Abstract:
An in particular frustoconical hollow body ( 1 ) which can be stabilized by positive air pressure and which can be anchored to a base support ( 30 ) by way of bracing means is composed of a plurality of flexible material webs ( 4  to  12 ) which each extend in the peripheral direction of the hollow body ( 1 ). The mass in relation to surface area of the material webs ( 4  to  12 ) varies over the length of the hollow body ( 1 ).

Description:
The invention concerns an in particular frustoconical hollow body which can be stabilised by positive air pressure and which can be anchored to a base support by way of bracing means and which is composed of a plurality of flexible material webs which each extend in the peripheral direction of the hollow body. 
     BACKGROUND OF THE INVENTION 
     Hollow bodies which are held in a stable position by a continuous feed of air by means of a blower and in which there is admittedly a given positive pressure but which are not inflated as that air can escape again at least one location are frequently used for advertising purposes. By way of example DE 94 07 294 U discloses an advertising tube, which is 3 meters in diameter and 27 meters in height. An additional water container is provided in the region of the ground in order to achieve the necessary stability in relation to the ground while cables, which can be anchored to the ground for guying purposes extend to about three quarters of the height of the hollow body. 
     Recent times have seen the organisation of aerobatic flying competitions in which the aircraft must fly a course which is defined by overdimensional ‘slalom gates’. The gates comprise two ‘slalom poles’ which are set up at a spacing of for example 10 to 14 meters and which are 18 meters in height. The gates have to be negotiated in accordance with given rules, which are not essential here. 
     The individual slalom poles are hollow bodies of the kind set forth in the opening part of this specification which are not cylindrical but conical, wherein the hollow body axis extends inclinedly so that the generatrices, which define the gate, of the two hollow bodies are in mutually parallel relationship. The hollow bodies are composed of a plurality of flexible material webs comprising a material, which tears immediately when it comes into contact with a part of the aircraft. That means that there is no resistance such as to endanger the aircraft and the damaged hollow body collapses into itself and is replaced by a new one. 
     Fixing to a support foundation is implemented by way of guying cables which can only be arranged up to a low height above the ground (about two to two and a half meters) so that the stability which is to be achieved exclusively by the positive air pressure hitherto entailed problems, in particular as the hollow bodies must withstand wind speeds of up to 50 kph. Guying cables, which are fitted further up would endanger the aircraft. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore the object of the present invention is to improve the stability and steadiness of such a hollow body. That is achieved in that the mass in relation to surface area of the material webs varies over the length of the hollow body. 
     By this means the hollow body wall is sufficiently strong in the lower region so that it can withstand the loadings from the upper region of the hollow body without guying cables, and tears so easily in the upper region that an aircraft coming into contact therewith does not encounter any resistance which is detrimental to its flight. 
     In that respect a continuous reduction in the mass in relation to surface area from the anchoring side to the free end is not necessary. Thus the strip of material from which the guying cables extend is preferably of a substantially higher mass in relation to surface area than for example the strip of material, which rests on the base support. Nonetheless it is preferably provided that the mass in relation to surface area of the material webs is greater in the region of the anchorable end of the hollow body than in the region of the free end. 
     The material webs are not only of different masses in relation to surface area but they are preferably also of different materials or materials which have been treated differently. By way of example heavier material webs can comprise a PD- or PVC-coated polyester fabric while lighter material webs are formed in particular in the endangered region towards the free end at least in part from a rip stop fabric. Rip stop fabrics usually have in spaced relationship stronger warp and weft threads in order to guide and restrict tears. For the lighter material webs however it is also advantageously possible to use rip stop fabrics which involve stronger warp threads which extend in the peripheral direction of the hollow body and only identical weft threads or stronger weft threads at great spacings so that a tear parallel to the warp threads is not necessarily braked. 
     The positive air pressure is maintained in the hollow body by at least one blower, in particular with an internal combustion engine, which is preferably disposed in a housing. 
     The air pressure in the interior of the hollow body is in that case desirably set at between 5 and 35 mbars, preferably 10 and 15 mbars. With respect to the real bursting pressure, that is to say that pressure at which the hollow body bursts, the positive pressure is desirably at least 10%, preferably at least 30% and still more preferably at least 50% of the real bursting pressure of the hollow body. That taut inflation provides that, in the event of an aircraft coming into contact with the hollow body, the latter bursts explosively as directly as possible or close to the location of impact and as a result no pieces of fabric remain hanging from the aircraft. 
     In regard to the theoretical bursting pressure (that mathematically ascertained value of the internal pressure in relation to the tearing force of the fabric in accordance with the respective technical data sheet), advantageous positive pressure values in the hollow body are between 3% and 50% of that theoretical bursting pressure of the hollow body material, preferably between 5% and 25% of the theoretical bursting pressure. It is to be noted that the tearing force of technical fabrics is weakened by production procedures and joins such as for example sewing so that the real bursting pressure is reached markedly earlier than the theoretical bursting pressure. The theoretical bursting pressure however can be more easily ascertained on the basis of technical data sheets. 
     For the major part the material webs are closed and joined together by zip fasteners to afford the in particular frustoconical hollow body portions, material webs near the anchoring can also be fixedly sewn. 
     For dismantling, in a preferred configuration, there is provided at least one desired separation location, which is disposed approximately at the middle of the hollow body. When the desired separation location is opened the free part quickly blows out and the remaining part quickly collapses into itself as the cross-sectional area at the desired separation location, particularly in the case of a frustoconical shape, is a good deal bigger than the cross-sectional area of all leaky openings which are necessary to maintain the stabilising positive pressure. A rapid reduction is necessary in particular in the case of a stronger wind as the hollow body, which is no longer stabilised would be caught by the wind in the manner of a sail, in which case damage could scarcely be avoided. 
     The desired separation location preferably also includes a zip fastener which preferably does not include a slider and which is opened at the two mutually overlapping ends. While all other zip fasteners are completely covered by a hook-and-loop closure strip, in the case of the zip fastener at the desired separation location only the opened ends are secured by a removable connection. The removable connection preferably includes a tongue which bridges over the ends and which is fixed by means of a hook-and-loop fastener to the two material webs and which is provided with a rip cord. 
     For dismantling therefore on the one hand the tongue is opened by pulling on the rip cord and the zip fastener is triggered to burst open while on the other hand the burst-away upper half is captured by holding fast the catch line which hangs down from the free end. Optionally, in particular when dealing with longer or higher hollow bodies, two such desired rupture locations may also be of advantage. 
     The peripherally extending warp threads of the material webs are preferably those, which stretch due to the positive air pressure by about 5% to 6%. By virtue of suitable diametral bracing means or the like it is possible, instead of a circular truncated cone, to achieve for example a truncated cone with an elliptical base surface, wherein the major ellipse axes of two hollow bodies which are brought together to form a ‘gate’ then lie in the line of the gate and the stability in the plane of the gate is further improved in order to avoid fluctuations in the spacing between the free end regions as far as possible. 
     Special shapes for the hollow bodies, specific configurations and handling and processing means for delivering items of information to the pilots or to the public, for example including advertising, are readily possible. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawing: 
         FIG. 1  shows a diagrammatic view of a hollow body, partly in exploded form, 
         FIG. 2  shows a gate, which is made up from two hollow bodies, 
         FIG. 3  shows the overlap region of the desired separation location without securing connection, and 
         FIG. 4  shows the overlap region in section taken along line IV-IV in  FIG. 3  with securing connection. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hollow bodies  1  according to the invention are preferably used in pairs as shown in  FIG. 2  for setting up ‘gates’  31  of an agility course for aircraft and therefore represent large-dimensioned ‘slalom poles’. The hollow bodies  1  can be set up vertically and can be anchored to any desired support, not only on the ground but also on pontoons or the like floating in water. The hollow bodies  1  however can also be arranged hanging from high bridges or projecting horizontally from walls or the like, wherein particularly in the latter case they can also be used individually as there is no need for the ‘gate’ to be delimited downwardly. Anchorage to the base  30  is effected by means of bracing means in the form of guying cables  14  which are arranged at a height of about two to two and a half meters on the hollow body  1 . By virtue of the guying cables  14  which can only be provided close to the base  30  the hollow body cannot be formed from one material web but is composed of a plurality of and in the specific embodiment nine material webs  4  to  12  which have different properties. The material webs comprise in particular fabrics whose warp threads extend in the peripheral direction, wherein at least material webs  4 ,  5  and  6  in the region of the anchorage are heavy fabrics, in particular coated polyester fabrics, while at least those material webs  10 ,  11  and  12  in the region of the free end are fabrics which are as light as possible and which, in the event of the aircraft coming into contact therewith, do not form any resistance such as to endanger it, in particular polyester rip stop fabrics. 
     A preferred embodiment is of the following structure, considered in an upward direction: 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                   
                   
                 Continued 
                 Continued 
               
               
                   
                   
                 Mass in relation 
                 Tearing strength 
                 Tearing strength 
                 tearing strength 
                 tearing strength 
               
               
                   
                   
                 to surface area in 
                 of the warp 
                 of the weft 
                 of the warp 
                 of the weft 
               
               
                   
                 Material 
                 grams per square 
                 threads in 
                 threads in 
                 threads in 
                 threads in 
               
               
                 Component 
                 designation 
                 metre 
                 Newtons 
                 Newtons 
                 Newtons/5 cm 
                 Newtons/5 cm 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Ground 
                 Polyurethane- 
                 170 
                 2500 
                 1500-1600 
                 350-400 
                 250 
               
               
                   
                 coated polyester 
               
               
                   
                 fabric 
               
               
                 Material web 4 
                 Polyurethane- 
                 170 
                 2500 
                 1500-1600 
                 350-400 
                 250 
               
               
                   
                 coated polyester 
               
               
                   
                 fabric 
               
               
                 Material web 5 
                 Polyvinyl 
                 680 
                 3000 
                 2800 
                 300  
                 300 
               
               
                   
                 chloride-coated 
               
               
                   
                 polyester fabric 
               
               
                 Material web 6 
                 Polyurethane- 
                 170 
                 2500 
                 1500-1600 
                 350-400 
                 250 
               
               
                   
                 coated polyester 
               
               
                   
                 fabric 
               
               
                 Material web 7 
                 Polyvinyl 
                 350 
                 1100 
                 1000 
                 60 
                  30 
               
               
                   
                 chloride-coated 
               
               
                   
                 polyester fabric 
               
               
                 Material web 8 
                 Polyurethane- 
                 120 
                 1300 
                  800 
                 40 
                  50 
               
               
                   
                 coated polyester 
               
               
                   
                 fabric 
               
               
                 Material web 9 
                 Polyester rip stop 
                 100 
                 750-800 
                 650-800 
                 40-50 
                 40-45 
               
               
                   
                 fabric 
               
               
                 Material webs 
                 Polyester rip stop 
                 60 
                  480 
                  860 
                 30-90 
                 30-80 
               
               
                 10, 11 and 12 
                 fabric 
               
               
                   
               
             
          
         
       
     
     As mentioned each hollow body  1  as shown in  FIG. 1  or  FIG. 2  is composed of the material webs  4  to  12 , wherein they are cut in such a way as to afford an inclined truncated cone in which the shortest generatrix is perpendicular to the ground and the connecting seam of each web of material is provided in diametrically opposite relationship in the longest generatrix. 
     The ground and the three adjoining material webs  4 ,  5 ,  6  and possibly also  7  can be sewn together. An inlet or a window  13  is provided in the material web  4  for a blower, which ensures an ongoing positive air pressure in the hollow body. Additional anchoring tags for the guying cables  14  are provided at the material web  5 , which is conspicuously heavier. The material web  4  can also have a further closable inlet so that it is possible for people to go into the interior, for example to provide lighting. 
     The hollow body  1  is of a preferred height of 18 meters corresponding to the rules applicable at the present time in relation to aerobatic competitions and the width of a ‘gate’  31  as shown in  FIG. 2  is between 8 and 14 meters. It will be appreciated that if a hollow body  1  is damaged during a competition, repair or installation of a fresh hollow body  1  as quickly as possible is a necessity. For that reason in particular the material webs  9 ,  10 ,  11  and  12  which are in danger of being damaged in the region of the free end are connected together by zip fasteners and hook-and-loop fasteners covering the zip fasteners, or other restorable connections, so that a material web can be quickly replaced. 
     After an event the hollow bodies must be taken down, in which case when the stabilising positive air pressure in the interior is no longer present, a phase occurs, which is without any problem only when there is no wind. When there is a wind the unstable hollow bodies are exposed thereto similarly to a sail and are blown away, torn out of the anchorage and/or damaged even more. In order to avoid that the hollow body  1  is provided with a desired separation location  15  (see  FIG. 2 ) at which extremely rapid separation of the hollow body into two parts can be effected in specifically targeted fashion. The desired separation location  15  is preferably provided approximately at the middle. 
     At the desired separation location  15  the two material webs  8  and  9  are connected by a zip fastener  16 , which does not have any slider and which is opened in its two mutually overlapping end regions ( FIG. 3  and  FIG. 4 ). The zip fastener  16  does not withstand the positive air pressure in the hollow body  1 , by virtue of its opened ends  21 , and separation takes place in a few seconds, whereby the free end region  4  is blown off and the anchored part quickly collapses into itself by virtue of the large opening. Provided at the free end  3  is a catch line  19  so that the light-weight free end region which involves the material webs  9 ,  10 ,  11  and  12  can be pulled down to the ground. 
     The desired separation location  15  is secured by a connection  17  which is releasable by way of a rip cord  18  from the ground and which comprises a tongue  22  ( FIG. 4 ) which covers over the overlapping ends  21  and which is fixed to the material web  8  and to the material web  9  by means of hook-and-loop fasteners  23 ,  24 . If separation is to be effected at the desired separation location, a pull is applied to the rip cord  18  and the tongue  22  releases the ends  21  so that the zip fastener  16  can be opened as described. 
     At the anchorage end  2  the hollow body  1  is preferably of a diameter of 5 meters while at the free upper end  3  it is of a diameter of 75 centimeters. The blower preferably produces a positive pressure of about 5 to 35 mbars, which has proven to be advantageous for the dimensioning of the hollow body  1 . 
     It will be appreciated that the invention is not restricted to the embodiments illustrated. By way of example the hollow bodies do not have to be implemented in the form of posts projecting from the ground. Rather, other configurations are also possible, for example arcuate configurations, in which the length of the hollow body is then the extent along the notional longitudinal centre line of the arc.