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volume of the exhaust gases increases as the absolute temperature so it would increase by the ratio of 3000/1700 or 33 per cent. The exhaust nozzle area required to pass a given mass flow of air varies as the gas volume and inversely as the velocity. Therefore, in the above example it would be necessary to increase the exhaust nozzle area by  or 33 per cent when the afterburner is turned on. It is Interesting to note that the exhaust nozzle area must be increased by about the same per cent as the desired thrust boost.
Another somewhat curious fact is the means by which the actual increase in thrust obtained by afterburning is imposed on the engine. Since the pressure downstream of the turbine is the same with and without afterburning, the forces on the engine components are unchanged. However, without afterburning there is a high-pressure force acting on the converging walls of the exhaust nozzle in an aft direction. This force is carried in tension through the tail pipe to the engine structure. With the afterburner in operation, the nozzle area is increased and the pressure force on the converging walls of the exhaust nozzle is decreased. It can be soon then that the added thrust appears as a reduction in tension in the engine tall pipe.
The above performance figures apply only to the static thrust condition. When the engine is moving through the air, the net thrust of the engine is no longer equal to the jet thrust of the nozzle, but is equal to the difference between the nozzle thrust, and the ram drag; the ram drag being the momentum force associated with accelerating the incoming air up to airplane speed. As the velocity of the engine through the air increases, the airflow through the engine and the pressure ratio across the exhaust nozzle increase resulting in a large increase in both jet thrust
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