Rebuilding the Clippers

Pan American's Atlantic Division maintenance department has taken on its biggest job yet — replacing structural members of Boeing 314s. And through pre-engineering they're doing it in strikingly fast time.

What is undoubtedly the most comprehensive overhaul job yet undertaken by an airline maintenance department is today in progress at an American Airways' Atlantic Division headquarters at LaGuardia Field, NY, where the first of eight Boeing 314 Clippers scheduled to "get the works" is literally being rebuilt.

This project is no mere refurbishing of eight large flying boats for it includes, as a precautionary measure, replacement of a minimum of eight wing spar-chord members, more than 20 wing web members, and 23 hull bulkhead members. Magnitude of the job is best shown by the fact that it was necessary to build jigs capable of supporting not only wings but also hulls of these 84,000-lb gross weight craft.

And, as the size of both the military and commercial planes increases, the project assumes more than mere interest; it becomes important as a handbook of experience. First step in the completely pre-engineered process was to remove tail surfaces, propellers, engines, hydrostabilizers ("sea wings" peculiar to this type of craft), wingtips and, finally, outer wing panels. Inasmuch as the airplane had major parts removed, precautions had to be taken to keep the airplane in balance while it was moved on the beaching gear. This was accomplished by using sandbags in the bow.

All components were removed under the chain hoist in the center of the marine terminal hangar, then the hull was nosed into a corner where the craft would not interfere with routine servicing of sister ships remaining. in service.

Here the hull and its beaching gear were raised — 20" at the aft end of the step to get it in flying position — then the hull was attached to jigs at the wing center section fittings. These jigs, 28' high and weighing approximately 6,000 lb each, were attached along the bottom by heavy steel tie-through members to assure alignment and eliminate the necessity of anchoring them to the hangar floor. Additional alignment checks are provided by jigs attached to the hydrostabilizer fittings.

With the hull attached to the jigs, the beaching gear was withdrawn from the aft end of the airplane and six hull bottom cradles were installed, three forward and three aft of the hydrostabilizer jigs. These hull-bottom cradles are constructed of welded steel angle members with wood and canvas padding cut to fit the hull curves. They serve both to distribute the weight of the hull bottom and also to hold it in position while main structural members are being replaced.

Interior of the airplane was completely stripped, with the multitude of parts going to storage, salvage, or specialized repair departments, and then replacement of hull structural members began. These include the vertical square tubular members running from the wing center section spars down through the hydrostabilizer attaching points to the truss structure forming the bottom of the hull, also the majority of the tubular members in the corresponding bilge trusses.

To do this, it was first necessary to disconnect the deck (or cabin flooring) from the main lounge, as well as the next two compartments, so that both front and rear spar bulkhead lower truss structures could be removed as units. This, in turn, required removal of chine and keel sections to permit loosening of the hull bottom skin to give access to the truss sections. Similarly, skin along the sides of the hull near the vertical members was loosened and peeled back to give access to them.

In each case, skin was loosened by very careful drilling of rivet heads, then popping out the rivet. Thus, replacement of the skin can be made with the same size rivets used in original construction of the Clippers.

Removal of the vertical hull members would appear to be a simple cutting-away job; but such was not the case, for the members themselves have been used as templates for replacement members. Thus it has been necessary to remove bolts and rivets with extreme care to avoid making the holes in the gusset plates and other attaching members any larger than allowable limits called for in the original design.

Members being replaced in both wings are the front and rear spar upper and lower chord members from the wing attachment terminal through the first splice, or from the outer wing panel attaching point outboard through seven ribs, a matter of 174", and web members in the area. Replacement order is as follows: Rear spar lower, front spar lower, rear spar upper, and front spar upper.

After the hull had been nosed into the hangar corner, the outer wing panels were placed in their jigs at right angles to each other and close enough to the hull to permit uninterrupted normal maintenance on other craft.

As in the case of the hull jigs, wings — also constructed by the Atlantic Division's maintenance department — were made of welded steel angle and I-beam members with machined fittings. One of these jigs supports the wing at the wingtip fittings, the other at the outer panel-to-center section fittings. In addition, there is a flap jig, consisting of four pyramidal stands supporting a heavy steel bar attached to the flap fittings and serving as an alignment jig to insure accuracy during removal and replacement of the rear spar chord members. Load distribution is effected by a wooden framework placed under each spar extending from the wingtip jig inboard to the splice where chord members were being replaced.

With the wings in jigs, fabric covering (which extends from the rear spar to the trailing edge) was removed. In order to gain access to the rear spar chord clip-attaching bolts, the lower chord members of seven trailing edge ribs were cut approximately 12" aft of the spar. This 12" section was removed by drilling out rivets through chord and spar clip and also the rivets attaching the trapezoidal rib chord gusset plates to the rear spar cap.

In all wing work, as in the hull, removal of rivets and bolts required extreme care to keep holes from being enlarged. And here, too, removal of the members themselves required extreme care, both to utilize the members as templates for replacement structures and to prevent scratching of gussets and webs remaining in place.

Four types of alignment checks are scheduled for the job. They are, first: Airplane assembly check, made with the craft mounted on its beaching gear before removal of any component parts, such as hydrostabilizers, tail surfaces, etc; second, hull check with hull mounted on support jigs before disassembly of the hull structure; third, wing check with wings mounted on jigs before disassembly of outer wing structure; and, fourth, airplane assembly recheck made on beaching gear after all replacement work is completed and component parts reinstalled.

Checks are also made for both hull and wings after replacement of each member, and the engineering schedule calls for additional checks to be made at any time desired by the engineering department.

Long before the first of the eight craft scheduled for the replacement program had been taken from service, the entire operating plan had been organized in minute detail by engineering and shop personnel. The section of the report dealing with "Preparation of Airplane," for example, listed and described 34 separate steps in this preliminary procedure.

"Removal of Aircraft Equipment," broken into three divisions, embraced a listing and description of 36 steps. Procedures for disassembling and replacing wing members embraced introductory and general note instructions, together with work procedure includes a general section and 33 steps. Even reinstallation of component parts and equipment are established in detail, this part of the job being broken into 19 separate steps.

This "forehand" work was all done while the Clippers remained in service (as one means of getting them back in the air at the earliest possible moment). Despite the fact that a very tight schedule has been set, A P Elebash, division engineer; F J Zerilli, project engineer; Walter Smith, assistant shop superintendent, and F Licari, assistant chief of metal shop, firmly believe they will be able to reduce the time on the second plane by 25% to 30%, with succeeding craft being "given the works" and put back in service in just about half the time required for the first.

This article was originally published in the July, 1944, issue of Aviation magazine, vol 43, no 7, pp 175-177, 269-270.
The original article includes 5 photos.
All photos by Pan American Airways.