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Gottfried Sachs - One of the best experts on this subject based on the ideXlab platform.
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Effect of slotted wing tips on Yawing Moment characteristics.
Journal of theoretical biology, 2005Co-Authors: Gottfried Sachs, Mochammad Agoes MoelyadiAbstract:The aerodynamic Yawing Moment characteristics of bird wings with slotted tips are dealt with. Emphasis is placed on the effect of sweep which the separated feathers constituting the wing tips show and which can reach significant values. Reference is made to basic aerodynamic characteristics of wings with sweep which yields a stabilizing Yawing Moment significantly larger than that of unswept wings. Then, the Yawing Moment characteristics are determined for a wing, the features of which are considered as representative of bird wings with sweep in their slotted tips. A sophisticated aerodynamic procedure is used for obtaining results of high precision. It is shown that the sweep in the slotted wing tips yields a stabilizing Yawing Moment of significant magnitude, considerably increasing with the lift coefficient. To make the significance of wing tip sweep for the ability to generate Yawing Moments more perspicuous, a wing modification the slotted tips of which are unswept is considered for comparison. It turns out that this wing shows Yawing Moments which are substantially smaller. A physical insight into the effect of slotted wing tip sweep on the aerodynamic Yawing Moment characteristics is provided by showing the underlying mechanism. From the results presented in this paper it follows that the sweep in slotted wing tips provides a substantial contribution to the aerodynamic Yawing Moment and, thus, to yaw stability. It may be concluded that this is an essential reason why there is sweep in the slotted tips of bird wings.
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Aerodynamic Yawing Moment characteristics of bird wings.
Journal of theoretical biology, 2005Co-Authors: Gottfried SachsAbstract:The aerodynamic Yawing Moments due to sideslip are considered for wings of birds. Reference is made to the experience with aircraft wings in order to identify features which are significant for the Yawing Moment characteristics. Thus, it can be shown that wing sweep, aspect ratio and lift coefficient have a great impact. Focus of the paper is on wing sweep which can considerably increase the Yawing Moment due to sideslip when compared with unswept wings. There are many birds the wings of which employ sweep. To show the effect of sweep for birds, the aerodynamic characteristics of a gull wing which is considered as a representative example are treated in detail. For this purpose, a sophisticated aerodynamic method is used to compute results of high precision. The Yawing Moments of the gull wing with respect to the sideslip angle and the lift coefficient are determined. They show a significant level of yaw stability which strongly increases with the lift coefficient. It is particularly high in the lift coefficient region of best gliding flight conditions. In order to make the effect of sweep more perspicuous, a modification of the gull wing employing no sweep is considered for comparison. It turns out that the unswept wing yields Yawing Moments which are substantially smaller than those of the original gull wing with sweep. Another feature significant for the Yawing Moment characteristics concerns the fact that sweep is at the outer part of bird wings. By considering the underlying physical mechanism, it is shown that this feature is most important for the efficiency of wing sweep. To sum up, wing sweep provides a primary contribution to the Yawing Moments. It may be concluded that this is an essential reason why there is sweep in bird wings.
Mochammad Agoes Moelyadi - One of the best experts on this subject based on the ideXlab platform.
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Effect of slotted wing tips on Yawing Moment characteristics.
Journal of theoretical biology, 2005Co-Authors: Gottfried Sachs, Mochammad Agoes MoelyadiAbstract:The aerodynamic Yawing Moment characteristics of bird wings with slotted tips are dealt with. Emphasis is placed on the effect of sweep which the separated feathers constituting the wing tips show and which can reach significant values. Reference is made to basic aerodynamic characteristics of wings with sweep which yields a stabilizing Yawing Moment significantly larger than that of unswept wings. Then, the Yawing Moment characteristics are determined for a wing, the features of which are considered as representative of bird wings with sweep in their slotted tips. A sophisticated aerodynamic procedure is used for obtaining results of high precision. It is shown that the sweep in the slotted wing tips yields a stabilizing Yawing Moment of significant magnitude, considerably increasing with the lift coefficient. To make the significance of wing tip sweep for the ability to generate Yawing Moments more perspicuous, a wing modification the slotted tips of which are unswept is considered for comparison. It turns out that this wing shows Yawing Moments which are substantially smaller. A physical insight into the effect of slotted wing tip sweep on the aerodynamic Yawing Moment characteristics is provided by showing the underlying mechanism. From the results presented in this paper it follows that the sweep in slotted wing tips provides a substantial contribution to the aerodynamic Yawing Moment and, thus, to yaw stability. It may be concluded that this is an essential reason why there is sweep in the slotted tips of bird wings.
Brent R. Cobleigh - One of the best experts on this subject based on the ideXlab platform.
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Comparison of X-31 Flight and Ground-Based Yawing Moment Asymmetries at High Angles of Attack*
2016Co-Authors: Brent R. Cobleigh, Mark A. CroomAbstract:Significant Yawing Moment asymmetries were encountered during the high-angle-of-attack envelope expansion of the two X-31 aircraft. These asymmetries caused position saturations of the thrust-vectoring vanes and trailing-edge flaps during some stability-axis rolling maneuvers at high angles of attack. The two test aircraft had different asymmetry characteristics, and ship 2 has asymmetries that vary as a function of Reynolds number. Several aerodynamic modifications have been made to the X-31 forebody with the goal of minimizing the asymmetry. These modifications include adding transition strips on the forebody and noseboom, using two different length strakes, and increasing nose bluntness. Ultimately, a combination of forebody strakes, nose blunting, and noseboom transition strips reduced the Yawing Moment asymmetry enough to fully expand the high-angle-of-attack envelope. Analysis of the X-31 flight data is reviewed and compared to wind-tunnel and water-tunnel measurements. Several lessons learned are outlined regarding high-angle-of-attack configuration design and ground testing. NOMENCLATURE Cd cylinder drag coefficient Cn Yawing Moment coefficien
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comparison of x 31 flight and ground based Yawing Moment asymmetries at high angles of attack
2001Co-Authors: Brent R. Cobleigh, Mark A. CroomAbstract:Abstract : Significant Yawing Moment asymmetries were encountered during the high angle-of-attack envelope expansion of two X-31 aircraft. These asymmetries caused position saturations of the thrust-vectoring vanes and trailing-edge flaps during some stability-axis rolling maneuvers at high angles of attack. The two test aircraft had different asymmetry characteristics, and ship 2 has asymmetries that vary as a function of Reynolds number. Several aerodynamic modifications have been made to the X-31 forebody with the goal of minimizing the asymmetry. These modifications include adding transition strips on the forebody and noseboom, using two different length strakes, and increasing nose bluntness. Ultimately, a combination of forebody strakes, nose blunting, and noseboom transition strips reduced the Yawing Moment asymmetry enough to fully expand the high angle-of-attack envelope. Analysis of the X-31 flight data is reviewed and compared to wind tunnel and water tunnel measurements. Several lessons learned are outlined regarding high angle-of-attack configuration design and ground testing. (23 refs.)
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High-angle-of-attack Yawing Moment asymmetry of the X-31 aircraft from flight test
12th Applied Aerodynamics Conference, 1994Co-Authors: Brent R. CobleighAbstract:Significant Yawing Moment asymmetries were encountered during the high-angle-of-attack envelope expansion of the two X-31 aircraft. These asymmetries led to position saturations of the thrust vector vanes and trailing-edge flaps during some of the dynamic stability axis rolling maneuvers at high angles of attack. This slowed the high-angle-of-attack envelope expansion and resulted in maneuver restrictions. Several aerodynamic modifications were made to the X-31 forebody with the goal of minimizing the asymmetry. A method for determining the Yawing Moment asymmetry from flight data was developed and an analysis of the various configuration changes completed. The baseline aircraft were found to have significant asymmetries above 45 deg angle of attack with the largest asymmetry typically occurring around 60 deg angle of attack. Applying symmetrical boundary layer transition strips along the forebody sides increased the magnitude of the asymmetry and widened the angle-of-attack range over which the largest asymmetry acted. Installing longitudinal forebody strakes and rounding the sharp nose of the aircraft caused the Yawing Moment asymmetry magnitude to be reduced. The transition strips and strakes made the asymmetry characteristic of the aircraft more repeatable than the clean forebody configuration. Although no geometric differences between the aircraft were known, ship 2 consistently had larger Yawing Moment asymmetries than ship 1.
Jehanzeb Masud - One of the best experts on this subject based on the ideXlab platform.
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Aircraft spin characteristics with high-alpha Yawing Moment asymmetry
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering, 2017Co-Authors: Bilal Malik, Suhail Akhtar, Jehanzeb MasudAbstract:This paper analyzes the open-loop spin dynamics of a fighter configuration that exhibits Yawing Moment asymmetry at high angles of attack. High-fidelity aerodynamic model, in a look-up-tables form,...
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analysis of spin characteristics of a high performance aircraft with high alpha Yawing Moment asymmetry
AIAA Atmospheric Flight Mechanics Conference, 2016Co-Authors: Jehanzeb Masud, Bilal Malik, Suhail AkhtarAbstract:This paper presents methodology of spin analysis of a multirole fighter aircraft, in open loop configuration, having aerodynamic asymmetry in Yawing Moment at high angles of attack. High fidelity aerodynamic model is developed in the form of lookup tables from static, coning and oscillatory coning test data obtained from Rotary Balance wind tunnel tests. Steady spin modes are predicted by solving 3-DOF aircraft model in conjunction with developed aerodynamic model using Nelder-Mead Simplex Optimization Routine. The natural tendency of an aircraft to yaw to the right at high angles of attack has resulted in prediction of significantly higher number of right spins as compared to left spins. 6-DOF time history simulations performed from selected initial conditions of steady spins showed that flat spins, both right and left are oscillatory and unstable. Proposed spin recovery strategies using aerodynamic control surfaces are found to accelerate spin recovery of left flat spins. However right flat spins which span across the whole range of aileron and elevator deflections do not respond to attempted recovery actions.
Feng Liu - One of the best experts on this subject based on the ideXlab platform.
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Influence of Plasma Actuations on Forebody Side Forces and Wakes
2015Co-Authors: Zijie Zhao, Chao Gao, Feng Liu, Shijun LuoAbstract:The variation of the asymmetric force and vortex wake on a 20 ◦ circular-cone forebody with angle of attack from 35 ◦ to 70 ◦ at zero sideslip are investigated. A pair of plasma actuators is designed and placed near the apex of the forebody. The pressure distributions over the forebody are measured in a low-turbulence 3.0 m × 1.6 m low-speed open-circuit wind tunnel at freestream velocity 5 m/s and Reynolds number of 50, 000 based on the cone base diameter. The pressure data are used to calculate the side force distribution along the forebody axis and to infer the salient features of the separated flow over the forebody under three modes of controls: plasma-off, plasma port-on and plasma starboard-on. Effects of the plasma actuations on vortex wake and side force over the cone forebody at angle of attack upto 70 ◦ are identified. Nomenclature Cn = Yawing Moment coefficient about cone base, Yawing Moment/q∞SD Cp = pressure coefficient CY = overall side-force coefficient, overall side force/q∞S CY d = ensemble-averaged local side-force coefficient, local side force/q∞d D = base diameter of circular cone forebody d = local diameter of circular cone forebody F = frequency of a.c. voltage source L = length of circular cone forebody q ∞ = free-stream dynamic pressure Re = free-stream Reynolds number based on D U ∞ = free-stream velocity Vp−p = peak-to-peak voltage of a.c. voltage source w = input power of a.c. voltage source x = body-axis coordinate measured from apex to base α = angle of attack θ = meridian angle measured from windward generator, positive when clockwise I
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Flow over Delta Wing with Low Dorsal Fin-PIV Study
47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009Co-Authors: Xuanshi Meng, Zhide Qiao, Chao Gao, Feng LiuAbstract:A recent theoretical and experimental work done on the vortex flow over slender flatplate delta wing with low dorsal fin is reviewed, and a particle image velocimetry (PIV) study is conducted to further the investigation. The distributions of the vorticity component normal to the cross-flow planes show significant flow asymmetry and non-conicity over the wing-fin combination at a high angle of attack and enhance the validation of the theoretical prediction that adding a low dorsal fin to the wing may destabilize the symmetric and conical vortex pair. Ideals for further work are suggested. Nomenclature b = wing span c0 = wing root chord Cn = Yawing-Moment coefficient, Yawing Moment aboutZ-axis/q∞Sb hL = local height of dorsal fin K = Sychev similarity parameter, tan α/tan ǫ q∞ = free-stream dynamic pressure S = wing area s = local semi-span of wing U∞ = free-stream velocity v, w = cross-flow velocity components X, Y, Z = balance body axes, Fig. 4 x, y, z = body axes of the wing α = angle of attack ǫ = semi-apex angle of wing β = sideslip angle ωx = axial vorticity, ∂w/∂y ∂v/∂z
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Asymmetry Features Independent of Roll Angle for Slender Circular Cone
47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009Co-Authors: Chao Gao, Feng LiuAbstract:Based on a comprehensive low-speed pressure-measurement data for a cone of semi-apex angle 10 ◦ over whole roll angle range at high angles of attack up to 35 ◦ , the present paper shows that there exist asymmetry features which are independent of roll angle and, thus, applicable to models having the same geometry specifications. Verifications are made by comparing with available experimental data in literature. Mechanisms for the asymmetricforce features are identified. Nomenclature Cn = Yawing-Moment coefficient about cone base, Yawing Moment/q∞SD Cp = pressure coefficient CY d = local side force coefficient, local side force/q∞d CY 0 = overall side force coefficient, overall side force/q∞S D = base diameter of circular cone d = local diameter of circular cone L = length of circular cone q∞ = free-stream dynamic pressure Re = Reynolds number based on D � = angle of attack � = meridian angle measured from windward generator, positive when clockwise � = roll angle, positive when clockwise