The chief factors contributing to the solution of the problem of blind flying consist of a new application of the visual radio beacon, the development of an improved instrument for indicating the longitudinal and lateral position of an airplane, a new directional gyroscope, and a sensitive barometric altimeter, so delicate as to measure the altitude of an airplane within a few feet of the ground.
Thus, instead of relying on the natural horizon for stability, Lieut. Doolittle uses an "artificial horizon" on the small instrument which indicates longitudinal and lateral position in relation to the ground at all time. He was able to locate the landing field by means of the direction-finding long-distance radio beacon. In addition, another smaller radio beacon had been installed, casting a beam fifteen to twenty miles in either direction, which governs the immediate approach to the field.
To locate the landing field the pilot watches two vibrating reeds, tuned to the radio beacon, on a virtual radio receiver on his instrument board. If he turns to the right or left of his course the right or left reed, respectively, begins doing a sort of St. Vitus dance. If the reeds are in equilibrium the pilot knows it is clear sailing straight to his field.
The sensitive altimeter showed Lieut. Doolittle his altitude and made it possible for him to calculate his landing to a distance of within a few feet from the ground.
Probably the strangest device of all that Lieut. Doolittle has been called upon to test in Mr. Guggenheim's war against fog is a sort of heat cannon that goes forth to combat like a fire-breathing dragon of old. Like the enemies of the dragon, the fog is supposed to curl up and die before the scorching breath of the "hot air artillery" although the fundamental principle behind the device is a great deal more scientific than such an explanation sounds. It is, in brief, based on the known fact that fog forms only in a very narrow temperature zone which lies between the saturation and precipitation points of the atmosphere. If the air grows a little colder the fog turns into rain and falls; if it is warmed very slightly the mist disappears and the air is once more normally clear, although its humidity is very close to the maximum.
