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Article
Publication date: 1 September 1936

J.H. Crowe

THE fundamental problem of aerofoil theory is to predict accurately the characteristics of wings of various sections and plan form when the former may be any function of the…

Abstract

THE fundamental problem of aerofoil theory is to predict accurately the characteristics of wings of various sections and plan form when the former may be any function of the latter. The vortex theory of aerofoils enables us to predict the chief properties of aerofoils below the stall. We are, however, interested also in the conditions obtaining at and above the stall. In the present state of the art we are obliged to rely on wind tunnel tests. The number and variety of wings that would have to be tested in order to give us at all a comprehensive survey of the possibilities of taper, aerodynamic twist and varying section are so great that wind tunnel tests can so far only be said to have touched the fringe of the problem.

Details

Aircraft Engineering and Aerospace Technology, vol. 8 no. 9
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 8 February 2013

Joydeep Bhowmik, Debopam Das and Saurav Kumar Ghosh

The purpose of the work is to design a flapping wing that generates net positive propulsive force and vertical force over a flapping cycle operating at a given freestream…

Abstract

Purpose

The purpose of the work is to design a flapping wing that generates net positive propulsive force and vertical force over a flapping cycle operating at a given freestream velocity. In addition, an optimal wing is designed based on the comparison of the force estimated from the quasi‐steady theory, with the wind‐tunnel experiments. Based on the designed wing configuration, a flapping wing ornithopter is fabricated.

Design/methodology/approach

This paper presents a theoretical aerodynamic model of the design of an ornithopter with specific twist distribution that results generation of substantial net positive vertical force and thrust over a cycle at non‐zero advance ratio. The wing has a specific but different twist distribution during the downstroke and the upstroke that maintains the designed angle of attack during the strokes. The wing is divided into spanwise strips and Prandtl's lifting line theory is applied to estimate aerodynamic forces with the assumptions of quasi‐steady flow and the wings are without any dihedral or anhedral. Spanwise circulation distribution is obtained and hence lift is calculated. The lift is resolved along the freestream velocity and perpendicular to the freestream velocity to obtain vertical force and propulsive thrust force. Experiments are performed in a wind tunnel to find the forces generated in a flapping cycle which compares well with the theoretical estimation at low flying speeds.

Findings

The estimated aerodynamic force indicates whether the wing geometry and operating conditions are sufficient to carry the weight of the vehicle for a sustainable flight. The variation of the aerodynamic forces with varying flapping frequencies and freestream velocities has been illustrated and compared with experimental data that shows a reasonable match with the theoretical estimations. Based on the calculations a prototype has been fabricated and successfully flown.

Research limitations/implications

The theory does not take into account the unsteady effects and estimates the aerodynamic forces at wing level condition. It doesn’t predict stall and ignores structural deformations due to aerodynamic loads. The airfoil section is only specified by the chord, zero lift angle of attack, lift slope, profile drag coefficient and angle of attack as given inputs. To fabricate a light weight wing that maintains a very accurate geometric twist and camber distribution as per the theoretical requirement is challenging.

Practical implications

Useful for designing ornithopter wing (preferably bigger) involving an unswept rigid spar with flapping and twisting.

Originality/value

The novelty of the present wing design is the appropriate spanwise geometric twisting about the leading edge spar.

Details

International Journal of Intelligent Unmanned Systems, vol. 1 no. 1
Type: Research Article
ISSN: 2049-6427

Keywords

Article
Publication date: 1 January 1945

W.J. Duncan

A NUMBER of attempts have already been made to present a simple and easily understood account of wing flutter 1,2,3,4,5,6, but it appears that the subject is still obscure and…

Abstract

A NUMBER of attempts have already been made to present a simple and easily understood account of wing flutter 1,2,3,4,5,6, but it appears that the subject is still obscure and difficult to many. Accordingly another elementary presentation of the subject is given in this paper, and the problem is approached in a new way. Emphasis is placed on explaining how flutter can happen; that is, on the physical mechanism by which an aeroplane wing can become a species of air engine and extract energy from the passing air. This explanation is greatly helped by experiments with a mechanism which has been called the “flutter engine”, consisting of a rigid aerofoil so arranged that when placed in an airstream it can oscillate and drive a flywheel.

Details

Aircraft Engineering and Aerospace Technology, vol. 17 no. 1
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 March 1954

E.G. MA Broadbent and A.F.R.Ae.S.

THE primary duties of an aircraft design team are to design an aircraft capable of meeting a certain specification of performance and manoeuvrability with suitable flying…

Abstract

THE primary duties of an aircraft design team are to design an aircraft capable of meeting a certain specification of performance and manoeuvrability with suitable flying qualities, and to ensure that it will be strong enough to withstand any aerodynamic loads it may suffer in flight. It will be found that the aircraft when built is not a rigid structure, but this in itself is not important. We are all familiar with the flexing of an aircraft's wings when struck by a sharp gust of wind in flight, but as long as the wings are strong enough no harm is done. On the contrary, in a passenger aircraft the flexibility of the wings in bending will have a favourable effect, as it will cushion the passengers to some extent from the suddenness of the gust. Flexibility of the structure, however, is not always beneficial and it often introduces new difficulties in the designer's problems. These difficulties arise when the deformation of the aircraft structure introduces additional aerodynamic forces of appreciable magnitude. The additional forces will themselves cause deformation of the structure which may introduce still further aerodynamic forces, and so on. It is interactions of this type between elastic and aerodynamic forces which lead to the oscillatory phenomenon of flutter, and to the non‐oscillatory phenomena of divergence and reversal of control. The study of these three aero‐elastic problems becomes more important as aircraft speeds increase, because increase of design speeds leads to more slender aircraft with thinner wings, and therefore to relatively greater flexibility of the structure. The dangers, in fact, are such that the designers of a modern high‐performance aircraft have to spend considerable effort on the prediction of aero‐elastic effects in order that suitable safeguards can be included in the design. By far the greatest part of this effort is spent on flutter, which will be discussed in Parts II, III and IV of this series, but any of the three problems may force the designers to increase the structural stiffness of parts of the aircraft. The wing skin thickness on a modern aircraft, for example, is nearly always designed by consideration either of aileron reversal or wing flutter. Divergence is usually less important but as it is the simplest of the three phenomena to treat analytically, we shall study it first.

Details

Aircraft Engineering and Aerospace Technology, vol. 26 no. 3
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 July 1951

R. Tatham

AERONAUTICAL engineers are afflicted by various ‘centres’ which will not stay put. Weights engineers spend much of their time chasing the elusive centre of gravity up and down the…

Abstract

AERONAUTICAL engineers are afflicted by various ‘centres’ which will not stay put. Weights engineers spend much of their time chasing the elusive centre of gravity up and down the fuselage, the aerodynamicist worries about the centre of pressure, and the structural engineer, in addition to these, is cursed with the flexural centre and the shear centre. The main trouble connected with the flexural and shear centre seems to be historical in origin. No real attempt appears to have been made to keep pace with the development of wing structures from the old simple two‐spar, fabric‐covered, constant‐section wing. It is still quite common to see the flexural centre of a wing defined as the point at which a load must be applied, so as to produce bending of the wing without twist. In general, something more precise is required, and, particularly in these days of tapered, swept‐back, stressed‐skin wings, it would seem desirable to review the old definitions and usages of terms such as flexural centre, and flexural axis in order to avoid confusion and possible misstatements or misapplications. The advent of stressed‐skin construction has brought into fairly general use the term shear centre, which is often confused with the flexural centre, although the two points do not necessarily coincide. The use of sweep‐back has caused further confusion concerning the definition of twist. It is hoped that this brief survey may indicate the nature of the confusion that is known to exist—and, perhaps, lead to an authoritative decision, which may standardize terms and definitions.

Details

Aircraft Engineering and Aerospace Technology, vol. 23 no. 7
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 November 1937

A.W. Quick

IF I am to cover the development of the Ju 86 wing in this short paper, it will be obvious that I shall not be able to touch upon all the aerodynamic problems encountered. Thus I…

Abstract

IF I am to cover the development of the Ju 86 wing in this short paper, it will be obvious that I shall not be able to touch upon all the aerodynamic problems encountered. Thus I shall deal particularly with the modern problem of lateral stability about the longitudinal axis, or “wing‐dropping.”

Details

Aircraft Engineering and Aerospace Technology, vol. 9 no. 11
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 March 1937

J.H. Crowe

THE basic theory of stability has undergone no important modification since the publication of Professor G. H. Bryan's book on Stability in Aviation in 1911. The stability…

Abstract

THE basic theory of stability has undergone no important modification since the publication of Professor G. H. Bryan's book on Stability in Aviation in 1911. The stability equations derived therein serve to‐day with the difference that axes and symbols have now been standardised and with the additional refinement of a non‐dimensional form of the stability equation introduced by H. Glauert. Due to the vastly increased knowledge of aerodrynamic characteristics, however, the stability derivatives are more readily assessable in any particular design case. This applies more particularly to longitudinal stability calculations which may, and indeed often arc, carried through with no wind tunnel tests available apart from a lift and drag curve for the aerofoil section used. There has also been some extension of the use of stability charts for deriving an approximate knowledge of the behaviour of the aeroplane when it receives a disturbance. These charts are exceedingly useful for obtaining periodic time and damping factor, but the assumptions on which they are based should be clearly realized.

Details

Aircraft Engineering and Aerospace Technology, vol. 9 no. 3
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 3 July 2017

Andrzej Tarnowski

This paper aims to describe the concept of morphing tailless aircraft with discontinuous skin and its preliminary kinematic solution. Project assumptions, next steps and expected…

Abstract

Purpose

This paper aims to describe the concept of morphing tailless aircraft with discontinuous skin and its preliminary kinematic solution. Project assumptions, next steps and expected results are briefly presented.

Design/methodology/approach

Multidisciplinary numerical optimization will be used to determine control allocation for wing segments rotation. Wing demonstrator will be fabricated and tested in wind tunnel. Results will be used in construction of flying model and design of its control system. Flight data of morphing demonstrator and reference aircraft will result in comparative analysis of both technologies.

Findings

Proposed design combines advantages of wing morphing without complications of wing’s structure elastic deformation. Better performance, stability and maneuverability is expected due to wing’s construction which is entirely composed of unconnected wing segments. Independent control of each segment allows for free modeling of spanwise lift force distribution.

Originality/value

Nonlinear multipoint distribution of wing twist as the only mechanism for control and flight performance optimization has never been studied or constructed. Planned wind tunnel investigation of such complex aerodynamic structure has not been previously published and will be an original contribution to the development of aviation and in particular to the aerodynamics of wing with discontinuous skin.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 4
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 1 May 1944

W.L. Morse

THE present article is the application of Schrenk's approximate method to two cases, one a wing without twist and the other the same wing with twist, the nomenclature of Schrenk's…

Abstract

THE present article is the application of Schrenk's approximate method to two cases, one a wing without twist and the other the same wing with twist, the nomenclature of Schrenk's article having been altered to conform to British usage, and a certain amount of explanatory matter added in order to make the method more easily understood.

Details

Aircraft Engineering and Aerospace Technology, vol. 16 no. 5
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 6 March 2017

Mengmeng Zhang and Arthur Rizzi

A collaborative design environment is needed for multidisciplinary design optimization (MDO) process, based on all the modules those for different design/analysis disciplines, and…

387

Abstract

Purpose

A collaborative design environment is needed for multidisciplinary design optimization (MDO) process, based on all the modules those for different design/analysis disciplines, and a systematic coupling should be made to carry out aerodynamic shape optimization (ASO), which is an important part of MDO.

Design/methodology/approach

Computerized environment for aircraft synthesis and integrated optimization methods (CEASIOM)-ASO is developed based on loosely coupling all the existing modules of CEASIOM by MATLAB scripts. The optimization problem is broken down into small sub-problems, which is called “sequential design approach”, allowing the engineer in the loop.

Findings

CEASIOM-ASO shows excellent design abilities on the test case of designing a blended wing body flying in transonic speed, with around 45 per cent drag reduction and all the constraints fulfilled.

Practical implications

Authors built a complete and systematic technique for aerodynamic wing shape optimization based on the existing computational design framework CEASIOM, from geometry parametrization, meshing to optimization.

Originality/value

CEASIOM-ASO provides an optimization technique with loosely coupled modules in CEASIOM design framework, allowing engineer in the loop to follow the “sequential approach” of the design, which is less “myopic” than sticking to gradient-based optimization for the whole process. Meanwhile, it is easily to be parallelized.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 2
Type: Research Article
ISSN: 1748-8842

Keywords

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