Fiera or Le invention The present invention relates to an arrangement in a bar, which is intended to hang down beneath a helicopter or the like in order to carry equipment, such as saw equipment for tree lopping, which must be manoeuvred by the helicopter.

Background of the invention Helicopters are nowadays used for an ever-increasing number of operations that formerly could only be carried out from the ground. One such operation is to clear power line lanes, that is to saw off tree branches and the like that extend too close to a power line. This is done by means of saw equipment, which is mounted on a bar suspended from the helicopter, the bar carrying a number of saw blades, a motor for driving the blades and requisite transmission elements. The part of the bar that carries the saw blades may be 5 metres in length, for example, and may be connected to a carrier bar of approx. 15 metres, fixed in the helicopter.

Equipment of this type is described in the US patent specifications 4554781 and 4815263. In order to allow the helicopter to set the saw equipment down on stands on the ground, for example, the bars are provided with articulated joints. The bar according to US patent specification 4554781 is moreover designed with an angled part in order to prevent the helicopter interfering with the bar when setting down, see Figure 2.

In use, however, the bar hangs straight down beneath the helicopter so that the points of articulation remain situated essentially along a straight line between the bar that carries the saw blades and the fixing point in the helicopter.

This also applies to the arrangement according to the second US patent specification 4815263.

A safety problem with known arrangements of this type is that serious accidents can occur as a result of the bar suspended from the helicopter being forced upwards and in through the helicopter body. This may happen, for example, if the helicopter for any reason such as a temporary engine malfunction suddenly descends some metres in height, so that the bar carrying the saw blades strikes the ground or other solid underlying surface. The same effect can occur if the saw blades get caught when they are forced down through branches.

Object of the invention The main object of the present invention is to provide an arrangement in bars for mounting suspended working equipment on helicopters, which eliminates or substantially reduces the risk of accidents caused by the upper end of the suspension bar being forced upwards towards the helicopter.

The invention is based on the realisation that this can be achieved by designing the bar connected to the helicopter in such a way that compressive forces acting on the bottom end of the bar cannot be transmitted to the upper end of the bar connected to the helicopter.

The special characteristic of an arrangement of the type specified in the first paragraph is that the bar is designed so that if its bottom end is subjected to an upwardly directed compressive force, the said force is deflected or substantially attenuated before it reaches the upper end of the bar connected to the helicopter, so that no upwardly directed force of harmful magnitude strikes the helicopter.

A temporary engine malfunction or the like, which may cause the helicopter to suddenly descend a number of metres so that the bar strikes against the ground will therefore not result in the bar being forced upwards and into the helicopter.

One way of achieving this result is to design the bar with an articulated knee joint, which in the working position is situated to the side of a line extending between the bottom and upper ends of the bar, connected to the working equipment and the helicopter respectively. Such a design of the bar means that the compressive force, which acts on the bottom end of the bar, will cause the bar to swivel about the articulated knee joint, which is thereby forced out laterally without transmitting any significant force to that part of the bar situated above it.

According to an especially preferred embodiment the bar connected to the helicopter is designed in the form of at least two tubes telescopically displaceable in relation to one another. In the working position the tubes are fully extended and cannot rotate relative to one another. The tubes can, however, be pushed together by exerting a force at the end of the lower tube. This force will therefore not be transmitted to the fixing in the helicopter.

Further characteristic features of the invention will be evident from the claims below.

The invention will be described in more detail below with reference to the embodiments shown by way of example on the drawings attached.

Brief description of the figures Fig. 1 shows a helicopter with saw equipment for clearing power line lanes and the like.

Fig. 2 shows the fixing arrangement in the helicopter on a larger scale.

Fig. 3 shows an embodiment of the bar connected to the helicopter with the bar telescoped.

Fig. 4 shows the bar according to Fig. 3 fully extended.

Fig. 5 shows an alternative embodiment of the bar connected to the helicopter.

Fig. 6 and 7 show the bar according to Fig. 5 in a position in which its bottom end is subjected to an upwardly directed compressive force.

Fig. 8 shows the bar according to Fig. 5 telescoped.

Detailed description of preferred embodiments Figure 1 shows a helicopter 1 with equipment for clearing power line lanes or the like suspended therefrom. The said equipment comprises a number of saw blades 3 mounted along a boom 2, the saw blades being driven from a combustion engine 4 by way of transmission elements arranged in the boom. The saw equipment may be of conventional rigid type and is connected by way of an articulated joint 6 to a bar 5 suspended in the helicopter 1. In the embodiment shown the bar 5 is designed in the form of two telescopic tubes 7 and 8, displaceable in relation to one another, which may be made of aluminium and have a total length of approximately 15 metres. The upper tube, in this case the inner tube 7, is connected to an upper mounting plate 9 with an eye or hook 10 for mounting on the helicopter, see Figure 3.

As will be more clearly seen from Figure 2, the plate 9 is provided with two torque arms 11 pivoted to the plate, the other ends of which arms are connected to

the two helicopter landing skids, each by way of a ball-and-socket joint 30. The arms 11 absorb torsional movements of the plate 9 and the tube 7, which must not be capable of rotating relative to the helicopter.

Figure 3 shows the bar 5 on a larger scale, parts of the outer tube 8 and the inner tube 7 having been cut away to show the construction more clearly. The bar 5 is intended to be suspended in the helicopter by way of the mounting eye 10, whilst the saw equipment is intended to be pivotally fitted to the bar 5 by means of an articulated shaft 6 at its bottom end. A link 31 may be arranged between the bar 5 and the helicopter, see Figure 2.

The inner tube 7 is connected so that it cannot rotate to the mounting plate 9, which is in turn coupled so that it cannot rotate via the torque arms 11 to the helicopter. The articulated shaft 6 is arranged in a lower coupling part 12, fixed so that it cannot rotate in the outer tube 8, which coupling part projects out through the bottom end of the tube 8. A fibre casing 13, which slides against the outer surface of the tube 7 when the outer tube 8 is displaced relative to the inner tube 7, is fixed in the upper part of the outer tube. 14 and 15 denote two steel casings arranged around the inner tube 7, which in the fully extended position of the outer tube 8, see Figure 4, go into the machined seats (not shown) on the inner surface of the fibre casing 13. In this position the inner and outer tubes 7,8 are held precisely positioned in relation to one another without any mutual play. 16 denotes a split plastic ring, which slides against the inside of the outer tube when this is extended in relation to the inner tube 7.

The bottom edge section of the fibre casing 13 is designed with a number of recesses 17, in this case 4 recesses, having wedge-shaped lateral surfaces and a

rounded top. The steel casing 15 is designed with at least one, preferably two engaging elements 18 of corresponding shape projecting towards the outer tube.

When the outer tube 8 is extended the recesses 17 will take on the function of the seats, which receive the wedge-shaped projections 18, see Figure 4, and stop the extension of the outer tube 8. The fibre casing 13 and the outer tube 8 will thereby be securely locked so that they cannot rotate to the inner tube 7 and thus also to the plate 9.

The use of the wedge-shaped or triangular seats 17 and projections 18 facilitates telescoping of the telescopic tubes 8 and 7 once a work operation is completed. This can otherwise be difficult if the helicopter has been turned somewhat, so that a torsional force prevails between the outer tube and the inner tube, which locks them relative to one another and makes any axial displacement of the outer tube 8 relative to the inner tube 7 more difficult. With the wedge-shaped engaging surfaces of the seat 17 and the interacting projection 18, such a torsional force provides a component in an axial direction, which facilitates telescoping of the telescopic tubes.

As can be seen from Figure 4, the suspension eye 10 is connected to a piston rod 19 running through the mounting plate 9, the piston rod being connected to a piston 20, which runs in a housing 21. The piston is depressed towards its lower limit position by means of a compression spring 22. The housing 21 is suitably oil-filled, the piston 20 being provided with overflow elements, which allow the oil with a certain resistance to pass from the chamber above the piston 20 to a chamber below the piston 20, when the latter is drawn upwards as a result of a large, instantaneous tensile force in the eye 10. This provides a damping function, the purpose of which will be described in more detail below.

The arrangement described above is used as follows.

In the starting position the saw equipment 2,3,4 and the telescopic bar 5 pivotally fixed thereto are lying on the ground. A lifting hook 32 situated on the helicopter 1 is then pivotally coupled to the lifting eye 10, for example by way of a link 31, following which the torque arms 11 are fixed to the helicopter landing skids by means of the ball-and-socket joints 30, so that the telescopic bar 5 can only swing backwards and forwards in one direction relative to the helicopter 1. When the helicopter then lifts off, the telescopic tube 5 will be swung upwards in relation to the boom 2 with the saw blades 3 remaining on the ground. When using previously known bars of fixed length the helicopter, in order to avoid the saw equipment being dragged along the ground, must ascend in such a way that the lifting eye 10 describes a circular arc with its centre at the point of articulation 6. The pilot has therefore hitherto generally endeavoured to generate a slight pressure against the suspension bar. However, it is difficult to judge this pressure precisely, for which reason there is a risk that the bar will be snapped by the load.

When using a telescopic bar 5 the pilot does not need to generate any such pressure and any deviation by the suspension eye 10 from the circular arc movement will be compensated for by extension or telescoping of the tubes 7 and 8 relative to one another. It is therefore advisable to start the lifting operation with the tube 8 half extended.

When the helicopter has reached a height such that the saw equipment is also lifted clear of the ground, the weight of the latter will pull the outer tube 8 down into its lower limit position shown in Figure 4. The

outer tube, which is connected so that it cannot rotate to the boom 2 carrying the saw blades 3, is thereby automatically locked in the desired rotational position relative to the inner tube 7, so that the blades 3 are located on the correct side of the boom 2 for the intended direction of cutting. This means that the blades 3 must be facing, that is to say situated between the boom 2 and the trunk of the tree, the branches of which are to be sawn off.

Because the bar 5 is telescopic, the outer tube 8 will be pushed up on the inner tube 7 at the occurrence of a compressive force at the bottom end of the saw equipment. This can occur if the helicopter, as a result of temporary engine malfunction, for example, descends towards the ground so that the saw equipment strikes the ground. A similar risk can also arise if the saw blades 3 get caught in the branches of a tree and the helicopter suddenly loses height. With the arrangement described this will merely result in the outer tube being pushed upwards to a corresponding extent on the inner tube. The risk of the helicopter and its crew being damaged or injured as a result of the suspension tube being pushed into the helicopter in such an event are thus eliminated or greatly reduced.

As the saw blades must be situated on the right side of the boom 2 in relation to the tree trunk, there is a need to be able to turn the saw equipment through 180° relative to the suspension bar 5. This need arises, for example, when clearing in sharply sloping terrain, where the helicopter cannot saw down a slope with a steep incline, since the tail section is thereby at risk of coming into contact with the ground. With previous equipment it has therefore been necessary to use extension bars, so that the saw equipment is suspended at greater distance beneath the helicopter.

Alternatively the saw equipment has had to be set down on the ground and disconnected from the helicopter

before turning it through 180° and suspending it in the helicopter again.

Using the arrangement according to the invention described above, the helicopter pilot, in order to perform such a rotation, merely has to lower the saw equipment so that the lower part rests on the ground and then lower the helicopter by at least a further 7 cm, so that the triangular engaging element 18 is released from the associated seat 17. The pilot can then turn the helicopter through 180° and lift the equipment from the ground. The engaging element 18 will thereby interact with a seat 17 situated on the opposite side of the fibre casing 13 and again rotationally lock the outer tube 8 in the new position relative to the inner tube 7. The desired number of adjustment positions between the outer and inner tube 8,7 can be obtained as a function of the number of seats 17 and/or engaging elements 18.

The function of the damping arrangement described above, comprising the spring 22, the piston 20 and the housing 21, is to reduce the stresses acting on both the suspension hook 32 in the helicopter 1 and on the saw equipment if the telescopic bar 5 is extended too rapidly. Such rapid extension may occur, for example, if the bar is unintentionally telescoped by contact with thick branches of a tree and then released again.

Figure 5 shows an alternative embodiment of the suspension bar 5. In this case the bar comprises two bars 23 and 24 pivoted to one another, of which the bar 23 is intended to be pivotally fixed in the helicopter and the bar 24 to be pivotally fixed in the boom 2, which carries the saw blades 3. At their opposing ends, each bar is provided with an angled section 25, which sections at their outer ends are pivoted to one another by means of a joint pin 26. In the working position the weight of the saw equipment produces a

tensile force in the bars 23 and 24, which holds these in the position shown in Figure 5, the angled section 25 of the bottom bar resting on a stop heel 33, which projects from the angled section of the upper bar.

If the helicopter should suddenly lose height, so that the saw equipment rests against the ground and a compressive force occurs on the bottom end of the bar 24, the bars 23 and 24, see Figures 6 and 7, will be swivelled relative to one another about the axis of articulation 26, since this is situated to the side of a line connecting the outer ends of the bars 23 and 24, see Figure 5. The compressive force occurring at the bottom end of the bar 24 will therefore result in folding of the complete bar 23,24 about the axis of articulation 26, and any harmful compressive force will not be transmitted to the suspension hook 32 of the helicopter.

The bar shown in Figures 5-7 can even be folded up to half its original length, as illustrated in Figure 8.

The invention has been described above with reference to embodiments shown by way of example in the drawings attached. As the person skilled in the art will readily appreciate, however, these can also be varied in several respects within the scope of the claims whilst retaining the intended function of eliminating the risk of harmful compressive forces acting on the helicopter as a result of working equipment, for example, coming into contact with the ground. The telescopic bar shown may be modified, for example, so that the outer tube is connected to the mounting plate and the inner tube to the saw equipment. Furthermore, the positions of the stop elements and corresponding seats may also be reversed.