Abstract:
A cowling assembly for a vehicle includes a generally external surface having secured thereto or adjacent thereto, an elongate lightning protection strip member. The lightning protection strip member includes a lightning diverter strip connected to a lightning conductor strip. The lightning diverter strip at least when subjected to high electric field, enabling an ionized channel to be established along the diverter strip to divert the lightning along the lightning diverter strip to the lightning conductor strip. The lightning conductor strip conducts the lightning from the lightning diverter strip to an earth of the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Priority is claimed to United Kingdom patent application Ser. No. 0514256.7 filed Jul. 12, 2005 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     TECHNICAL FIELD 
     This invention relates to a cowling assembly for a vehicle and more particularly, but not exclusively, to a forward cowling such as a nose cap assembly or a radome for an aircraft. 
     BACKGROUND OF THE INVENTION 
     Operational equipment such as radar and the like transmitting and sensory equipment, is commonly forwardly mounted on an aircraft, e.g. in the nose of the aircraft. The equipment is protected from the environment by a cowling or nose cap assembly which on most aircraft is constructed predominantly from material which is transparent to electromagnetic radiation at the operational frequencies of the equipment. Typically the cowling assembly is made of a fiber reinforced honeycomb structure. Such materials, however, do not provide protection against lightning which can puncture the nose cap assembly and cause severe damage to the electronics or sensory equipment. 
     For lightning protection, it is known to provide conductive strips on the general external surface of the nose cap assembly. The conducting strips are typically of a material and are of sufficient cross sectional area, to capture a leader channel of the lightning, and conduct it, for example, to the (metallic) air frame, so as to protect the nose cap assembly and the operational equipment behind it. Although the metallic conducting strips are efficient at providing lightning protection, they can interfere with the proper operation of the sensory equipment. For example, where the equipment is radar, the presence of metallic strips can obstruct the radar&#39;s view. 
     It also is known to utilize a lightning diverter strip consisting of metal elements which are insulated from one another. Such a strip may be made virtually, if not completely transparent to electromagnetic radiation under normal conditions. When subjected to high electrical field conditions, as can be experienced if the nose cap assembly is struck by lightning, the material enables an ionized channel to be established along the surface of the diverter strip to divert the attachment point of the lightning arc by extending the arc length along the path above its surface. The use of diverter strips may provide for less sufficient lightning protection than conducting strips of corresponding cross section. However, diverter strips are widely used in order to not obscure the reception of electromagnetic radiation by sensory equipment housed behind the cowling. 
     Where the cowling is large, such that very long diverter strips would be required to extend along the nose cap assembly external surface from a window position in front of the sensory equipment to the air frame, lightning diverter strips do not offer sufficient lightning protection. While lightning conductor strips could be used in the place of the lightning diverter strips, the conductive strips would then tend to obscure the window in front of the sensory equipment. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one feature of the invention, a cowling assembly for a vehicle is provided to include a generally external surface having secured thereto or adjacent thereto, one or more elongate lightning protection strip members. At least some of the lightning protection strip members including a lightning diverter strip part and a lightning conductor strip part. The lightning diverter strip part, at least when subjected to high electric field, enables an ionized channel to be established along the diverter part to divert the lightning along the lightning diverter strip part to the lightning conductor strip part. The lightning conductor strip part conducts the lightning from the lightning diverter strip part to an electrical earth of the vehicle. 
     In an assembly in accordance with one embodiment, the length of lightning diverter strip part may be maintained sufficiently short that it will function in a proper manner to capture the lightning and prevent the lightning from puncturing the cowling assembly. The diverter strip part need only divert the lightning to the conductor strip part which may capture the lightning and conduct it to earth. 
     As used herein, “earth” means a position of common potential throughout a frame of the vehicle, such as the airframe where the vehicle is an aircraft, or the chassis or body where the vehicle is a land vehicle, or a hull where the vehicle is waterborne, rather than the ground. 
     By “strip” we mean a structure which is typically longer than the maximum dimension of its cross section, for example, at least ten times greater. Typically the diverter and conductor strip parts each have a width dimension along the surface of the cowling which is greater, for example, at least five times greater, than a height dimension being the extent to which the strip parts project upwardly from the external surface of the cowling assembly. 
     In one embodiment, the diverter strip part includes a plurality of conductive, usually metallic, elements each of relatively small length along the diverter strip part, which elements are insulated from one another along the diverter strip part. The conductor strip part preferably is metallic, for example, of copper or aluminum. The diverter and conductor strips may be connected together by at least one conductive connector, such as a rivet or other fastener, or by direct electrical contact. 
     The cowling assembly may include a window portion where maximum transparency to electromagnetic radiation is required. Electromagnetic radiation sensory equipment may be mounted behind the window portion, and at least the majority of the lightning protection strip member over the window portion are provided by the diverter strip part. Preferably the conductor strip part does not extend significantly over the window portion. The invention has particular but not exclusive application to a cowling assembly for an aircraft. It should be understood that it may be used for protecting electronics in other types of vehicles, or for radar or other electronics which is not on a vehicle but is located where it may be exposed to lightening. 
     According to one embodiment of the invention, an aircraft is provided with a cowling assembly according to the first aspect of the invention. The aircraft may include electromagnetic radiation sensory equipment mounted behind a window portion of the cowling assembly. The window extends over an area through which a significant proportion of electromagnetic radiation to be sensed by the sensory equipment, passes. The cowling assembly may be, for example, a nose cap assembly for the aircraft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a is a front elevational view of a cowling assembly in accordance with one aspect of the invention in the form of an aircraft nose cap assembly; 
         FIG. 1   a  is an enlarged fragmentary view of part of a lightning diverter strip of the aircraft nose cap of  FIG. 1 ; and 
         FIG. 2  is a is an side elevational view of an aircraft having a cowling assembly in accordance with the second aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, a cowling assembly  10  is shown in the form of a nose cap assembly for an aircraft  12  for mounting at a forward end of an airframe of the aircraft  12 . The cowling assembly  10  provides protection against the environment for operation equipment, such as sensory equipment which senses electromagnetic radiation. In this example, the sensory equipment is radar equipment  14  which in use is mounted behind the cowling assembly  10 . It should be understood that the type of electronic equipment protected by the cowling assembly  10  is not a part of the invention. The cowling assembly  10  is commonly known as a radome and typically is made as a fiber reinforced honeycomb structure which is generally transparent to electromagnetic radiation, at least at the operational frequencies of the radar or other sensory or transmitting equipment  14 . 
     The cowling assembly  10  has a bulbous external surface  15 . A window portion  16  is located immediately in front of the radar or other equipment  14  through which a significant proportion of electromagnetic radiation to be sensed by the equipment  14 , passes. 
     To provide for lightning protection for the aircraft  12  and the equipment  14  behind the cowling assembly  10 , the external surface  15  of the assembly  10  is provided with a plurality of lightning protection strip members  18   a - 18   d.    
     Each lightning protection strip member  18   a - 18   d  includes a lightning diverter strip  20  and a lightning conductor strip  22  although in another embodiment, some lightning protection strip members  18   a - 18   d  which are only diverter strips and/or only conductor strips may be provided. 
     In accordance with one embodiment of the cowling assembly  10 , the lightning protection strip members  18   a - 18   d  provide for a lightning strike on the cowling assembly  10  to be captured and first diverted e.g. from free ends  21  of the diverter strips  20 , along the surface of the diverter strips  20  to the respective conductor strips  22  which each extend to an earth afforded by the airframe of the aircraft, as indicated at  25 . 
     As shown in  FIG. 1   a,  each diverter strip  20  includes a plurality of surface mounted metallic elements  20   a  in this example, each coated with an oxide or other resistive coating, and insulated from one another along the length of the diverter strip  20  by insulation  20   b , and being provided as a surfacing on a layer of electrically resistive material  20   c . The diverter strip  20  is secured to or at least adjacent to, the external surface  15  of the cowling assembly  10 , as shown in  FIG. 1 . The general construction of such diverter strips is well established and actual details of the construction do not form any part of the present invention. The diverter strips  20  are however made so as not to obscure the window portion  16  and areas close to the window portion  16 , through which a significant proportion of the electromagnetic radiation to be transmitted or sensed passes, i.e., the diverter strips  20  are of small cross section, so as to be at least virtually transparent to the electromagnetic radiation frequencies to be sensed. 
     The conductor strips  22  are electrically connected to their respective diverter strips  20 , in this example by connective elements which in this example are rivets  26  or other fasteners, and the conductor strips  22  each extend to and electrically connect to the airframe earth  25 . 
     In this example, the diverter strips  20  each have a free end  21  although in another example, the diverter strips  20  or at least some of them, may be connected at each end to a respective conductor strip  22 . 
     The free ends  21  of the diverter strips  20  in the example illustrated are distant from the airframe  25 , but in another example the diverter strips  20  may extend close to the airframe  25  in which case lightning which attaches to the diverter strips  20  may be diverted to the respective conductor strips  22  of the lightning protection members  18  to the airframe  25 , or direct to the airframe  25  depending upon where on the cowling assembly  10 , the lightning strike occurs. 
     It can be seen that in this example, the conductor strips  22  do not extend significantly over the window portion  16  or at least a crucial central area  19  thereof, and thus although the conductor strips  22  are not transparent to electromagnetic radiation to be sensed, the conductor strips  22  do not obscure or otherwise significantly interfere with the passage of electromagnetic radiation at least though the window portion  16  where the most significant proportion of the radiation passes. The conductor strips  22  may be made of copper or aluminum or any other very electrically conductive material. 
     The lightening protection strip members may be applied to a large cowling assembly  10  where, if the lightning protection strip members were wholly diverter strips, would provide inadequate lightning protection, or if they were wholly conductor strips would then interfere with the passage of electromagnetic radiation to the sensory equipment  14  mounted behind the cowling assembly  10 . 
     In the example shown in  FIG. 1 , there are provided an upper pair of lightning protection strip members  18   a ,  18   b , and a lower pair of lightning protection strip members  18   c ,  18   d . However, more or less of the lightening protection strip members may be provided, as required by different shaped and different size cowling assemblies. The configuration of the window portion  16  over which desirably the conductor strips  22  do not significantly extend, will depend upon the nature of and position of the sensory or other operation equipment  14  mounted behind the cowling assembly  10 . Preferably, the diverter strips  20  of the lightning protection strip members  18  extend for at least 50% of the lengths of each protection strip member, and each diverter strip  20  has a length which is at least ten times greater than the maximum cross sectional dimension, in this case the width dimensions  30  of the diverter strips  20 . 
     The conductor strips  22  preferably each have a length which is at least ten times greater than the maximum cross sectional dimension, in this case the width dimensions  31  of the conductor strips  22 , and preferably in both the diverter strips  20  and conductor strips  22 , the widths of the strips  20 ,  22  which extend along the external surface  15  of the cowling assembly  10  each have a width dimension  30 ,  31  along the external surface  15  of the cowling  10  which is greater, and preferably at least five times greater, than a height dimension being the extent to which the strips  20 ,  22  project upwardly from the external surface  15 . 
       FIG. 2  shows the cowling assembly  10  mounted on the front of an aircraft  12  which, in this drawing, is illustrated as a helicopter. The cowling assembly  10  protects radar or other sensitive electronics mounted on the front of the helicopter. 
     Although the invention has been described in relation to a cowling assembly  10 , and more particularly a nose cap assembly for an aircraft, the cowling assembly may be applied to other cowlings for aircraft or to other vehicles such as land vehicles or boats which have electronics located where they could be damages by lightening.