But...do airplanes have tailpipes? Yes, but the one in cars doesn't. What it is and what it is used for
Looking at the 'tail' of many commercial aircraft, one can see the presence of a tube sticking out of the fuselage. The [...]
Looking at the 'tail' of many commercial aircraft., you can see the presence of A tube sticking out of the fuselage. This is as true for modestly sized airplanes, such as the Airbus A220, as it is for the king of all passenger aircraft: the Airbus A380. And, of course, for Boeings as well, 747 including.
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It may be that someone has wondered: 'but do airplanes also have tailpipes like cars?". No. Or, rather, yes. But that 'pipe' is, of course, not the exhaust from the engines that propel the jets. But rather The discharge of a piece of equipment known as an APU (Auxiliary Power Unit, Auxiliary Power Units).
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The first passenger plane model to fit it as standard was the Boeing 727, in 1963. Its function in those days was, if you will, even more 'vital' than it is today. Most airports, in fact, lacked equipment capable of supplying electricity to aircraft during their stops on the ground. In many cases, generators were also lacking.
And the APU was introduced precisely to provide autonomy for the airplane even during 'turnarounds' between flights, so that there was light and heat on board and that the on-board systems, including the pneumatic ones that controlled the flight surfaces, were active even with the engines off.
Since then, all passenger planes mount an APU, which is usually housed in the rear of the fuselage, between the two horizontal (aileron) and vertical (tail) wheelhouses. Powered by A1 fuel (the same as the engines), needs an exhaust emission system, which is precisely the 'tailpipe' that we notice in the back of so many aircraft.
Sometimes, as in the case of MD-80s that were in operation until a few years ago, or Boeing 717s, the 'pipe' is not there. But there are grids or simple 'holes' in the end of the fuselage (as on the Boeing 777) that act as an exhaust for the gases emitted by the APU.
Nowadays, most major airports have power supply systems running under the aprons and have terminals at aircraft parking pads, whether these are connected to the terminal with jet bridges or remote. When an aircraft parks and shuts down its engines, it is connected to these terminals, which provide it with power without the need to activate the APU or a generator, and thus zeroing out aircraft ground emissions.
However, there is an additional function of the Auxiliary Power Unit that always requires it to be started: starting the actual engines. Thrusters can be turned on by the pilots only when the rotation of their blades has resulted in sufficient compression within the turbine to 'ignite' the fuel flowing into it. That pressure is determined when the engine blades are turning at least 20-30% of their maximum speed.
But today's engines are so big and heavy That no electric motor is powerful enough. Here then is the APU, in turn triggered by a small electric motor, Provides enough energy to spin the blades of today's turbofans at a speed sufficient to result in adequate pressure in the turbine for kerosene combustion.
The APU is subsequently deactivated, but it must also be able to be turned back on at cruising altitude on the ETOPs aircraft, i.e., the twin-engines operating on long-haul routes (such as the Dreamliners, B777s, and A330s that are popular today), in case one of the two engines has a failure and needs to be shut down, to ensure sufficient 'power' to the on-board systems.