Abstract:
An aircraft de-icing system is disclosed in which a laser beam generator is positioned on an aircraft, a beam of radiant energy is generated and directed toward the critical surfaces of the aircraft to create a footprint upon the surface of the aircraft, and the beam is manipulated so that the footprint is moved about the aircraft surface for removing ice, snow or water from the critical aircraft surfaces. One or more laser beam generators are preferably disposed remotely from the area to be de-iced, and the beams are preferably reflected from one or more mirrors so that the mirrors may be adjusted to enable the beams to illuminate the critical surfaces of the aircraft. The laser beams preferably have a wavelength that is preferentially reflected by the aircraft surface and absorbed by ice, snow and water, so that the beam heats and removes ice, snow and water from the aircraft surface as the beam&#39;s footprint is moved thereabouts.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to aircraft de-icing and, more particularly, to a system and method of onboard de-icing. 
     Ice formation on aircraft surfaces, particularly wing surfaces, during cold weather is a problem that can have catastrophic consequences. Ice increases aircraft weight and can reduce lift and interfere with the functioning of moving parts. A number of systems are available and in use for preventing icing or for de-icing an aircraft surface while an aircraft is in flight. These include de-icing devices which remove ice by scraping or cracking, devices which melt the ice with microwave heating and devices which employ electrothermal heating within the structure to be de-iced. These devices are typically slow and inefficient. They must also typically be positioned in or adjacent the area to be de-iced and lack the flexibility to de-ice different surfaces and moving parts of the airfoil. 
     It has also been proposed to use ground based laser light systems to de-ice aircraft. Such systems typically use complex, bulky and cumbersome booms to hold laser light generators in close proximity to an aircraft surface and to manipulate the laser light generators about the aircraft surface to be de-iced. In U.S. patent application Ser. No. 08/706,598, filed by the present inventor, a laser de-icing method and system are disclosed which overcome many of the problems of earlier laser de-icing systems. The entire content of U.S. patent application Ser. No. 08/706,598 is incorporated by reference herein as if set forth fully herein. While laser de-icing offers a relatively fast and efficient way of removing ice from an aircraft and reduces or eliminates the need to spray outer surfaces with glycol solutions for de-icing on the ground, earlier approaches of others to laser de-icing are not without problems. For example, ground based systems proposed by others do not permit in flight de-icing and significantly limit the flexibility of the system to de-ice the aircraft when and where needed. Furthermore, glycol based de-icing systems must use additional glycol mixtures and compounds to enable the aircraft to travel from the de-icing station to the runway and to preserve the ice free condition during take-off. The anti-icing glycol mixtures and compounds provide several minutes of ice free conditions. If the aircraft exceeds the specified “safe” period, the aircraft must return to the de-icing station. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a system and method of onboard aircraft de-icing using a laser beam. 
     It is a still further object of the present invention to provide a system and method of the above type that permits the laser beam to be manipulated so that a footprint of the beam may be moved about the surface of the aircraft. 
     It is a still further object of the present invention to provide a system and method of the above type that uses a laser beam having a wavelength which is preferentially reflected by aircraft surfaces and absorbed by ice, snow or water. 
     It is a still further object of the present invention to provide a system and method of the above type that uses a laser beam generator that generates optical energy in the 10 micron to 11 micron wavelength range. 
     It is a still further object of the present invention to provide a system and method of the above type that uses a CO 2  or CO laser beam generator. 
     It is a further object of the present invention to provide a system and method of the above type in which the equipment needed for the system may be easily affixed to and removed from an aircraft. 
     It is a still further object of the present invention to provide a system and method of the above type that permits de-icing of an aircraft on the ground and in the air. 
     It is a still further object of the present invention to provide a system and method of the above type that may be powered by auxiliary power sources already present on aircraft or that may be powered by additional power sources installed on aircraft. 
     It is a still further object of the present invention to provide a system and method of the above type that permits the laser beam that provides the flexibility to de-ice different areas and structures at and about the critical surface areas of the aircraft. 
     It is a still further object of the present invention to provide a system and method of the above type that provides flexibility in treating hard to reach regions of an aircraft surface. 
     It is a still further object of the present invention to provide a system and method of the above type that permits a beam generated by a single laser beam generator to quickly and easily treat a large region on an aircraft surface without regard for whether the region is horizontal, vertical, sloping, rounded or any combination thereof. 
     It is a still further object of the present invention to provide a system and method of the above type which can maintain critical surfaces in an ice free condition during taxiing and takeoff, thereby reducing or eliminating the need to use anti-icing gel fluids that are presently used. 
     It is a still further object of the present invention to provide a system and method of the above type which can prevent in flight ice formation on critical surfaces without reducing aerodynamic performance of the critical surfaces. 
     It is a still further object of the present invention to provide a system and method of the above type in which the radiant energy of the beam is absorbed at or near the surface of the ice so that ice may be melted or vaporized selectively without substantial portions of the optical energy reaching the aircraft surface. 
     Toward the fulfillment of these and other objects and advantages, the aircraft de-icing system of the present invention involves positioning a laser beam generator on an aircraft, generating a beam of radiant energy, directing the beam toward the aircraft to create a footprint upon a surface of the aircraft, and manipulating the beam so that the footprint is moved about the aircraft surface for removing ice, snow or water from the aircraft surface. The laser beam generator is preferably disposed remotely from the area to be de-iced, and the beam is preferably reflected from a mirror so that the mirror may be manipulated to move the footprint about the aircraft surface. The beam may have a wavelength that is preferentially reflected by the aircraft surface and absorbed by ice, snow and water, so that the beam heats and removes ice, snow and water from the aircraft surface as the beam&#39;s footprint is moved thereabouts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above brief description, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is an overhead schematic view of a de-icing system of the present invention.; 
     FIG. 2 is a schematic view of a de-icing system of the present invention; 
     FIG. 3 is a view showing overlapping footprints created on an aircraft surface by a laser beam, an ice detection system, and a visible light source in accordance with an alternate embodiment of the system of the present invention; 
     FIG. 4 is a schematic view of an alternate embodiment of an ice detection and de-icing system of the present invention; and 
     FIG. 5 is a schematic view of a de-icing system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the reference numeral  10  refers in general to a de-icing system of the present invention. An auxiliary power unit  12  provides power via cables  13  to a radio frequency or microwave generator  14  that then transmits the power to the individual laser beam generators  16  via coaxial cables or waveguides  18 . Each laser beam generator  16  generates a beam  20  which passes through a conduit  22 , strikes a mirror  24  and is reflected toward the aircraft  26  where the beam forms a footprint  28  on the surface  30  of the aircraft. Drivers  32  are operatively connected to the mirrors  24  to manipulate or move the mirrors  24  to move the beams  20  about the aircraft surface  30 . 
     The auxiliary power unit  12  is part of the existing aircraft power system of the kind which is typically present in commercial aircraft and which can supply several hundred kilowatts of electrical power for powering the system  10 . The auxiliary power unit  12  is typically disposed adjacent a gas turbine engine  34  on a wing  36 . It is of course understood that a self-contained unit, including its own power supply, could be used or that some combination of different power sources could be used. As best seen in FIG. 2, the auxiliary power unit  12  is operably connected to a radio frequency or microwave generator  14  by cables  13  to provide power to the radio frequency or microwave generator  14 . The radio frequency or microwave generator  14  then transmits the power to the individual laser beam generators  16  using coaxial cables or waveguides  18 . In an alternate embodiment depicted in FIG. 5, the gas turbine  34  powers a turbo pump  37  and turbo generator  39  to circulate a gas such as CO 2  through a recirculation loop  41  which includes a heat exchanger  43 . The recirculation loop  41  passes through the conduit  22  for generating a beam  20  within the conduit  20 . 
     A compact laser beam generator  16 , preferably a CO 2  laser beam generator, is used to generate an efficient, high power, infrared laser beam  20 . An example of a compact CO 2  laser beam generator is described in U.S. Pat. No. 5,689,523, issued to Seguin, the entirety of which is incorporated by reference herein as if fully set forth herein. The laser efficiency is preferably within a range of approximately 30% to approximately 50%, and more preferably approximately 33%. It is understood that other laser beam generators may be used. For example, a CO laser beam generator may generate a beam with similar efficiencies, having a wavelength substantially within the range of approximately 9 microns to approximately 11 microns. The power of the generated beam  20  is preferably substantially within a range of approximately 25 kW to approximately 50 kW and is more preferably approximately 50 kW. The wavelength of the beam  20  is preferably selected from a range that is preferentially reflected by the aircraft surface  30  and absorbed by ice, snow and water  38 . The wavelength is preferably substantially within a range of approximately 8 microns to approximately 15 microns, is more preferably substantially within a range of approximately 9 microns to approximately 11 microns, and is most preferably within a range of approximately 10 microns to approximately 11 microns. It is understood that different wavelengths may be used and that wavelengths may be used which are preferentially absorbed or reflected by various areas of the aircraft surface or by ice, snow or water  38 . 
     The optical absorption depth of a beam  20  having a wavelength of approximately 10 microns to 11 microns in ice, snow and water  38  is approximately 0.1 mm, so the infrared optical energy is absorbed at the surface of the ice, snow or water, and the ice, snow or water is melted or evaporated selectively without significant amounts of the optical energy reaching the aircraft surface  30 . In contrast, the metals comprising much of the aircraft surface  30  reflect approximately 90% to approximately 95% of optical energy at a wavelength of approximately 10 microns to approximately 11 microns, so little of the optical energy is absorbed by the metal surfaces, making it possible to use such beams  20  without significantly increasing the temperature of such metal surfaces. Composite structures located at various portions or regions of an aircraft surface  30  may be painted with a metal pigment paint to reflect the optical energy. Conversely, critical surfaces may also be treated with absorptive paints and materials to absorb and conduct thermal energy to other critical areas. Also, the optical absorption depth of 10 to 11 micron energy in plastic and glass is approximately 1 to 2 mm, so passengers and pilots are protected from scattered light in the unlikely event that the beam  20  is accidentally pointed at an aircraft window. Similarly, work crews may be protected using protective clothing, optical glasses or goggles and helmets as would typically be worn in cold weather. 
     Conduits  22  are disposed to run along opposite sides of the fuselage  40  for housing the laser beam generators  16  and for providing a passageway for the beams  20  as the beams  20  pass from the laser beam generators  16  to the mirrors  24 . A desired number of generators  16  may be disposed at various locations along the conduit  22  for directing beams  20  directly toward the aircraft surface  30  or for directing beams  20  toward mirrors  24  which in turn reflect the beams  20  to the aircraft surface  30 . The conduits  22  may be affixed to the outside of the fuselage  40  or may be secured within the fuselage and may extend to regions other than the fuselage to route or “pipe” beams  20  as desired. The conduits  22  and, in fact, the entire system  10  may be easily serviceable and may be easily removable for those aircraft  26  not operating in potentially icing conditions. 
     The mirrors  24  are high average power metal mirrors, such as cooled copper mirrors, similar to those developed by the military for directing laser beams in applications such as anti-missile systems for aircraft. The metal mirrors  24  expand the 25 kW laser beam  20  such that the intensity or power density is substantially within a range which is preferably from approximately 5 kW/m 2  to approximately 50 kW/m 2 , is more preferably from approximately 10 kW/m 2  to approximately 50 kW/m 2 , and is most preferably approximately 25 kW/m 2 . A power density of 25 kW/m 2  is about 25 times that of sunlight at sea level on the equator, or 25 suns. The mirrors  24  reflect the beams  20  toward the aircraft surface  30  so that the beams  20  impinge upon and create footprints  28  on the aircraft surface having an area of approximately 0.5 m 2 . The mirrors  24  may be movable between a deployed position in which at least a portion of the mirrors  24  are disposed externally to the fuselage  40  or conduit  22  and a retracted position in which the mirrors are disposed within cavities in the fuselage or conduit. As one alternative, the mirrors  24  may be permanently positioned within a cavity in the fuselage  40  or conduit  22  or, similarly, may be permanently positioned with at least a portion disposed externally to the fuselage or conduit Germanium or salt beam splitters or laser windows may be used to pass the beam simultaneously to more than one conduit  22  or mirror  24  but are not preferred because of the cost and complexity of fabricating such beam splinters or laser windows with sufficient capabilities for use with the system. 
     Drivers or motors  32  are used to align and control movements of the mirrors  24  to permit the mirrors to move the reflected beams  20  so that the footprint  28  of each beam may be moved about the aircraft surface  30 , for example, along leading edges of the wings and tail sections  42 . The speed at which the footprints  28  will move across the surface  30  will vary depending upon such things as ice thickness and other conditions but can easily fall within a range of approximately 0.1 m/s to approximately 1.0 m/s. It is understood that the laser beam generators  16  may direct the beams  20  directly toward the aircraft surface  30  without the use of mirrors  24 , in which case drivers or motors  32  may be operatively connected to the laser beam generators so that the footprint  28  may be moved about the aircraft surface  30 . 
     In an alternate embodiment, depicted in FIGS. 3 and 4, the system  10  may be equipped for remote detection of ice using a thermal monitoring system like the system described in more detail in U.S. patent application Ser. No. 08/706,598, filed by the present inventor. As discussed in that application, the wavelength of the beam  20  is selected from a range that is preferentially reflected by the aircraft surface  30  and absorbed by ice, snow and water  38 . In that regard, for a beam  20  having a wavelength within a range of approximately 10 microns to approximately 11 microns, the aircraft surface  30  reflects such a beam  20  with approximately 90% to 95% efficiency, whereas ice, snow and water strongly absorb such radiation. Accordingly, as the beam  20  scans the aircraft surface  30 , regions of the aircraft surface that are covered with ice, snow or water  38  will experience temperature rises at relatively increased rates as compared to regions clear thereof. The thermal monitoring system uses an infrared thermal camera  44  that generates a beam  46  having a wavelength different from that of beam  20 . The wavelength of beam  46  is preferably within a range of approximately 1 to 2 microns and is more preferably approximately 1.5 microns. As best shown in FIG. 4, the beam  46  passes from the infrared thermal camera  44  through the 1 to 2 micron near infrared narrow band transmission filter  48  and is reflected by the near infrared beam splitter  50 , salt window  52  and mirrors  24  to create a footprint  53  on the aircraft surface  30 . The camera  44  can resolve temperature differences of approximately 1 or 2 degrees C. and can create an image of a scanned aircraft surface  30  to highlight regions experiencing temperature rises at relatively increased rates, indicating the presence of ice, snow or water  38  which are preferentially absorbing the long wavelength thermal energy. The thermal monitoring system can therefore be used to detect the presence of ice, snow or water  38  on an aircraft surface  30  and to document the location of the ice, snow or water by imaging the region of interest as it is scanned. The system may also be used to determine ice thickness by determining the time required to melt through the ice to the underlying reflective aircraft surface  30  using a stationary beam  20 . Pre-programmed point measurement of ice thickness over the surface can also be used to build a point-by-point map of the surface ice thickness. The remote ice detection and imaging capabilities of the thermal monitoring system also permit the thermal monitoring system to continually monitor the aircraft surface  30  for the presence of ice, snow or water and to verify, confirm or certify that the aircraft  26  is substantially free of ice, snow or water during flight or after treatment. 
     As best seen in FIGS. 3 and 4, a visible light source  54 , for example a source of a visible, low power laser beam  56 , such as a red HeNe beam having a wavelength of approximately 0.62 microns, may be used in connection with the system  10  to highlight the location of the footprint  28  of beam  20  as the beam  20  footprint  28  scans, or is moved about, the aircraft surface  30 . The visible beam  56  passes through a visible beam narrow band transmission filter  58 , is reflected by visible mirror  60 , passes through beam splitter  50  and is reflected by Zinc Selenide window  52  and mirrors  24  so that it creates a footprint  62  on the aircraft  26  that substantially overlaps with the footprints  28  and  53  of beams  20  and  46 . The footprint  62  of beam  56  also moves with the footprints  28  and  53  created by beams  20  and  46  as the footprints scan or move about the aircraft surface  30 . 
     As indicated in FIG. 4, computer based controls  64  may be used for such things as aircraft image recognition, laser or mirror positioning and control, and temperature sensing and imaging. Computer controls permit the beam  20  to follow a pre-determined scan pattern designed for the particular aircraft or conditions. Computer controls  64  also permit instantaneous beam positioning and intensity control for safety purposes. In that regard, the laser intensity is controllable by the computer controls in a sub-second time scale such that the laser power can be adjusted over a large range, such as from approximately 10% to approximately 100% as the beam  20  is scanned across an aircraft  26 . The computerized control  64  permits the system to apply thermal energy in a predetermined pattern, monitor surfaces for ice, snow and water  38 , control exposure for instantaneous safety control and certify aircraft condition during flight or at the end of the de-icing or anti-icing procedure. 
     In operation, an operator engages auxiliary power unit  12  to provide power to the radio frequency or microwave generator  14  which in turn powers the laser beam generators  16 . Beams  20  are generated and pass through conduits  22  to mirrors  24  where the beams  20  are reflected by the mirrors  24  to impinge upon and create footprints  28  upon the aircraft surface  30 , such as on leading edges of the wings  36  and tail section  42 . Drivers  32  manipulate the mirrors  24  to move the footprints  28  of the beams  20  about the aircraft surface  30 . The movement may be in a predetermined pattern or may be based upon manual controls and observation. Each beam  20  melts or evaporates the ice, snow or water  38  as its footprint  28  moves about the surface  30  of the aircraft. If used, the thermal monitoring system monitors the aircraft surface for the continued presence of ice, snow or water  38 . Unlike radiant systems or laser systems lacking the flexibility to treat hard to reach areas, the directivity of the laser beam  20  permits the present system  10  to treat interior compartments, such as air brakes and aileron, when they are opened during de-icing. In that regard, once the beam  20  enters the interior compartments, it will reflect from the metal surfaces and bounce around the interior compartment to reach most or all of the areas therein. 
     Upon completion of a predetermined pattern, or upon certification or verification by the thermal monitoring system or other means that the aircraft  26  is or has been placed in an acceptable condition, the system  10  is deactivated. The system  10  may be used while the aircraft is on the ground or in flight. Of course, the present de-icing system  10  may also by used in place of or in combination with other de-icing or anti-icing methods. For example, after de-icing an aircraft  26  using another method, the present system  10  may be used as an anti-icing measure as the aircraft  26  taxis to or waits on a runway. 
     An order of magnitude estimation of the laser power requirements necessary to deliver radiant energy to critical areas of an aircraft  26  while in flight is shown in Table 1. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Laser Size Calculations and Power Requirements for Airborne Systems 
               
             
          
           
               
                 Parameter 
                 Case 1 
                 Case 2 
                 Units 
               
               
                   
               
               
                 Critical Surface Area 
                 20 
                 20 
                 m 2   
               
               
                 Average Laser Power Density 
                 5 
                 10 
                 suns 
               
               
                   
                 5,000 
                 10,000 
                 W/m 2   
               
               
                 Total Laser Power 
                 100 
                 200 
                 kW 
               
               
                 Laser Efficiency 
                 0.33 
                 0.33 
               
               
                 Electrical + Pump Power 
                 303 
                 606 
                 kW 
               
               
                 Horsepower Equivalent 
                 404.04 
                 808.08 
                 Hp 
               
               
                 Energy Conversion Efficiency 
                 0.50 
                 0.50 
               
               
                 Engine Horsepower Requirements 
                 808.08 
                 1616.16 
                 Hp 
               
               
                   
               
             
          
         
       
     
     The calculations illustrate that an onboard de-icing system  10  of the present invention is feasible because commercially available CO 2  laser beam generators  16  are presently on the market with average power levels of 50 kW and larger, and existing aircraft power systems on commercial aircraft can supply up to several hundred kilowatts of electrical power. 
     Other modifications, changes and substitutions are intended in the foregoing, and in some instances, some features of the invention will be employed without a corresponding use of other features. For example, although the present invention is described for use in connection with aircraft  26 , the system  10  may be used to detect and remove ice, snow and water  38  from other surfaces, as well. Further, it is understood that the term aircraft as used herein includes but is not limited to airplanes, jets, helicopters, and space craft. Similarly, it is understood that the term aircraft surface as used herein includes moving and nonmoving parts and components. Further still, although the beam  20  is described as being manipulated to move the footprint  28  about the surface  30  of the aircraft, it is understood that the location of the footprint  28  may be fixed relative to the aircraft surface  30 . Also, the system  10  may be used in connection with the removal of substances other than or in addition to ice, snow and water. Further, the de-icing system  10  may be used without using the ice detection system described and without using the accompanying visible light source  54  for tracking. Further still, the ice detection system may operate independently of the de-icing system  10 , and beam  46  need not track beam  20  as the footprints  53  and  28  of the beams move about the aircraft surface  30 . Also, any number, configuration or arrangement of conduits  22  may be used, or the system  10  may be used without conduits  22 . Although a CO 2  laser beam  20  is preferred, any number of suitable coherent beams of radiant energy may be used, including but not limited to CO lasers. Also, although the beams  20 ,  46  and  56  are shown as traveling over the same path over much of their lengths, separate mirror or optical systems may be used for one or more of the beams. Of course, measurements and other numerical values given in connection with such things as preferred ranges for efficiencies, power, wavelengths and other values, are given by way of example and are not intended to limit the scope of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.