Aeroplane Construction and Operation

by John B. Rathbun

Typical Wing Assembling Shop

CHAPTER IX. WING CONSTRUCTION.

General Wing Frame Layout. In many ways, the frame of the wing is one of the most important structural parts of the aeroplane. It not only maintains the proper aerodynamic form of the aerofoil, but also transmits the air pressure and lift to the body of the machine, and therefore carries the entire weight of the aeroplane when in flight. In spite of the heavy loading on this frame it has been brought to a remarkable degree of strength and lightness. Not only is "Brute" strength necessary, but it must also be rigid enough to properly retain the outlines of the aerofoil with the heaviest loadings, hence the efficiency of the aeroplane greatly depends upon the stiffness as well as strength. The contour of the entering edge must be particularly accurate and well supported since it is at this point that the greater part of the lift is obtained, and where a slight deviation in form will materially affect the lift and drag.

The fabric surface, on which the air pressure is exerted, must transmit the pressure and lift to the main structural members through the parts that give form to the surface. The fabric surfacing, being flexible and pliant, must be supported at frequent intervals by the forming members which in effect are similar to the joists of a floor system. The forming members are then supported in turn by longitudinal beams, or girders, that transmit the pressure to the point where the load is applied. The girders not only carry the lifting force, but must also take care of the drag which acts at right angles to the lift. To pass girders that are sufficiently strong, and yet within the limits of weight, through the narrow space between the top and bottom surfaces of the wing is not always the simplest of problems.

Figs. 1 and 2 show typical wing frames in diagrammatic form, the upper views are the plans, while at the bottom are sections taken through the wing. The outlines of the sections are curved to the outlines of the aerofoil adopted for the wings, and after this outline is drawn out to scale, we must maneuver our structural members so that they will lie entirely between the surfaces.

In Fig. 1, the forming ribs are indicated by R, these being the members curved to the aerofoil form. They are spaced along the length of the wing at intervals of about one foot and the fabric is applied to the top and bottom edges of the rib. The ribs are fastened to the front spar F, and the rear spar S. The spars are equivalent to beams, and are for the purpose of transmitting the lift of the ribs to the body. A thin strip E (nosing) running along the entering edge of the wing, serves to hold the fabric taut at this point and also forms it to the shape of the aerofoil entering edge. The thin trailing edge strip (T) performs the same purpose, and the wing outline is completed by the "End bow" (A) which retains the fabric at the wing tips. Between the front spar F and the rear spar S is the trussed "Drag bracing," which binds the two spars into a truss in a horizontal direction, and against the drag of the surfaces. This consists of the "Drag" wires or cables (d) and the short wood struts (e), although in many cases the ribs are strengthened at the point of attachment of the drag wires and serve as struts. The aileron G is located at the outer tip and is hinged to the rear spar or to an extension of the rear spar. Between the spars are thin strips known as "battens" which stiffen the ribs sideways, these are shown by (F).

Fig. 1. (Left) Wing Assembly with Spar to the Rear of the Entering Edge. Fig. 2. (Right) Assembly with the Front Spar at the Entering Edge.

Metal connection clips C, at the end of the wing spars, are for attaching the wings to the body, or for connection of the two halves of the upper wing of a biplane. Looking at the lower sectional view we see the interplane struts of a biplane attached to the front and rear spars as at (m) and (n). Referring to the plan view, the location of the struts is indicated by * * * at the points where the drag-bracing is attached to the spars.