[49APU] 737NG尾部的这个排放口是干啥的？为什么会朝前？

在737NG后部机身右侧，APU舱门前面有一个排放口，可能很多人平时都没太注意到。

本期问题

这个孔是用来排啥的？很奇怪，它的孔朝前的，是要借助风冷吗？

这个孔不同于一般的排放口，在手册里学术名字叫「APU Air Inlet Scoop」：

它并不是传统意义上的排放口，而是属于APU舱防火墙系统的一部分：

▲检查口没有堵塞或异物

SDS部分对它的描述：

SDS 49-10-00

The APU insulation panels are not easily damaged, however, it the panels are punctured, you should repair the damaged panel as soon as possible. If you do not repair a puncture immediately, the panel can store fluids in the insulation. If fluids get into the insulation material, you must replace the panel.The air inlet scoop replaces the foam and support insulation (egg crate) that were installed between the APU insulation panels and the bulkhead. During an airplane operation, the air inlet scoop supplies forced outside air through the empty space between the APU insulation panels and the bulkhead for ventilation and for the removal of flammable or unwanted fluids.The location of the air inlet coop is behind the forward insulation panel and adjacent to the forward right side of the APU cowl door.

可以看出，这些飞机APU隔热板和隔框之前没有填充泡沫和支撑，而是存在空隙，就有这个勺状进气口。在飞机飞行期间，外部冲压空气通过勺状进气口进入 APU 隔热板和舱壁之间，用于通风和去除易燃或多余的液体。

它的件号是354A4070-7或-6：

当然机队有两种构型。有些飞机APU隔热板和隔框之前填充了泡沫和支撑，就没有这个勺状进气口：

下面借用网上（yinlei.org）的一张图片，说明737NG尾部的各种进排气口：

① 尾部白色防撞灯（频闪灯） white anti-collision light（strobe light）

② APU引射空气进口 eductor inlet

③ APU发动机排气口 APU engine exhaust

④尾椎接近盖板 tailcone access panel

⑤ APU余油排放口 APU drain mast

⑥APU勺状进气口 APU air inlet scoop

⑦ 尾撬 tail skid

⑧ APU进气门 APU air inlet door

⑨后部排水口 aft drain mast

⑩ 厨房通风口 galley vent inlet

⑪ 滑梯灯 slide lights

⑫ 正释压活门 positive pressure relief valve

⑬ 外流活门 outflow valve

⑭ 负释压活门 negative pressure relief valve