The Case of the Dirigible
Not very much is being heard of performances of dirigible balloons just at present. They have shown themselves to be lacking in stanchness and effectiveness under reasonable variations of weather. We must have fabrics that are stronger for their weight and more impervious. Envelopes must be so built structurally as to resist deformation at high speeds, without having any greatly increased weight. A cheap way of preparing pure hydrogen gas is to be desired.
Most important of all, the balloon must have a higher speed, to make it truly dirigible. This, with sufficient steering power, will protect it against the destructive accidents that have terminated so many balloon careers. Here again arises the whole question of power in relation to motor weight, though not as formidably as is the case with the aeroplane. The required higher speeds are possible now, at the cost merely of careful structural design, reduced radius of action, and reduced passenger carrying capacity.
Better altitude control will be attained with better fabrics and the use of plane fin surfaces at high speeds. The employment of a vertically-acting propeller as a somewhat wasteful but perhaps finally necessary measure of safety may also be regarded as probable.
Giraudon’s Wheel Aeroplane
The Orthopter
The aviplane, ornithoptère or orthopter is a flying machine with bird-like flapping wings, which has received occasional attention from time to time, as the result of a too blind adherence to Nature’s analogies. Every mechanical principle is in favor of the screw as compared with any reciprocating method of propulsion. There have been few actual examples of this type: a model was exhibited at the Grand Central Palace in New York in January of this year.
The mechanism of an orthopter would be relatively complex, and the flapping wings would have to “feather” on their return stroke. The flapping speed would have to be very high or the surface area very great. This last requirement would lead to structural difficulties. Propulsion would not be uniform, unless additional complications were introduced. The machine would be the most difficult of any type to balance. The motion of a bird’s wing is extremely complicated in its details—one that it would be as difficult to imitate in a mechanical device as it would be for us to obtain the structural strength of an eagle’s wing in fabric and metal, with anything like the same extent of surface and limit of weight. According to Pettigrew, the efficiency of bird and insect flight depends largely upon the elasticity of the wing. Chatley gives the ratio of area to weight as varying from fifty (gnat) to one-half (Australian crane) square feet per pound. The usual ratio in aeroplanes is from one-third to one-half.