Glidden and Stevens Getting Away in the "Boston"
(Leo Stevens, N.Y.)
Field and Speed
An aerostat (non-dirigible balloon), unless anchored, drifts at the speed of the wind. To the occupants, it seems to stand still, while the surface of the earth below appears to move in a direction opposite to that of the wind. In the sketch, if the independent velocity of a dirigible balloon be PB, the wind velocity PV, then the actual course pursued is PR, although the balloon always points in the direction PB, as shown at 1 and 2. If the speed of the wind exceed that of the balloon, there will be some directions in which the latter cannot progress. Thus, let PV be the wind velocity and TV the independent speed of the balloon. The tangents PX, PX´, include the whole “field of action” possible. The wind direction may change during flight, so that the initial objective point may become unattainable, or an initially unattainable point may be brought within the field. The present need is to increase independent speeds from thirty or forty to fifty or sixty miles per hour, so that the balloon will be truly dirigible (even if at low effectiveness) during practically the whole year.
Suppose a dirigible to start on a trip from New York to Albany, 150 miles away. Let the wind be a twenty-five mile breeze from the southwest. The wind alone tends to carry the balloon from New York to the point d in four hours. If the balloon meanwhile be headed due west, it would need an independent velocity of its own having the same ratio to that of the wind as that of de to fd, or about seventeen and one-half miles per hour. Suppose its independent speed to be only twelve and one-half miles; then after four hours it will be at the position b, assuming it to have been continually headed due west, as indicated at a. It will have traveled northward the distance fe, apparently about sixty-nine miles.