Increasing Flight Speed Research Articles

Nonlinear Aeroelastic Response of High-aspect-ratio Flexible Wings

The aeroelastic analysis of high-altitude, long-endurance (HALE) aircraft that features high-aspect-ratio flexible wings needs take into account structural geometrical nonlinearities and dynamic stall. For a generic nonlinear aeroelastic system, besides the stability boundary, the characteristics of the limit-cycle oscillation (LCO) should also be accurately predicted. In order to conduct nonlinear aeroelastic analysis of high-aspect-ratio flexible wings, a first-order, state-space model is developed by combining a geometrically exact, nonlinear anisotropic beam model with nonlinear ONERA (Edlin) dynamic stall model. The present investigations focus on the initiation and sustaining mechanism of the LCO and the effects of flight speed and drag on aeroelastic behaviors. Numerical results indicate that structural geometrical nonlinearities could lead to the LCO without stall occurring. As flight speed increases, dynamic stall becomes dominant and the LCO increasingly complicated. Drag could be negligible for LCO type, but should be considered to exactly predict the onset speed of flutter or LCO of high-aspect-ratio flexible wings.

Vortex wake and flight kinematics of a swift in cruising flight in a wind tunnel

In this paper we describe the flight characteristics of a swift (Apus apus) in cruising flight at three different flight speeds (8.0, 8.4 and 9.2 m s(-1)) in a low turbulence wind tunnel. The wingbeat kinematics were recorded by high-speed filming and the wake of the bird was visualized by digital particle image velocimetry (DPIV). Certain flight characteristics of the swift differ from those of previously studied species. As the flight speed increases, the angular velocity of the wingbeat remains constant, and so as the wingbeat amplitude increases, the frequency decreases accordingly, as though the flight muscles were contracting at a fixed rate. The wings are also comparatively inflexible and are flexed or retracted rather little during the upstroke. The upstroke is always aerodynamically active and this is reflected in the wake, where shedding of spanwise vorticity occurs throughout the wingbeat. Although the wake superficially resembles those of other birds in cruising flight, with a pair of trailing wingtip vortices connected by spanwise vortices, the continuous shedding of first positive vorticity during the downstroke and then negative vorticity during the upstroke suggests a wing whose circulation is gradually increasing and then decreasing during the wingbeat cycle. The wake (and implied wing aerodynamics) are not well described by discrete vortex loop models, but a new wake-based model, where incremental spanwise and streamwise variations of the wake impulse are integrated over the wingbeat, shows good agreement of the vertical momentum flux with the required weight support. The total drag was also estimated from the wake alone, and the calculated lift:drag ratio of approximately 13 for flapping flight is the highest measured yet for birds.

Wake structure and wingbeat kinematics of a house-martinDelichon urbica

The wingbeat kinematics and wake structure of a trained house martin in free, steady flight in a wind tunnel have been studied over a range of flight speeds, and compared and contrasted with similar measurements for a thrush nightingale and a pair of robins. The house martin has a higher aspect ratio (more slender) wing, and is a more obviously agile and aerobatic flyer, catching insects on the wing. The wingbeat is notable for the presence at higher flight speeds of a characteristic pause in the upstroke. The essential characteristics of the wing motions can be reconstructed with a simple two-frequency model derived from Fourier analysis. At slow speeds, the distribution of wake vorticity is more simple than for the other previously measured birds, and the upstroke does not contribute to weight support. The upstroke becomes gradually more significant as the flight speed increases, and although the vortex wake shows a signature of the pause phase, the global circulation measurements are otherwise in good agreement with surprisingly simple aerodynamic models, and with predictions across the different species, implying quite similar aerodynamic performance of the wing sections. The local Reynolds numbers of the wing sections are sufficiently low that the well-known instabilities of attached laminar flows over lifting surfaces, which are known to occur at two to three times this value, may not develop.

Wing beat kinematics of a nectar-feeding bat,Glossophaga soricina,flying at different flight speeds and Strouhal numbers

High-speed film analysis showed that the wing beat kinematics in Glossophaga soricina change gradually with increasing flight speed, indicating that there is no sudden gait change at any particular, critical, flight speed. The flight of two adult specimens was studied over a range of flight speeds (1.23-7.52 ms(-1)) in a 30 m long flight tunnel. During the upstroke in hovering and slow flight there is a tip-reversal or supination of the handwings, which thus produce a backward flick. This backward motion successively disappears at speeds V approximately 3.2 ms(-1), above which the wingtip path becomes more vertical or directed upwards-forwards relative to the still air (the stroke plane angle increasing with flight speed as alpha=44.8V(0.29)). We found no correlations between either span ratio SR (the ratio of the wing span on the upstroke to that on the downstroke) and V, or downstroke ratio (the duration of the downstroke divided by the total stroke period) and V. On the other hand, SR decreases significantly with increasing wing beat frequency f, SR proportional to f(-0.40). The Strouhal number (St=f x amplitude/V), a dimensionless parameter describing oscillating flow mechanisms and being a predictor of the unsteadiness of the flow, decreases with the speed as St proportional to V(-1.37). Close to the theoretical minimum power speed (4-6 m s(-1)) G. soricina operates with a Strouhal number in the region 0.17<St<0.22, which is associated with efficient lift and thrust production. At slower speeds, 3.4-4 m s(-1), St is 0.25-0.4, which is still within the favourable region. But at speeds below 3 m s(-1) St becomes higher (0.5<St<0.68), indicating that unsteady effects become important, with unfavourable lift and thrust production as a result. Only at these speeds do the bats perform the backward flick during the upstroke, which may produce thrust. This may serve as a compensation in some bats and birds to increase aerodynamic performance.

Vortex wakes of birds: recent developments using digital particle image velocimetry in a wind tunnel

Abstract A flying animal generates a trail of wake vortices that contain information about the time history and magnitude of aerodynamic forces developed on the wings and body. Methods for visualising and recording wake vortices have been developed, allowing quantitative measurements by digital particle image velocimetry (DPIV). Results from DPIV experiments in a wind tunnel are presented for four passerine species of differing size and morphology. The normalised vorticity and its integrated quantity, circulation (Γ) both decline gradually with increasing flight speed. The measured circulations are successfully explained by a simple aerodynamic model where a normalised circulation, Γ/Uc, represents half the time-averaged lift coefficient, which is &gt;2 at 4 m s−1 for a thrush nightingale.

Impaired flight ability prior to egg‐laying: a cost of being a capital breeder

Summary To investigate flight ability in captive Zebra Finches during reproduction we compared change in escape take‐off ability and wing load of reproducing females with their mates and non‐reproducing females when attacked by a model raptor. Initially females had 18% higher wing load than males. Non‐reproducing females and females that had started egg‐laying flew slower than males. Reproducing females reduced wing load during egg‐laying and flew faster when the clutch was completed. Non‐breeding females remained on high wing load and flow slower than breeding females that had completed their clutch. The increase in flight speed of breeding females was explained by a reduction in wing load during egg‐laying. Zebra Finches use accumulated reserves to produce eggs and pay a cost in terms of reduced flight ability, but then regain flight performance when the clutch is laid, probably demonstrating a predation cost of capital breeding in birds.

Foraging strategies of shy albatross Thalassarche cauta breeding at Albatross Island, Tasmania, Australia

The foraging zones and behaviour of shy albatross Thalassarche cauta were studied at Albatross Island, Tasmania, Australia, during the 1995/96 and 1996/97 breeding seasons, using a combination of archival recorders and satellite telemetry. Birds foraged exclusively in the neritic zone, at a maximum distance of 200 km from the colony, making wide use of continental shelf waters off northwest Tasmania. The duration of foraging trips, the distances traveled and the activity ranges of the birds (i.e. 95% isopleths from Kernel home range analyses) were greatest during incubation (2.8 d, 754 km, 24 667 km 2 ), least during chick-brood (1.1 d, 273 km, 19 067 km 2 ), and intermediate during early chick-rearing (1.8 d, 426 km, 19 400 km 2 ). At the population level, the foraging zones of the birds (i.e. the 50% home range isopleths) were highly consistent between years, overlapping by 43% during both the incubation and chick-brooding stages across 3 breeding seasons. Overall, the foraging zones of males and females were similar in both size and location. Individual birds did not return to the same locations to feed from 1 trip to the next; however, their foraging was not random. On successive trips birds maintained a constant heading from the colony, repeatedly searching the same broad patches of ocean, a degree of site fidelity maintained within a single breeding stage. They flew for 72% of the daytime and 39% of the night, and their rate of travel was significantly higher during the day. Combined with a diet predominated by prey found at or near the surface dur- ing the day, these data suggest that shy albatross are largely diurnal feeders. Nocturnal activity was strongly influenced by moon phase, with increased time spent flying and increased flight speed dur- ing full moon. Consistent traveling speeds, foraging trip durations and foraging locations across years suggest relatively stable prey availability and/or accessibility for shy albatross breeding off the northwest coast of Tasmania.

Relationships between body mass, motor output and flight variables during free flight of juvenile and mature adult locusts, Schistocerca gregaria.

Little information is available about how the adult locust flight system manages to match the aerodynamic demands that result from an increase in body mass during postmoult maturation. In Schistocerca gregaria of both sexes, flight variables, including flight speed, ascent angle and body angle, were investigated under closed-loop conditions (i.e. during free flight) as a function of adult maturation. Motor patterns were examined by telemetric electromyography in juvenile and adult mature animals of both sexes. Functional relationships between particular flight variables were investigated by additional loading of the animals and by reductions in wing area. The results indicate that an increase in flight speed as the flight system matures enables it to match the aerodynamic demands resulting from increases in body mass. Furthermore, the data suggest that this postmoult increase in flight speed is not simply a consequence of the increase in wingbeat frequency observed during maturation. The instantaneous body angle during flight is controlled mainly by aerodynamic output from the wings. In addition, the mean body angle decreases during maturation in both sexes, and this may play an important part in the directional control of the resultant flight force vector.

Flight kinematics of black-billed magpies and pigeons over a wide range of speeds

To investigate how birds that differ in morphology change their wing and body movements while flying at a range of speeds, we analyzed high-speed (60 Hz) video tapes of black-billed magpies (Pica pica) flying at speeds of 4-14 m s-1 and pigeons (Columba livia) flying at 6-20 m s-1 in a wind-tunnel. Pigeons had higher wing loading and higher-aspect-ratio wings compared with magpies. Both species alternated phases of steady-speed flight with phases of acceleration and deceleration, particularly at intermediate flight speeds. The birds modulated their wingbeat kinematics among these phases and frequently exhibited non-flapping phases while decelerating. Such modulation in kinematics during forward flight is typical of magpies but not of pigeons in the wild. The behavior of the pigeons may have been a response to the reduced power costs for flight in the closed wind-tunnel relative to those for free flight at similar speeds. During steady-speed flight, wingbeat frequency did not change appreciably with increasing flight speed. Body angle relative to the horizontal, the stroke-plane angles of the wingtip and wrist relative to the horizontal and the angle describing tail spread at mid-downstroke all decreased with increasing flight speed, thereby illustrating a shift in the dominant function of wing flapping from weight support at slow speeds to positive thrust at fast speeds. Using wingbeat kinematics to infer lift production, it appeared that magpies used a vortex-ring gait during steady-speed flight at all speeds whereas pigeons used a vortex-ring gait at 6 and 8 m s-1, a transitional vortex-ring gait at 10 m s-1, and a continuous-vortex gait at faster speeds. Both species used a vortex-ring gait for acceleration and a continuous-vortex gait or a non-flapping phase for deceleration during flight at intermediate wind-tunnel speeds. Pigeons progressively flexed their wings during glides as flight speed increased but never performed bounds. Wingspan during glides in magpies did not vary with flight speed, but the percentage of bounds among non-flapping intervals increased with speed from 10 to 14 m s-1. The use of non-flapping wing postures seemed to be related to the gaits used during flapping and to the aspect ratio of the wings. We develop an 'adverse-scaling' hypothesis in which it is proposed that the ability to reduce metabolic and mechanical power output using flap-bounding flight at fast flight speeds is scaled negatively with body mass. This represents an alternative to the 'fixed-gear' hypothesis previously suggested by other authors to explain the use of intermittent flight in birds. Future comparative studies in the field would be worthwhile, especially if instantaneous flight speeds and within-wingbeat kinematics were documented; new studies in the laboratory should involve simultaneous recording of wing kinematics and aerodynamic forces on the wing.

Neuromuscular control and kinematics of intermittent flight in the European starling (Sturnus vulgaris)

Electromyographic (EMG) and kinematic data were collected from European starlings (Sturnus vulgaris) flying at a range of speeds from 8 to 18 m s-1 in a variable-speed windtunnel. Their flight at all speeds consisted of alternating flapping and non-flapping phases. Wing postures during non-flapping phases included glides, partial-bounds and bounds. Glides were performed proportionally more often within each speed and were longer in duration than either of the other two non-flapping postures, but the percentage of bounds increased markedly with increasing flight speed. The shift from flap-gliding at slow speeds towards flap-bounding at fast speeds was consistent with reducing mean power output relative to continuous flapping. The starlings often combined more than one non-flapping posture within a single non-flapping period. Transitions between non-flapping postures, as well as transitions between bounds and subsequent flapping, were classified as 'pull-outs'. Pull-outs consisted of an increase in wingspan but no change in wingtip elevation. The pectoralis and supracoracoideus exhibited electrical activity during glides but not during bounds. The scapulohumeralis caudalis was not active during glides, but this muscle and the supracoracoideus were typically active during partial-bounds and pull-out phases. The scapulohumeralis caudalis occasionally showed activity during bounds, which may reflect its role as a humeral retractor. The frequency and duration of non-flapping intervals in starlings were less during EMG experiments than during non-implanted flights. During flapping phases, relative intensity and duration of EMG signal and wingbeat frequency increased with flight speed, whereas flapping or non-flapping cycle duration, the percentage of a cycle spent flapping and the number of wingbeats in a cycle were all greatest at 8 m s-1. Wingbeat amplitude was smaller at intermediate speeds, but differences among speeds were not significant. These variables allowed indirect estimates of power output and suggested that minimum power speed for starlings was near 12 m s-1 and that power output increased at both slower and faster speeds. Within windtunnel speeds, muscle activity changed in relation to wingspan at mid-upstroke, wingtip excursion, wingbeat frequency, acceleration, velocity, altitude and horizontal position.

Several considerations regarding the variable blade length rotor

Introduction S INCE the revolutionary breakthrough of Cierva and the engineering achievements of Sikorsky, the general layout of the conventional helicopter rotor has not changed much. Though popular and widespread, this arrangement has some major limitations, one of the principal ones being the unsymmetric loading of the rotor disc. Serious difficulties also appear at the tip of the advancing blade (Mach number effects), and at the inner region of the retreating blade (reverse flow). Hence, significant research is still carried out to properly model the blade oscillatory aerodynamics in forward flight, with nonlinear unsteady effects being currently considered using advanced computational techniques.However, the reader's attention is drawn to the fact that there are alternative designs for dealing with some of these problems. One of these alternative designs is the advancing blade concept (ABC) in which two counter-rotating coaxial rotors are used, thus somehow balancing the global loading. However, the ABC design is still not free from Mach number effects on the advancing tip, and needs to deal with the additional constraint of preventing the counter-rotating blades contacting each other while flapping. Another alternative design is the variable length blade (VLB). The increase in tip Mach number on the advancing blade is compensated by the reduction in blade length, with a complementary effect taking place on the retreating blade (cyclic VLB). Or one can decrease the overall rotor diameter as flight speed increases (collective VLB). Such concepts were studied in some depth about two decades ago, and their merits and limitations were highlighted. But, due to technological difficulties at that time, the VLB concept did not pass the research stage. However, with the recent years developments in active control and smart materials technologies, it is the belief of the authors that this alternative design should be given a fresh re-evaluation.

FLIGHT PHYSIOLOGY OF NEOTROPICAL BUTTERFLIES: ALLOMETRY OF AIRSPEEDS DURING NATURAL FREE FLIGHT

Airspeed measurements during natural free flight were made on a total of 270 neotropical butterflies representing 62 species. Morphological data were obtained from the same individuals for which airspeeds had been determined. Flight speed was positively correlated with body mass, thoracic mass and wing loading. Controlling for body mass, higher wing loadings were correlated with increased flight speed. Flight speed and wing aspect ratio were negatively correlated. No consistent correlations were found between airspeed and wing length, wing area or body length. Released butterflies and butterflies encountered in natural free flight did not differ substantially in flight speed allometry. The observed scaling of flight speeds was similar to that derived for a much smaller sample of butterflies flying in an insectary, although absolute values of flight speed were approximately three times higher in natural flight and correlation coefficients of allometric regressions were typically lower. These results suggest that butterfly airspeeds under natural conditions can reasonably be predicted from morphological measurements, and that studying flight in enclosed spaces preserves the allometry of flight speeds.

Locomotor mimicry in butterflies? The associations of positions of centres of mass among groups of mimetic, unprofitable prey

With detailed measurements of flight-related morphological parameters of 18 species within the tribe Heliconiini and 10 of their non-heliconiine comimics, I found that morphological parameters relevant to flight biomechanics are associated with three escape tactics of these Neotropical butterflies: evasive flight, distastefulness, and mimicry. Two distinct character suites, one pertaining to the position of centre of body mass and another pertaining to wing shape, were identified using principal-components analysis. A third component correlated most highly with the position of centre of wing mass. Mimicry groups were best discriminated by the positions of centres of body and wing mass, suggesting that these features converged within mimicry groups. Centres of mass were positioned nearer to the wing base in mimicry groups composed of more palatable species, presumably decreasing the radial moments of inertia of the body and wings and increasing flight speed and turning performance. Predation has selected for body morphology that increases flight speed and manoeuvrability in palatable butterflies, whereas the morphology of distasteful species compromises flight performance. Convergent selection may reduce morphological differences of species within mimicry groups arising from distantly related lineages, and hence it may have enhanced the morphological diversification of palatable and unpalatable butterflies within lineages that have more recently evolved distastefulness.

Flight morphology of Neotropical butterflies: palatability and distribution of mass to the thorax and abdomen.

We test whether palatability of Neotropical butterflies is associated with distribution of mass to the thorax and abdomen. Thoracic mass is predominantly muscle mass, whereas abdominal mass includes organs of digestion, food storage, and reproduction. To escape from predation, butterflies palatable to the rufous-tailed jacamar (Galbula ruficauda) use fast, erratic flight, whereas unpalatable butterflies have defensive chemicals and slow, regular flight patterns. We adjusted for effects of phylogeny and report partial correlations for two levels of analysis: 1) comparisons among-lineage means, which test for correlations between traits of distantly related lineages, and 2) comparisons among deviations from lineage means (or within lineages), which test for correlations between traits of more closely related species.Among lineages for both males (n=10 lineages) and females (n=9), palatability and thoracic mass were positively correlated, whereas palatability and abdominal mass were negatively correlated. An inverse correlation between thoracic and abdominal mass is a consequence of the two segments composing 75% of the total body mass. Predation, indexed by palatability, may select for increased flight speed and thoracic mass at the expense of the abdomen, but relative flight speed and thoracic mass were not significantly correlated.Within lineages (n=45 species for each sex), thoracic mass was uncorrelated with palatability in both sexes. Relative flight speed correlated positively with thoracic mass and negatively with body mass. Palatability and abdominal mass were negatively correlated for males but not females. Hence differences between the sexes in mass distribution suggest differences in reproductive constraints and predation stress.

Thermoregulatory physiology of the carpenter bee,Xylocopa varipuncta

The carpenter beesXylocopa varipuncta maintain thoracic temperatures of 33.0°C to 46.5°C during continuous free flight from 12°C to 40°C. Since the thoracic temperature excess is not constant (decreasing from 24°C at low air temperatures to 6°C at high) the bees are thermoregulating. We document physiological transfer of relatively large amounts of heat to the abdomen and to the head during pre-flight warm-up and during artificial thoracic heating. Most of the temperature increase of the head is due to passive conduction, while that of the abdomen is due to active physiological heat transfer despite a series of convolutions of the aorta in the petiole that anatomically conform to a counter-current heat exchanger. Although the thermoregulatory mechanisms during flight are far from clarified, our data suggest that thermoregulation involves a strong reliance on active convective cooling through increased flight speed.

Analysis of the aerodynamic performance of birds during bounding flight

A new analysis of bounding flight is presented. The rise and fall in this style of flight are explicitly taken into account, and the aerodynamic performance required to achieve curvature of the flight path during the powered phase is included. It is shown that this flight style may be viewed as a strategy for increasing flight speed without incurring the penalty of increased energy expenditure associated with increased flight speed under conditions of steady horizontal flight.

輸送機の高速化とその諸問題 : SSTの課題(&lt;小特集&gt;交通機械の高速化とその諸問題小特集号)

輸送機の高速化とその諸問題 : SSTの課題(&lt;小特集&gt;交通機械の高速化とその諸問題小特集号)

Effect of Thrust on the Longitudinal Oscillations of Missiles

Exact linearized solutions are provided for the longitudinal oscillations of missiles when the trajectory is nearly horizontal and the thrust is either zero, a specified constant value, or increasing with the square of the increasing flight speed. The results indicate that in all cases any increase in the thrust, or any acceleration along the nearly horizontal trajectory, will directly increase the damping of the angle-of-attack oscillations, whose increase in frequency is at first negligible, and then grows very slightly with time.

Effects of Air Ions on Duration and Rate of Sustained Flight of the Blowfly, Phoenicia sericata Meigen

AbstractThat insect flight is influenced by air ions was shown when blowflies, Phoenicia sericata Meigen, were exposed to air ions at ion currents of about 3.4 × 10−11 amp. Positive ions resulted in longer, faster flights than did normal laboratory air, and there were steep increases and decreases in speed. Negative ions resulted in relatively fast, steady flight that usually lasted longer than in positively ionized or in laboratory air. After exposure to positive ions, exposure to alternating polarities resulted in a steady net increase in flight speed but exposure to alternating polarities after exposure to negative ions had no effect on flight.

Noise Radiation from Jet Aircraft in Flight

The radiation characteristics of a jet aircraft in flight (directivity patterns for octave bands) have been determined as a function of flight speed. Accurate control of flight path and velocity and correlation of the aircraft's momentary position with each moment of the pressure time curve had to be achieved before reliable results were obtained. The maximum over-all sound pressure level, which occurs for a stationary jet at an angle of 140° to 150° from the aircraft's nose, decreases with increasing flight speed with a reduction of the total sound power output by up to 6 db. This decrease in noise power output is less than expected theoretically from the reduced relative velocity of the gas jet to the surrounding atmosphere. The noise radiated toward the front of the aircraft increases with increasing speed and above Mach number 0.7 the maximum of the over-all sound pressure appears at an angle of 20° to 30° from the aircraft's nose. This is accompanied by an increase in the total noise output, which is attributed to radiation from the turbulent flow generated by the moving aircraft as demonstrated by high-speed glides.