girder structure was usually constructed of wood and wire. However, the chief designer for Fokker, Reinhold Platz, came from a welding background, and the later Fokker aircraft such as the Dr.1 triplane and D-VII had welded steel tube girder fuselages. The second type of fuselage structure, developed as early as 1912, was the monocoque , a French word meaning “single shell.” First developed by the Swiss engineer Ruchonnet, the monocoque structure was adopted by Louis Bechereau Figure 10.26 Wing and rib structural design for the Fokker Dr.1 triplane and the Fokker D-VII. Both had cantilevered wings with thick airfoil sections. (Source: S. T. G. Andrews and S. F. Benson, The Theory and Practice of Airplane Design , E. P. Dutton and Co., New York, 1920.) 10.7 Historical Note: Evolution of Flight Structures 795
796 CHAPTER 10 Flight Vehicle Structures and Materials for the design of the highly streamlined (for its day) Deperdussin airplane. A Deperdussin racer was the winning airplane in the 1913 Gordon Bennett Cup at Reims, with a phenomenal speed of 124.5 miles per hour. A Deperdussin equipped with pontoons also won the Schneider Cup race in the same year. A monocoque fuselage, such as that shown in Fig. 10.28, was made by laying thin strips of wood over a mold contoured to the desired fuselage shape. (Tulip wood was used for the Deperdussins.) Usually three layers of wood were used in this fashion, with the strips of wood running at right angles to the layers underneath. Each layer was glued to the other. Then two layers of fabric were glued to the outside of the shell and one layer of fabric on the inside. The fuselage was molded in two half-shells, which were subsequently glued together to form one single shell. The monocoque shells were amazingly thin, from 3 to 4 millimeters, and were both lightweight and strong. All of the stress in the monocoque fuselage was carried in the skin, so this monocoque design was the forerunner of stressed-skin aircraft structures. A clear advantage of the monocoque design was that fuselages could be made aerodynam- ically clean (streamlined). Disadvantages were that battle damage was more difficult to repair, and the cost of manufacture was considerably more than for the conventional girder type. For these reasons only a few airplane designs during World War I used monocoque fuselages. The third type of fuselage construction, which became popular toward the end of World War I, was a combination of the first two. Called the monocoque–girder type , or more commonly the veneer type , it consisted of a boxlike structure made up of four longitudinal longerons and internal bulkheads to which wood panels were Main longerons Strut Transverse strut Motor supports Motor supporting beams Figure 10.27 Generic girder fuselage design. (Source: O. Pomilio, Airplane Design and Construction , McGraw-Hill, New York, 1919.)
glued, as shown in Fig. 10.29. Compare the (then conventional) girder construction shown in Fig. 10.27 with the veneer construction in Fig. 10.29. Missing in Fig. 10.29 are all of the internal struts and bracing seen in Fig. 10.27; the wood panels, glued or attached by nails or screws, provided the required stiffening.