Aeroplane Construction and Operation

by John B. Rathbun

Patching Fabric. The majority of dopes can be used as cement for patching, but as dope will not stick to varnish, all of the varnish around the patch must be thoroughly removed with some good varnish remover. The varnish must be thoroughly cleaned off or there will be no results. Before applying the dope, the patch must be well stitched all around the edges, then cemented with the dope. The patch must now be covered with at least five coats of thin dope as in finishing the surface. Particular attention must be paid to filling the dope in the stitching.

CHAPTER X. WING CONSTRUCTION DETAILS.

Types of Ribs. The rib first used by the Wright Brothers consisted of two spruce strips separated by a series of small pine blocks. Practically the same construction was used by Etrich in Austria. With the coming of the monoplane, and its deep heavy spars, the old Wright rib was no longer suitable for the blocks were not efficient in thick wing sections. The changes in the wing form then led to the almost universal adoption of the "I" type rib in which an upper and lower flange strip are separated by a thin vertical web of wood. At present the "I" rib is used on nearly every well known machine. It is very strong and light, and is capable of taking up the end thrust of the drag wires, as well as taking care of the bending stresses due to the vertical loading or lift.

Fig. 1 shows the original Wright rib with the "Battens" or flanges (g) and the spacing blocks B. The front spar is at the leading edge (F), and the rear spar at S. An "I" beam, or "Monoplane" type is shown by Fig. 2, and as will be seen is more suitable for deep spars such as (F’) and S'. The upper and lower flanges (g) are separated by the thin perforated web (w), the sectional view at the right showing the connection between the flanges and the web. Lightening holes (h) reduce the weight of the web, with enough material left along the center of the web to resist the horizontal forces. The web is glued into a slot cut in the flanges, and the flanges are then either tacked to the web with fine nails, or bound to it by turns of thread around the flange.

On the average machine, the web is about 3/16 thick, while the flanges are from 3/4 to 1 inch wide, and from 3/16 to 1/4 inch thick. On the very large machines, the dimensions of course are materially increased. At the strut locations in biplanes, and the point of cable bracing attachment in monoplanes, the ribs are increased in strength unless the end thrust of the stay wires is taken up by a separate strut. At the point of stay connection in the old Nieuport monoplane the rib was provided with a double web thus making a hollow box form of section great enough to account for the diagonal pull of the stays.

Fig. 1. Wright Type Rib with Battens and Block Separators. Fig. 2. Monoplane or "I" Type of Rib with Solid Web.

Fig. 3 shows the Nieuport monoplane ribs, which are good examples of box ribs. The sections at the left are taken through the center of the ribs. The wing chord tapers from the body to the wing tip, while the thickness of the wing section is greatest at the middle, and tapers down both toward the tips and toward the body. The upper section is located at the body, the second is located midway between the body and the tip, and the other two are near the tips, the bottom being the last rib at the outer end. The ribs shown are of box form as they are at points of connection, but the intermediate ribs are of the "I" type shown by Fig. 2.

Fig. 3. Nieuport Monoplane Ribs. This Wing Is Thickest in the Center and Washes Qut Toward Either End, Thus Making All of the Ribs Different in Curvature and Thickness. At the Point of Stay Wire Attachment Double Webbed Box Ribs Are Used.