Abstract:
An aircraft engine nacelle inlet is provided with an inlet cowling. The inlet cowling includes an inner lip, an outer lip, and a leading edge portion connecting the inner and outer lips. Heating elements are provided proximate the leading edge, either on an inside surface of the cowling or on an outside surface. An inner barrel portion and an outer barrel portion of the nacelle inlet define a space therebetween. Ice protection-related equipment such as controllers, cables, switches, connectors, and the like, may reside in this space. One or more access openings are formed in the outer barrel to enable an operator to gain access to this equipment. The inlet cowling attaches to the inner and outer barrels with its outer lip extending sufficiently far in the aft direction to cover the access opening. When the cowling is removed, the access opening is uncovered, thereby permitting access to the equipment.

Description:
RELATED APPLICATIONS 
   This application is a Divisional of U.S. patent application Ser. No. 11/111,834, filed Apr. 22, 2005, now U.S. Pat. No. 7,469,862, whose contents are incorporated by reference. 
   This application is also related to U.S. patent application Ser. No. 11/111,835, “Aircraft Engine Nacelle Inlet Having Electrical Ice Protection System”, filed Apr. 22, 2005 by the same inventors as the present application, and having substantially the same specification. 

   BACKGROUND 
   The invention relates to ice protection systems for aircraft, and more specifically relates to an aircraft equipped with a low power high efficiency electrical ice protection system. 
   The accumulation of ice on aircraft wings and other structural members in flight is a danger that is well known. Such “structural members” include any aircraft surface susceptible to icing during flight, including wings, stabilizers, rotors, and so forth. Ice accumulation on aircraft engine nacelle inlets also can be problematic. Attempts have been made since the earliest days of flight to overcome the problem of ice accumulation. While a variety of techniques have been proposed for removing ice from aircraft during flight, these techniques have had various drawbacks that have stimulated continued research activities. One approach that has been used is so-called thermal ice protection. In thermal ice protection, the leading edges, that is, the portions of the aircraft that meet and break the airstream impinging on the aircraft, are heated to prevent the formation of ice or to loosen accumulated ice. The loosened ice is blown from the structural members by the airstream passing over the aircraft. 
   In one form of thermal ice protection, heating is accomplished by placing an electrothermal pad(s), including heating elements, over the leading edges of the aircraft, or by incorporating the heating elements into the structural members of the aircraft. Electrical energy for each heating element is derived from a generating source driven by one or more of the aircraft engines. The electrical energy is intermittently or continuously supplied to provide heat sufficient to prevent the formation of ice or to loosen accumulating ice. 
   With some commonly employed thermal ice protection systems, the heating elements may be configured as ribbons, i.e. interconnected conductive segments that are mounted on a flexible backing. When applied to a wing or other airfoil surface, the segments are arranged in strips or zones extending spanwise or chordwise along the aircraft wing or airfoil. When applied to the engine inlet the heating elements can be applied either in the circumferential or radial orientation. One of these strips, known as a spanwise parting strip, is disposed along a spanwise axis which commonly coincides with a stagnation line that develops during flight. Other strips, known as chordwise parting strips, are disposed at the ends of the spanwise parting strip and are aligned along chordwise axes. Other zones, known as spanwise shedding zones, typically are positioned on either side of the spanwise parting strip at a location intermediate the chordwise parting strips. 
   In one preferred form of ice protection, an electrical current is transmitted continuously through the parting strips so that the parting strips are heated continuously to a temperature above 32 degrees Fahrenheit. In the spanwise shedding zones, on the other hand, current is transmitted intermittently so that the spanwise shedding zones are heated intermittently to a temperature above about 32 degrees Fahrenheit. 
   One problem associated with providing such electrothermal ice protection systems on the nacelle inlets of aircraft engines involves providing sufficient numbers of access openings in the inner or outer barrels of the engine inlet for accessing and servicing the heating equipment such as heater elements and associated components. Providing such access openings proximate to the leading edge of the nacelle inlet can create non-smooth interruptions or protuberances along the otherwise smooth aerodynamic surface of the engine inlet. These interruptions or protuberances can interfere with the desired natural laminar airflow into and around the engine inlets, and may contribute to the creation of unwanted noise and drag. 
   Therefore, there is a need for a thermal ice protection system for the nacelle inlet of an aircraft engine that provides effective ice protection action, that includes a plurality of conveniently positioned service access openings for use in servicing and maintaining the ice protection system components, and that maintains a smooth aerodynamic inlet shape that results in substantially natural laminar airflow along the critical surfaces of the inlet. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present invention is directed to an aircraft engine nacelle comprising an inner support comprising an outer barrel portion and an inner barrel portion connected to the outer barrel portion; and a removable inlet cowling attachable to the inner support, the removable inlet cowling having an outer lip, an inner lip, and a leading edge extending between the outer and inner lips, and at least one ice protection electrical heater associated with the leading edge of the removable inlet cowling; wherein: the outer barrel portion has at least one service access opening therein, and the outer lip covers the service access opening, when the inlet cowling is attached to the inner and outer barrel portions. 
   In another aspect, the present invention is directed to a method for servicing ice protection electrical heating equipment located between an inner barrel and an outer barrel of a nacelle. The inventive method comprises removing an inlet cowling having an outer lip that normally covers at least one service access opening formed in the outer barrel to thereby uncover said at least one service access opening, said inlet cowling having been previously provided with at least one ice protection electrical heater that is connected to said ice protection electrical heating equipment; and accessing the ice protection electrical heating equipment through the at least one service access opening to thereby service the same. 
   In yet another aspect, the present invention is directed to a nacelle inlet for an aircraft engine nacelle having an outer barrel, the nacelle inlet comprising electrical heating means for selectively heating at least a portion of a nacelle inlet surface, and access means for selectively accessing the electrical heating means, the access means being configured to promote laminar airflow over the nacelle inlet surface. The access means may comprise at least one service access opening in the outer barrel, and a removable cowling covering the service access opening to thereby promote laminar airflow over the nacelle inlet surface. 
   In still another aspect, the present invention is directed to an electric ice protection system for an aircraft engine nacelle having an inner barrel and an outer barrel. The ice protection system comprises an engine inlet cowling having an outer lip configured for engagement with at least a portion of the outer barrel, an inner lip configured for engagement with at least a portion of the inner barrel, and a leading edge extending between the outer and inner lips; at least one parting strip electrical heater attached to the cowling proximate to the leading edge; and a plurality of shed zone electrical heaters arranged side by side on either side of the parting strip electrical heater, wherein the outer barrel has at least one service access opening therein, and the outer lip is configured to cover said at least one service access opening. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a portion of an aircraft engine having a nacelle inlet thermal ice protection system according to the invention; 
       FIG. 2  is a perspective view of the aircraft engine of  FIG. 1  with the inlet cowling detached; 
       FIG. 3  is an enlarged perspective view of a forward portion of the aircraft engine of  FIGS. 1 and 2 ; 
       FIG. 4  is a cross-sectional view of a nacelle inlet for an aircraft engine according to the invention; 
       FIG. 5  is an exploded cross-sectional view of the nacelle inlet of  FIG. 4  with the inlet cowling detached; 
       FIG. 6  is a rear perspective view of a portion of an aircraft engine showing an ice protection electrical heater arrangement on the inner surface of an inlet cowling; 
       FIG. 7  is a front perspective view an inlet cowling showing the ice protection electrical heater arrangement of  FIG. 6 ; 
       FIG. 8  is a rear perspective view of the inlet cowling of  FIG. 7  showing placement of ice protection electrical heaters on an inner surface of the inlet; 
       FIG. 9   a  shows a cross-sectional view of a cowling in which the heater is part of an inner layer of the cowling; and 
       FIG. 9   b  shows a cross-sectional view of a cowling in which the heater is part of an outer layer of the cowling. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a portion of an aircraft engine nacelle  100  equipped with one embodiment of a nacelle inlet thermal ice protection assembly  10  according to the invention. The engine nacelle  100  includes a substantially cylindrical inner barrel  102  and a concentric outer barrel  104 . The nacelle inlet assembly  10  is disposed on the forward edges of the engine&#39;s nacelle inner and outer barrels  102 ,  104 . The nacelle inlet assembly  10  has a smooth aerodynamic shape that substantially promotes natural laminar airflow along the forwardmost surfaces of the engine nacelle  100 . 
   As shown in  FIG. 2 , the nacelle inlet assembly  10  includes a removable inlet cowling  40 . The inlet cowling  40  includes an inner lip  16 , an outer lip  14 , and a leading edge portion  12  connecting the two. The aft edge  18  of the outer lip  14  mates with the nacelle inlet assembly  10  along a split line  60 . The aft edge  18  and split line  60  are positioned a substantial distance downstream of the leading edge portion  12 , thereby providing a smooth, aerodynamic surface on the outer lip  14  between the leading edge  12  and the split line  60 . The lip cowling  40  may be a single continuous 360° airfoil that covers an entire engine inlet, or may comprise a plurality of separable, arcuate cowling segments placed in a circumferential arrangement. In one embodiment, the separable cowling segments have airfoil cross-sections that are placed side by side in a circumferential arrangement. 
   As shown in  FIGS. 2 and 3 , the nacelle inlet assembly  10  further includes a forward support  30 . The support  30  may be substantially permanently connected to the inner and outer barrels  102 ,  104  of the aircraft engine nacelle  100 , or may be integrally constructed therewith. The forward support  30  provides strength and rigidity to the nacelle inlet assembly  10 . As shown in  FIG. 3 , the forward support  30  includes an inner barrel portion  32 , an outer barrel portion  36  and a forward wall portion  34  connecting the inner and outer barrel portions. The forward support  30  may house a plurality of spaced ice protection electrical heater switch boxes  28  for relaying electric power to the ice protection system&#39;s heaters, which are described in detail below. As shown in  FIG. 6 , electric power from a pylon electrical junction box  20  may be supplied to one or more control boxes  26  via power feeder harness  24 , and may be supplied from the control box  26  to the heater switch boxes  28  via power supply harnesses  27 . 
   As shown in  FIGS. 2 and 3 , the outer barrel portion  36  of the forward support  30  includes a plurality of circumferentially spaced service access openings  38  therethrough. Each of the service access openings  38  is located proximate to one or more associated heater switch boxes  28 , and provides access to at least one of the heater switch boxes  28  from outside the outer barrel portion  36 . 
   As shown in  FIGS. 1 and 4 , when the inlet cowling  40  is installed on the forward support  30 , the outer lip  14  covers each of the respective service access openings  38  in the outer barrel portion  36  of the forward support  30 . Therefore, this arrangement precludes the need for an individual cover for each service access opening  38 . This arrangement also provides a continuous smooth aerodynamic lip surface  14  proximate to the leading edge  12  that helps promote natural laminar airflow across the nacelle during flight. 
   As shown in  FIGS. 1 ,  2  and  3 , the inlet cowling  40  is connected to the forward support  30  along both aft edges  18 ,  19  by pluralities of suitable removable fasteners  50 . For example, the fasteners  50  may include bolts, rivets, or other suitable fasteners having substantially flush profiles. Preferably, the fasteners are of a type that is easily installed and removed by service personnel. 
   Further details of the nacelle inlet assembly  10  are shown in  FIGS. 4 and 5 . As shown in  FIG. 4 , the inlet cowling  40  substantially conforms to the shape of the forward support  30  except for a ice protection electrical heater pocket  80  formed between the leading edge  12  of the cowling  40  and the forward wall  34  of the forward support  30 . The pocket  80  provides space for a plurality of ice protection ribbon heaters  70   a ,  70   b ,  70   c ,  72  mounted on the inner surface of the leading edge  12  of the inlet cowling  40 , as well as for an electrical connector  76  which connects to electrical connector  74  mounted on the forward wall  34 . 
   The first and second electrical connectors  74 ,  76  automatically connect to one another, making a plug and socket-type connection, when the inlet cowling  40  is adjusted from a first position in which it is separated from the inner and outer barrel portions to a second position in which it covers the inner and outer barrel portions. Alternatively, connectors  74  and  76  may be electrically connected (or disconnected) by manually attaching (or detaching) a cable extending between the two. Electric power is supplied to the heaters  70   a ,  70   b ,  70   c ,  72  from the heater switch boxes  28  via heater supply harness  29  and electrical connectors  74 . In the embodiment shown, the electrical connectors  74  are mounted on the forward wall  34  of the forward support  30 . 
   As shown in  FIG. 4 , the inner barrel portion  32  of the forward support  30  may include an acoustic portion  33 , known to those skilled in the act, for attenuating engine noise. In the arrangement shown, the aft edge  19  of the inner lip  16  adjoins the forward support  30  at a position that is immediately forward (or upstream of) of the acoustic portion  33 . 
     FIGS. 4 and 5  show the maintenance and service access features of the nacelle inlet assembly  10 . With the inlet cowling  40  removed, the service access openings  38  are uncovered, and various ice protection electrical heating equipment such as the heater switch boxes  28 , heater supply harnesses  29 , power supply harnesses  27 , and electrical connectors  74  can be easily accessed by service personnel extending his or her hand  150  through the service access openings  38 . In addition, the removed inlet cowling  40  provides ready access to the ice protection electrical heaters  70   a ,  70   b ,  70   c ,  72 , and associated electrical connectors  76  mounted on the inside surfaces of the cowling  40 . If required, the removable inlet cowling  40  can be easily replaced with a second inlet cowling  40 , and can be separated from an associated engine nacelle  100  for remote service or repair. 
     FIGS. 6 and 7  show one possible arrangement for the ice protection electrical heaters  70   a ,  70   b ,  70   c , and  72 . First, one or more parting strip heaters  72  are provided along an inner surface of the leading edge  12  of the removable cowling  40 . Preferably, each parting strip heater  72  is positioned to be substantially coincident with an airflow stagnation line along the engine inlet&#39;s leading edge  12 . Second, a plurality of shed zone heaters  70   a ,  70   b ,  70   c  are provided in substantially side by side relation along the inside surface of the leading edge  12 , thereby substantially covering the entire inside surface of the leading edge  12 . Although adjacent shed zone heaters may abut one another if they are electrically isolated from each other, more preferably, they are spaced apart from one another by a gap of between about 0.04″ to about 0.5″; other gap spacings may also be employed. In this arrangement, power can be supplied substantially constantly to the parting strip heater(s)  72  to provide more or less continuous ice protection along the airflow stagnation line. 
   Power also can be intermittently supplied to the shed zone heaters  70   a ,  70   b , and  70   c  to shed accumulated ice on either side of the stagnation line. In the arrangement shown, for example, pulses of electrical power may be supplied in sequence to shed zone heaters  70   a , to shed zone heaters  70   b , to shed zone heaters  70   c , again to shed zone heaters  70   a , etc. The distribution of electric power to the various heaters  70   a ,  70   b ,  70   c , and  72  is controlled by one or more electrical supply control boxes  26 . This cyclic rationing of electric power between the various shed zone heaters  70   a ,  70   b ,  70   c  acts to minimize the amount of electric power that must be derived from an aircraft&#39;s finite electrical generation capacity, while effectively providing ice protection to the engine inlet&#39;s leading edge  12 . 
   It is understood that one may operate the heating system such that all shed zone heaters designated  70   a  are active for a first period of time, then all shed zone heaters designated  70   b  are active for a second period of time and finally all shed zone heater designated  70   c  are active during a third period of time. It is further understood that these three periods of time need not necessarily be of equal duration and that they need not necessarily be contiguous—i.e., there may be some intervening periods during which none of these three sets of shed zone heaters is on. It is also understood that other numbers of sets of heaters may be provided—for instance, two sets, four sets, or five sets, etc. 
     FIG. 8  shows one possible arrangement for installing the heaters  70   a ,  70   b ,  70   c ,  72  on the inner surface of the inlet cowling  40 . In this arrangement, a parting strip heater  72  is mounted on the inner surface of the lip cowling  40  proximate to the underside of the airflow stagnation line at the leading edge  12 . Next, a plurality of shed zone heating pads  70   a ,  70   b ,  70   c  are applied over the parting strip heater  72  such that the heater pads  70   a ,  70   b ,  70   c  cover substantial portions of the inside surface of the leading edge  12  on each side of the parting strip heater  72 . The heaters  70   a ,  70   b ,  70   c ,  72  may be any type of substantially flat, foil, or ribbon heater capable of supplying sufficient heat energy to the cowling  40  to effectively de-ice the cowling  40  while in service. The heating elements  70   a ,  70   b ,  70   c ,  72  may be configured as “ribbons”, i.e. interconnected conductive sections, that are mounted on a flexible backing. For example, the low-power electric heaters  70   a ,  70   b ,  70   c ,  72  may be like the ice protection electrical heaters described in U.S. Pat. No. 5,475,204, assigned to Goodrich Corporation. Alternatively, the ice protection electrical heaters  70   a ,  70   b ,  70   c ,  72  may be like those described in U.S. patent application Ser. No. 10/840,736, filed on May 6, 2004. The disclosures of U.S. Pat. No. 5,475,204 and U.S. patent application Ser. No. 10/840,736 are hereby incorporated by reference in their entireties. And so, when in use, adjacent portions of the inlet cowling may be sequentially heated by alternatingly supplying current to the plurality of electrical ribbon heaters. Suitable electric wiring  74  supplies electric power to the ice protection electrical heaters  70   a ,  70   b ,  70   c ,  72  from one or more heater switch boxes  28 . 
     FIG. 9   a  shows a cross-section of an inlet cowling  40   a  in which the ice protection electrical heater is spaced apart from the ice  950  by one or more layers. The structural skin  904  of the cowling  40   a  provides support for the layers above. These layers include a first insulation layer  906 , a heater layer  908  atop the first insulation layer, a second insulation layer  910  atop the heater layer  908 , and an erosion shield  912  atop the second insulation layer  910 . Heat from the heater layer  908  passes through the second insulation layer  910  and the erosion shield to melt the ice  950 . 
   In one embodiment, the thickness of the inlet cowling is on the order of 0.1″-0.2″. The structural skin  904  is formed of a metallic or composite material having a thickness between about 0.02″ and 0.10″; the first insulation layer  906  is formed of an electrically inert (i.e., electrically insulative) material having a thickness between about 0.01″ and 0.04″; the heater layer  908  comprises electrical heaters formed of a metallic or conductive material on a nonconductive plastic film or other substrate and having a thickness between about 0.005″ and 0.020″; the second insulation layer  910  is formed of an electrically inert (i.e., electrically insulative) but thermally conductive material having a thickness between about 0.01″ and 0.04″; and the erosion shield  912  comprises a thermally conductive metallic skin or coating having a thickness between about 0.002″ and 0.020″. 
   Instead of being mounted on the inner surface of the inlet cowling  40  as shown in  FIGS. 4-6 , the ice protection electrical heaters  908  may be mounted on the outer surface. When positioned on the outer surface, the ice protection electrical heaters are more directly exposed to the ice and so the energy efficiency of the system may improve. Through holes may be formed in some of the underlying layers of the cowling  40  at spaced apart intervals to accommodate wires and other connections to deliver current to the ice protection electrical heaters.  FIG. 9   b  shows a cross-section of an inlet cowling  40   b  in which the heater forms the outer surface of the cowling  40   b . Again, the structural skin  924  of the cowling  40   b  provides support for the layers above. These layers include a first insulation layer  926 , and a heater layer  928  atop the first insulation layer  924 , all having substantially the same composition and thickness ranges discussed above with respect to  FIG. 9   a . In this instance, however, the heater layer  928  is exposed to the elements and so must also serve as the erosion shield. 
   In both  FIGS. 9   a  and  9   b , a wire or cable  930  provides current to the heater layers  908 ,  928 . preferably, the wire is connected to the heater via an electrical solder connection  932 , as seen in these figures. It is understood in these figures that each of the heater layers may comprise multiple individual ice protection electrical heaters. 
   Engine inlets in accordance with the present invention may realize efficient ice protection with lower weight inlet structure, as compared to a conventional hot air thermal anti-ice (TAI) system. Furthermore, eliminating the pressures and temperatures associated with a traditional TAI system simplifies certain aspects of nacelle design. For instance, traditional split lines between the inlet major components are driven by the thermal anti-ice system and the acoustic requirements. The electrical system of the present invention generally does not rely upon these limitations and may therefore allow for these locations to be optimized for other design criteria. As an example, moving the traditional split line between the inlet lip and the outer barrel aft improves the aerodynamic performance of the inlet and allows the lip to be incorporated into a design that promotes natural laminar flow while also covering an access opening. 
   The above description of various embodiments of the invention is intended to describe and illustrate various aspects of the invention, and is not intended to limit the invention thereto. Persons of ordinary skill in the art will understand that certain modifications may be made to the described embodiments without departing from the invention. All such modifications are intended to be within the scope of the appended claims.