Forward-swept wing
A forward-swept wing is an aircraft wing configuration in which the quarter-chord line of the wing has a forward sweep. The configuration was first proposed in 1936 by German aircraft designers.[1] Perceived benefits of a forward-swept wing design include
- Mounting the wings further back on the fuselage, allowing for an unobstructed cabin or bomb bay, as the root of the wingbox will be located further aft, and
- Increased maneuverability, due to airflow from wing tip to wing root preventing a stall of the wing tips and ailerons at high angle of attack. Instead, stall will rather occur in the region of the wing root on a forward-swept wing.
- This reversed spanwise airflow should reduce wingtip vortices, generating less drag and allowing a smaller wing.
Possible drawbacks of a forward-swept wing include
- When using a conventional metal construction: A reduced divergence speed or, in order to avoid this, an increased wing weight, as wing stiffness needs to be increased.
- A forward-swept wing becomes unstable when the wing root stalls before the tips, causing a pitch-up moment, exacerbating the stall. This effect is more significant with a large forward-sweep.
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[edit] Military use
Not until World War II did designs incorporating forward-swept wings appear (excluding unrealized projects, e.g. Polish Z-17 / Z-18 / Z-47 "Sęp" series); such as the experimental Junkers Ju 287 bomber. After the war, the Soviet Union used Ju 287 as a base for OKB-1 EF 140 prototype. In 1948, the Soviet Union created the Tsybin's LL-3.[2] The prototype subsequently had a great impact on the Sukhoi's SYB-A, which was completed in 1982.
NACA, the precursor to the United States' NASA, researched the advantages of forward-swept wings on the Bell X-1, but encountered structural problems with twisting wingtips. Stronger materials were needed, and the aerodynamic benefits seemed minimal or nonexistent.
The concept continued to be dismissed as highly impractical until the late 1970s, when DARPA began investigating the use of newer composite materials to avoid the problem of reduced divergence speed through aeroelastic tailoring. Fly-by-wire technology allowed for the design to be dynamically unstable and improved maneuverability. Grumman built two X-29 technology demonstrators, first flying in 1984, with forward swept wings and canards. Maneuverable at high angles of attack, the X-29 remained controllable at 67° angle of attack.[3] Advances in thrust vectoring technology and a shift in air combat tactics toward medium range missile engagements decreased the relevance of a highly agile fighter aircraft. In 1997, Sukhoi introduced the Su-47 fighter prototype at the Paris Air Show. It has not yet entered production, although it underwent a series of flight tests and performed at several air shows.
[edit] Civilian use
The following civilian aircraft feature wings exhibiting a forward sweep:
- The CZAW Parrot[4]
- The 1964 HFB-320 business jet, of which 50 were built, had a forward-swept wing to allow an unimpeded cabin without a wing spar passing through it.
- The Saab Safari, Bölkow Junior & ARV Super2 all have shoulder wings for increased visibility, necessitating forward-swept wings to maintain correct CofG.
- The Scaled Composites Boomerang, a prototype piston twin design which would allow for safe handling in the event of a single engine failure.
- The Cessna NGP, a prototype single-engine aircraft intended to eventually replace the Cessna 172 and Cessna 182.
- The SZD-9 Bocian and PZL Bielsko SZD-50 Puchacz, multi-purpose two-seat sailplanes designed and built in Poland
Many high-wing training gliders with two seats in tandem have slightly forward-swept wings in order to enable the wing root to be located further aft to prevent the wing from obscuring the rear occupant's lateral visibility. Typical examples are the Schleicher ASK 13 and the Let Kunovice LET L-13 Blaník.
[edit] See also
[edit] References
- ^ US Centennial of Flight Commission. "Forward-Swept Wings". Retrieved 22 August 2005.
- ^ Russian Aviation Page: Sukhoi S-37 Berkut (S-32)
- ^ NASA. "Dryden Fact Sheet - X-29". Retrieved 22 August 2005.
- ^ CZAW web site
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