Blown flap
They use air blown through nozzles to shape the airflow over the rear edge of the wing, directing the flow downward to increase the lift coefficient.
Internal blown flaps were used on some land and carrier-based fast jets in the 1960s, including the Lockheed F-104, Blackburn Buccaneer and certain versions of the Mikoyan-Gurevich MiG-21.
They generally fell from favour because they imposed a significant maintenance overhead in keeping the ductwork clean and various valve systems working properly, along with the disadvantage that an engine failure reduced lift in precisely the situation where it is most desired.
In a conventional blown flap, a small amount of the compressed air produced by the jet engine is "bled" off at the compressor stage and piped to channels running along the rear of the wing.
The similar upper-surface blowing system arranges the engines over the wing and relies completely on the Coandă effect to redirect the airflow.
Lachmann[9] states the Arado and Dornier aircraft used an ejector-driven single flow of air which was sucked over part of the trailing edge span and blown over the remainder.
[8] In the United States, a Grumman F9F Panther was modified with flap blowing based on work done by John Attinello in 1951.
[13] During the 1950s and 60s, fighter aircraft generally evolved towards smaller wings in order to reduce drag at high speeds.
However, large flaps tend to add considerable complexity, and take up room on the outside of the wing, which makes them unsuitable for use on a fighter.
[16] After prolonged development problems, the BLCS proved to be enormously useful in compensating for the Starfighter's tiny wing surface.
The Lockheed T2V SeaStar, with blown flaps, had entered service in May 1957 but was to have persistent maintenance problems with the BLCS which led to its early retirement.
[18] Blown flaps were used on the North American Aviation A-5 Vigilante, the Vought F-8 Crusader variants E(FN) and J, the McDonnell Douglas F-4 Phantom II and the Blackburn Buccaneer.
For instance the General Dynamics F-16 Fighting Falcon has a wing loading of 78.5 lb/ft2 (383 kg/m2), and uses leading edge extensions to provide considerably more lift at higher angles of attack, including approach and landing.
Powered high-lift systems, such as externally blown flaps, are not used for civil transport aircraft for reasons given by Reckzeh,[21] which include complexity, weight, cost, sufficient existing runway lengths and certification rules.
