With the urgent need for aircraft manufacturers to speed up the processes of aircraft building from the inception of design to the delivery of the finished product, methods are being sought constantly which will bring about this result. While the urge is desirable, the means taken to accomplish this end must be aligned with good engineering and must produce sound results or it is wasted effort.
Quite often there is available a supply of skilled workmen who may be 'poured on' to the mechanical phase of constructing and assembling the first of a new-design airplane. The full brunt of three shifts of men may be brought to bear if necessary. But this means of rushing completion of the initial airplane is generally not applicable to that phase of the work where the major slowup occurs, which is in the intermediate work between engineering stage and shop, when a multitude of detail drawings and the construction of necessary tools, forms and layouts are concerned. It is here that there is a tremendous amount of drafting labor and shop conversion work which often has been the "bottleneck" at the beginning of production. The very nature of this phase of preliminary production work has resulted in considerable pressure being built up at this stage, tending to hold back orderly progress to smooth production.
The lofting approach to this phase of development has proved a boon in relieving this pressure, since it materially speeds up the whole transition process of converting an engineering conception into direct factory aids for workmen, such as tools and fixtures. The method previously accepted has been to transmit to the shop engineering directions through numerous detail drawings. The drafting problem alone, while using this procedure, can become tremendous, especially in the development of large aircraft.
Prior to the adoption of lofting methods, the recording of a shape on paper by the engineering department was usually done on a smaller scale than the actual. The shop had to translate each such drawing back to full scale before constructing any needed forms, assembly boards, fixtures or other necessary shop aids. Variations would result from individual interpretations, particularly where a faired line or double curvature was involved. Difficulties consequently followed in assembly and elsewhere.
Lofting, being a more natural intermediary, and particularly because it is conducted firsthand and to full scale, not only eliminates a large percentage of the difficulties experienced with previous methods, but materially reduces the number of engineering drawings ultimately necessary.
Lofting has another advantage over the older method and a rather subtle one, in that it brings the engineering personnel into a more direct contact with shop processes and problems. The full value of this factor is difficult to estimate, but it is considerable. There are many men in aircraft engineering departments who have not had the advantage of shop experience. Due to the current urgent need of trained technical men they are often snatched up at the completion of their formal education and set to work without an intermediate shop phase. Lofting lifts the fog that is apt to descend upon such embryo engineers who have not had their training mellowed through shop experience. The more intimate shop contacts afforded through the medium of lofting serves as a refreshing stimulant for engineers and draftsmen alike, and opens another important bond between shop and engineering. This, of itself, results in closer cooperation and a speeding up of the transition phase from initial engineering to line production.
Lofting as applied to aircraft production follows the practice used in ship building. This applies to laying out of hull or fuselage bulkheads, belt frames, etc, on a full size scale. In addition, aircraft lofting is applied to the wing, tail, furnishings and armament groups.
The work done by lofting for each group may be broken down into the following categories:
Briefly, here is how lofting works: Starting with the preliminary design of the airplane in engineering; the beam, overall length, and the height of hull or fuselage are determined, after which a small scale drawing is made showing the desired shape. Next, centerline drawings of the wing structural parts, such as bulkheads, belt frames, and spars are made and the structural sizes determined. From this point the lofting department, which works as an integral part of engineering, takes up the work and lays down and fairs a full-size body plan (vertical sections), full size water lines (horizontal sections), buttock lines (longitudinal sections), and any diagonal or special sections necessary to make a completely faired job. No tolerance is allowed in this work as every line must check perfectly with all others related to it. In this manner the lofting department produce a set of master plans, and from these all subsequent lofting work is built. The contour of any part, as for example a belt frame, is lifted from the master plan and transferred directly to a layout board.
After the contour is singled out from the master plan and on a board of its own, and is checked for accuracy, the structural members are drawn directly on the surface of the layout board. By this procedure of transferring from the master plan to layout boards a great number of layouts can be made to progress simultaneously, all originating from the one full-size master plan.
From the contour and structural layout board, the necessary drill templates locating all rivets and cutouts are laid out and sent to the shop for completion. Where locating fixtures are required the tool design department is notified so that the fixtures will be available when required. The lofting department likewise furnishes the contours for all bumping forms, master layouts required by tool design, and templates required for parts procured by subcontract outside the parent plant.
The layout boards are used in the making of several kinds of templates: marking templates, drill templates, mark and prick punch templates, drop-hammer templates, shaper form templates, templates for form blocks, etc. These are all checked back directly against the layout board and the structural information it carries. The lofted layout board is the turned over to the tool department to have form blocks put on it. These blocks transform the layout board directly into an assembly board, by providing three-dimensional support for the various members which are to become a part of the assembly. Since the templates for the various part were taken from the lofted layout board, and the tool department worked directly on this original layout (or drawing), and since this is all full-scale work, there is slight room for error or misinterpretation. As a matter of fact, the layout phase has been completely eliminated for the tool builders, with obvious economy of time and effort.
The lofting method lifts from engineering a good deal of tedious drafting, makes the actual full-scale layout and hands it to the shop for construction. Lofting likewise lifts from the tool and shop departments the work of expanding detail drawings to full scale before attacking tooling. Likewise, the lofting method greatly facilitates rapid construction of preliminary mockups.
An example of what can be done with the aid of lofting may be given in the case of the most recent engineering achievement at Consolidated design and construction of the twin-engined, 52-place Model 31 flying boat. Only ten months were require to design, construct, and test fly this entirely new ship, whereas previous development projects dealing with flying boats of comparable size, have required two years or more. While this particular case should not be taken a a direct comparison between various current planes, and the time taken to produce them since each new model has its own special problems nevertheless it may be taken as a fair example of the net benefits obtained through application of lofting method to the process of initial development of new aircraft designs.
This article was originally published in the January, 1940, issue of Aviation magazine, vol 39, no 1, pp 34-35, 88.
The original article includes 2 photos.
Photos are not credited but are certainly from Consolidated.