Oblique wing
Overview
 
An oblique wing is a variable geometry wing
Swing-wing
A variable-sweep wing is an aeroplane wing that may be swept back and then returned to its original position during flight. It allows the aircraft's planform to be modified in flight, and is therefore an example of a variable-geometry aircraft....

 concept. On an aircraft so equipped, the wing is designed to rotate on center pivot, so that one tip is swept forward while the opposite tip is swept aft. By changing its sweep angle in this way, drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

 can be reduced at high speed (with the wing swept) without sacrificing low speed performance (with the wing perpendicular).
The oldest examples of this technology are the unrealized German aircraft projects Blohm & Voss and P.202 Messerschmitt Me P.1009-01 from the year 1944, based on a Messerschmitt Patent.
Encyclopedia
An oblique wing is a variable geometry wing
Swing-wing
A variable-sweep wing is an aeroplane wing that may be swept back and then returned to its original position during flight. It allows the aircraft's planform to be modified in flight, and is therefore an example of a variable-geometry aircraft....

 concept. On an aircraft so equipped, the wing is designed to rotate on center pivot, so that one tip is swept forward while the opposite tip is swept aft. By changing its sweep angle in this way, drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

 can be reduced at high speed (with the wing swept) without sacrificing low speed performance (with the wing perpendicular).

History

The oldest examples of this technology are the unrealized German aircraft projects Blohm & Voss and P.202 Messerschmitt Me P.1009-01 from the year 1944, based on a Messerschmitt Patent. The constructer Dr. Richard Vogt
Richard Vogt (aircraft designer)
Richard Vogt was a German engineer and aircraft designer.He is well known as a designer of unique warplanes, including an asymmetrically-shaped reconnaissance aircraft and a nuclear-powered bomber, during and after World War II.- Biography :Richard Vogt was born in Schwäbisch Gmünd, a town in the...

 was brought after the war to the USA during Operation Paperclip
Operation Paperclip
Operation Paperclip was the Office of Strategic Services program used to recruit the scientists of Nazi Germany for employment by the United States in the aftermath of World War II...

.
The oblique wing concept was rediscovered by Robert T. Jones
Robert T. Jones
Robert T. Jones, , was an aerodynamicist and aeronautical engineer for NACA and later NASA. He was known at NASA as "one of the premier aeronautical engineers of the twentieth century",.-Designer:...

, an aeronautical engineer at the NASA Ames Research Center
NASA Ames Research Center
The Ames Research Center , is one of the United States of America's National Aeronautics and Space Administration 10 major field centers.The centre is located in Moffett Field in California's Silicon Valley, near the high-tech companies, entrepreneurial ventures, universities, and other...

, Moffett Field
Moffett Federal Airfield
Moffett Federal Airfield , also known as Moffett Field, is a joint civil-military airport located between northern Mountain View and northern Sunnyvale, California, USA. The airport is near the south end of San Francisco Bay, northwest of San Jose. Formerly a United States Navy facility, the former...

, California. Analytical and wind tunnel
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...

 studies initiated by Jones at Ames indicated that a transport-size oblique-wing aircraft, flying at speeds up to Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

 1.4 (1.4 times the speed of sound), would have substantially better aerodynamic performance
Aerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...

 than aircraft with more conventional wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...

s.

So far, only one manned aircraft, the NASA AD-1
NASA AD-1
-References:CitationsBibliography* AD-1 Construction Completed, Dryden X-Press, Feb. 23, 1979, p. 2.* Robert E. Curry and Alex G. Sim, In-Flight Total Forces, Moments, and Static Aeroelastic Characteristics of an Oblique-Wing Research Airplane * Robert E. Curry and Alexander G...

, has been built to explore this concept. It flew a series of flight tests starting in 1979
1979 in aviation
This is a list of aviation-related events from 1979:-January:* January 12 – Pilatus Aircraft acquires Britten-Norman.* January 30 – Varig Boeing 707-320C PP-VLU, a cargo plane, disappears over the Pacific Ocean 30 minutes after departing Tokyos Narita International Airport. Its wreck is...

.

Theory

The general idea is to design an aircraft that performs with high efficiency as the Mach number increases from takeoff to cruise conditions (M ~ 0.8, for a commercial aircraft) Since two different types of drag dominate in each of these two flight regimes, uniting high performance designs for each regime into a single airframe is problematic.

At low Mach numbers induced drag
Lift-induced drag
In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is a drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars...

 dominates drag concerns. Airplanes during takeoff and gliders are most concerned with induced drag. One way to reduce induced drag is to increase the aspect ratio
Aspect ratio (wing)
In aerodynamics, the aspect ratio of a wing is essentially the ratio of its length to its breadth . A high aspect ratio indicates long, narrow wings, whereas a low aspect ratio indicates short, stubby wings....

 of the lifting surface. This is why gliders
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...

 have such long, narrow wings. An ideal wing has infinite span and induced drag is reduced to a two dimensional property. At lower speeds, during takeoffs and landings, an oblique wing would be positioned perpendicular to the fuselage like a conventional wing to provide maximum lift and control qualities. As the aircraft gained speed, the wing would be pivoted to increase the oblique angle, thereby reducing the drag and decreasing fuel consumption.

Alternatively, at Mach numbers increasing towards the speed of sound and beyond, wave drag
Wave drag
In aeronautics, wave drag is a component of the drag on aircraft, blade tips and projectiles moving at transonic and supersonic speeds, due to the presence of shock waves. Wave drag is independent of viscous effects.- Overview :...

 dominates design concerns. As the aircraft displaces the air, a sonic wave is generated. Sweeping the wings away from the nose of the aircraft can keep the wings aft of the sonic wave, greatly reducing drag. Unfortunately, for a given wing design, increasing sweep decreases the aspect ratio. At high speeds, both subsonic and supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...

, an oblique wing would be pivoted at up to 60 degrees to the aircraft's fuselage for better high-speed performance. The studies showed these angles would decrease aerodynamic drag, permitting increased speed and longer range with the same fuel expenditure.

Fundamentally, it appears that no design can be completely optimized for both flight regimes. However, the oblique wing shows promise of getting close. By actively increasing sweep as Mach number increases, high efficiency is possible for a wide range of speeds.

It is theorized that an oblique flying wing could drastically improve commercial air transportation, reducing fuel costs and noise in the vicinity of airports. Military operations include the possibility of a long endurance fighter/attack vehicle.

NASA airliner research

There has also been investigations into an OFW platform being developed into a transcontinental airliner. NASA Ames performed a preliminary design study of a theoretical 500-seat supersonic airliner using the concept in 1991. Following this study, NASA built a small remote-controlled demonstrator aircraft with a 20 foot (6.1m) wingspan. It flew only once, for four minutes in May, 1994, but in doing so, it demonstrated stable flight with oblique wing sweep from 35 degrees to 50 degrees. Despite this success, the NASA High Speed Research program, and further oblique wing studies, were canceled.

DARPA Oblique Flying-Wing (OFW) Project

The United States Defence Advanced Research Projects Agency (DARPA) has awarded Northrop Grumman
Northrop Grumman
Northrop Grumman Corporation is an American global aerospace and defense technology company formed by the 1994 purchase of Grumman by Northrop. The company was the fourth-largest defense contractor in the world as of 2010, and the largest builder of naval vessels. Northrop Grumman employs over...

 a $10.3 million (USD) contract for risk reduction and preliminary planning for an X-plane OFW demonstrator., known as the Switchblade.

The program aims at producing a technology demonstrator aircraft to explore the various challenges which the radical design entails. The proposed aircraft would be a pure flying wing
Flying wing
A flying wing is a tailless fixed-wing aircraft which has no definite fuselage, with most of the crew, payload and equipment being housed inside the main wing structure....

 (an aircraft with no other auxiliary surfaces such as tails, canards
Canard (aeronautics)
In aeronautics, canard is an airframe configuration of fixed-wing aircraft in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing...

 or a fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

) where the wing is swept with one side of the aircraft forward, and one backwards in an asymmetric fashion. This aircraft configuration is believed to give it a combination of high speed, long range and long endurance. The program entails two phases. Phase I will explore the theory and result in a conceptual design, while Phase II will result in the design, manufacture and flight test of an aircraft. The outcome of the program will result in a dataset that can then be used when considering future military aircraft designs.

Wind tunnel tests for the aircraft design has been completed. The design was noted to be "workable and robust."

External link

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