It is a known problem that birds may fly into the engines of aircraft, which may lead to considerable damage to the interior of the engines, in particular to the rotor blades. This may cause the engine to completely or partially cease to function, with all the associated consequences.

In the prior art, it is known to protect the engines by positioning a grate, which is formed for example by a mesh, in front of the air inlet. The drawback of a solution of this nature is that the incoming flow of air is impeded, resulting in a loss of power and making the engines less economical. Owing to the additional costs which this entails, it has not hitherto proven economical to use protective installations of this nature in practice.

The object of the present invention is to provide a device which protects the engines against birds but on the other hand does not have the drawback of impairing the performance of the engines to an unacceptable degree.

This object is achieved by the fact that the protection according to the present invention is characterized in that the engine according to the present invention comprises a device with elements which can move between a first, inactive position, in which the air inlet is substantially open, and a second, active position, in which elements form a protection in front of the inlet opening.

The advantage of this device compared to the known devices is that the protection may optionally be used or unused. If the protection is not required, for example because the aircraft is flying at a great height, the protection can be folded away. As a result, the incoming flow of air is no longer impeded, and the aircraft can fly economically.

By contrast, during take-off and landing, there is a relatively high risk of birds flying into the engines. Also, the consequences of an engine not functioning correctly are relatively dangerous in particular at low heights. Therefore, the protection will be used primarily during take-off and landing. When the aircraft has climbed to a greater height, the risk of collision with birds has decreased considerably. Moreover,

the consequences of an engine which is not functioning correctly can often be dealt with more easily at such heights. Since the protection is in the inactive position throughout most of the flight, the consumption by the engines is normal throughout almost the entire flight, and the additional fuel costs are kept relatively low.

To allow the protective elements to be folded away easily, it is preferable for them to be attached at one end to a positioning device which is able to move the elements between the active and inactive positions. It has proved advantageous for the elements to be shaped in such a way that, by being rotated at their fixed end, they can be moved between the active and inactive positions. By providing the elements or parts which are connected thereto with a fork, it is possible to transmit the rotation thereby.

For their part, the forks can be actuated by pins which are connected to an actuating body. In this way, a plurality of elements can be moved simultaneously and in a simple way.

To obtain a good level of relatively uniform protection for the engine, depending on the shape of the engine, it may be desirable for the elements to be of different shapes and lengths. This very much depends on the shape of the engine and the size of the birds against which the engine needs to be protected. In a preferred embodiment, the elements are shaped as substantially elongate, curved, aerodynamically shaped bars, which will be referred to in the present invention as whalebones.

To make the device as robust as possible and to prevent components of this device entering the engine, for example as a result of an installation or construction fault, it is preferable for substantially all the components of the positioning device to be positively locked together. This means that the movement of most of the components is limited since they are enclosed by the shape of other components. It is preferable for the elements to be spring-mounted and/or themselves to be highly resilient. This makes it possible to prevent the impact of a collision from damaging the elements and also the positioning devices themselves excessively.

It is important that collisions with birds be detected. This is because if a collision has occurred, there is a risk that the bird will be stuck to the protection. If the protection is then retracted, it is still possible for the bird to enter the engine. Therefore, in such an event, it is best to leave the protection in the active position. It is therefore

preferable for the device and/or the elements to be provided with a detection device for detecting collision between an object and the guard device.

In one embodiment, the elements, in the active position, extend substantially radially with respect to the shaft of the engine. To cause the minimum possible disruption to the aerodynamics of the engines when the elements are in the inactive position, it is preferable for the elements, in the inactive position, to extend substantially tangentially with respect to the shaft of the engine. It may be desirable for the elements, in the inactive position, also to extend substantially parallel to the circumference of the engine.

In a preferred embodiment, the actuating body extends substantially in a plane, which is at right angles to the shaft of the engine, parallel to the circumference of the said engine. This ensures that all the elements can be moved simultaneously by means of one actuating body. This limits the number of components required for the protective device.

It is preferable for the positioning device to be situated substantially in the front edge of the engine. The front edge means that part of the outer wall which adjoins the front side of the said engine. Furthermore, for the aerodynamics it is advantageous for the elements, in the inactive position, to drop into a recess in the front edge. It may be expedient for the elements to be covered in the inactive position, in order to improve the aerodynamics still further.

To enable the impact of the birds to be absorbed successfully, it is preferable for the elements, in the active position, to form a point extending forwards from the engine. As a result, the birds will tend to graze past the protection, with the result that the forces on the elements are reduced. This also has the advantage that it will be less easy for the birds to stick to the protection, with the result that there is less obstruction to the incoming flow of air. If the point is made to extend forwards from the front edge and substantially adjoin the outer wall of the engine, there is an increased likelihood of the bird sliding off the protection.

It will be clear that it must be possible for the protection to be actuated from the aircraft. Therefore, it is preferable if the positioning device can be controlled from the cabin of the aircraft by means of a communications system. Since it is safer, following a collision with a bird, for the protection where the collision has taken place

not to be folded away, it is preferable for the device for detecting collisions to emit a signal to an indicator in the cabin of the aircraft.

In the following text, an embodiment of the invention will be explained in more detail with reference to a number of drawings, in which: Figure 1 shows an aircraft which is provided with engines having the protection; Figure 2 shows a front view of an engine from Figure 1; Figure 3 shows a partially cut-away side view of this engine; and Figure 4 shows an enlarged view of the positioning device.

Description of the figures Figure 1 shows an aircraft 1, which is provided with engines 2 according to the present invention. In the illustrated position of the whalebones 3, the protection 4 extends across the entire air inlet, so that it is impossible for any birds 4 to fly into the engines during take-off and landing. When the aircraft is flying at a high altitude, and consequently there is a relatively low risk of collision, the protection can be folded away.

Figure 2 shows a front view of one of the engines 2, in which the protective device 4 is once again covering the entire inlet opening. The shape and position of the whalebones is selected in such a way that a grate is formed which blocks birds of a defined minimum size. In the present embodiment, the device 3 comprises curved whalebones 5 which extend substantially radially outwards in the drawing. The whalebones 3 are of different lengths, so that they do not get in the way of one another in the centre. It can also be seen that whalebones 3 of equal lengths would unnecessarily block the flow of air in the centre, since the protection as in the embodiment shown is already sufficiently fine-meshed.

The embodiment shown is particularly suitable for engines which are circular in cross section. For engines with a different cross section, it may be desirable to use a design specifically for that shape.

Figure 3 shows how the whalebones 3 are connected to the engine via the positioning devices 5, see also Figure 4. The positoning device 5 is accommodated in a recess 6 in the front edge 7 of the engine. Since the whalebones, in the inactive position, are likewise accommodated in the recess 6, the geometry of the engine, and therefore its aerodynamic properties, are not affected.

By rotating the whalebones about the axis of rotation R, they can be rotated out of their radial position shown into a substantially tangential position. If the recess 6 is closed successfully, the entire protective device has no adverse effect on the general aerodynamic properties of the engine 2.

As shown in Figure 4, the whalebones 3 are mounted by means of a rotary element 8, in order to enable rotation from the substantially radial position shown in Figure 2 into a tangential position.

It can be seen in Figure 4 that the whalebones are provided with a fork 9 which engages on a pin 10 which is attached to an actuating body 11. The actuating body may, for example, be an annular body which coordinates the movement of all the whalebones, so that they can be moved simultaneously.

The spring element 12 is provided in order to absorb the impact of a collision with a bird, so that the load imposed on the whalebones 3 is reduced. In the embodiment shown, it can be seen that the positioning device 6 does not comprise any loose components and that all the components are positively locked together. This has the advantage that the device requires less maintenance and that components will not easily become detached in the event of assembly or construction faults.

Since the whalebones 3 are curved, in the folded-in position they substantially follow the contour of the outer wall of the engine 2, with the result that they can be accommodated in the recess 6. By covering the opening 13, it is possible to cover up the whalebones and the positioning device, so that the aerodynamic properties of the engine are not affected.