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Technical Paper

General Approach to the FLUTTER PROBLEM

1941-01-01
410125
AGENERAL approach to the flutter problem is outlined, which can be used to investigate any mode of flutter of any structure provided the air-forces are known. ...The method can be used to investigate the possibility of flutter on such structures as airplane wings, tail surfaces, and bomb doors, aircraft propeller blades, vehicular bridges, buildings, and so on. ...With a well-known solution for the air-forces for two-dimensional flow over an airfoil with an aileron, equations have been derived which can be used to determine the flutter speed for the wing or tail surfaces of any conventional airplane. The use of still-air vibration tests in obtaining the structural friction of structures, and in checking a part of the flutter computations experimentally is indicated.
Technical Paper

Flutter Characteristics of the Slab Tail

1967-02-01
670260
Unlike conventional controls, however, there are no rules nor criteria for flutter prevention for slab configurations. The several types of flutter than can occur in a slab tail installation have been studied in the hope that a meaningful flutter criterion can be developed. ...The several types of flutter than can occur in a slab tail installation have been studied in the hope that a meaningful flutter criterion can be developed. Unfortunately, too many independent parameters affect the flutter characteristics for this objective to be realized. ...Unfortunately, too many independent parameters affect the flutter characteristics for this objective to be realized. The influence of these parameters is shown, and some rules are derived which should be useful to the slab tail designer.
Technical Paper

Effect of Non-Linearity on Flutter of Automobiles

2003-03-03
2003-01-0310
Consequently, a deeper understanding was obtained concerning the effect of play and friction on the flutter of steering system. This study explained flutter phenomenon by using mathematical model for driver/vehicle system. ...Flutter is not a simple phenomenon derived from non-linearity of the tire's cornering characteristics or existence of the tire unbalanced mass, but rather is a compound dynamic phenomenon.
Technical Paper

Advanced Flutter Design Techniques

1973-02-01
730935
Included are discussions of the extensive application of automated procedures in the use of high-speed digital computers for flutter analysis and the dependence on highly sophisticated wind tunnel flutter model construction techniques to provide reliable experimental data. ...The general characteristics of flutter problems affecting the structural design of both subsonic and supersonic transport aircraft are discussed in relation to configuration constraints resulting from mission performance and environmental impact requirements.
Technical Paper

Flutter Problems of Business Airplanes

1965-02-01
650387
Flutter problems of business airplanes may be separated into two main groups -- the technical problems faced by the designer, and the problems faced by the flutter analyst. ...Flutter problems of business airplanes may be separated into two main groups -- the technical problems faced by the designer, and the problems faced by the flutter analyst. Business airplanes have as many components as military or commercial machines, hence the flutter analysis may be just as complicated. ...Business airplanes have as many components as military or commercial machines, hence the flutter analysis may be just as complicated. The problem of the analyst, to complete this analysis in a minimum time and with minimum expenditure, is discussed in this paper.
Technical Paper

Aircraft Wing Flutter: An Applied Approach

2010-10-17
2010-36-0513
In the last decades, the evolution of aircraft design has been influenced so much by aeroelasticity, and in particular, flutter. Flutter is a characteristic aircraft phenomenon of external excited vibrations, working on the resonance gap, which involves the structural airplane elements and if it was not reported can be the source of critical failures of wings or control surfaces. ...The present paper will give a general vision about flutter phenomenon in airplanes wings, specifically on planes of the aero design, which ones usually disregards this kind of study. ...Using data from aero design planes its possible presents how a mechanical engineer can use considerations of flutter to the project and analysis. With support of accelerometers the modal frequency of wing can be finding and it supplies data and graphs to justify values to maximum speed recommend and frequencies band that should be avoid.
Technical Paper

Use of Generalized Coordinates in FLUTTER ANALYSIS

1944-01-01
440156
THIS paper presents some further developments of the method of generalized coordinates in flutter analysis, a method which has been described by the author in a previous paper.1 The paper is composed of three distinct parts: Part I shows in detail the calculations by which this method was applied to a flutter model; the method of application of generalized coordinates to a simple flutter problem, and the check with experimental results is shown. ...THIS paper presents some further developments of the method of generalized coordinates in flutter analysis, a method which has been described by the author in a previous paper.1 The paper is composed of three distinct parts: Part I shows in detail the calculations by which this method was applied to a flutter model; the method of application of generalized coordinates to a simple flutter problem, and the check with experimental results is shown. ...Part II is a manual for the carrying out of more complicated flutter problems by this method; this manual has been in actual use for some time and has been very successful.
Technical Paper

Airplane Vibrations and Flutter Controllable by Design

1933-01-01
330030
Test pilots also should be interested in this subject because it may help them in deciding proper action when a case of flutter is encountered and to recognize vibrations which may lead to destructive flutter. The present-day methods of stress analyses, imperfect though they are in certain respects, and the design load-factors in current use are adequate to provide all the strength needed in airplane structures for flight in rough air, and for all necessary maneuvers. ...THE purpose of this paper is to pass on to airplane designers the things that have been learned in the last year about flutter and vibration of structures to which control surfaces are attached in order that, benefiting by all experience available, this great source of danger in new designs may be controlled.
Technical Paper

Preliminary Study of Algorithm for Real-Time Flutter Monitoring

1991-09-01
912001
This paper describes an algorithm for real-time flutter monitoring. An auto-regressive (AR) model with time varying coefficients is used for continuous monitor of the nonstationary flutter parameters. ...An auto-regressive (AR) model with time varying coefficients is used for continuous monitor of the nonstationary flutter parameters. AR coefficient change rates as well as AR coefficients can be obtained recursively by the Kalman filter implementation.
Technical Paper

Response Characteristics of a Wing in Supersonic Flow Near Flutter Boundary

1991-09-01
911999
As the dynamic pressure approaches to the flutter boundary, the estimated stability parameter and its scattering monotonically decreases while the damping, the conventional flutter estimation criterion, scattered so much near the flutter boundary....In this paper we examine numerically the subcritical flutter characteristics of wings in a supersonic flow. Especially the scattering property of the criterion parameters which are used in order to estimate a flutter boundary, is studied. ...Especially the scattering property of the criterion parameters which are used in order to estimate a flutter boundary, is studied. The wing response due to the flow turbulence is expressed by the autoregressive moving-average process through Akaike's estimation procedure.
Technical Paper

Some Special Investigation Areas in Light Aircraft Flutter

1972-02-01
720309
A brief description is given of one approach taken by a manufacturer of light business and personal aircraft to the flutter analysis of propeller whirl flutter, twin-boom aircraft, T-tail configuration, servo tabs, and all-moving tail.
Technical Paper

Flutter Tests of the Mated 747 Shuttle Carrier Aircraft-Orbiter

1977-02-01
770971
Flutter tests of the mated 747 shuttle carrier aircraft-orbiter are discussed from the viewpoint of the flutter engineer of the prime Space Shuttle contractor, the Space Division of Rockwell International. ...Flutter tests of the mated 747 shuttle carrier aircraft-orbiter are discussed from the viewpoint of the flutter engineer of the prime Space Shuttle contractor, the Space Division of Rockwell International.
Technical Paper

Flutter Analysis with Hydraulic Servos -a Technique for Modeling Actuator Dynamics

2013-09-17
2013-01-2194
The next step has been the inclusion of the servo-actuator dynamics into flutter equations (open loop flutter). The equations governing the dynamics of the servo-actuator are added to the aeroelastic stability equations after a suitable manipulation based on a derivative approach. ...The present paper is focused on techniques aimed at including hydraulic servo-actuator dynamics into linear flutter equations. A large aircraft has been taken as test case for setting up the methodology. ...Starting from a set of flutter analyses performed at different stiffness values of the control surface rotational degree of freedom a minimum requirement for the elevator stiffness is obtained.
Technical Paper

Torsional Vibration Modeling of Driveline System for EV Low-Frequency Flutter

2015-06-15
2015-01-2191
Firstly, dynamometer test is performed, signals of motor speed and seat rail acceleration are obtained, the frequency characteristics of flutter is determined using the order analysis and time frequency analysis. Then four types of modeling and analysis are investigated facing the drive-line torsion vibration problem, including single model without electromagnetic stiffness, branch model without electromagnetic stiffness, single model considering electromagnetic stiffness and branch model considering electromagnetic stiffness. ...The results show that, modeling taking into account the electromagnetic stiffness and branches can reflect more low-frequency characteristics helps to reveal the low-frequency longitudinal flutter of the researched electric vehicle.
Journal Article

CFD-based Modelling of Flow Conditions Capable of Inducing Hood Flutter

2010-04-12
2010-01-1011
This paper presents a methodology for simulating Fluid Structure Interaction (FSI) for a typical vehicle bonnet (hood) under a range of onset flow conditions. The hood was chosen for this study, as it is one of the panels most prone to vibration; particularly given the trend to make vehicle panels lighter. Among the worst-case scenarios for inducing vibration is a panel being subjected to turbulent flow from vehicle wakes, and the sudden peak loads caused by emerging from a vehicle wake. This last case is typical of a passing manoeuvre, with the vehicle suddenly transitioning from being immersed in the wake of the leading vehicle, to being fully exposed to the free-stream flow. The transient flowfield was simulated for a range of onset flow conditions that could potentially be experienced on the open road, which may cause substantial vibration of susceptible vehicle panels.
Journal Article

Flutter Initiation Under Steady - State and Accelerated Free Stream Velocities

2011-10-18
2011-01-2785
The traditional approach to determining flutter in a linear aeroelastic system, such as a wing, is to define flutter as the lowest velocity at which simple harmonic motion first occurs. ...While simple harmonic motion is a useful rule of thumb definition, such a definition does not adequately and sufficiently describe the behavior of the wing before or after flutter. Further, the traditional definition could provide a misleading flutter velocity point. ...The motivation for the present investigation of damped motion through energy dissipation due to material properties and bifurcations is to better understand the fundamentals of flutter, with applications to elastic and viscoelastic composite flight and automotive vehicles.
Technical Paper

Analysis of Active Flutter Suppression with Leading- and Trailing-Edge Control Surfaces via μ-Method

2005-10-03
2005-01-3421
The nominal and robust stability margins, modal properties, critical flutter airspeeds and frequencies are computed to predict the flutter of the aeroelastic system and to investigate the aeroservoelastic stability in μ-framework. ...Mathematical models and implementation issues of active flutter suppression are described. The multi-input/multi-output aeroservoelastic systems and algorithms are developed by μ-control law to account for the uncertainty parameters/perturbations associated with the unsteady dynamic pressure, the variable structural damping and the nonlinear structural stiffness. ...The simulation results are presented for the comparisons among: a) the uncontrolled wing section, b) the active wing section with a single trailing-edge flap controller (K1) activated, and, c) the one with both the leading- and trailing-edge flap controllers (K2 and K1) activated to demonstrate the improved effectiveness for flutter suppression by using two control surfaces.
Journal Article

ℒ1 Adaptive Flutter Suppression Control Strategy for Highly Flexible Structure

2013-09-17
2013-01-2263
The aim of this work is to apply an innovative adaptive ℒ1 techniques to control flutter phenomena affecting highly flexible wings and to evaluate the efficiency of this control algorithm and architecture by performing the following tasks: i) adaptation and analysis of an existing simplified nonlinear plunging/pitching 2D aeroelastic model accounting for structural nonlinearities and a quasi-steady aerodynamics capable of describing flutter and post-flutter limit cycle oscillations, ii) implement the ℒ1 adaptive control on the developed aeroelastic system to perform initial control testing and evaluate the sensitivity to system parameters, and iii) perform model validation and calibration by comparing the performance of the proposed control strategy with an adaptive back-stepping algorithm. ...The aim of this work is to apply an innovative adaptive ℒ1 techniques to control flutter phenomena affecting highly flexible wings and to evaluate the efficiency of this control algorithm and architecture by performing the following tasks: i) adaptation and analysis of an existing simplified nonlinear plunging/pitching 2D aeroelastic model accounting for structural nonlinearities and a quasi-steady aerodynamics capable of describing flutter and post-flutter limit cycle oscillations, ii) implement the ℒ1 adaptive control on the developed aeroelastic system to perform initial control testing and evaluate the sensitivity to system parameters, and iii) perform model validation and calibration by comparing the performance of the proposed control strategy with an adaptive back-stepping algorithm. ...The effectiveness and robustness of the ℒ1 adaptive control in flutter and post-flutter suppression is demonstrated. Results and discussion will follow with pertinent conclusions and future outlooks.
Technical Paper

A Technique for Performing Closed Loop Flutter Evaluation on a Joined Wing UAV

2013-09-17
2013-01-2197
For this test case the pitch control law is included in the flutter equations, obtaining a model to perform closed loop flutter calculations. The extra degrees of freedom of control surfaces and additional terms due to the control law have been modeled by means of dynamic sub-structuring approach. ...The present paper is focused on techniques aimed at including control law dynamics into linear flutter equations. An UAV in an unconventional joined wing configuration has been taken as test case for setting up the methodology. ...This is advantageous when already written codes for flutter evaluation are available since the requested modifications are minimal. For the test case two models of the control law have been prepared: a detailed representation and a “reduced” representation, with less degrees of freedom for the control law.
Technical Paper

Unsteady Transonic Aerodynamics in Frequency Domain and Calculation of Flutter Characteristics of Aircraft

1995-05-01
951182
This paper describes a finite-difference method for unsteady transonic flow computation in frequency domain and transonic flutter prediction of complete aircraft configurations. The unsteady TSD equation as well as the boundary conditions are split into the in-phase and out-of-phase components in frequency domain by a nonlinear harmonic averaging technique. ...The unsteady pressure distributions for a rectangular wing and the ONERA M6 wing are analyzed and compared with other results to verify the code. The flutter characteristics for the AGARD I-445.6 wing, a cropped delta wing and a fighter configuration are computed and the results are discussed.
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