Aircraft engine nacelle inlet having electrical ice protection system

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.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. 11/111,834, entitled, “Aircraft Engine Nacelle Inlet Having Access Opening For Electrical Ice Protection System”, filed even date herewith 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 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.

In another aspect, the present invention is directed to an aircraft engine nacelle comprising an inner support comprising an outer barrel portion, an inner barrel portion, and a forward wall connecting the outer and inner barrel portions; 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 portion of the removable inlet cowling.

In yet another aspect, the present invention is directed to an aircraft engine nacelle heater assembly for an aircraft engine nacelle having an inner barrel, an outer barrel, a forward wall connecting the inner and outer barrels, and a first electrical connector on the forward wall. The heater assembly comprises an inlet cowling removably connectable to an aircraft engine nacelle and configured to cover at least a portion of the inner barrel and at least a portion of the outer barrel, when connected to said aircraft engine nacelle; and at least one ice protection electrical heater associated with the inlet cowling, the ice protection electrical heater including a second electrical connector; wherein the second electrical connector is configured to connect to the first electrical connector, when the inlet cowling covers the inner and outer barrel portions.

In still another aspect, the present invention is directed to a method of preventing ice accumulation on an aircraft engine nacelle inlet having an airflow stagnation line therealong. The method comprises continuously heating the aircraft engine nacelle inlet along a stagnation line that extends at least partly along a circumference of said aircraft engine nacelle inlet; and sequentially heating the aircraft engine nacelle inlet within spaced zones on each side of the stagnation line so as to prevent ice buildup on the aircraft engine inlet.

DETAILED DESCRIPTION

FIG. 1shows a portion of an aircraft engine nacelle100equipped with one embodiment of a nacelle inlet thermal ice protection assembly10according to the invention. The engine nacelle100includes a substantially cylindrical inner barrel102and a concentric outer barrel104. The nacelle inlet assembly10is disposed on the forward edges of the engine's nacelle inner and outer barrels102,104. The nacelle inlet assembly10has a smooth aerodynamic shape that substantially promotes natural laminar airflow along the forwardmost surfaces of the engine nacelle100.

As shown inFIG. 2, the nacelle inlet assembly10includes a removable inlet cowling40. The inlet cowling40includes an inner lip16, an outer lip14, and a leading edge portion12connecting the two. The aft edge18of the outer lip14mates with the nacelle inlet assembly10along a split line60. The aft edge18and split line60are positioned a substantial distance downstream of the leading edge portion12, thereby providing a smooth, aerodynamic surface on the outer lip14between the leading edge12and the split line60. The lip cowling40may 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 inFIGS. 2 and 3, the nacelle inlet assembly10further includes a forward support30. The support30may be substantially permanently connected to the inner and outer barrels102,104of the aircraft engine nacelle100, or may be integrally constructed therewith. The forward support30provides strength and rigidity to the nacelle inlet assembly10. As shown inFIG. 3, the forward support30includes an inner barrel portion32, an outer barrel portion36and a forward wall portion34connecting the inner and outer barrel portions. The forward support30may house a plurality of spaced ice protection electrical heater switch boxes28for relaying electric power to the ice protection system's heaters, which are described in detail below. As shown inFIG. 6, electric power from a pylon electrical junction box20may be supplied to one or more control boxes26via power feeder harness24, and may be supplied from the control box26to the heater switch boxes28via power supply harnesses27.

As shown inFIGS. 2 and 3, the outer barrel portion36of the forward support30includes a plurality of circumferentially spaced service access openings38therethrough. Each of the service access openings38is located proximate to one or more associated heater switch boxes28, and provides access to at least one of the heater switch boxes28from outside the outer barrel portion36.

As shown inFIGS. 1 and 4, when the inlet cowling40is installed on the forward support30, the outer lip14covers each of the respective service access openings38in the outer barrel portion36of the forward support30. Therefore, this arrangement precludes the need for an individual cover for each service access opening38. This arrangement also provides a continuous smooth aerodynamic lip surface14proximate to the leading edge12that helps promote natural laminar airflow across the nacelle during flight.

As shown inFIGS. 1,2and3, the inlet cowling40is connected to the forward support30along both aft edges18,19by pluralities of suitable removable fasteners50. For example, the fasteners50may 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 assembly10are shown inFIGS. 4 and 5. As shown inFIG. 4, the inlet cowling40substantially conforms to the shape of the forward support30except for a ice protection electrical heater pocket80formed between the leading edge12of the cowling40and the forward wall34of the forward support30. The pocket80provides space for a plurality of ice protection ribbon heaters70a,70b,70c,72mounted on the inner surface of the leading edge12of the inlet cowling40, as well as for an electrical connector76which connects to electrical connector74mounted on the forward wall34.

The first and second electrical connectors74,76automatically connect to one another, making a plug and socket-type connection, when the inlet cowling40is 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, connectors74and76may be electrically connected (or disconnected) by manually attaching (or detaching) a cable extending between the two. Electric power is supplied to the heaters70a,70b,70c,72from the heater switch boxes28via heater supply harness29and electrical connectors74. In the embodiment shown, the electrical connectors74are mounted on the forward wall34of the forward support30.

As shown inFIG. 4, the inner barrel portion32of the forward support30may include an acoustic portion33, known to those skilled in the act, for attenuating engine noise. In the arrangement shown, the aft edge19of the inner lip16adjoins the forward support30at a position that is immediately forward (or upstream of) of the acoustic portion33.

FIGS. 4 and 5show the maintenance and service access features of the nacelle inlet assembly10. With the inlet cowling40removed, the service access openings38are uncovered, and various ice protection electrical heating equipment such as the heater switch boxes28, heater supply harnesses29, power supply harnesses27, and electrical connectors74can be easily accessed by service personnel extending his or her hand150through the service access openings38. In addition, the removed inlet cowling40provides ready access to the ice protection electrical heaters70a,70b,70c,72, and associated electrical connectors76mounted on the inside surfaces of the cowling40. If required, the removable inlet cowling40can be easily replaced with a second inlet cowling40, and can be separated from an associated engine nacelle100for remote service or repair.

FIGS. 6 and 7show one possible arrangement for the ice protection electrical heaters70a,70b,70c, and72. First, one or more parting strip heaters72are provided along an inner surface of the leading edge12of the removable cowling40. Preferably, each parting strip heater72is positioned to be substantially coincident with an airflow stagnation line along the engine inlet's leading edge12. Second, a plurality of shed zone heaters70a,70b,70care provided in substantially side by side relation along the inside surface of the leading edge12, thereby substantially covering the entire inside surface of the leading edge12. 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)72to provide more or less continuous ice protection along the airflow stagnation line.

Power also can be intermittently supplied to the shed zone heaters70a,70b, and70cto 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 heaters70a, to shed zone heaters70b, to shed zone heaters70c, again to shed zone heaters70a, etc. The distribution of electric power to the various heaters70a,70b,70c, and72is controlled by one or more electrical supply control boxes26. This cyclic rationing of electric power between the various shed zone heaters70a,70b,70cacts to minimize the amount of electric power that must be derived from an aircraft's finite electrical generation capacity, while effectively providing ice protection to the engine inlet's leading edge12.

It is understood that one may operate the heating system such that all shed zone heaters designated70aare active for a first period of time, then all shed zone heaters designated70bare active for a second period of time and finally all shed zone heater designated70care 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. 8shows one possible arrangement for installing the heaters70a,70b,70c,72on the inner surface of the inlet cowling40. In this arrangement, a parting strip heater72is mounted on the inner surface of the lip cowling40proximate to the underside of the airflow stagnation line at the leading edge12. Next, a plurality of shed zone heating pads70a,70b,70care applied over the parting strip heater72such that the heater pads70a,70b,70ccover substantial portions of the inside surface of the leading edge12on each side of the parting strip heater72. The heaters70a,70b,70c,72may be any type of substantially flat, foil, or ribbon heater capable of supplying sufficient heat energy to the cowling40to effectively de-ice the cowling40while in service. The heating elements70a,70b,70c,72may be configured as “ribbons”, i.e. interconnected conductive sections, that are mounted on a flexible backing. For example, the low-power electric heaters70a,70b,70c,72may 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 heaters70a,70b,70c,72may 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 wiring74supplies electric power to the ice protection electrical heaters70a,70b,70c,72from one or more heater switch boxes28.

FIG. 9ashows a cross-section of an inlet cowling40ain which the ice protection electrical heater is spaced apart from the ice950by one or more layers. The structural skin904of the cowling40aprovides support for the layers above. These layers include a first insulation layer906, a heater layer908atop the first insulation layer, a second insulation layer910atop the heater layer908, and an erosion shield912atop the second insulation layer910. Heat from the heater layer908passes through the second insulation layer910and the erosion shield to melt the ice950.

In one embodiment, the thickness of the inlet cowling is on the order of 0.1″-0.2″. The structural skin904is formed of a metallic or composite material having a thickness between about 0.02″ and 0.10″; the first insulation layer906is formed of an electrically inert (i.e., electrically insulative) material having a thickness between about 0.01″ and 0.04″; the heater layer908comprises 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 layer910is 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 shield912comprises 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 cowling40as shown inFIGS. 4-6, the ice protection electrical heaters908may 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 cowling40at spaced apart intervals to accommodate wires and other connections to deliver current to the ice protection electrical heaters.FIG. 9bshows a cross-section of an inlet cowling40bin which the heater forms the outer surface of the cowling40b. Again, the structural skin924of the cowling40bprovides support for the layers above. These layers include a first insulation layer926, and a heater layer928atop the first insulation layer924, all having substantially the same composition and thickness ranges discussed above with respect toFIG. 9a. In this instance, however, the heater layer928is exposed to the elements and so must also serve as the erosion shield.

In bothFIGS. 9aand9b, a wire or cable930provides current to the heater layers908,928preferably, the wire is connected to the heater via an electrical solder connection932, 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.