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Aviation History
1949
1949 - 0455.PDF
MARCH IOTH, 1949 FLIGHT 291 five per cent at a height of only fourthousand feet, due to the lowered pres- sure of atmospheric oxygen; and the sub-sequent decline at greater heights was proportionate. Night vision could becompletely abolished by glare. Hearing.—Another factor on which apilot's efficient operation depended was accuracy of hearing: This was necessaryfor air-to-air and air-to-ground commu- nication, as well as intercommunicationwithin an aircraft. Accurate interpre- tation of auditory signals as used invarious approach systems was essential if correct vital reactions were to be ob-tained. The constant bombardment of the ear by noise over a period of time,as experienced by an aviator, had been shown to cause a diminution in hearingacuity, known as aviation deafness. A recent introduction, the electricaudiometer, had revealed that persons who had been subjected to excessivenoise over a long period might suffer from a considerable degree of deafnessstarting in the high tone range and, pro- gressive by nature, ultimately includinglow tones as well. It was significant that the frequencies of inner marker beaconswere 1,300 c.p.s. and fan markers 3,000 c.p.m. The chief method of protection for air-crew was by means of suitably designed ear-pads and, secondly, the protectionof the aircraft cabin as a whole by. suit- able insulation of the fuselage. Thestructure of pressure cabins materially assisted in this respect. Investigations into the effect of jetnoise on auditory acuity were proceeding at present, said the lecturer, and therewas evidence to show that the effect of high-frequency noise on hearing was aproblem which required constant atten- tion, including special measures for thesound-proofing of cabins. Oxygen.—The effect of oxygen-lack on aviators, although recognized to a cer- tain degree, was not given the promi- nence it deserved until the late war. Many pilots would recall that for a num- ber of years they had flown at certain heights without using oxygen and with- out any apparent deterioration in their physical or mental condition. Experi- mental evidence had, however, yielded irrefutable proof that relatively serious defects in a person's physiological mech- anism did occur at lower heights than was at one time supposed. Dr. Bergin recounted the various symptoms of oxygen-starvation, parti- cularly with reference to its effects on eyesight. Then, continuing his review, he passed on to the question of equili- brium. Dangerous Illusions Equilibrium.—A sense of equilibrium was essential for safe flying, and, when in an aircraft, was conveyedto the pilot, first by his instruments, and secondly by his own sensations. A variety of impres- sions, visual, cerebral, and sensory, went to make up the general picture of a per- son's attitude in space, and if all these senses were working normally and vision was unimpaired an accurate estimate could be made. In flying, however, acceleration forces, effects of gravity and other factors produced false impressions by stimulation of these organs, and many illusions as to position could be pro- duced. Three important illusions which might occur in flying by night were dangerous by reason of the fact that false impres- B 21 sions of the movements of other aircraftmight be given. They were as follows: — (1) The auto-kinetic illusion, a visual one, consisting of the apparent movement of an object, such as a light, when fixated against a uni- form dark background, other visual aids being absent. There- was usually a short delay before its onset and the average duration of each phase was about ten seconds; it was experienced at some time by all normal persons. (2) The oculo-gyral illusion, caused by a combination of visual and non- visual factors, namely, conflicting impulses received from the eye and semi-circular canals respec- tively. It consisted of the apparent movement of objects resulting from stimulation of the x , semi-circular canals following angular acceleration. Thus a sta- tionary object appeared to move in a direction opposite to that of rota- tion. (3) The oculo-gravic illusion, caused by a conflict of impressions between the eye and the otolith organ. It consisted of the apparent displace- ment of an object in space as a result of stimulation of the oto- lith organs by acceleration. Ex- periments conducted with a fixed light in an aircraft in complete darkness, observed under different degrees of acceleration, indicated that such sensations of motion and displacement of the light might occur at any time between 10 deg and 60 deg of bank, and increased with increasing bank. They always occurred during banks of 40 deg or more. The illusions described were very little reduced by habituation, which made them all the more dangerous. Their occurrence might be largely prevented or cut short by several methods. First, the presence of lights in different vertical and horizontal planes was almost com- pletely successful in abolishing the con- dition. Thus, when only the tail light of an aircraft was visible, auto-kinesis might occur, but, if lights in different locations, such as wing tips, nose and tail, were used, the condition was abolished. Secondly, the interruption of vision would eliminate the condition and for this reason flashing lights were to be pre- ferred to steady ones. Alternatively, the pilot might interrupt steady fixation by blinking. Thirdly, localization by means of other lights on the ground prevented the onset of the condition. Lastly, the fixation on some other point such as a windshield frame or canopy helped in reducing the intensity of the illusion. A pilot's training taught him to subor- dinate these powerful impulses and rely entirely on his instruments, but a pilot who was suffering from fatigue, lack of oxygen, or adverse psychological disturb- ances, might find that he was obeying his impulses rather than his training. Fatigue.—The signs and symptoms of advanced fatigue were self-evident, the early stages not so. Factors producing fatigue were length of individual flights, numbers of landings and take-offs, and type of aircraft. Weather was also a most important factor. Fear and appre- hension were also high on the list and, in addition, glare, noise, vibration, in- sufficient oxygen or inadequate circula- tion of air all acted adversely on a per-son's state of physical fitness which in turn led to fatigue. Every effort should be made to avoidthe factors which contributed to fatigue by such means as adequate rest andrelaxation for crews in between and during flights, suitable diet, properlytimed, and the maintenance of the nearest approach to normal living con-ditions within the aircraft by mainten- ance of correct temperature, ventilation,humidity, and oxygen requirements in the cabin. The provision of flying aids aimed atreducing other fatiguing factors. The introduction of the automatic pilot wasan important advance in this respect, but it was for consideration how muchautomaticity of control was desirable from a psychological point of view. Diet and Alcohol.—Extensive investi- gation during the war revealed that a normal, well-balanced diet was adequate for the needs of flying personnel. The effects of alcohol on man were so well known, said Dr. Bergin, as not to war- rant -further discussion except to say that its indiscriminate consumption by air- crew when on flying duty was only men- tioned to be condemned, as representing a grave hazard in flying operations. Comfort and Convenience Turning from the man to the machine, the lecturer said that the closest co-opera- tion between designers, operators, and medical advisers should take place at the very earliest stages in an aircraft's life, if satisfactory operating conditions were to be obtained. Seats should be designed in conjunc- tion with the advice of persons skilled in the application of anthropometry, with ample individual adjustment for varia- tions in build, and particular care taken with such problems as correct support for the lower part of the back, taking into account the fact that the '' lumbar curve" was very much greater than was generally imagined. In windshield design, the first aim of an aeronautical designer was to approacli as near to aerodynamic perfection as pos- sible, but this was not always compatible with adequate visibility for the pilot The windshield must be so arranged that neither in design nor in material did its use entail muscular or ocular strain on the part of the pilot, which could quickly produce fatigue. The best angle of visi- bility for comfort and efficiency was about 15 deg from the horizontal. Great strides had been made in recent years with regard to cockpit and instru- ment layout. If eye fatigue was to be avoided, instruments should be at such a distance that the normally seated pilot did not have constantly to use his power of accommodation in order to focus on his instruments. If he was forced to accommodate frequently, he would become fatigued and readings would become blurred and indistinct. The opti- mum distance was between 23m and 27111. Two important features of controls to which insufficient constructive thought had been given were, first, that of their being recognizable by touch alone and, secondly, of their being reachable in all positions which the pilot was likely to assume in flight. Shapes for various con- trols were to a large extent standardized by S.B.A.C. practice, but could, in the opinion of many, still be bettered. Dr. Bergin touched on the selection of suitable personnel for flying duties. For
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