Boxwing

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Ultralight Sunny

With closed wing (German about "box kite-wing", English: box wing or box-wing or joint wing ) is a special wing arrangement for aircraft referred. The use of two superimposed wings, which are connected at their ends by vertical surfaces or arcs, results in u. U. a very stable flight behavior. In the course of the development of aviation, the vertical surfaces on the wing tips had different functions. With swept flying wings according to Dunne they mainly acted as a replacement for the side fins; in later designs, which approached the duck or tandem concept , a reduction in the induced drag through the formation of tip vortices was a primary goal (see winglets ). Through various spatial variations, elements of the tandem, duck or flying wing concept can theoretically be combined (all horizontal surfaces generate lift). In addition to the improved pull-over strength of the tandem / duck concept, the compact design as a double-decker is an additional argument for using the boxwing wings.

history

Blériot IV

The box kite principle was already known in ancient China. The aircraft of the first few hours were partly based on this principle. With his legendary “14 bis”, Alberto Santos Dumont practically built a backward-flying box kite. As early as 1906, Louis Blériot and Gabriel Voisin designed the Blériot III, a double-decker in a box wing-like configuration. The first aerodynamic calculations were published in 1924 by Ludwig Prandtl . The first application of the boxwing concept in the form used today goes back to Alexander Lippisch , who designed a corresponding double-decker for Heinkel at the beginning of the 1930s, but which did not get beyond the model test phase. The upper wing was not swept throughout, while the lower wing was swept backwards. The rudder surfaces each established the connection between the wings, but were not located at the wing tips, but further inside. The effect of the “closed system” was thus not given. A design by Luigi Colani in 2001 , who designed a passenger aircraft with a wingspan of 80 m, also showed a strong similarity to the Boxwing concept .

Practical use

In addition to its use in model airplanes , this wing concept was also implemented in some ultralight aircraft . These include the Ligeti Stratos , which flew for the first time in 1985, and the Sunny from 1989. The wing types used complement each other. The upper surface has the layout of a swept delta wing . The surface turns into the wind without any steering action. In the case of weight-controlled ultralight aircraft, this self-control behavior requires constant counter-steering by the pilot. In boxwing aircraft, this counter-steering force is canceled out by the lower, straight wing. In practice, a pilot does not have to take any compensatory control interventions in cross winds . The Sunny flies in the desired direction without increasing resistance, pushing it sideways, but without losing speed .

In addition, the box wing area prevents the aircraft from stalling . Since the upper surface generates 2/3 of the total lift, the aircraft simply takes the aircraft's nose downwards when it loses speed and builds up lift again due to the higher speed. The lower surface always generates lift and keeps the aircraft stable without causing it to tip over.

See also

Web links

Individual evidence

  1. Conceptual Design of a Medium Range Box Wing Aircraft (PDF; 137 kB)
  2. ^ Karl R. Pawlas: Tailless or Duck - Heinkel RRG Doppeldecker, a reconnaissance project from 1932 , in aviation lexicon, article number 3111-100-1 Description of the Lippisch draft in the aviation lexicon
  3. ^ Howard Levy: Stratos , in Airplane Monthly, April 1987, pp. 184 ff.
  4. The story of the SUNNY Boxwing