A conventional design of cargo barrier for the restraint of cargo on the main deck of a freighter or combi aircraft comprises a net attached to attachment points on the interior structure of the aircraft. However, this type of design can often be compromised by restrictive radial load limits set by the airframe manufacturer and applied to the attachment points on the aircraft structure. This problem is aggravated when the maximum permissible longitudinal distension of the net is low, as a net that has a lower distension at higher loads results in greater radial loading at the attachment points. In addition, the location of the attachments provided by the airframe manufacturer may not necessarily be in the best positions for a symmetrical and efficient net design.

A common alternative to the use of a net barrier is the use of a rigid barrier, or bulkhead. Such a barrier will restrain the movement of cargo without being significantly distended or causing high radial loading of the attachment points. However, rigid barriers are heavier, more expensive and lack the operational flexibility of a net.

According to the present invention, a cargo barrier in or for installation in an aircraft comprises a peripheral frame structure of rigid material and a cargo restraining net, the frame structure being, in the aircraft, attached to attachment points on the interior structure of the aircraft and the net being attached to attachment points on the frame structure, the frame structure and net, in use, forming a barrier across an interior space of the aircraft in order to restrain longitudinal movement of cargo within the aircraft.

The combination of net and rigid frame structure barrier disclosed in the present application has the advantages of lower weight, lower cost and increased operational flexibility over rigid bulkhead type barriers. At the same time, the use of such a barrier results in reduced radial loading on the aircraft attachment points when compared to the use of known net barriers, because the radial loading caused by distension of the net is first applied to a frame structure which alleviates this load. The use of a peripheral

frame structure also provides the advantage that net attachments can be placed in the most effective positions for an efficient net design.

The frame structure may comprise separate sections which interconnect to form the frame structure, such an arrangement facilitating installation of the barrier inside the aircraft. Preferably hollow box sections are used which can provide resistance to twisting of the structure without an excessive weight penalty.

The interior space may be the upper deck of the aircraft between a deck floor and the interior of the upper fuselage.

The frame structure may be shaped to form a close fit with the fuselage and deck at the location of attachment and may in use be sealed therebetween and have a smoke barrier incorporated with the net.

The frame structure may be shaped to form, at the location of attachment, a close fit with the interior of the upper fuselage and extend below the deck floor.

At least part of the frame structure may be arcuate, as viewed from the face of the barrier, in order to better resist radial loading caused by distension of the cargo net.

The net may comprise materials that have a low extension at breaking point such as metallic cables or plastics fibre cables (such as aramid fibre cables). Such a barrier allows undesirable longitudinal distension of the net to be reduced, while still providing the aircraft attachment points with protection from the increase in radial loading that the use of such low extension materials inevitably causes.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying, diagrammatic and not to scale, drawings, in which:- Fig. 1 is a transverse cross section of an aircraft upper deck cargo area showing an installed net barrier, as known in the art ;

Fig. 2 is a perspective view of a portion of an aircraft upper deck including the cross section of Fig. 1 ; Fig. 3 is a plan cross section of the net barrier of Fig. 1 showing distension of the barrier under load ; Fig. 4 is a transverse cross section of an aircraft upper deck showing an installed cargo barrier according to the present invention; Fig. 5 is a perspective view of a portion of an aircraft upper deck including the cross section of Fig. 4; and Fig. 6 is a plan cross section of the cargo barrier of Fig. 4 showing distension of the net under load.

Figs. 1 and 2 show a known net barrier 1 for restraining longitudinal movement of cargo within an upper deck cargo area of an aircraft 2, the barrier comprising a net 3 directly attached to attachment points 4 on the fuselage 5 of the aircraft 2 and floor 6 of the upper deck.

If longitudinal cargo movement occurs with this known net barrier, loading of the net barrier 1 results and the net barrier 1 distends from its normal position 7 to a longitudinally distended position 8 by a distance X, as shown in Fig. 3 This distension results in a force with a radial component being applied to the net fixing points.

As shown in Figs. 4 and 5, a cargo barrier 9 comprises a peripheral frame structure 10 made of rigid material and a cargo restraining net 11. The net 11 is attached to attachment points 12 on the frame structure 10, and the frame structure 10 is attached to attachment points (not shown) on the fuselage 5 of the aircraft 2 and floor 6 of the upper deck. In the drawings, a single outer curved line represents both the fuselage 5 of the aircraft 2 and the outer edge of the structure 10, indicating the close fit between the frame and the fuselage.

In the embodiment shown in Fig. 4 and 5, the frame structure 10 comprises a partially circular member 13, which follows the inner contour of the fuselage 5 around the upper deck cargo area, and a floor level member 14, which extends across the floor 6 and links the ends of member 13. The frame 10 can be attached to the aircraft 2 at the desired longitudinal location using either attachment points provided for attachment of a conventional net barrier 1 (when converting from an existing barrier to a low extension version) or purpose made connections (which may be preferable for new installations). Optionally, the frame 10 may be connected to the aircraft 2 via drag straps (which may be made of textile/flexible or rigid material) to allow longitudinal displacement of the barrier from the aircraft attachment points provided by the aircraft manufacturer.

If desired, the frame structure 10 can be sealed against the existing inner fuselage surfaces and floor panels of the aircraft in order to provide a smoke-proof seal when a smoke barrier (not shown) is incorporated alongside the net.

The frame structure 10 should have a high resistance to twisting, in order to avoid imposing high radial loads to the airframe as a result of the couple generated by the difference between the loading and the restraint planes. Preferably this is achieved by utilizing frame structure members 13,14 of hollow box structure, though where the members are curved it is likely that they will be formed as a fabrication, rather than an extruded section.

Preferably the members 13,14 will be made in sections 15 in order to facilitate installation of the frame structure in the aircraft. If the layout of the frame structure is as shown in Figs. 4 and 5, at least five sections are likely to be necessary around the fuselage and three on the floor, in order to keep the size of each section manageable and to facilitate removal when access to the aircraft liners and the systems or structure behind a section is required.

The attachment points 12 for the net 11 are located around the inner periphery of the frame structure 10. Separating the net attachments 12 from the aircraft structure gives the potential to have adjustable or alternative positions for them. This may be useful for

accommodating different and potentially more effective net layouts for different cargoes with a minimum of engineering intervention. For example, it would be possible to increase the number of net attachments combined with a greater number of closer pitch, lighter duty, net members, thus spreading the load more evenly into the frame.

Referring now to Fig. 6 loading of the cargo barrier 9 causes the net 11 to distend from its normal position 16 to a longitudinally distended position 17 by a distance Y.

If low longitudinal distension Y of the net 11 is required, there are various ways this can be achieved. One is to use greater quantities of a conventional, normal extension material so that the net is working at low stress levels and, hence, near the lower end of its stress-strain curve. However, this tends to lead to a more heavy and bulky net.

Preferably therefore, the net incorporates low extension materials, in particular metallic cables or plastics fibre cables (such as aramid fibre cables), in order to reduce longitudinal distension of the net under load to a level significantly less than that achieved by a conventional net.

The net 11 may be formed as matrix of vertical and horizontal members, as shown in Fig. 4 and 5, or as a series of radial and circumferential members formed into a"spider" net. It is likely to be normal in appearance, but variations can include combinations of conventional and low extension net materials. To facilitate access past the net, it can be equipped with a number of quick-release attachment fittings down each side and possibly across at least part of the floor so that it may be partially disconnected from the frame.

The size of frame required, in order to react or alleviate the radial loads expected, can be calculated as set out below. The calculations are based on a Boeing (RTM) B737- 700C aircraft and a cargo barrier as shown in Figs. 4 and 5 having hollow box structure members and an Airbus (RTM) A300 aircraft and a cargo barrier as shown in Figs. 4 and 5 having hollow box structure members.

B737-700C The existing cargo barriers in a B737-700C have a perimeter of 400.489 inches and are designed to take a forward load of 405000 Ibf, giving a load share of 1011.26 lbf per inch run. Although the aircraft has a total of 24 fuselage attachments giving an average spacing of 16.69 inches, the actual spacing of fuselage attachments can be as much as 24 inches, so the required frame structure member size must be calculated from this worst case scenario; 1011. 26 lbf per inch run gives a total load to be transmitted of 24270 lbf over a 24 inch stretch. The worst situation would be the application of this load on a member through a single net attachment (Point Load) mid way between fuselage attachments and the best would be a uniformly distributed load (UDL) through multiple net attachments-in reality the situation will be somewhere between the two.

The required member modulus is based on 1/y = M/a, where I is the moment of inertia, y is the distance from a neutral axis to an extreme point, M is the maximum bending moment (WL/8 for a Point Load and WL/12 for a UDL where WL is the bending moment) and a is the tensile strength of the material selected (for the purposes of this example, a value of 6005 aluminium alloy of 265 N/mm2 (38435 lbf/in2) has been assumed).

Based on the details above, and if one assumes that the net adopts a deflected shape that is circular in profile (it is appreciated that in practice the net is highly unlikely to assume a circular profile on loading-however the profile actually adopted usually leads to lower radial loads such that, for the purposes of the present analysis which is interested in orders of magnitude, this assumption is acceptable), the following table of deflection angles (0), resultant loads, radial loads and member moduli (based on radial load only) for a range of net deflections is obtained (0 being the angle between the pre-deflected net and the deflected net, taken at the point of attachment to the frame structure).

Table 1

Displacement 0 O Resultant Radial Load 1/y (Point I/y (UDL) (Ins) (R=24270/ (Y=24270/Load) WL wu, Sin #° lbf) Tan #° lbf) 8# in3 12# in3 6 10.16 137587 135429 10.571 7.047 8 13.52 103813 100937 7.878 5.252 10 16.85 83728 80133 6.255 4.170 12 20.16 70421 66106 5.160 3.440 18 29.85 48761 42292 3.301 2. 201 24 39.15 38441 29811 2. 327 1. 551 30 47.61 32861 22154 1. 729 1. 153 36 56. 14 29227 16284 1.271 0.847 For a box section of outer dimensions B x D and inner dimensions b x d, the moment of inertia about a neutral axis INA = (BD3/12)- (bd3/12) and y = D/2.

With a member cross section of four inches square with a one-quarter inch wall thickness, the 1/y = 4. 414 in3. This would allows the frame structure to react the loads incurred by a net displacement of 12 inches. This size of section has a cross-sectional area of 3.75 inches2 which, for the 400.489 inch perimeter, leads to a volume of 1501.84 inches3. Made from 6005 aluminium alloy of density 2.71 g/cm3 (0.0979 lb/in3), such a frame structure would weigh 147.03 lb (-67 kg).

A300 The existing cargo barriers in an A300 have a perimeter of about 540 inches and are designed to take a forward load of 993315 lbf, giving a load share of 1839.47 lbf per inch run. The spacing of fuselage attachments is 18 inches, on average, but can be as

high as 20.28 inches* between attachments 14 and 15 (*There is one position at the sidewall/floor intersection between fittings 21 and 22 with a higher gap of 27.94 inches, but this would be treated separately). Over 20. 28 inches the load will be 37304.5 Ibf. As before, the following table is based on the 1/y value for the two extremes of a point load at mid-span (Point Load) and a uniformly distributed load (UDL), and also on the same material, 6005 Al alloy of 265 N/mm2 (38435 lbf/in2).

Table 2 Displacement 0'Resultant Radial Load 1/y (Point I/y (UDL) (Ins) (R=37304.5/ (Y=37304. 5/Load) WL WL Sin 0 Ibf) Tan 0 Ibf) 8O in3 12a in3 6 6.7 319742 317558 20.945 13.963 8 8. 9 241125 238222 15.712 10.475 10 11.1 193767 190143 12.541 8.361 12 13.3 162158 157809 10.408 6. 939 15 16.6 130578 125135 8.253 5.502 18 19.9 109597 103053 6.797 4.531 24 26. 3 84195 75480 4.978 3.319 30 32.6 69240 58331 3.847 2.565 36 38.6 59794 46731 3.082 2.055 Thus, with a frame section of four inches square with a one-quarter inch wall thickness, I/y = 4.414 in3. This will allow for an extension of around 24 inches. The weight would increase in proportion to the circumference, so would increase to (540/400) x 147 = 198 lb (-90 kg).

Although Figs. 4 and 5 show one particular design for the frame structure, other layouts would also be suitable. For example, the floor level member could be positioned below the floor surface level, with due consideration for any aircraft systems that may be in that area, in order to reduce the impediment to a clear passage for personnel on the main

deck. Alternatively, instead of having a floor level beam the frame structure could be designed as a completely circular member in order to take advantage of the more efficient shape, depending on the degree of access to the underfloor area, space available and structure of the particular aircraft concerned.

Although the above example describes frame structure members 13,14 which are hollow box sections, they could instead be of different shapes, for example circular.