Search results

1 – 10 of over 1000
To view the access options for this content please click here
Article

Achuthan C. Pankaj, G. Shanthini, M.V. Shivaprasad and M. Manjuprasad

Traditional dynamic and flutter analysis demands a detailed finite element model of the aircraft in terms of its mass and stiffness distribution. However, in absence of…

Abstract

Purpose

Traditional dynamic and flutter analysis demands a detailed finite element model of the aircraft in terms of its mass and stiffness distribution. However, in absence of these details, modal parameters obtained from experimental tests can be used to predict the flutter characteristics of an aircraft. The purpose of this paper is to develop an improved and reliable method to predict the flutter characteristics of an aircraft structure of unknown configuration under an anticipated aerodynamic loading using software such as MSC Nastran and experimental modal parameters (such as mode shapes, natural frequencies and damping) from ground vibration tests.

Design/methodology/approach

A finite element model with nodes representing the test points on the aircraft is created with appropriate boundary constraints. A direct matrix abstraction program has been written for NASTRAN software that carries out a normal modes analysis and replaces the mass normalized eigenvalues and vectors with the experimentally obtained modal parameters. The flutter analysis proceeds with the solution of the flutter equation in the flutter module of NASTRAN.

Findings

The method has been evaluated for a light composite aircraft and its results have been compared with flight flutter tests and the flutter speeds obtained from the finite element model with actual stiffness and mass distributions of the aircraft.

Research limitations/implications

The methodology developed helps in the realistic prediction of flutter characteristics of a structure with known geometric configuration and does not need material properties, mass or stiffness distributions. However, experimental modal parameters of each configuration of the aircraft are required for flutter speed estimation.

Practical implications

The proposed methodology requires experimental modal parameters of each configuration of the aircraft for flutter speed estimation.

Originality/value

The paper shows that an effective method to predict flutter characteristics using modal parameters from ground vibration tests has been developed.

Details

Aircraft Engineering and Aerospace Technology, vol. 85 no. 2
Type: Research Article
ISSN: 0002-2667

Keywords

To view the access options for this content please click here
Article

Zdobyslaw Goraj and Wojciech Chajec

The purpose of this paper is to find an influence of the reduced stiffness of actuators, located on the most outer parts of ailerons, flaperons, rudders, elevators and…

Abstract

Purpose

The purpose of this paper is to find an influence of the reduced stiffness of actuators, located on the most outer parts of ailerons, flaperons, rudders, elevators and elevons on the excitation of flutter. This phenomenon is especially important for unmanned aerial vehicles because they continuously use all these control surfaces for trimming and stabilisation and on the other hand, the numerous statistics show that failure of elements of flight control systems are still the most probable reasons of aircraft critical failure.

Design/methodology/approach

Flutter calculations were performed by use of the classical modal approach. The normal vibrations of the free aircraft were measured in the ground vibration test (GVT). Test results were used either for verification of the FEM model of the structure – in this case for flutter calculation the MSC.Nastran software was used, or directly for flutter calculation. Based on the flutter analysis, the control surfaces critical for flutter were determined.

Findings

These so‐called critical control surfaces –, i.e. surfaces responsible for flutter excitation at first – are localized on outer parts of wing and empennage. It was found that the critical surfaces should have been mass balanced or should be irreversible. In the second case, i.e. when the control surfaces are irreversible, the actuators and drivers should have been of a high reliability, because disconnection of these elements could involve flutter.

Research limitations/implications

This approach within the computational analysis is limited to linear case, otherwise NASTRAN software cannot be used for flutter analysis. GVTs could be performed successfully independently if the structure has linear or non‐linear properties.

Practical implications

It was found that before any flight the stiffness in the flight control system of all control surfaces must carefully be checked and kept above the critical stiffness value. Safety level strongly depends on the reliability of actuators used on such unmanned aerial vehicles. The simulation of disconnection (as a result of damage) of selected control surfaces is possible even if the GVT were provided on undamaged vehicle. To do it, the rotational mode of so‐called “free control surface” should be prepared (as an artificial resonant mode) for all deflected control surfaces; next all the resonant modes should be orthogonalized, relative to this artificial control surfaces mode.

Originality/value

This paper was based on two big European and national projects, and all presented results are original and were never published before. Some selected graphs were shown during the EASN Workshop, Paris, September 2010 at the presentation entitled: “Aeroelastic analysis of remotely controlled research vehicles with numerous control surfaces”.

Details

International Journal of Structural Integrity, vol. 2 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

To view the access options for this content please click here
Article

E.G. Broad bent

IN Parts I, II and III of this series we have discussed the physical nature of divergence, control reversal and various forms of flutter, and have seen how these phenomena…

Abstract

IN Parts I, II and III of this series we have discussed the physical nature of divergence, control reversal and various forms of flutter, and have seen how these phenomena can be predicted by theory. The flutter problem is so complicated, however, that the aircraft designer needs the assistance of certain guiding principles; otherwise he may find when the aircraft is ready to fly that the flutter calculations which are just completed show that drastic modifications to the aircraft are necessary. These principles form the basis of this concluding part of the series and have two main objects: first to avoid large changes in design on flutter grounds and secondly to obtain a high efficiency from the flutter calculations.

Details

Aircraft Engineering and Aerospace Technology, vol. 26 no. 6
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article

D.J. Johns and P.C. Parks

The effect of structural damping on panel flutter has received little treatment in the literature but the available information suggests that such an effect may be…

Abstract

The effect of structural damping on panel flutter has received little treatment in the literature but the available information suggests that such an effect may be destabilizing. By considering a two‐dimensional, simply‐supported panel and using linear piston theory for the aerodynamic forces an analysis is presented in which the effect of hysteretic structural damping is considered. The main emphasis is on flat unbuckled panels, although a brief investigation of buckled panels is also presented, and it is concluded that there is an interdependence of structural and aerodynamic damping, which in the range of Mach numbers for which piston theory is valid, shows the destabilizing effect of structural damping. This effect is apparently more pronounced at high altitudes. A comprehensive bibliography of panel flutter is also included.

Details

Aircraft Engineering and Aerospace Technology, vol. 32 no. 10
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article

Zhang Ruili, Yang Zhichun and Gao Yang

The purpose of this paper is to propose a new approach to determine the aeroelastic instability of truncated conical shells. In the proposed approach the governing…

Abstract

Purpose

The purpose of this paper is to propose a new approach to determine the aeroelastic instability of truncated conical shells. In the proposed approach the governing equation of flutter for a truncated conical shell is established using Love's thin shell theory and the quasi-steady first-order piston theory.

Design/methodology/approach

The derivatives in both the governing equations and the boundary conditions are discretized with the differential quadrature method, and the critical flutter chamber pressure is obtained by eigenvalue analysis.

Findings

The influence of the shell geometry parameters, such as semi-cone angle, radius-thickness ratio and length-radius ratio, on the critical flutter chamber pressure is studied. Results are also presented to indicate the stabilizing effects of aerodynamic damping and the destabilizing effects of the curvature correction term of piston theory on flutter of truncated conical shell.

Originality/value

The present approach is an efficient method for the free vibration and flutter analysis of truncated conical shells due to its high order of accuracy and less requirement of virtual storage and computational effort.

Details

Multidiscipline Modeling in Materials and Structures, vol. 10 no. 1
Type: Research Article
ISSN: 1573-6105

Keywords

To view the access options for this content please click here
Article

Charles B. Lyman

MUCH reference is made in the aeronautical field to the flutter problem and the subject is receiving the attention of many persons engaged in research, testing, and…

Abstract

MUCH reference is made in the aeronautical field to the flutter problem and the subject is receiving the attention of many persons engaged in research, testing, and design. Many aeronautical engineers are well acquainted with some aspect of the problem, and although only a few are concerned with its several phases it is safe to say that all aeronautical men regard it with some degree of interest. It is fitting, therefore, that although it has been adequately treated by many authors from other points of view, a statement be here made summarizing the flutter problem as one of the aeroplane designer. In order that the exact nature of this problem be appreciated it is first necessary that a few of the fundamentals be reviewed.

Details

Aircraft Engineering and Aerospace Technology, vol. 13 no. 11
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article

W.J. Duncan

Flutter is a species of oscillatory instability affecting parts of aircraft, such as their wings. However, in as much as an aircraft is a single system, it would always be…

Abstract

Flutter is a species of oscillatory instability affecting parts of aircraft, such as their wings. However, in as much as an aircraft is a single system, it would always be more accurate to say that flutter is an oscillatory instability affecting an aircraft as a whole. There arc, of course, many kinds of oscillatory diseases which afflict aeroplanes and other aircraft, but the flutter disease is characterized by the feature that both aerodynamic actions and distortional oscillations of the structure play an essential part. Thus, if an aeroplane could be made rigid it would not flutter. Needless to say, it is quite impossible to make an aeroplane, or indeed any other structure, strictly rigid but it is true that increasing the structural stiffness is one of the basic methods for avoiding flutter troubles, a fact duly insisted upon by the Airworthiness Authorities in all countries. Likewise, an aeroplane would not flutter if it were projected in a vacuum so that the aerodynamic actions were annulled, but then the sustaining force would also be absent. Both distortion and aerodynamic actions play a part in many kinds of oscillation other than flutter and several of these, such as ‘snaking’, fall'within what is regarded as the domain of ‘stability and control’. However, in such oscillations the structural distortions are not essential for the occurrence of instability.

Details

Aircraft Engineering and Aerospace Technology, vol. 24 no. 2
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article

Wojciech Chajec

A low-cost but credible method of low-subsonic flutter analysis based on ground vibration test (GVT) results is presented. The purpose of this paper is a comparison of two…

Abstract

Purpose

A low-cost but credible method of low-subsonic flutter analysis based on ground vibration test (GVT) results is presented. The purpose of this paper is a comparison of two methods of immediate flutter problem solution: JG2 – low cost software based on the strip theory in aerodynamics (STA) and V-g method of the flutter problem solution and ZAERO I commercial software with doublet lattice method (DLM) aerodynamic model and G method of the flutter problem solution. In both cases, the same sets of measured normal modes are used.

Design/methodology/approach

Before flutter computation, resonant modes are supplied by some non-measurable but existing modes and processed using the author’s own procedure. For flutter computation, the modes are normalized using the aircraft mass model. The measured mode orthogonalization is possible. The flutter calculation made by means of both methods are performed for the MP-02 Czajka UL aircraft and the Virus SW 121 aircraft of LSA category.

Findings

In most cases, both compared flutter computation results are similar, especially in the case of high aspect wing flutter. The Czajka T-tail flutter analysis using JG2 software is more conservative than the one made by ZAERO, especially in the case of rudder flutter. The differences can be reduced if the proposed rudder effectiveness coefficients are introduced.

Practical implications

The low-cost methods are attractive for flutter analysis of UL and light aircraft. The paper presents the scope of the low-cost JG2 method and its limitations.

Originality/value

In comparison with other works, the measured generalized masses are not used. Additionally, the rudder effectiveness reduction was implemented into the STA. However, Niedbal (1997) introduced corrections of control surface hinge moments, but the present work contains results in comparison with the outcome obtained by means of the more credible software.

Details

Aircraft Engineering and Aerospace Technology, vol. 91 no. 3
Type: Research Article
ISSN: 1748-8842

Keywords

To view the access options for this content please click here
Article

E.G. Broadbent

WE concluded Part II of this series with the remark that a different outlook is needed for problems of control surface flutter than for those of wing flutter. There are…

Abstract

WE concluded Part II of this series with the remark that a different outlook is needed for problems of control surface flutter than for those of wing flutter. There are two reasons for this. Wing flutter must be investigated carefully early on in the design of an aircraft so as to provide a safe aircraft without a severe weight penalty, whereas the weight penalty of avoiding control surface flutter is usually small, although not negligible, and modifications can often be made at short notice, so it is important to make a full investigation as late as possible before flight when all the data are available in a reliable form. The second reason is that with wing flutter, as with aileron reversal and divergence, it is usual to think of safety margins in terms of forward speed or possibly wing torsional stiffness; with control surface flutter, on the other hand, quite different types of safety factor become the rule.

Details

Aircraft Engineering and Aerospace Technology, vol. 26 no. 5
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article

N.P. Shevloff

IT is commonly held that today we are living in the age of the specialist. Within the aircraft industry, no one is more vulnerable to having this label of specialist…

Abstract

IT is commonly held that today we are living in the age of the specialist. Within the aircraft industry, no one is more vulnerable to having this label of specialist thrust upon him than the flutter and vibration engineer, but I submit that far from having the narrow outlook which is taken to be the specialist's chief property, the flutter man has to be part stressman and part aerodynamicist; he must also have a working knowledge of the application of electronics to modern vibration test techniques and computing machinery, to say nothing of being part mathematician and, not least, part engineer, for we must not forget that after all, strange as it may seem at times to some of us, in the calm of our design offices, we are engaged in the engineering business.

Details

Aircraft Engineering and Aerospace Technology, vol. 26 no. 8
Type: Research Article
ISSN: 0002-2667

1 – 10 of over 1000