Fabrics are obtainable in various colors, painted, varnished, or wholly uncoated. The rubber and cotton mixtures are regularly woven in France and Germany for aeroplanes and balloons. The cars and machinery are frequently shielded by a fabricated wall. Weights of envelope materials range from one twenty-third to one-fourteenth pound per square foot, and breaking stresses from twenty-eight to one hundred and thirty pounds. Pressures (net) in the main envelope are from three-fifths to one and a quarter ounces per square inch, those in the ballonets being somewhat less. The Patrie of 1907 had an envelope guaranteed not to allow the leakage of more than half a cubic inch of hydrogen per square foot of surface per twenty-four hours.
Manufacturing the Envelope of a Balloon
Inspecting the Envelope of Andrée’s Balloon “L’Oernen”
The best method of cutting the fabric is to arrange for building up the envelope by a series of strips about the circumference, the seams being at the bottom. The two warps of the cloth should cross at an angle so as to localize a rip or tear. Bands of cloth are usually pasted over the seams, inside and out, with a rubber solution; this is to prevent leakage at the stitches.