Air International 1999-05
N.Beckett - Foreplanest Foremost or should the tail wag the dog? /Technology/
With tailplane and foreplane leading edges up, this Sukhoi Su-27K is deriving favourable trim for high lift in its landing configuration.
Although most of the lift is derived from the wing, the forebody (especially with strokes) and centrebody also contribute. Vortices generated at incidence, by the F-16’s leading-edge extension, (seen here during a high-g manoeuvre) interact with the wing leading edge vortex and increase the wing lift.
The predecessor Mirage III, with natural stability, loses lift due to the upwards deflected flaperons needed to trim.
The relaxed longitudinal stability of the Mirage 2000 allows the wing trailing edge flaperons to be neutral during the landing approach.
With foreplane deflected fully nose down and wing trailing edge flaperons fully up, the Saab Gripen's landing run is much reduced, without recourse to a braking 'chute. Braking effectiveness is increased due to download on the undercarriage. Aerodynamic drag is provided by the ‘barn door’ foreplane.
A large tailplane deflection (leading edge down) is needed to achieve and trim the high angle of attack required by the Grumman F-14 Tomcat as it comes off the catapult, full of fuel and at a relatively low speed.
One of the main benefits of the foreplane delta, such as that adopted for the Eurofighter Typhoon, is that it offers especially high supersonic agility. With a suitably positioned centre of gravity, it can also provide particularly high subsonic turn rates.
All variable sweep wing aircraft, with high lift flap systems, inevitably employed aft tails. A typical example is the Grumman F-111, the EF-111 electronic warfare variant of which is seen here in formation with the aircraft displaying its full range of wing sweep angles.
This wind tunnel model of the Eurofighter concept demonstrator EAP, shows the favourable foreplane/wing flowfield interaction.
A Saab Viggen touching down. The large flap deflection necessary on the foreplane to trim is clearly seen on this canard delta which lacks relaxed stability.