FORWARD-SWEPT WING AIRCRAFT


The Grumman X-29 Banking in flight.

Forward-Swept Wing Aircraft
Tech Level: 9

Forward-swept wing (FSW) glider designs are in use, mostly as training vehicles. However, this article focuses on FSW jet aircraft.

This radical design was first proposed in 1936 by German designers and was developed by Germany toward the end of World War II, with the Junkers Ju 287 experimental aircraft built in 1944. Decades later, it served as a test bed for a number of advanced flight concepts during the 1980s and 1990s, under the official designation of the X-29 program. Two flight demonstrators were built over the course of the decade-long program by the Grumman Aerospace Corporation for the US military. The Russian Air Force also developed a FSW demonstrator aircraft, the Sukhoi Su-47, in the late 1990s.

Though both the US and Russian versions were considered impressive design successes, the forward-swept wing jet remains a curiosity, with no mainstream jet craft, either civilian or military, using the design. However, it has proven itself a very solid and potentially useful concept, and in the decades to come it may be revived.

Forward-swept wing jets are occasionally seen in fiction, including being the transportation mode of choice for the X-Men for many years.

The main advantage of FSW jet aircraft lie in their superior maneuverability. In simple terms, the airflow over the wing travels from wingtip to the wing roots along the central body of the aircraft. This is in contrast to conventional aircraft, which has the airflow travel from the central axis of the aircraft out over the wingtips. When flying at severe angles, conventional jets experience stalls along their wingtip airflow that can result in decreased lift and a loss of control. In a FSW jet, these stalls are instead angled toward the central body, ensuring proper airflow over their ailerons at angles of attack up to 67 degrees. Thus, FSW aircraft can prove much more controllable when performing extreme maneuvers than conventional aircraft.

A secondary advantage is that the FSW configuration allows for up to 15% better lift to drag ratio at transonic speeds.

However, the aircraft does have a number of potential drawbacks. A number of FSW aircraft were researched by the US and USSR during the Cold War, based on the Junkers JU 287. However, they encountered a problem with wingtip twisting. The metals and materials used at the time were simply not strong enough to handle the stresses of the configuration in transonic flight, especially on the leading edge of the wings. The wingtips would tend to bend up, and if the stresses were high enough, could even rip the wings off the fuselage. FSW jets would have to wait until the development of much stronger and lighter composite materials decades later.

Computer controls are also essential. FSW jets are inherently unstable aerodynamically. In a way, this is good, as its part of what allows the vehicle its high potential maneuverability. However, the various aerodynamic forces acting on its unusual shape can easily pull it out of a pilotís control. Computers are used to make many minute corrections every second to ensure the aircraft remains stable, similarly to the flight computers used in the B-2 Bomber, another inherently unstable aircraft. The X-29 had six computers, all redundantly checking the same conditions, and would make correction only if the majority of them Ďagreedí on the course of action. The system typically could make up to 40 such corrections per second a needed.

The Sukhoi Su-47 also employed a thrust vectoring system that helped to address the instability problem with greater efficiency, and allowed even greater maneuverability and agility overall.

Forward-swept wing jet aircraft would be extremely effective fighters at transonic speeds, able to out-maneuver most other types of jets. Their greater agility would also help them survive potential missile attacks. However, in the post-Cold War era, the need for dogfighting jets has greatly diminished, and most parties saw little reason to invest in this new technology. In the future, however, needs may change as the world situation evolves, and the Forward-Swept Wing jet may someday come into its own.


Airflow, forward swept wings vs standard swept wings.

FURTHER INFORMATION

http://www.centennialofflight.gov/essay/Evolution_of_Technology/foward_sweep/Tech9.htm

http://www.nasa.gov/centers/dryden/news/FactSheets/FS-008-DFRC.html

http://en.wikipedia.org/wiki/Forward-swept_wing

http://en.wikipedia.org/wiki/Sukhoi_Su-47


Article added 06/01/10

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