Page 205 - The Jet Engine

Vertical/short take-off and landing

Fig. 18-14 Flap blowing engine.

25. At high ambient temperatures, the engine may
run into a turbine temperature limit before reaching
its maximum r.p.m. and suffer a thrust loss as a
result. Restoration of the thrust can be achieved by
means of water injection into the combustion
chamber (Part 17) which allows operation at a higher
turbine gas temperature for a given turbine blade
temperature. If desired, water injection can also be
used to increase the thrust at low ambient tempera-
tures.

Lift burning systems
26. The thrust of the four nozzle lift/propulsion
engine may be boosted by burning fuel in the bypass
flow in the duct or plenum chamber supplying the
front nozzles. This is called plenum chamber burning
(P.C.B.) (fig. 18-16) and thrust of the by-pass air may
be doubled by this process. This thrust capability is
available for normal flight as well as take-off and
landing and so can be used to increase manoeuvra- Fig. 18-15 Thrust increases with short lift
bility and give supersonic flight.
ratings.
27. The thrust of a remote lift jet can also be
augmented by burning fuel in a combustion chamber Ejectors
just upstream of the lift nozzle (fig. 18-17). This 28. The principle of the ejector is that a small, high
system is commonly known as a remote augmented energy jet entrains large quantities of ambient air by
lift system (R.A.L.3.). The thrust boost available from viscous mixing and an increase in thrust over that of
the burner reduces the amount of airflow to be the high energy jet results. A number of projected
supplied to it and therefore reduces the size of the V/STOL aircraft have incorporated this concept using
ducting needed to direct the air from the engine to either all the engine exhaust air or just the bypass
the remote lift nozzle. flow.

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