True Blind Flight

' I A H E theory and practice of so-called "blind flying" -*• is now well understood, thanks to the valuable work of Ocker, Crane, Stark and other pioneers in this field. It is now fully realized that the pilot, either consciously or unconsciously, depends on some outside visual reference to maintain flight and that when deprived of such a reference his only recourse is the reading of suitable instruments which provide a substitute. That the most experienced air man cannot fly in the fog without suitable instruments is no longer challenged in aeronautical circles. The knowledge that even birds are unable to fly without sight is convincing proof of the inadequacy of animal senses to permit orientation in space. A series of experiments conducted by the writer has established that aural "reference axes" may be substituted readily for visual ones in blind flying (instrument flying)—thus freeing the eyes from their present instrument board-bondage during flight through fog and making it possible to use them without interruption for important developments that may be occurring either outside or inside the airplane. In other words, the ears are capable of supplanting the eyes in blind flying. It is the object of this paper to describe experiments with an apparatus designed to produce and use sound as a reference in blind flying. The possibilities of such a system are obvious. Every pilot who has had occasion to fly by instruments knows the tremendous burden this type of flying imposes on the eyes, even after long practice has reduced to a minimum the nervous strain of translating the various dial readings into actual movement of the controls. H e knows, too, that there are many things bearing on his safety and peace of mind and calling for visual attention in addition to the concentration which his blind flying instruments require. There are fuel gauges and engine instruments to watch which, at any moment, may flash a warning of vital import. There is the necessity of maintaining a continual watch ahead and below for breaks in the fog, other ships, and the sudden appearance of obstacles. Only the man who has flown blind without a co-pilot to help him knows how often one wishes that he dared take his eyes off the instrument board long enough to jot down a radio weather sequence or study his map and decide what he is going to do next. Sight plays such an important part in our daily activities that we seldom stop to think of the remarkable role played by the sense of hearing. Through the mechanism of our ears we are able to distinguish instantly differences in the frequency of sound and at the same time detect change in beat or rhythm. Furthermore, our ears detect the direction of sound through what is known as the "binaural" sense with which virtually everyone is endowed. This directional sense is based on the ability of the brain to interpret differences in phase and volume of sound which occur when sound waves strike the ears unevenly. Curiously enough, the binaural sense is effective even though the ears are not equally sensitive, those who are partly deaf in one ear being able to recognize the direction from which a sound comes through experience and mental compensation.