Page 187 - The Jet Engine

Fig. 16-7 A simplified typical afterburner nozzle control system.

20. Assuming a gas temperature before afterburn-
ing of 640 deg. C. (913 deg. K.) and with afterburn-
ing of 1,269 deg. C. (1,542 deg. K.). then the
temperature ratio = 1,542 = 1.69. 913

The velocity of the jet stream increases as the
square root of the temperature ratio. Therefore, the
jet velocity = ^/T.69 = 1.3. Thus, the jet stream
velocity is increased by 30 per cent, and the increase
in static thrust, in this instance, is also 30 per cent
(fig. 16-8).
21. Static thrust increases of up to 70 per cent are
obtainable from low by-pass engines fitted with after-
burning equipment and at high forward speeds
several times this amount of thrust boost can be
obtained. High thrust boosts can be achieved on low
by-pass engines because of the large amount of
oxygen in the exhaust gas stream and the low initial Fig. 16-8 Thrust increase and temperature
temperature of the exhaust gases. ratio.

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