IN CASE THE AIRCRAFT MUST LAND IN WATER

The present invention relates to a new construction of a false keel as given in the introduction of the subsequent claim 1. In particular, we aim at providing a false keel device to control the movements of an aircraft in waves, when it lands at sea, or on inland waters.

With the invention we wish to be able to preclude and prevent a helicopter, which must make an emergency landing at sea, from overturning or capsizing as a consequence of the influence of rough sea and wind.

Furthermore, the invention shall be explained with reference to use on an aircraft such as a helicopter that has emergency landed at sea, in order to prevent overturning as a consequence of waves coming in from the front and/or the sides. Today, there are no solutions that prevent a helicopter from capsizing after an emergency landing at sea. Normally helicopters have built-in floating pontoons that are blown up when they come into contact with the sea, so that the helicopter does not sink.

For example, the helicopter types that are used to bring personnel to and from offshore installations have two engines, and are constructed so that they are able to land approximately in a controlled fashion, even with little or no power to the rotors. However, the most critical situation arises after the helicopter has made an emergency landing. If there is rough sea /waves and/or wind of a certain velocity, there is a great danger that the helicopter may flip over and capsize. This is due to the engine and the rotor being placed high up in the helicopter construction, something which gives the helicopter a high point of gravity. At a certain wave height and wind force the helicopter will flip over in spite of the floating pontoons around the hull being released. Several studies have shown that a large proportion of those who work offshore are anxious and afraid during the transport between land and their own installation. The fear is mainly unfounded, as the number of accidents per flying hours is low. Still, large accidents associated with helicopters connected with traffic related to the petroleum operations occur regularly. Therefore, it is required for all offshore workers to have attended and passed a basic safety course before they are cleared for work offshore, and can then be brought to and fro by helicopter. This is a course in ISO 60, with emphasis on training and exercises where one shall make one's way out of a helicopter that is turned upside down in the water, when strapped down and wearing a survival suit. Many experience this as uncomfortable, and the oil worker's trade unions have gained acceptance for those attending a repetition course every fourth year not needing to attend this training if they do not want to. Both illnesses and psychological traumas have been demonstrated to be a consequence of this course alone.

To capsize in the sea is naturally enough of a terror scenario for the offshore workers to rightly fear. There is a wide understanding that only a few people would act rationally and correctly in spite of having been trained for situations like this in a reservoir under essentially different conditions than those one will experience in a real situation.

Safety and working environment have high priority in the offshore industry. Every year considerable sums are used to increase safety. Much focus is given to the safety related to the helicopter trips to and from the North Sea. Both the oil companies and the offshore companies are interested in finding solutions that can contribute to the transport of personnel to and from the different installations becoming even safer. The same goes for the manufacturers of the helicopters. It is an aim of this invention to provide a device that can stabilise an aircraft that has landed on the sea as a consequence of an emergency situation. Furthermore it is an aim to provide a stabilising device that is based on a lightweight frame construction, which can be installed in both the new aircrafts that are being built in factories, and on aircrafts that are already in use. The device according to the invention is characterised in that the undercarriage of the aircraft comprises a keel surface, where said keel surface is a foldable sheet of cloth that can be reset between a passive folded position in the undercarriage of the aircraft, and an unfolded use position dropped down into the sea. According to a preferred embodiment, the keel surface/cloth sheet is coupled to a pole- formed body which, by swinging between a storage position in the undercarriage of the aircraft and a position dropped down into the sea, can reset the sheet to the unfolded use position dropped down into the sea. According to a preferred embodiment the device comprises two mutually parallel pole bodies that can swing, each with their associated cloth sheet to be extended, and the pole bodies are mutually connected with a cross strut.

It is particularly preferred that the two poles are hinged so that they can rotate, and are mounted in the undercarriage of the aircraft, to be rotated about a common axis X-X for the guiding of the keel surfaces between a storing position and a use position.

According to a yet another preferred embodiment, the four ends of the poles comprise weight elements to stabilise their dropped down position in the sea.

According to yet another preferred embodiment, it is important that the cloth sheets, when in an extended position, have the shape of a circular sector, and the two cloths are mutually folded with spacers fastened between the cloths at a mutual distance apart, and adjoining the periphery of the free arch periphery of the cloths. According to yet another preferred embodiment, each cloth sheet has a shape and surface as a circular sector, fastened with one of its straight sides to a frame part in the undercarriage, while the other straight side is fastened along the rail, whereby the construction has the form of, and functions corresponding to, a Chinese fan.

According to yet another preferred embodiment, fastened to the lower part of the pair of poles is a trap body of perforated or holed cloth material, or a net material, for flow-through of water to and from the inner volume defined by the trap, as the trap is held extended by a number of rigid rings that are fastened inside the trap bag with a given distance between each ring, and the bottom part of the trap alternatively comprises a weighting body to hold the trap in the correct position in the sea.

In particular, it is preferred that the trap is rotary connected to the pair of poles, so that it can swing about an axis Y-Y, and can be stored in a cassette together with the upper false keel part in connectionwith the underside of the vessel. The hinge joint can, in particular, comprise a locking device that "clicks" into place when the construction is completely unfolded, so that the false keel is locked and held in a use position.

The invention shall be explained in more detail in the following with reference to the enclosed figures, in which: Figure 1 shows a helicopter that has landed at sea and floats on the surface.

Figure 2 shows the device according to the invention dropped down into the sea underneath the helicopter and acting to dampen its movements in the sea. Figure 3 shows the device dropped down into the sea corresponding to the situation in figure 2, but seen from below at an angle.

Figure 4 shows a side outline of the device in the undercarriage of the helicopter in an intermediate position where it is partially dropped down.

Figure 5 shows the same as figure 4, seen from above at an angle. Figure 6 shows a next intermediate step in the dropping down, where the second element that can drop down is about to be rotated downward.

As an introduction, reference is made to figure 1, which shows a helicopter 10 that has landed on the sea 14 and floats on the surface of the water 12. The arch shape of the surface indicates a swell or wave in the sea that the helicopter follows with its movements.

The helicopter 12 comprises a main rotor 11, a stabilising rotor 13, and an undercarriage 16 with a set of landing wheels 17, and comprises a built-in cassette 20 in which the keel construction (figure 2) is stored with a movement-dampening keel surface that is dropped down and acts to dampen the movements of the helicopter.

A cross section of the movement-dampening keel surface in the construction is shown schematically, in particular in figure 3, with reference also given to the vertical outline in figure 2.

Two longitudinally running frame beams 30 and 32, respectively, are mounted mutually spaced apart on the undercarriage of the helicopter 10, i.e. longitudinally running with respect to the longitudinal direction of the helicopter. They define schematically the cassette 20 in which the device is fitted.

A longitudinal running rail 34 (or side member in an assembled construction) is hinged about an axis 38 (also given as X-X) in the front edge of the frame beam 30, in order to enable the rail to be reset from an inserted horizontal position in the cassette (figure 1) to an

approximately vertical position (figure 2) in the sea 14. A keel sheet of a cloth or canvas 40 with a shape and surface like a circular sector is fastened at its one straight side 41 (with radius extension) to the upper frame beam, while the other straight side 43 is fastened along the rail 34. Along the free arch-formed sector circle 46, the cloth is reinforced with a double fold 47. At the free end of the rail, at its lower edge, a weight element 48 is arranged in the form of a weight, which ensures that the rail is standing/hanging stably in the sea in the dropped down position as shown in figure 2. In the storing position the keel cloth sheet is folded together inside the cassette 20 between the frame beam 30 and the rail 34. When the rail is dropped down, the cloth is extended into a relatively taught, flat, vertical cloth sheet. The function of the construction corresponds to that of a Chinese fan.

According to the invention, a corresponding parallel construction is arranged off a rail 36 that can be dropped down, and a cloth sheet 42 in the cassette 20 in the undercarriage of the helicopter, with the same dimensions as the one mentioned above, and such that they are placed at a mutual distance apart. The main plane of the two preferably vertically are generally arranged cloth sheets that lies in the longitudinal direction of the helicopter, so that they, as best as possible, can take up and dampen the movements from waves that come, mainly, in towards the helicopter from the sides.

The two rails 34 and 36 are mutually folded together at the lower end via a common cross strut 49. Furthermore, the two parallel rails 34, 36 can be folded together with cross struts (not shown in the figure) corresponding to the cross strut 49. These struts can be of a suitable plastic material. With the side members 34 and 36 and cross struts 49 the construction has the same shape as a ladder. Water can flow freely in and out of the gaps in the cloth between the cross struts 49.

Furthermore, the two cloth sheets 40 and 42, respectively, are mutually folded together via a number of spacer rods 50 with an approximately same width as the distance between the rail members 34,36. This contributes to retaining the parallel positioning between the two circle sector-shaped cloth sheets, and their flat shape used as stabilising elements. The poles 50 are preferably arranged mutually spaced apart over a short distance adjoining the periphery of the free arch periphery of the cloths, indicated by 51, so that the cloth sheets 40,42 are held stably in the sea without uncontrolled flapping when the helicopter moves.

The whole construction of side-members and cloth is thereby well held up to dampen the movements of the helicopter, in particular lurching, in the sea as a consequence of the influence of waves and the wind. The side-members 34,36 are lightweight, extruded profiles of a light metal, such as aluminium or titanium, with a low weight and high breaking strength, or they can also be from another lightweight composite material or hard plastic. Both the cross struts 49 and the spacers between the cloths can be made from plastic, aluminium, or hard plastic. The cloth can be a common canvas or from plastic corresponding to the materials that are used in sails and tents.

To prevent the construction from swinging about the upper hinged joint X-X when the helicopter lurches as the sea comes in from the front, the hinged joint can further comprise a locking device that "clicks" into place when the construction is completely dropped and swung down. This means for example that the two side-members, when they have reached the down position, glide into a barbed construction where a pawl latch glides over the side- member and from which they cannot be pulled out. Thereby, the false keel is locked and held in this position.

To provide a further stabilisation of the aircraft (the helicopter) the construction comprises an extra element of a trap that is fastened to the underside of the construction, and which offers an increased resistance against lurching movements.

A trap has a form of a sack of a perforated/holed cloth or net material that is kept extended by a number of rigid rings that are fastened inside the trap bag with a given distance between each ring. These rings can be made from plastic or metal. The trap according to the invention is shown by 60 in the figures. The trap can be rectangular as shown in the figures, or it can be in the shape of a cone. The rings, indicated in general by the number 68 in the figures, have a gradually decreasing diameter from the bottom 62 of the trap and to the uppermost 64 where they are fastened to the lower end of the side-member pair 34,36 by a hinge via the same cross piece 49 which is at the bottom of the pair of side-members. With such a decreasing diameter of the rings 68, they can be inserted into each other with the cloth/net folded together in a very space saving way, in the passive storing position of the system inside the cassette 20 in the undercarriage of the helicopter. The figure shows that the rings 68 are covered by a cloth having a number of holes/openings 70. When the trap is dropped down, as shown in figure 6, to the position in figure 2, the rings 68 fall down and extend the cloth/net for the formation of an internal trap body that is filled with water. The water will then flow freely in and out of the trap via the holes so that the inertia of the system and thereby the dampening of the movements of the false keel are increased considerably. A weight 74 (for example, of lead) can be fitted optionally at the bottom of the trap 60 to ensure that the trap will quickly fall down into its vertical position and also retain this perpendicular position in the sea. Furthermore, it is preferred that the trap has a rectangular shape as shown in the figures, rather than said cone shape. Rectangular surfaces will offer better movement dampening in the sea, and more optimally break the movements in the sea.

When this lower form of the trap is fitted, the two elements will together strongly increase the dampening of lurching of the helicopter. As mentioned, the trap is folded together in the passive position so that it takes up the smallest volume possible in height and breadth when is packed down. The rings can be square or rings of two different sizes that go into each other alternate times. Or squares/rings that gradually go down in size so that they together do not take up more vertical space than what a single ring/square does on its own. The material that is used in the trap is a "dead" material that will build up as little as possible when the trap is folded. The material can be fastened to the squares/rings by double-sided sewing or the like.

The weight of the rings/squares is adjusted so that they provide just enough downward pull to sufficiently stabilise both cloths 40 and 42, respectively. The trap 70 is connected to the bottom part of the cross-members via the shaft 49 by a hinge, and is not released (dropped down) from the cassette 20 before it is filled with water and the side-members are folded out 34,36. The folding out and folding in of the construction are analogous to the movements of an accordion or Chinese fan as indicated in figure 5. The solution is comprised of two parallel rectangular struts 34 and 36, respectively, in titanium/aluminium or a similar material of a low weight and high breaking strength, which is integrated with and fastened via a hinge under the body of the aircraft at the front and which extends backwards under the main part of the body of the aircraft. Over the struts where they are integrated under the body of the aircraft lie lamellas in layers with armoured and reinforced carbon fibre cloth 40 or a similar material which has a low weight and high breaking strength, that is "folded " out and down when the struts are released at the rear edge. According to an alternative solution the trap can be comprised of an extended box with the same external dimensions as those shown in the figures. The box can be a telescopic construction with a number of part boxes, with one gliding into the next, and as extended reaches its full length when the construction is flipped down into the sea under the helicopter.

Thereby, a construction is provided that has a rigidity that allows it to function according to its objective, and is light weight so that it does not significantly contribute to a weight increase of the helicopter. A cassette with in-built poles, a cloth sheet and trap that can be dropped down, hidden inside the undercarriage of the helicopter, does not need to weight more than about 50 kg. The dimensioning of the elements of the construction depends of course on the size of the helicopter it will be adapted to.

The construction is such that it will primarily be released automatically when the helicopter lands on the sea, but it can also happen manually. Such a false keel is intended to be used once only. But if the helicopter is not damaged in any way or can be rescued and brought in for repair, the construction can of course be assembled and packed into the cassette to be used again if an emergency landing in the sea should occur. However, normally one must dismantle the old one and replace it with a new one if the helicopter can be repaired and put back into operation.