THOSE who fly airplanes are not overfond of getting the maximum performance out of “ships” that have piled up their flying hours well into the hundreds since overhaul. The control sticks are loose and wobbly in their bearings, and the stabilizers are either too hard to roll or work with suspicious ease. The landing gear of landplanes rattles on taking off and landing, and the whole structure of seaplanes begins to feel loose. The fabric covering the surfaces is dead, and the planes feel heavy. Engines begin to use more oil than they should, and do not run so smoothly. Even when an engine is pulled and replaced by a new one, vibration is greater. You can shake the wings and tail and feel them rattle. Everything seems to be wearing— not enough to warrant replacing any particular part, but just enough so that one does not pull back so heartily on the stick when coming out of a dive, and so that one would a little rather have a plane with a little less time for a long cross-country or crosswater trip.
The worst thing is the uncertainty of the things that can’t be seen. Parts of fuselages and hulls that can be opened up have been cleaned and refinished two or three times as opportunity permitted. One would like to put the plane out of commission and have a look at everything, just to make sure. The small amount of corrosion that is found whenever a couple of weeks are available for opening things up is just enough to indicate that there is probably more deterioration going on elsewhere—inside the wings, underneath the lower longerons, around the keel plating, everywhere where the real vital strength of an airplane resides. There is not time in a tight gunnery schedule, a concentration period for the development of tactics, or a long cruise, to lay the planes up for the work one would like to do. The squadron must be kept full in order to meet the schedules and to avoid the heavy penalties of planes out of commission during gunnery, and the spare planes must be kept as stand-bys and used to replace crashes.
It seems as though the vitals of an airplane are the very parts that are covered up the most. The little dents and worn and broken places that one can see are not so bad. You at least know what to expect from them, and handle the plane accordingly. Nearly everyone, though, has seen some amazing things in the way of deterioration when things were really opened up. It is only an occasional plane that gets that way. It doesn’t happen frequently enough to warrant shortening schedules to do more upkeep work in the squadrons. Still, if a pilot rolls the wings off a plane with several hundred hours flying time since overhaul and lives, he is apt to hear some unkind remarks passed on his lack of judgment in treating such a plane in such a manner.
The Air Station at San Diego has helped considerably by installing fuselage covers that lace so that the entire bottom of a fuselage can be opened up. Then one can have a look, and can take preservative measures without knocking off all other work for the occasion. It’s too bad they can’t devise a bottom for a big boat that will snap on, or wing coverings that can be hinged up. They could, were it not for the weight involved. But even then, it wouldn’t put the air stations and overhaul bases out of a job, for this is only one feature of a major overhaul.
The time that planes should be kept in service before sending them to major overhaul cannot be worked out from a formula. So much depends on the ever-changing types of construction (that indicate progress in design and consequently improvement in performance), on the service to which the planes have been put, on the varying opportunities for maintenance in the squadrons, and on the technical skill of the operating personnel. Administrative considerations also enter into the problem. It may sometimes be best to overhaul planes a little sooner than one would like in order that they may be ready for a cruise in good shape, or it may be desirable to feed in a few planes in order to keep the overhaul base from becoming disorganized. Some types of planes under some conditions of service need overhaul badly at the end of 250 hours, and others can go for 500 hours and, short of accident, still be in fairly good condition. No one, with the means to do otherwise, would think of driving an expensive automobile year after year without laying it up in the shop for a general inspection, repairs, and tuning up. Apart from considerations of safety, economy of naval material requires similar periods for expensive airplanes. The average naval airplane, built to low factors of safety, is in the air and is operating under far more difficult and severe conditions, about as many hours per year as the average automobile is on the road.
The reconditioning of naval planes differs in one important respect from the overhaul of commercial aircraft. Design changes are always found necessary and desirable as a type of airplane acquires use in service. It is only possible for the squadrons to incorporate those changes that are imperative for safety or for the military use of the planes as intended. Other changes, many of them of a nature that will lengthen the service life of the airplanes, must accumulate until a well-equipped base can accomplish them, usually during major overhaul when the concealed parts can be got at and worked on.
The central design section of the Bureau of Aeronautics, and through that section, the civilian designers and builders of the airplanes, are dependent upon the overhaul bases for reports and recommendations regarding design features that affect maintenance and very frequently structural strength. A great many of the design changes on various types of planes have originated at the bases, and often, due to the lack of availability of airplanes or drawings elsewhere, the specific methods of incorporating design changes are best determined there. The bases also provide a reservoir of experience in various shop processes, technique, methods, and special equipment. An attempt is consequently made to keep personnel there who are as far as possible qualified in design training and experience. That that personnel should also be qualified in airplane operation goes without saying, for they should have as broad a viewpoint as possible towards the material with which they work, and should merit the unqualified confidence of the operating personnel in their methods and decisions.
When an airplane is taken into the shops of the San Diego station for major overhaul, it is completely disassembled by a shop that does nothing else. And this means disassembled, for every part that will come apart is taken apart. The fabric is stripped from the wings and control surfaces; the engine is removed; the landing gear and tail-skid assembly removed and disassembled; struts, wires, engine, and surface controls taken out; cowling, fairing, and instruments removed; and all the hundreds of parts that are bolted or screwed to the skeleton fuselage frame put in boxes. Every part is tagged with a small copper burr bearing a number assigned to that particular airplane.
The necessity for such complete disassembly is twofold. First, a thorough inspection is impossible without removing all the parts that would otherwise make inspection difficult, if not impossible, and second, a proper paint and finish job cannot be done on assembled parts, and the life of a plane depends largely on its protective finish.
The fuselage, or hull, being, so to speak, the backbone of the plane, is scheduled through the shops to final completion, an estimate of cost and time having previously been made before the plane is taken into the shops. The wings, floats, and other parts that join on to the fuselage are scheduled to meet the fuselage as necessary, and due allowance must be made for the work load on the various shops and the personnel that will be available to do the work.
After disassembly the skeleton fuselage and all the little parts are cleaned. Everyone knows that a clean surface is the secret of a good paint job. Steel fuselages and parts that are not too soft or fragile are sand-blasted to a beautiful satin finish, and are immediately given a priming coat of paint, for otherwise they would begin to oxidize and deteriorate overnight. Steel grit is used for the blasting material on steel parts that are heavy enough to stand this treatment, rounded beach sand under low pressure on other parts, and hand cleaning on still others. Duralumin fuselages made up of complex built-up structures are not sand-blasted, but are cleaned by brushing with mild cleaning compounds that will not injure the soft duralumin. Parts that do not contribute to strength, such as cowling and fairing, are immersed in tanks and cleaned chemically.
At this point it is possible to eliminate the greater portion of parts that are beyond repair. After cleaning away the dirt, rust, and corrosion, a decision can be made as to whether reenforcement and strengthening can be economically employed. Most of the fuselages that must be stricken from the Navy list because of deterioration wind up their naval careers at this point.
The usual run of fuselages or hulls are then repaired. Broken longerons and other members are spliced or replaced; dents, kinks, and deformations that weaken the strength are reenforced, usually by welding, and the entire structure made sound throughout. All elongated holes for the attachment of wires, fittings, and assemblies are brought back to their original tolerances by filling with welded metal and redrilling, by reaming and bushing, or by replacement of parts, which usually have to be manufactured in other shops for the purpose. The use of oversize bolts and pins is avoided as far as possible in order that all parts may be interchangeable in the field. The brace wires are put back in, and the fuselage straightened and aligned. At this point fuselages are occasionally found to be beyond repair, as they are sometimes distorted and warped so that they cannot be brought back to their former accuracy of shape, even with the application of heat. If they are not properly aligned, the wings and control surfaces cannot be finally assembled so that the plane will be in proper aerodynamic balance.
Meanwhile repair has been made of all the minor parts. Bent members are straightened and reenforced and improvements incorporated. They are painted and as good as new in both strength and appearance by the time they are ready for replacement in the fuselages. Certain parts such as control wires and electrical wiring are always renewed. Steel bolts and fittings are cadmium plated in order to increase their resistance to corrosion and to insulate them against electrolytic action when in contact with dissimilar metals. Holes for pins and bolts are brought back to their original dimensions. Certain parts, depending on the design of the airplane, require heat treatment if they are made up new or if it has been necessary to apply heat in repairing them. All the parts that have been distributed throughout the various minor shops for repair and reconditioning come back to the plane from which they were originally taken. It is only when one sees the complexity of a modern fuselage and the diversity of types of airplanes that are overhauled at San Diego that the necessary experience and skill of the mechanics can be realized.
The last things that are put back in the fuselage or hull are the tanks, piping, and wiring. The tanks meanwhile have gone through the same process of cleaning and repair, and a special technique must be developed and maintained for this work as for nearly every other branch of airplane overhaul work. During the repair of the tanks themselves it is necessary to remove fittings, strainers, gages, etc., and send them all to different shops that specialize in the particular class of work, and get them back to the tanks from which they came at the proper time for assembly and installation.
The fuselages are then covered and doped, and are now ready for final assembly. Meanwhile the wings have been overhauled. Repairs are made to the internal structure of the wings, spars spliced, ribs replaced, or damaged members reenforced in order that the original strength may be restored in every respect. Fabric covers are stitched, slipped over the surfaces, rib-stitched, and secured in place, and finally doped to the proper condition of tautness. Control surfaces must be handled in the same manner, and all wear and play removed from hinges and attachments. The art of a skilled metal smith is so different from that of a woodworker that wooden wings have to be handled by entirely different personnel from metal wings. Minor parts of wings frequently have to be handled in other shops, as in the case of repair of a fitting, which may involve sheet metal work, welding, machining, plating, and finally painting before it can be replaced in the wing from which it came.
Everything else that goes into the final installation is similarly handled. A special shop repairs and reconditions wheels, another works on flotation bags, still others on magnetos, radio, batteries, and fire extinguishers. Landing gear and external struts must be made to fit their attachments without play or lost motion. Flying and landing wires must be reconditioned or replaced. Corrosion must be arrested on floats, and members that show signs of corrosion reenforced or replaced.
Since the engines carry their own logs and histories with them, no effort is made to put the same engine back into the plane from which it came. The overhaul of engines is scheduled on a productive basis and kept separate from the airplane schedule. The engines, like the airplanes, are first disassembled. Ignition wiring and spark plugs are removed, and carburetors and magnetos taken off and sent to separate shops for further disassembly, cleaning, repair, and replacement of parts. Cylinders are taken off and sand-blasted. Crank cases are disassembled, pumps and other assemblies removed, and the pistons and rods broken down. After cleaning, new bushings and pins are inserted, journals stoned down to the original tolerances, crank shafts straightened, valves re-cut, and other repairs and replacements made as necessary to bring the engine back to its original clearances. Even the spark plugs are disassembled and reconditioned. Parts return to the same engine from which they were taken, and the minor and major assemblies are put together until the engine is again complete.
The engine is now put on the belting-in stand, where it is turned over by external power to work in the moving parts without imposing the additional stresses due to heat and power. It is then placed on the test stand and carefully run in and its functioning checked. Special test propellers are used in order that full power may be developed and the engine still kept cool. When finally found to be satisfactory, it is greased for preservation and sent to store. Like the airplanes, the engines are brought back to their original condition insofar as it is possible to do so, and in some respects, particularly when changes have been incorporated, the overhauled engines, like the planes, are even better than new.
When the entire airplane is finally assembled, the work is again specialized. The crews that install the engines cannot be expected to rig and align the wings and tail surfaces. The flotation gear is installed by a special crew, and tested to see that the bags inflate properly and evenly. Recharged bottles containing the gas for flotation are put in. Cowling is also installed by a separate crew, for there is always a considerable amount of straightening, cutting, and trying connected with a neat cowling installation. When the plane is completed, the engine is turned up on the beach to check the functioning of the fuel and oil systems, to insure that there is no harmful vibration, and to give the engine itself further time to work itself in. Finally the airplane is looked over and checked by the officers under whose supervision the various parts of the overhaul have been accomplished.
Then the airplane goes on the line for flight test. Here any errors in alignment, balance, and general functioning are finally found by actual test and corrected. The plane is flown again and again until it is satisfactory as an airplane in all respects. During this time it is impossible to avoid getting a certain amount of dirt and oil on the plane. The final coat of finish is consequently not applied until after the completion of flight tests, and when the airplane is delivered to the operating units it is spick and span in appearance and known to be sound throughout.
Few naval officers, even those who are in aviation, who have not been connected with modern overhaul work, realize how careful and thorough a job of reconditioning can be done. Most officers do know, however, that accident statistics in the Navy show that the work is well done, and that the necessary technique and knowledge is increasing. It has to increase, for new materials, requiring familiarity with new processes, are continually coming into use. A few years ago duralumin was unknown and cadmium plating had not been applied to aircraft. The use of welding is widespread in airplane design, particularly with chrome molybdenum steel, but the welds must be made with extreme skill, for there is no excess factor of safety to fall back on. Today the use of duralumin sheets covered with a thin layer of aluminum is commencing, which will necessitate further increases in repair technique to keep pace with the new materials. The anodic process for protecting duralumin from corrosion is being adopted and stainless steel is finding a wider application. Shop equipment and tools must also keep up with commercial developments outside of the Navy. Tungsten carbide drills, semi-automatic hand tools, mechanical drawbenches, and many forms of special equipment make it possible to do work that previously was out of the question, and make possible a greater output of work. Special tools and machines are developed at San Diego that eventually find a commercial application.
At San Diego there are an average of more than fifty airplanes going through the shops simultaneously in various stages of major overhaul. There are thirteen different types of airplanes being worked on in the shops at the present time. About forty engines of five different types are simultaneously in the engine overhaul shops. In order to accomplish this work, it is necessary to specialize the men into forty-four different shops. Many of these shops are again specialized within themselves, as in the necessary division between wooden- and metal-wing repair.
All of this work, including the upkeep and maintenance of shop tools and equipment, planning, scheduling, estimating, keeping track of progress, shop storerooms, supervising, transportation, testing, clerical work, obtaining of material, development work of all sorts, and all the other auxiliary functions, is done by a complement of about five hundred enlisted men, five commissioned officers, and two warrant officers. The tour of duty for enlisted men is two years, extended in a few special cases. Leave and the average amount of illness reduces the effective complement to less than 450 men, out of which must come supervisors and overhead of all sorts. The sort of lost time that is unavoidable in military organizations reduces each man’s working time to less than thirty-five hours a week.
From the nature of the work that is accomplished, it is clear that the men must be specialized on their jobs. The man who has been taught how to control the temperatures of the heat-treatment baths for duralumin, and to support the work in the electric furnaces so that it will not warp during treatment, cannot be readily replaced by a man who has been installing complex parts in a certain type of fuselage, and the expert metal worker who has been splicing metal wing beams cannot be expected to shoot trouble on a lathe that is out of commission. The full two years of duty is barely enough to enable a man properly to perform his own particular job or operation. The experience that he gains is valuable, but it is only a limited sort of experience. After two years at the San Diego Air Station, a man who is an accomplished fabric stitcher, and who knows all the intricacies of the machine with which he works, must be sent to sea where the chances are that no stitching is ever done; or another, who has learned to weld chrome molybdenum tubular fuselages, goes to a squadron operating planes that do not even have fuselages.
Conversely the station, for a replacement metal-shop foreman, receives a chief who has been in charge of operating planes in a squadron. The turnover of labor is appalling. Not even the full two years of shore duty is available in most cases, for there was a turnover of more than 100 per cent at San Diego during the past year. A labor turnover of 50 per cent would put a commercial concern on the rocks, and make the supervisors gray-haired.
The repair stations have somehow managed to do their work under these conditions, and to do it creditably. They could continue to do it in the same manner in the future if it were not for certain changing conditions that have been foreseen which give rise to problems that are still unsolved. Perhaps the most important of these is the fact that naval aviation is still expanding rapidly. The five-year construction program authorized by Congress will be completed in another year. The Battle Fleet, which is served by San Diego, has been largely already cared for in this program. The number of airplanes throughout the Navy, however, is being increased, and those same airplanes must be overhauled and reconditioned somewhere. The outlying stations are now being built up with suitable airplanes, but already the facilities of San Diego are being called upon to overhaul airplanes for Pearl Harbor and the Asiatic Fleet. San Diego has not quite been able to take care of the requirements of the fleet alone in the past two years. The services of outside contractors and the shifting of work loads to other stations are resorts that have already had to be used. Both methods of taking care of the excess of work are unsatisfactory.
Civilian contractors will do the definite items of work specified in the contract, but no more, unless the contract is modified accordingly. No contract can be drawn up covering the work found necessary on overhaul, because the nature of the work cannot be foreseen until a portion of it has been completed. Unless contracts are drawn up in so general a way that the costs would be prohibitive to the Navy, the Navy will be the loser in the thoroughness of the work performed.
The time element is of extreme importance in a military organization, and particularly so in short-lived airplanes. An airplane out of operating service means not only a loss in availability for operation, but a loss due to approaching obsolescence. When the five-year program is completed, there will still not be enough spare and reserve airplanes to put operating airplanes out of commission long enough to accomplish the overhauls at civilian plants, or to accomplish other than minor transfers to distant naval stations, not to mention the transportation charges and the work loads on the other stations.
The five-year program, moreover, will not complete the expansion of naval aviation. There is no question but that the addition of new carriers to the fleet will necessitate a further increase in the number of airplanes, and it is probable that additional planes will be needed for the program of cruiser building. The published policy of the Navy Department is to develop the application of airplanes to all types of surface ships. So far the application has been made to battleships and cruisers alone, and the extent to which airplanes can be put on board even those vessels is far beyond what has already been accomplished. Additional airplanes can be put to sea in far greater numbers than heretofore, even without the addition of new surface ship tonnage to the fleet. It is reasonable to believe that this will be done as fast as tactical and strategical considerations can absorb the additional planes.
The surface ships—even the great Lexington and Saratoga—cannot possibly take care of the major overhaul of their own airplanes. Neither space nor man power is available. The most that they can do is to carry spares of the major assemblies, such as wings, landing gears, control surfaces, engines, etc., compactly stowed in the small spaces that will be available; and to replace damaged parts with these spares, accumulating the damaged material for overhaul elsewhere. A real major overhaul cannot be accomplished on a combatant ship, and nothing less is acceptable for reasons of economy of both life and material.
Even a new design of carrier cannot be expected to take care of the overhaul of its own airplanes. We are already so limited by the provisions of the Washington treaty, and may be still so further limited by the London treaty, that it is imperative that every bit of available space on new carrier designs be put into stowage for operating airplanes. Space for spreading out disassembled airplanes and for the necessary shop equipment is not legitimate on combatant carriers. A double penalty would be incurred in the living, messing, and berthing space and tonnage for the additional personnel to accomplish the overhauls, and the designers are hard put to find space for the operating personnel on carriers as they are now conceived.
Relief must be sought in several directions. The aviation repair facilities of the Medusa, the Vestal, and such general fleet repair vessels, can be expanded, but not to any considerable extent without interfering with the other functions of those ships. Aviation fleet repair ships, designed solely for that purpose, can eventually be built, but they are a long way in the future, will cost a great deal of money, and will require a large overhead in naval ratings other than aviation to operate them. The effectiveness of such vessels as compared to a shore base will necessarily be low, due to their inherent limitations of space, transportation, accessibility to supply markets, testing facilities, etc., but they appear to be an eventual necessity for reasons other than taking care of part of the total work load.
Meanwhile the necessity for increasing the output of existing overhaul bases is already upon us. Much can be done at San Diego and elsewhere in expansion of output. With the short tours of duty of the enlisted workmen and the tremendous labor turnover, far less can be done than if trained men could be retained to make use of their training.
The use of civilian labor to replace the enlisted personnel has been suggested. Unless the total enlisted force of the Navy is substantially increased, this will be an ultimate necessity. The objection that the enlisted personnel would lose valuable training is easily met by the fact that their training in a modern overhaul base is necessarily so specialized that it is of little value elsewhere—even of little value in any other job on the same base. There are, however, other better-founded objections, such as that desirable shore billets for enlisted personnel would be eliminated, and that legislation, with increased cost to the naval budget, would be necessary. It appears that the increased cost can hardly be avoided. More and older airplanes can scarcely be overhauled at a reduction in total cost.
In the meantime, two partial solutions have been suggested that would considerably ease the situation. One of them is to extend to three years the shore duty of the enlisted personnel at the overhaul bases, and to four years or more the shore duty of the key personnel—shop supervisors and highly specialized chief petty officers whose duties require an unusual amount of experience. The other is to make use of the sixteen-year men by reenlisting them for duty on their station, either making them extra numbers so as not to unduly retard promotions, or recalling them to active duty in the Fleet Reserve. These measures would make it possible to develop methods that would expand the output of work now obtained, instead of dissipating time and energy in going over old ground with new and untrained personnel. The rate of output will naturally increase with total experience, but its rate of increase would be considerably accelerated by making fuller use of what experience exists. These suggestions also have the merit of being the least expensive palliatives that can be applied, viewed from the very practical standpoint of dollars and cents.
The airplane overhaul bases take great pride in the part that they have had in establishing the enviable record for safety enjoyed by aviation in the Navy, and in the economical manner in which they have done their work. Under no circumstances can their standards of workmanship be lowered. Their work, which is done under difficulties, is increasing, and can be expected to increase in the future. Either more money or more men with which to do that work must eventually be forthcoming. In the meanwhile, minor changes in policy will go far to enable them to keep up, and to retain the well- merited confidence that the aviators in the fleet have in the condition of their overhauled engines and airplanes.