Yawing Moment Characteristics Research Articles

CFD Based Determination of Aerodynamic Effects on Birds with Extremely Large Dihedral

Using a sophisticated aerodynamic method, the effects of extremely large dihedral on the aerodynamic characteristics of birds are determined. With this method, it is possible to generate solutions for the addressed aerodynamic problem, which shows a high complexity due to interference effects caused by dihedral and pronounced 3-dimensional flow properties as well as due to complex wing geometries. From the obtained results it follows that extremely large dihedral has substantial effects on the aerodynamic force characteristics. There are significant changes in the lift, the drag and the side force, thus affecting the flight performance. Furthermore, the obtained results show that the aerodynamic rolling and yawing moment characteristics are influenced by extremely large dihedral to a high degree. This is a significant outcome for lateral-directional stability because the aerodynamic rolling and yawing moment characteristics have a determinative influence here.

Tail effects on yaw stability in birds

Bird tails, which are an aerodynamic surface in the horizontal plane, are treated with regard to their effects on yaw stability. Reference is made to wings of very small aspect ratio similar to the values of bird tails in order to identify features which are significant for the aerodynamic yawing moment characteristics due to sideslip. It is shown that there are yawing moments of considerable magnitude for this aspect ratio region. Furthermore, the lift coefficient, which also exerts an influence, is included in the treatment of yaw stability. To show more concretely the addressed effects for birds, the yawing moment characteristics of the wing–tail combination of a pigeon, which is considered as a representative example, are treated in detail. For this purpose, a sophisticated aerodynamic method capable to deal with the mutual flow interactions between the tail and the wing is used to compute results of high precision. The yawing moment characteristics of the pigeon wing–tail combination with respect to the sideslip angle and the lift coefficient are determined, with emphasis placed on the contribution of the tail. It is shown that there is a significant contribution of the tail to yaw stability. The findings of this paper on the contribution of the tail to the yawing moment characteristics are supported by an evaluation of existing experimental data. Furthermore, the physical mechanisms are considered which are the reasons for the stabilizing role of the tail. These effects concern the contribution of the drag acting at the tail to the yawing moment. In addition, it is shown that extended legs and feet, when exposed to the airflow, can contribute to yaw stability.

Effect of slotted wing tips on yawing moment characteristics

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.

Aerodynamic yawing moment characteristics of bird wings

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.

The side load distribution on a Rover 800 saloon car under crosswind conditions

Abstract The response of a car to windy conditions is governed by the aerodynamic yawing moment characteristics, which are conventionally determined from steady-state wind tunnel tests. While the overall loads acting on the vehicle can be determined, the contribution to the whole, from specific areas of the car is not apparent. The pressure distribution over the external surfaces of a full scale car has been measured and the results used to derive the distribution of side force and yawing moment components.

Effect of Reynolds number on the aerodynamic forces on a container model

The models and the two wind tunnels used to investigate the effect of wind on containers being transported on stanchion wagons are described. The results of the drag, side force, and lift measurements carried out from 0° to 90° yaw and for Reynolds numbers ranging from 1/6th to full-scale are presented and discussed. Rolling moment, pitching moment and yawing moment characteristics are briefly discussed.

Unsteady wind-tunnel interference in aircraft dynamic experiments

An analysis of existing oscillatory and rotary test data was undertaken to identify the origins of the observed wind-tunnel interference effects and interpret the aircraft aerodynamic characteristics. Logical arguments based on the limited experimental data point to the existence of interference flow mechanisms involving the coupling between unsteady flowfields near the model, the tunnel walls, and around the model support. Oscillatory crosscoupling derivatives measured on the standard dynamics model were significantly affected at low angles of attack while the nonlinear yawing moment characteristics of the HIRM 2 aircraft configuration at high incidence were masked completely in rotary tests performed in a small test section. Both of these very different problems may be attributed to unsteady wind-tunnel interference. Analytical corrections are not feasible at present, but experimental solutions can be implemented. Predictions of vehicle dynamics at high alpha based on dynamic wind-tunnel data can be affected by the interpretation given to the prevailing interference flow phenomena.

Fickle effect of nose microasymmetry on the high-alpha aerodynamics

Uose ?~~croasymmetry has been shown to determine the direction and magnitude of the large sideforce generated by a slender forebody at high angles of attack. It has also been shown that this force can cause the yawing moment characteristics of an advanced aircraft to vary between several highly nonlinear types, requiring extensive testing to define. The present paper shows that such extensive tests would he of little help, and that the coupling between vehicle motion and forebody flow separation, the so called moving-wall effect, will determine the characteristics in free flight.

Influence of Wing, Fuselage, and Tail Design on Rotational Flow Aerodynamics Beyond Maximum Lift

The NASA Langley Research Center has initiated a broad general aviation stall/spin research program. A rotary balance system was developed to support this effort. This system, located in the Langley spin tunnel, makes it possible to identify airplane aerodynamic characteristics in a rotational flow environment, and thereby permits prediction of spins. This paper presents a brief description of the experimental setup, testing technique, five model programs conducted to date, and an overview of the rotary balance results and their correlation with spin tunnel free-spinning model results. It is shown, for example, that there is a pronounced nonlinear dependency of the aerodynamic moments on rotational rate and that these moments are very configuration dependent. Fuselage shape, horizontal tail, and, in some instances, wing location are shown to appreciably influence the yawing moment characteristics above an angle of attack of 45 deg.

Influence of the Static and Dynamic Aerodynamic Characteristics on the Spinning Motion of Aircraft

Since the aerodynamics strongly influence the spinning motion to be experienced by an aircraft, a prerequisite for analytically computing the spin is an awareness of the aerodynamic characteristics of an aircraft throughout the stalled angle-of-attack region. Obtaining this aerodynamic information is a formidable task and in some instances is beyond the present state-of-the-art. It is important, therefore, that the aerodynamic characteristics which have a significant influence on the spin be identified, so that future research efforts can be directed towards accurately determining the important aerodynamic characteristics. Consequently, the roles that the static, damping, cross and acceleration aerodynamic derivatives play in the spin were established during an analytical study and are discussed in this paper. For instance, it was found that the yawing moment characteristics associated with the lateral control and the effective dihedral are the two most important aerodynamic parameters involved in the spinning phenomenon; whereas the aerodynamic acceleration derivatives and the cross derivative Cnp play an insignificant role. The information of this study can be also employed for identifying aerodynamic fixes that are most likely to act as antispin devices and for conceiving automatic control techniques for spin prevention or spin recovery.