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Climb and Service Ceiling

Climb and Service Ceiling August, 1932 AIRCRAFT ENGINEERING Ove r a Wid e Range of Aeroplane Types Time to Ceiling is practically Constant By J . L. Hutchinson, B.A., A.F.R.AE.S. wher e s.c. represents service ceiling and s.l. sea T has long been a subject of comment a t Martle- level. This can be written sha m Heath that practically all the aircraft I pu t through performance trials there take approximatel y the same time to reach the service ceiling—about 40 minutes. Tabulate d below are values for te n aircraft tested No w dh/dt= rat e of change of height with time =C. a t Martlesham of widely different types chosen a t random: an d as it is found in practice that the curve of Service Ceiling rat e of climb against height always conforms closely Type Height ft. Time. Min. Earl y Troo p Carrier .. .. 9,000 40 t o a straight line, the slope of the line, is Heav y Bomber .. .. .. 12,000 40 Ligh t Aeroplane .. .. .. 12,500 47 constant . If H is the absolute ceiling and C the Torped o Carrier, 1923 . . .. 12,800 48 0 Single Seater Scout, 1922 .. 15,000 41 rat e of climb a t sea level, from Fig. 1 Two-engine d Bomber, 1923 .. 16,000 47 Genera l Purpose .. .. 18,000 40 Two-engined Bomber, 1927 .. 21,000 46 Single-Seater Tighter .. .. 29,000 42 Henc e Mode m Fleet Tighter .. .. 31,000 42 I t will be seen tha t the time varies from 40 to 48 minutes only, though the table includes a wide variet y of aircraft from light aeroplanes to multi­ engined troop carriers with service ceilings from 9,000 to 31,000 ft. To be strictly comparable the climb should be mad e at full throttle throughout, but the list contain s aircraft with gated and supercharged engines. Simple calculation shows, however, that in no case does the throttling a t low altitudes make I n design various considerations operate to reduce more than 2 or 3 minutes difference. th e range of practicable loadings. C. of A. require­ A t first sight it might be expected that, as the ment s stipulate a certain minimum performance heigh t of th e service ceiling varie s so muc h between an d preclude th e use of excessively high wing load­ different aircraft, the time to get there would vary ings with their inevitable high landing speeds, and over a wide range. The examples given show that high power loadings with their small speed range. thi s is not the case and, on reflection, it is perhaps not so surprising since the higher the service Fact s which tend to keep loading u p are ceiling the greater is the climbing ability of the (1) Low wing loading reduces top speed; aircraft. In fact, a machine chasing its ceiling is no t unlike a dog chasing its tail—the greater the (2) Low power loading is expensive in initial effort the faster does the objective recede. costs, in fuel and in maintenance. I t is interesting to establish a formula for the Detail s of the aircraft at the International Aero tim e as follows:— Show at Olympia in 1929 (published in AIRCRAFT If a t any height h th e rate of climb is C th e time ENGINEERIN G of September 1929) show that for th e majority of aircraft exhibited required is w ranges from about 8 to 16 since the service ceiling is the height at which C an d wl from 6 t o 18 is 100ft /min. I have calculated th e values of t from the formula Thi s formula can be expressed as a quotient * Th e autho r is indebted to the Air Ministry for permission to ove r these ranges of w and w1. The results are publish this paper, for which, however, he is solely responsible. presente d in Fig. 2. Th e numerical values of t are underestimated by th e formula and the choice of the constants could possibly b e improved. But th e important point is in which the divisor increases as C illustrated—tha t there is a wide range of aircraft over which the time to the service ceiling is prac­ tically constant. increases, an d the dividend H generally increases 1. Variation of t with power loading. wit h C also, which is consisten t with th e supposition Th e curves of t against w1 a t constant w are flat tha t the quotient will be roughly constant and toppe d and reach a maximum within the range of independen t of C . w1 considered. Or, in other words, the variation I t now remains to evaluate H and C in general 0 i n t over a range of w1 around th e critical value is term s Useful expressions for our purpose, estab­ small. With further increase of w1 t falls rapidly, lished by Diehl in terms of wing and power loading as is true in fact, e g., when the power loading is ar e given below. For thei r derivation reference can so high that the rate of climb a t sea level is only be mad e t o Warner' s Airplane Design, Chapter XVI. 100 ft./min. 2. Variation of t with wing loading As w increases t decreases. This is exemplified showin g how intimately dependent is rate of climb in practice when the wing area is so inadequate on power loading. tha t th e service ceiling is a t sea level. The rate of Fo r the absolute ceiling fall-off of time is small for normal values of w1. Whe n w1 = 10 the average fall-off is less than 1 min. per 1 lb. per sq. ft. change in wing loading. is fairly representative of American practice. Accordin g to the Figure t would be unusually Th e final formula for the time to the service small for a combination of abnormally high wing loadin g and small power loading. In this con­ ceiling therefore becomes, in terms of the funda­ menta l aeroplane characteristics, wing and power nection if is unfortunate that figures for the loadin g Schneider Troph y aircraft are not available. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

Climb and Service Ceiling

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb029580
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Abstract

August, 1932 AIRCRAFT ENGINEERING Ove r a Wid e Range of Aeroplane Types Time to Ceiling is practically Constant By J . L. Hutchinson, B.A., A.F.R.AE.S. wher e s.c. represents service ceiling and s.l. sea T has long been a subject of comment a t Martle- level. This can be written sha m Heath that practically all the aircraft I pu t through performance trials there take approximatel y the same time to reach the service ceiling—about 40 minutes. Tabulate d below are values for te n aircraft tested No w dh/dt= rat e of change of height with time =C. a t Martlesham of widely different types chosen a t random: an d as it is found in practice that the curve of Service Ceiling rat e of climb against height always conforms closely Type Height ft. Time. Min. Earl y Troo p Carrier .. .. 9,000 40 t o a straight line, the slope of the line, is Heav y Bomber .. .. .. 12,000 40 Ligh t Aeroplane .. .. .. 12,500 47 constant . If H is the absolute ceiling and C the Torped o Carrier, 1923 . . .. 12,800 48 0 Single Seater Scout, 1922 .. 15,000 41 rat e of climb a t sea level, from Fig. 1 Two-engine d Bomber, 1923 .. 16,000 47 Genera l Purpose .. .. 18,000 40 Two-engined Bomber, 1927 .. 21,000 46 Single-Seater Tighter .. .. 29,000 42 Henc e Mode m Fleet Tighter .. .. 31,000 42 I t will be seen tha t the time varies from 40 to 48 minutes only, though the table includes a wide variet y of aircraft from light aeroplanes to multi­ engined troop carriers with service ceilings from 9,000 to 31,000 ft. To be strictly comparable the climb should be mad e at full throttle throughout, but the list contain s aircraft with gated and supercharged engines. Simple calculation shows, however, that in no case does the throttling a t low altitudes make I n design various considerations operate to reduce more than 2 or 3 minutes difference. th e range of practicable loadings. C. of A. require­ A t first sight it might be expected that, as the ment s stipulate a certain minimum performance heigh t of th e service ceiling varie s so muc h between an d preclude th e use of excessively high wing load­ different aircraft, the time to get there would vary ings with their inevitable high landing speeds, and over a wide range. The examples given show that high power loadings with their small speed range. thi s is not the case and, on reflection, it is perhaps not so surprising since the higher the service Fact s which tend to keep loading u p are ceiling the greater is the climbing ability of the (1) Low wing loading reduces top speed; aircraft. In fact, a machine chasing its ceiling is no t unlike a dog chasing its tail—the greater the (2) Low power loading is expensive in initial effort the faster does the objective recede. costs, in fuel and in maintenance. I t is interesting to establish a formula for the Detail s of the aircraft at the International Aero tim e as follows:— Show at Olympia in 1929 (published in AIRCRAFT If a t any height h th e rate of climb is C th e time ENGINEERIN G of September 1929) show that for th e majority of aircraft exhibited required is w ranges from about 8 to 16 since the service ceiling is the height at which C an d wl from 6 t o 18 is 100ft /min. I have calculated th e values of t from the formula Thi s formula can be expressed as a quotient * Th e autho r is indebted to the Air Ministry for permission to ove r these ranges of w and w1. The results are publish this paper, for which, however, he is solely responsible. presente d in Fig. 2. Th e numerical values of t are underestimated by th e formula and the choice of the constants could possibly b e improved. But th e important point is in which the divisor increases as C illustrated—tha t there is a wide range of aircraft over which the time to the service ceiling is prac­ tically constant. increases, an d the dividend H generally increases 1. Variation of t with power loading. wit h C also, which is consisten t with th e supposition Th e curves of t against w1 a t constant w are flat tha t the quotient will be roughly constant and toppe d and reach a maximum within the range of independen t of C . w1 considered. Or, in other words, the variation I t now remains to evaluate H and C in general 0 i n t over a range of w1 around th e critical value is term s Useful expressions for our purpose, estab­ small. With further increase of w1 t falls rapidly, lished by Diehl in terms of wing and power loading as is true in fact, e g., when the power loading is ar e given below. For thei r derivation reference can so high that the rate of climb a t sea level is only be mad e t o Warner' s Airplane Design, Chapter XVI. 100 ft./min. 2. Variation of t with wing loading As w increases t decreases. This is exemplified showin g how intimately dependent is rate of climb in practice when the wing area is so inadequate on power loading. tha t th e service ceiling is a t sea level. The rate of Fo r the absolute ceiling fall-off of time is small for normal values of w1. Whe n w1 = 10 the average fall-off is less than 1 min. per 1 lb. per sq. ft. change in wing loading. is fairly representative of American practice. Accordin g to the Figure t would be unusually Th e final formula for the time to the service small for a combination of abnormally high wing loadin g and small power loading. In this con­ ceiling therefore becomes, in terms of the funda­ menta l aeroplane characteristics, wing and power nection if is unfortunate that figures for the loadin g Schneider Troph y aircraft are not available.

Journal

Aircraft Engineering and Aerospace Technology – Emerald Publishing

Published: Aug 1, 1932

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