Aeroplane Construction and Operation

by John B. Rathbun

Fig. 21. Curtiss J N 4-B Fuselage Boxed for Shipment.

With some of the later speed scouts, the body entirely fills the gap between the wings and the top plane is fastened directly to the top members of the fuselage. This makes windows necessary in the sides of the fuselage. When vertical water-cooled motors are used on speed scouts, the front view is entirely cut off, for these are very large motors and project above the fuselage for a considerable distance. This obstruction is avoided in the Curtiss speed scout shown, by the use of a "V" type motor. It will be noted that these two scouts, especially the Nieuport, are of excellent stream line form, a very important item with such high speed machines. The propeller of later Nieuports is provided with a conical spinner cap which evidently reduces the head resistance to a considerable extent. The different portions of the machine are indicated by the same figures as in the case of the reconnaissance machine.

CHAPTER XII DETAILS OF FUSELAGE CONSTRUCTION

Classification of types. While there are a number of methods adopted in building up the fuselage structure, the common type is the "wire truss" in which wood compression members are used in connection with steel wire or cable tension members. Four wooden "longerons" or "longitudinals" run the entire length of the body and are bent to its general outline. The longitudinals are spaced at the correct distance by wood compression members, which in turn are held in place by wire cross bracing. This method of trussing forms a very strong and light structure, although rather complicated, and difficult to build. The cross-section is rectangular, although in many cases the body is converted into a circular or elliptical section by the use of light wood formers fastened to the main frame.

Another well known type is the "Monocoque" body, first used on the Gordon-Bennett Deperdussin monoplane. This fuselage is a circular shell built up of three-ply tulip wood, thus forming a single piece body of great strength. The three-ply shell is really a veneer, the layers proceeding spirally around the body, each layer being securely glued to its neighbor. Between each layer is a scrim layer of treated silk, and another fabric layer is generally glued to the outside of the shell. The shell is very thin, the total thickness of the three layers of wood and fabric in modern machines being rather less than 1.5 millimeters (about 1/16 inch). In the original "Deps" this was somewhat greater, 0.15 inch. Monocoque construction as a rule is heavy and expensive, but offers the great advantage of strength, perfect alignment at all times, and of offering resistance to rifle and shell fire. If the longitudinals of a truss type are struck with a bullet, or shell fragment, the entire fuselage is likely to fail, but a monocoque body may be well perforated before failure is likely to take place.

The American L. W. F. Tractor Biplane has a monocoque body in which spruce laminations are used instead of hardwood. One ply runs longitudinally while the other two layers are spiralled to the right and left respectively. Between each layer is a scrim layer of treated silk, the whole construction being covered with a final layer of fabric, several coats of waterproof compound, and four final coats of spar varnish. When used for seaplanes the wood plies are stitched together with strong wires to prevent separation due to dampness. Since spruce is used in place of hardwood, the construction is lighter than in European models, and the L. W. F. Company claim that it is lighter than the usual truss construction. An additional advantage of the monocoque construction is that the pilot is protected against splinters or penetration by the limbs of trees when making a forced landing in the brush.

Another form of monocoque construction was adopted by the French builder, Bleriot, at the beginning of the war. The fuselage of this machine was covered with papier-mache, the ash longitudinals being buried in this mixture. The papier-mache is built up with glue and silk threads. This construction is very light and strong, but is expensive and difficult to protect against moisture. The front of the fuselage is protected with a 3 millimeter steel armor plate to protect the pilot against bullets and shrapnel. The papier-mache portion of the body is not easily splintered by bullets.

A third form of monocoque, experimented upon by the author, is the steel shell type in which the three-ply wood veneer is supplanted by a thin steel shell. This outer shell is strengthened by suitable stiffener angles. With a shell thickness of 0.013 inch, the strength is equal to the strength of a wood shell and is slightly less in weight. It has the advantage of being easily and cheaply formed into shape and is absolutely proof against the influences of heat and moisture. It cannot splinter, will not catch fire and offers a maximum resistance against penetration. There is yet much experimental work to be done before the construction is perfected.

About midway between the truss fuselage and the monocoque is the veneer construction used on many of the modern German aeroplanes. In general, this may be described as being a veneer shell fastened to the conventional wood longitudinals. Stay wires are not in general use, the veneer taking the shear due to the bending movement. Six longerons are used instead of four, the two additional members being located midway on the vertical sides. Transverse wood frames take the place of the transverse stay wires used in the truss type. Examples of this type are met with in the "Albatros de Chasse" and in the "Gotha" bomb dropper. The single seater, "Roland," has a fuselage of circular section, with a true monocoque veneer construction, but German-like, reinforces the construction with a number of very small longitudinals. In this machine there are 6 layers, or plies, of wood reinforced by fabrics. The entire thickness of the wood and fabric is only 1.5 millimeters (1/16 inch).

Steel tube fuselage dates back to the beginning of the aeroplane industry. In this type the wood longitudinals of the wood truss type are replaced with thin gage steel tubes, the cross struts being also of this material. The diagonal bracing may be either of steel wire, as in the wood frames, or may be made up of inclined steel tube members that perform both the duty of the stay wires and struts. For the greatest weight-efficiency, a steel tube body should be triangular in section rather than square. A triangular section saves one longitudinal and a multitude of wire struts and connections since no transverse bracing is necessary. Connections on a steel tube fuselage are difficult to make and are heavy. They require much brazing and welding with the result that the strength is uncertain and the joint is heavy.