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
面積
壓力
速度
圖20-2 表示計算推力所需值的假設(shè)的燃燒室
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 加力燃燒
23.當(dāng)發(fā)動機(jī)裝有加力燃燒室（第16章）時，通過排氣系統(tǒng)的氣體就再次被加熱，以提供附加的推力。加力的作用是增大排氣的體積，因而在推進(jìn)噴管處產(chǎn)生更高的出口速度。
at the propelling nozzle.
加力燃燒室推進(jìn)噴管
推進(jìn)噴管
向后總推力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.假設(shè)在以前計算時用的發(fā)動機(jī)裝上加力噴管和推進(jìn)噴管，推進(jìn)噴管的新的狀態(tài)如下：
……
=2，676磅向后的作用力
因此，與前面第17段中的計算相比，可以看出，負(fù)推力從-5，587磅減至-2，676磅；因而整個正推力增加了2，911磅，相當(dāng)于推力增大了25%以上。
25.為了獲得帶加力燃燒的發(fā)動機(jī)的總推力，第20段中的計算應(yīng)該采用上述數(shù)字。
羅爾斯-羅伊斯公司
RBl68 Mk807發(fā)動機(jī)
Rolls-Royce RB168 MK807
布萊克本
“寧巴斯”發(fā)動機(jī)
Blackburn Nimbus
“寧巴斯”（Nimbus）是從A129渦輪軸發(fā)動機(jī)發(fā)展而來。A129是按專利生產(chǎn)的透博卡（Turbomeca）公司的“阿都斯特”（Aetouste）的改型。這種“寧巴斯”產(chǎn)生968馬力的功率，但用于直升機(jī)時額定功率為710馬力。這種發(fā)動機(jī)用在韋斯特蘭公司的“黃蜂”（Wasp）和“偵察兵”（Scout）直升機(jī)上，4臺700馬力的發(fā)動機(jī)用于實(shí)驗(yàn)型5RN-2氣墊船上。
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.
緒言
1．一種發(fā)動機(jī)的性能要求顯然在很大程度上在于為之設(shè)計的發(fā)動機(jī)工作類型。渦輪噴氣發(fā)動機(jī)的作功能力用推力來衡量，它產(chǎn)生于推進(jìn)噴管或噴口處，而渦輪螺槳發(fā)動機(jī)的作功能力以軸馬力(s.h.p.)來度量，它產(chǎn)生于螺旋槳軸處。不過，這兩種類型的發(fā)動機(jī)主要按它們在一定的重量、油耗和迎風(fēng)面積條件下產(chǎn)生的推力或軸馬力的總值來評定。
第二十一章 性能
21: Performance
Contents Page
Introduction 215 Engine thrust on the test bench 217
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