PAR thrust

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Power Augmented Ram thrust (PAR thrust) is a technique used on Wing In Ground-Effect (WIG) crafts and surface‑effect ships to boost lift by using displaced air. Air from jet exhaust or from the slipstream of main or assist engines is directed under the wing or hull to create a stronger air cushion. This lets the craft take off at lower speeds than would otherwise be needed. Some designs use PAR only during takeoff; others keep it on to maintain lift.

Notable examples include the KM and Lun Ekranoplanes, which placed jet engines ahead of the wing and directed thrust downward under it. The KM needed about 10 turbojets to achieve takeoff, with eight operating in PAR mode; once in level flight, some engines were throttled back or shut off. A-90 Orlyonok used a huge nose turboprop for takeoff power and two large nose ducts to provide PAR; these ducts pointed permanently downward during takeoff, while the engines were shut down in flight to save fuel. Other craft with PAR include Burt Rutan's PARLC and Russian designs such as Strizh PE-201, Volga 2, and Ivolga. On surface‑effect ships, PAR may be required constantly to generate enough lift for normal operation.