The factors defining the aerodynamic characteristics of an air¬ craft is on one hand the geometry of the supporting surfaces and on the other hand the surface smoothness of the supporting sur¬ faces . Rough surfaces may deteriorate the flying performance to a considerable degree . Ice and snow coatings may cause so rough surfaces that flying is rendered impossible . During flight the built-in de-icing system of the aircraft is sufficient but at ground intervals de-icing must be performed before start under unfavourable meteorological conditions .

In certain cases it might be sufficient to sweep the wings clear of loose snow but more efficient actions are most often required. In general a hot mixture of water and gl col is sprayed, whereby the glycol provides a certain preventive effect, which is inten¬ ded to remain , until the aircraft has climbed into the air . Upon heavy snow fall the treatment must be performed immediately be¬ fore start.

The spraying of the de-icing liquid is generally performed by a team consisting of a spraying machine operator and a driver , who drives the tank truck with the spraying machine . The spraying machine operator stands on a lifting platform, from v/hich he treats those portions of the aircraft which can be reached by the jet from the spraying machine . The truck is driven around the aircraft so that all portions of the aircraft can be treated.

Under favourable conditions the aircraft is occupied for only about five minutes by the treatment but time studies have shown that on the average a team will work 45 minutes on each aircraft . It is not rare that .delays of air services occur because many planes are queueing to be de-iced. Th s , de-icing will frequent¬ ly cause a bottle-neck in the traffic capacity of the air port .

The method has been critici zed, since excess glycol may penetrate into the ground and in the long run ruin the ground water.

In order to reduce these risks special locations have been ar¬ ranged at 'the new air ports of Paris and Montreal ,

is to be performed. Through drainage sys tems the treatment liquid can be recovered and re-used . De-icinσ is performed by the aircraft by its own engines passing between two large scaffolds , on which 4 to 6 men are placed. By means of hand- operated jet nozzles the men spray the aircraft as it passes .

In Sweden the authorities have developed an interest in the hea risks of the method for the s taff involved. Stricter safety dir tives have been issued.

In US patent specification 791 024 a central de-icing installat is disclosed consisting of a pair of in the longitudinal direc¬ tion of the aircraft self-propelled towers on either side of th air-craft. Each tower is provided with a hinged boom, which ex¬ tends inwardly over the aircraft . By means of a plurality of hinges the boom is pivotable in the vertical plane . The boom carries a conduit with nozzles for spraying de-icing liquid or compressed., air. The installation is intended to operate so that the towers are driven in pairs externally of the wing tips alon the parked aircraft. The inwardly projecting boo ^' ms and their hinges are actuated so that the nozzles of the conduit are lo- cated adj acent and directed towards the surfaces to be de-iced.

The purpose appears to have been to solve the problem of rapid¬ ly spraying the necessary surfaces of the aircraft.

The Canadian patent specification 150 370 discloses an installa tion for recovering and re-using de-icing liquid and arrangeme for spraying de-icing liquid. .

In a system of ducts on the parking ramp the de-icing liquid ru off from the aircraft , is then collected and conducted in pipes to a purification plant. After having been analyzed in respect of dilution the liquid can either be rejected (should tie glycol content be too low) or else be treated by freezing or destina¬ tion so that the ^" concentration of glycol is increased. If re¬ quired, fresh glycol is added to the solution , which is finally heated and stored in a s torage tank , until it is to be used again . The inventor of this sys tem appears to presume that a de-icing liquid should be used consisting of a solution of app¬ roximately equal parts of water and glycol .

For the spraying of the de-icing liquid it is indicated that two or four vehicles should be placed at strategical locations on the de-icing ramp . Each vehicle is provided with a two-part boom, which is moved inwardly towards the parked aircraft. The boom carries a conduit with a nozzle , through which the liquid is sprayed onto the aircraft .

The object of the present invention is to provide a more rapid , efficient and safe de-icing at a lower cost and without risks for the staff and the environment. It is discussed below how the 10 present invention , in preferred embodiments thereof , will ful¬ fil these requirements in comparison with other types of instal¬ lations .

A more rapid de-icing is attained by having the aircraft to pass through a stationary de-icing installation , all surfaces of the 5 aircraft being treated as they pass the spraying device . Without time delay also downwardly and laterally directed surfaces are de-iced . The treatment time will be a fu n ction of the velocity of the aircraft through the installation and will depend only on the fact that the aircraft must spend sufficient time to be 0 sprayed with the required amount of treatment liquid . The dimen¬ sions of nozzles , valves , pumps , etc. included in the spraying device will thus determine the treatment time . The costs for sufficient dimensions of these standard articles are trivial in this connection and will hardly form any restricting factor. 5 If it is assumed that the aircraft is driven through the plant or ins tallation at a velocity of 6 km/h (fast walking speed) the treatment time will be 42 sec . for an aircraft with a length of 70 m.

In plants according to US patent specification 791 024 the treat- 0 ment time will be equal to the maximum time required, for either moving the arrangement along the length of the aircraft , or for the operator to actuate all booms and valves . To be capable of treating the largest commercial airplanes of today the two in¬ terconnected towers mus t have a dis tance of about 65 m between 5 the support points on the ground and a free internal height of about 21 m. . Since the structure also mus t carry s torage tanks for the treatment liquid , driving engines , pumps , cabins for_

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the staff, a plurality of large, movable booms, etc., it is evident that it will be of such dimensions that it cannot reas ably be moved as rapid as an airplane is running. The installa tion comprises a plurality of booms, which are to be moved and pivoted in a vertical direction at the same time as several te of valves are to be opened and closed. It is hardly possible f one operator alone to manage to perform all these operations w in a half minute or somewhat more, which are at disposition, i the plant is to be competitive.

In installations according to the Canadian patent specificatio 150 370 a plurality of relatively conventional vehicles is use and the spraying is controlled manually. Consequently, the tre ment time will depend on the amount of vehicles and staff to b used. Said patent specification hardly provides any improvemen as compared with conventional methods in this respect.

A more efficient de-icing is provided according to the present invention, on one hand, by the automatization of the spraying process and, on the other h-and, by the separation of the remed melting of snow and ice from the preventive spraying with glyc The automatization makes it possible for experts to define the absolutely most efficient treatment process in the form of a program and this process is then identically repeated at each treatment. The separation of remedying and preventive de-icing makes spraying of the airplane with concentrated glycol as the last treatment before start possible, concentrated glycol havin a longer remaining preventive effect than the 50% glycol soluti which is used at present and is supposed to be used according the two cited patents.

Safety in flight will thus be increased both by the two feature of the present invention as mentioned above and by the rapidity of the process, which removes any temptation in situations hard to judge to refrain from de-icing for avoiding delays.

The requirement of safer de-icing in this connection means that the process must not be dangerous to the aircraft and its cargo and that the operative reliability should be high.

introduce any new type of risks for the aircraft . If the por¬ tals are made sufficiently wide , there will hardly be any risk of collision . The reliability in operation of the spraying de- vice will be high , since the number of movable parts is limited.

The reliability of the apparatus recovering the treatment liquid will be high , since unmixed liquids are used, whereby simple and uncomplicated means can be utilized.

Plants according to the US patent specification 791 024 are pro- vided ith a plurality of movable booms of subs tantial si ze , sup¬ ported by a movable structure . Since de-icing is to be performed immediately before start, the aircraft will be fully tanked and fully loaded when it is de-iced. A malfunction or an incorrect operation of any one of the many movable parts may therefor have disas trous consequences . Further , a large niamber of movable parts have an unfavourable influence on the reliability in operation .

The Canadian patent specification 150 370 discloses a recovery- plant , the object of which is to analyze the treatment liquid which has run off and restore the glycol concentration to the values desired . All checking and control problems with the acco - panying risks of interruption of the service caused thereby are avoided by the use of unmixed liquids , which is according to the present invention .

The total costs of de-icing can be separated into capital costs for the plant , operating costs in the form of staff costs , costs of material and other costs of operation and traffic costs for the aircraft treated.

The sys tem according to the present invention affords lower _. total cos ts than both methods presently used and the systems according to the mentioned patent speci fications for all airports , except poss ibly for such with the smalles t traffic .

The sys tem according to the invention , due to the s tationary location and the simple design thereof , will be more economic to cons truct and maintain . The possibility of uti li zing the plants also for the "cleaning of aircrafts will distribute the fixed

^• cos s s . ¬ duce the staff cos ts to a minimum. The recovery of the treatmen liquids will reduce both the consumption of liquids and the heating costs . The traffic costs for a treated aircraft can be assumed to be directly depending on the time during which the aircraft due to waiting or de-icing is prevented from performin useful traffic work . The great capacity of the system will keep these costs low . Finally , the improved safety in flight should be attached a considerable value , also in economic terms .

Risks of health for the staff are eliminated, on one hand, by the automatization rendering all staff unnecessary , possibly with the exception of a supervisor, and, on the other hand , by the possibility of placing the staff indoors . The risks for the external environment are reduced, since all treatment liquid is circulating within a closed system.

An exemplary , preferred embodiment of the invention will be des ribed below. The drawings comprise Fig. 1 ^* , which shows a fronta view of the sys tem according to the invention . Fig . 2 , illustra ting a prinicipal sketch of a programming assembly in the syste according to the invention , Fig. 3 , which shows a cir c it dia¬ gram of a part of the programming assembly , and Fig . 4 a princi pal diagram of a wind compensator in the system according to th invention .

The aircraft to be de-iced is running through one or more sta- tionary portals 1 , see Fig. 1. Each portal supports a conduit 2 which is provided with a plurality of nozzles 3 directed toward the aircraft 10 . Through the nozzles the treatment liquid is sprayed onto the aircraft. The spraying is individually control led by means of a remotely controlled valve for each nozzle .

If several different types of aircraft are to be treated, the conduit 2 must be designed in such a manner that the largest ' aircraft 10 can pass unimpeded therethrough . If a small aircraf is treated the conduit in this case will be far away from the aircraft , which causes action of wind and cooling of the liquid jets to be considerable . In order to avoid this disadvantage , t portal 1 may. support a plurality of different conduits , which a

designed so that they closely conform with the profile of the aircraft as seen from the front. These conduits can be lifted in the portal. The conduit designed for the largest type of air¬ craft is fixedly mounted and when it is to be used, all other conduits are lifted thereover, so that they do not impede the pas¬ sage of the aircraft. When a smaller aircraft is to be treated, the conduit designed therefor is lowered into operating position. Treatment liquid is sprayed only through those nozzles 3 that are mounted on the conduit used for the occasion.

At present it appears to be conventient to use two portals 1, one for the spraying with hot water and one for the spraying with non- diluted glycol. At the first portal all snow and ice is washed off by hot water. An abundant spraying will secure a good result with¬ out other disadvantages than increased heating costs for the water.

At the second portal 1 the aircraft 10 will receive a showering of concentrated glycol, which prevents coatings of snow and ice until the aircraft is airborne. A thrifty and accurately directed spraying is desirable in order to avoid a film of glycol on the windows and glycol in the engines and in air conditioning instal- lations.

The system according to the invention may also be designed with only one portal 1, if it is to be used for the spraying of only one liquid or with three or more portals, if it is intended for spraying the aircraft with a corresponding number of different liquids.

The portals 1 are disposed over a roadway 11 for the aircraft 10 prepared for this puspose. The roadway is provided with a system of draining ducts 4, 5 for each portal. The draining ducts collect the liquid sprayed beside the aircraft or having run off the air- craft. The treatment liquid is conducted to a collecting tank 6 and therefrom to an installation 7 for purification and possibly heating or destination, before it is pumped into a storage tank 8. From the storage tank the liquid is again pumped 9 into the con¬ duit 2, when the next aircraft is treated.

The distance between the portals is determined by how long dis-

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tance the wind can force the jets of liquid . The portals should be so far from each other that the different treatment liquids not mixed on the ground. By using unmixed and non-diluted liqui and keeping them separated from each other the recovery process can be made simple .

The aircraft is driven along the roadway by its own engines or drawn by a tractor or by the roadway being provided with such a inclination that the aircraft will run along the roadway by its own weight, whereby the engines need not be in operation .

It is also possible to design the system so that the aircraft i stationary , while the portal is displaceable along the aircraft (e . g. , on rails ) .

A plurality of position sensors for the aircraft are provided along the roadway a-p i Fig . 2. The object thereof is to record how far the aircraft has reached on its way along the roadway and to provide a signal to open those valves which the aircraft has reached and to close those valves which the aircraft has pa sed. The position sensors may comprise pressure responsive mean in the roadway or photoelectric cells , which Eeact , when the air craft interrupts a light beam transversally of the roadway or metal detectors embedded into the roadway , e . g. , of the type co sisting of a coil , supplied with a high- frequency A. C . When a m tal object, e . g . an aircraft wheel , appears sufficiently close to the coil , the inductance thereof will change . The position sensing may also be performed by means of a range finder, loca¬ ted in the extension of the roadway in a direction forwards or backwards . Each range finder controls the actuating current to relays , wh ich open and close the valves 31-49 to the nozzles in the conduit. When the nose of the aircraft 10 has arrived in under the portal , the first range finder is triggered , which closes the actuating current to the relays that open the val¬ ves being di rected towards the nose of the aircraft , whereby the treatment liquid is sprayed onto the nose of the aircraft. As the aircraft passes in under the portal , the position sensor are triggered one by one and the sprayinq from the various nozz les is s tarted and interrupted , as the aircraft s urfaces pass b

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e nozz es. or a conven e n a rc a r nozzles will be open and spraying all the time from the moment the nose tip arrives in under the portal until the most rear¬ ward tail tip has passed under the portal. The most external nozzles spraying the wing tips, on the other hand, will be open only from the moment the front edges of the wing tips pass the nozzles until the rear edges of the wing tips pass the nozzles.

Which valves are to be opened or closed, when a certain position sensor is triggered, is determined by e.g. an electronic printed circuit card or the like, which is adapted to the type of air¬ craft to be treated. The printed circuit cards are made replace¬ able so that different types of aircraft can be treated.

Fig. 3 shows in a section of a circuit diagram how the position sensors g,h, and i actuate the valves 31, 32, 33 and 34 through the- relays g31~, g32~, g33~, g34~, h31", h32', h33~, h34", i31~, i32", i33 ^* and 134".

The nose wheel of the aircraft triggers the position sensor h, whereby the control circuit is .closed and the actuating current passes from the current source 20 through the relays h34", h33~ and h32'. Fine lines in Fig. 3 indicate leads for the actuating current, and thick lines symbolize the operating current. The re¬ lays h32", h.33" and h34"then close the operating current from the source 22 of operating current to the valves 32, 33 and 34, which are opened so that the treatment liquid is sprayed through the nozzles.

In the next moment the aircraft will leave the position sensor h, whereby the control circuit is opened and the relays h32~, h33 ^' ', and h34~ will then be without current and break the operating current to the valves 32, 33 and 34, which will thus stop the spraying of liquid through the corresponding nozzles. As the air¬ craft leaves the position sensor h, however, it will trigger the position sensor , which, according to the circuit diagram, will open the valves 31 and 32 via the relays i31" and i32".

The leads for the actuating current are assembled on a printed circuit card A and by means of contact members connected to the

position sensors i ,h , g , the current source 20 and the relays i31'- 34 ' , h31 '- 34 " , g31'- 34 ' in a pattern adapted to the type or aircraft to be treated.

Fig. 2 shows the general design of the printed circuit card for a Boeing Model 747-200 with a span of 59 .64 m and a length of

70 . 66 m. A McDonnell- Douglas DC-9-21 has a span of 28. 45 m. The wing tips thereof will reach just outside the inner engines of B- 747 , and therefore a printed circuit card for a DC-9-21 would not on any occasion switch on the valves 31 , 32 , 33 , 47 , 48 and 49 , since they are located outside of the wing tips . When side wind the condition may be changed by the wind compensator , see the description thereof . A DC-9-21 is 31. 85 m long , and therefo all spraying of liquid is terminated, when the nose wheel actua¬ tes the position sensor i , since the aircraft is then completel past the portal . When tail wind or headwind, however, the wind compensator may change this condi t ion .

The wind may cause a drift of the liquid, which has a long dis¬ tance to pass between the nozzle and the aircraft. In order to secure a favourable result of the treatment, a plurality of . printed circuit cards may be formed for each type of aircraft, which are modified so as to compensate for different wind direc¬ tions and wind forces . If the distance between the position sen¬ sors is 1 m and so strong a wind is blowing straight from behin that the drift of the jet of liquid will be 1 m, a printed cir- cuit card is used, which is modi fied in such a manner that those valves that should have been opened and closed by a certain po¬ sition sensor are actuated first by the next position sensor . Measuring instruments for wind force and wind direction are used for controlling the selection of printed circuit cards .

In the most primitive embodiment this is performed by the per¬ son operating the de-icing plant reading the wind force and wind - direction and selecting a printed circuit card for the type of aircraft , adapted to the wind conditions . In a more automati zed embodiment one set of printed circuit cards is provided for each type of aircraft , each individual card being adapted to a cer¬ tain wind direction as well as to a certain wind force . Wind di¬ rection indicators and anemometers connect that particular prin-

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ted circuit card of the set which is adapted to the existing wind conditions. Such an arrangement would be capable of reac¬ ting to rapid variations of wind direction and wind force. The structural design of such a wind compensator is exemplified in Fig. 4.

On the right hand side of Fig. 4 a wind compensator is shown, which comprises a wind direction indicator B and an anemometer C and a plate D supporting relays. On the left hand side of the figure there are shown two printed circuit cards, 0 and Nl, of totally thirteen printed circuit cards required in this example and the relay plate A with the relays h31' , h32', h33', g31', g32', g33'and g34'. To the far left the position sensors g,h, and i are shown. At the bottom of the illustration the valves 31, 32, 33 and 34 are shown.

The wind direction indicator B comprises a centrally pivoted, rotatable contact arm 50 and a vane or the like (not shown) , which turns the contact arm a convenient number of contact plates 52, 54, 56, 58, one for each wind direction. In the Fig. 4 the use of four wind directions is shown, N,E,S and W but it is understood that more or fewer may be used. Via the contact arm an actuating current (fine, broken line) is supplied to one of the four contact plates and therefrom to the relay plate D.

The anemometer C comprises a movable contact arm 60, a centri¬ fugal regulator or the like (not shown) , which moves the con- tact arm from one end position when no wind to the other end po¬ sition at maximum wind force, and a suitable number of inter¬ mediate contact plates, one for each wind force interval. In the embodiment illustrated four wind force intervals are used, 0 for no wind and III for maximum wind force, with the inter- mediate positions I and II, but more or fewer intervals can be used. Via the contact arm an actuating current (fine, continuous line) is supplied _^ to one of the contact plates and from there to the relay supporting plate D.

On the relay supporting plate D the two control currents from the wind direction indicator B and the anemometer C are combined

at a number of connecting points. If all wind directions should be combined with all wind forces, 4 x 4 = 16 connecting points would be required, but since the wind direction is unimportant at the wind force = 0, only thirteen connecting points are re- quired in the example, viz.:

Will, SHI, EIII, NIII, WII, SII, EII, Nil, WI, SI, El, NI, and . 0.

In each connecting point two series connected relays 24, 26 are provided. One relay 24 is actuated by the control current from the wind direction indicator B and the second 26 by the anemo¬ meter C. In order to allow the operating current (thick, broken line) from the operating current source 28 to pass through the connecting point in question it is necessary that both relays are closed. In a cut out section in the illustration of the con tact point Nil it is shown that the control current from the sector N of the wind direction indicator has closed one 24 of the two relays, while the second relay 26 breaks the operating current, since the anemometer is not in position II but in posi¬ tion 0.

Each connecting or contact point (i.e. Will, SIII, EIII,....NI and 0) on the relay supporting or contact plate D is connected to one particular printed circuit card. There are thus thirteen printed circuit cards in the set but only the cards 0 and NI are shown in the illustration. The remaining eleven have -been omitte for the sake of clarity.

In Fig. 4 it is shown by means of small arrows how the system is working. The wind direction indicator B points towards N and control current is_ supplied to the contact points NIII, Nil and NI. The anemometer C, however, indicates 0, whereby the deffec- tion of the wind direction indicator is unimportant. Via the con tact point 0 the printed circuit card 0 is connected. Since the position sensor h is triggered, the control current will pass

through the relays h34 ' , h33' and h 32 ' , which will open the valves 34 , 33 and 32 .

If a blast of wind should move the contact arm 60 of the anemo¬ meter C into position I , the two series connected relays 24 , 26 in the contact point NI would close , the printed circuit card NI being connected. According to the printed circuit card NI the two valves 31 and 32 are connected , when the position sensor is in the position h . The two farthest nozzles 31 (and 49 ) in the por¬ tal , see Fig. 2 , are thus spraying treatment liquid, in spite of the wing tips having still not arrived under the nozzles . However , the blast of wind drives the jet of liquid in the direction S (it is presumed that the aircraft is moving in the direction N) , where¬ by the jet of liquid will hit the wing tip , before it has arrived in under the portal 1.

The movement of the aircraft 10 relative the portal 1 can also cause to start and stop the spraying by means of a plurality of sensors , which actuate the valves to the nozzles directly without the assistance of any programming assembly . A system operating in this manner can be designed so that a number of light sources are placed in the jet direction of the nozzles , preferably in the ground but other locations may also be used. The light sources are formed and directed so that they emit a narrow light beam towards a photo-electric cell placed adjacent each nozzle . The photo-electric cell controls the electrically operated valve be- longing to the nozzle . As long as the light beam between the light source and the photo-electric cell is unbroken , the valve is kept closed by the photo-electric cell . When an object breaks the light beam, the photo-electric cell reacts and -opens the valve to the nozzle , whereby the de-icing liquid is sprayed onto the ob ject. When the object has passed the light source and the nozzle , the light beam will again illuminate the photo-electric cell , which will then cause the valve to be closed 'and the spraying to be ter¬ minated. The photo-electric cell assembly used may also be of the type having a light source and a photoelectric cell mounted ad- j acent each other , wherein the photo-electric cell reacts to light which has been radiated from the light source and has been ref¬ lected from, an object in front of the light source .

In addition to light, sound can also be used for sensing the p sition of the aircraft. A device of this kind is preferably fo med so that the sound source and the sound receiver are locate in line with the jet direction of the nozzle , one beyond that of the room in which the aircraft will move and the other adja the nozzle . As long as the sound can pass unimpededly between sound source and the sound receiver, the valve to the nozzle i kept closed but when an object arrives in front of the nozzle thus deteriorates the sound transmission , the valve will be op and the spraying of treatment liquid starts .

This way of controlling the treatment without using programmin assemblies enables the treatment of any type of aircraft witho any preparations , such as , e . g. production of printed circuit cards or selection of printed circuit cards . The advantage res in the fact that the system does not need to be supervised by person but can be made completely automatic, that the cost of gramming assembly is avoided and that all types of aircrafts ( all other objects ) can be treated without any preliminaries . T treatment liquid will in this system reach all parts of an air craft located in front of a nozzle , even those parts which it possibly desirable to avoid treating, e . g. , windows and air in lets . This disadvantage may be of minor importance , if a liqui is used, which is harmless to those parts of the aircraft, e . g hot water. If other liquids are used, the disadvantages can be eliminated by directing no nozzle towards the region in which e . g. , the windows of the aircraft will pass .

Above it was indicated that one or more liquids are to be used as de-icing medium. However , under certain conditions gases ma be used with advantage , such as , e . g. , water steam or glycol s The advantages of using steam instead of liquid is that the he energy content per unit weight is higher in steam. Thereby the required quantity of energy for melting snow and ice can be tr ferred to the aircraft with a smaller weight of de-icing mediu Hereby the drainage installations can be designed with smaller dimensions or possibly be completely eliminated. The jet of ste has also more heat energy in relation to its kinetic energy th a jet of liquid has . If too much kinetic energy is trans ferred

to the aircraft , mechanical damage will occur in the form of buckles in the sheet metal . By using jets of steam the risk of mechanical damage of the aircraft is thus reduced. As an alter¬ native it is possible , with the same risk of damage , to allow the aircraft to pass more rapidly through the portal and still receive the necessary amount of heat energy .

In addition to liquid and steam it is also possible to use ra¬ diation energy for de-icing , e . g . ^* , light within or beyond the range of wave-lengths which are perceptible to the human eye . The use of radiation energy will eliminate the risk of mechani¬ cal damage of the aircraft . No arrangements are required for col¬ lecting and treating de-icing liquid or condensed de-icing steam. Only melted snow or ice may need to be removed. Energy losses to the atmosphere are reduced to a minimum.

As a source of radiation may be used e . g . a heating lamp , a so called infrared radiator , laser or microwave generator or the type used in microwave ovens . The radiation can be controlled by means of position sensors and with or without a programming assembly in the same manner as described above for the spraying with liquid or steam.

The description has so far only treated arrangements for the removal of snow and ice from aircraft. However, there is a further type of coating on the surfaces of aircrafts which con¬ stitutes an inconvenience , namely dirt . Dirt in the form of dust , soot, crushed insects , excrement of birds , etc . is deposited on all surfaces of the aircraft, both during flight and when the aircraft is standing on the ground. This process of making dirty generally proceeds rather slowly and , therefor , constitutes no risk for the safety in flight . However , the dirt impairs the sur- face smoothness of the aircraft and increases the air drag and thereby the fuel consumption . Regarding the commerci al air traf¬ fic , in addition dirt makes the aircraft look uglier , counter¬ acting the impression of perfection which every air line company are seeking .

Before the accumulation of dirt has become too serious , the ai r¬ craft is therefor cleaned. This is usually performed by manual

brushing of the aircraft with cleaning means and the aircraft is rinsed with clean water afterwards . The staff doing the job uses movable stairs and other staf foldings in order to reach al parts of the planes . These scaffoldings must be moved frequentl which together with the primitive cleaning methods cause the pr cess to be both time consuming and costly .

The arrangements described above for ejecting de-icing liquids can also be used for ejecting cleaning liquids . It is preferabl to first have the aircraft sprayed in a first portal with a suitable cleaning liquid, which dissolves the dirt, and in the next portal the aircraft is then rinsed with clean water.

The liquid is transferred to the aircraft by a jet. The kinetic energy of the jet of liquid provides a processing of the layer of dirt or ice . This processing is intensified by having the je of liquid pulsate or oscillate and by vibrating the layer of di or ice by exposing it to sound of proper frequency . The frequen of the sound is varied cyclicly for the purpose of effectively affecting the layers or coatings with different natural vibrati frequencies . The sound is transmitted to the aircraft through the liquid column which is formed through the air by the jet. T sound producing means are mounted adj acent the nozzles on the c duit for the liquid in the portal .

In comparison with the manual method described above , the clean in the system according to the present invention can be expecte to be somewhat less efficient , since the mechanical treatment o the dirt layer with a brush is eliminated. However, since the method will only require a fraction of the time necessary for t manual method, it is possible to repeat the cleaning much more frequently at the same cos t and thereby attain an equal total effect or in any case extend the intervals between necessary manual cleanings .

Roadway or driving path , portals , position sensors , programming assemblies , pumps , valves , no zzles , supply conduits and drainag ducts may be common for de-icing and cleaning liquids , while it might be preferable to provide separate collecting tanks , treat-

ment tan s an s torage an s or eac n o qu use . system arranged in this manner can be used alternatingly for cleaning and de-icing or aircraft.

By utili zing the system in this manner for two separate pur¬ poses the economy thereof will be improved .

The system according to the invention has been described above as adapted for de-icing and cleaning of aircrafts . However , the prin¬ ciples of the operation of the sys tem can be used in any system which objects are to be exposed to spraying or radiation . Systems according to the invention can thus be designed for automatic sur¬ face treatment of objects in a sequence by e .g . , sandblasting , zinc spraying , ground coating , finishing lacquering and drying with heat radiation . De-icing systems may be located at s trategic points along a railway network for automatic operation when re¬ quired for melting away snow and ice accumulated on the bogies of the trains and threatening to cause interruptions of the service .

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