Designing rudders with, on the one hand, a pivotably fixed front rudder part, and on the other a rear rudder part pivotably fixed in connection with the trailing edge of the front rudder part, is known in the art.

There are still problems with the known solutions, however, such as the fact that with these solutions it is not possible by turning the rudder to produce optimised rudder action flow conditions around the rudder parts irrespective of the turning direction, for which reason relatively large rudder volumes are required in order to obtain the intended rudder action.

An object of the present invention is to produce an arrangement of the aforementioned type, by means of which the volume and weight of the rudder can be reduced whilst retaining or improving the rudder characteristics. The object has been achieved by an arrangement having the characteristics specified in claim 1.

Preferred embodiments of the arrangement in addition have any one or more of the characteristics specified in the subordinate claims.

The arrangement according to the invention has numerous advantages: By means of this arrangement the fin volume/rudder volume and weight can be reduced in aircraft and watercraft. In the case of large transport aeroplanes the arrangement can be used, for example, on the vertical rudder in order to permit lower landing speeds. The arrangement may also be used in elevators on aircraft, in order to give increased aerodynamic lift and manoeuvrability at low speeds. In watercraft the arrangement may be used to give improved manoeuvrability.

The invention will be explained in more detail below with the aid of examples of embodiments of the present invention and with reference to drawings attached, in which: Fig. 1 shows a schematic diagram of a rudder according to the invention in a non- turned position.

Fig. 2 shows a schematic diagram of the arrangement according to figure 1 in a position turned in one direction indicated by solid lines and in a position turned in the other direction indicated by dashed lines.

Fig. 3a shows a schematic diagram giving a perspective view of one example of an embodiment of a mechanical system for obtaining the rudder characteristics according to the invention in a non-turned position.

Fig. 3b shows the mechanical system according to figure 3a in a turned position.

The same reference numbers are used for identical or similar parts in the description of all figures.

Figure 1 shows a rudder 1 in a non-turned position, the rudder being arranged at the trailing edge 3a of a wing-shaped structure 3 extending largely in one plane 2. The rudder 1 is capable of turning in either direction, as required, about the trailing edge 3a of the wing-shaped structure 3, in order to form angles with the plane 2. A front rudder part 4 is pivotably fixed to the trailing edge 3a of the wing-shaped structure 3.

Behind the front rudder part there is a separately and pivotably fixed rear rudder part 5, which narrows rearwards. The rudder parts 4,5 are operatively connected so that in the position shown they form a rudder surface in the same main plane as the wing- shaped structure and substantially continuous therewith, in that the front rudder part 4 is designed so that in this position trailing edges of its outer surfaces substantially connect with outer surfaces of the rear rudder part in connection with the leading edge of the rear rudder part 5.

The front rudder part 4 comprises two front rudder halves 4a, 4b, separately pivoted up against one another, which are either suspended and pivoted in bearing brackets on the leading wing-shaped structure 3 or suspended and pivoted in a bracket, which is pivotable in relation to the leading wing-shaped structure.

In the position shown there is a space between the rudder halves 4a, 4b, created by designing these with a cross-section narrowing towards their respective trailing edges. Outer surfaces of the rudder halves 4a, 4b are terminated at respective trailing edges, which trailing edges in the position shown substantially contact the outer surfaces of the rear rudder part 5, so that front and rear rudder halves 4,5 together form a substantially continuous rudder surface.

Figure 2 shows how turning the rudder according to figure 1 imparts both a backwards displacement, a so-called Fowler movement, to the rear rudder part 5 relative to the front rudder part 4, and a greater turning angle compared to the turning angle of the front rudder part 4, so that a flow gap 6 is formed between front and rear rudder part 4,5. Turning the rudder in the opposite direction is accomplished in a similar manner. Turning in the opposite direction is shown by dashed lines.

By turning the rudder 1 a reciprocal torsional movement has been imparted to both front rudder halves 4a, 4b by control elements (not shown), so that their trailing edges have been brought closer together at a distance from the leading edge of the rear rudder part 5. This has given the front rudder part 4 and the gap 6 a more optimal flow configuration compared to two-piece rudders hitherto known.

Mechanical cam link members actuated by means of control elements can be used as means, when turning the rudder 1, for imparting both a backwards displacement to the rear rudder part 5 relative to the front rudder part 4 and a greater turning angle compared to the turning angle of the front rudder part 4, as illustrated in figure 3.

Alternatively control elements, which act directly on each rudder part respectively may be used, such as electrically, hydraulically, pneumatically or otherwise actuatable servomotors (not shown).

The control elements are moreover designed in turning to impart a reciprocal turning movement to the rudder parts 4,5 with angular gear ratio designed for optimum flow, and to impart a backwards displacement to the rear rudder part 5, so that the gap 6 thereby formed assumes a flow-optimised gap width for each turning angle.

Figure 3a shows an example of how control of the turning and displacement movements of the rudder parts can be achieved by means of cam link members and articulated arms. In the unturned position shown here the rudder parts are situated in

the position illustrated in figure 1, in which the rudder parts 4,5 form a substantially continuous rudder surface in the same plane as the leading wing-shaped structure 3.

When turning into the turned position has been completed, as in figure 3b, the rear rudder part 5 has been displaced backwards whilst the trailing edges of the front rudder halves 4a, 4b have been brought closer to one another, producing the flow gap 6 between the rudder parts 4,5.

The fully formed flow gap 6 allows the flow to pass around the rudder parts 4,5 in such a way that the efficiency of the rudder is increased compared to two-part rudders hitherto known, in which the rear rudder part 5 is not shifted backwards when turning and in which the front rudder part 4 is not divided into two parts and in turning therefore retains its profile.

The construction and function of the aforementioned cam link member and articulated arm design will now be briefly described with reference to figures 3a and 3b.

The rudder halves 4a, 4b are pivoted about a shaft 7, which is fixed to the structure 3 by means of two arms 8, only one of which is visible in the figure. An articulated arm 9, which is pivoted on an arm 10, connected to the structure 3, about a shaft 11, is articulated at its one end to the rudder half 4a about a shaft 12, and at its other end is articulated to the rudder half 4b about a shaft 13. The connections of the articulated arm 9 to the rudder halves 4a, 4b are releasable in such a way that in turning in the direction shown in figure 3b results in release from the shaft 12; turning in the opposite direction implies release from the shaft 13.

The rudder part 5 has two pairs of bearing brackets 14a, 14b. An articulated arm 15 is pivotably locked in between the shaft 12 and a shaft 16, which passes through the bearing brackets 14a.

The person skilled in the art will understand that corresponding articulated arms, which are arranged laterally reversed in order to achieve upwards turning in the figure, are situated on the hidden side of the figure.

The function is as follows: When a compressive force is produced, for example by means of a cylinder-piston unit 17, between the structure 3 and the shaft 12, the locking here being released, the articulated arm 9 is turned about the shaft 11 at the end of the articulated arm 10.

The articulated arm 9 is fixed at its other and, that is at its attachment 13 to the rudder half 4b, which means that it is turned clockwise as a result of the compressive force from the cylinder-piston unit 17.

Because the length of the articulated arm 9 between the shafts 11 and 12 is greater than between the shafts 11 and 13, the shaft 13 will have a slower circular movement than the shaft 12, which results in the rear rudder part 5 moving downwards faster than the rudder half 4a. The rear rudder part 5 is, as stated, operatively connected to the articulated arm 9 by way of the articulated arm 15, but is also connected to the rudder half 4a by way of an articulated arm 18 and to the rudder half 4b by way of a link 19. As a result of the clockwise movement of the rudder part 5, the rudder half 4b is thereby forced by the articulated arm 18 to move upwards, that is counter to the rudder part 4a, whilst the gap 6 is opened It will be appreciated that movement in the opposite direction to that described above will require release at the shaft 13 and laterally reversed articulated arms on that side of the arrangement shown in figures 3a, 3b remote from the viewer.

It will be obvious to a person skilled in the art that the turning/displacement can be achieved in many alternative ways to that shown in figures 3a-3c. The reciprocal turning angles of the rudder parts 4 and 5 and the rearward displacement of the rear rudder part 5 can be accomplished, for example, by means of control elements designed to act directly on each rudder part. The said control elements may be manual or electrical, hydraulic, pneumatic or other suitable servomotors.