Gliding flight: drag and torque of a hawk and a falcon with straight and turned heads, and a lower value for the parasite drag coefficient

2000 ◽  
Vol 203 (24) ◽  
pp. 3733-3744 ◽  
Author(s):  
V.A. Tucker
Keyword(s):  
Wind Tunnel ◽  
Mathematical Models ◽  
Drag Coefficient ◽  
High Speed ◽  
Aerodynamic Drag ◽  
The Body ◽  
Head Turning ◽  
Drag Coefficients ◽  
Spiral Path ◽  
Gliding Flight

Raptors - falcons, hawks and eagles in this study - such as peregrine falcons (Falco peregrinus) that attack distant prey from high-speed dives face a paradox. Anatomical and behavioral measurements show that raptors of many species must turn their heads approximately 40 degrees to one side to see the prey straight ahead with maximum visual acuity, yet turning the head would presumably slow their diving speed by increasing aerodynamic drag. This paper investigates the aerodynamic drag part of this paradox by measuring the drag and torque on wingless model bodies of a peregrine falcon and a red-tailed hawk (Buteo jamaicensis) with straight and turned heads in a wind tunnel at a speed of 11.7 m s(−)(1). With a turned head, drag increased more than 50 %, and torque developed that tended to yaw the model towards the direction in which the head pointed. Mathematical models for the drag required to prevent yawing showed that the total drag could plausibly more than double with head-turning. Thus, the presumption about increased drag in the paradox is correct. The relationships between drag, head angle and torque developed here are prerequisites to the explanation of how a raptor could avoid the paradox by holding its head straight and flying along a spiral path that keeps its line of sight for maximum acuity pointed sideways at the prey. Although the spiral path to the prey is longer than the straight path, the raptor's higher speed can theoretically compensate for the difference in distances; and wild peregrines do indeed approach prey by flying along curved paths that resemble spirals. In addition to providing data that explain the paradox, this paper reports the lowest drag coefficients yet measured for raptor bodies (0.11 for the peregrine and 0.12 for the red-tailed hawk) when the body models with straight heads were set to pitch and yaw angles for minimum drag. These values are markedly lower than value of the parasite drag coefficient (C(D,par)) of 0.18 previously used for calculating the gliding performance of a peregrine. The accuracy with which drag coefficients measured on wingless bird bodies in a wind tunnel represent the C(D,par) of a living bird is unknown. Another method for determining C(D,par) selects values that improve the fit between speeds predicted by mathematical models and those observed in living birds. This method yields lower values for C(D,par) (0.05-0.07) than wind tunnel measurements, and the present study suggests a value of 0.1 for raptors as a compromise.

A Study of the Base Drag of Tractor-Trailer Trucks

1978 ◽  
Vol 100 (4) ◽  
pp. 443-448 ◽  
Author(s):  
C. H. Marks ◽  
F. T. Buckley ◽  
W. H. Walston
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Pressure Distribution ◽  
Aerodynamic Drag ◽  
Base Pressure ◽  
Drag Coefficients ◽  
Vehicle Configuration ◽  
Yaw Angle ◽  
Base Drag

Measurements were made of the base pressure distribution and the aerodynamic drag of a variety of 1/8th-scale tractor-trailer truck models in a wind tunnel at yaw angles ranging from 0° to 20°. Base-drag coefficients and overall aerodynamic-drag coefficients were calculated from this data. The measurements show that the base-drag coefficient of typical tractor-trailer trucks does not vary much with vehicle configuration, and that base drag constitutes approximately 13 to 15 percent of the total aerodynamic drag at zero yaw. The base drag increases in magnitude and also becomes a larger part of the overall aerodynamic drag as yaw angle increases, reaching about 18 to 25 percent of the overall drag at 20° yaw. Streamlining the forebody of the vehicle has little effect on the base-drag coefficient, but increases the fraction of the overall aerodynamic drag due to the base.

scholarly journals Structure Clearance Design in Wind Tunnel Tests with Implications for Aerodynamic Drag of High-Speed Trains

2021 ◽  
Author(s):  
Zhixiang Huang ◽  
Hanjie Huang ◽  
Weiping Zeng ◽  
Li Chen ◽  
Renyu Zhu
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Drag Coefficient ◽  
Distribution Pattern ◽  
High Speed ◽  
Aerodynamic Drag ◽  
High Speed Train ◽  
Wind Tunnel Tests ◽  
High Speed Trains

Abstract The influences of vestibule diaphragm gap, wheel-rail clearance, and strut-plate gap on the aerodynamic drag of a 1/8th-scale high-speed train model were investigated in an 8 m×6 m wind tunnel. The Reynolds number was set to 2.2×106 based on train height. It was found that the variation of the vestibule diaphragm gap changed the aerodynamic drag distribution pattern of each car; the drag coefficient of the head and middle cars might change as high as 45%; however, the change in the drag coefficient of the total train was very small. The effects of the strut-plate gap on the aerodynamic drag of each car and the total train were small. The effect of the wheel-rail clearance on the drag of the head car was not significant. It was suggested that the vestibule diaphragm gap, strut-plate gap and wheel-rail clearance of the 1:8 scale high-speed train model should not be greater than 11, 10, and 9 mm, respectively.

Gliding Flight of the White-Backed Vulture Gyps Africanus

1971 ◽  
Vol 55 (1) ◽  
pp. 13-38 ◽  
Author(s):  
C. J. PENNYCUICK
Keyword(s):  
High Speed ◽  
Lift Coefficient ◽  
The Body ◽  
East African ◽  
Induced Drag ◽  
Gliding Flight ◽  
Vertical Speed ◽  
Statistical Sense ◽  
Pass Through ◽  
Comparison Measurements

1. Glide-comparison measurements were made on ten species of East African soaring birds using a Schleicher ASK-14 powered sailplane. Horizontal and vertical speed differences between bird and glider were measured by a photographic method, and used to estimate the bird's horizontal and vertical speeds relative to the air. The analysis refers to the white-backed vulture, since by far the largest number of measurements was obtained on this species. 2. A regression analysis using a two-term approximation to the glide polar yielded an implausibly high estimate of induced drag, which was attributed to a lack of observations at lift coefficients above 0.72. An amended glide polar was constructed assuming elliptical lift distribution and a maximum lift coefficient of 1.6 to define the low-speed end, while the high-speed end was made to pass through the mean horizontal and sinking speeds of all the experimental points. This curve gave a minimum sinking speed of 0.76 m/s at a forward speed of 10 m/s, and a best glide ratio of 15.3:1 at 13 m/s. It did not differ significantly (in the statistical sense) from the original regression curve. 3. In comparing the estimated circling performance, based on the amended glide polar, with that of the ASK-14, it was concluded that the rates of sink of both should be comparable, but that the glider would require thermals with radii about 4.3 times as great as those needed to sustain the birds. The conclusions are consistent with experience of soaring in company with birds. 4. In an attempt to assess the adaptive significance of the low-aspect-ratio wings of birds specializing in thermal soaring, the white-backed vulture's circling performance was compared with that of an ‘albatross-shaped vulture’, an imaginary creature having the same mass as a white-backed vulture, combined with the body proportions of a wandering albatross. It appears that the real white-back would be at an advantage when trying to remain airborne in thermals with radii between 14 and 17 m, but that the albatross-shaped vulture would climb faster in all wider thermals; on account of its much better maximum glide ratio, it should also achieve higher cross-country speeds. It is concluded that the wing shape seen in vultures and storks is not an adaptation to thermal soaring as such, but is more probably a compromise dictated by take-off and landing requirements. 5. The doubts recently expressed by Tucker & Parrott (1970) about the results and conclusions of Raspet (1950a, b; 1960) are re-inforced by the present experience.

Aerodynamics of Gliding Flight of a Black Vulture Coragyps Atratus

1970 ◽  
Vol 53 (2) ◽  
pp. 363-374 ◽  
Author(s):  
G. CHRISTIAN PARROTT
Keyword(s):  
Wind Tunnel ◽  
Wing Area ◽  
Drag Coefficients ◽  
Wing Span ◽  
Drag Forces ◽  
Gliding Flight ◽  
Black Vulture ◽  
Air Speed

1. A black vulture (mass = 1.79 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. 2. The minimum sinking speed was 1.09 m/s at an air speed of 11.3 m/s. 3. The maximum ratio of lift to drag forces was 11.6 at an air speed of 13.9 m/s. 4. 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.

A new moving model test method for the measurement of aerodynamic drag coefficient of high-speed trains based on machine vision

2017 ◽  
Vol 232 (5) ◽  
pp. 1425-1436 ◽  
Author(s):  
Zhiwei Li ◽  
Mingzhi Yang ◽  
Sha Huang ◽  
Dan Zhou
Keyword(s):  
Machine Vision ◽  
Drag Coefficient ◽  
Model Test ◽  
High Speed ◽  
Aerodynamic Drag ◽  
Full Scale ◽  
Test Method ◽  
Test Accuracy ◽  
Friction Resistance ◽  
Aerodynamic Drag Coefficient

A moving model test method has been proposed to measure the aerodynamic drag coefficient of a high-speed train based on machine vision technology. The total resistance can be expressed as the track friction resistance and the aerodynamic drag according to Davis equation. Cameras are set on one side of the track to capture the pictures of the train, from which the line marks on the side surface of the train are extracted and analyzed to calculate the speed and acceleration of the train. According to Newton’s second law, the aerodynamic drag coefficient can be resolved through multiple tests at different train speeds. Comparisons are carried out with the full-scale coasting test, wind tunnel test, and numerical simulation; good agreement is obtained between the moving model test and the full-scale field coasting test with difference within 1.51%, which verifies that the method proposed in this paper is feasible and reliable. This method can accurately simulate the relative movement between the train, air, and ground. The non-contact measurement characteristic will increase the test accuracy, providing a new experimental method for the aerodynamic measurement.

On the Penetrator Nose Drag Measurements

2010 ◽  
Author(s):  
Joseph P. Holland ◽  
Yesenia Tanner ◽  
Phillip A. Schinetsky ◽  
Semih Olcmen ◽  
Stanley Jones
Keyword(s):  
Wind Tunnel ◽  
Power Series ◽  
Viscous Fluid ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Terminal Velocity ◽  
Force Balance ◽  
Supersonic Wind Tunnel ◽  
Buoyant Force ◽  
Nose Shape

In the current study, a rigid body penetrator nose shape that is optimized for minimum penetration drag [1] has been tested to determine the aerodynamic drag of such a penetrator in comparison to three additional nose shapes. Other nose shapes tested were an ogive cylinder, a 3/4 power series nose, and a standard cone. Fineness ratio for the studied nose geometries was chosen as l/d = 1 to maximize variation of the aerodynamic drag forces acting on the nose shapes. This paper discusses the measurements carried out in the University of Alabama’s 6″ × 6″ supersonic wind tunnel, using a 4 component force balance system. In separate experiments, drop tests were made in a viscous fluid to determine the skin-friction effects on these nose shapes. Supersonic wind-tunnel experiments were performed on each of the nose shapes at nine different Mach numbers ranging from 2 to 3.65. Results show that the nose shape optimized for penetration has the lowest drag coefficient of all the shapes at each Mach number within an uncertainty of 5.75%. In the viscous flow drop-test experiments, each nose shape was dropped from rest through water and then separately through viscous fluid (Nu-Calgon vacuum pump oil) under freefall conditions. Each drop was recorded via videotape, and the video was then analyzed to find the terminal velocity of each individual nose shape. Using classical dynamics equations, the weight, buoyant force, and experimentally determined terminal velocity are used to determine the drag force applied to each nose cone shape. Results indicate that while the optimal shape has a lesser drag coefficient than tangent ogive and the cone, the 3/4 power series shape is observed to have the least drag coefficient. In addition to the experiments performed, results on further investigation of the optimal nose shape for penetration are presented. The nose shape has been split into a series of line segments, and a program written has been utilized to search through numerical space for the combination of line segment slopes that produces the nose geometry with the lowest nose shape factor. The results of the numerical analysis in this study point to a different nose shape than the “optimal nose” shape tested in the current study.

scholarly journals A wind-tunnel case study: Increasing road cycling velocity by adopting an aerodynamically improved sprint position

2019 ◽  
pp. 175433711986696
Author(s):  
Timothy Crouch ◽  
Paolo Menaspà ◽  
Nathan Barry ◽  
Nicholas Brown ◽  
Mark C Thompson ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Time Trial ◽  
Force Measurements ◽  
Sampling Errors ◽  
Repeated Testing ◽  
Road Cycling ◽  
Wind Tunnel Study

The main aim of this study was to evaluate the potential to reduce the aerodynamic drag by studying road sprint cyclists’ positions. A male and a female professional road cyclist participated in this wind-tunnel study. Aerodynamic drag measurements are presented for a total of five out-of-seat sprinting positions for each of the athletes under representative competition conditions. The largest reduction in aerodynamic drag measured for each athlete relative to their standard sprinting positions varied between 17% and 27%. The majority of this reduction in aerodynamic drag could be accounted for by changes in the athlete’s projected frontal area. The largest variation in repeat drag coefficient area measurements of out-of-seat sprint positions was 5%, significantly higher than the typical <0.5% observed for repeated testing of time-trial cycling positions. The majority of variation in repeated drag coefficient area measurements was attributed to reproducibility of position and sampling errors associated with time-averaged force measurements of large fluctuating forces.

Aerodynamic Drag on Vehicles in Tunnels

1969 ◽  
Vol 91 (4) ◽  
pp. 694-706 ◽  
Author(s):  
S. William Gouse ◽  
B. S. Noyes ◽  
J. K. Nwude ◽  
M. C. Swarden
Keyword(s):  
Laminar Flow ◽  
Drag Coefficient ◽  
Surface Area ◽  
Incompressible Flow ◽  
High Speed ◽  
Aerodynamic Drag ◽  
Diameter Ratio ◽  
Infinite Body ◽  
Tunnel Wall ◽  
Wetted Surface Area

The purpose of this study was to investigate the aerodynamic drag on vehicles moving in guideways of varying degrees of enclosure. The reason for this study was that several potential high speed ground transport system concepts involve high speed motion of vehicles in enclosed guideways for significant portions of their travel time. Analytical and experimental investigations have been carried out. The analytical studies developed the solution for the aerodynamic drag on a vehicle in an enclosed guideway in laminar flow. The analysis is based on an analogy between the governing equations for the unsteady flow resulting when an infinite body is started impulsively from rest and the steady flow that results from steady motion of a semi-infinite body. The results of this analysis for laminar flow provided a base from which to begin in turbulent flow and were used to justify the basing of a drag coefficient on the wetted surface area of a vehicle rather than the frontal area of a vehicle. Preliminary experiments were executed using spheres as vehicle models. Final experimental studies were carried out using cylindrical models in circular tunnels of various lengths and various degrees of wall porosity. A drop testing apparatus was employed and results were obtained for Reynolds number of the order of 5 · 105. Results to date indicate that for vehicle length-diameter ratios of the order of 15 and above, with tunnel to vehicle diameter ratios of 1.5 and greater, a drag coefficient based on the wetted surface area of the vehicle is independent of the vehicle length-diameter ratio for incompressible flow. Results also indicate that, for incompressible flow, employing a tunnel model with a closed end simulates a tunnel length-diameter ratio of infinity. Tunnel wall porosity, assuming relatively unobstructed motion of fluid outside the porous wall, has a marked effect on decreasing the aerodynamic drag on vehicles moving in enclosed guideways and that for the range of variables investigated (clearance ratio as low as 1.4) tunnel wall porosity of 20 per cent is adequate for all the significant drag reduction that is possible. Qualitative predictions of loss coefficient analytical modeling and literature on transonic flow wind tunnel testing with porous walls are in agreement with the data presented.

Experimental Studies on Aerodynamic Characteristics of Pantograph System According to the Pantograph Cover Configurations for High Speed Train

2011 ◽  
Author(s):  
Yeongbin Lee ◽  
Minho Kwak ◽  
Kyu Hong Kim ◽  
Dong-Ho Lee
Keyword(s):  
Wind Tunnel ◽  
High Speed ◽  
Aerodynamic Drag ◽  
Aerodynamic Force ◽  
Experimental Studies ◽  
Wind Tunnel Test ◽  
Aerodynamic Characteristics ◽  
Experimental Models ◽  
High Speed Train ◽  
Drag And Lift

In this study, the aerodynamic characteristics of pantograph system according to the pantograph cover configurations for high speed train were investigated by wind tunnel test. Wind tunnel tests were conducted in the velocity range of 20∼70m/s with scaled experimental pantograph models. The experimental models were 1/4 scaled simplified pantograph system which consists of a double upper arm and a single lower arm with a square cylinder shaped panhead. The experimental model of the pantograph cover is also 1/4 scaled and were made as 4 different configurations. It is laid on the ground plate which modeled on the real roof shape of the Korean high speed train. Using a load cell, the aerodynamic force such as a lift and a drag which were acting on pantograph system were measured and the aerodynamic effects according to the various configurations of pantograph covers were investigated. In addition, the total pressure distributions of the wake regions behind the panhead of the pantograph system were measured to investigate the variations of flow pattern. From the experimental test results, we checked that the flow patterns and the aerodynamic characteristics around the pantograph systems are varied as the pantograph cover configurations. In addition, it is also found that pantograph cover induced to decrease the aerodynamic drag and lift forces. Finally, we proposed the aerodynamic improvement of pantograph cover and pantograph system for high speed train.

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