Lightning Line Brews Triple Trouble for Axis

By J H Sreenan
Works Manager, Lockheed Aircraft Corp

First complete story of revolutionary mechanized assembly of striking P-38 fighter. New production line has already more than doubled — and may soon triple — output of Lockheed Lightnings.

Since Jan 27, 1939, when the prototype of the Lockheed P-38 Lightning made its first flight, a record of some sort or other has been achieved that our organization cannot take credit for, other than having precipitated it. I refer to the flow of controversies that have swirled about this revolutionary fighter plane design.

Combat missions in all theaters of the war have resolved the arguments that raged about the plane's possible performance and characteristics, and another contention is daily being answered in the Lockheed plants.

When the P-38 was first introduced, its design provoked considerable debate as to its probable performance. When this was answered by actual flights, the controversy shifted to whether or not the design could be put into large scale production. This skepticism on the part of production engineers, together with the ever increasing demands of our Air Forces, needled our production staff into evolving many manufacturing systems and methods that are new to the industry.

From a production standpoint, it must be readily admitted there were abundant grounds for skepticism. The Lightning's design contains more subassemblies than any other fighter type, presenting a really tough problem in coordination. Its more than 30,000 individual parts is about double that of standard type fighter planes. It is more complex, has more compound curves, requires more forgings, more blind riveting, more spot and roll welding, and it contains a considerable amount of stainless steel that presented new forming and welding problems which had to be licked, all of which complicated the production problem.

How well we have solved these problems is attested by the production volume which has already sent hundreds upon hundreds of P-38s to fighting fronts and training centers throughout the world. That volume has just been more than doubled, and may shortly be tripled, both without benefit of plant expansion.

The P-38 has not only been produced in volume, but is currently being assembled on continuously moving lines with inclusion of many subassembly lines as well as final assembly.

Core of the Lightning is the box-like center section of the wing. And major strength of this section stems from the main beam, a slightly V-shaped, girder-like structure made up of four main subsections and joined at the center with a grid section. The shear beam detail assembly of the main beam is the heaviest stressed part of the airplane.

Here, at the very start of manufacture is one of the hundreds of bits of ingenuity that, combined, have made it possible to build this plane in "impossible" volume. Machine design engineers created a special 30 ft long spar miller, with three high-cycle cutting heads, operating in three planes simultaneously, that mills a spar cap 20 ft long in a matter of minutes where several hours were formerly required.

This beam construction of the center wing section, with its aluminum alloy extrusion caps, has been a handy structure from which to "hang things" and accounts for the P-38's ability to carry 165-gal droppable gas tanks, or bombs weighing up to 2,000 lb under each wing. Main and aft beams, assembled in jigs of unusually heavy steel construction, are built up from a box-type foundation beam anchored to the floor. Uprights establish anchor points and provide alignment plates and template through which bolt and rivet holes are drilled. Both main and aft beams are assembled in jigs of convenient working height, and in the same position they eventually occupy in the plane.

The fore and aft beams are connected by crossmembers and to this grid, at the aft beam edge, the preassembled trailing edge portion of the center wing section is attached, using jigs which hold the assembly vertical with its leading edge downward. Next, the upper and lower skin assemblies are added, each composed of inner and outer flat stock panels riveted to a corrugated stiffener between them. Such construction reduces the usual number of wing ribs and provides smooth surfaces both inside and outside the wing. This "smooth skin" external surface increases aerodynamic qualities —and manufacturing difficulties. It requires use of 100° angle rivets and exacting riveting techniques.

In another jig, the joined center and trailing edge sections acquire tank sections, one on each side of the cockpit floor area. When these sections are joined and pickup work is completed, the assembly is lifted by traveler crane and placed in normal flight position on a castered height-adjustable dolly, and supported by two adjustable jacks and anchored jigs which attach to brackets later used to fasten outer wing panels in position.

In this working position fuselage and booms are added, the former minus cockpit housing and cowling over the armament compartment and the latter in fore and aft sections, which are joined together after the fore boom sections are attached to the center wing section. Both fuselages and booms are assembled on mechanized lines that are continuously moving as they reach final assembly stages.

Lightning fuselages, though smaller in all ways than standard types, present far more manufacturing problems than standard designs because of their small size, shape, smooth skin surface, and high concentration of equipment within them. Because the unusually heavy armament —four .50-cal machine guns and one 20-mm cannon —is concentrated in the nose section ahead of the pilot, a considerable portion of this smaller space must be assigned to accommodation of unusually heavy structural members.

Add the problems posed by doubling of many instruments and controls because of the twin engines, the small space which permits but one workman at a time in the cockpit, and it becomes apparent why it is absolutely necessary to make installations throughout the assembly stages so cockpit requirements will be at a minimum at final assembly.

The nose section is one of eleven major fuselage components and is assembled rather completely before others are joined to it. Preassembled structural members are joined in a jig designed to rigidly establish and maintain the highly critical dimensions and so installations can begin there almost as soon as initial structures are joined.

Because of the compactness mentioned above, with resulting inaccessibility becoming more and more acute as the section grows, this and all other assemblies receive the greatest possible amount of installations at each stage of assembly. This number is considerably greater than has been common practice on our lines or those of other producers.

Right and left lower "quarter panels" and structural members of the cockpit sides are preassembled separately and joined in indexing jigs designed for maximum convenient working positions. Panels and structural members are equipped with the major part of the tubing, wiring, and other equipment, before being joined to the nose section.

Mating of nose and side sections, which follows panel pickup work, is achieved in stationary jigs that form another "station" on the line along, which flow the nose and side panels. They are merely tacked together in the jig, to save jig time, and then moved to castered cradles for finish riveting, rigging of more parts, plumbing, electrical equipment, armament blast tubes, armor plate, and installation of the armament compartment floor. While this work is in progress, the cradled fuselage moves through 15 working stations to emerge ready for joining to the center wing section.

An outstanding feature of these cradles is the indexing design which permits rotation of the assembly for more convenient working positions. Seldom does an assembly remain in a single position while in a given working position or station. Rotation rings are not connected to the cradles, merely revolving in cradle channels, and they are built in two half-section parts for quick removal and replacement affording greater accessibility.

At the end of the fuselage line, a sling is attached to the assembly and it is carried by traveler crane to a position in the pre-mating "reserve" of the body group mating department to await attachment to the center wing section.

Right and left booms are assembled in fore and aft sections, the latter being known (because of its shape) as the "hour glass section." These offer difficult manufacturing problems because their strength is achieved through the union of webs, brackets, and skin, the latter butt-joined and, like all other P-38 surfaces, flush riveted. The small interior dimensions and extensive use of stainless steel in the booms further complicate their assembly.

Installations, following the routine used throughout on Lightning assembly, are virtually complete inside the boom sections before the fore section is joined to the center wing section and the aft section is added to the fore section. These include control cables, wiring, the coolant tubing to radiators contained within air scoops mounted on the aft-boom sections near its point of union with the fore-boom section. Stressed throughout, so torque is transmitted through the plane, added strength is gained by cupping the extreme edges of all lightening holes in bulkheads and brackets. Micarta strips projecting beyond the metal edges provide additional stiffening and give protection against any cutting of cables, wires, and tubing.

Fore sections of the booms are the first joined to the center wing section. Aft booms are then joined and the fuselage follows, in what are called "body mating jigs." There is completion of about one-third of the mating operations in these jigs, so arranged that direction of flow is toward the head of the continuously moving final assembly line.

Parts requiring coordination only are handled in the first mating jigs, then removed and numbered to return to the plane late in final assembly. Hydraulic jacks are used in the mating jigs to offset the drop caused by the constantly increasing additional weight of added components, the jacks being adjusted at successive stages to offset weight increases predetermined through calculations.

Upon completion of mating and joining operations, the assembly (which includes the major part of the empennage) is lifted by traveler crane, and moved to the transfer section at the head of the first leg of the final assembly line. There it is lowered, in normal flying position, to the final assembly carriage which supports it at three points —under the nose and at two points under the center section on the main beam at about CG.

Base of the carriage is a rectangular I-beam frame carried on eight flanged casters. It is 20 ft wide and 22 ft long and pulls a platform trailer 20 x 18 ft. that provides the working platform under the booms and empennage. Each carriage is equipped with numerous air and electrical outlets and its own transformer for converting 440 V to 120 V because of the electrical load required.

Adjustable nose pads to protect the fuselage nose skin are mounted on a long-travel jack for maintaining desired positions, as more and more weight is added to the plane, and to allow operation of the nose landing gear and check of installations. Removable sections of the carriage floor provide openings required when the main landing gear is added, thus permitting both installation and operation for checking purposes.

Railings around edges of the carriage prevent workers from stepping off accidentally, and six different floor and stand levels provide convenient working heights for all sections of the plane. These range from a bare 6 in through 10, 12, 25, 40 and 52 in from the floor. Workers ride on the carriages — currently at 4 in per min, but soon to be increased — through the 27 working and inspection stations of the line. Size of the crews "per station" varies from 8 to 16.

Because of the large number of new employees, including a high percentage of women most of whom are without previous factory experience, safety is the keynote of the new 1ine's equipment and installations.

For the first two legs of the three-leg final assembly line, carriages are hooked up as "trains" by couplers that automatically engage when bumped together and which are released by hand. Draglines under the last two planes on the first leg, and under the first two of the second leg, pull the train on the first and push it in the opposite direction on the second. The third leg is powered throughout its length so the craft can be moved on the carriages, or without them on their own wheels. Individual tow bars will connect either the carriage or the nose wheel to the dragline of the third leg, and planes can be mixed there, some on and some off of the carriages, if required. Power trolley and air lines for the first two legs are mounted above the floor and in the floor, and they are covered by hinged steel plates on the third leg.

Transfer areas are located at the ends of the three legs and are used for moving carriages sidewise, on flat steel strips embedded flush with the surface, from the first to the second legs at the door end of the building, and from the second to the third legs at the beginning end. However, when the carriage is not required on the third leg, the plane is lifted off (in the transfer area at the end of the second leg) by travel crane and placed on its own wheels in position to proceed through the final leg. The carriage is then returned to the loading area at the head of the first leg.

It is in the transfer area, at the head of the first leg, that the partially assembled plane is lifted from a jig in the body group mating department by traveler crane and lowered to the carriage. When fastened to the carriage, the coupler is engaged to the second carriage on the line and the plane begins its trip through the 24 assembly, one checkout, one inspection, and one rework stations of the line.

For the first two legs, the carriage passes between continuous platforms, the floor levels of which are 42 in from the building floor and project toward the plane 18 in from their supporting bases, providing an "escape" area in case a workman on a lower level of the carriage should find it necessary to get off the carriage at the floor level or has accidentally stepped off at the side. These platforms along the side of the line are flush with the side working levels of the carriages. Clearance between stationary and moving platforms is less than 1 in.

The stationary side platforms are 4½ ft wide and provide, below their floors, bins of varying sizes for point-of-use storage of parts and tools. At the out- side or back edge of these platforms are almost continuous work benches which also provide space for additional point-of-use storage of parts, tools, and materials. Air lines, with frequently spaced outlet points and power conduits for tools to be used at the benches, are provided at the back edge of the benches. Rules forbid workers connecting tools used on the carriages to the bench outlets. They must use utilities connected to the moving carriages, and side-stand workers must use outlets on the benches.

At convenient intervals, the continuous work bench is broken to provide space for 4-ft wide "magazine type" racks of metal trays for supplies, such as screws, rivets, bolts, nuts, cotters, washers, clips, and coils of small wire. The assortment of such items at each location is selected to meet the requirements of that working area only.

Access to these continuous platforms is from the ends and at 40-ft intervals throughout their length. At the 40-ft "breaks," which are covered by hinged floor boards, ladder-like steps extend down to the building-floor aisle that runs the length of the platform, and beside the steps is space for removable ramps up which heavy testing and greasing equipment is rolled to the stations where it is required. Stationary platforms and the carriages are painted white with the edges of the platforms bearing a 4-in wide orange stripe to caution workers.

Outside of the continuous stationary platforms, with a 3-ft aisle between, is a row of 6-ft high shelving designated as "feeder racks." Beyond these racks is another, wider aisle up which stock is delivered to the feeder racks. Parts are grouped in kits made up from feeder racks and then are moved across the aisle to the point-of-use racks under the floor and bench of the platform.

Previously cheeked out or assigned kits of parts to be installed on the top levels of the carriages, such as on outboard and tops of booms, cockpit, and other upper sections, are stocked in shelves beneath the bench. Those to be installed on lower levels, such as lower fuselage, wheel wells, and underside of the wing, are stocked in the shelves below platform floor levels.

Along the edges of the continuous platforms, measure marks are painted every foot, beginning at 0 at the head of each line and continuing for the full length of the line. At each 5-ft mark, the figure indicating its distance from the starting 0 is painted in. The main beam of each ship is used as a reference point and as planes pass the footmarks the beam indicates, first, progress of the craft and, second, starting and completion points of assigned jobs.

Group leaders are furnished job assignment sheets giving the foot-mark at which a job shall start and the mark at which it must be completed, the number of men required for each job, and the location of stocked kits in the adjacent racks. A kit code, for example, listed as "C 140 T" would indicate a kit of parts stocked in rack "C" at foot-mark "140" in the top tier "T" of stationary racks.

Above the final assembly floor is a system of traveler cranes reaching all areas. And, where required, transfer track links provide means for bringing two of the hoists on to a single crane. It is in slings, after their attachment to these cranes, that outer wing panels are suspended to be given the shake test for loose parts and other foreign matter.

Power for the three chain conveyor units is supplied by a 2-hp motor using a load of 1.4 hp to exert 6,000 lb of push or pull on each line, through a gear reduction from 1,150 rpm to 0.06 rpm.

Although the space occupied on the line by one plane is designated as a "station," there is no stationized work area. Group leaders' assignment sheets indicate the starting foot-mark and the point of completion. If, owing to the nature of the job, it is impossible or impractical to make a definite break in a job between work areas, the crew continues through following stations until it is complete. This is especially true of rigging and checkout operations. If, due to changing shifts, one crew turns over an incomplete assignment to another, the completion foot-mark is the important point to the second crew.

All jobs have specified starting places and must be completed in the distance allowed. This may mean that some operators perform more than one job while others do only part of a longer operation. Special pickup crews handle makeup or rework jobs at the earliest possible moment, to avoid having such work accumulate into a "jam" that might force a plane out of the lineup, or necessitate halting the line.

Typical of a long-cycle, multi-man operation is the main beam rigging, a job on which a five-man crew works through two stations and installs the parts in seven kits. After listing the kit numbers and stipulating that a five-man crew be used, the assignment sheet gives these instructions:

In the first station of the first leg, 22 jobs are assigned. Of that number three carry over to the next station where they are completed, but jobs which follow them do not finish and carry over to the third station. Sixteen jobs are assigned to the second station and 26 to the third. The average per-station throughout the first leg's nine stations is 16. On the second leg the average is 17 and on the third, 12. Three of the final leg's stations are devoted to checkout, inspection, and "squawks," this accounting for the low average of per-station job assignments.

At the beginning of the second leg outer wing panels are hung, in the first station. Engines are installed in the second station. They arrive from a mechanized dressup line paralleling the second leg, but flowing in the opposite direction and reaching a close proximity to the installation point on the second leg.

Typical of the job assignment per-station is that of "Station 1642," which has 16 jobs, or the average on the first leg of the line. As listed in the Job & Procedure Manual they are:

  1. Main Beam Rigging —Continued. Original 5-man crew accompanies ship into Station 1642 and finishes rigging as described in 1641. (All surface control and coolant shutter cable systems are to be brought to tension. All brackets are to be completed.) Since this work will be completed prior to the end of the station interval, the five men will work at the following minor jobs before picking up a. new ship at the end of the station interval.
  2. LH Oxygen Bottle Support —Kit 1642-41L. This job includes installation of the support on the aft side of the 265 boom bulkhead and installation of wire assembly No 196224 which runs through bulkhead 265 from its "J" box on the forward side and clips to the outboard flange of the oxygen bottle support. Two men are required: One in the manhole of the aft boom and one in the aft portion of the forward boom well.
  3. . RH Oxygen Bottle Support. This job is assisting another man install the RH support. Refer to Item 4.
  4. . RH Oxygen Bottle Support —Kit 1642-41R. Before installing support on aft side of 265 bulkhead it will be necessary to loosen "J" box on forward side of bulkhead to secure access to the bottom three outboard screws. When support is secure the "J" box must be replaced. Job requires assistance of second man above.
  5. Rig Fuel Selector —Kit 1642-26. Install all parts (pulleys, fairleads, cables, etc) and connect turn-barrels. (Tensioning and selling to be done in 1643.) See Item 2 of 1641 and Item 2 of 1643.
  6. Complete and Sell Push-Pull Tube, LH. Roller brackets are to be adjusted and safetied. Complete installation is to be made upon the push-pull tube. Job is to be sold to inspection.
  7. Complete & Sell Push-Pull Tube, RH. See item 6.
  8. Drop Tank Plumbing —1642-31L. The job consists of installing the fuel line that goes from the main beam fitting to the lower tail cone and the fuel line through the main beam to the front tank area.
  9. Shear Beam Plumbing LH (assist). This job consists of assisting another man to install the LH front shear beam assembly. See item 12.
  10. Coolant Vent LH 1642-42. The coolant vent tube is to be inserted in place. It will not be clipped to any structure until the stainless steel baffle is installed.
  11. Install LH Supercharger 1642-40L. The supercharger well is to be cleaned and sold to inspection. Secure the assistance of the other supercharger installer to drop the supercharger in place. Complete and sell the installation.
  12. Shearbeam Plumbing LH 1642-20L. This job consists of ball checking and installing the LH shearbeam plumbing assembly. The fairleads are to be attached to the fuselage webs. Connection with fuselage tubes will not be made until the next station. Another workman will assist part of the time and will lubricate the fittings and help attach the assembly to the shearbeam. See Item 9, also Item 6 Station 1643.
  13. Install RH Supercharger 1642- 40R. Identical to Item 11.
  14. Shearbeam Plumbing-RH. 1642- 20R. Identical to Item 12. Also see Item 9.
  15. Drop Tank Plumbing-1642-31R. Identical to Item 8.
  16. Shearbeam Plumbing —RH (assist). Identical to Item 9. Also see Item 12.

The nose landing gear is installed in the first station of the second leg, at the same time the outer wing panels are being hung. In the next station, at the same time the engines are being placed, the main landing gear links are installed, but the gear proper is installed two stations later.

Without attempting to detail the step-by-step installations and operations performed on the three legs of the final assembly line —377 of which are specifically covered by the Job & Procedure Manual — some idea of the coordinating problems which have been solved is given, however, in the following listing of the main installations and operations in their chronological order on the new line:

After the final checkout, inspection and necessary rework of "squawks" in the last three stations of the line, the plane is towed on its own wheels to the camouflage shop.

Throughout the three legs of the final assembly line, continuous Lockheed inspections exert a constant control over the work and keep it up to specification. On critical items, Army inspection also keeps watch during installation as well as in the final inspection station.

The terrific expansion of the aircraft industry, coupled with essential design modifications, has prevented development of coordination to what might be called a precision point. The stage has now been reached, however, where volume becomes the keynote, something that can be attained only through giving the best tools to the worker on the job.

We feel we have taken the greatest step yet made by Lockheed in this direction in the installation of the new mechanized, continuously moving assembly line system. When the tributary line installations now in progress are completed, the flood-tide of P-38s this new system will pour out to the fighting fronts will add a spectacular chapter to the saga of US industrial history. We at Lockheed sincerely hope that would-be dictators of the future will not make the fatal mistake of current ones when they base plans of conquest on the assumption that the United States is potentially big and strong, but can never get into big production soon enough. Large volume manufacture of Lightnings —suddenly doubled and which may be tripled in a matter of weeks is further proof to the contrary.

This article was originally published in the September, 1943, issue of Aviation magazine, vol 42, no 9, pp 121-134, 309-310.
The original article includes a photo of a P-38 in flight and 23 photos of the assembly line, and two detail drawings and a full-page schematic of the parts flow (with stage numbers) of the subassemblies used.
Photos are not credited.

The captioned photos show a great deal of structural detail of the P-38: