46．发动机设计的主要考虑因索，尤其是对于民用运输机来说，是低的耗油率和重量。由于采用了内外涵道原理，借助于先进的机械和气动特性并使用了更好的材料，使发动机设计得到相当大的改进。随着向更高涵道比即15：1的范围发展的趋势，三转子和对转的后风扇发动机可达到这种压力比和涵道比。它们的转子短而压气机级数少，从而得到一种更轻和结构更加紧凑的发动机。
Performance
从这一点至65，617英尺音速不变
从这一点至65，617英尺大气温度不变
图21-10 国际标准大气
Fig. 21-10 International Standard Atmosphere.
by-pass ratio engine, the weight reduction compared with a pure jet engine is in the order of 20 per cent for the same air mass flow.
49. With a high by-pass ratio engine of the triple-spool configuration, a further significant improvement in specific weight is obtained- This is derived mainly from advanced mechanical and aerodynamic design, which in addition to permitting a significant reduction in the total number of parts, enables rotating assemblies to be more effectively matched and to work closer to optimum conditions, thus minimizing the number of compressor and turbine stages for a 47．耗油率与热效率和推进效率有直接关系，也就是与发动机的总效率有关。从理论上来说，高的热效率需要高的压力，这实际上还意味着高的涡轮进口温度。在纯涡轮喷气发动机中，这种高温度将导致高的喷气速度，因而会降低推进效率(第40段)。然而，正如第43段谈到的，利用内外涵道原理，将一定比例的低压压气机或风扇出口空气从旁路排出。以降低平均喷气温度和速度，可以有效地同时达到高的热效率和推进效率。随着高涵道比和总增压比的先进技术发动机的问世，耗油率又得到进一步明显的改进。
48．纯喷气发动机的涡轮比较重，因为它们要处理所有气流，而内外涵发动机的涡轮只处理一部分气流；因而高压压气机、燃烧室和涡轮可以缩小尺寸。增大流过涡轮的每磅空气的功率以充分利用它们的能力，可采用提高增压比和涡轮进口温度的方法来实现。显然，内外涵发动机比较轻，因为不仅减小了高压转动组件的直径，而且对一定的功率输出而言。发动机比较短。对一种低涵道比发动机来说，在空气质量流量相同时，与纯喷气发动机相比，重量减轻的数量级达20％。
Performance
given duty. The use of higher strength light-weight materials is also a contributory factor.
50. For a given mass flow less thrust is produced by the by-pass engine due to the lower exit velocity. Thus, to obtain the same thrust, the by-pass engine must be scaled to pass a larger total mass airflow than the pure turbo-jet engine. The weight of the engine, however, is still less because of the reduced size of the H.P. section of the engine. Therefore, in addition to the reduced specific fuel consumption, an improvement in the power-to-weight ratio is obtained. 49．对三转子布局的高涵道比发动机来说，单位重量又获得很大改进。这主要得益于先进的机械和气动设计，它除了允许大大减少零件的总数外，还使转动组件能更加有效地匹配并且工作更加接近于最佳状态，因而在负载一定时，使得压气机和涡轮级数最少。采用高强度的轻质材料也是一个重要因素。
50．对一定的质量流量来说，由于排气速度较低，内外涵发动机产生的推力较小。因此，为了获得同样的推力，内外涵发动机必须按比例比纯涡轮喷气发动机通过更大的总质量流量。然而，由于发动机的高压部分的尺寸减小，发动机的重量仍然较轻。因此，除了耗油率减少外，功率重量比也得到提高。
Rolls-Royce RB168 Mk202/Mk203
Rolls-Royce RB39 Clyde
Encouraged by results obtained from the Trent, Rolls-Royce decided to go ahead with an engine designed from the start as a turbo-prop. Named the Clyde it utilized the axial compressor from the Metrovick F2 as first stage and a scaled up supercharger impeller from a Merlin as second stage. First running in August 1945 at 2000 shp, later engines produced up to 4200 shp.
绪言
1．在航空燃气涡轮发动机的设计阶段，设计、制造、发展和产品支援之间应保持密切联系，以确保最后的设计在工程规范和制造工艺能力之间的协调。
22: Manufacture
第二十二章 制造
Contents Page
Introduction 229 2．由于这种发动机具有很高的推重比，所以其功能要求每个部件具有尽可能高的性能。为了符合这种要求，每个部件必须造得重量尽可能轻，费用尽可能低，而且在很长的使用寿命期中具有机械完整性。因此，制造中采用的方法是多种多样的，通常取决于每个部件必须完成的任务。
绪言
制造策略
Manufacturing strategy 230 Forging 231 锻造
铸造
Casting 233 Fabrication 234 组装加工
焊接
Welding 235
Tungsten inert gas (T.I.G.) welding Electron beam welding (E.B.W.)
Electro-chemical
machining (E.C.M.) 237 Stem drilling Capillary drilling
Electro-discharge machining (E.D.M.) 238 Composite materials and sandwich casings 240 钨惰性气体(T.I.G.)焊接
电子束焊接(B.E.W.)
电化学加工(E.C.M.)
深孔钻削
微孔钻削
电火花加工(E.D.M.)
复合材料和夹芯壳体
检验
Inspection 240
INTRODUCTION 3. No manufacturing technique or process that In any way offers an advantage is ignored and most
1. During the design stages of the aircraft gas available engineering methods and processes areturbine engine, close liaison is maintained between employed in the manufacture of these engines, Indesign, manufacturing, development and product some instances, the technique or process may support to ensure that the final design is a match appear by some standards to be elaborate, time between the engineering specification and the man-consuming and expensive, but is only adopted after ufacturing process capability.
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