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In Rostov started production of the most load-lifting rotary-wing car The Russian holding «Helicopt[...]
Wave-riders
At hypersonic speed it is possible to use a somewhat different method to produce lift. An example of this type of configuration is the so-called ‘caret wing’ (Fig. 8.21). In this, as in all similar configurations, the top surface is
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Fig. 8.21 Caret wing wave-rider A shock wave extends between the two swept leading edges and gives high pressure on lower surfaces |
aligned with the air stream so that it does not provide any contribution to the lift. The wing has supersonic leading edges at the hypersonic cruise Mach number and the shock wave generated by the lower surface is trapped within the leading edges. The pressure increase behind the shock wave generates the required lift.
Other configurations use the shock wave generated by the fuselage, rather than a thick wing; this shock wave being similarly ‘trapped’ by the wing. An example of this is shown in Fig. 8.22. Such configurations provide potentially acceptable lift/drag ratios at hypersonic speed. They have the additional advantage that their aerodynamic characteristics will be acceptable throughout the supersonic and subsonic speed ranges as they are effectively slender delta wings.
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Fig. 8.22 Alternative wave-rider configuration Here the shock wave is generated by the conical fuselage, and ‘trapped’ under the wing |
pressure
Fig. 8.23 Surface fuel burning
Schematic arrangement of a proposed wave-rider aircraft
The air is compressed through a series of shock waves. Fuel is injected and burned as in a ramjet. The heated exhaust is at a relatively high pressure, and acts on the lower rear surface of the wing to produce components of lift and thrust
It is interesting to observe that these configurations feature either blunt wing trailing edges, blunt fuselage bases, or both. At subsonic speeds such features are very bad from the point of view of drag production. With the wave-rider it is, however, difficult to design suitable ‘shock capturing’ geometries which do not exhibit these features. Fortunately the base drag produced is of much smaller significance.
In any event the blunt base provides a convenient site for the engines and by ejecting hot exhaust gases from the base we can eliminate the drag contribution from this region. This is another example of an integrated aircraft where the propulsive system forms part of the aircraft aerodynamic system.
High Mach number flight opens up a number of interesting propulsion possibilities. Because of the compression produced by the shock waves, fuel can be directly injected into the air stream and burned, effectively producing an external ramjet (Fig. 8.23). It is possible to do this, not only on the base of the aircraft but also on the lifting surfaces thus producing an integrated lift/propulsion system.
It must, though, be remembered that such a device will cease to work at low speed and alternative means of propulsion will be necessary with associated performance penalties due to increased weight.
