinforced by stringers and hydro-pressed bulkheads, to which is attached the horizontal and vertical stabilizers, the latter being divided above and below the forward empennage boom.

The flush-riveted stabilizer is built up in standard, all-metal airfoil style and is supported as a partially fixed ended beam from the two tail booms. It consists of two aluminum alloy shear beams and a skin of smooth sheet suitably stiffened by means of aluminum alloy extruded bulb angles. The rear spar carries the elevator hinge brackets and bearings, the end of the elevator torque tube and the elevator tab actuating unit. On the under surface, 3-7/8 in to the left of the airplane center line is a plate nut for plumb-bob attachment, and on the leading edge at the center line is an eye for alternate radio antenna attachment.

Stabilizer tips are also made up with a smooth aluminum alloy skin, flush-riveted to hydro-pressed 24ST ribs and channel strips, and attach to the empennage booms by means of 40 screws around the inboard contour. Right and left stabilizer tips are interchangeable.

The elevator has an area of 24.5 sq ft and angular movement of 23° up and 8½° down. It is statically balanced by four weights, one in each boom and two at the centerline. It is metal covered, flush-riveted and its internal structure is similar to that of the stabilizer and other control surface units. Its trim tab, placed at the plane of symmetry, has an area of 1.73 sq ft, and is controllable from the pilot's cockpit. It attaches by means of stainless steel piano-type hinges.

Vertical fins are full cantilever and attach rigidly to the tail booms with no external bracing. They are made up of multiple shear webs, ribs, and covering of aluminum alloy stiffened by means of aluminum alloy extruded bulb sections. They are constructed in two sections each, attaching above and below the empennage boom. In the upper sections are the rudder tab actuating units, a navigation light showing on the outboard side only, one elevator control pulley and two rudder tab control pulleys. Each lower section carries one elevator control pulley and a steel shoe to protect the lower tip against damage in the event of a tail down landing. The rudder hinge brackets and torque tubes attach to the rear spars of the stabilizers. Right and left fins or vertical stabilizers are interchangeable. They have a combined area of 24.42 sq ft.

Rudders are of all-metal construction, flush-riveted and have a total surface area of 21.36 sq ft and angular movement of 28° right and left. Tabs in the trailing edges each have an area of 1.37 sq ft. Rudder balance weights extend forward of the hinge line into recesses in the rear edge of the fins.

The entire empennage assembly is manufactured as a unit and is quickly detachable for repair.

The control system consists of rudder pedal hangers of the full stirrup type, and toe type brake pedals, and half "Y" built-up aluminum alloy control column for the elevator on which is mounted a control wheel for the ailerons. The control wheel has open upper and lower segments and the upper corner of each of the two closed segments has one control button on the near side and one trigger type switch on the far side. Double 3/16" diameter, extra flexible preformed tinned carbon steel control cables extend from the rudder pedals and control column back through the fuselage, diverging outward at the center section main beam to each boom.

One set of control cables for both elevator and rudders extends aft through each boom. Anti-friction type tearing pulleys and micarta or fiber guide blocks are used throughout the entire cable system. All control system bell cranks and masts for actuating the control system are mounted on antif­riction bearings and are housed entirely within the airplane contour. Inspection and service openings with flush-type cover plates are provided throughout.

Fuselage or gondola of the P-38 attaches to the center section at the plane of symmetry of the airplane and its line of juncture is covered by fillets. Its maximum height is 72" and its greatest width 38". It is fabricated of high strength aluminum alloy and is of stiffened monocoque construction, except where reinforcements for cutouts renders this impractical. High strength aluminum-coated, aluminum alloy-formed bulkheads are spaced 15 in apart and form the skeleton to which the smooth Alclad skin is flush-riveted. Cockpit enclosure incorporates side panels which may be lowered by the pilot, a top center transparent panel hinged at the top aft edge to permit entrance of the pilot when the left side panel is lowered, and which can be instantly released by means of a quick-release mechanism. Side panels can be opened or closed on the ground or in flight at reduced speed and may be locked in the open, closed or any intermediate positions. Center panel of the front windshield is of bullet-proof glass.

The Lightning's tricycle landing gear is fully retractable with automatically opening and closing wheel well doors. The main gear has single oleo-­pneumatic shock struts with a 10-in travel, and is hydraulically operated. Wheels are 36 in in diameter and are equipped with brakes. Main gears retract backward and up into the forward booms.

Nose gear is also of the single oleo-pneumatic shock strut type with a half type wheel fork. It is hydraulic and has a shock strut travel of 12". The nose wheel diameter is 27". Retraction is backward and up into a well in the fuselage.

Current P-38s are equipped with turbosupercharged 12 cylinder liquid-cooled V-1710 Allisons with a military and takeoff rating of 1,520 hp to 27,000 ft at 3,000 rpm. They are equipped with three-blade full feathering constant speed Curtiss electric propellers of 11' 6" diameter geared at a 2.00:1 ratio. Low pitch setting of blade at 42" station is 22.7°, and high pitch is 57.7° with a feather angle of 87.5°. Clearances are: to ground, level landing, approximately 16"; to fuselage, 9½"; to leading edge of wing, approximately 60".

Carburetors are Bendix-Stromberg PD-12K7, and differ from the conventional vented float chamber type in that the fuel system is closed from fuel pump to discharge nozzle. Fuel is delivered to the carburetor by the engine driven fuel pump at a pressure of 16 to 18 psi. Fuel delivered to the carburetor is metered in accordance with the mass air flow through the throat as registered by the venturi tube and automatic mixture control unit. Metered fuel then passes through the discharge tube to the discharge nozzle where it is sprayed into the air stream entering the internal supercharger.

Ignition voltage is provided by a dual, high tension magneto and is distributed to spark plugs through two separate engine driven, high tension distributors. Magneto timing is fixed and fires the exhaust bank of sparkplugs six degrees before the intake bank plugs. All high tension ignition cables are shielded to prevent radio interference. Two spark plugs are used for each cylinder, the exhaust plugs being cooled by a blast of cooling air conducted from the airplane slip stream through two aluminum alloy sparkplug cooling manifolds. Magnetos are pressurized Bendix-Scintilla DFLN-6, providing double ignition from a single unit, and mounted by two bolts between the cylinder banks at the upper rear section of the P-38's engines.

Throttle, mixture and propeller governor controls are levers mounted in the side control stand at the pilot's left in the cockpit. The starting system is composed of: a start switch with three positions, off, RH, and LH; an engage switch with three positions, off, RH, and LH; two starters, with manual crank extensions; and two booster coils. Start and engage switches are located atop the main switch box adjacent to the master ignition switch in the cockpit. The starters are located on the lower right-hand side of each engine accessory case; and manual crank extensions are accessible through doors in the engine cowl panels.

Engines are cooled with ethylene glycol, Spe AN-E-2, by separate systems, each consisting of a radiator mounted on each side of each aft boom, air scoops and exit flaps that control the flow of air through the radiators, a temperature-reactant four-way valve that automatically controls the exit flaps by hydraulic operation of an actuating cylinder, an engine-driven coolant pump, a coolant supply tank mounted astride the engine propeller reduction gear case, an absolute-pressure valve that vents the supply tank to the atmosphere and compensates for pressure variations.

Five drain cocks are installed at low points of the system and a bleed cock is located at the highest point. A tee restrictor is located between the cylinder banks to prevent excessive coolant bypassing. A coolant temperature bulb is inserted in the coolant outlet tube on the inboard side of each engine. The supply tank provides for coolant storage space and vents the system to the atmosphere through the sniffle valve which maintains a constant absolute pressure of 23 psi in the system at all altitudes.

An independent pressure-lubrication system provides oil for each engine with oil gravity-fed from the reservoir tank through the hopper and the slide valve for inverted flight, to the pressure pump. Flow then is through a check valve which opens at 1 lb pressure and closes when engine is stopped, to a strainer and thence to the engine. Three oil passages distribute oil from the strainer to the supercharger and all accessory drives contained in the accessories housing. From the strainer outlet, oil is also distributed to the moving parts of the engine. From the main scavenger pump outlet oil flows to the temperature regulator and when the oil is hot and does not exceed a pressure of 75 psi, it enters the regulator and flows through the core, out of the radiator, and back to the tank. Oil tanks are fabricated from 3SO aluminum alloy and are mounted on the front face of each firewall. Temperature regulation is automatically controlled by an electric actuator motor connected to the air duct exit flap.

Separate fuel systems supply each engine, with the two interconnected so that fuel from any tank except the outer wing tanks, is available for either engine. Three tanks supply each engine: (1) Main (2) reserve and (3) outer wing leading edge. In addition, droppable fuel tanks are carried under the center wing on both sides of the gondola and inboard of the engine nacelles. Electrically driven fuel boost pumps are mounted in the lower aft section of the fuselage and in the outer wing to assist the engine driven fuel pumps.

Air intake scoops on the outboard sides of the forward booms provide air for the induction system. From the scoop air passes through an intake filter, if desired, and through the intake duct to the turbosupercharger compressor. It is discharged from the compressor into a duct leading to the intercooler and thence enters the engine induction system where it is mixed with fuel and distributed to the engine cylinders. AiResearch intercoolers are mounted on four Lord mounts bolted to the engine trusses. The cooling air flow through the intercooler radiator may be manually controlled by an electric motor-operated shutter.

Superchargers are General Electric, exhaust-driven turbo type mounted as previously mentioned, immediately behind the rear shear beam of the wing in the forward booms. Automatic electric regulators are connected through a push-pull rod and bellcrank linkage from the throttle control pulley at the firewall and operate in combination with the throttles.

The hydraulic system of the P-38 operates the landing gear, landing gear doors wing flaps, coolant radiator exit flaps, and aileron boosters. Pressure is supplied by two engine-driven variable volume pumps and maintains a fluid pressure in the system of 1,350 psi. An auxiliary hand pump with a reserve supply of fluid provides for the operation of all units should the drive system fail. An emergency hydraulic system with separate lines and reservoir using the auxiliary hand pump for pressure source, provides a means of extending the landing gears in case the main hydraulic system fails. Fluid capacity of the main system is 10 gal and aluminum alloy tubing is used throughout the airplane, with all tubes grounded by means oi bonding clips and fairleads.

Oil filtering is accomplished at the reservoir in such a way that no unfiltered fluid can reach the system from either return line or by refilling. The hydraulic system is supercharged for maximum high altitude efficiency.

Electrical system is 24 VDC single wire except for the 115 V alternating current supplied by the inverter for the remote compass. A 24 V battery is supplemented by two 100-ampere generators to provide power to drive motors and to operate radios, actuating solenoids, instruments, lights and heaters. Engine starters, oil cooler and intercooler flaps, auxiliary fuel pumps, remote compass inverter, turbo regulator, dive flaps, and propeller motors are all electrically powered. Electric solenoids control the armament, droppable tanks and bombs, and outer wing tank flow, oil dilution valves, and coolant flap override mechanism. Electrically operated instruments include the landing gear warning lights; oil, coolant and carburetor air temperature indicators; fuel level gauges, remote compass indicator, and tachometers.

Armament of the P-38 is unusual in that four .50-cal machine guns and one 20-mm cannon, firing in a 20" diameter, or a 20" x 8" rectangular pattern have been proven one of the most effective combinations ever mounted in a fighter. The small number of the guns is more than overcome by their concentration in the fuselage ahead of the pilot, where they fire straight ahead rather than in a converging fire from wing guns.

The gun compartment is located in the upper forward portion of the fuselage. Machine gun ammunition is contained in four drawer-type trays. Cannon ammunition is provided from a drawer type tray. Expended links and cartridge cases are discharged through chutes leading to openings in the skin below the armament compartment. Expended cannon shell cases and links are discharged into a compartment between bulkheads on the lower right hand side of the fuselage. Sighting is by means of a Lynn gun sight, installed on the center line of the airplane, just aft of the bullet-proof windshield.

Bomb supports and type D-820 Interstate bomb shackles are attached to the under side of the center section, midway between the fuselage and each boom. They carry either bombs of from 100 to 2,000 lb or droppable fuel tanks. Also mounted in the left droptank support fairing is a type M-6 gun camera. It may be operated independently or in conjunction with the guns.

Armor plate consists of small pieces of face-hardened steel, attached separately to facilitate handling, removal and replacement. The pilot is protected from frontal attack by armor plate mounted on the aft bulkhead of the armament compartment and by a bulletproof glass windshield. Two pieces of armor plate line the back and bottom of the pilot's seat and give protection from below and behind. A single piece of armor plate mounted behind and above the seat provides additional rearward protection. Armor plate on inboard sides of the superchargers or circular deflectors on the superchargers protect the pilot against possible fragmentation of turbosupercharger blades.

The photographic version, known as F-5B, is a modification of the standard P-38J. The armament compartment is redesigned to accommodate any one of four arrangements of aerial cameras. Combinations of type K-18 with 24-in lens cone and type K-17 with 6-, 12-, or 24-in, lens cones are used in each arrangement. Cameras are remotely operated by a type A-1 electrical control and the camera lens apertures are controlled by a remote diaphragm control

A Sperry Type A-4 gyro pilot provides automatic control of the direction and attitude of the camera ship in flight.

The control units, which are mounted in the lower center of the instrument panel give the pilot a visual check on the operation of the automatic pilot at all times in addition to serving as flight instruments when the automatic pilot is not in use. It uses the airplane's vacuum and hydraulic systems as power sources for its operation.

Furnishings include, in addition to pilot's seat, flare pistol, glare shield, and other standard items, a rearview mirror fastened to the front portion of the top hatch, a demand oxygen system, and a cockpit heating system.

Cockpit heat is by hot air, the intensifier tube in both engine exhaust manifolds being ducted into the cockpit and directed on the pilot's feet. A flexible defroster tube may be used to defrost the top of the canopy.

While much of the design and equipment information given here probably appears as "standard" now, it should be recalled that when the P-38 first introduced it, such was not the case. And every design feature, every installation, every alternate was introduced through necessity to meet the new conditions encountered at the Lightning's higher speed and ceilings. With the recent addition of dive flaps and aileron boosters, the Lightning again pioneers through use of these devices to help combat the effects of compressibility. The P-38 thus overcomes any disadvantages of large size and weight. The present airplane is an improvement upon the plane the enemy so aptly named the "Fork-Tailed Devil."

This article was originally published in the August, 1944, issue of Aviation magazine, vol 43, no 8, pp 123-147.
A PDF of a draft of this article, recovered from microfilm, includes 16 photos, a 3-view and 27 drawings and diagrams, and 7 data tables. Photos are not credited.

A vectorized 3-view drawing has been created from the 3-view drawing in the article.


Diagrams and drawings: