Therefore, assuming values of mass flow, pressure and area to be the same as in the previous calcula-tions i.e.
Area of propelling nozzle (A) = 332 sq.in. Pressure (P) = 6 lb. per sq.in.
(gauge) Atmospheric Pressure (P) = 0 lb. per sq.in.
(gauge) Mass flow (W) = 153 lb. per sec. Velocity (vJ) = 1,917 ft. per sec.
The thrust WVJ
= (P . P0) . A +. 0
g
153 X 1,917
= (6 . 0). 332 +. 0
32
= 1,992 + 9,166
= 11,158 lb., the same as previously calculated
Thrust distribution
by combining the gas loads on the individual engine locations.
21. On engines that operate with a non-choked nozzle, the (P-P0) A function does not apply and the thrust results only from the gas stream momentum change.
Inclined combustion chambers
22. In the previous example (Para. 14) the flow through the combustion chamber is axial, however, if the combustion chamber is inclined towards the axis of the engine, then the axial thrust will be less than for an axial flow chamber. This thrust can be obtained by multiplying the sum of the outlet thrust by the cosine of the angle (see fig. 20-2). The
Base cosine = and for a given angle
Hypotenuse
is obtained by consulting a table of cosines. It should be emphasized that if the inlet and outlet are at different angles to the engine axis, it is necessary to multiply the inlet and outlet thrusts separately by the cosine of their respective angles.
AFTERBURNING
23. When the engine is fitted with an afterburner (Part 16), the gases passing through the exhaust
面积
压力
速度
图20-2 表示计算推力所需值的假设的燃烧室
212 system are reheated to provide additional thrust. The effect of afterburning is to increase the volume of the exhaust gases, thus producing a higher exit velocity 加力燃烧
23.当发动机装有加力燃烧室（第16章）时，通过排气系统的气体就再次被加热，以提供附加的推力。加力的作用是增大排气的体积，因而在推进喷管处产生更高的出口速度。
at the propelling nozzle.
加力燃烧室推进喷管
推进喷管
向后总推力2，676磅
Thrust distribution
24. Assuming that an afterburner jet pipe and propelling nozzle are fitted to the engine used in the previous calculations, and the new conditions at the propelling nozzle are as follows-
OUTLET Area (A) = 455 sq.in.
Pressure (P) = 5 lb. per sq.in.
(gauge)
Velocity (vJ) = 2,404 ft. per sec.
Mass flow (W) = 157 lb. per sec.
The thrust WVJ
= (A xP) +.16,745
g
157 x 2,404
= (455 x 5) +.16,745
32
= 14,069 - 16,745
= 2,676 lb. acting in a rearward direction.
Therefore, compared with the previous calculation in para. 17, it will be seen that the negative thrust is reduced from -5,587 lb. to -2,676 lb.; the overall positive thrust is thus increased by 2,911 lb; which is equivalent to a thrust increase of more than 25 per cent.
25. To arrive at the total thrust of the engine with afterburning the calculations in para. 20 should use the above figures. 24.假设在以前计算时用的发动机装上加力喷管和推进喷管，推进喷管的新的状态如下：
……
=2，676磅向后的作用力
因此，与前面第17段中的计算相比，可以看出，负推力从-5，587磅减至-2，676磅；因而整个正推力增加了2，911磅，相当于推力增大了25%以上。
25.为了获得带加力燃烧的发动机的总推力，第20段中的计算应该采用上述数字。
罗尔斯-罗伊斯公司
RBl68 Mk807发动机
Rolls-Royce RB168 MK807
布莱克本
“宁巴斯”发动机
Blackburn Nimbus
“宁巴斯”（Nimbus）是从A129涡轮轴发动机发展而来。A129是按专利生产的透博卡（Turbomeca）公司的“阿都斯特”（Aetouste）的改型。这种“宁巴斯”产生968马力的功率，但用于直升机时额定功率为710马力。这种发动机用在韦斯特兰公司的“黄蜂”（Wasp）和“侦察兵”（Scout）直升机上，4台700马力的发动机用于实验型5RN-2气垫船上。
The Nimbus was developed from the A129 turbo-shaft which, in its turn, was a modified Turbomeca Artouste built under licence. The Nimbus developed 968 hp, but for helicopter use was flat-rated at 710 hp. The engine was used in Westland Wasp and Scout helicopters and four 700 hp units were used to power the experimental 5RN-2 hovercraft.
绪言
1．一种发动机的性能要求显然在很大程度上在于为之设计的发动机工作类型。涡轮喷气发动机的作功能力用推力来衡量，它产生于推进喷管或喷口处，而涡轮螺桨发动机的作功能力以轴马力(s.h.p.)来度量，它产生于螺旋桨轴处。不过，这两种类型的发动机主要按它们在一定的重量、油耗和迎风面积条件下产生的推力或轴马力的总值来评定。
第二十一章 性能
21: Performance
Contents Page
Introduction 215 Engine thrust on the test bench 217
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