A number of powered lift systems has been developed for VSTOL and STOL aircraft. These systems yield maximum lift coefficients of 10 and above (for example, NASA’s research aircraft QSRA). A good review was published by Gratzer and Goodmandson (1973), and Nelms and Anderson (1984).
One recent, yet very effective idea of producing additional lift is to use the airflow from a turbojet engine (exaust gas). This flow must be diverted downwards. There are several means to achieve this. Some examples:
The systems sketched below (elaborated from Boeing studies, 1975) are among the most efficient. They use at least part of the thrust generated by a jet engine. This can be done through auxiliary pressure (internally or externally blown flaps, augmentor flaps), or by direct use of the jet thrust (vectored thrust), as in Fig. 3.
Circulation control can be achieved both at the leading edge (with a rotating cylinder) or ar the trailing edge with a similar device, using the so-called Coanda effect (not shown).
Figure 1: Augmentor Flap
Figure 2: Internally Blown Flap
Figure 3: Vectored Thrust
Some current applications include the cargo aircraft C-17 Globemaster (design based on McDonnell-Douglas YC-15), which has externally blown flaps; the Antonov An 72/74 (various versions), that has over-the-wing blowing; the BAe Sea Harrier, that uses vectored thrust.