a compendium of tech stuff

Jan 18, 2010

On 7:44 PM by Lalith Varun   1 comment



A variable-sweep wing is an aircraft wing that can be swept back or front and then returned to its original position during flight. It allows the aircraft's geometry to be modified in flight, and is an example of variable geometry. With different wing positions allowing for greater efficiency and performance in various flight modes, these aircraft are more versatile than aircraft with fixed wings. During the World War I and II, one would notice that most of the aircrafts had wings perpendicular to the fuselage and in very rare cases a couple of degrees swept back. But with the advent of jet engines after the World War II which gave a boost to the speed of the aircrafts, the traditional wing shapes weren't that efficient at such high speeds. So jet planes started using tapered wings, but this came at a cost of low efficiency at lower speeds.

And hence came the need for an aircraft which can alter its wing geometry in mid flight. This feature gives the airplane the best possible performance characteristics for any given speed. The German
Messerschmitt company first tested planes with variable wing geometry during World War II. The Messerschmitt P-1101's wings could be moved to different sweep angles, only while the plane was on the ground. Based on the Messerschmitt design, the U.S. developed a working test craft, the Bell X-5, which was slightly larger than the P-1101 and could change its wing-sweep angle while in flight.

Designers had to take into consideration many factors regarding sweep while designing a swing wing. Swept back wings make the aircraft more stable at high speeds while forward swept wings allows the aircraft to be agile. In the 1990s,
Northrop Grumman tested variable-geometry wings on another plane with the "Switchblade" nickname. The Northrop Bird of Prey had three wing configurations:
  • full-back position - The wings were perpendicular to the fuselage for low-speed flight.
  • intermediate position - The wings were swept forward for exceptional maneuverability.
  • full-forward position - The leading edge of the wings folded in against the fuselage, allowing the trailing edge to become the front of the wing for high speeds. This resulted in a triangular, or delta wing shape.
Lets now know how the wings position affects its performance, unswept wings are efficient at low speeds, providing a great amount of lift compared to the amount of induced drag exerted on the plane. Unswept wings are very bad at dealing with wave drag. Swept wings cut down on drag caused by turbulence at the wingtips. But the real advantage of swept wings comes in supersonic flight -- the configuration cuts down on wave drag by redistributing the shock waves along the plane's aerodynamic profile. They are ideal for these high-speed conditions. Unfortunately, they do not allow for heavy payloads at lower speeds. Swept wings are also inefficient and burn too much fuel to stay aloft, which reduces the range of the aircraft. Thus an aircraft with a variable sweep wing has become the need of the hour. The mechanisms required to make the wing movements function were complicated and heavy. They also took up a lot of space, cutting down on efficiency and payload. Swing wings were largely abandoned for more simplistic designs. Northrop Grumman plans a scaled-down test model with a 40-foot wingspan for 2010, with a full-size, fully-functional Switchblade ready for flight in 2020. As the project moves into the scale and full-sized phases, costs will likely escalate into the billions of dollars. Hopefully in the coming years we'll be having fully operational variable sweep wing aircrafts.

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