Wing Oscillations Research Articles

A theoretical and experimental investigation of the effects of a steady angle of attack on the nonlinear flutter of a delta wing plate model

Limit cycle oscillations (LCO) of wings on certain modern high performance aircraft have been observed in flight and in wind tunnel experiments. Whether the physical mechanism that gives rise to this behavior is a fluid or structural nonlinearity or both is still uncertain. It has been shown that an aeroelastic theoretical model with only a structural nonlinearity can predict accurately the limit cycle behavior at low subsonic flow for a plate-like wing at zero angle of attack. Changes in the limit cycle and flutter behavior as the angle of attack is varied have also been observed in flight. It has been suggested that this sensitivity to angle of attack is due to a fluid nonlinearity. In this investigation, we study the flutter and limit cycle behavior of a wing in low subsonic flow at small steady angles of attack. Experimental results are compared to those predicted using an aeroelastic theoretical model with only a structural nonlinearity. Results from both experiment and theory show a change in flutter speed as the steady angle of attack is varied. Also the LCO magnitude increased at a given velocity as the angle of attack was increased for both the experiment and theory. While not proving that the observed sensitivity to angle of attack of LCO in aircraft is due to a structural nonlinearity, the results do show that a change in the aeroelastic behavior at angles of attack can be caused by a structural nonlinearity as well as a fluid nonlinearity. In this paper, only structural nonlinearities are considered, but an extension to include aerodynamic nonlinearities would be very worthwhile.

Novel Strategy for Suppressing the Flutter Oscillations of Aircraft Wings

A new strategy, based on the nonlinear phenomenon of saturation, is proposed for controlling the flutter of a wing. The concept is illustrated by means of an example with a rather flexible, high-aspect wing of the type found on such vehicles as high-altitude long-endurance aircraft and sailplanes. The wing is modeled structurally as an Euler-Bernoulli beam with coupled bending and twisting motions. A general unsteady nonlinear vortex-lattice technique is used to model the flow around the wing and provide the aerodynamic loads. The structure, the flowing air, and the controller are considered the elements of a single dynamic system, and all of the coupled equations of motion are simultaneously and interactively integrated numerically in the time domain. The results indicate that the aerodynamic nonlinearities alone can be responsible for limit-cycle oscillations and that the saturation controller can effectively suppress the flutter oscillations of the wing when the controller frequency is actively tuned.

Novel strategy for suppressing the flutter oscillations of aircraft wings

Novel strategy for suppressing the flutter oscillations of aircraft wings

Flow structure on stalled delta wing subjected to small amplitude pitching oscillations

The flow past a harmonically oscillating delta wing is investigated using high image-density particle image velocimetry. The overall objective is to alter the development of the leading-edge vortex and decrease the extent of stall on the wing. To this end, instantaneous velocity fields, contours of constant vorticity, and streamline patterns are obtained over an entire plane of the flow at successive instants of the wing motion. The degree of repeatability of the flow patterns during successive cycles of the wing oscillation is highly dependent on the dimensionless frequency of oscillation; it is possible to generate flow patterns that are phase locked at every cycle, as well as every other cycle, of the wing motion. In each case, a well-defined leading-edge vortex appears, and the instantaneous extent of the stall region is decreased relative to that on a stationary wing at the same angle of attack. However, cycle-averaged patterns show only minor departures from the flow structure on the stationary wing. Ensemble-averaged patterns, obtained by phase referencing to the wing motion, reveal that small-scale vortical structures originating in the unstable leading-edge shear layer are averaged out; the overall vorticity levels of the entire flowfield are lowered substantially, even for the average of only a small number of instantaneous images.

Self-induced roll oscillations of low-aspect-ratio rectangular wings

Experimental investigation of small aspect ratio rectangular wings mounted on a free-to-roll sting balance indicated that self-induced roll oscillations are possible when the aspect ratio of such wings is less than 0.5. The oscillations are probably driven by the periodic changes in the location and strength of the side edge vortices, as it has been shown for the 'wing rock' motion of delta wings, where similar changes in the leading edge vortex strength and position cause the roll oscillations. During the roll oscillation cycle the roll angle, normal force, and the side force were recorded and presented for three wings with aspect ratios of 0.25, 0.35, and 0.47. This data indicates that the lift loss during roll oscillations of rectangular wings is less than what was measured for similar delta wings. Also, the flow field of such slender rectangular wings at high angles of attack is more complicated due to the additional leading edge vortex, when compared with the flow field over slender delta wings.

Do honey bees encode distance information into the wing vibrations of the waggle dance?

An optical technique detected the wing vibration frequency of worker honey bees in an observation hive during the straight run of the waggle dance. Wing oscillation frequencies were recorded from dancing bees after they had visited a feeding station located from 50 to 1600 m from the hive. The bees vibrated their wings more rapidly after they visited nearby stations than when they foraged at more distant feeding stations. For example, the mean frequency of 315 Hz at 50 m dropped to only 207 Hz at 1600 m. Wing vibration frequency appears to be another factor to be added to the elements in the dance known to indicate the distance bees must fly to food sources. These known elements include the duration of the straight run and the number of wagtail movements in the run.

Exact solutions to the oscillations of composite aircraft wings withwarping constraint and elastic coupling

Exact solutions within the framework of standard aeroelastic bending and twisting assumptions are found to the free oscillations of composite aircraft wings with warping constraint and elastic coupling. The problem is treated as a regular boundary-value problem consisting of two fourth-order partial-differential equations coupled by the presence of elastic coupling. This system, which is linear, is therefore equivalent to an eighth-order ordinary-differential equation. Classical linear methods are used to extract fundamental solutions that are superimposed appropriately to obtain an exact functional form for the mode shapes. These mode shapes are then required to satisfy the necessary boundary conditions, a process that leads to the formulation of the required eigenvalue problem. The eigenvalues are extracted numerically by using appropriate ordering of the eight roots of the operator equation. The bending-torsion frequencies obtained as a result of this analysis are compared favorably with existing results. New insights made possible by these results, which are preliminary, appear to be that 1) the first coupled frequency decreases with increasing coupling, and 2) the phenomenon of modal transformations found by earlier investigators is explainable in terms of some conservative intermodal energy transfer.

Acoustic studies on the mechanism of sound production in the mating songs of the melon fly,Dacus cucurbitae Coquillett (Diptera: Tephritidae)

The sound production mechanism in the male mating songs for the melon flyDacus cucurbitae Coquillett was acoustically investigated to determine whether sounds resulted from free wing-fanning or stridulation produced by contact between wing and abdominal pecten. Waveforms in the songs of normal (pecten-present) males showed more complex vibrations than those of pecten-removed males. The total harmonic distortion in normal songs was greater than that of the pecten-removed songs. Female (pecten-absent) songs showed different sound signatures on the oscillogram and frequency spectrum from normal male songs. The female songs had more harmonic components than the normal male songs. These results suggest that wing/pecten stridulation of normal male songs produces complicated wing oscillations with a small number of harmonics of near-periodic waveforms and a high harmonic distortion. They also suggest that the free wing-fanning observed during female and pecten-removed male songs produces simple and uniform wing oscillations with many harmonic contents of complex-periodic waveforms and low harmonic distortion. Despite the occurrence of some acoustic differences, pecten-removal did not positively influence the rate of copulation.

On the mechanism of speed and altitude control in Drosophila melanogaster

ABSTRACT The total power output of tethered flying Drosophila melanogaster in still air depends on translational velocity components of image flow on the eye, whereas the orientation of the average flight force in the midsagittal plane of the fly is widely independent of visual input (Götz, 1968). The fly does not seem to control the vertical and the horizontal force component independently. Freely flying flies nevertheless generate different ratios between lift and thrust, simply by changing the inclination of their body. By the combined adjustment of the body angle and the total power output a fly appears to be able to stabilize height and speed (David, 1985). Here a possible mechanism is proposed by which the appropriate torque about the transverse body axis could be generated. Translational pattern motion influences the posture of the abdomen and the plane of wing oscillation. Thus the position of the centre of gravity relative to the flight force vector is changed. When abdomen and stroke plane deviate from an equilibrium state, a lever is generated by which the force vector will rotate the fly about its transverse axis.

Energetics and optimum motion of oscillating lifting surfaces of finite span

The energetics of an unswept wing of finite span oscillating harmonically in combined pitch and heave in in viscid incompressible flow are determined in closed form. The calculations are based on a recently developed low-frequency unsteady lifting-line theory. The energetic calculations for the wing consist of sectional and total values of thrust, leading-edge suction force, power required to maintain the wing oscillations, and energy-loss rate due to vortex shedding in the wake, where the latter quantity is only defined for the entire wing. These results are used to analyse the optimum motion of a wing oscillating harmonically: optimum motion minimizes the power input for fixed average total thrust. The optimum solution is found to be unique (at least for low reduced frequencies), in contrast to the two-dimensional optimum, which is non-unique. Numerical results are presented for the energetics and optimum motion of an elliptic wing.To understand better the structure of the known solution for the optimum motion of an oscillating two-dimensional airfoil, the solution is recast in terms of the normal modes of the energy-loss-rate matrix. It is found that one of the modes, termed here the ‘invisible mode’, plays a central role in the optimum solution and is responsible for its non-uniqueness. The three-dimensional optimum, which is unique, does not have an invisible mode.

Control of locomotion in marine mollusc Clione limacina. I. Efferent activity during actual and fictitious swimming.

The marine mollusc Clione limacina swims by making rhythmic movements (with a frequency of 1-5 Hz) of its two wings. Filming demonstrated that the wings perform oscillatory movements in the frontal plane of the animal. During both the upward and downward movements of the wing, its posterior edge lagged behind the anterior one, i.e. the wing plane was inclined in relation to the longitudinal axis of an animal. As a result of this inclination, the wing oscillations in the frontal plane produce a force directed forwards. In restrained animals with the body cavity opened (a whole-animal preparation), the wing position, electrical activity in the wing nerve and activity of two identified efferent neurons (1A and 2A) were recorded during locomotory wing movements. There were two bursts of activity in the wing nerve during the locomotory cycle, the first one corresponding to the excitation of efferent neurons controlling the wing elevation, and the second one, to the excitation of efferent neurons controlling the lowering of the wing. Neurons 1A and 2A fired reciprocally at the beginning of the phase of elevating and lowering the wing, respectively. During excitation of one of the neurons, an IPSP appeared in its antagonist. A pair of isolated pedal ganglia of Clione was capable of generating the locomotory rhythm ("fictitious swimming"). In fictitious swimming, as in actual swimming, there were two bursts of activity in the wing nerve per locomotory cycle, and the 1A and 2A neurons fired reciprocally. Homologous neurons from the left and right ganglia fired inphase.(ABSTRACT TRUNCATED AT 250 WORDS)

Bending effects on structural dynamic instabilities of transonic wings

Nonclassical flutter has been observed during transonic conditions associated with flight and wind tunnel testing of various fighter and bomber aircraft As contrasted with classical flutter the underlying mechanism has been ascribed to a phase lag between lift variations and wing motions Based on the observations that the wing oscillations were restricted to bending mode shapes similar to the free fundamental, the phenomenon was idealized as the lift induced forced oscillation of a Cantilever beam simulating the wing. Coupling with the aerodynamics occurs through the beam equation forcing term, representing the lift, and the tangency boundary condition for the unsteady transonic small disturbance equation for the latter Strip theory has been used with a suitably revised version of LTRAN2 to supply the aerodynamic input The resulting time integration algorithm provides a procedure to determine the destabilizing effects of sweepback Computations with the method closely predict flutter frequencies observed for the HiMAT canard during wind tunnel testing, as well as for the B-l wing in flight tests in two out of three cases Qualitative behavior of the oscillation agrees for these conditions For the third case, damped oscillations are predicted rather than the amplified ones observed Reasons for the discrepancy are provided, involving the second bending mode of these oscillations in contrast to the fun damental assumed by the current approach Specific recommendations for refinements of the procedure in volving inclusion of modal coupling analysis of limit cycle aspects and three dimensional phenomena are given

Dokumentation der Flügelgittereinstellung der freien Handschwingen beim Aufschlag sowie der Daumenfitticheinstellung beim Abschlag des Wellensittichs

Budgerigars(Melopsittacus undulatus) were filmed during forced climbing flight at a rate of 1500 pictures per second. Qualitative information on the movement of the primaries during upstroke, the effect of the slit-wing of free wings, the oscillations of the free wings themselves, the effect of the phasic oscillations of the tail and its outspread side feathers and other kinematic details were obtained from these photographs. Qualitative aspects of this type are discussed. Furthermore, some quantitative data on the aerodynamic significance of the free wings during upstroke are given.

The neuromuscular basis of courtship song inDrosophila: The role of the direct and axillary wing muscles

1. Power for both flight and for courtship song inDrosophila is provided by the indirect, myogenic, flight muscles (Fig. 7). The axillary and direct wing muscles (Fig. 1) control wing extension, most of the parameters of wing movement and the timing of song pulses. The role of these muscles during song was investigated electrophysiologically. 2. Most of the axillary muscles fire during pulse song inter pulse intervals (Figs. 4, 5). It is suggested that the role of some of these muscles is to depress the wing or otherwise distort the thorax so as to stretch the dorsal ventral muscles thus initiating their contraction to produce the sound producing up-stroke of the wing. 3. The basalar muscles fire synchronously with wing movements on the up-stroke of flight, sine song and pulse song (Fig. 2). The mode of action of these muscles is not clear but they are probably concerned with maintaining tension of the thoracic box and thus affect the amplitude of wing movement. They may also effect wing extension. 4. The sternobasalar muscle also fires on the upstroke but only during pulse song and not sine song (Fig. 3). It is suggested that contraction of the sternobasalar muscle dampens the wing oscillation so that only single cycle pulses of sound are produced. 5. Lesions of the sternobasalar muscle are accompanied by the production of polycyclic sound pulses and this supports the above hypothesis (Fig. 6).

BEHAVIORAL MUTANTS OF DROSOPHILA MELANOGASTER. II. BEHAVIORAL ANALYSIS AND FOCUS MAPPING

Several simple tests have been applied to study the behavior and performance of mutants of Drosophila melanogaster isolated in the preceding study (Homyk and Sheppard 1977). The tests showed that many mutants have specific behavioral abnormalities and that most mutants can easily be distinguished from an Oregon-R control on the basis of their behavioral phenotypes. Mutants representing six genes hop poorly and are unable to initiate wing oscillation when tethered. Mutations in four genes reduce the level of spontaneous motor activity of flies and increase the excitability threshold necessary to induce high activity motor functions such as running and flying. The latter mutants are referred to as hypoactive. Another class, stress-sensitive, including mutations in three genes, are reversibly paralyzed by mechanical shock. Mosaic analyses suggest that six mutations affect muscular tissue and two others affect neural tissue. It is also shown that tan mutants fail to retract their forelegs during flight and that the focus responsible for this behavioral phenotype is the compound eye. Specific behavioral abnormalities of several mutants are discussed in conjunction with previous studies from many laboratories concerning the participation of neural, sensory and muscular elements producing behavior in normal (nonmutant) insects. Such considerations are an essential prelude to anatomical and physiological studies of the mutants in Drosophila.

A Note on Flight Flutter Testing

An attempt has been made to correlate theoretically calculated decay effects of wing oscillations at subcritical flutter speeds with results obtained during actual flight flutter testing at these speeds. The theory discussed has been found to give reasonably good agreement with the limited number of test data obtained in flight from a single airplane. Conclusions of a general nature are as yet unwarranted, but a t least a new point of view is presented which applies to interpretation of both test and theoretical results.

The Problem of Wing Oscillation

THE steady increase in speed and use of thin aerofoils compels a deeper consideration of the problem of oscillation. In recent years there has been a tendency to the building of large aeroplanes. This is closely connected with the problem of oscillation. The author in a first approximation tries to solve, from a proportionality point of view, the question of influence of kind of material and size of aeroplane on wing flexural and torsional natural frequencies. Following the idea of solving this problem from a qualitative and not from a quantitative point of view, the conception of proportionality instead of equality is introduced. The idea of “wing torsional rigidity” is created, being inversely proportional to the angle of twist at the end of wing. Applying Newton's Law, at first the flexural and torsional natural frequency of an oscillating rod is found. Afterwards the method is used in the case of an oscillating tubular member. The results are checked by Rayleigh's Method. Lastly, the influence of size of wings having similar shape is taken into consideration.

Aeroplane Wing Flutter

VIOLENT oscillations of particular parts of an aeroplane structure have been observed and studied since early days. The theory of wing oscillations is, however, rather more modern and was initiated, it is believed, by A. G. von Baumhauer and C. Koning, who presented a paper at the International Air Congress in 1923. Since that year the subject has been much developed both abroad and in this country. The literature has grown rapidly, and a detailed notice of the papers cannot here be attempted.