A SYSTEM FOR DISSIPATION OR DISPELLING OF FOG

Abstract: A system for dissipating or dispelling fog comprises a launching tube (5) for a projectile, together with a substantially cylindrical projectile (1) which consists of a material which results in the dispelling or dissipation of fog. The non-jacketed projectile (1) is made of the fog-dissipating or fog-dispelling material (1a) which is provided around an explosive device (2a) for dispersal of the fog-dissipating material (1a) which constitutes the projectile body. The ratio between the projectile's weight and the launching tube's cross section area for a given launching height should be less than or equal to a constant (k1) and the ratio between the launching tube's length and diameter should be greater than or equal to a constant (k1) whose value is dependent on the value of the constant (k1).

Description: A system for dissipation or dispelling of foσ The invention concerns a system for the dissipation or dis¬ pelling of fog, wherein the system comprises a subsantially cylindrical launching tube for a projectile together with the projectile which consists of a material which results in the dispelling or dissipation of fog. Fog creates a major problem for a number of activities in society. Examples of this are various forms of transport and outdoor arrangements such as sports meetings and the like. Fog constitutes a serious problem for air traffic in particular. When airports have to close due to fog, this entails major expenses for the airlines and delays for the passengers since the planes normally have to be redirected to other, fog-free airports. In addition to this are the considerable risks which fog entails for transport and above all for air traffic. Theoretically it is today possible for planes to make completely blind landings with the aid of modern instrument landing systems, but for reasons of safety there exist international requirements for varying degrees of minimum visibility from the end of the runway. It is well known in the art that fog can be cleared from airports, motorways, harbours and sports centres by the dispersal of fog-dissipating materials such as dry ice or other chemicals from an aircraft. The dispersal of such fog- dissipating materials causes the water particles in the fog to condense into precipitation which falls in the form of either snow or rain, thus achieving the desired improvement in visibility. Similar measures are also known from the technique for inducing artificial precipitation. In the literature a great number of methods are known and described for dispersing the fog-dissipating material. As already mentioned, for this purpose both aircraft and installa- tions on the ground are used. When dispelling fog at heights which are relevant for e.g. airports, it has usually been found to be necessary to disperse the fog-dispelling material from an aircraft or launch it from the ground, for instance with rockets. The use of aircraft for fog dispersal, however, is very expen¬ sive and launching from ground-based installations has, in order to reach the desired heights, used means which leave debris on the ground. The latter is particularly undesirable at airports, since debris which falls down after the launch and lands on the runway can be sucked into aircraft engines and furthermore generally represents a safety risk for traffic. The object of the present invention, therefore, is to provide a system for dissipation or dispelling of fog which will avoid the above-mentioned and other disadvantages, since, in addition to providing fog clearance at low cost, the system does not result in debris falling to the ground. Another object is to avoid the projectile being destroyed due to the acceleration forces at the moment of launching. These objects are achieved according to the invention with a system which is characterized in that the projectile is a non- jacketed projectile and is made of the fog-dissipating or fog- dispelling material which is provided around an explosive charge for dispersal of the fog-dissipating material which constitutes the projectile body, that the ratio between the projectile's weight and the launching tube's cross section area for a given launching height should be less than or equal to a constant k*-_, and that the ratio between the launching tube's length and diameter should be greater than or equal to a constant V-2 whose value is dependent on the value of the constant k^. Further features and advantages of the system according to the present invention are described in the independent claims. The invention will now be described in more detail in associa¬ tion with embodiments illustrated in the accompanying drawing. Fig. 1 is a section through a projectile according to the present invention. Fig. 2 is a launching tube according to the present invention. Fig. 3 shows how the system according to the present invention is used for dispelling fog at an airport. Fig. 4 is a second embodiment of the system according to the present invention. Fig. 5 is a section through a second embodiment of the launching tube according to the present invention. Fig. 1 is a section through a projectile 1 according to the present invention. The projectile 1 is substantially cylindri¬ cal in shape and consists of a projectile body la with a cavity or central boring 2 in the interior of the projectile body la. The projectile body la is made of a material which consists in its entirety of a fog-dissipating material. This material can for instance be carbon dioxide in solid form, for instance dry ice. In the production of the projectile 1 there is used dry ice which is crushed or in particle form, the dry ice being compressed into the shape of the desired projectile body. Thus the projectile body la and the fog- dissipating material are identical. In the interior of the projectile 1 and surrounded by the fog-dissipating material la there is provided a cavity or a central boring 2 which is adapted to receive an explosive charge 2a. On detonation the explosive charge 2a blows apart the projectile body of the fog- dissipating material la, thereby dispersing the material in the form of fine particles and thus achieving the desired fog- dispelling effect over a large area. In the embodiment in fig. 1 at the rear end of the projectile 1, i.e. adjacent to the fog-dissipating material la there is provided a disk-shaped booster or propelling charge with the same diameter as the projectile. The booster charge can be a powder charge which is surrounded by a protective membrane which keeps the powder particles in place as well as being completely incinerated together with the booster charge when it is fired. The booster charge 4 and the explosive charge 2a in the cavity 2 create a pyrotechnic chain and this can be advantageously achieved by having the explosive charge 2a connected with the boster charge 4 via an transfer-initiator 3 which is ignited at the same time as the booster charge and burns during a predetermined period, thus causing the explosive charge to be ignited and detonate at the desired height. It is evident that the transfer-initiator 3 can therefore be adapted to suit different detonation or launching heights. The explosive charge 2a can, e.g., be a detonating fuse. The only requirement for the explosive charge 2a is that it should completely pulverise the projectile body. In the system according to the invention there is included a launching tube 5 which is illustrated in fig. 2. The launching tube has a length L and a diameter D and is in addition provided with a magazine 6 for the projectiles 1. The magazine is connected with the lower part of the launching tube which constitutes the launching chamber, and which is connected with an electrical ignition device 7 which ignites the booster charge 4 in the projectile 1. The launching tube 5 is further designed in such a manner that the elevation α can be adjusted. The application of the system according to the invention for dispelling fog at an airport, for example, is illustrated in fig. 3. Here the launching tube 5 with the magazine 6 are ad¬ vantageously located on a carriage 8, which is shown driving parallel to a runway of width B. The projectiles are fired from the launching tube with elevation α and caused to detonate at a specified height H over the runway. Principally H is identical with the launching height and is selected so as to ensure that the projectile path is as parallel as possible to the runway surface at the moment of detonation, thus achieving the most effective dispersal possible of the fog-dissipating material over the runway. The detonation points over the runway are indicated by 9, 10 and 11 respectively, point 9 being located above the runway's centre line and points 10 and 11 being located on each side of this in order to obtain fog clearance over a greater width. As described above, the power is provided for the firing of the booster charge 4 which in an above-mentioned embodiment and in fig. 1 is illustrated as a part of the projectile 1, but which can, of course, also be provided as a separate booster charge which is provided in the firing chamber (not shown) in the launching tube 5. As a rule the booster charge 4 will constitute a powder charge of a known type which is normally used in artillery or for launching of pyrotechnic devices. However, the firing of the projectile 1 can also be carried out in other ways and fig. 4 illustrates an embodiment where compressed air is used as a propelling force. Here too the launching tube 5 is supplied with a magazine 6 for projectiles. Those projectiles which are not shown, however, comprise only the projectile body la of the fog-dissipating material, the transfer-initiator 3 and the explosive charge 4. In fig. 4 the launching chamber (not shown) in the launching tube 5 is connected with the pneumatic accumulator 13 which is fed by a compressor 14 and here too the entire launching system is mounted on a carriage or trolley. The lower part of the launching tube 5, i.e. the firing chamber is surrounded by a housing 12 for the trigger mechanism (not shown) and the ignition device 7 which in this case only has to ignite the transfer-initiator, an event which occurs at the moment of firing. Finally the projectile 1 can also be fired by means of a spring mechanism. This is illustrated in fig. 5 which illu¬ strates schematically a section of the launching tube 5 with the projectile 1 and a relaxed compression spring device 15 which is used for the firing. With the present invention it is achieved that when the explosive charge 2a detonates, the projectile 1 is completely destroyed and does not leave any debris which can fall down on the runway. The projectile 1 is manufactured entirely of materials which are either dispersed as fine particles or pulverised completely on detonation of the explosive charge 2a. As mentioned above, the actual projectile body is formed by compressing the fog-dissipating material la into the desired shape. Such a projectile naturally does not possess the same mechanical strength as a projectile where the fog-dissipating material is for instance surrounded by a casing of for instance metal, plastic or other materials. During firing the projectile is exposed to acceleration forces which can lead to the projectile being destroyed at the actual moment of firing due to the stresses created in the projectile body. This will be avoided if the ratio between the projectile's weight and the launching tube's cross section area is less than or equal to a constant k^ which is dependent on the launching height. Disregarding the air resistance, the launching height is given by the formula F sin 2 V2sinα .. . mg mg where H is the launching height or detonation height, F the firing force, L the acceleration length, α the elevation, m the projectile's mass and g the weight's acceleration, while V is the exit velocity. It will be seen that the launching height is proportional to the firing force F, the acceleration length L, normally the launching tube's length and sin 2 and inversely proportional to the projectile's mass m and the acceleration of gravity g, i.e. to the weight of the projectile. Similarly the launching height H is also proportional to the square of the exit velocity V and sin^α as well as inversely proportional to the acceleration gravity g. These relations should, of course, only be regarded as approximate, since no consideration has been given to the air resistance amongst other factors. Since L and g are constant and it is assumed that ct in most cases will be approximately constant, the launching height will be substantially dependent on the force F and the projectile's mass m. At the same time the mechanical stresses to which the projectile is exposed are determined by the projectile's diameter and weight and the pressure effect which the launching force F exerts on the projectile in the acceleration phase. From experience the following relation is relevant: where P is the weight of the projectile in kp and D the projectile's diameter in cm, so that the constant k* j _ has the designation kp/cm 2 . Tests show that for a launching height of 300 m k^ should be approximately 0.075 kp/cm 2 , wherefrom it can be inferred that the numerical value of k^ is dependent on the launching height H expressed in metres in the following way: k = 22,5 (3) H For such a value of k^ it follows that the ratio between the acceleration length L, i.e. in practice the launching tube's length and its diameter D, i.e. the calibre should conform to the following relation - λ k, ~ 12 (4) D Δ i.e. that L should be 12 times the diameter of the launching tube. With a launching height of 300 which is the most suitable for obtaining the regulation runway visibility in fog clearance at airports, k^ will therefore be 0.075 kp/cm 2 and corre¬ spondingly for the above-mentioned relation between launching height H and k^ the ratio will be L/D > k2 ~ 12. As a launching tube there is used a modified 120 mm mortar which in the above-mentioned example, therefore, should have a tube length of 144 cm. In tests with a launching tube of this kind, success has been achieved with the simultaneous use of projectiles with a weight of 8 kp, i.e. the ratio 4P/πD 2 is approximately 0.07, thereby ensuring that the projectile is not destroyed at the moment of firing. Normally dry ice will be the preferred material for fog clear¬ ance, but other materials such as chalk, silica gel or other compounds could also be used. Dry ice will be used primarily for dispelling advection fog at a temperature of under 0 degrees C, while a material such as chalk can be used for dispelling fog at temperatures above zero. However, it should be understood that the projectile body can be made of any kind of materials which have proved suitable for dispelling fog or for generating precipitation in the manner used by the invention. Furthermore it should be understood that the application of the system according to the invention is not limited to fog clearance, but can also be utilized for creating artificial precipitation.

Claims: PATENT CLAIMS 1. A system for dissipating or dispelling fog, wherein the system comprises a launching tube (5) for a substantially cylindrical projectile (1) , together with the projectile (1) which consists of a material (la) which results in the dispelling or dissipation of fog, characterized in that the projectile (1) is a non-jacketed projectile and is made of the fog-dissipating or fog-dispelling material (la) which is provided around an explosive charge (2a) for dispersal of the fog-dissipating material (la) which con¬ stitutes the projectile body, that the ratio between the projectile's weight and the launching tube's cross section area for a given launching height should be less than or equal to a constant k^, and that the ratio between the launching tube's length and diameter should be greater than or equal to a constant k2 whose value is dependent on the value of the constant k^. 2. A system according to claim 1, characterized in that the explosive charge (2a) is provided in a central boring (2) in the projectile (1) . 3. A system according to claim 2, characterized in that the projectile (1) is made in one piece with a booster or propelling charge (4) , the booster charge (4) and the explosive charge (2a) creating a pyrotechnic chain. 4. A system according to claim 3, characterized in that the pyrotechnic chain comprises a transfer-initiator (3) inserted in the projectile (1) between the explosive charge (2a) and the booster charge (4) . 5. A system according to any of the preceding claims, characaterized in that the fog-dissipating material (la) is carbon dioxide in solid form (dry ice) . 6. A system according to any of the claims 1-4, characterized in that the fog-dissipating material (la) is calcium carbonate (chalk) . 7. A system according to claim 1, characterized in that the launching tube (1) is connected with an air accumulator (13) which is connected to a compressor (14) for firing of the projectile (1) by means of compressed air. 8. A system according to claim 1, characterized in that in the launching tube (1) there is provided a compression spring device (15) for firing of the projectile (1) by means of spring power. 9. A system according to claim 7, characterized in that the numerical value of the constant k^ is given by the formula - 22.5 1 ~ H where H is the numerical value of the launching height in metres, and that the constant k2 = 12 for the given relation between the numerical values for k^ and H, when the pro¬ jectile's weight is expressed in kiloponds and the launching tube's diameter is centimetres.

Inventors: HAMARSNES JOHANS, KIELLAND JAN O, KJOLSETH PAUL, HAMARSNES, JOHANS, KIELLAND, JAN, O., KJOELSETH, PAUL
Applicants: HAMARSNES JOHANS, KIELLAND JAN O, KJOELSETH PAUL, HAMARSNES, JOHANS, KJOELSETH, PAUL
Application year: 1993
Main classification: E01H13
IPC codes: E01H13