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Aviation History
1949
1949 - 0072.PDF
FLIGHT JANUARY 13TH, 1949 Physiological Aspects of Flying . . ... seconds at 2g radial, one minute 15 seconds at 3g radial. Onesubject was unable to complete the task at 3g. The acceleration developed in rocket-propelled take-offs ofpiloted aircraft would be limited by the personnel carried. It would be important to learn what maximum g in the trans-verse position, relative to the pilot as experienced when seated, could be tolerated while still allowing him to perform accuratemovements with hands and feet. If the pilot was in the prone position head forward, linear acceleration at take-off wouldrepresent positive g and on landing negative g would be experienced. The tolerance of man to positive g when fullystretched out was known to be very low, and the limiting g for this position should be determined. Concerning negative g, Dr. Lovelace said that at the AeroMedical Laboratory at Wright Field it had been found that exposure to negative g for several seconds would lead to over-distension and rupture of vessels within the head, but expo- sure to higher accelerations for tiroes under 0.3 seconds did 'not cause such injury. Means were necessary to exert counter pressure on the veins in the head and neck. Experimentsusing monkeys had indicated that confusion and unconscious- ness resulting from relatively long exposure to negativeaccelerations above 3g might be the result of a reduction in cerebral blood flow due to arterial pressure drop. The eventual aim was to design aircraft and equipment thatwould function in any part of the world at an operational temperature range of from —60 deg F to +160 deg F. Inaddition to the effect of solar heat upon the man without cabin cooling, the temperature in the cockpit of some aircraftcould easily reach 180 deg F at extremely high speeds. It had been necessary to develop experimental flying clothingthat could be ventilated internally. Results had indicated that it might soon be possible to protect pilots over the tempera-ture range quoted by the use of a single lightweight clothing assembly. Regarding noise and vibration, the author said that Armyand Navy pilots had uniformly expressed their great appre- ciation of lack of noise and vibration during flights in jetaircraft, stating that there was less fatigue present. ..-;.": Pressurization and Decompression Cabin pressurization was next discussed, and a definitionof comfort was given as '' the state in which one is unconscious of adaptation to environment." Passengers did not have asense of comfort or complete freedom of sensation above 5,000ft until they were acclimatized. Normal healthy peoplecould accommodate to altitudes as high as 12,000ft. Loss of presssure in present-day pressurized aircraft couldbe considered a minor hazard in view of existing laboratory and flight test information. The degree of compression thatone could stand safely was determined by the extent and the rate of expansion of the internal body gases. It had beendemonstrated that for rapid or instantaneous decompressions (0.01 seconds or less) a relative gas expansion of 2,3approached the maximum tolerable. The area of fuselage surface lost by structural failure hadin the long run to be evaluated by tests. For preliminary design purposes it could be assumed to be in the area of ajettisonable bubble canopy, a nose section or an escape hatch door. For a commercial aircraft (2,000 cu ft capacity and up)flying with a cabin differential of 6.55 Ib/sq in at 40,000ft., the largest allowable explosive orifice was 7,000 sq in, or a hole8ft in diameter. Such a hole was ten times larger than that normally expected, thus decompression could be considereda minor hazard for the type of aircraft. Decompression experiments on human subjects had indi-cated that the normal ear could easily adjust itself to a rate of pressure loss of 100 lb/sq in per second. This was nottrue when suffering from colds or respiratory infections, and a passenger with an occluded sinus would suffer severely frompain when either the volume or the .pressure of the trapped gases increased as little as 30 per cent regardless of the rateof decompression. Lessons that could be applied to passenger aircraft wereobvious. Restricted passageways between compartments should be avoided. This precaution was especially importantas the height of aircraft increased, and regular exits should have safety harness or nets across the inside during flight toprevent passengers and crews from being accidentally blown overboard The Army Air Force had recently announced the develop-ment of a pressurized flying suit that would enable aircrews to fly at altitudes above 60,000ft and low pressures approaching avacuum and to escape from aircraft if the necessity arose. Yet the suit was sufficiently flexible for them to carry out thenduties in comfort. Personal equipment for air crews must not only providethe maximum comfort and efficiency in flight but also be designed to be of use in the event of emergency, bale-out orforced landing. The U.S. Air Forces' training programme would soon include for fighter pilots instruction in the useof the ejector seat. Some 300 ejections with dummies and volunteers had been made without serious injury to test per-sonnel and a system for emergency escape from aircraft at speeds up to 600 m.p.h. had been developed. With presentcatapult and ejection seats subjects could be ejected with a velocity of 60-64 ft/sec with maximum acceleration of I5g—5 to log less than that considered the safe skeletal tolerance. The Germans had found that a pilot ejected from a cockpitcould withstand ram pressures on the unprotected head up to 480 m.p.h. for a few seconds without tearing tissues. Withproper positioning of headrests on ejector seats it was found that the head could be kept erect duringthe ejection stroke,thereby preventing hyper extension. Modifications to the ribbon type parachute used in Germanyand now undergoing constant test in America would undoubtedly provide for safer escape from high-speed aircraftat both low and high altitudes. .,"..' I Baling Out at Transonic Speeds Safety provisions for the pilot of the Douglas D.558 Sky- streak in case of extreme urgency at transonic speeds entered discussions in 1945. The device finally chosen consisted of a mechanical fastening of pilot's compartment to remainder of fuselage by means of four bomb-rack-type hooks, operated mechanically by a pull handle located above centre of the instrument panel. A 60-lb pull on the handle completed successively, a two-second decompression of the pressurized cockpit and release of bomb-rack hooks. The pilot baled out by pulling a cable handle at right hip location. A io-lb pull on the handle simultaneously released the pilot's backrest and shoulder harness fastening, allowing him to move or fall out of the rear of the cockpit. Should the speed of the aircraft be below that indicating a nose-breakaway escape, the pilot could jettison the bubble canopy section by a 20-30 lb pull on a cable located near the right knee level. Human engineering is now being applied to the field of linear decelerative forces of rapid onset, brief duration, and high magnitude and their effect on the human body. The Aero Medical Laboratory of the Air Materiel Command has in process of development a linear decelerator, located at Muroc Experimental Air Base, with which it will be possible to apply linear decelerative forces within the range of 5 to loog peak magnitude, 0.01 to 0.5 sec duration, and 100 g/sec to 10,000 g/sec rate of application. This linear aircrew decelera- tor can achieve speeds of 220 m.p.h. with a maximum of 3.2g acceleration, and, by means of exceptionally powerful friction brakes in series, can be brought to a stop in as little as 11ft. Thus, it will be possible to take actual crash data, ditching data, or parachute-opening shock data, and reproduce these forces at will under controlled conditions for analysis and study. The toxic effects of carbon dioxide at both ground level and altitude deserved more study. Although direct evidence in the literature was meagre, a recent review of the problem (White, 1948) tentatively fixed the maximum safe allowable carbon dioxide concentration at ground level at 5 volumes per cent for 5 minutes or less, 4 volumes per cent for 15 minutes or less, and 1 volume per cent for not more than two hours. Carbon dioxide was better tolerated at altitude, and tolerance, being a function of the partial pressure, allowed calculation of altitude equivalents from ground level data. Four volumes per cent carbon dioxide at ground level, for example, was equivalent to 5, 6, and 7.5 volumes per cent at pressure altitudes of 5,000, 10,000 and 15,000 feet respec- tively. Most modern airliners carried considerable amounts of carbon dioxide for fire-fighting purposes and some had been tested in flight against hazardous carbon dioxide concentration. It was doubtful whether the problem had had widespread appreciation, since no relevant civil regulations existed. . ft5: ALVIS PROGRESS REVIEWT HE recent annual general meeting of Alvis, Ltd., was presided over by Mr. J. J. Parkes, the managing direc- tor, in the absence through illness of the Chairman, Mr. A. E. Nicholson, J.P. In the Chairman's statement, refer- ence was made to the growing utilization of the Alvis Leonides engine. After speaking of the breaking of the international speed record for helicopters by the Fairey Gyrodyne, which was powered by a Leonides engine, it was stated that pro- duction orders had been received from both Bristols and West- lands for Leonides engines for use in helicopters. B 20
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