Such plastic fencing is well known, being installed primarily where a metal fence could create a disturbance of the radar image for approaching aircraft. Radar and ILS signals are disturbed by metal objects positioned between the moving object and the radar source, a circumstance which creates hazard during the aircraft landing procedure. (ILS stands for Instrument Landing System ; such a system makes it possible for aircraft to land even under very poor visibility condi- tions.) In a known embodiment this fencing is equipped for the pur- pose of sturdiness with rails placed on the top and bottom edges, as well as rails placed between the top and bottom edges in such numbers that the fencing can withstand mecha- nical stress.

Although such fences with rails affixed at intermediate posi- tions are sturdy, they nonetheless have the disadvantage that due to the intermediately placed rails they can more easily be climbed over by unwelcome persons at the airport in ques- tion.

It is an object of the present invention to provide a fencing panel that, on the one hand, possesses sufficient mechanical strength to withstand the great stress of the stream of gases produced by aircraft during takeoff and landing and to offer resistance to the great wind stresses which are characteris-

tic of the open spaces around airports, and that, on the other hand, is free of rails attached intermediately so that the ease with which the fencing panel can be climbed over is greatly diminished.

To this end the invention is characterized by the fact that the ends of the bars are joined by gluing to two rails and the fencing panel is free of any other rails and the hardened plastic is reinforced with 25 to 75 % reinforcement fibres by weight.

The percentage by weight of reinforcement fibres is relative to the total amount of hardened plastic and reinforcement fibres.

It turns out that the inclusion of reinforcement fibres of a suitable type in quantities of from 25 to 75 /Oo by weight relative to the total weight of fibre plus plastic produces an optimal combination of properties in the plastic.

On the one hand, the fencing panel as such proves to be sufficiently sturdy to withstand wind velocities of up to 300 km/hour caused by the backwash of aircraft during takeoff and landing, while, on the other hand, excellent weather durability is obtained.

The fencing panels and the parts of these panels can in principle be constructed of any type of hardenable plastic extraordinarily good results are obtained by constructing the fencing parts out of fibre-reinforced thermosetting polymers, in particular out of vinyl ester resin and isophtalic poly- ester resin.

For the reinforcement fibres, in principle all the usual types of reinforcement fibres can be utilized, such as glass fibres, nylon fibre, aramide fibre, mineral fibres and many

others ; from the economic point of view, preference is given to glass fibre.

Very good results are achieved with a product obtained by pultrusion, a process in which a thermosetting resin is applied by immersion to a continuously moving band of longi- tudinally reinforcing fibres, after which reinforcement fibre mats providing transverse reinforcement are applied, followed by coating with a protective surface film. The structure thus composed is formed into the desired shape in a moulding matrix, with the moulding matrix functioning at the same time as curing station for the synthetic resin. The product which emerges from the matrix is completely cured and be removed from the apparatus sawed to length. With such pultrusion methods, sections with all different shapes can be produced, such as U, T, I, L and 0 profile sections, which are known under the applicant's general trademark UTILOs sections.

In particular, in the fencing panel according to the inven- tion the hardened plastic will be reinforced with from 30 to 55 Y0 by weight of reinforcement fibres, and by preference with at least 50 % by weight of reinforcement fibres present.

With respect to the penetrability of a fence constructed of the fencing panels according to the invention, as well as with respect to its transparency, an openness percentage for the fencing of between 20 and 60 % will in general be selected ; more specifically, an openness of + 50 Z will be sufficient.

Beams sections with a rectangular cross-section function suitably as rails for the fencing, while bars with a circular cross-section function suitably as the vertical bars. Natu- rally, other shapes can also be utilized.

To produce a fencing panel according to the invention, in the tubular rails with rectangular cross-section holes are

produced which have cross-sectional dimensions that are slightly larger than the outer cross-sectional dimensions of the bars. When gluing, a layer of glue is applied in the space between the outer surface of the bars and the inner surface of the corresponding holes in the rail.

In order to further increase the difficulty of climbing over a fence constructed with fencing panels according to the invention, a saw-toothed edge is glued onto one of the rails in such a manner that the tips of the teeth extend essen- tially in the plane of the bars of the fencing panel in a direction pointing away from the bars.

The fencing panel according to the invention is constructed in such a way that with its bars oriented in an essentially vertical direction it can be connected to two posts set up in an essentially vertical position. The interlocking connection between the fencing panel and the corresponding vertically- oriented posts is itself well known and requires no further description here.

In a particularly attractive embodiment of the fencing panel according to the invention there is an anti static means included in the fibre-reinforced hardened plastic to prevent the static charging of the fencing panel by the high-velocity stream of gases produced by landing aircraft. The quantity is not critical and generally amounts to between 0.1 and 1.0 % by weight relative to the total weight of hardened plastic and reinforcement fibres. The antistatic means to be used for this purpose are known to the specialist. The addition of these anti static means prevents the possibility of grass fires resulting from the discharge of sparks.

The invention also relates to a fencing system comprising a large number of essentially vertically installed posts anchored either in or on the ground and fencing panels attached between the posts, which fencing panels are charac-

terized by the fact that they are fencing panels according to the above described invention.

The invention will now be described on the basis of the drawing, in which - Figure la shows a fencing panel according to the inven- tion as part of an installed fence - Figure 1b shows the construction in Figure la in the cross-section AA - Figure 2 shows an enlarged view of a fencing panel according to Figure 1.

The number 1 in Figure 1 indicates a number of bars of a fencing panel in which 2 indicates the rails. Posts are indi- cated by 3, in which the fencing panel is anchored according to a known method. A saw-toothed section which is glued to the rail is indicated by 4 ; the teeth of this saw-toothed section extend in a direction pointing away from the bars 1.

1', 2' and 4' and 1", 2" and 4", respectively, indicate the parts of the adjoining fencing panels.

In a typical example, the bars 1 have an outside diameter of 50 mm and a centre to centre distance between the bars of 102.5 mm. Accordingly, the open space between the bars is 52.5 mm, which is small enough to prevent an intruder from exerting sufficient force to bend the bars apart by putting an arm between them. With a view to the above purpose, the typical maximum distance between the bars is 55 mm.

Isophtalic polyester resin is a suitable material from which to make the bars 1 and the rails 2, while the posts 3, for example, are by preference made of vinyl ester resin rein- forced with glass fibre. By the presence of a protective surface film, as previously described in the discussion of the pultrusion process, optimal protection against long-term exposure of the reinforcement fibres to chemical and atmos- pheric influences is achieved so that the diffusion of

components of these influences to the reinforcement fibres is prevented.

It turns out that a good result is obtained if the elastic modulus (E) of the parts of the fencing panel is at least 20,000 newtons per mm2.

In a typical example, a fence comprising fencing panels according to the invention is 2.5 meters high, while the width of the fencing panels will be approximately 3 meters.

Typically, the posts 3 which are used have a rectangular cross-section with a larger dimension of 152 mm and a smaller dimension of 90 mm, and with a wall thickness of between 6 and 8 mm. With a typical composition of glass f'ibre and vinyl ester resin, such a tube has a moment of inertia with respect to the X axis of 10.13 x 106 mm4.

In Figure lb, the cross-section AA shown for Figure 1 speaks for itself. It can be seen how the ends of the fencing panels are set into the posts 3.

Figure 2 shows in enlarged detail a fencing panel such as specified in Figure 1, in which the same parts are indicated with the same numbers. It can be seen that the bars 1 rest with their ends against the side of the rail 2 opposite the side of the rail 2 into which the bars are inserted. The gluing takes place between the ends of the bars 1 and the wall against which they rest and between the side of the bars 1 and the close-fitting wall of the rail 2 surrounding them. By preference, the gluing is carried out in such a way that a bead of hardened glue forms around the bar 1 on the outer surface of the rail 2 into which this bar is inserted.

A suitable two-component gluing system, such as an epoxy resin hardener system, is used for gluing the bars as well as for gluing the sawtooth 4 shown schematically above.