Single Assembly Line Produces Both Bombers and Transports

By R C Sebold,
Chief Engineer, and
S J Powell,
Factory Manager, Fort Worth Division

Design and production coordination at Consolidated's Texas plant turns out both B-24 Liberator bombers or C-87 Liberator Express cargo transports without cutting production rate. Most changes are made on final assembly line.

A minor cyclone hit Consolidated Aircraft Corp's Texas plant when the Army Air Forces sent through a rush order for conversion of B-24 Liberator bombers into transports.

The Liberator had already won a name for itself as an adaptable transport in the hectic days of the evacuation of Java, when it soon became known that vital personnel and important cargo could be carried in the roomy fuselage and with additional cargo packed in the racks where bombs once had gone. Other bombers available couldn't be adapted as sorely-needed cargo carriers to move big loads great distances as easily as could the B-24, so while the former rained bombs on advancing Japs, the Liberators shuttled virtually unsung in the background. But they brought out the sorely needed equipment and invaluable men that are fighting again.

The immediate necessity for moving cargos up out of reach of submarines' ship-sinking torpedoes brought Consolidated a hurry-up order to really make transports out of its bombers — transports that can carry over six tons more than 3,000 mi, at speeds in excess of 300 mph, a combination feat unmatched by any airplane now in mass production. O

ne of the first C-87s — the Army designation for the cargo version — off the longest mechanized straight production line in the aircraft industry carried Wendell Willkie and a party of high officials on their globe-circling mission and became the first American plane to fly over the treacherous expanses of the Gobi Desert as well as the first to fly from China to the United States via Alaska during wartime. Another brought decorations to Lt Gen H H Arnold and to the crew by setting a 44-hr. flying time record from Brisbane, Australia, to Washington, DC. Including stopovers, the entire trip took only 77 hr, 5 min.

From the outside there is little difference between the B-24 and the transport. The bomb bay has been refaired and replaced with a belly covering, the bombardier's compartment in the nose has been closed in, with a door installed to permit loading of cargo in the space. The tail gun turret has been rearranged by adding a door through which long airplane parts, such as wing flaps, ailerons, and stringers, can be put endwise into the ship, and a 6-ft square cargo door was cut into the tail fuselage.

But, while the lines were little changed, the conversion involved a tremendous amount of engineering, calling on the ingenuity of Consolidated design engineers as well as assembly line experts. Adding to the difficulty was the necessity of tooling production so that both bomber and transport could be built on the same line.

In Consolidated's production setup, the center section of the plane's 110-ft wing spread is the key subassembly. It moves from the wing bucks to the bomb bay mating jigs where bomb bay catwalk, side panels, and bomb racks are riveted together. Farther down the line, this center structure goes into the fuselage mating fixture, where nose and tail fuselage sections are added. From the mating fixture the plane is lifted to the final assembly line and conveyors pull it through station after station while workmen add inside installations, outer wing panels, motors, propellers — everything needed to make it a finished ship.

Legion were the design problems involved in achieving this flexibility, which met requirements for both bomber and transport and brought two production records to the Texas plant.

One was substitution of the refaired belly section for bomb bay doors, bomb racks, and catwalk. Attempts first were made to fit the belly into the bomb bay mating fixture and rivet it to the side panels assembled there to the wing center section. But the arrangement proved unsatisfactory, so the wing now comes to the bomb bay fixture and picks up side panels and a "stretcher" bar, the arms of which reach between the side panels to hold them rigidly in place while window openings are cut.

When this assembly reaches the fuselage mating fixture, giant jacks support the wing center section and the nose and tail fuselage sections are brought by overhead crane to wheeled cradles which move them into the mating fixture. Here a locating bar jig, stretching from nose to tail fuselage sections, is slipped in as a means of alignment. It substitutes for the catwalk which serves a similar purpose in the mating of the bomber components.

Nose and tail are then riveted to the wing center section and the locating jig and stretcher bar is removed. A wooden stand is put beneath the aft end of the tail for support and the wheeled cradle is rolled backwards out of the way to give clearance for insertion of the belly.

Built on separate jigs and a unit in itself, this section covers the gaping maw of the Liberator's long bomb bays and when it reaches the mating jig, lacks only trimming of skin and stringers of being a completely finished unit. Once slipped in place, overlapping skin and belt frame are cut to proper alignment and riveted in position. Splice plates are riveted and bolted and the ship is ready for lifting out of the mating fixture.

Structural changes in the C-87 necessary to carry heavy cargo loads are made almost entirely in the tail fuselage section. Bulkheads are "beefed up" and bell frames and flooring supports added. But the major conversion changes involve putting in the 6-ft-square cargo door — big enough to permit loading of complete engines and huge packing crates.

From one of the bulkheads which is reinforced to take most of the load of the aft end belly tie-in, to a bulkhead on the empennage side of the cargo door, strengthening sections are added. A longeron is inserted in place of stringers at the top and bottom of the door and a heavier reinforcing skin riveted all around the opening and extended underneath the fuselage.

Sills, hinges, and finishing strips complete the opening and ready it for the door, which is added along the final assembly line.

While the plane is still in the fuselage mating jig, the remaining windows are located and cut. Three of the seven on each side are included in the side panel which is attached to the wing center section in the bomb bay mating fixture and have been cut before the assembly reaches the fuselage tie-in operation. The other four are cut a step or so previous to addition of the belly.

A steel template is fitted to the longeron at the bottom edge of the side panel and the remaining windows scribed. All seven are about 12 in high and 18 in wide and are located about 2 ft apart. They reach from just beneath the wing along the length of the ship toward the cargo door.

When the scribing has been completed, the template is removed and cutting-out of the window begins. First, skin rivets are drilled out, then the opening cut with machine reamers. Interfering stringer portions are sawed away and reinforcing headers put in. A window sill is added on the inboard side and beveled-edge window patches riveted on the outboard side. Final assembly stations complete the fairing with Plexiglas windows.

In converting the bomber, each change brought others. Putting in windows, for example, necessitates complete rerouting of the surface control cables as well as changes in the intercommunication lines and electrical wiring.

Most of these cables are lowered and run beneath the window level. Putting them there brought them into the cargo area, so compressed fiber wood paneling has been added as a protective covering. These panel sections are soaked in hot water tanks in the anodizing department, formed, and dried. Then they are attached with rivets and bolts to the inboard edge of fuselage bulkheads.

Since the paneling extends only to the window levels, in places where the cables have to be routed higher — above the cargo door opening, for instance — special dural guard plates and covering must be installed.

Another change was required by the cargo tie-down brackets to provide lashing points, and these, in turn, called for reinforcing of bulkheads at those stations. Still another problem was provision of heat for the transport passengers and jiffy-removable seats so that the plane could carry cargo as well as men. Ducts from the heater are run along the sides of the C-87 at floor level — and that made it necessary to shorten the seat legs on the outboard sides.

Then the reservoir for the hydraulic system which operates wing flaps and landing gear had to be shifted from the bomb bay area, where it had been in the Liberator bomber, to the flight deck compartment in order that it would not clutter up valuable cargo space.

Other changes moved the navigator and his table from what had been the bombardier's compartment up to the flight deck. This caused a shifting of the radio operator's position. And the astrodome, which had been above the navigator in the nose, was moved back

Relocation of oxygen tank racks and installation of lines to outlets by each seat are other innovations in the transport, as is the canvas and Kapok sound-proofing and finishing trim which lines the interior of the fuselage. The trim is attached by means of lift-a-dot fasteners and studs and can be easily removed.

Additional cargo space has been gained by refairing the bombardier`s compartment and replacing its glass- paneled nose with an 18-in fuselage extension and a cup-shaped cargo door. Here, too, bulkheads and floor supports are strengthened and protective paneling and insulating trim installed.

The Army Air Forces' need for transports was so pressing that the first few C-87s off the line were practically tailor- made. There was no time to wait while jigs were built and subassemblies tooled up. The first few transports were completed practically by hand simultaneously with the job of making dies, form blocks, and jigs for the cargo doors, belly covering, and the hundreds of other changes.

But the first Liberator Express was more than 30 days ahead of schedule in coming off the line — a second production record for Consolidated's Texas plant. The first record was achieved last April with the turning out of the first B-24 bomber 100 days ahead of schedule — exactly a year from the day ground was broken for construction of the first building.

Now an uninterrupted flow of bombers and transports move down the long assembly line. By not changing for the C-87, the complicated jigs in which bulkhead and stringer and piece of skin become bomber nose and tail fuselage sections, Consolidated saved months of tooling time. Once out of the jigs, the sections can become either a bomber or a transport, depending on which the AAF needs most.

Since the conversion changes are comparatively minor structural or installational variations, it has been found feasible to make them along the final assembly line. And because of the tremendous length of that line in Consolidated's plant, those changes can be broken down into hundreds of stations, permitting a division of the employees — a few to each station to make their installations unimpeded by other workmen who would have to be crowded in with a shorter line. This means less time for each ship in each station —grater production rates.

Winning the war can't wait for tomorrow. And today's cargos are moving in today's Consolidated planes.

This article was originally published in the April, 1943, issue of Aviation magazine, vol 42, no 4, pp 126-133, 403-404.
The original article is heavily illustrated, with 24 photos showing steps in the construction process; many are pairs highlighting the key structural differences between the bomber and transport versions.
Photos are not credited, but are certainly from Consolidated.

Photo captions: