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Aviation History
1956
1956 - 0350.PDF
350GHT I The prototype XP6M in the final assembly stage at Baltimore. A pair of Allison J71 turbo jets are visible in the background. Producing *the First SeaMaster By ADOLPH VLCEK, JR.* IN keeping with the many innovations in the XP6M MartinSeaMaster design, the manufacturing plan for the prototypeintroduced new concepts in experimental aircraft production. First, design requirements for volume producibility were madean integral part of the original experimental designs. Second, the job was scheduled through regular production channels, usingstandard procedures and regular production workers and machines. Third, during construction the ruling principle was"do it with what we have"—no new machines or equipment were purchased except one or two items which could not be improvised.The result was a calculated saving of 25 per cent over the usual experimental construction methods and this, on a multi-milliondollar contract, was a worthwhile saving. Producibility Planning. Chief feature of the producibilityplanning is the assembly break-down which, taking advantage of the small cross-sectional area of the hull, makes it possible toassemble the hull in sectional fixtures like a landplanc instead of the giant hull docks required for most seaplanes. The first modelwas built in a one-piece hull dock but the production models will be assembled in movable sectional fixtures without delay due toredesign. Another producibility feature is the extensive use of forgings and castings in the airframe structure. Normally fittingson large experimental ships are hogged and milled out of bar stock, but, since the SeaMaster was designed for production from itsinception, castings and forgings were specified frequently. Martin's own production foundry aided considerably in carrying out thispolicy, since it is equipped to make one or two parts of a given design at low cost. Producing a ship loaded with advanced designfeatures without buying a great deal of new equipment required unusual ingenuity and improvisation. Thick Wing Skins. The thick, tapered wing skins representeda distinct departure from conventional design and required development of several special processes. For example, rivet holes *Tooling Manager, Glenn L. Martin Co., Baltimore, Maryland. THIS article is one of the first to describe details of the constructionof a large high-speed prototype. The Martin P6M SeaMaster embodies numerous unusual features, some of which are structural (and are dealtwith here) while others are of a military nature, such as the rotating weapons-bay door upon which can be mounted various stores or acamera pod. The Glenn Martin company of Baltimore unfortunately lost the first prototype late last year when it had completed only a littlemore than 50 hours' flying. As a result, the special military equipment fitted in the second prototype has had to be removed and replaced byexperimental equipment to continue flight tests. Nevertheless, the pro- gramme has not been seriously delayed, and the U.S. Navy expect touse many P6Ms for all kinds of military purposes involving new techniques, such as refuelling from submarines. Production P6Ms willbe powered by four Pratt and Whitney J75 turbojets, and it is expected that one airframe may be used for experiments in nuclear power. had to be drilled normal to the contoured surface. This requiredan ingenious bridge-type drilling and riveting fixture which was about 100ft long by 15ft high [illustrated on p. 352—Ed.]. Navy specifications required the skins to be drilled and trimmedbefore anodizing, which added about 30 per cent more surface to the already huge surface of the skins and called for unusualanodizing facilities. An old, unused anodizing tank was enlarged to take the 40-ft skins. It was moved close to an installed generatorof sufficient capacity to provide the power requirements. The floor had to be shored up to carry the load of the large tank, thegreat volume of anodizing solution, and the 800-lb skins. Experi- mental tests were made to develop new process schedules whichwould produce the unusual conditions required by the engineering specifications. Finally, the anodizing operation was donesuccessfully at a cost far below expectations. Development of a sealing method for the integral wing fueltanks required an extensive research programme in which several methods of sealing were tested. A method of applying a doublethick fillet of EC 801 sealant to the joints and rivet holes was found to meet the requirements.
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