1、A BRIEF STUDY OF THE EFFECTS OF TURBOFAN-ENGINE BYPASS RATIO ON SHORT- AND LONG-HAUL CRUISE AIRCRAFT Aruid L. Keith, Jr. Lungley Reseurch Center Humpton, Vu. 23665 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, 0. C. DECEMBER 1975 I Provided by IHSNot for ResaleNo reproduction or networki
2、ng permitted without license from IHS-,-,-TECH LIBRARY KAFB, NM 19. Security Classif. (of this report) 20. Security Classif. (of this page) Unclassified Unclassified I IIIII I I lllll I lllll Ill1 Ill 21. NO. of pages 22. Price 43 I $3.75 2 Government Accession No. I - - - 1 Report No NASA TN D-7890
3、 A BRIEF STUDY OF THE EFFECTS OF TURBOFAN- ENGINE BYPASS RATIO ON SHORT- AND LONG- - 4. Title and Subtitle HAUL CRUISE AIRCRAFT 7. Author(s) hid L. Keith, Jr. 9. Performing Organiation Name and Address NASA Langley Research Center Hampton, Va. 23665 2. Swnsoring Agency Name and Address National Aero
4、nautics and Space Administration Washington, D.C. 20546 _. 5 Supplementary Notes 3. Recipients Catalog No. .- 5. Report Date December 1975 6. Performing Organization Code 8. Performing Organization Report No. L-9898 .- 10. Work Unit No. 505-04-1 1-01 11. Contract or Grant No. ._ - 13. Type of Report
5、 and Period Covered Technical Note - - . -_- 14 Spomoring Agency Code 6 Abstract A brief study of the effects of turbofan-engine bypass ratio on Breguet cruise Large thrust lapse rates at high range and take-off distance for subsonic cruise aircraft has shown significant differ- ences between short-
6、 and long-haul aircraft designs. bypass ratios caused severe reductions in cruise range for short-haul aircraft because of increases in propulsion system weight. fraction (ratio of propulsion weight plus total fuel weight to gross take-off weight), are less sensitive to propulsion-system weight and,
7、 accordingly, were not significantly affected by bypass-ratio variations. Both types of aircraft have shorter take-off dis- tances at higher bypass ratios because of higher take-off thrust-weight ratios. Long-haul aircraft, with a higher fuel 7. Key-Words- (Suggested by Authoris) ) Bypass ratio Crui
8、se range Turbofan engine . 18. Distribution Statement Unclassified - Unlimited For ale by the National Technical Information Service, Springfield, Virginia 221 61 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A BRIEF STUDY OF THE EFFECTS OF TURBOFA
9、N-ENGINE BYPASS RATIO ON SHORT- AND LONG-HAUL CRUISE AIRCRAFT Arvid L. Keith, Jr. Langley Research Center SUMMARY A brief study has been made of the effects of varying tui-ofan-engine “ypass ratios from 3 to 12 on the Breguet cruise range and balanced-field take-off distance of short- and long-haul
10、aircraft. These aircraft were assumed to cruise at a Mach number of 0.8 at an altitude of 11 000 m (36 089 ft). The study showed that the large thrust lapse rate of high - bypass -ratio engines caused severe reductions in the cruise range of short-haul air- craft (low ratio of propulsion weight plus
11、 fuel weight to gross take-off weight, called fuel fraction). This result was due to an increase in the propulsion weight of the high-bypass- ratio engines. Long-haul aircraft (higher fuel fraction) are less sensitive to increases in propulsion weight, and accordingly the net effects of increasing b
12、ypass ratio were not sig- nificant. Both types of aircraft had shorter take-off distances with increasing bypass ratio because of higher take-off thrust-weight ratios. INTRODUCTION Continued development of the turbofan engine has resulted in an increase in bypass ratio from low values (1 to 1.4) to
13、moderately high values (4 to 8); this has brought about significant improvements in subsonic aircraft cruise performance and reductions in aircraft noise. These moderately high-bypass-ratio engines have evolved through technological advances in overall pressure ratio, turbine inlet temperature, hot-
14、parts cooling, and materials. These engines provide (1) better cruise economy because of lower specific fuel consumption, (2) lower noise in and around the airport community because of lower core-engine and fan-jet velocities, and (3) shorter take-off distances and faster climbout because of the hig
15、her take-off thrust of engines that are sized for matching of cruise net thrust with cruise drag (hereinafter referred to as cruise thrust-drag matching or thrust-drag matched engines). Shorter take-off distances and faster climbout also reduce community noise. It has been suggested that engines wit
16、h bypass ratios even higher than those of present engines would provide further gains in cruise economy, shorter take-off distances, and lower noise. Lower cruise specific fuel consumption is inherent in higher bypass-ratio Provided by IHSNot for ResaleNo reproduction or networking permitted without
17、 license from IHS-,-,-1l111llII II I1 I1 Ill I I II cycles for basic engines of a given technology level. Thrust lapse rate, the rate at which engine net thrust decays with flight speed, is also a function of bypass ratio, and engines which are sized specifically for cruise thrust-drag matching will
18、 certainly produce increases in take-off thrust with increases in bypass ratio. Furthermore, with high bypass ratios, if the exhaust flow, which is at a lower velocity, could be directed over or through wing-flap systems to increase take-off lift coefficients, shorter take-off distances, faster clim
19、bout, and still lower noise could be realized. Short take-off and landing aircraft thus could be con- figured to meet noise requirements expected for future aircraft without sacrifices in flight performance. The potential improvements offered by high-bypass-ratio engines may not be fully realized, h
20、owever, because of aircraft installation effects. with bypass ratio, propulsion systems sized to provide cruise thrust-drag matching will become larger and heavier as bypass ratio is increased. Increases in propulsion-system weight would require either an increase in aircraft gross take-off weight t
21、o perform the same mission requirement or a displacement of fuel or payload for aircraft having the same gross weight. Performance losses due to engine-installation effects and propulsion-system cruise drag can reduce the advantage of lower cruise specific fuel consumption provided by the high-bypas
22、s- ratio engine; the lower fan pressure ratios of high-bypass-ratio engines of a given techno- logical level result in greater sensitivity to installation effects. Since thrust lapse rate increases Thus, it is not clear that the advantages of lower cruise specific fuel consumption, increased take-of
23、f thrust, lower noise, and possibly lift augmentation at take off, which are attributable to increases in bypass ratio, can be attained without important influences on overall aircraft flight efficiency and cruise range. The weight of the engine and propulsion package and the specific fuel consumpti
24、on are of great importance to short-haul aircraft, for which the total fuel is a relatively small fraction of gross take-off weight. haul aircraft, the weight of the engine and propulsion package is of lesser importance; cruise specific fuel consumption and propulsion-system drag are the more import
25、ant param- eters associated with aircraft performance. For long- A brief study was therefore made to analyze the influence of turbofan-engine bypass ratio on Breguet cruise range and balanced-field take-off distance for configurations ranging from short-haul, short take-off and landing aircraft to l
26、ong-haul, conventional aircraft. The parameters varied for the base study were engine bypass ratio, from 3 to 12; take-off wing loading, from 2394 to 4788 Pa (50 to 100 lbf/ft2); and ratios of propulsion-system weight plus fuel weight to gross take-off weight (fuel fractions) from 0.2 to 0.4. a crui
27、se Mach number of 0.8 at an altitude of 11 000 m (36 089 ft) was assumed. Lift drag polars of the airframe alone (no propulsion drag) typical of subsonic cruise aircraft with the assumed wing loadings were used in the study. For the calculations The overall aircraft cruise lift-drag ratio 2 Provided
28、 by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-was determined by adjusting the airframe lift-drag ratio to include the isolated propulsion drag of engines sized for cruise thrust-drag matching. Although it is recognized that selection of a specific cruise s
29、peed, altitude, and wing loading would not provide optimum cruise performance for every bypass ratio, these param- eters were held constant for the basic part of the study so that the singular effect of bypass ratio on the study parameters could be evaluated. In several instances, sensitivity of cru
30、ise range to nacelle drag, propulsion weight, and altitude matching was studied. performance and weights used in the study are considered representative of the advanced technology that would be available in the period 1980 to 1985. Engine SYMBOLS Values are given in both SI and U.S. Customary Units.
31、 The measurements and calcu- lations were made in U.S. Customary Units. A a CD CL D d Fn h L M 9 R cross-sectional area, meters2 (feet*) sonic speed, knots D drag coefficient, - qoos L lift coefficient, _ qoos drag, newtons (pounds force) balanced-field take-off distance, meters (feet) net internal
32、engine thrust, newtons altitude, meters (feet) lift, newtons (pounds force) Mach number dynamic pressure, pascals (pounds force per feet2) Breguet cruise range, nautical miles (pounds force) 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I II I1 I
33、I II 11Il11 I1 I I I I S SFC W W X Subscripts: cr d f fuel i max nac Prop r T t tc 4 wing area, meters (feet) specific fuel consumption, per hour weight, newtons (pounds force) weight flow rate of air, newtons per second (pounds force per second) fuel fraction, or ratio of propulsion-package weight
34、plus total fuel weight to gross Wprop + Wfue1,t WT take-off weight, cruise descent final fuel initial maximum nacelle propulsion reserves take-off total climbout and acceleration from take-off to cruise Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,
35、-wb wing-body (total aircraft less engines) 00 free stream Abbreviations: CTOL conventional take-off and landing STOL short take-off and landing PROCEDURE The present brief study is intended to show only the effects of turbofan-engine bypass ratio on Breguet cruise range and balanced-field take-off
36、distance of subsonic cruise aircraft typical of short- and long-haul designs. A complete analysis of engine-bypass-ratio effects throughout the total flight envelope of such aircraft is beyond the scope of this study. Although the study results would be influenced to an extent by bypass-ratio effect
37、s at flight conditions other than cruise, the predominant effects occur during the cruise flight segment. To perform this analysis, it was necessary to obtain take-off and cruise performance characteristics of turbofan engines defined for a broad range of bypass ratio, weight and cruise drag of the
38、propulsion package, and airframe aerodynamics typical of subsonic cruise aircraft. It was necessary to assume a fuel usage schedule to define the fraction of total fuel that would be available during cruise operation. these parameters and describes how they were combined to provide parametrically de
39、fined aircraft that are designed to match cruise thrust with cruise drag. This section of the paper presents Engine specific performance at static or take-off conditions (fig. 11, ratios of cruise net thrust to take-off thrust, and cruise specific fuel consumption at a Mach number of 0.8 and an alti
40、tude of 11 000 m (36 089 ft) (fig. 2) are considered representative of engines possibly in service in the period 1980 to 1985. ratios from 3 to 8 were obtained from engine manufacturers estimates of engines with overall pressure ratios of 25 and maximum turbine inlet temperatures of 1533 K (2760 R).
41、 Engine performance for bypass ratios up to 12 was obtained by calculating the performance from extrapolated data for engine component performance, fan pressure ratios, core-engine nozzle pressure ratios, and temperatures. A 1 00-percent fan-face total pressure recovery, no horsepower for bleed-air
42、extraction, and a nozzle gross thrust coefficient of 0.985 are assumed for all engines. The data points shown for bypass 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Drag coefficients of isolated nacelles (propulsion package) as a function of by
43、pass ratio In the correlations, engine bypass ratio was known for (fig. 3) were obtained from correlations of nacelle drag data at the selected cruise Mach number. each of the several nacelle diameters, so that nacelle drag coefficient determined as a function of bypass ratio. Dnac/qm with nacelle d
44、iameter Dnac/qmAnac could be Thrust-weight ratios of the bare engine and of the total propulsion package for the advanced technology engines are presented in figure 4 as a function of bypass ratio. The solid-line curves for the bare engine and the total propulsion package represent averages of estim
45、ated weight data from several engine manufacturers; these engines were originally designed to give different thrust levels with small differences in design fan pressure ratio, overall pressure ratio, maximum turbine inlet temperature, and nacelle-installation weight. The weight for each engine was s
46、caled from the original quoted take-off thrust level to new take-off thrust levels defined by a common cruise thrust from the empirical relation Estimates of thrust-weight ratio from an aircraft manufacturers data, converted by the same weight scaling procedure, are shown in figure 4 for comparison.
47、 Bare engine thrust-weight ratios of several current operational engines, also scaled with the empirical relation, are in- dicated by the symbols. Cruise lift-drag polars for several take-off wing loadings are presented in figure 5. Ini- tially, a single polar for a complete airframe (aircraft witho
48、ut propulsion package) was avail- able from the literature for a take-off wing loading of 4788 Pa (100 lbf/ft2). of the polars for the intermediate and lowest wing loadings was accomplished by reducing the minimum drag coefficient of the initial polar by 0.0013 and 0.0027, respectively, to maintain
49、the same fuselage drag and thus provide equivalent payload space for the three wing loadings. a subsonic transport aircraft is approximately 30 percent of the total airframe drag. Breguet cruise range in nautical miles was determined by using the expression Construction It was assumed for these incremental drag values that the fuselage skin friction of R= Wi,cr a In - Wf,cr
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