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Aviation History
1943
1943 - 0444.PDF
i8o FLIGHT FEBRUARY I8TH, JO. 43 High-altitude Flight Structural, Physical and Aerodynamic Problems Revieived : The Meteorological Factor : Pressurising the Cabin By W. NICHOLS, A.R.Ae.S. PROBLEMS relating to high-altitude flight werereceiving attention in commercial aviation someyears before the war. In 1937 flight at an altitude of three to four milea was being seriously considered by the big airline operators in America. The comfort of prospective passengers at such altitudes was also receiving attention. Tests had been made upon pilots and air crews in altitude chambers, i.e., airtight rooms from which air can be pumped to simulate conditions at great altitude. These tests not- only showed the faulty reactions of the human frame under condi- tions of insufficient oxygen, they also provided data on the proper amount that should be furnished for cor- rect reactions. A fairly accurate conception of the problem had" been formed when war broke out. In military aviation con- siderable progress has been and is being made in con- nection with high-altitude . and stratosphere flight. For obvious reasons the results of such research cannot be included in this article, but in a later section a full description of some of the German developments relat- ing to pressurised cabins will be given. The present article must confine itself mainly to the problems likely to be encountered in the future development of commercial .aviation. Flight at great altitudes by the aid of the super- charged or pressurised cabin offers certain definite advan- tages in speed and freedom from meteorological difficulties. The airline operator is not, however, interested in actual air speed but with the so-called block-to-block time or actual time involved from point of departure to destination. 8 10 ~"' E 14 16 18 TRIP LENGTH — HUNDREDS OF High-altitude flight can only offer advantages under these conditions over a route of considerable mileage, for both climb and glide incidental to such flight must be considered. Even for a 2,000-rnile range it is necessary to use approximately 35 per cent, distance for the climb and descent. For a 700-mile range practically the entire dis- tance is required for these purposes. The rates of climb and' glide are governed by three factors: physiological, aerodynamic and structural limita- tions. With regard to the physiological limitation, rate of change of pressure ex- perienced by the passenger should not exceed values corresponding to a climb of 500 ft./min., or a glide of 300 ft./min. Therefore, if the cabin remains unsuper- charged these appear to be the limits of the climb and glide. An analysis of the aero- dynamic limitations shows the best rate of climb to be somewhat higher than the maximum for passenger comfort, and maximum rate of glide should likewise be higher, that is, 1,500ft. to SO 22 MILES 24 26 28 30 Time saved by cruising at high altitude final apfc^^sft \ Interior of a projected pressurised air liner by the GeneralAircraft Co. It is to seat 35 passengers. 2,000 ft./min. The thirdfactor, structural limita- tions, ' introduces no diffi-culty during the climb. During the glide, however, the aircraft is restricted to arate of glide such that dynamic pressure or indicated air speed does not exceed a certain allowable value inherentin the design. These factors can affect the efficiency of a flight as follows: For aircraft with no pressurised cabin, climb and glide will be limited by the physiological factor; thus efficiency in climb and glide is greatly impaired with this type of aircraft. With cabin supercharging the limit on the climb will be imposed by aerodynamic considerations, thus giving the greatest efficiency, while on the glide the limits will in general be due to the structural factor, thus approaching the most efficient operation more closely than in the case of the unsupercharged cabin. Time Economy The aircraft with a pressurised cabin is, therefore, more 'desirable from an efficiency standpoint, efficiency here meaning economy in time only. A considerable gain is possible at the greater altitudes for the greater distances. This now raises the point over what distances are flights at great altitude, say, 40,000ft. justified. From aerodyna- mic considerations alone one can arrive at the following conclusions: — * (1) Flights of 500 miles or U'.«s should be restricted to alti- tudes below 15,000 feet. (2) Flights at altitudes of 15,000 feet to 25,000 feet are ad- vantageous over distauces 01*500 to 1,000 miles.. (3) Flights at altitudes above .25,000 feet should be justified for distances of l.ofco to 1,500 miles. (4) Flights at altitudes oi 40,000 feet are not cconomicallv justified for trips oi less than 3,000 miles. .The above conclusions result from the aerodynamic, physiological and structural factors. The meteorological factor, however, also has to be considered. Concerning
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