In presenting what might be called a pictorial preview of the Douglas Aircraft Co's B-17F Flying Fortress plant, it should be emphasized that this article will cover only those methods, equipment, and systems created by the Douglas organization for the manufacture, quickly and in great numbers, of this famous bomber.
The excellent and proven design of the B-17 and the means for its manufacture conceived and developed by its designers, the Boeing Aircraft Co, and adopted by Douglas, have been covered before in these pages. But, because this article is confined to Douglas innovations, it should not be construed as an attempt to compare and appraise the values of the different methods, machines, and manufacturing concepts of these two companies.
Chief source of this country's high living standard is its ability to produce goods in endless variety, of unsurpassed quality, quickly, economically, and in volume unequaled by any other nation on earth. Among the many abilities of Americans that make possible such production is the ingenuity by which different groups achieve similar or identical results, but with widely varying, sometimes seemingly opposite, methods.
Manufacture of the Flying Fortress by Boeing, Douglas, and Vega is another example of this American talent for achieving a desired result, but by widely varying, highly individualistic methods. The Boeing and Douglas systems, for example, might be called opposites. Where Boeing uses a very short final assembly line several of them Douglas uses a long one. Whether one is better than the other is a matter of opinion not pertinent to the subject matter of this article. The end results of both systems are identical bombers produced in rapidly accelerating volume and with steadily increasing efficiency in man-hours of human energy expended per ship.
When we were asked by our government to double the capacity of this new plant and launch production of the B-17, we looked upon the request as a challenge and an opportunity seldom afforded an industrial organization. It was an opportunity to create a factory that would include ideas representative of our entire accumulation of manufacturing experience, plus some that were still only theories. Naturally, with a war in progress and the very life of the nation at stake, the American people were demanding a great volume of planes in record-breaking time. It was to be expected that under such circumstances we would make some mistakes. It is a source of considerable satisfaction to us that subsequent operation of this B-17 plant has proved that we made very few.
Economy was the keystone of our plans, "economy" here being defined as the ability to manufacture a needed product in the required quantities, quickly, and with the least possible human effort. Creating from scratch, as we did, in cooperation with the government, it was possible to decide whether capital investment or time saving would be permitted to dominate decisions. Under prevailing conditions, time saving was chosen, and we built accordingly. There is no question that the facilities of this plant required great capital investment in plant space. However, the time saving and energy conservation already achieved indicates the choice was wise.
Throughout this plant the physical attitude of each working position is as natural and energy conserving as it is possible to make it. Jigs, carriers, platforms, stands, and racks are designed and located to minimize the drain on both physical and nervous energy and thereby increase personnel effectiveness and goodwill.
As this is largely and assembly plant, with considerable fabrication done elsewhere, its innovations are chiefly in carriers, dollies, jigs, testing devices, and conveyors, with a few in machines such as those which do multiple drilling operations in already partially fabricated parts.
Tracing the actual flow in the plant, starting with stock storage, we encounter one of the few instances where later developments indicated improvement could be made in the original layout. Because it was imperative to have flexibility, within the limitations imposed by mass production, our original stockroom was a large, centralized unit located in one corner of the main building. It was thought this would permit future shifting of lines, if that was found necessary, without disturbing the source of prefabricated parts.
Subsequent developments proved this plan disadvanatgeous, and a switch was made to decentralized, smaller stockrooms called "receiving points." These are located adjacent to working positions and are the responsibility of the leadman in charge of each position or station. Because the number of parts in each is small, there is less need for reliance on records and therefore less opportunity for error and "lost" material. Leadmen and clerks quickly become familiar with the parts for which they are responsible, and they see to it that proper quantities are on hand at all times.
This constant watch cuts the need for large reserves and considerably reduces our inventory. But most important, because leadmen are responsible both for the maintenance of their working schedules and for having the materials with which to maintain those schedules, responsibility is clearly established and authority to meet it possessed. This arrangement has created a self-sufficiency that extends from the individual working positions or stations on up through departments to whole buildings.
Supervision stems from a supervisor down through assistant supervisors to leadmen. Under each supervisor are three or more assistant supervisors. Under each of these are 15 to 20 leadmen, and each leadman has 20 or 30 production workers, about 70 percent of whom are women.
Actual assembly of the ship begins in a more or less conventional system, with the various sections originating in stationary, tie-together jigs. With this initial work completed, the Douglas procedure is first discernible as fuselage sections (for example) are lifted from the stationary jigs and transported by overhead crane to the head of parallel fore and aft section lines. There they are attached to carriers which travel on overhead tracks, through many stations, to the joining position in the last station.
By deliberately designing these lines long and with numerous stations we prevented crowded working conditions and thereby increased efficiency and added to worker comfort. With only one, two, or three workers in a compartment, or outside of it, we can arrange lighting, for instance, to suit the needs of each worker instead of forcing some employees to do their jobs under the handicap of shadows or insufficient light. This line was one of the first, so far as we know, to provide fluorescent lighting wherever it was needed, whether inside or outside, with temporarily installed fixtures that remain in place until they are no longer required. These fixtures also provide plug-in sockets for drills, electrically driven rivet guns, and other tools.
By having the fore and aft fuselage section lines parallel we saved structural steel supporting columns and floor space and made one line of electric and air outlets and work bench spaces serve both. And at the end, fore and aft sections are handy for joining.
A small item, perhaps, but one of considerable importance, is the rule that line workers cannot carry tools into the fuselage sections in metal tool boxes. To back up this rule, there are conveniently located tiers of shelves filled with wooden tool trays which are assigned to workers and in which they lock their tools with their own or company-furnished padlocks. It would be difficult to estimate the possible damage which this provision has prevented, but it has been considerable. Corners of heavily loaded, metal tool boxes may very easily dent or otherwise damage fuselage skin and other aluminum alloy parts, thus entailing costly, time-consuming rework.
About midway on the fuselage lines, the sections enter the paint booth, where still another Douglas-devised innovation saves time and provides worker comfort and health protection. To carry off excessive fumes, waterfalls are provided. Because both ends of the room had to open to permit entry and exit of the sections, these waterfalls generate a center-to-ceiling-to-side-to-floor circulation that carries fumes and excess paint particles upward and toward the side walls, where they are deposited in the waterfalls or exhausted through the outlet air ducts. So well has this circulatory system worked that the white paint of the booth's interior, including the floor, is entirely free of accumulations of camouflage pigment. So effective are these air currents that workmen seldom need or use respirators, and even with spraying in progress the room is almost entirely free of fumes.
From the paint booth the fore and aft section lines branch into three installation lines, two for the fore section because of the greater time required for installations, and one for the aft sections. As the sections emerge from the paint room their carriers roll into an overhead track transfer which moves them sidewise to the head of whichever line is desired, then permits them to roll forward into it.
Our stress on worker comfort and efficiency is exemplified on these lines by the conveniently placed platforms which are attached to the wing brackets and the cradle of the carriers. They ride clear of the floor, travel through the stations where they are needed, and are quickly removed when no longer required.
Since, under our system, each department tests and proves its own work, the means for doing so are provided at each point necessary. These tests are made and work is approved before a section is permitted to move to the next station. In the case of control cables from the pilot's cockpit out through the wings, a jig for establishing their correct length and testing their tension is attached to the upper wing brackets, outside of the fuselage. When cable lengths have been set, under proper tension, the jig is removed for use on another section following.
In the final station of the fuselage section lines the aft section is lowered from its carrier to a floor cradle and moved sidewise across the aisle between the two lines and placed in position for joining to a fore section, the latter remaining attached to the overhead carrier until joining has been completed.
After joining, the lower portion of the two fore section cradles are detached from the overhead carrier, the cradles themselves remaining attached to the fuselage, which is lowered to dollies that connect to the same axles of the cradles to which the overhead carriers were attached. Supported fore and aft on these dollies, the joined fuselage moves, tail foremost, to the first station of another line at right angles to the overhead lines, where the fuselages move sidewise through seven stations while tubing, wiring, and other connections are made.
In later stations of this sidewise line, the nose section, empennage assembly, and ball turret are installed. After that the fuselage moves into one of the final stations, where the right and left inner wings, transported by overhead crane from the inner wing lines, arrive and are joined.
With the inner wings in place the now rapidly shaping Fortress is given its hydraulic checks and inspections before proceeding to the final leg of the assembly line.
Among the Douglas-devised machines which have helped to break production bottlenecks are two drilling machines of rather unusual design. One drills the spar chord (a hollow square extrusion) and the mating extrusion cap in their correct relative position for joining. A gantry type, this machine grips the spar chord and the mating cap, together with a drill template that eliminates piloting, and drills hundreds of holes both accurately and at high speed. The drill is electrically driven with pneumatic control and has a solenoid cut-off to avoid drilling through both walls of the spar chord. Two operators, facing each other, each direct a drill as they move down the length of the chord, both seated directly above their work. Automatic vacuum clamps eliminate most of the usual tedious, time-consuming setup ordinarily required for such an operation.
For drilling the outboard and inboard ends of spars, a jig with vertical drills was developed. Both fore and aft spars are clamped on their sides while the vertical terminal drill, with floating drill chuck, locates and drills eight drive-fit holes through the spar ends and fittings within a tolerance of 0.0003. Drilling and reaming in one operation, through both chrome molybdenum steel and dural, this machine saves one complete operation and does not scratch the finish of the molybdenum or dural.
At the outboard end, another drill fixture, with radial arm, swings over both fore and aft spars to drill through spars and fittings of both upper and lower chords. Nine drive-fit holes are thus drilled in each chord. The drill is electrically driven and pneumatically controlled. Drilling operations progress at both ends of spars simultaneously. One setup is eliminated and absolute accuracy is assured for operations that fix the angle of attack of the wing.
Assembly of the inner wing sections begins in a jig which we redesigned from a series of side-by-side, stationary jigs into one jig of eight stations. Instead of assembling components and building up a wing section to a virtually complete state before lifting it out, we applied the progressing line principle here, too. Components and parts are tied together in a cradle carrier in the first station, with critical points established to those that follow fall automatically into place. Then the wing assembly progresses through seven additional stations of this three-level jig where finish riveting and other work is completed. Instead of placing the work and moving the various groups of specialized workers from jig to jig, we place the workers and move the work past them.
After leaving the jig, the inner wing sections both rights and lefts are turned from a vertical to a horizontal position and attached to carriers of another overhead system. Assembly continues for about half the length of these lines, and after passing through a paint booth, installations are performed in the second half. The sections travel "backward," with the trailing edges forward.
At the three-quarter point, the four engines arrive on dollies of our own design that permit clockwise rotation of each engine for installation of mounts and accessories. When ready for attaching to the nacelle, each engine is rolled into position, a three-segment, hinged, channeled clamp or band is released, and the engine is picked up by a hoist and raised to the joining position.
With installations complete, a check of electrical circuits is made by a unit, devised in the plant, which takes the place of normal fuselage circuits. This unit tests the entire inner wing section before final assembly.
The fuselage and inner wing lines, the former moving sidewise as mentioned before, come together at a corner of the rectangle formed by the assembly lines (actually a corner of the building). Inner wings are lifted from their carriers by overhead crane, which swings them into position for joining to the fuselage. When that is accomplished and connections are completed, the fuselage is raised from its cradles and for the first time rests on its own landing gear wheels.
After checkouts and inspections have been made and all work is approved, a floor dragline tows the plane backward on its wheels to the last leg of the assembly line, one that is longer than those previously mentioned and parallel to the fuselage and inner wing lines. There, in the first station, the outer wings are attached and installations of remaining armor and armament begin.
As these installations are completed, engine cowlings, doors, plates, etc, are placed, and inspections are finished as the plane moves into the final station where "squawks" are corrected. The now-completed Fortress emerges from the plant to the flight ramp, moving backward as it enters this line, with a crew of handlers furnishing motive power.
Externally and internally these Douglas-built Flying Fortresses are no different from those manufactured by Boeing and Vega, but the manufacturing arrangement that produces them is quite different. Whether our system or that of the other two companies is best is not the important thing just now. What is important is that from the battle fronts come increasingly frequent mentions of aggressive and successful actions by ever-growing numbers of these big bombers.
To the end that their numbers will continue to increase, faster and faster as the weeks roll by, this Douglas B-17 plant is dedicated.
This article was originally published in the July, 1943 issue of Aviation magazine, vol 42, Number 7, pp 130-135, 313-314, 318.
The PDF of this articlePDF of this article [ PDF, 14.9 MiB ] includes fourteen captioned photos of various manufacturing processes.
Photos are not credited, but are certainly from Douglas.