Patent Publication Number: US-2016229515-A1

Title: Windshield of aircraft

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a windshield of an aircraft, and more particularly, to a heater provided in the windshield. 
     2. Description of the Related Art 
     A windshield of an aircraft includes a heater in order to prevent occurrence of fogging due to a temperature difference and adhesion of ice (Japanese Patent Laid-Open No. 2011-225076). 
     In Japanese Patent Laid-Open No. 2011-225076, a thin film of ITO (indium tin oxide), gold, silver, or the like is formed on a windshield panel as the heater. The fogging of the windshield and the adhesion of ice thereto are prevented by heat generated from the thin film to which a current is supplied. 
     The windshield of the aircraft, and the heater provided in the windshield need to have reliability against lightning. 
     Countermeasures against a direct strike of lightning are taken such that a high current of lightning striking a frame or the like of the windshield is spread to the airframe, which is a conductor. It is also necessary to take countermeasures against an induced current flowing through the heater of the windshield due to a strong magnetic field in association with the lightning current. 
     That is, it is necessary to avoid problems that a high induced current exceeding an allowable limit of a conductive film or an electrically-heated wire provided in the windshield as the heater flows through the conductive film or the electrically-heated wire, and a voltage of a controller connected to the heater is increased beyond a withstand voltage by an induced current flowing into the controller. 
     While an electromagnetic shield is typically used for avoiding generation of an induced current by an external magnetic field, it is difficult to ensure visibility required for the windshield while providing the windshield with shieldability high enough to block the strong magnetic field in association with the lightning current. 
     An object of the present invention is to provide effective countermeasures against an induced current that is induced in a heater of a windshield in a lightning strike. 
     SUMMARY OF THE INVENTION 
     The present invention is a windshield of an aircraft, including a conductive member that is configured to generate heat when a current is supplied, wherein the conductive member is oriented in a lateral direction that is a horizontal direction included in an in-plane direction of the windshield. 
     The lateral direction in which the conductive member of the present invention is oriented is the horizontal direction. This is defied based on an attitude of the aircraft that is parked or cruising. The lateral direction in which the conductive member of the present invention is oriented corresponds to the horizontal direction of the parked or cruising aircraft. 
     The conductive member that functions as a heater of the windshield allows a current to flow in the direction in which the conductive member is oriented. 
     Therefore, when the conductive member is oriented in the horizontal lateral direction included in the in-plane direction of the windshield, a current flows through the conductive member along the lateral direction. 
     Also, when the conductive member is oriented in a longitudinal direction perpendicular to the lateral direction in the in-plane direction of the windshield, a current flows through the conductive member along the longitudinal direction. The longitudinal direction includes a component in a vertical direction. 
     A current of lightning striking the aircraft flows from an upper side to a lower side in the vertical direction in most cases. 
     Thus, when the component in the vertical direction is included in the direction in which the conductive member is oriented as in the above conductive member that is oriented in the longitudinal direction, an induced current flows through the conductive member in a direction in which a change in a magnetic flux of a magnetic field generated around the lightning current is hindered by electromagnetic induction from the magnetic field (Lenz&#39;s law). 
     On the other hand, when the conductive member is oriented in the horizontal lateral direction as in the present invention, almost no induced current can flow through the conductive member in the direction in which the change in the magnetic flux in association with the lightning current is hindered. Therefore, the induced current is suppressed. 
     The conductive member in the present invention can be configured as a belt-like member along the in-plane direction of the windshield, and a line-like member that is wired in the in-plane direction of the windshield. 
     As the conductive member in the present invention, three conductive members to which a three-phase alternating current is supplied can be prepared. 
     An aircraft of the present invention includes the above windshield. 
     In accordance with the present invention, even when the conductive member of the windshield is placed in the magnetic field in association with the lightning current, the induced current induced in the conductive member can be suppressed. Therefore, it is possible to ensure reliability by avoiding damage to the conductive member, and an electric wire and a controller etc. connected to the conductive member by the induced current. 
     Since the induced current can be coped with by setting the direction in which the conductive member is oriented to the lateral direction in the present invention, it is not necessary to cover the conductive member with an electromagnetic shield. Consequently, it is possible to ensure sufficient visibility required for the windshield. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating an appearance of a windshield of an aircraft according to a first embodiment of the present invention; 
         FIG. 2  is a schematic view illustrating the windshield and an anti-icing/anti-fogging device shown in  FIG. 1 ; 
         FIG. 3  is a schematic view illustrating a windshield and an anti-icing/anti-fogging device according to a comparative example; 
         FIGS. 4A and 4B  are schematic views for explaining that an induced current flows through conductive layers oriented in a longitudinal direction of the comparative example shown in  FIG. 3  in a lightning strike; 
         FIG. 5A  is a schematic view for explaining that an increase in a magnetic flux is hindered, and  FIG. 5B  is a schematic view for explaining that a decrease in a magnetic flux is hindered; 
         FIGS. 6A and 6B  are schematic views for explaining that an induced current hardly flows through conductive layers of the embodiment of the present invention in a lightning strike; 
         FIG. 7A  is a schematic view for explaining that the conductive layers of the embodiment of the present invention hardly contributes to hindering a change in a magnetic flux, and  FIG. 7B  is a schematic view for explaining that the induced current hardly flows even when the aircraft is slightly inclined; and 
         FIG. 8  is a schematic view illustrating a windshield and an anti-icing/anti-fogging device of an aircraft according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments of the present invention will be described by reference to the accompanying drawings. 
     First Embodiment 
     An aircraft  1  shown in  FIG. 1  includes a windshield  10  and an anti-icing/anti-fogging device  20  that prevents fogging of the windshield  10  and adhesion of ice thereto at a front end of a nose  1 A. 
     The windshield  10  includes main windshields  10 A and  10 A that ensure a front field of view from the inside of a cockpit, and side windshields  10 B and  10 B that ensure a side field of view from the inside of the cockpit. The windshields  10 A,  10 A,  10 B, and  10 B are symmetrically disposed. 
     In the following, the windshields  10 A,  10 A,  10 B, and  10 B are collectively referred to as the windshield  10 . 
     The windshield  10  is a laminate including a plurality of transparent windshield panels  11  formed of glass, acrylic resin, or the like. 
     The laminate includes a layer that absorbs a shock, and a heater that constitutes the anti-icing/anti-fogging device  20  (conductive layers  21 ,  22 , and  23  in  FIG. 2 ). 
     The windshield  10  is curved along a shape of an airframe in which the windshield  10  is installed. 
     The windshield  10  is fixed to the airframe by a retainer  12  with a surface on an aircraft outer side directed obliquely upward. 
     The retainer  12  is disposed along an outer peripheral portion of the windshield panel  11  and an inner peripheral portion of an opening of the airframe. 
     The retainer  12  is formed of a metal material such as aluminum alloy, and is grounded to the airframe directly or via a fastener or the like. 
     The anti-icing/anti-fogging device  20  prevents or suppresses fogging of the windshield  10  due to a temperature difference between outside air and air within the cockpit, and adhesion of frost and ice to the outer surface of the windshield  10  in contact with outside air. 
     The anti-icing/anti-fogging device  20  includes the conductive layers  21 ,  22 , and  23 , and a controller  24  that applies a current to the conductive layers  21 ,  22 , and  23  as shown in  FIG. 2 . 
       FIG. 2  shows the windshield  10  by simplifying its shape. 
     The three belt-like conductive layers  21 ,  22 , and  23  are disposed along a curved in-plane direction of the windshield  10 . The conductive layers  21 ,  22 , and  23  are independent of each other. 
     The conductive layers  21 ,  22 , and  23  correspond to a three-phase alternating current applied by the controller  24 . The conductive layers  21 ,  22 , and  23  function as the heater by generating heat when a current is supplied. 
     Although delta connection is employed for connection of the conductive layers  21 ,  22 , and  23  in the present embodiment, star connection may be also employed. 
     The conductive layers  21 ,  22 , and  23  are provided in each of the windshields  10 A,  10 A,  10 B, and  10 B. 
     The conductive layers  21 ,  22 , and  23  are transparent or substantially transparent thin films of ITO (indium tin oxide), gold, silver, or the like. The conductive layers  21 ,  22 , and  23  can be formed on the windshield panel  11  by vapor deposition or the like. Alternatively, a base film where the conductive layers  21 ,  22 , and  23  are formed may be interposed between layers of the windshield  10 . 
     The conductive layers  21 ,  22 , and  23  can be provided at an appropriate position in a thickness direction of the windshield  10 . For example, when the windshield  10  includes an outer panel disposed on the aircraft outer side and an inner panel disposed on an aircraft inner side as the windshield panels  11 , the conductive layers  21 ,  22 , and  23  can be provided on a surface on the aircraft inner side of the outer panel, a surface on the aircraft outer side of the inner panel, or the like. 
     All of the conductive layers  21 ,  22 , and  23  are configured to be oriented in a lateral direction DH that is a horizontal direction included in the in-plane direction of the windshield  10 . 
     Each of the conductive layers  21 ,  22 , and  23  is designed as a circuit that allows a current to flow along the lateral direction DH. 
     The conductive layers  21 ,  22 , and  23  are preferably formed linearly from one end to the other end along the lateral direction DH. The conductive layers  21 ,  22 , and  23  extend over a substantially entire lateral width (a dimension in the horizontal direction) of each of the windshields  10 A,  10 A,  10 B, and  10 B. 
     The conductive layers  21 ,  22 , and  23  are arranged at a predetermined interval in a longitudinal direction DV of the windshield  10 . The longitudinal direction DV is perpendicular to the lateral direction DH in the in-plane direction of the windshield  10 . 
     The conductive layers  21 ,  22 , and  23  are electrically insulated from the retainer  12  disposed along the outer peripheral portion of the windshield panel  11 , and the airframe. 
     The conductive layers  21 ,  22 , and  23  of the present embodiment are not limited to a rectangular shape shown in  FIG. 2 , and may be set to a configuration oriented in the lateral direction DH in consideration of the shape of the windshield  10 . The configuration oriented in the lateral direction DH corresponds to the circuit that allows a current to flow along the lateral direction DH that is a direction connecting positions from which a current is drawn (opposite end portions to which an electric wire is connected in the present embodiment) in each of the conductive layers. 
     A width of the conductive layer  21  may be changed in a length direction of the conductive layer  21 . The same applies to the conductive layers  22  and  23 . 
     Also, lengths of the conductive layers  21 ,  22 , and  23  may be different from each other. 
     The conductive layers  21 ,  22 , and  23  are connected to the controller  24  by electric wires  25 A,  25 B, and  25 C as shown in  FIG. 2 . The electric wire  25 A is connected to an A point between the conductive layers  21  and  22 . The electric wire  25 B is connected to a B point between the conductive layers  22  and  23 . The electric wire  25 C is connected to a C point between the conductive layers  21  and  23 . 
     The controller  24  applies a drive current to the conductive layer  21  by electric power received from a power supply line that is mounted on the aircraft  1 . 
     The controller  24  can control heat generation amounts of the conductive layers  21 ,  22 , and  23  by changing a frequency or a voltage of the applied drive current. 
     The electric wires  25 A,  25 B, and  25 C are wired in a region less affected by a magnetic field in association with lightning, such as the inside of the retainer  12  and the inside of the airframe. 
     The electric wires  25 A,  25 B, and  25 C, and the controller  24  can be made redundant if necessary. 
     The windshield  10  and the anti-icing/anti-fogging device  20  need to have reliability against lightning. 
     A current of lightning striking a metal member such as the retainer  12  ( FIG. 2 ) provided in the windshield  10  and a wiper (not shown) is spread to the airframe to which the metal member such as the retainer  12  is grounded. Therefore, it is possible to avoid damage to the windshield  10  by a shock or heat generated by the high current of lightning. 
     It is also necessary to avoid flowing of an excessive induced current through the conductive layers  21 ,  22 , and  23  by a strong magnetic field generated around the lightning current. 
     In the present embodiment, an induced current induced in the conductive layers  21 ,  22 , and  23  is suppressed by setting the direction in which the conductive layers  21 ,  22 , and  23  are oriented to the lateral direction DH without blocking the strong magnetic field in association with the lightning current by an electromagnetic shield. Description will be made in the following. 
     First, a typical configuration ( FIG. 3 ) of the conductive layer that is the heater of the windshield will be described. 
     A windshield  8  shown in  FIG. 3  includes three conductive layers  81 ,  82 , and  83  corresponding to a three-phase alternating current. All of the conductive layers  81 ,  82 , and  83  are oriented in the longitudinal direction DV perpendicular to the lateral direction DH in an in-plane direction of the windshield  8 . 
     Each of the conductive layers  81 ,  82 , and  83  is designed as a circuit that allows a current to flow along the longitudinal direction DV. 
     An induced current flowing through the conductive layers  81 ,  82 , and  83  of the windshield  8  by a magnetic field in association with a lightning current will be described by reference to  FIGS. 4A and 4B . 
     The aircraft  1  is likely to be struck by lightning generated between the aircraft  1  and a thundercloud existing above the aircraft  1 . Thus, lightning is modeled by a lightning current I T  flowing from an upper side to a lower side in a vertical direction D 0  ( FIG. 4A ). 
     A magnetic field H having a magnetic flux density B is generated around the lightning current I T  according to Ampere&#39;s law (right-hand corkscrew rule). A magnetic flux  101  of the magnetic field H is formed concentrically around the lightning current I T . A wavefront  100  formed by the magnetic flux  101  is perpendicular to the lightning current I T . 
     When the magnetic field H is generated by a lightning strike to the retainer  12  ( FIG. 3 ) or the like of the windshield  10 , an induced electromotive force proportional to a change in the magnetic flux  101  is generated in a conductor (the conductive layers  81 ,  82 , and  83 ) through which the magnetic flux  101  of the magnetic field H passes, and an induced current I ID  flows (Faraday&#39;s law of induction). The induced current I ID  flows in a direction in which the change in the magnetic flux  101  is hindered (Lenz&#39;s law). 
     Therefore, when the magnetic flux  101  is increased by the lightning strike, the induced current I ID  flows through the conductive layers  81 ,  82 , and  83  in a direction indicated by an arrow in  FIG. 4B  from the lower side to the upper side so as to generate a magnetic flux  102  in a direction in which the magnetic flux  101  is canceled. At this time, the magnetic flux  102  of a magnetic field H′ generated around the induced current I ID  is formed around the induced current I ID  on a wavefront  103  perpendicular to the induced current I ID . 
     When the magnetic field H is decreased by spreading the lightning current I T  to the airframe, the induced current I ID  flows through the conductive layers  81 ,  82 , and  83  from the upper side to the lower side so as to generate the magnetic flux  102  in the same direction as the magnetic flux  101 . 
     By the way, ease with which the induced current I ID  flows depends on a direction in which the conductor placed in the magnetic field H is oriented. 
     All of the conductive layers  81 ,  82 , and  83  shown in  FIG. 4B  are oriented in the longitudinal direction DV. The longitudinal direction DV includes a component in the vertical direction D 0 . 
     When the component in the vertical direction D 0  is included in the direction in which the conductive layers  81 ,  82 , and  83  are oriented, the direction of the magnetic flux  102  on the wavefront  103  perpendicular to the induced current I ID  includes the direction in which the change in the magnetic flux  101  is hindered. 
     A case in which the increase in the magnetic flux  101  is hindered will be described by using magnetic fluxes M 11  and M 12  on the wavefront  100  and magnetic fluxes M 21  and M 22  on the wavefront  103  as an example by reference to  FIG. 5A . 
     The magnetic fluxes M 11  and M 12  approximate the magnetic flux  101  ( FIG. 4A ) formed around an axis of the lightning current I T  in a straight line, and are both perpendicular to the vertical direction D 0 . 
     The magnetic fluxes M 21  and M 22  approximate the magnetic flux  102  ( FIG. 4B ) formed around an axis of the induced current I ID  in a straight line, and are both perpendicular to the longitudinal direction DV. 
     The magnetic flux M 21  positioned on the wavefront  103  includes a component M 21 ′ in a direction opposite to a direction of the magnetic flux M 11  positioned on the wavefront  100 . The component M 21 ′ contributes to canceling the magnetic flux  101 . 
     Also, the magnetic flux M 22  positioned on the wavefront  103  includes a component M 22 ′ in a direction opposite to a direction of the magnetic flux M 12  positioned on the wavefront  100 . The component M 22 ′ contributes to canceling the magnetic flux M 12 . 
     As indicated by a relationship between the magnetic fluxes M 21  and M 22  and the magnetic fluxes M 11  and M 12  described above, the magnetic flux  102  contributes to hindering the increase in the magnetic flux  101 . 
     The same applies to a case in which the decrease in the magnetic flux  101  is hindered. 
     As shown in  FIG. 5B , the magnetic flux M 21  positioned on the wavefront  103  includes the component M 21 ′ in the same direction as the direction of the magnetic flux M 11  positioned on the wavefront  100 . 
     Also, the magnetic flux M 22  positioned on the wavefront  103  includes the component M 22 ′ in the same direction as the direction of the magnetic flux M 12  positioned on the wavefront  100 . 
     As indicated by a relationship between the magnetic fluxes M 21  and M 22  and the magnetic fluxes M 11  and M 12  described above, the magnetic flux  102  contributes to hindering the decrease in the magnetic flux  101 . 
     Based on the above description, when the component in the vertical direction D 0  is included in the direction in which the conductive layers  81 ,  82 , and  83  are oriented (the longitudinal direction DV), the induced current I ID  flows through the conductive layers  81 ,  82 , and  83  according to Lenz&#39;s law. 
     That is, based on the existence of the conductive layers  81 ,  82 , and  83  that allow a current to flow in the direction in which the magnetic flux  102  that hinders the change in the magnetic flux  101  is generated, the induced current I ID  flows through the conductive layers  81 ,  82 , and  83  placed in the magnetic field H. 
     Next, the conductive layers  21 ,  22 , and  23  of the present embodiment will be described. 
     As shown in  FIGS. 6A and 6B , all of the conductive layers  21 ,  22 , and  23  are oriented in the lateral direction DH that is the horizontal direction. 
     When it is assumed that a current I flows through each of the conductive layers  21 ,  22 , and  23 , a magnetic flux  104  of a magnetic field generated around the current I flowing along the lateral direction DH in which the conductive layers  21 ,  22 , and  23  are oriented is formed on a wavefront  105  perpendicular to the current I. The wavefront  105  and the horizontal wavefront  100  perpendicular to the lightning current I T  are perpendicular to each other. 
     Accordingly, the magnetic flux  104  in all directions on the wavefront  105  hardly builds a relationship of canceling or increasing the magnetic flux  101  with the magnetic flux  101  in all directions on the wavefront  100 . 
     As shown in  FIG. 7A , for the wavefront  105  as a whole, the magnetic flux  104  that does not contribute to canceling or increasing the magnetic flux  101  at all is dominant, and the change in the magnetic flux  101  is hardly hindered by the magnetic flux  104 . 
     Based on the above description, even when the conductive layers  21 ,  22 , and  23  are placed in the strong magnetic field H in association with the lightning current I T , the induced current (the above current I) hardly flows through the conductive layers  21 ,  22 , and  23 . 
     The wavefront  100  and the wavefront  105  may not be in a strict perpendicular relationship as shown in  FIG. 7B  depending on an attitude of the aircraft  1  and a direction of the lightning current I T . 
     However, based on an attitude of the aircraft  1  that the aircraft  1  can assume in a normal condition, and a lightning strike situation of the aircraft  1 , other components of the magnetic flux  104  than a component of the magnetic flux  104  that cancels or increases the magnetic flux  101  are dominant as compared to the canceling or increasing component. Thus, the induced current flowing through the conductive layers  21 ,  22 , and  23  is suppressed. 
     In accordance with the present embodiment described above, it is possible to avoid problems that a high induced current exceeding an allowable limit of the conductive layers  21 ,  22 , and  23  flows through the conductive layers  21 ,  22 , and  23 , the electric wires  25 A,  25 B, and  25 C connected to the conductive layers  21 ,  22 , and  23  are burnt out by the induced current, and a voltage of the controller  24  is increased beyond a withstand voltage by the induced current flowing into the controller  24  through the electric wires  25 A,  25 B, and  25 C. Even when the induced current flows into the controller  24  through the electric wires  25 A,  25 B, and  25 C as unexpected noise  106  as shown in  FIG. 2 , the noise  106  is sufficiently smaller than the noise  106  in the typical example ( FIG. 3 ). 
     In accordance with the present embodiment, it is possible to prevent deterioration of the conductive layers  21 ,  22 , and  23  with the conductive layers  21 ,  22 , and  23  overheated by the induced current flowing in a lightning strike, and damage to the controller  24  with the controller  24  exceeding the withstand voltage by the induced current. It is thus possible to ensure sufficient reliability of the windshield  10  and the anti-icing/anti-fogging device  20  against lightning strikes. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described by reference to  FIG. 8 . 
     In the following, different points from those of the first embodiment will be mainly described. 
     In the second embodiment, electrically-heated wires  26 ,  27 , and  28  that are wired in an in-plane direction of a windshield  15  are used as a heater of the windshield  15 . 
     The electrically-heated wires  26 ,  27 , and  28  are provided in the windshield  15  by embedding the electrically-heated wires  26 ,  27 , and  28  in the windshield panel  11  or sandwiching the electrically-heated wires  26 ,  27 , and  28  between the windshield panels  11 . 
     The electrically-heated wires  26 ,  27 , and  28  correspond to a three-phase alternating current applied by the controller  24 , and generate heat when a current is supplied. 
     All of the electrically-heated wires  26 ,  27 , and  28  are wired in a loop shape oriented in the lateral direction DH that is included in the in-plane direction of the windshield  15 . The electrically-heated wires  26 ,  27 , and  28  are formed linearly from one end to the other end along the lateral direction DH. 
     The electrically-heated wires  26 ,  27 , and  28  are arranged at a predetermined interval in the longitudinal direction DV of the windshield  15 . 
     Each of the electrically-heated wires  26 ,  27 , and  28  is designed as a circuit that allows a current to flow along the lateral direction DH in which the electrically-heated wires  26 ,  27 , and  28  are oriented. 
     As long as the electrically-heated wires  26 ,  27 , and  28  are oriented in the lateral direction DH, the electrically-heated wires  26 ,  27 , and  28  can be wired in an appropriate form such as a rectangular shape and a ladder shape. 
     Since the electrically-heated wires  26 ,  27 , and  28  are oriented in the lateral direction DH similarly to the above conductive layers  21 ,  22 , and  23 , the induced current I ID  is hardly induced similarly to the description in the first embodiment (see  FIGS. 6A, 6B , and  7 A) even when the electrically-heated wires  26 ,  27 , and  28  are placed in the magnetic field H in association with the lightning current I T . 
     Therefore, it is possible to prevent burnout of the electrically-heated wires  26 ,  27 , and  28  and the electric wires  25 A,  25 B, and  25 C and damage to the controller  24 . 
     The constitutions described in the aforementioned embodiments may be also freely selected or appropriately changed into other constitutions without departing from the gist of the present invention. 
     The windshield of the present invention can be configured to include two conductive members to which a single-phase alternating current is applied. In this case, the two conductive members may be formed so as to be oriented in the horizontal direction (the lateral direction DH) included in the in-plane direction of the windshield.