GB2466307A

GB2466307A - A net comprising a net body and a plurality of lifting loops formed from at least two materials

Info

Publication number: GB2466307A
Application number: GB0823313A
Authority: GB
Inventors: Stephen Mark Trafford; Mohammed Amir Khan; Timothy David Pollock; Michael Ian Andrewartha
Original assignee: Amsafe Bridport Ltd
Current assignee: Amsafe Bridport Ltd
Priority date: 2008-12-22
Filing date: 2008-12-22
Publication date: 2010-06-23
Also published as: WO2010073033A1; GB0823313D0

Abstract

A net (2, 30) comprising a net body (4, 32) and a plurality of lifting loops (16, 38), wherein the net (2, 30) is formed from at least two materials differing in their relative properties.

Description

Lifting Net The present invention relates to a lifting net, particularly, but not exclusively, to a helicopter under-slung load equipment (HUSLE) net.

Lifting nets are a broad classification of nets which can be used to lift an object, or objects.

Typically the object(s) are placed on the centre of the net and the net material is gathered around the object(s) to provide a sling which enables the object(s) to be lifted.

HUSLE nets are a particular form of lifting net which are used for transporting goods by helicopter, either when there is no room in the helicopter for the goods, or when for reasons of speed or efficiency it is preferred to keep the goods outside of the helicopter. HUSLE nets have been around for a number of years and are particularly favoured by the military for the movement of supplies and equipment into areas of conflict or natural disaster. HUSLE nets generally consist of a braided nylon net body and a plurality of lifting loops made from nylon webbing. The net body is generally square or octagonal in shape. The material used for the net body is generally a flat, hollow nylon braid and the material used for the lifting loops is generally flat nylon webbing. Each net generally has four pairs of lifting loops and each pair of lifting loops is provided with a hook. The net is also provided with a stirrup, which is attached to one of the hooks on one of the pairs of lifting loops. In use of the net it is laid out flat and a load is placed on the centre of the net body. The hooks on the lifting loops are then collected together and the remaining hooks are attached to the stirrup. The stirrup is then attached to a suitable attachment point on the underside of a helicopter.

Lifting nets and HUSLE nets have been used satisfactorily for a number of years. The object of the present invention is to overcome some of the problems associated with them, or at least to offer an alternative to them.

According to the present invention there is provided a net comprising a net body and a plurality of lifting loops, wherein the net is formed from at least two materials differing in their physical properties. As noted above, it is known to manufacture HUSLE nets with a net body made from nylon braid and lifting loops made from nylon webbing. Although the net body and the lifting loops in the prior art may have different physical properties this is down to the way in which the nylon is treated, i.e. braided or formed into webbing. The actual material, e.g. Nylon 66, is the same and therefore the prior art nets can be regarded as being constructed from a single material. Nets according to the present invention are formed from at least two materials which themselves have different physical properties, regardless of how they are treated, i.e. whether they are braided or formed into webbing. It is envisaged that in a net according to the present invention the two materials could be braided or formed into webbing, or treated in any other way as is known in the art.

A net constructed according to the present invention has the advantage that the different materials can be incorporated into different areas of the net to provide particular properties where they are required. This is particularly desirable where a material has useful properties but there are reasons why it would not be desirable or practical to use that material to construct the whole of the net.

In an embodiment of the invention the net is formed from a combination of materials differing in their relative strengths. A net constructed in this manner may incorporate a stronger material, i.e. one which has a relatively higher maximum load at break, in areas of the net which will experience higher loading, or be exposed to higher wear, during use of the net.

Such higher strength materials may, for example, be more expensive than the relatively weaker material and it may therefore not be desirable to construct the complete net from the stronger material. A net according to the present invention may be designed such that the relatively stronger material takes a proportionately larger portion of the load during use of the net and the relatively weaker material is more responsible for defining the shape of the net and ensuring that it is able to perform its basic function. This can lead to a net which will have a longer lifespan and will be less likely to require repair.

In an embodiment of the invention the net is formed from a combination of materials differing in their relative elongation at break. A net constructed in this manner may incorporate a low elongation material, i.e. one which has a relatively lower elongation at break, in areas of the net which will experience higher loading during use of the net. Such low elongation materials may, for example, be more expensive than the relatively higher elongation material and it may therefore not be desirable to construct the complete net from the low elongation material. A net according to the present invention may be designed such that the relatively lower elongation material takes a proportionately larger portion of the load during use of the net.

In an embodiment of the invention the net is formed from a combination of materials which differ in their weight. The combinations envisaged include a relatively light weight/low strength material with a relatively heavier/stronger material and a relatively light weight/high strength material with a relatively heavier/weaker material. Such combinations enable nets to be designed to suit their intended use. It is also possible to utilise various combinations of materials to improve the overall weight, lifespan and/or cost of the net as appropriate.

In an embodiment of the invention a first one of the two materials is selected from the group comprising: nylon; polyester; and polyethylene.

In an embodiment of the invention a second one of the two materials is selected from the group comprising: ultra-high molecular weight polyethylene; and an aramid.

In an embodiment of the invention the net is formed from a combination of nylon and a high tenacity polymer. In an embodiment of the invention the net is formed from a combination of nylon and an ultra-high molecular weight polyethylene (UHMWPE). The UHMWPE has the advantage of being lighter than nylon and having a higher strength to weight ratio.

Advantageously, the UHMWPE may be Dyneema� or Spectra�. Various combinations of nylon and UHMWPE are envisaged, as will be described in more detail in relation to the figures.

In an embodiment of the invention the net is formed from a combination of nylon and an aramid. Aramids have the advantage of being lighter than nylon and having a higher strength to weight ratio. Advantageously, the selected aramid is Kevlar�. Various combinations of nylon and aramids are envisaged, as will be described in more detail in relation to the figures.

In an embodiment of the invention at least a minimum footprint area of the net body is formed from a different material to the remainder of the net body. The footprint area of the net is the area at the centre of the net body onto which the load is placed. In an embodiment of the invention the footprint area of the net, and in particular the maximum loading area, is marked on the body of the net. In an embodiment of the invention the maximum loading footprint of the net body is formed from a different material to the remainder of the net body.

By utilising a different material for at least a minimum footprint area it is possible to, for example, increase the strength of the net body in this region. By selecting appropriate materials to be used in this area it will be possible to reduce the overall weight of the net and to increase the lifespan of the net.

In an embodiment of the invention the net body is formed from a different material to the lifting loops. By utilising a different material for the net body it is possible to, for example, use a lighter and/or stronger material for the net body. It is also possible to select materials which will increase the lifespan of the net.

In an embodiment of the invention the net body comprises at least two adjacent rows of net mesh which differ in their relative properties. In an embodiment of the invention the net body comprises alternating rows of net mesh which differ in their relative properties. It is possible to design nets which incorporate specific materials in the areas where they are most needed. It has been found that nets which incorporate alternating sections of different materials can be particularly effective in sharing loads, while offering advantages in terms of weight reduction, durability and cost effectiveness.

In an embodiment of the invention a border cord of the net is formed from a different material to the net body. A border cord of the net is a cord of net material which runs around the perimeter of the net body. This area of the net may experience increased wear during normal use of the net and it is also the part of the net to which the lifting loops attach. By utilising a different material for a border cord it is possible to, for example, increase the strength of the net in this region. This can reduce the damage caused to the net by wear during use and will increase the lifespan of the net and/or reduce the likelihood of damage occurring to the net. By selecting appropriate materials to be used in this area it is also possible to reduce the overall weight of the net.

In an embodiment of the invention at least one row of outer net mesh of the net body, i.e. a row of net mesh adjacent to the border cord, is formed from a different material to the remainder of the net body. In an embodiment of the invention at least two rows of outer net mesh of the net body are formed from a different material to the remainder of the net body.

The outer rows of net mesh may be subjected to greater loads during use of the net and by selection of appropriate materials it may be possible to increase the lifespan of the net.

In an embodiment of the invention the lifting loops are formed from a different material to the net body. The lifting loops may experience increased loading and increased wear during normal use of the net. By utilising a different material for the lifting loops it is possible to, for example, increase the strength of the net in this region. This can reduce the damage caused to the net by wear during use and will increase the lifespan of the net and/or reduce the likelihood of damage occurring to the net. By selecting appropriate materials to be used in this area it is also possible to reduce the overall weight of the net.

In an embodiment of the invention the net body is square. In an embodiment of the invention the net body is octagonal.

For a better understanding of the present invention reference will be made to the accompanying drawings in which: Fig. 1 shows a plan view of a first embodiment of the present invention; Fig. 2 shows a plan view of a second embodiment of the present invention; Fig. 3 shows a plan view of a third embodiment of the present invention; and Fig. 4 shows a plan view of a fourth embodiment of the present invention.

The present invention relates to lifting nets in general, but is described in relation to helicopter lifting nets known as helicopter underslung load equipment (HUSLE) nets. The nets illustrated in Figs. 1-4 show different features of the present invention. It is envisaged that a net according to the present invention may incorporate one or more of the features illustrated and described. In addition, as will be discussed in more detail below, Figs. 1 and 3 illustrate nets with a square net body and Figs. 2 and 4 illustrate nets with a octagonal net body. Unless otherwise stated the features described can be incorporated into both square and octagonal nets.

Figs. 1 and 2 show the two most common configurations of HUSLE nets. The net in Fig. 1 has a square net body and the net in Fig. 2 has an octagonal net body. The basic construction of the square and octagonal HUSLE nets will be described with reference to Figs. 1 and 2, but Figs. 3 and 4 also show a square and octagonal net respectively. Although these shapes are the most common form of HUSLE nets the present invention is not limited to such shapes and could apply equally to other shapes of net, e.g. rectangular, as will be readily appreciated by the skilled person.

Turning now to Fig. 1, this shows a HUSLE net 2 with a square net body 4. The net body 4 is defined by a plurality of interconnecting net strands 6 which are formed from a flat, hollow nylon braid. The intersections 8 between the net strands 6 are in the form of knotless intersections, as is well known in the art of net making. A border cord 10 is provided around the perimeter of the net body 4. The border cord 10 is a single strand of flat, hollow nylon braid, but it could also comprise multiple strands of braid. The net body 4 is square and on each of two opposing edges 12, 14 there are provided two pairs of lifting loops 16. The lifting loops 16 are formed from a flat nylon webbing. The webbing is wrapped around the border cord 10 at each end and then stitched together to define the lifting loops 16. The webbing of each of the pair of lifting loops 16 passes through an aperture in a hook 18, which serves to secure the pair of lifting loops 16 together. In total there are four pairs of lifting loops 16 and each is provided with its own hook 18. One of the hooks 1 8a is further attached to a stirrup 20. As will be described in more detail below, the stirrup is attached to a helicopter in use of the HUSLE net 2.

In the centre of the net body 4 there is a square central panel 22 formed from a braided material which has different physical properties to the remainder of the nylon net body 4.

The net material in the central panel 22 is constructed in the same manner as the remainder of the net body, e.g. interconnecting net strands formed with knotless intersections, and the net material is spliced into the remainder of the net body as is well known in the art. The central panel is known as the net footprint, as it represents the area of the net onto which a load may be built up for transportation. Since it comes into contact with the load and it is also the part of the net which comes into contact with the ground during landing, the net footprint is generally subject to a higher degree of wear than the remainder of the net body. For this reason it is desirable to incorporate a stronger, higher tenacity material into the net footprint in order to increase the lifespan of the net and make it less susceptible to damage through normal usage. The central panel 22 may advantageously be formed from an ultra-high molecular weight polyethylene (UHMWPE), such as Dyneema� or Spectra�. Other materials with a high strength to weight ratio, e.g. aramids such as Kevlar�, are also favoured as suitable materials for use in the central panel. Materials such as Dyneema�, Spectra� and Kevlar� also tend to be much lighter than nylon of a similar strength, so they can help to reduce the total weight of the net 2, which is desirable in terms of a reduction in transportation costs. The central panel may represent the maximum loading footprint of the net 2, i.e. the maximum area onto which a load may be built up. The central panel 22 is shown as square panel, but it will be appreciated that it may be octagonal, rectangular, or any other shape to suit the particular net 2.

The use of the HUSLE net 2 is fairly straightforward and is the same for both the square net shown in Figs. 1 and 3 and the octagonal nets shown in Figs. 2 and 4. The use of the net will be described in relation to the net of Fig. 1, but it will be understood that it applies equally to all of the nets according to the present invention. HUSLE nets can be used to transport military vehicles and are therefore suitable for carrying loads up to 7000kg.

Firstly, the net 2 is laid out on the ground, much as shown in Fig. 1. Next, the load to be carried is placed in the middle of the net, i.e. on the central panel 22 or "footprint". In some cases the net 2 will be provided with markings to indicate the maximum loading permitted for the net 2, both in terms of size and weight. Once the load has been put in position the four hooks 18 are gathered together and attached to the stirrup 20, which is provided on one of the pairs of lifting loops 16. The stirrup 20 is then attached to the helicopter and the load is ready to be lifted.

Turning now to Fig. 2, this shows a plan view of a second embodiment of a net 30 according to the present invention. As discussed above, the net is a HUSLE net with an octagonal net body 32. The net body 32 is defined by a plurality of interconnecting net strands 34 which are formed from a braid. The intersections 36 between the net strands 34 are in the form of knotless intersections, as is well known in the art of net making. A border cord 37 is provided around the perimeter of the net body 32.

The net body 32 is a regular octagon and pairs of lifting loops 38 are provided on alternating edges of the net body 32. The lifting loops 38 are formed from a flat nylon webbing and the webbing is attached to the border cord 37 at each end to define the lifting loops 38. The webbing of each of the pair of lifting loops 38 passes through an aperture in a hook 40, which serves to secure the pair of lifting loops 38 together. In total there are four pairs of lifting loops 38 and each is provided with its own hook 40. One of the hooks 40a is further attached to a stirrup 42. As discussed above in relation to Fig. 1, the stirrup is attached to a helicopter in use of the HUSLE net 30.

The net body 32 is formed from a combination of rows of net mesh formed of flat, hollow nylon braid 44 and rows of net mesh formed from a braided material 46 which has different physical properties to the nylon braid ("the other material"). The net strands are spliced together as is well known in the art. The net body 32 is constructed symmetrically with three rows of nylon braid 44 running across a central axis (A-A) of the net 30. Either side of the three central rows of nylon braid 44 there is provided a single row of net mesh formed from the other material 46. There is then one further row of net mesh formed from nylon braid 44 and the remainder of the net body 32 is formed from the other material 46. This construction ensures that the net mesh at the locations where the lifting loops 38 attach are formed from the other material 46. It is believed that the net meshes in these areas are subjected to proportionateley larger forces when the net 30 is lifted. It is therefore possible to design a net which is reinforced in these areas with a material which is better able to deal with the higher forces exerted. This can have benefits in terms of reducing wear on the net 30 and extending the lifespan of the net 30.

The net 30 may advantageously be formed from a combination of nylon and an ultra-high molecular weight polyethylene (UHMWPE), such as Dyneema� or Spectra�. Other materials with a high strength to weight ratio, e.g. aramids such as Kevlar�, are also favoured as suitable materials for use as the other material 46. Materials such as Dyneema�, Spectra� and Kevlar� also tend to be much lighter than nylon of a similar strength, so they can help to reduce the total weight of the net 30, which is desirable in terms of a reduction in transportation costs.

The combination of nylon braid 44 and UHMWPE braid 46 simply illustrates one possible construction of the net 30. It is envisaged that a wide variety of combinations are possible within the scope of the present invention. It is envisaged that alternating rows of nylon and another material could offer many of the benefits of the other material, without incurring the high costs which may otherwise be associated with a net which was made totally from, for example, Dyneema�. Ultimately, the construction of the net 30 will depend on its end use, but it is envisaged that high tenacity braid, such as UHMWPE or aramid braid, can advantageously be incorporated into any part of the net 30 which experiences high loading or high abrasion during use of the net.

Fig. 3 shows a third embodiment of a net according to the present invention. As discussed above, Fig. 3 shows a HUSLE net 2 with a square net body and, as such, it is constructed in much the same way as the net of Fig. 1 and like parts will be numbered the same.

The net body 4 is defined by a plurality of interconnecting net strands 6 which are formed from a braided material. The intersections 8 between the net strands 6 are in the form of knotless intersections, as is well known in the art of net making. A border cord 10 is provided around the perimeter of the net body 4. The net body 4 is square and on each of two opposing edges 12, 14 there are provided two pairs of lifting loops 16. The lifting loops 16 are formed from a flat nylon webbing. The webbing is attached to the border cord 10 at each end to define the lifting loops 16. The webbing of each of the pair of lifting loops 16 passes through an aperture in a hook 18, which serves to secure the pair of lifting loops 16 together.

In total there are four pairs of lifting loops 16 and each is provided with its own hook 18. One of the hooks 18a is further attached to a stirrup 20. As discussed above in relation to Fig. 1, the stirrup is attached to a helicopter in use of the HUSLE net 2.

The border cord 10 is formed from a high-tenacity polymer braid, such as UHMWPE. The net body 4 is formed from a combination of rows of net mesh formed of nylon braid 24 and rows of net mesh formed of a braided material 26 which has different physical properties to the nylon braid 24 ("the other material 26"). The net strands of the net mesh are spliced together as is well known in the art. The net body 4 is constructed symmetrically with a central row of nylon braid 24 running across a central axis (B-B) of the net 2. Either side of the central row of nylon braid 24 there is provided a single row of net mesh formed from the other material 26. There is then a repeating pattern of two rows of net mesh formed from nylon braid 24 and one row of net mesh formed from the other material 26. This construction ensures that the net mesh at the locations where the lifting loops 16 attach are formed from the other material 26. It is believed that the net meshes in these areas are subjected to proportionateley larger forces when the net 32 is lifted. It is therefore possible to design a net which is reinforced in these areas with a material which is better able to deal with the higher forces exerted. This can have benefits in terms of reducing wear on the net 2 and extending the lifespan of the net 2. When a force is exerted on the lifting loops 16 during lifting of the net 2 it is transmitted along the net mesh of the other material 26. This means that most of the load is taken up by the other material 26 and the nylon braid 24 is more responsible for defining the shape of the net 2. It is therefore possible to use a lighter weight nylon braid, which can help to reduce the overall weight of the net 2 without reducing the strength of the net 2.

The net 2 may advantageously be formed from a combination of nylon and an ultra-high molecular weight polyethylene (UHMWPE), such as Dyneema� or Spectra�. Other materials with a high strength to weight ratio, e.g. aramids such as Kevlar�, are also favoured as suitable materials for use in the central panel. Materials such as Dyneema�, Spectra� and Kevlar� also tend to be much lighter than nylon of a similar strength, so they can help to reduce the total weight of the net 2, which is desirable in terms of a reduction in transportation costs.

As with Fig. 2, the particular combination of nylon braid 24 and UHMWPE braid 26 simply illustrates one possible construction of the net 2. It is envisaged that a wide variety of combinations are possible within the scope of the present invention. It is envisaged that alternating rows of nylon and another material could offer many of the benefits of the other material, without incurring the high costs which may otherwise be associated with a net which was made totally from, for example, Dyneema�. Ultimately, the construction of the net 2 will depend on its end use, but it is envisaged that high tenacity braid, such as UHMWPE or aramid braid, can advantageously be incorporated into any part of the net 2 which experiences high loading or high abrasion during use of the net. Advantageously, the UHMWPE, or similar high tenacity material, may be incorporated into the net meshes which are associated with the lifting loops 16. In this way a major portion of the load transmitted to the net 2 can be taken up by this material.

Turning now to Fig. 4, this shows a fourth embodiment of a net according to the present invention. As discussed above, Fig. 4 shows a HUSLE net 30 with an octagonal net body 32 and, as such, it is constructed in much the same way as the net of Fig. 2 and like parts will be numbered the same.

The net body 32 is defined by a plurality of interconnecting net strands 34 which are formed from a braided material. The intersections 36 between the net strands 34 are in the form of knotless intersections, as is well known in the art of net making. A border cord 37 is provided around the perimeter of the net body 32.

The net body 32 is a regular octagon and pairs of lifting loops 38 are provided on alternating edges of the net body 32. The lifting loops 38 are formed from a flat webbing and the webbing is attached to the border cord 37 at each end to define the lifting loops 38. The webbing of each of the pair of lifting loops 38 passes through an aperture in a hook 40, which serves to secure the pair of lifting loops 38 together. In total there are four pairs of lifting loops 38 and each is provided with its own hook 40. One of the hooks 40a is further attached to a stirrup 42. As discussed above in relation to Fig. 1, the stirrup is attached to a helicopter in use of the HUSLE net 30.

The majority of the net body 32 is formed from a flat, hollow nylon braid. However, the two outer rows of net mesh 33 are formed from a braided material which has different physical properties to the nylon braid. The net strands of the net mesh are spliced together as is well known in the art. In addition, the border cord 37 is formed from the same material as the outer two rows of net mesh 33. The lifting loops 38 are also formed from flat webbing which has different physical properties to the nylon braid which forms the majority of the net body 32. The border cord 37, the outer two rows of net mesh 33 and the lifting loops 38 may advantageously be formed from an ultra-high molecular weight polyethylene (UHMWPE), such as Dyneema� or Spectra�. Other materials with a high strength to weight ratio, e.g. aramids such as Kevlar�, are also favoured as suitable materials for use in the border cord 37, the outer two rows of net mesh 33 and the lifting loops 38. Materials such as Dyneema�, Spectra� and Kevlar� also tend to be much lighter than nylon of a similar strength, so they can help to reduce the total weight of the net 30, which is desirable in terms of a reduction in transportation costs.

The marginal regions of the net, such as the outer regions of the net body 32 and the lifting loops 38, are often subjected to higher loads and the use of high tenacity materials in these regions may help to prolong the life of the net 30.

The embodiments of the invention illustrated in Figs. 1-4 are by way of example only and it will be clear to the skilled person that many variations are possible within the scope of the invention defined by the claims.

Claims

Claims 1. A net comprising a net body and a plurality of lifting loops, wherein the net is formed from at least two materials differing in their relative properties.
2. A net according to claim 1, wherein the net is formed from a combination of materials differing in their relative strengths.
3. A net according to claim 1 or claim 2, wherein the net is formed from a combination of materials differing in their relative elongation at break.
4. A net according to any preceding claim, wherein a first one of the two materials is selected from the group comprising: nylon; polyester; and polyethylene.
5. A net according to any preceding claim, wherein a second one of the two materials is selected from the group comprising: ultra-high molecular weight polyethylene; and an aramid.
6. A net according to any preceding claim, wherein at least a minimum footprint area of the net body is formed from a different material to the remainder of the net body.
7. A net according to claim 6, wherein a maximum footprint area of the net body is formed from the different material.
8. A net according to any one of claims 1-5, wherein the net body is formed from a different material to the lifting loops.
9. A net according to any one of claims 1-5, wherein the net body comprises at least two adjacent rows of net mesh which differ in their relative properties.
10. A net according to claim 9, wherein the net body comprises alternating rows of net mesh which differ in their relative properties.
11. A net according to any preceding claim, wherein a border cord is formed from a different material to the net body.
12. A net according to any preceding claim, wherein at least one row of outer net mesh of the net body is formed from a different material to the remainder of the net body.
13. A net according to claim 12, wherein at least two rows of outer net mesh of the net body are formed from a different material to the remainder of the net body.
14. A net according to any preceding claim, wherein the lifting loops are formed from a different material to the net body.
15. A net according to any preceding claim, wherein the net body is square.
16. A net according to any preceding claim, wherein the net body is octagonal.
17. A net substantially as hereinbefore described with reference to the accompanying drawings.