Closed wing

Last updated

An annular closed wing Annular box wing.svg
An annular closed wing

A closed wing is a wing that effectively has two main planes which merge at their ends so that there are no conventional wing tips. Closed wing designs include the annular wing (commonly known as the cylindrical or ring wing), the joined wing, the box wing, and spiroid tip devices. [1]

Contents

Like many wingtip devices, the closed wing aims to reduce the wasteful effects associated with wingtip vortices which occur at the tips of conventional wings. Although the closed wing has no unique claim on such benefits, many closed wing designs do offer structural advantages over a conventional cantilever monoplane.

Characteristics

The Spiroid winglet is a closed wing surface attached to the tip of a conventional wing. Spiroids.png
The Spiroid winglet is a closed wing surface attached to the tip of a conventional wing.

Wingtip vortices form a major component of wake turbulence and are associated with induced drag, which is a significant contributor to total drag in most regimes. A closed wing avoids the need for wingtips and thus might be expected to reduce wingtip drag effects.

In addition to potential structural advantages over open cantilevered wings, closed wing surfaces have some unique aerodynamic properties:

The upshot is that although closed systems can produce large induced-drag reductions relative to a conventional planar wing, there is no significant aerodynamic advantage that uniquely accrues to their being closed rather than open. [1]

Configurations

Various types of closed wing have been described:

History

Pioneer years

The Bleriot IV replaced the forward one of its predecessor's annular wings with a conventional biplane wing Bleriot IV.jpg
The Blériot IV replaced the forward one of its predecessor's annular wings with a conventional biplane wing

An early example of the closed wing was on the Blériot III aircraft, built in 1906 by Louis Blériot and Gabriel Voisin. The lifting surfaces comprised two annular wings mounted in tandem. The later Blériot IV replaced the forward annular wing with a biplane and added a canard foreplane to make it a three-surface aircraft. It was able to leave the ground in small hops before being damaged beyond repair.

Based on the work of G.J.A. Kitchen, Cedric Lee and G. Tilghman Richards built and flew several annular-wing aeroplanes in which the fore and aft segments were on the same level. The first was a biplane. It was followed by a series of monoplanes, the last of the line remaining in use until 1914. [3]

World War II

In 1944, the German designer Ernst Heinkel began working on an annular-wing VTOL multirole single-seater called the Lerche , but the project was soon abandoned. [4]

Postwar

During the 1950s, the French company SNECMA developed the Coléoptère, a single-person VTOL annular wing aircraft. The aircraft proved dangerously unstable despite the development and testing of several prototypes, and the design was abandoned. [5] Later proposals for closed-wing designs included the Convair Model 49 Advanced Aerial Fire Support System (AAFSS) and the 1980s Lockheed "Ring Wing" concept.[ citation needed ]

Dr. Julian Wolkovitch continued to develop the idea in the 1980s, claiming it was an efficient structural arrangement in which the horizontal tail provided structural support for the wing as well as acting as a stabilizing surface. [6] [7] [8]

The Spiroid winglet, a design currently under development by Aviation Partners, is a closed wing surface mounted at the end of a conventional wing. The company announced that the winglets fitted to a Gulfstream II reduced fuel consumption in the cruise phase by over 10%. [9] [10]

The Finnish company FlyNano flew a prototype of a closed wing ultralight aircraft, the FlyNano Nano on 11 June 2012. [11] [12]

An aircraft was also designed and constructed with a closed wing in Belarus. [13]

Miscellaneous modern examples include:

Closed wings remain mostly confined to the realms of studies and conceptual designs, as the engineering challenges of developing a strong, self-supporting closed wing for use in the large airliners which would benefit most from increases in efficiency have yet to be overcome.

The closed wing is also used in water, for surfboard fins of the type also known as the tunnel fin. [15]

Lockheed Martin Environmentally Responsible Aviation Project

AOK Spacejet at Paris Air Show 2013 AOK Spacejet at Paris Air Show 2013.jpg
AOK Spacejet at Paris Air Show 2013

During 2011, the Environmentally Responsible Aviation Project at NASA's Aeronautics Research Mission Directorate invited study proposals towards meeting NASA's goal of reducing future aircraft fuel consumption by 50% compared to 1998. Lockheed Martin proposed a box wing design along with other advanced technologies. [16] [17]

Prandtl Box Wing

In 1924, the German aerodynamicist Ludwig Prandtl suggested that a box wing, under certain conditions, might provide the minimum induced drag for a given lift and wingspan. [18] In his design, two offset horizontal wings have vertical wings connecting their tips and shaped to provide a linear distribution of side forces. The configuration is said to offer improved efficiency for a range of aircraft.

In the 1980s, the Ligeti Stratos used this approach. [19] [20] The name "PrandtlPlane" was coined in the 1990s in research by Aldo Frediani et al. of the University of Pisa. [21] It is currently also used in some ultralight aircraft. [22]

Full-scale prototype of an ultralight amphibious PrandtlPlane, developed during IDINTOS project and presented at Creactivity 2013 (Pontedera, Italy). IDINTOS project exposition at Creactivity 2013 (Pontedera, Italy).jpg
Full-scale prototype of an ultralight amphibious PrandtlPlane, developed during IDINTOS project and presented at Creactivity 2013 (Pontedera, Italy).

IDINTOS [22] (IDrovolante INnovativo TOScano) is a research project, co-funded by the regional government of Tuscany (Italy) in 2011 in order to design and manufacture an amphibious ultralight PrandtlPlane. The research project has been carried out by a consortium of Tuscan public and private partners, led by the Aerospace Section of the Civil and Industrial Engineering Department of Pisa University, and has resulted in the manufacturing of a 2-seater VLA prototype. [23]

The configuration is also claimed to be theoretically efficient for wide-body jet airliners. The largest commercial airliner, the Airbus A380, must make efficiency trade-offs to keep the wingspan below the 80-meter limit at most airports, but a closed wing with optimal wingspan could be shorter than that of conventional designs, potentially allowing even larger aircraft to use the current infrastructure. [24]

C-wing

The C-wing is a theoretical configuration in which much of the upper centre section of a box wing is removed, creating a wing that folds up and over at the tips but does not rejoin in the centre. A C-wing can achieve very nearly the same induced-drag performance as a corresponding box wing, as shown by the calculations illustrated below. [25]

Each of the first three rows in the illustration shows a different C-wing configuration as it is taken through a sequence of theoretical induced-drag calculations in which the wingtips are brought closer together, culminating in the limiting case on the right, where the gap has been taken to zero and the configuration has become a closed box wing (referred to as the "Quasi-closed C-wing" because the calculations were carried out in the limit as the gap went to zero).

Nonplanar wings: results for the optimal aerodynamic efficiency ratio e Inducd drag minimization.jpg
Nonplanar wings: results for the optimal aerodynamic efficiency ratio ε

The parameter ε is the optimal aerodynamic efficiency ratio [25] and represents the ratio between the aerodynamic efficiency of a given non-planar wing and the corresponding efficiency of a reference classical cantilevered wing with the same wing span and total lift. Both efficiencies are evaluated for their respective optimal lift distributions. Values of ε greater than 1 indicate lower induced drag than that of a classical cantilevered wing for which ε = 1. [25]

Note that all of the C-wing configurations have ε greater than 1 and that there is little difference (no difference to the two decimal places shown in two of the cases) between a configuration with a substantial gap (the second entry in each row) and the corresponding closed configuration (the third entry in each row). This is because the optimum lift loading calculated for the quasi-closed cases is very small over the upper centre section, and that part of the wing can be removed with little change in lift or drag.

The lift distributions shown here for the quasi-closed cases look different from those typically shown for box wings in the classical literature (see Durand, figure 81, for example). [2] The classical solution in Durand was obtained by a conformal-mapping analysis that happened to be formulated in a way that led to equal upward loadings on the horizontal panels of the box. But the optimum lift distribution is not unique. [1] A constant inward loading (corresponding to a particular constant circulation) can be added to a classical loading like that shown by Durand to obtain a loading like those in the quasi-closed cases below. The two methods of analysis give different-looking versions of the optimum loading that are not fundamentally different. Except for small differences due to the numerical method used for the quasi-closed cases, the two kinds of loading are in principle just shifted versions of each other.

Related Research Articles

<span class="mw-page-title-main">Wing</span> Appendage used for flight

A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expressed as its lift-to-drag ratio. The lift a wing generates at a given speed and angle of attack can be one to two orders of magnitude greater than the total drag on the wing. A high lift-to-drag ratio requires a significantly smaller thrust to propel the wings through the air at sufficient lift.

<span class="mw-page-title-main">Monoplane</span> Fixed-wing aircraft with a single main wing plane

A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple planes.

<span class="mw-page-title-main">Flying wing</span> Tailless fixed-wing aircraft that has no definite fuselage

A flying wing is a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, nacelles, blisters, booms, or vertical stabilizers.

<span class="mw-page-title-main">Aspect ratio (aeronautics)</span> Ratio of an aircrafts wing span to its mean chord

In aeronautics, the aspect ratio of a wing is the ratio of its span to its mean chord. It is equal to the square of the wingspan divided by the wing area. Thus, a long, narrow wing has a high aspect ratio, whereas a short, wide wing has a low aspect ratio.

<span class="mw-page-title-main">Lift-to-drag ratio</span> Measure of aerodynamic efficiency

In aerodynamics, the lift-to-drag ratio is the lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. It describes the aerodynamic efficiency under given flight conditions. The L/D ratio for any given body will vary according to these flight conditions.

Lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, in aerodynamics, is an aerodynamic 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 with airfoil wings that redirect air to cause a downforce. It is symbolized as , and the lift-induced drag coefficient as .

<span class="mw-page-title-main">Wingtip device</span> Aircraft component fixed to the end of the wings to improve performance

Wingtip devices are intended to improve the efficiency of fixed-wing aircraft by reducing drag. Although there are several types of wing tip devices which function in different manners, their intended effect is always to reduce an aircraft's drag. Wingtip devices can also improve aircraft handling characteristics and enhance safety for following aircraft. Such devices increase the effective aspect ratio of a wing without greatly increasing the wingspan. Extending the span would lower lift-induced drag, but would increase parasitic drag and would require boosting the strength and weight of the wing. At some point, there is no net benefit from further increased span. There may also be operational considerations that limit the allowable wingspan.

<span class="mw-page-title-main">Flight control surfaces</span> Surface that allows a pilot to adjust and control an aircrafts flight attitude

Aircraft flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude.

<span class="mw-page-title-main">Wingtip vortices</span> Turbulence caused by difference in air pressure on either side of wing

Wingtip vortices are circular patterns of rotating air left behind a wing as it generates lift. The name is a misnomer because the cores of the vortices are slightly inboard of the wing tips. Wingtip vortices are sometimes named trailing or lift-induced vortices because they also occur at points other than at the wing tips. Indeed, vorticity is trailed at any point on the wing where the lift varies span-wise ; it eventually rolls up into large vortices near the wingtip, at the edge of flap devices, or at other abrupt changes in wing planform.

<span class="mw-page-title-main">Elliptical wing</span> Airplane wing with an elliptical shape

An elliptical wing is a wing planform whose leading and trailing edges each approximate two segments of an ellipse. It is not to be confused with annular wings, which may be elliptically shaped.

<span class="mw-page-title-main">Canard (aeronautics)</span> Aircraft configuration in which a small wing is placed in front of the main wing

In aeronautics, a canard is a wing configuration in which a small forewing or foreplane is placed forward of the main wing of a fixed-wing aircraft or a weapon. The term "canard" may be used to describe the aircraft itself, the wing configuration, or the foreplane. Canard wings are also extensively used in guided missiles and smart bombs.

<span class="mw-page-title-main">Tailless aircraft</span> Aircraft whose only horizontal aerodynamic surface is its main wing

In aeronautics, a tailless aircraft is an aircraft with no other horizontal aerodynamic surface besides its main wing. It may still have a fuselage, vertical tail fin, and/or vertical rudder.

<span class="mw-page-title-main">Washout (aeronautics)</span> Characteristic of aircraft wing design

Washout is a characteristic of aircraft wing design which deliberately reduces the lift distribution across the span of an aircraft’s wing. The wing is designed so that the angle of incidence is greater at the wing roots and decreases across the span, becoming lowest at the wing tip. This is usually to ensure that at stall speed the wing root stalls before the wing tips, providing the aircraft with continued aileron control and some resistance to spinning. Washout may also be used to modify the spanwise lift distribution to reduce lift-induced drag.

<span class="mw-page-title-main">Wing configuration</span> Describes the general shape and layout of an aircraft wing

The wing configuration of a fixed-wing aircraft is its arrangement of lifting and related surfaces.

<span class="mw-page-title-main">Fuel economy in aircraft</span> Aircraft fuel efficiency

The fuel economy in aircraft is the measure of the transport energy efficiency of aircraft. Fuel efficiency is increased with better aerodynamics and by reducing weight, and with improved engine brake-specific fuel consumption and propulsive efficiency or thrust-specific fuel consumption. Endurance and range can be maximized with the optimum airspeed, and economy is better at optimum altitudes, usually higher. An airline efficiency depends on its fleet fuel burn, seating density, air cargo and passenger load factor, while operational procedures like maintenance and routing can save fuel.

<span class="mw-page-title-main">Outboard tail</span>

An outboard tail is a type of aircraft tail or empennage which is split in two, with each half mounted on a short boom just behind and outboard of each wing tip. It comprises outboard horizontal stabilizers (OHS) and may or may not include additional boom-mounted vertical stabilizers (fins). OHS designs are sometimes described as a form of tailless aircraft.

<span class="mw-page-title-main">NASA X-57 Maxwell</span> Cancelled experimental NASA electric aircraft

The NASA X-57 Maxwell was an experimental aircraft being developed by NASA, intended to demonstrate technology to reduce fuel use, emissions, and noise. The first flight of the X-57 was scheduled to take place in 2023, but the program was cancelled due to problems with the propulsion system.

<span class="mw-page-title-main">Prandtl-D</span> Type of aircraft

The Preliminary Research Aerodynamic Design to Lower Drag, or Prandtl-D was a series of unmanned experimental glider-aircraft developed by NASA under aerodynamicist Albion Bowers. The acronym is a reference to early German Aerospace Engineer Ludwig Prandtl, whose theory of the bell-shaped lift distribution deeply influenced Bowers.

<span class="mw-page-title-main">Annular lift fan aircraft</span>

An annular lift fan aircraft is a conceptual vertical takeoff and landing (VTOL) aircraft that was first systematically and numerically investigated in 2015. This concept was proposed to offer a VTOL solution for both high hovering efficiency and high cruise speed, using a large annular lift fan instead of the relatively small conventional circular lift fans used in the Ryan XV-5 Vertifan and the F-35B Lightning II (JSF).

The Diamond was a British single seat ultralight aircraft, developed by Arthur Luff in the 1980s. It was notable for its radical design.

References

  1. 1 2 3 4 5 Kroo, Ilan (June 2005). Nonplanar Wing Concepts For Increased Aircraft Efficiency (PDF). VKI Lecture Series on Innovative Configurations and Advanced Concepts for Future Civil Aircraft. Archived (PDF) from the original on 2022-03-07. Retrieved 2022-04-07.
  2. 1 2 von Kármán, Th.; Burgers, J. M. (1935). Durand, William F. (ed.). Division E: General Aerodynamic Theory-Perfect Fluids. Aerodynamic Theory: a General Review of Progress Under a Grant of the Guggenheim Fund for the Promotion of Aeronautics. Vol. 2. Berlin: Julius Springer. doi:10.1007/978-3-642-91485-0. ISBN   978-3-642-89628-6.
  3. ↑ Lewis, Peter M. H. (1962). British Aircraft 1809–1914. London: Putnam. pp. 340–343. LCCN   64035723. OCLC   1301968. OL   5924340M.
  4. ↑ "Heinkel Lerche (Lark)". Military Factory. 2020-10-27. Archived from the original on 2021-12-28. Retrieved 2022-04-07.
  5. ↑ Davis, Jeremy (July 2012). "Cancelled: Vertical Flyer". Air & Space/Smithsonian . ISSN   0886-2257. OCLC   1054386888. Archived from the original on 2022-04-07. Retrieved 2022-04-07.
  6. ↑ USpatent 4365773,Wolkovitch, Julian,"Joined wing aircraft",issued 1982-12-28
  7. ↑ "Future Technology and Aircraft Types". Stanford University . Archived from the original on 2012-07-12. Retrieved 2012-07-04.
  8. ↑ Wolkovitch, Julian (1986-03-01). "The joined wing - An overview". Journal of Aircraft. 23 (3): 161–178. doi:10.2514/3.45285. ISSN   0021-8669.
  9. ↑ "Types of Blended Winglets and Spiroid Technology". Aviation Partners . Archived from the original on 2021-05-18. Retrieved 2022-04-07.
  10. ↑ USpatent 5102068,Gratzer, Louis B.,"Spiroid-tipped wing",issued 1992-04-07, assigned to Aviation Partners Boeing
  11. ↑ Grady, Mary (2012-06-12). "FlyNano Goes Electric, Starts "Airborne Test Flights"". AVweb. Archived from the original on 2022-04-07. Retrieved 2012-07-07.
  12. ↑ FlyNano (2012-06-12). "Airborne". Archived from the original on 2022-03-16. Retrieved 2012-07-07.
  13. ↑ "Planes with ellipse wings, creative oddity of the past". gizmowatch.com. Archived from the original on 2013-01-24. Retrieved 2010-01-06.
  14. ↑ "Nonplanar Wings: Closed Systems". Stanford University . Archived from the original on 2011-08-11. Retrieved 2012-07-04.
  15. ↑ "Turbo Tunnel Fin". TurboTunnel. Archived from the original on 2021-06-12. Retrieved 2022-04-13.
  16. ↑ Barnstorff, Kathy (2012-01-27). "New Ideas Sharpen Focus for Greener Aircraft". NASA . NASA Langley Research Center. Archived from the original on 2022-03-25. Retrieved 2012-12-17.
  17. ↑ Rosenblum, Andrew; Pastore, Rose (2012-05-01). "The Jets of the Future". Popular Science . Archived from the original on 2021-12-08. Retrieved 2012-12-17.
  18. ↑ Prandtl, L. (1924). "Induced Drag of Multiplanes". Technische Berichte. National Advisory Committee for Aeronautics Technical note No. 182. 3 (7): 309–315. OCLC   1121049802.
  19. ↑ "Ligeti Stratos History". LGT Aerospace. 2010-09-20. Archived from the original on 2013-09-17. Retrieved 2022-04-07.
  20. ↑ "Ligeti Stratos". Projet Plaisir (in French). Archived from the original on 2022-01-02. Retrieved 2022-04-07.
  21. ↑ Frediani, Aldo (June 2005). The Prandtl Wing. VKI Lecture Series on Innovative Configurations and Advanced Concepts for Future Civil Aircraft. Archived from the original on 2022-04-07. Retrieved 2022-04-07.
  22. 1 2 "IDINTOS". Archived from the original on 2021-05-06. Retrieved 2022-04-07.
  23. ↑ Cipolla, Vittorio; Frediani, Aldo; Oliviero, F.; Pinucci, M.; Rizzo, Emanuele; Rossi, R. (2016-07-01). "Ultralight amphibious PrandtlPlane: the final design". Aerotecnica Missili & Spazio. 95 (3): 125–135. Bibcode:2016AeMiS..95..125C. doi:10.1007/BF03404721. hdl: 11568/867708 . ISSN   0365-7442. S2CID   195242441. Archived from the original on 2022-04-07. Retrieved 2022-04-07.
  24. ↑ Frediani, Aldo; Cipolla, Vittorio; Rizzo, Emanuele (2012). "The PrandtlPlane Configuration: Overview on Possible Applications to Civil Aviation" . In Buttazzo, G.; Frediani, Aldo (eds.). Variational Analysis and Aerospace Engineering: Mathematical Challenges for Aerospace Design. Springer Optimization and Its Applications. Vol. 66. Boston: Springer. pp. 179–210. doi:10.1007/978-1-4614-2435-2_8. ISBN   978-1-4614-2434-5.
  25. 1 2 3 Demasi, Luciano; Dipace, Antonio; Monegato, Giovanni; Cavallaro, Rauno (2014-01-10). "An Invariant Formulation for the Minimum Induced Drag Conditions of Non-planar Wing Systems". 52nd Aerospace Sciences Meeting. AIAA SciTech Forum. American Institute of Aeronautics and Astronautics. doi:10.2514/6.2014-0901. ISBN   978-1-62410-256-1.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.