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Aviation History
1942
1942 - 1911.PDF
SEPTEMBER IOTH, 1942 FLIGHT . 291 •• Fig. 7. Smoothing the surface of a fuselage half-shell by sanding, after pressure "cooking" and before it is removed from the solid mould. placed on forms as in Figs. 3 and 4. New ways of wrap ping are constantly being discovered. One method is to staple the strips of each layer together as it is assembled to hold them in place, then remove the staples as the next layer is applied. Applying Fluid Pressure "Cooking" follows completion of the build-up. This is the most special feature of the whole process, and its development to the stage of success was a tedious-, expen sive and nearly discouraging undertaking. Fluid pressure by means of steam, air or water was indicated as nccessary for applying equal pressure to all surfaces, but moisure had to be excluded from the wood forms, as otherwise the plywood wrinkled and broke and the forms warped, making removal of the shell impossible. Wrapping with rubber strips was tried but failed. A big rubber bag was made for enclosing the form and shell, but it cracked and split under heat and pressure. Finally, du Pont engineers developed a moisture-proof membrane for bags which serves the purpose and withstands numerous cookings. A» operation in the making of bags is shown in Fig. 5. Special mechanism was devised also for exhausting air from the bags, and this is covered in the patent. ^Bags enclosing moulds and shells are wheeled into con- ^ntional autoclaves (Fig. 6), which are then sealed, and steam and air in exact proportions are admitted in several ways to control the heat in all parts of the tank. Both water and hot air also have been used for the pur pose. The pressure applied ranges from 20 to 50 lb./sq. in., depending on the article being made and thick ness of the plywood. The heat employed varies also with the article made and with the type of plastic, ranging from 190 to 300 deg. Fahr., which avoids the possibility that high heat of a mechanical process would convert the moisture content in wood veneer into steam and disrupt the fibres. Smoothing the exterior surface of the shell with a portable sander (Fig. iter its removal from the tank and Fig. 8. Finished fuselage made by bonding two moulded-sides together. The weight of the shell is only 72 lb. PLYWOOD AND PLASTIC CONSTRUCTION bag is the next operation. A complete fuselage may be made*in two halves joined together along a longitudinal- vertical plane, resulting in a small-plane fuselage weighing only 72 lb. (Fig. 8). The first complete aircraft built by Vidal was a small one designed for private use and named the Summit. All but the engine, undercarriage and other mechanical operating parts were moulded together, and it was powered__ with a 75 h.p. engine. This little aircraft showed an increase in speed of 20 m.p.h. over its conventional proto type owing to absence of air drag and vibration because of the smoothness and rigidity of the skin. That was in 1938, but the war prevented the company from going forward with production. Later, however, the Langley twin-engine aircraft, moulded by the Vidal method, was built by the Langley Aircraft Corp. on Long Island and flown in many parts of the country.* Orders Placed The Army and the Navy have tested aircraft fuselages, wings, floats and skis and small boats made by the processr"" and they and various aircraft manufacturers have been placing orders quietly with the licensees. The process is believed to have almost unlimited possi bilities of application, and for certain uses the plywood structures have higher strength / weight ratio than metal construction. It is admittedly not economically practical for the manufacture of some quantity production articles such as automobile bodies, and could not effect an im portant cost-saving in fighter and bomber aircraft, in which "the greater expense is for engines, undercarriages and many other parts and items of equipment which can—"~~ not be duplicated in wood and plastic. The inventor's greatest interest, however, is in small private aircraft, which are simpler in design, powered with low power, have relatively low-cost engines, little mechani cal equipment and are, as yet, produced in small quantities. Superior aircraft of this type can be built by the process at a considerable saving in cost. [The reference to the troubles experienced in the evolu tion of the so-called Vidal process is interesting in view of the fact that both in Germany and Great Britain use has been made of rubber bags in autoclaves when applying—-" "the Schwarz protective covering to wooden airscrew glades. The problem was, of course, different, since prob ably both pressures and temperatures were lower.—ED.] * A description of this machine was published in our issue of Oct. 30, 1941
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