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[[image:flying.wing.arp.750pix.jpg|thumb|right|250px|[[Northrop YB-49]] flying wing.]]

'''Flying wing''' is the generic designation given for a [[fixed-wing aircraft]] configuration which is capable of stable, controllable flight without the aid of lifting surfaces other than the main [[wing]] itself, that is, without auxiliary surfaces such as "tails" and "canards". Additionally, the term is usually applied to aircraft in which most of the payload is tranported inside the main wing, the latter comprising most of its structural volume. A variation of such configuration in which a payload bearing [[fuselage]] is present is usually known by the less restrictive designation of "[[tailless aicraft]]".

Historically, the flying wing has been defended by many as potentially the most efficient aircraft configuration from the point of view of [[aerodynamics]] and structural weight. Such a notion usually comes from the idea that the absence of any aircraft components other than the wing should naturally provide those benefits. On the other hand, the aircraft's wing should be able to provide flight stability and control "by itself", a requirement which in principle imposes additional constraints to the wing design problem. Therefore, the expected gains in weight and [[drag]] could also be be partially or totally impaired due to design compromises needed to provide stability and control.

==Design Issues==
Although the discussion about flying wing aircraft usually surrounds the balance between aerodynamic/weight performance and stability/control requirements, those are by no means the only important design factors. Other issues such as (but not limited to) high-speed compressibility effects, useful payload volume, cabin pressurization, satisfaction of certification safety requirements and industrial/commercial risk must also come into play to determine wether or not the flying wing configuration is the best solution for a given aircraft mission.
==Stability and Control==
Flight stability can be loosely defined as the ability of an aircraft to recover its original flight state after suffering a transitory external force perturbation, such as imposed by wind gusts or arbitrary pilot control input. In recent years, automatic flight control  systems could be used to achieve that goal with relatively little limitations, but at the expense of system sophistication, as in the case of most modern [[fighter aircraft]]. However, the "traditional" way of providing flight stability is to design the aircraft aerodynamic and mass distribution characteristics in such a way that it is inherently stable when in flight.

As a first requirement for that, the aircraft must be '''statically stable''': whenever it is disturbed from its flight path, aerodynamic forces and moments must arise in directions that tend bring the aircraft back to its original flight state. A classical simplified example is that of an [[arrow]] in flight. The arrow is built such that its [[center of gravity]] (CG) is positioned at a point which is ahead of the point where the resultant of aerodynamic forces is applied, its [[aerodynamic center]] (AC). Whenever the arrow is misaligned to the relative wind due to some disturbance, the increase in resultant aerodynamic force (lift) on the AC produces a moment around the CG which tends to make the arrow realign to the relative flow.

Like the arrow, any aircraft can be made statically stable, regardless of its external configuration, provided its aerodynamic center (AC) lies behind the center of gravity (CG). The main difference between the two scenarios is that, unlike the arrow, the aircraft must continuously generate a [[lift (force)|lift]] force that opposes its weight, making sustained flight possible. Therefore, an aircraft in flight has an ever present present moment component around its CG, due to the lift force it generates at some point behind it. An opposing moment must be generated to achieve balance, in a process generically referred to as "[[Trim (disambiguation)|trimming]]".

For conventional, "tailed" aircraft configurations, the trimming moment is provided by auxiliary lifting surfaces: horizontal and vertical ("fins") stabilizers, usually rear-mounted on relatively long fuselages. The forces produced by such surfaces can be varied either by adjusting their incidence or through the use control surfaces, in the form of movable trailing edge sections such as elevators and [[rudder|rudders]]. That arragement provides a quite convenient way of producing trimming and control moments, since relatively small forces on the tail surfaces are required due to the fuselage "level arm" available.

Flying wings must provide trimming and control moments without such a surface/fuselage set. That is by no means impossible, but the question is wether it can be done while preserving an aerodynamic efficiency level high enough not to reduce or anullate the gains expected from the absence of the fuselage.

There are two well known solutions for the longitudinal trimming of flying wings:

# Usage of wing section [[airfoil]] shapes which produce some amount of "nose-up" pitching moment. Usually called "reflex" airfoils, they generally rely on some level of reduced or even reversed aerodynamic loading (i.e. "lifting down") on the trailing edge region to produce the effect of a "built-in tail". Although there are viable designs which fully rely on this kind of solution, like the [[Fauvel]] and [[Marske Aircraft]] series of saiplanes, the use of such airfoils is generally regarded as not very efficient. The requirement to generate the favourable pitching moment causes impacts such as increased drag and reduced maximum lift, believed by many to be not compensating in the overall design. On the other hand, there is probably no definitive published work definitely proving those disvantages based on actual facts and data, for a wide set of application scenarios.
# Adequate "tailoring" of wing planform and spanwise lift distribution shape to produce the required "nose-up" trimming moment. The most usual solution of this kind is to use a backward swept wing with appropriate chord and twist distributions to control the spanwise load. In simple terms, the wing tips may be thought to be working partially as horizontal stabilizers, displaced backwards from the genter of gravity by the application of wing sweep. This kind of solution is freqüently associated to the use of low or null [[pitching moment]] [[airfoil]]s. Successful aircraft such as the [[Northrop]] flying wings and the [[Horten brothers|Horten]] series of sailplanes and fighters have applied this kind of design solution in the past.

==History==
The flying wing configuraton has been seriously considered by many aircraft designers since the early years of aviation, probably due to its natural appeal as a minimal design solution. Some examples of early flying wing aircraft are the [[John William Dunne|Dunne]] series of biplane aircraft and [[Waldo Waterman|Waldo Waterman's]] [[Waterman Whatsit|Whatsit]].

The configuration was studied extensively in the 1930s and 1940s, when it was seen as a natural solution to the problem of building an [[airliner]] large enough to carry a reasonable passenger load and enough fuel to cross the [[Atlantic Ocean|Atlantic]] in regular service. The flying wing's potentially large internal volume and low drag made it "a natural" for this role, and was studied in depth by [[Jack Northrop]] in the [[United States]], and [[Alexander Lippisch]] and the [[Horten brothers]] in [[Germany]], where [[Hugo Junkers]] had in 1910 patented a wing-only glider concept.

Junkers started work in 1919 on his "Giant" JG1 design, intended to seat passengers within thick wings, but in 1921 the Allied Aeronautical Commission of Control ordered the incomplete JG1 destroyed for exceeding post-war size limits on German aeroplanes. Junkers conceived futuristic flying wings for up to 1,000 passengers; the nearest this came to realisation was in the 1931 [[Junkers G-38]] 34-seater ''Grossflugzeug'' airliner, which seated passengers in cabins inside the leading edge of the inboard wing panels. The biggest land plane of its day, and nicknamed 'The Flying Hotel' one G-38 entered service with Lufthansa; it was later put to military use until being destroyed by retreating British troops in Athens in 1941. Japan built multiple G-38s, under license from Junkers, and flew them as bombers.  

Several late-war German military designs were based on the flying wing concept (or variations of it) as a proposed solution to extend the range of the otherwise very short-range [[jet engine]]d aircraft. Most famous of these would be the [[Horten Ho 229]] fighter.  This aircraft, first flown in 1944, combined not only a flying wing, or ''Nurflügel'', design, but was powered by twin jet engines.  The surving prototype remains in storage with the Smithsonian Institute in an unrestored state.  

After the war, a number of experimental designs were based on the flying wing concept, but a number of problems arose. Some general interest remained until the early 1950s, when the concept has been proposed as a design solution for long range [[bomber]]s. Such trend culminated in the [[Northrop Corporation|Northrop]] [[Northrop YB-35|YB-35]] and [[Northrop YB-49|YB-49]], which did not enter production. Those designs did not necessarily offer a great advantage in range and presented a number of technical problems, leading to the adoption of "conventional" solutions like the [[Convair]] [[Convair B-36|B-36]] and the [[Boeing]] [[B-52 Stratofortress|B-52]].

[[Image:Usaf.b2.spirit.750pix.jpg|thumb|[[B-2 Spirit]]]]
Interest in the flying wing configuration was renewed in the 1980s as a way to design aircraft with low [[radar]] reflection cross-sections. [[Stealth]] technology relies on shapes which only reflect radar waves in certain directions, thus making the aircraft hard to detect unless the radar receiver is at a specific position relative to the aircraft - a position that changes continuously as the aircraft moves. The tailplanes and engine intakes of a conventional jet, and especially its round fuselage, reflect radar in all directions, while the flat and nearly-horizontal surface of a flying wing only reflects radar in a couple of specific directions. In addition, if the edges of the wings are straight rather than curved, then they only reflect radar at angles perpendicular to these straight segments, rather than in all directions. This approach eventually led to the Northrop [[B-2 Spirit]] [[stealth]] bomber. In this case, the aerodynamic advantages of the flying wing are not the primary needs. However, modern computer-controlled fly-by-wire systems allowed for many of the aerodynamic drawbacks of the flying wing to be minimized, making for an efficient and (artificially) stable long-range bomber.

Apparently, the flying wing concept still remains at its best in the slow-to-medium speed range, and there has been continual interest in using it as a tactical [[airlift]]er design. [[Boeing]] continues to work on paper projects for a [[Blended Wing Body]] Lockheed [[C-130 Hercules]] sized transport with better range and about 1/3rd more load, while maintaining the same size characteristics. A number of companies, including [[Boeing]], [[McDonnell Douglas]] and [[de Havilland]] did considerable design work on flying-wing [[airliner]]s, but to date none have entered production.

==See also==
*[[Boeing X-48]] - blended-wing-body aircraft in the design phase
*[[Boeing Sonic Cruiser]] - blended-wing-body aircraft designed but never produced, superseded by the [[Boeing 787]]
* [[Northrop N-9M]] - a surviving flying experimental aircraft and flying wing for the B-35 and B-49 bombers.

==External links==
*[http://members.cox.net/rebid/bldwing.htm Flight to the Future] by Joe Mizrahi, Wings, April 1999, Vol. 29, No. 2
*[http://www.nurflugel.com/ The Nurflügel page]
*[http://www.warbirdforum.com/edwards.htm Glen Edwards and the Flying Wing]

== Copyright ==
"Original data received from Wikipedia on April 23, 2006. Credit given to original authors can be seen [http://en.wikipedia.org/w/index.php?title=Flying_wing&action=history Here]."

[[Category:Military Aircraft]]