When future historians consider World War II, they will particularly note that our "magic carpet" of aviation featured a sturdy, flexible warp without which the colorful woof and pile could not have been held together.
Disclosed as a prime element in that warp will be the record of the C-47 or C-53 or R4D-1 which we will quickly recognize as one plane, not three. The old reliable Douglas DC-3.
This craft became illustrious many years before its war record began, 700 DC-3s being in service prior to Pearl Harbor. In a steady, though small, stream, this transport rolled from Douglas assembly lines before Dec 7, 1941, and thereafter it was ordered into large-scale production.
By June 1, 1942, production was quadrupled doubled again in the second six months of the year then redoubled in the first half of 1943. By this year's end, it is expected that the DC-3 output will attain a monthly rate bettering the number produced in fully 5½ yr before we went to war.
So rapid was the increase in production that, by the time U-boat sinkings had set up a clamor for cargo planes, C-47s were rolling off the line faster than they could be ferried away. In a single month, production exceeded schedules by more than 60 craft, and the schedule called for several times that figure.
Affectionately known as the "Work Horse of the Air," the slightly revised DC-3 has been called "our unarmed combat plane". For through sky transport it licks the undersea wolf packs without fighting them. What's more, it
Established the Burma Road of the Air:
supplied the defenders of Midway with drinking water;
flew in the supplies that kept the Marines fighting on Guadalcanal;
made possible the campaigns against Buna and Gona;
parachuted food, medicines and ammunition to "Wingate's Mob" of British guerrillas behind Jap lines in Burma;
ferried from England the troops that seized airfields during the African invasion;
operated daily schedules over the African express routes;
towed gliders and carried paratroopers to Sicily;
evacuated wounded from every front on which Allied Nations troops have fought;
and performed almost countless other workhorse jobs in all climates and under every known hazard of weather and warfare.
Wherever Allied Nations outposts have been, or will be, located, there the DC-3 will be found. And when its numerous noses are counted, their total will undoubtedly arouse decided curiosity concerning the plants that produced them; hence this description of one of the Douglas C-47 assembly lines: Comprising five major components fuselage, empennage, center wing section, and two outer wing panels the DC-3 assembly system incorporates a number of manufacturing concepts that may well predicate standard practice, especially on large transport craft.
The fuselage breakdown effects a compromise between the longitudinal-panel and station-joined-section methods, this compromise utilizing both methods. The tail stub is assembled from an upper and lower section and joined at a conventional station ring. Then center or main fuselage section is assembled from longitudinal top, side, and bottom panels. And the nose it joined to the fuselage along a stepped junction that is part longitudinal and part station ring.
The nose section, containing the pilot's cockpit, is composed of five separately assembled components cockpit roof, windows, nose cone, bottom and floor, and the upper nose section. Roof, window frames, upper nose, and cone all start assembly in small jigs in sufficient volume to feed adequately nine joining jigs.
Upper nose subassembly channels and stiffeners are tied together in a small jig, then moved to the joining jig. There the window frames, cockpit roof framing, and upper nose structure are joined. Skinning begins immediately, the skins being held through pilot holes in the channels and stiffeners from which the holes for the rivets are also drilled. Drilling and riveting is done by the same crew. The upper nose section, including the pilot's cockpit enclosure, is completed, including the overhead instrument panel, before it is joined to the side and bottom assemblies.
The floor section starts in small subassembly jigs where 14 stations are tied together. These and the longerons are then joined in the first position of a nine-position, moving assembly line.
Framing is finished in the first two positions, and skinning begins in the third. There is Clecoing in the third, fourth, and fifth positions, and riveting in the sixth to ninth positions. While on this line, the assembly is carried on its side, in vertical tubular steel jigs mounted on grooved wheels that run on inverted "V" rails. The line doubles back to the starting point, saving floor area.
On the first side of this two-leg line, framing, skinning, and cutout work is completed, with the tunnels that carry the tubing and electrical wiring being attached in the second and third positions. The carrier jigs pass between stationary work platforms of the two-level type, moving at scheduled intervals under manual power.
From this line a bottom subassembly is transferred to a dolly of a seven-station line, without tracks, where preassembled side panels, including the pilot's cockpit section are then added.
After joining bottom, side, and top sections, the assembly moves on the same carrier to the installation section. Here, on two side-by-side lines, insulation, some equipment and instruments, considerable tubing, the rudder pedals, control columns, window deicer system, and other items, are installed. Then the nose section, now complete and ready for joining to the main fuselage, is trundled to reserve storage near the fuselage joining line.
For one of its units, the fuselage proper includes the top section reaching from the ring joint at the tail stub forward to the pilot's escape hatch in the nose section. This is the longest subassembly in the airplane and has a width of about one-fourth the circumference.
It is built up in a 16-position, two-leg assembly line where massive tubing jigs, one for each position, hold the assembly in a vertical position between two-deck work platforms and supports for overhead electrical and air outlets.
In the first position, all frame segments and longerons are installed, while in the second position skinning is begun and carried on through successive steps until, in the eighth position. the top section is all skinned and a major portion of the riveting has been accomplished. Then the unit crosses over and begins its return journey on the other leg of the assembly line. When it stops opposite the starting point, the completed unit is removed and placed in the main fuselage joining jig.
Another main portion of the fuselage is the bottom section, from the trailing edge of the wing aft to the ring joint. Its width covers about one-fourth of the circumference and contains the floor support beams and the lower portion of the large cargo door sill. It is built on a 16-position two-leg assembly line, running between single and double deck work platforms.
On the bottom section, frame segments and longerons, as well as some skins, are first Clecoed in place, after which skinning is continued in the succeeding positions. Another unique assembly procedure is seen here; for after the longerons and skins have been Clecoed in the jig, the entire assembly less the frame segments is removed in one panel to be Erco-riveted. This assembly is replaced from a back log of panels that have been previously riveted.
By the eighth position, the entire bottom section is skinned and 50 percent of the riveting has been accomplished. On the returning leg, the remaining riveting is done, leaving a position each for installation, pickup, and inspection.
There are six side panels for the fuselage right-hand forward, center, and rear; plus left-hand forward, center, and rear. These have the cabin window, side auxiliary exits, and cargo door openings. Aft and center panels contain the fuselage-to-wing attaching points, and are made up on a 22-position, two-leg mobile line with two to live jigs for each unit. These jigs alternate right and left in order to provide a steady flow of side panels to the joining position.
Fuselage joining is accomplished in one of two jigs. Here the bottom and top sections and the side panels are joined together with the remaining ring joint segments and some internal structure. After these components are riveted firmly (but not completely) together, the fuselage is removed by an overhead crane and placed on a dolly on one of the double fuselage lines for the balance of the riveting to be accomplished in the next five positions. Here the troop seat beams and the huge cargo door are fastened in place before the fuselage goes to the installation department for air ducts, wiring, floors, and everything that will not interfere with later operations.
At the end of the line are four jigs where the fuselage is fastened to pads duplicating the center wing attach points while the nose is riveted in place together with internal structures such as bulkheads and floor support beams.
At this point, the fuselage has the instrument panel, rear cargo floors, control pedestal, Servo unit, battery supports, heat system, cabin windows, cockpit windows, and many minor installations, and is ready for paint shop and joining to the center wing.
Center wing sections are assembled on moving lines of both the floor and overhead carrier types. Subassemblies are divided into trailing edge, main tank section, leading edge, and nacelles. The leading edge includes the secondary tank section.
Trailing edge assembly is commenced in stationary jigs where ribs, stringers, skin panels, "Z" sections, and intercostals are riveted together. A feature of these jigs is the counterbalancing of suspended drill templates, which can be quickly lowered and Clecoed in position and just as quickly released and raised when drilling is finished.
The section is then moved to one of three main jigs where the bottom skin panel is added. After being securely fastened, the trailing edge section is attached to a floor carrier which proceeds between continuous, two-level platforms where riveting is completed and initial installations are made.
From this line the section moves to the "telescoping" position, a jig where five sections of the wing are telescoped together and tack-riveted sufficiently to permit lifting from this position to the master joining jig.
The main tank or mid-section is started in a carrier jig, held stationary while initial assembly is accomplished, then moved sidewise to the head of a manually powered line, where movement is intermittent. Bulkheads and the rear spar are joined in the stationary position. Corrugations are picked up in the third and fourth positions of the line, and skin is fitted in the fifth station.
An eight-inch, power-driven hole saw, moving along a parallel track, cuts fuel tank filler openings. The skin is then installed and tack-riveted before the carrier is moved to the second leg of the line on which it will return to the starting area. The bottom panel and attach angles are installed while the carrier is held in gates on the track. All other riveting and pickup work is completed in the last four stations of the line. The tank section is then transported by traveler crane to the telescoping position.
The leading edge assembly is started in one of three vertical stationary jigs where the front spar and bulkheads are riveted together. The component is then transferred to a carrier where it is held in a vertical position. In the first station, the preassembled leading edge is added. Corrugations, cantribs, skin, and front panel are then added in the next eleven stations, and finish riveting, pickup and installations are completed on the second leg of twelve stations, which double back to the starting area. A traveler crane then picks up the nose section and transports it to the telescoping position, leading edge downward, where it is lowered into the nacelles.
Nacelles are assembled in right and left halves on a "merry-go-round", in alternate jigs of a 24-station line. When tied together, the halves are moved across an aisle to an overhead suspension line, or another merry-go-round where the two halves are joined to form a right or left nacelle, with rights and lefts alternating in the carriers. When a pair of nacelles have been once around on this overhead line, they are ready for attaching to the center wing section and are transferred on dollies to the telescoping jig.
Order of assembly in the telescoping position is as follows: Nacelles are placed front end down on the floor level; leading edge is lowered into the open ends of the nacelles; next comes the main tank; then the structure is topped by the trailing edge. When the components have been tack-riveted together sufficiently to lift, the section is transferred to one of four master joining jigs. Standing on the nacelles, the section is firmly joined, with work progressing at platforms on three levels.
Removed by a traveler crane, the section enters one of two parallel 12-station completion and installation lines. Riveting is completed in the first seven stations, and installations occupy the other five.
The assembled section is then moved on the same dollies to a reserve area adjacent to the final assembly line.
The center wing section, removed from its dollies and attached to others in flight position, is rolled into the first position of the final assembly line. There the fuselage, still on the carriers on which it left the final fuselage line, is lifted by traveler crane and lowered onto the center wing section. The tail stub is then attached and further joining operations are completed in the second and third positions.
Installation of the empennage is next completed, and in the seventh position the ship is raised for installation of the main landing gear. Wing-to-fuselage fillets and fuel tank covers are installed in this position.
For the next four positions the main cabin and cargo floors, oil coolers, and the glider towing equipment are installed, followed by empennage control rigging, installation of engine tail pipes, and miscellaneous firewall equipment before hanging the engines, the next operation.
Engine hookup and engine control rigging requires three positions, and installation of center wing compression ribs, pilot's seats, and hydraulic tests, including landing gear operations, are completed in three more.
In the last three positions of the first leg of the line, engine cowlings and propellers are installed, and the propeller controls are hooked up. Then the plane moves forward, on its wheels, to one of two reserve positions at the head of the final leg of the line. There the wheels are run onto carriers which run on one rail and a steel plate, with another carrier running on the concrete floor under the tail wheel. These carry the plane at a 30° angle (to conserve space) as outer wing panels are attached in the first working position.
Hanging the outer wing panels, rigging the flaps and ailerons, and installation of batteries require two positions, while completion and testing of electrical and radio equipment and a check of the automatic pilot occupy two more.
The company's inspection is accomplished next and is followed by squawk corrections, pick-up work, and final inspection. Army inspection and pickup take two positions more, and final camouflage paint operations are completed in the last station of the line. After moving out of the plant, field operations are performed on the flight ramp, then the plane is ready for flight tests.
Late in the week of Aug 15-21, the 2,000th C-47 version of the DC-3, rolled from these lines. Exactly how many more than that have been produced since Pearl Harbor cannot be revealed, nor can the actual count of those on order, but whatever the current or eventual total, they will be coming from one of the most completely mechanized assembly systems in the world.
This article was originally published in the October, 1943, issue of Aviation magazine, vol 42, no 10, pp 135-141, 349.
The original article includes 17 assembly-line photos and an exploded breakdown drawing.
Photos and drawing are not credited, but are certainly from Douglas.