A device for yaw steering of aircraft

The present invention relates to a device for yaw control of an aircraft with a slender nose at high angle of attack and speeds especially up to Mach 0.5. The nose can be pointed or more or less rounded. In the flight of such aircraft, such as airplanes and guided missiles, with high angle of attack, that is, angle between the longitudi­nal symmetry axis of the aircraft and the existing wind vector, in the range of 20° - 80°, most notably 35° - 70°, a problem arises in controlling the aircraft in yaw, that is, to impose upon the aircraft a controlling yaw moment about an axis at right angles to its longitudinal sym­metry axis in its plane of symmetry. The reason is that the body and supporting surfaces of the aircraft increas­ingly with increasing angles of attack are located be­tween the wind vector and the active control surfaces of the aircraft, that is, the rudder. Under these conditions, even a large rudder angle δ_r will become more or less in­effective. Especially for modern fighter airplanes with a large requirement for maneuverability there has been pre­sented for a long time a great need for a controllable steering means effective even at large angles of attack. The object of the invention is thus to provide a simple, reliable device for yaw control of an aircraft with a slender nose at high angles of attack and speeds especi­ally up to Mach 0.5. Such a device is characterized ac­cording to the invention in that ports are arranged at both sides of the nose portion of the aircraft, separated from the mentioned plane of symmetry, which ports are so arranged, in controllably variable positions on both sides of the nose portion that at least one port on one side, communicated for flow with at least one port on the other side, produces such an asymmetrical departure of body nose air vortices from the sides that by reason of the pressure difference between the sides thus arising a con­trollable yaw moment is obtained. In one embodiment of the invention the ports are arranged with continuously controllably variable positions. This can be obtained if, for example the ports are arranged in a part of the nose portion that is rotatable about an axis parallel with the longitudinal axis of symmetry of the nose portion. This can be most simply carried out if the nose portion in the immediate vicinity has a circular cross-section. In and of itself the cross-section need not be circular in order for a part of the nose portion to be rotatable or the ports movable, but that provides the simplest construction.

In an alternative embodiment the ports are arranged with stepwise controllably variable positions, for example, by having several ports arranged in each of the two sides of the nose portion, selectably connectable with one an­other. In this the ports in one side of the nose portion are connected with the ports in the other side by means of passages provided with controllable closure means such as flaps. The ports themselves can take various forms, but circular ports or ports in the form of elongated slots, with their longitudinal axis parallel to the longitudinal axis of the nose portion, would seem to be suitable. It is suitable to provide the ports with controllable closures, so that the drag during flight at high speeds is eliminated by keeping the ports closed in such flying to the extent that the device according to the invention need not be made use of for active yaw control.

The invention is more particularly described with ref­erence to the accompanying drawings, wherein:

• Fig. 1 shows the relationship between rudder effect and angle of attack α;
• Fig. 2 shows the relationship between yaw moment co­efficient and attack coefficient:

  • -a effect of rudder,
  • -b effect of device according to the invention;

• Fig. 3 is a cross-section of a device according to the invention;
• Fig. 4 is a side view of a device according to the invention;
• Figs. 5 and 6 are cross-section views of the device according to the invention, in operation;
• Figs. 7a and 7b show an alternative device according to the invention partly without active controlling effect and partly active with controlled effect;
• Fig. 8 shows the device of Figs. 7a and 7b seen from the side;
• Fig. 9 shows a further alternative device according to the invention, seen in cross-section;
• Fig. 10 shows the device of Fig. 9, seen from the side; and
• Fig. 11 shows the relationship between the yawing moment coefficient C_n and the angle of attack α with the employment of a device according to the invention.

In Fig. 1 is shown how the rudder effect for an air­craft, in this case an airplne with a fin 1 provided with a rudder 2, varies with increasing angle of attack α. In the figure the range 35° -70° is marked. Within that range occur unctrolled flow conditions about a slender nose on an aircraft which make themselves known by asymmetrical dis­charge of air vortices from both sides of the nose portion, spaced from the plane of symmetry. In the diagram the rud­der effect is given by , which is defined as the de­ rivative of C_n with respect to δ_r, that is, the slope of a curve in a diagram C_n as a function of δ_r. C_n is the yawing moment coefficient and is defined as "yaw moment (moment about an axis at right angles to the axis of long­itudinal symmetry of the aircraft in its plane of symmetry)/­dynamic pressure x wind area x wing span." As appears from the figure, the rudder effect, even at α = 40° is very weak, and over 60° has totally ceased. In Fig. 2 is illustrated, by curve a, how the yawing moment Cn produced by a rudder diminishes with increasing α, and by curve b the values of C_n that can be produced with a device according to the invention for angles of attack in the range of 35° to about 70°. The device, the effect of which is shown in Fig. 2, is shown in cross-section in Fig. 3 and from the side in Fig. 4. An aircraft's nose portion is designated by 3 and its plane of symmetry by 4. In the nose portion 3 two ports 5, 6 are arranged symmetrically in a part 7 which is rotat­able in relation to the rest of the nose portion around its longitudinal axis of symmetry. The cross-section of the nose portion is circular at this part.

The ports 5 and 6 are connected by a passage 8 that admits a flow of air. The prevailing wind vector is desig­nated by 9. In Fig. 3 the device according to the invention occupies a neutral position, which means that it does not exert any active controlling force beyond its effect of equalizing possible stochastically arising asymmetric flow conditions that arise within the range α = 20° - 80°, most notably 35° - 70°, which is marked in Fig. 1. If, however, the device is turned as in Fig. 5, there is active­ly produced an asymmetrical flow relationship around the nose portion 3, so that through the asymmetry of the dis­charge of air vortices 10 and 11 from the nose portion 3, a side force 12 arises which produces a controlling yaw moment. In Fig. 6 is shown how a corresponding right-hand rotation of the device according to the invention produces corresponding asymmetrical air vortices 13, 14 and a side force 15 arising therefrom that has an opposite direction compared with the side force 12. In Fig. 11 is shown, in the upper half of the diagram, the yaw moment that is pro­duced by the mention left-hand rotation of the device, as a function of the angle of attack α, and in the lower half of the diagram the corresponding effect of a right-hand ro­tation of the device.

The device shown in Fig. 3 and 4 is continuously rotat­able, which means that a desired yaw moment for a certain angle of attack can be obtained through a corresponding ro­tation of the device about its longitudinal axis.

In Figs. 7a, 7b and 8 is shown an alternative embodi­ ment of a device according to the invention particularly for stepwise controllable variation of the positions of the parts. The illustrated arrangement presents two ports 16, 18 in one side of the nose portion and two ports 17, 19 in its other side. Ports 16 and 17 are connected with one another by means of a straight passage 20, which is arranged at right angles to the longitudinal axis of sym­metry of the nose portion. From the port 18 a passage 21 leads inward to the center of the nose portion and connects with the passage 20. At the connection there is arranged a controllable flap means 22. In a corresponding manner a passage 23 leads to a connection location in the passage 20, with a controllable flap means 24 arranged in the con­nection location. As can be understood from the figure, the flap means 22, 23 can be selectably set so that con­nection is obtained between the ports 16, 17 (neutral posi­tion), 18, 17 (left-hand turning) or 16, 19 (right-hand turning). Through this positioning of the device there is brought about such asymmetry in the discharge of air vor­tices from the nose portion that controlling yaw moments to the left or right are obtained.

In Figs. 9 and 10 is shown a further embodiment of a device according to the invention for stepwise controllable variation of the positions of the ports. In one side of the nose portion are arranged three ports 25, 27, 29, and in the other side three ports 26, 28, 30. The ports are connected in pairs by straight passages 31, 32 and 33, so that the ports 25, 26 are connected by the passage 31, the ports 27, 28 by the passage 32, and ports 29, 30 by the passage 33.

In the passages are arranged controllable shut-off flaps, of which only the shut-off flap 34 in the passage 33 is shown. By controlling the shut-off flaps there is obtained the desired asymmetry in the discharge of air vortices through which the desired controlling yaw moment is obtained.