A SYSTEM FOR DISSIPATION OR DISPELLING OF FOG

The invention concerns a system for the dissipation or dispelling of fog, wherein the system comprises a subsantially cylindrical launching tube for a projectile together with the projectile which consists of a material which on dispersal in the atmosphere 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 installations 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.

As an example of the prior art may be cited US-A-2,052,626 which discloses a number of methods for dispelling of fog by means of a hygroscopic material, including dispersal from ground as from aircraft or ground-launched rockets. A method for dispersing the material from an aircraft is also disclosed in US-A-3,441,214. Finally mention must be made of US-A-3,127,107 which teaches the inclusion of ice-nucleating material in the form of silver iodide in a detonating fuse for the generation of a large amount of silver iodide crystals. The fuse can be detonated on the ground or carried aloft by balloons, aircrafts or rockets for detonation in the air.

The use of aircraft for fog dispersal, however, is very expensive 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.

Dispersal of fog-dissipating material directly from the ground by means of ground-based generators or detonation, as taught by US-A-3,127,107, while leaving no debris on the ground, is not accurate enough and too inefficient for quickly dispelling fog in airports.

The present invention relates to a system for dissipating or dispelling fog, which is operated from the ground and leaves no solid debris, in which the system comprises a launching tube for a substantially cylindrical non-jacketed projectile, where the projectile is made up of the fog-dissipating or dispelling material and an explosive charge which will explode and disperse the fog-dissipating or dispelling material once the projectile reaches a launching height defined through the expression:$$\mathit{\text{H}}\text{=}\frac{\mathit{\text{FL sin}}\text{α}}{\mathit{\text{mg}}}\text{=}\frac{{\mathit{\text{V}}}^{\text{2}}\mathit{\text{sin}}\text{α}}{\text{2}\mathit{\text{g}}}\text{,}$$ where H is the launching height, F the firing force, L the acceleration length, m the mass of the projectile, g the acceleration of gravity, α the elevation, and V the exit velocity, and with a relation between the weight of the projectile and the cross section area of the launching tube equal to or less than k₁= $\frac{\text{4}\mathit{\text{P}}}{\text{π}{\mathit{\text{D}}}^{\text{2}}}$, where P is the weight of the projectile in kp, D the diameter of the projectile in cm, whereby k₁ is a constant which value has to be determined empirically for the fog-dissipation or dispelling material used. Kp denotes kilopounds.

The present invention in its preferred embodiments advantageously provides a system for dissipation or dispelling of fog which will avoid the above-mentioned and other disadvantages of the prior art, since, in addition to providing fog clearance at low cost, the system does not result in debris falling to the ground.

The present invention in its preferred embodiments advantageously avoids the projectile being destroyed due to the acceleration forces at the moment of launching.

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 association 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 cylindrical in shape and consists of a projectile body la with a cavity or central boring 2 in the interior of the projectile body 1a. The projectile body 1a 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 1a, 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 1a 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 advantageously 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 illustrates 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 1a 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 k₁ which is dependent on the launching height. Disregarding the air resistance, the launching height is given by the formula$$\text{H =}\frac{\text{FLsinα}}{\text{mg}}\text{=}\frac{{\text{V}}^{\text{2}}\text{sinα}}{\text{2g}}$$ 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 acceleration of gravity, 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 sinα 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 sinα as well as inversely proportional to the acceleration of 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 sinα 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 subjected 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:$$\frac{\text{4P}}{{\text{πD}}^{\text{2}}}{\text{≤ k}}_{\text{1}}$$ where P is the weight of the projectile in kp and D the projectile's diameter in cm, so that the constant k₁ has the designation kp/cm². Tests show that for a launching height of 300 m k₁ should be approximately 0.075 kp/cm², wherefrom it can be inferred that the numerical value of k₁ is dependent on the launching height H expressed in metres in the following way:$${\text{k}}_{\text{1}}\text{=}\frac{\text{22,5}}{\text{H}}$$

For such a value of k₁ it follows that the ratio between the acceleration length L and the prosjectile's diameter D, i.e. in practice the launching tube's length and the calibre, should conform to the following relation$$\frac{\text{L}}{\text{D}}{\text{≥ k}}_{\text{2}}\text{≃ 12}$$ i.e. that L should be 12 times the calibre of the launching tube.

With a launching height of 300 m which is the most suitable for obtaining the regulation runway visibility in fog clearance at airports, k₁ will therefore be 0.075 kp/cm² and correspondingly for the above-mentioned relation between launching height H and k₁ 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 use of projectiles of e.g. dry ice with a weight of 8 kp, i.e. the ratio 4P/πD² 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 clearance, 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°C, while a material such as chalk can be used for dispelling fog at temperatures above 0°C. 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.