CHAPTER II. Covering the Planes.
The surfaces of a motor driven aeroplane are usually made of some material which is practically air tight. The Herring-Curtiss Co., use Baldwin’s rubberized silk, while most of the foreign aviators prefer a balloon cloth known under the name of "continental."
Ordinarily the surfaces of a glider are not covered with any preparation to make them air tight and is not necessary, but since it will considerably increase their efficiency it is offered as a suggestion to those who are able or care to undergo the expense.
Aero varnishes for this purpose are obtainable in the market and may be applied with an ordinary brush or by immersing the fabric. One gallon will cover approximately 100 square feet of ordinary Cambric, although much depends upon the weave. The more open or coarser the goods, the more varnish it will require, while fine fabrics take the least amount.
Varnish is expensive and is not considered in the estimate of cost made at the beginning of the book.
The surfaces are formed of cambric or muslin stretched tightly over the ribs. Thirty yards of material, one yard wide will be sufficient to cover the machine, including the rudders.
Seven strips 4 feet 6 1/2 inches long are cut and sewed together along the selvages so that a surface 4 feet 6 1/2 inches wide and a little over 20 feet long is formed. Twenty one strips, 4 feet 6 1/2 inches long and 1 1/2 inches wide are cut and sewed to the surface at right angles to the long edges and one foot apart, between their centre lines. The edges of these strips are turned under 1/4 of an inch on each side so that they form a reinforcement 1 inch wide which will come directly above each rib.
Fig. 20.—Method of hemming up edge of cloth.
Reinforcing. The long edges of the surface are then doubled back and hemmed, turning under 1/4 of an inch and forming a 3 inch hem as illustrated in the upper part of Fig. 20. This 3 inch hem is then doubled back one inch and sewed again so that the result is a two inch hem, composed of two thicknesses of cloth save for one inch back from the edge where it is made up of four thicknesses.
This reinforcing is necessary to avoid ripping and tearing the cloth out from under the tack heads when it is under pressure during a flight.
Fig. 21.—Section of cloth hemmed, and reinforcing strips sewn on.
The bottom planes. The cloth on the bottom planes is made up of two sections, divided by the space in the centre of the lower plane which the operator occupies. These sections are made and reinforced in exactly the same manner as that for the top plane just described but are one foot less than half as long.
The cloth is tacked over the front horizontal beam and then stretched tightly over the curved ribs and fastened with tacks at the ends. Fasten the corners of the cloth first and smooth it out before driving the tacks in the ribs. Ordinary brass headed upholsterer’s nails are used but they should not be long enough to pass all the way through the ribs.
A strip of felt 3/8 of an inch wide and four feet long is laid on the cloth directly over each rib so that it comes between the head of the tack and the cloth. This precaution may seem unnecessary to some, but it greatly reduces the liability of having the cloth tear when under pressure. The tacks along the ribs are spaced about 4 inches apart A heavy weight held against the under side of the rib by an assistant, when the tacks are driven in will provide a firm foundation to hammer against.
A very good method of fastening the cloth to the ribs is to sew a pocket on the under side of the surface and into which the ribs may be slipped.
The rear ends of the ribs may be fitted with metal tips by tapering the end down until it is round and measures 1/2 inch in diameter. A 1/2 inch brass ferrule such as that used on file handles is then forced on.
The rudder planes are covered on both sides. The fabric is stretched tightly over the frame and then tacked along the edges. The edges should be turned under before tacking so that there is no possibility of the cloth tearing out.
The cloth at the ends of the planes should be securely fastened to the struts by means of tacks. This will relieve the ribs of some of the strain and correct a tendency for them to pull in towards the centre.