Vertical/short take-off and landing - Lift engines

Lift engines

Fig. 18-10 A lift-jet engine.

13. The lift engine is designed to produce vertical thrust during the take-off and landing phases of V/STOL aircraft. Because the engine is not used in normal flight it must be light and have a small volume to avoid causing a large penalty on the aircraft. The lift engine may be a turbo-jet which for a given thrust gives the lowest weight and volume. Should a low jet velocity be necessary a lift fan may be employed.
14. Pure lift-jet engines have been developed with thrust/weight ratios of about 20:1 and still higher values are projected for the future. Weight is reduced by keeping the engine design simple and also by extensive use of composite materials (fig. 18-10). Because the engine is operated for only limited periods during specific flight conditions i.e. during take-off  and  landing,  the  fuel  system  can  be simplified and a total loss oil system (Part 8), in which the used lubricating oil is ejected overboard, can be used.