Our heavyweight helicopter equal in the world does not have
In Rostov started production of the most load-lifting rotary-wing car The Russian holding «Helicopt[...]
The exhaust nozzle
The exhaust gases leave the turbine at subsonic speed, and for subsonic aircraft they are normally accelerated by means of a simple fixed converging nozzle. The maximum Mach number that can be obtained in such a nozzle is 1, but as the gases are hot, the speed of sound in the exhaust is faster than that in the surrounding atmosphere. Thus, a converging nozzle can still theoretically be used at supersonic speeds. In practice, aircraft designed for supersonic flight normally require a variable geometry nozzle that can be adjusted to produce a convergent-divergent configuration for high speed flight. In a convergent-divergent nozzle, the jet can be accelerated to Mach numbers greater than 1.
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Fig. 6.35 Quarter-annular side intakes on the F-111 Note the quarter-conical spike in the upper corner to generate an external compression shock wave, and the slot for boundary layer removal This photograph shows the NASA modified aircraft fitted with the experimental variable-camber ‘mission adaptive wing’ (Photo courtesy of NASA) |
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178 THRUST AND PROPULSION |
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Fig. 6.36 A two-dimensional jet nozzle simplifies the mechanism for variable area, and enables the nozzle to be used for thrust vectoring, as on the F-22. For stealth reasons the nozzles are serrated |
Supersonic aircraft invariably use reheat, which also requires the use of a variable geometry nozzle. The designs are often complicated, involving a large number of moving parts, all of which have to stand up to very high temperatures. The complex interleaved plates of the Concorde variable geometry final outlet nozzle may be seen in Fig. 6.32.
The complexity of the nozzle mechanism may be reduced if a twodimensional design is used instead of the conventional axi-symmetric arrangement. The two-dimensional nozzle takes the form of a variable-geometry slot, as illustrated in Fig. 6.36, and can be arranged to produce thrust vectoring for control purposes, and STOL (short take-off and landing).
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Fig. 6.37 A simple ramjet The simplest form of jet propulsion. It is, however, inefficient below about Mach 3, and will not work at all at low speed |
