Gliding Flight Research Articles

Gliding Birds: The Effect of Variable Wing Span

ABSTRACT The equilibrium gliding performance of a bird is described by the relationship between sinking speed (V8) and air speed (V). When V3 is plotted against V, the points fall in a ‘performance area’ because the wing span is changed during gliding. The lowest Vs for each V in the performance area defines a ‘maximum performance curve’. This curve can be predicted by a mathematical model that changes the wing span, area and profile drag coefficient (CD pr) of a hypothetical bird to minimize drag. The model can be evaluated for a particular species given (a) a linear function relating wing area to wing span, and (b) a ‘polar curve’ that relates Cp.pr and the lift coefficient (CL) of the wings. For rigid wings, a single polar curve relates CD,pr to CL values at a given Reynolds number. The position and shape of the polar curve depend on the aerofoil section of the wing and the Reynolds number. In contrast, the adjustable wings of a laggar falcon (Falco jugger) and a black vulture (Coragyps atratus) gliding in a wind tunnel have CL, and CD,pr values that fall in a ‘polar area’ rather than on a curve. The minimum values of CD,pr at each CL bound the polar area and define a polar curve that is suitable for evaluating the model. Although the falcon and the vulture have wings that are markedly different in appearance, the data for either bird are enclosed by the same polar area, and fitted by the same polar curve for minimum CD,pr at each CL value. This curve is a composite of the polar curves for rigid wings with aerofoils similar to those found in avian wings. These observations suggest that the polar curves of other gliding birds may be similar to that of the falcon and the vulture. Other polar curves are defined by CL and CD,pr values for the falcon and the vulture gliding at a constant speed but at different glide angles. Each speed has a different polar curve; but for a given speed, the same polar curve fits the data for either bird. The falcon and the vulture gliding in the wind tunnel at a given speed were found to increase their drag by decreasing their wing span. This change increases induced drag and probably increases CD,pr for the inner parts of the wing because of an unusual property of bird-like aerofoil sections: wings with such sections have minimum values of CD,pr at CL values near 1, while conventional wings have minimum values of CD,pr at CL values near 0.

Design technique to reduce effects of tidal variations on an ILS glide slope system

A 330 MHz null-reference glide slope system design technique to minimise the reflecting surface variations is introduced. The runaway approach end of the site selected to test this design is over an ocean. Since the ocean forms part of the reflecting surface of the glide slope system, the tidal variations will affect the glide angle. The uniform theory of diffraction is used in the analysis and calculations are made for five tidal levels from high to low tide. The results of the simulations indicate that a glide path angle exists which is least sensitive to the tidal variations. Furthermore, this optimum angle provides smooth glide path structure.

Microwave-powered, unmanned, high-altitude airplanes

Performance analysis and sizing studies have been conducted for unmanned, microwave powered, low speed airplanes that must fly with long endurance at high altitude The necessity of locating the receiving antenna in the vehicle wing couples both vehicle sizing and flight mechanics with power transmission This leads to un conventional performance equations for flight modes using either continuous power transmission or boost glide flight paths Vehicle size is a direct function of payload weight and power requirements Analytic results indicate that a variety of strategies can be employed to enhance vehicle performance for a range of mission requirements and wind conditions

Performance Measures for Aircraft Carrier Landings as a Function of Aircraft Dynamics

A theory of performance measurement for operator controlled systems is presented. The theory permits synthesis of a system performance measure which scores performance on successive data samples based on the impact of the sampled performance on the overall summary of performance. Since performance is measured and evaluated on each sample, the dynamics of the controlled element, i.e., the aircraft, are effectively removed from the measurement eventhough the pilot (operator) continues to control the aircraft. While the theory directly applies to problems where the performance limiting factors are known, the method has been extended to apply to problems where the performance limiting factors are not known explicitly, but are known to be implicit in the performance data. This paper documents the development of measures for aircraft carrier landings for the glide path and angle of attack control channels. Flight data obtained from the Visual Technology Research Center, Naval Training Equipment Center, Orlando, Florida, was analyzed using the measures. The data on carrier landings were available on 9-track magnetic tape consisting of flights by four subjects each performing on 42 flights. Each flight was performed on a particular combination of glide path error display and day/night combination. Two types of glide path displays were used, resulting in four treatments (two displays and two light conditions). One display was the conventional glide path display and the other was a command display which incorporates error rate information with glide path error presentation. Each subject controlled the aircraft to a carrier landing three times with each treatment. The resulting performance scores were aggregated by subject, treatment, range to carrier deck, and error and error rate cells. The results suggest that the command display offers improved glide path control especially during day light conditions. Further, the measurement technique was shown to permit determination of the relationship between performance and factors that change during the flight - such as error and error rate magnitudes. The measurement technique bypasses the time delays due to aircraft dynamics - by accounting for them - permitting evaluation of performance on short (less than a second) intervals of flight. Consequently, observed differences in performance at different error and error rate magnitudes were detected suggesting that significant non-linear control techniques may have been exhibited by the pilots.

System for deploying a moored sensor aray

A system for automatically deploying a moored sensor array utilizing an elongated cylindrical container with a semispherical weighted nose which will assume a glide angle with respect to the horizontal and descend in a glide path. Cable to a surface buoy is dispensed from the container during the descent with sufficient scope (ratio of cable length to depth) to permit the surface buoy to move about in response to ocean currents without overstressing the cable. A sea anchor suspended from the buoy by an elastic member with extra length of cable between the suspended sea anchor and the buoy isolates wave motion of the buoy from the anchor on the ocean floor. Upon impact with the ocean floor, a switch in the nose of the container is closed to lock up the cable and eject an array package from the container. The array package contains buoyant material to cause it to float upwardly while paying out sensors attached along a length of cable packed in the array package.

Minimum and Maximum Endurance Trajectories for Gliding Flight in a Horizontal Plane

The problem of determining minimum and maximum endurance trajectories for subsonic gliding flight in a horizontal plane is considered. These trajectories are of interest for the low-level delivery of weapon systems where it is desirable to have a weapon remain in the air, yet close to the ground, while the aircraft delivering the weapon leaves the area. If the weapon is placed inside a small lifting vehicle, then the problem is to determine either minimum or maximum endurance trajectories for the vehicle that return to a designated target. This problem is formulated and numerical results are computed for a small lifting vehicle.

Autorotating flat-plate wings: the effect of the moment of inertia, geometry and Reynolds number

Free-flight and wind-tunnel measurements by previous investigators of the flat-plate autorotation phenomenon have been analysed. The variation of the autorotation characteristics with changes in the Reynolds number and the aspect ratio, thickness ratio and moment of inertia of the flat plate have been correlated. The interpretation of the role of the Reynolds number made in a previous investigation is shown to be incorrect. The tip-speed ratio, for the ranges of the dimensionless parameters investigated, is shown to be a function of only the plate aspect ratio, thickness ratio, and also the moment of inertia if the latter is sufficiently small. The lift and drag coefficients, and therefore the free-flight glide angle, are shown to be functions of the tip-speed ratio, the aspect ratio and the Reynolds numbers based on the chord and plate thickness.

Diving by Shearwaters

Journal Article Diving by Shearwaters Get access R. G. B. Brown, R. G. B. Brown Canadian Wildlife Service, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, Canada, B2Y 4A2 Search for other works by this author on: Oxford Academic Google Scholar W. R. P. Bourne, W. R. P. Bourne Address of second author: Department of Zoology, Tillydrone Avenue, Aberdeen, Scotland, AB9 2TN Search for other works by this author on: Oxford Academic Google Scholar Terence R. Wahl Terence R. Wahl Address of third author: Department of Biology, Western Washington University, Bellingham, Washington 98225 Search for other works by this author on: Oxford Academic Google Scholar The Condor, Volume 80, Issue 2, 1 April 1978, Pages 123–125, https://doi.org/10.2307/1367911 Published: 01 April 1978 Article history Accepted: 11 April 1977 Published: 01 April 1978

The Significance of Ground Effect to the Aerodynamic Cost of Flight and Energetics of the Black Skimmer (Rhyncops Nigra)

ABSTRACT The kinematics and aerodynamics of flapping and gliding flight by the black skimmer were investigated to evaluate the significance of ground effect to the foraging and daily energy budget of skimmers. Ground effect is an increase in lift and decrease in drag of an aerofoil when close to the ground. The duration of upstroke and downstroke, the wing movements and the pronation/supination of the wings during flapping flight of the skimmer are similar to other birds. Wing-beat frequency was 3·1 s−1 and flight velocity was 9·1 m s−1. The wing stroke was markedly asymmetric, with the majority of the stroke occurring above the plane of the body. During skimming, wing beats are intermittent and of low amplitude; flight velocity is 10·3 m s−1. Induced power, parasite power and profile power of skimmers were calculated after Tucker (1973) in the absence of ground effect, and the glide angle and sink velocity were calculated for gliding skimmers. Ground effect was shown to markedly reduce induced power requirements, and hence total power requirement, of flapping flight, and reduce the glide angle and sink velocity during gliding. The hydrodynamic drag of the lower mandible was estimated to be 10−4 N, which is insignificant compared to the total aerodynamic drag (0·4 N). Ground effect was shown to markedly increase foraging efficiency and facilitate the attainment of a positive daily energy balance. The significance of ground effect to other flying vertebrates was discussed.

Visual Perception of Pilots in Carrier Landing

Experimental investigations were performed in a visual carrier landing simulator to determine the accuracy and consistency with which Navy pilots can judge position on the glide slope and flight path during final approach. These studies covered conditions involving a quiet sea state in which there was no angular deck motion present, as well as a moving deck. The effects of dusk and night landings and the presence of the Fresnel Lens Optical Landing System (FLOLS) were includ ed. The results indicate that pilots' mean estimates of position when on-course are within a small fraction of a degree of being correct under dusk and night conditions, with a static or moving carrier, with and without the FLOLS. However, variability in judgment is high. Sensitivity to changes in position is reduced with a moving carrier, and falls to a low value of about 40% at night, without the FLOLS. Mean estimates of flight path are within 4 min of arc of being correct when the aircraft is flying toward the desired aim point under all ambient and ship conditions. Again, variability in judgment is high. Sensitivity to changes in aim point is low, falling to about 10% at night.

The pterostigma of insect wings an inertial regulator of wing pitch

1. The pterostigma of insect wings usually is a pigmented spot close to the leading edge far out on the wing, having a greater mass than an equally large wing piece in adjacent wing regions. 2. In several dragonfly (Odonata) species the position of the spanwise torsion axis of the wings, the mass distribution of the wings, and the position of the chordwise centre of mass in chordwise wing strips were determined. 3. In the dragonflies investigated, the torsion axis of the wing lies ahead of the chordwise centre of mass of the wing except at the pterostigma (Fig. 1). 4. A wing having its mass axis behind its torsion axis is very susceptible to self-excited coupled flapping and feathering vibrations, making gliding flight above a critical speed impossible. Due to unfavourable, inertial, wing pitching tendencies, a still lower speed limit is set to active flight. 5. Due to its mass contribution and favourable location, the pterostigma tends to raise these speed limits by causing favourable, inertial, pitching moments during the acceleration phases of wing flapping. 6. The favourable pitching moment of the pterostigma is proportional to the distance from the wing base to the pterostigma, and to the distance of the pterostigma ahead of the wing's spanwise torsion axis. The pterostigma usually has an optimal position at the leading edge of the wing near the wing tip, just where the wing curves backwards. Further optimization of pterostigma mass localization has been obtained in different ways in various insects, involving both pterostigma position (Fig. 4) and form (Fig. 5a). 7. The function of the pterostigma of raising the critical gliding speed, at which self-excited vibrations set in, was demonstrated in dragonflies. Although contributing only 0.1 % (one pterostigma) of the total dragonfly weight, it raised the critical speed by 10–25% in one species. 8. The pterostigma is common among the insect orders Odonata, Neuroptera, Psocoptera, Hemiptera, and Hymenoptera. By passive, inertial, pitch angle control, the pterostigma probably makes the wing beat more efficient in slow and hovering flight of small insects, while its raising of the critical flight speeds probably is of more importance to larger insects. The ability of active pitch angle control in many insects does not detract from the value of the pterostigma, since it contributes passively, without power expenditure, towards an efficient wing stroke.

A psychophysical evaluation of the accuracy of shape discrimination as an aircraft landing aid.

Pilots flying into unfamiliar airports may find it difficult to judge correctly the proper glide angle when landing. Several types of landing aids are now in use to eliminate this problem; however, they are typically expensive to install and maintain. A possible solution to this problem is the replacement of runway centerline striping with painted diamonds. Changes in the projected shape of the diamonds could provide glide angle information. It was the purpose of this study to evaluate the accuracy possible in detecting glide angle using this method. The just-noticeable difference between a square and a diamond shape was determined. This ratio was found to be 1.049/1.00 for the upper just noticeable difference and .945/1.00 for the lower just noticeable difference. This finding indicates that, if discrimination in the real world approaches this accuracy, deviations of approximately .17° above or below glide slope are detectable.

Aerodynamics of Gliding Flight of A Black Vulture Coragyps Atratus

ABSTRACT A black vulture (mass = 179 kg) gliding freely in a wind tunnel adjusted its wing span and wing area as its air speed and glide angle changed from 9·9 to 16·8 m/s and from 4·8° to 7·9°, respectively. The minimum sinking speed was 1·09 m/s at an air speed of 11·3 m/s. The maximum ratio of lift to drag forces was 11·6 at an air speed of 13·9 m/s. Parasite drag coefficients for the vulture are similar to those for conventional airfoils and do not support the contention that black vultures have unusually low values of parasite drag.

Aerodynamics of Gliding Flight in A Falcon and Other Birds

ABSTRACT A live laggar falcon (Falco jugger) glided in a wind tunnel at speeds between 6·6 and 15·9 m./sec. The bird had a maximum lift to drag ratio (L/D) of 10 at a speed of 12·5 m./sec. As the falcon increased its air speed at a given glide angle, it reduced its wing span, wing area and lift coefficient. A model aircraft with about the same wingspan as the falcon had a maximum L/D value of 10. Published measurements of the aerodynamic characteristics of gliding birds are summarized by presenting them in a diagram showing air speed, sinking speed and L/D values. Data for a high-performance sailplane are included. The soaring birds had maximum L/D values near 10, or about one quarter that of the sailplane. The birds glided more slowly than the sailplane and had about the same sinking speed. The ‘equivalent parasite area’ method used by aircraft designers to estimate parasite drag was modified for use with gliding birds, and empirical data are presented to provide a means of predicting the gliding performance of a bird in the absence of wind-tunnel tests. The birds in this study had conventional values for parasite drag. Technical errors seem responsible for published claims of unusually low parasite drag values in a vulture. The falcon adjusted its wing span in flight to achieve nearly the maximum possible L/D value over its range of gliding speeds. The maximum terminal speed of the falcon in a vertical dive is estimated to be 100 m./sec.

Landing task and pilot acceptance of displays.

The results of an analytical study of the landing task and an empirical study of pilot preferences of displays for landing in reduced weather minima suggest the following criteria for display evaluation. The information content of the display should allow one to initiate the final approach; to achieve departure and to know of departure from the glide angle; to maintain angle of attack, sink rate, roll attitude, and course; to determine crab angle, when to initiate flare, and heading during rollout. The presentation should be a compensatory display, a simple pictorial indication of the landing situation, and should be on the wind-screen. The display should provide redundant but independent information, require a minimum of user-supplied information, utilize a maximum of gain, provide for removal of a malfunctioning element, and be useful in other phases of landing. Alignment and other adjustments prior to use should be simple to accomplish and should be followed by a simple, foolproof checkout procedure.

Observations on gliding in the desert locust

Summary Observations on gliding flight by the Desert Locust in Eastern Africa and Arabia are recorded. It is shown that gliding is a not uncommon feature of adult behaviour; it has been recorded among fledglings, immature, and mature populations over a wide range of densities, and may be evinced by a considerable proportion of the individuals in a population. The observed duration of individual glides ranged from a few seconds to 150 seconds; in one series of observations individuals of a population of locusts passing overhead for 4 to 6 hours daily were seem to be in continuous gliding flight. Problems of maintenance of height by gliding locusts are discussed. It is suggested that gliding may be advantageous to the species, since it allows greater airborne endurance. Possible factors in the commencement and termination of gliding flight are discussed.

THE FODIES (PLOCEINAE) OF THE SEYCHELLES ISLANDS

Summary1. The endemic Foudia sechellarum (the Toq Toq) and the introduced F. madagascariensis (the Cardinal) occur in the Seychelles. The Toq Toq is now restricted to three island refuges, Frigate, Cousin and Cousine, while the Cardinal is found throughout the archipelago.2. Comparative study of their breeding biology and behaviour, mainly on Frigate, revealed the following details:(a) The populations of the two species are dispersed differently in the environment.(b) A proportion of the Toq Toq population probably breeds throughout the year while the Cardinal breeds between September and March.(c) The Toq Toq is primarily insectivorous, the Cardinal primarily graminivorous.(d) Nests are similar, though the Toq Toq structure is more bulky. The Toq Toq nests are sited in bushy trees, while Cardinals' occur in Coconut palms often at a considerable height.(e) Toq Toq eggs are white, clutch‐size 1–2, the Cardinal's eggs pale blue, clutch‐size 3.(f) Incubation and fledging periods and growth curves from a limited number of nests are given for each species.(g) Survival of Cardinals in the nest is better than Toq Toqs due to the greater predation suffered by Toq Toqs.(h) The Toq Toq moves in small family parties or couples taking insects mainly from below the fronds of palms. Aggregations occur at localized food supplies, washing and roosting places. Cardinals move in flocks congregating particularly around patches of seeding grass. The Toq Toq is a “contact species”, the Cardinal has “distance” characteristics. In an aviary, Toq Toqs were dominant over Cardinals at food bowls and on perches.(i) Both species establish territories when breeding, the Toq Toq's being as much as twice the size of the Cardinal's. Territorial behaviour is described.(j) The Toq Toq pair bond is probably complete prior to nesting and they may pair for life. The female is associated with the male in nest defence and building and there is no nest invitation behaviour. The Cardinal female comes to the territory from the flock, which the male leaves earlier, and is repeatedly attacked. Courtship sequences and display posture components are more aggressive in the Cardinal than in the Toq Toq. The Cardinal has a “Glide Flight” nest invitation.(k) The aberrant length of time spent in nest‐building by many male Cardinals and the frequent cases of nest demolition by the owners is supposedly due to the frequent failure of females to accept nests offered to them, even when courtship has apparently been satisfactory. The Seychelles population may not yet be fully adapted to the palm tree nest site.3. The coexistence of the two species is due to divergent adaptation to differing environments of origin the Toq Toq to the endemic forests of the Seychelles and the Cardinal to the open country of Madagascar. Both have shown flexibility in adjusting to the present coconut‐dominated vegetation of the Seychelles. The differences between them result from the degeneration of colour and voice in the Toq Toq on its remote islands and the differing methods of exploitation of contrasting food supplies. Differences in social organization correlate with food exploitation and are largely responsible for contrasts in territorial and courtship behaviour.4. These studies are considered in relation to other endemic Foudia populations and the genus is listed in three Species‐groups.

THE STRUCTURE OF THE SEA BREEZE FRONT AS REVEALED BY GLIDING FLIGHTS

WeatherVolume 14, Issue 9 p. 263-270 THE STRUCTURE OF THE SEA BREEZE FRONT AS REVEALED BY GLIDING FLIGHTS C. E. Wallington, C. E. Wallington Meteorological Office, DunstableSearch for more papers by this author C. E. Wallington, C. E. Wallington Meteorological Office, DunstableSearch for more papers by this author First published: September 1959 https://doi.org/10.1002/j.1477-8696.1959.tb00601.xCitations: 19AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume14, Issue9September 1959Pages 263-270 RelatedInformation

Observations on the structure of convection currents: Meteorological aspects of some South African gliding flights

Observations on the structure of convection currents: Meteorological aspects of some South African gliding flights

Observations on the structure of convection currents; meteorological aspects of some South African gliding flights

Abstract(1) During the early stages of convection, the upper limit of air currents ascending from the surface, as recorded by sailplane, is found to agree closely with the level of the intersection on the tephigram of the path curve through the surface temperature at the time and the environment curve given by the corresponding upper‐air temperature observations. Details are given of one series of observations showing clearly successive stages in the breakdown of a morning inversion; and the good and bad thermal soaring conditions encountered on different days are shown to be fully explained by differences in vertical temperature distribution.(2) In the absence of appreciable convection effects, the vertical extent of orographic up‐currents over a hill is shown to be correlated with the component of the surface wind perpendicular to the line of the ridge.(3) Examples of the distribution of convective up‐currents in relation to the surface topography and to the structure of the wind, together with the magnitude of these currents, are derived from detailed analyses of barographic records of cross‐country sailplane flights on which a suitable flight‐plan has been followed sufficiently rigorously. Observations are quoted indicating convective cells of horizontal extent about twice their depth and 9,000 to 12,000 ft. long in the direction of the wind, and providing an approximate value of the ratio of the masses of ascending and descending air within a given isobaric slice.(4) An analysis of sailplane flights made at a well‐marked cold front demonstrates the existence of a narrow but apparently continuous zone of rising air immediately ahead of the front, with a vertical velocity greater than can be accounted for by passive lifting of the warm air at the frontal surface. Surface and upper‐air temperatures in the warm air ahead of the front show that this effect may be explained in terms of the localisation of previously scattered convection currents in the highly unstable warm air into a narrow zone just ahead of the advancing cold air.