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Propelling nozzle
14. The propelling nozzle is of similar material and construction as the jet pipe, to which it is secured as a separate assembly. A two-position propelling nozzle has two movable eyelids that are operated by actuators, or pneumatic rams, to give an open or closed position (para. 4.). A variable-area propelling nozzle has a ring of interlocking flaps that are hinged to the outer casing and may be enclosed by an outer shroud. The flaps are actuated by powered rams to the closed position, and by gas loads to the interme-diate or the open positions; control of the flap position is by a control unit and a pump provides the power to the rams (para. 18).
CONTROL SYSTEM
15.
It is apparent that two functions, fuel flow and propelling nozzle area, must be co-ordinated for sat-isfactory operation of the afterburner system, These functions are related by making the nozzle area dependent upon the fuel flow at the burners or vice-versa. The pilot controls the afterburner fuel flow or the nozzle area in conjunction with a compressor delivery/jet pipe pressure sensing device (a pressure ratio control unit). When the afterburner fuel flow is increased, the nozzle area increases; when the afterburner fuel flow decreases, the nozzle area is reduced. The pressure ratio control unit ensures the pressure ratio across the turbine remains unchanged and that the engine is unaffected by the operation of afterburning, regardless of the nozzle area and fuel flow.

16.
Since large fuel flows are required for afterburn-ing, an additional fuel pump is used. This pump is usually of the centrifugal flow or gear type and is energized automatically when afterburning is selected. The system is fully automatic and incorpo-rates 'fail safe' features in the event of an afterburner malfunction. The interconnection between the control system and afterburner jet pipe is shown diagram-matically in fig. 16-5.

173 17. When afterburning is selected, a signal is relayed to the afterburner fuel control unit. The unit determines the total fuel delivery of the pump and controls the distribution of fuel flow to the burner assembly. Fuel from the burners is ignited, resulting in an increase in jet pipe pressure (P6). This alters the pressure ratio across the turbine (P3/P6), and the exit area of the jet pipe nozzle is automatically increased until the correct PS/PS ratio has been restored. With a further increase in the degree of afterburning, the nozzle area is progressively increased to maintain a satisfactory P3/P6 ratio. Fig. 16-6 illustrates a typical afterburner fuel control system.

17.當選用加力時，信號傳輸給加力燃燒室燃油控制裝置。該裝置決定泵的總供油量，并且控制分配給噴嘴組件的燃油流量。噴嘴噴出的燃油點燃后，使噴管壓力（P6）增加。這就改變了渦輪前后的壓力比（P3/P6），噴管出口面積自動增加一直到正確的P3/P6比恢復。隨著加力程度進一步加大，噴口面積也逐步增加以保持一個滿意的P3/P6比。圖16-6示出了一種典型的加力燃燒室燃油控制系統(tǒng)。

圖16-4 典型的加力噴管設(shè)備
18. To operate the propelling nozzle against the large 'drag' loads imposed by the gas stream, a pump and either hydraulically or pneumatically operated rams are incorporated in the control system. The system shown in fig. 16-7 uses oil as the
18.操縱推進噴口時要克服燃氣流作用的巨大“阻力”載荷，所以在控制系統(tǒng)中裝有一個泵和液壓或氣壓驅(qū)動的作動筒。圖16-7所示的系統(tǒng)使用了滑油周圍液壓介質(zhì)，但是有些系統(tǒng)使用燃油作為介質(zhì)。噴管的移動是通過液壓作動筒來實現(xiàn)的液壓作動筒由一個滑油泵加壓，泵的輸出由從壓力比控制裝置來的操縱桿控制。在要求增加加力程度時，加力燃燒室燃油控制裝置使燃油泵輸出量相應(yīng)增加，噴管壓力（P6）因此增加，改變了渦輪前后的壓力比(P3/P6)。壓力比控制裝置改變滑油泵的輸出量，造成了在噴口魚鱗片上的液壓作動筒載荷與燃氣載荷之間不平衡的狀況。燃氣載荷打開噴口以增加其出口面積，并且當噴口打開時，噴口面積的增加恢復了P3/P6比。壓力比控制裝置又改變滑油泵的輸出量直到液壓作動筒載荷及噴口魚鱗片上的燃氣載荷之間恢復平衡。

圖16-5 簡化的控制系統(tǒng)
Fig. 16-5 Simplified control system.
可變面積
推進噴管
加力燃燒室
推力的增加
 
19．由加力燃燒造成的推力的增加完全取決于燃油在燃燒之前和之后噴管絕對溫度的比。例如：忽略由于加力燃燒室裝置和燃氣流動量變化造成的微小損失，增加的推力可按照下面的方法進行計算。
壓力滑油
燃油進口
噴口
滑油泵
滑油進口
凸輪箱
加力燃燒室
燃油控制裝置
加力燃燒室燃油
駕駛員操縱桿
壓力比控制裝置
停車
正常范圍
加力燃燒室范圍
hydraulic medium, but some systems use fuel. Nozzle movement is achieved by the hydraulic operating rams which are pressurized by an oil pump, pump output being controlled by a linkage from the pressure ratio control unit. When an increase in afterburning is selected, the afterburner fuel control unit schedules an increase in fuel pump output. The jet pipe pressure (P6) increases, altering the pressure ratio across the turbine (P3/P6). The pressure ratio control unit alters oil pump output, causing an out-of-balance condition between the hydraulic ram load and the gas load on the nozzle flaps. The gas load opens the nozzle to increase its exit area and, as the nozzle opens, the increase in nozzle area restores the P3/P6 ratio and the pressure ratio control unit alters oil pump output until balance is restored between the hydraulic rams and the gas loading on the nozzle flaps.
　
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