How It Flies; or, The Conquest of the Air / The Story of Man's Endeavors to Fly and of the Inventions by Which He Has Succeeded

by Richard Ferris

Varnishing is the next process, the gores being treated in turn. Half of the envelope is varnished first, and allowed to dry in a well-ventilated place out of reach of the sun’s rays. The other half is varnished when the first is dry. A framework which holds half of the balloon in the shape of a bell is usually employed. In case of haste, the balloon may be blown up with air, but this must be constantly renewed to be of any service.

The first step in varnishing is to get one side (the outer, or the inner) coated with a varnish thin enough to penetrate the material: then turn the envelope the other side out and give that a coat of the thin varnish. Next, after all is thoroughly dry, give the outer side a coat of thick varnish closing all pores. When this is dry give the inner side a similar coat. Finally, after drying thoroughly, give both sides a coat of olive oil to prevent stickiness. The amount of varnish required is, for the first coat 1½ times the weight of the envelope, and for the second coat ½ the weight—of the thin varnish. For the thick coat on the outer side ⅓ of the weight of the envelope, and on the inner side about half as much. For the olive-oil coat, about ⅛ of the weight of the envelope will be needed. These figures are approximate, some material requiring more, some less; and a wasteful workman will cause a greater difference.

The neck of the balloon (also called the tail) is in form a cylindrical tube of the fabric, sewn to an opening in the bottom of the balloon, which has been strengthened by an extra ring of fabric to support it. The lower end of the tube, called the mouth, is sewn to a wooden ring, which stiffens it. The size of the neck is dependent upon the size of the balloon. Its diameter is determined by finding the cube of one-half the diameter of the balloon, and dividing it by 1,000. In length, the neck should be at least four times its diameter.

The apex of the balloon envelope is fitted with a large valve to permit the escape of gas when it is desired that the balloon shall descend. The door of the valve is made to open inward into the envelope, and is pulled open by the valve-cord which passes through the neck of the balloon into the basket, or car. This valve is called the manœuvring valve, and there are many different designs equally efficient. As they may be had ready made, it is best for the amateur, unless he is a machinist, to purchase one. The main point to see to is that the seat of the valve is of soft pliable rubber, and that the door of the valve presses a comparatively sharp edge of metal or wood so firmly upon the seat as to indent it; and the springs of the valve should be strong enough to hold it evenly to its place.

The making of the net of the balloon is another part of the work which must be delegated to professionals. The material point is that the net distributes the weight evenly over the surface of the upper hemisphere of the envelope. The strength of the cordage is an item which must be carefully tested. Different samples of the same material show such wide variations in strength that nothing but an actual test will determine. In general, however, it may be said that China-grass cordage is four times as strong as hemp cordage, and silk cordage is ten times as strong as hemp—for the same size cords.

The meshes of the net should be small, allowing the use of a small cord. Large cords mean large knots, and these wear seriously upon the balloon envelope, and are very likely to cause leaks. In large meshes, also, the envelope puffs out between the cords and becomes somewhat stretched, opening pores through which much gas is lost by diffusion.

The “star,” or centre of the net at the apex of the balloon, must be fastened immovably to the rim of the valve. The suspension cords begin at from 30° to 45° below the equator of the envelope, and are looped through rings in what are called “goose-necks.” These allow a measure of sliding motion to the cordage as the basket sways in the wind.

For protecting the net against rotting from frequent wetting, it is recommended to saturate it thoroughly with a solution of acetate of soda, drying immediately. Paraffin is sometimes used with more or less success, but tarring should be avoided, as it materially weakens the cordage. Oil or grease are even worse.

At the bottom of the net proper the few large cords into which the many small cords have been merged are attached to the ring of the balloon. This is either of steel or of several layers of wood well bound together. The ropes supporting the basket are also fastened to this ring, and from it hang the trail-rope and the holding ropes.