Three link failsafe engine mount

Abstract: A failsafe engine mount (19) that includes a first link (45), a second link (47), a third link (53), four uppcr connection locations (39a), (39b), (39c), (39d) on an upper fitting (31), and four lower connection locations (75a), (75b), (75c), (75d) on a clevis strip (73) of an engine casing (71), is disclosed. The first link (45) connects the first upper connection location (39a) with the first lower connection location (75a). The second link (47) has a first arm (49) that connects the second lower connection location (75b) with the second upper connection location (39b). The second link (47) further includes a second arm (51) that connects the second upper connection location (39b) with the third lower connection location (75c). The third link (53) has a first arm (55) that connects the third upper connection location (39c) with the fourth upper connection location (39d). The third link (53) further includes a second arm (57) arranged to connect the fourth upper connection location (39d) with the fourth lower connection location (75d). The first arm (55) of the third link (53) carries loads during a failure of the second link (47). In an alternative embodiment, the third link includes a peg (155) instead of a first arm. The peg inserts into a hole (159) in the upper fitting. During normal operations, the peg does not contact the hole surfaces. In either embodiment under normal operating conditions, the links work together to carry the vertical and horizontal/torsion loads of the engine. During a failed link operation, the remaining links work together to carry all loads.

Description: Field of Invention This present invention relates to a failsafe engine mount for attaching an engine casing of a jet engine to a support structure on an airplane, comprising: an upper fitting attachable to the airplane support structure, the upper fitting including a lower edge having first, second, and third upper connection locations located in a plane lying generally transverse to the longitudinal centerline of the engine; a clevis strip attached to the outer periphery of the engine casing in a plane lying generally transverse to the longitudinal centerline of the engine, the clevis strip including first, second, third, and fourth lower connection locations located in a plane lying generally transverse to the longitudinal centerline of the engine; a substantially straight first link connecting to the upper fitting at the first upper connection location and connecting to the clevis strip at the first lower connection location; a second link including a first arm and a second arm, the first arm connecting to the clevis strip at the second lower connection location and connecting to the upper fitting at the second upper connection location, the second arm connecting to the clevis strip at the third lower connection location; and a third link connecting to the upper fitting at the third upper connection location and connecting to the clevis strip at the fourth lower connection location. Such a failsafe engine mount is known from EP-A-0741074. Background of the Invention Airplane engines are typically mounted below an aircraft wing or near the tail section by an engine mount. Mounts are usually provided for both the forward portion of the engine and the aft portion of the engine, so as to distribute the engine load. Typical engine mounts include several components. One of the components is a generally planar upper fitting that has a mounting platform located along its upper edge that is used to attach the engine mount to a support structure of the aircraft, e.g., a wing strut or tail pylon. Multiple devises are located on the lower edge of the upper fitting and also along a portion of an engine casing. Multiple links, pinned in the clevises of both the upper fitting and the engine casing, connect the engine to the support structure. Similar engine mounts of this type are used at both the forward and aft portions of the engine. Engine mounts are designed to handle a variety of loads, during all phases of flight. The loads include vertical loads (the weight of the engine plus maneuver loads), axial loads (caused by the engine's thrust), side loads (caused by wind buffeting, for example), and torsion loads (caused by the rotary operation of the engine, or by the loss of a turbine blade). An engine mount must also accommodate thermal expansion and contraction of the engine relative to the mount. The effect of thermal expansion and contraction is most significant during cruise phase. During cruise, thermal expansion and contraction can cause an appreciable shift in the direction of loads acting on an engine mount. Almost all airplane engine mounts are designed to be failsafe, i.e., to prevent the engine from separating from the airplane. Failsafe operation is provided by a secondary, or backup, load-carrying system. Two types of secondary systems are common. The first type utilizes components of the thrust reverser (such as the translating cowl) to carry engine loads. The second type utilizes catcher links placed within the engine mount itself. Catcher links are additional links in the engine mount that are typically unloaded during normal operation. Should a primary (i.e., non-catcher) link fail, the catcher links are capable of cooperating with the remaining unfailed links to carry engine loads. Link failures may result from many causes, including failure of pins or devises; broken, deformed, missing, or mis-installed links; sheared pins; etc. Between the two types of secondary systems, the thrust reverser system is the more widely used approach. On most airplanes, the use of catcher links is a more efficient solution, because they require relatively much less weight and space. Currently, relatively few catcher link engine mounts are known, and of these, not many describe three-link systems. Applicant's earlier patent application EP-A-0 741 074 already describes a three link failsafe engine mount including an upper fitting that is attached to a support structure, e.g. a pylon suspended from the wing of an aircraft, and a clevis strip attached to the engine casing. Three links connect the clevis strip to the upper fitting, both of which include four connection locations. The first of the three links, an outer link, is straight, whereas the other two links are dog leg shaped. The middle dog leg link has its two outer ends connected to the two middle connection locations on the clevis strip, and its corner connected to the second of the connection locations in the upper fitting. The outer end connected to the third connection location on the clevis strip is connected thereto with play, such as to be unloaded under normal flight conditions. The dog leg third or outer link has one end connected to the fourth connection location in the clevis strip and its corner connected to the fourth connection location in the upper fitting. The other end of the dog leg outer link is connected with play to the third connection location of the upper fitting. All connections are by means of pin-and-clevis joints. Summary of the Invention In accordance with the present invention, an improved failsafe engine mount for attaching a jet engine to an aircraft support structure is provided, which efficiently distributes engine loads among several of the mount links during normal operation, as well as among the remaining links during a single link failure. The failsafe engine mount of the present invention is distinguished from the above-discussed prior art engine mount in that the third link includes a peg extending from an upper region of the third link, the peg being insertable into a hole formed in the upper fitting. Engine mounts formed in accordance with the invention can be attached to various locations on an airplane (e.g., under the wing or to the tail section) or on'an engine (e.g., at the forward portion of the engine or at the aft portion of the engine), with only slight modification to the sizings of the mount components being required. During normal operation of the engine mount of the invention, the first and third links carry the majority of the vertical loads, while the first arm of the second link carries most of the horizontal loads. Torsion loads are shared by all three links. If the first link fails, the second arm of the second link works to absorb some of the load previously carried by the first link. The peg of the third link and hole in the upper fitting can be sized and positioned to be unloaded during normal airplane operations and during a failure of the first link. The peg and the upper fitting hole can be arranged to work with the first link to carry the engine loads should the second link fail. In preferred embodiments, the peg of the third link is cross-sectionally ovoid in shape and the space between the peg exterior surfaces and the upper fitting hole surface during normal operations is in the range of about 2.54 mm (0.100 inches) to about 7.62 mm (0.300 inches), a preferred distance being about 6.4 mm (0.25 inch). The present invention provides a new and distinctly better engine mount. If any link fails, the vertical, horizontal, and torsion loads once carried by the failed link are efficiently distributed among the remaining links. The entire engine mount is relatively compact, thus making optimal use of the limited amount of space available in jet airplanes and providing greater ground clearance if used on an underwing engine. The present invention has a relatively wide load-couple during a failed link condition. The links are configured so that during normal operations the catcher links are unloaded, which eliminates unnecessary wear. In addition, there are no loose links to vibrate, thus component wear is reduced. Brief Description of the Drawings The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: FIGURE 1 is a side schematic view of a conventional aircraft engine mounted to a pylon below an aircraft wing by an engine mount formed in accordance with the present invention; FIGURE 2 is a rear view of a prior art failsafe engine mount , as seen when looking forward relative to the airplane; FIGURE 3 is a table of the coordinates of connection locations for one actual embodiment of the prior art engine mount, FIGURE 4 is a cross-sectional side view taken along line 4-4 of FIGURE 2; FIGURE 5 is a schematic view of the failsafe aft engine mount of FIGURE 2 during normal operation; FIGURE 6 is a schematic view of the failsafe aft engine mount of FIGURE 2 showing what occurs when a first link fails; FIGURE 7 is a schematic view of the failsafe aft engine mount of FIGURE 2 showing what occurs when a second link fails; FIGURE 8 is a schematic view of the failsafe aft engine mount of FIGURE 2 showing what occurs when a third link fails; FIGURE 9 is a rear view of a failsafe engine mount formed in accordance with the present invention, as seen when looking forward relative to the airplane, with portions shown in cross-section; FIGURE 10 is a schematic view of the failsafe aft engine mount of FIGURE 9 during normal operation; FIGURE 11 is a schematic view of the failsafe aft engine mount of FIGURE 9 showing what occurs when a first link fails; FIGURE 12 is a schematic view of the failsafe aft engine mount of FIGURE 9 showing what occurs when a second link fails; and FIGURE 13 is a schematic view of the failsafe aft engine mount of FIGURE 9 showing what occurs when a third link fails. Detailed Description of the Preferred Embodiment FIGURE 1 is a side schematic view of a conventional aircraft jet engine 11 supported by a pylon 17 located below an aircraft wing. The engine 11 is attached to the pylon 17 by an engine mount 19 formed in accordance with the present invention. More specifically, the engine mount 19 is attached to an aft portion of the engine 11 near the turbine rear frame 21. Thus, the engine mount 19 depicted in FIGURE 1 is an aft engine mount. While FIGURE 1 illustrates an aft engine mount, it is to be understood that engine mounts formed in accordance with the teachings of the present invention may be used in a variety of engine mounting locations. For example, they can be used as a forward or aft mount, or both. They can be used to mount the engine either under the wing or to the tail section of the aircraft. FIGURE 1 is meant to be illustrative, not limiting. In this regard, the following written description of a specific engine mount for use in the position shown in FIGURE 1 should also be considered as illustrative and not limiting. The precise position selected to use an engine mount formed in accordance with the present invention may require modification of the sizings of the mount components for that particular application. These modifications depend upon a variety of factors known to those skilled in the art of engine mounting, e.g., engine size, anticipated loads, aerodynamic considerations, etc. To facilitate understanding of the invention, the terminology in the description below refers to the location of the engine mount components relative to the orientation of the FIGURES. The terminology and illustrative FIGURES should not be construed to limit the present invention to only underwing, aft engine mounts. FIGURE 2 is a rear view of a prior art failsafe engine mount disclosed in EP-A-0 741 074 and suitable for use as in FIGURE 1, as seen by an observer standing behind the engine 11. In general, the engine mount 19 includes an upper fitting 31 and three links 45, 47, 53. The upper fitting 31 is attached to the pylon 17 (shown in FIGURE 1) or some other airplane support structure. The links 45, 47, 53 are arranged to connect four connection locations 39a, 39b, 39c, 39d on the upper fitting 31 with four connection locations 75a, 75b, 75c, 75d on a clevis strip 73 which is attached to an engine casing 71 (shown in FIGURE 5). Attachments of the links 45, 47, 53 to the upper fitting 31 and to the engine casing 71 at the various connection locations are accomplished using pin-and-clevis joints. During operation, the links 45, 47, 53 support the vertical and horizontal/torsion loads of the engine 11. Should a link fail, the remaining links are arranged to completely assume the loads previously carried by the failed link. The material used for the upper fitting 31, links 45, 47, 53, pins and clevises should be preferably Inconel, titanium, or stainless steel. In more detail, the upper fitting 31 has a mounting platform 33 formed along an upper surface for attaching the engine mount 19 to the pylon 17. The mounting platform 33 includes a plurality of bolt holes for accepting a bolt arrangement (not shown) that attaches the platform 33 to the pylon 17. The bolts transfer the vertical loads carried by the aft engine mount 19 to the pylon 17. The mounting platform 33 also includes one or more shear pin bores for accepting a shear pin arrangement (not shown) that also attaches the platform to the pylon 17. The shear pin arrangement transfers the side and thrust loads carried by the aft engine mount 19 to the pylon 17. The upper fitting 31 further includes a short rib section located below the mounting platform. The rib section includes structurally reinforced areas, or ribs 35, that carry engine loads between the mounting platform 33 and the links 45, 47, 53. The ribs 35 aid in controlling the alignment of the force vectors created by engine loads. Sufficient numbers of ribs 35 are included to ensure that the engine loads are fully supported. Because engine loads are transmitted primarily along the ribs 35, the areas in-between the ribs may be pocketed to reduce the weight of the upper fitting 31. Although the embodiments of the FIGURES show a rib section that is relatively compact, the height of the rib section may be increased in ways apparent to those skilled in the art, to allow an engine vibration isolator to be installed, should the need arise. Along the lower edge of the rib section are the four upper connection locations: one 39a for the first link 45; one 39b for the second link 47; and two 39c, 39d for the third link 53. The four upper connections 39a, 39b, 39c, 39d are located in a common plane lying generally transverse to the longitudinal axis 13 of the engine 11. As shown best in FIGURE 4, each upper connection location includes a clevis 41 with a pin hole 44a, 44b bored through each of two tines 42a, 42b of the clevis. One end of each of the links 45, 47, 53 is positioned between the clevis tines 42a, 42b and is held in place by a clevis pin 43 that passes through the pin hole 44a in one of the clevis tines 42a, through a hole 61 in the end of the link, and then through the pin hole 44b in other clevis tine 42b. This arrangement is described in further detail below. Returning to FIGURE 2, the contour of the lower edge of the upper fitting 31 is preferably determined by connecting lower arcs formed about each clevis pin hole, with simple curves. The lower arcs are formed by rotating a radius at each pin hole that is larger than the radius of the pin hole. Care should be taken to allow sufficient structure in the clevis tines 42a, 42b around each of the clevis pin holes 44a, 44b to carry the expected loads. The clevises 41 are formed by machining, preferably, Inconel, titanium, or stainless steel; and are shaped such that the ends of the links 45, 47, 53 will fit easily into their respective clevises 41 during all phases of flight. Care should be taken to ensure that adequate space for the links is available during both normal and failed-link operations, as discussed below. Referring to FIGURE 5, the clevis strip 73 is located along the radial upper edge of the engine case 71. The clevis strip 73 lies in a plane generally transverse to the longitudinal axis 13 of the engine 11, generally inline with the plane formed by the upper connection locations. The clevis strip 73 contains four lower connection locations: one 75a for the first link 45; two 75b, 75c for the second link 470; and one 75d for the third link 53. Each lower connection location 75a, 75b, 75c, 75d includes a clevis 41 with a clevis pin hole 44a, 44b bored through each of the tines 42a, 42b of the clevis (as shown in FIGURE 4). The other ends of the links 45, 47, 53 are each positioned between the tines 42a, 42b of a clevis and are held in place by inserting clevis pins 43 through both the tines 42a, 42b of the related clevis and through a hole 61 in the end of the link. The outer contour of the clevis strip 73 is determined by connecting lower arcs formed about each clevis pin hole, with simple curves. The lower arcs are formed by rotating a radius at each pin hole 44a, 44b that is larger than the radius of the pin hole. Care should be taken to allow sufficient structure around each of the clevis pin holes 44a, 44b to carry the expected loads. The following discussion of the three links 45, 47, 53 details three major aspects of the links. The first aspect is the general shape and location of the links relative to the upper fitting 31 and to the engine casing 71. The second aspect is the use of pin-and-clevis joints to attach the links to the upper fitting 31 and the engine casing 71. The third aspect is the operation of the links during normal operation and when a link fails. The three links 45, 47, 53 are installed side-by-side in a generally common plane lying transverse to the longitudinal axis 13 of the engine 11. The first link 45 is positioned on the left side of the aft engine mount 19, at roughly a 30° clockwise angle from the vertical, as shown in FIGURE 2. The first link 45 is substantially straight and fans outwardly from one end of the upper fitting 31. The first link 45 contains upper and lower link holes with spherical bearings, one hole at each end of the link 45. The upper hole of the first link 45 is connected to the upper fitting 31 at the first upper connection location 39a in the previously described pin-and-clevis manner. A more detailed description of a pin-and-clevis connection is given below. The lower hole of the first link 45 is attached to the engine casing 71 at the first lower connection location 75a, again using a pin-and-clevis joint. The second link 47 has a dog leg shape and includes a first arm 49 and a second arm 51. The arms 49, 51 are of the same general length and define an obtuse angle of roughly 145°. Three link holes are provided, one at the intersection of the two arms 49, 51 and one at each of the outer ends of the arms. The hole in the outer end of the first arm 49 is attached to the engine casing 71 at the second lower connection location 75b, which is located inwardly (relative to the airplane) of the first lower connection location 75a. The hole at the intersection of the two arms 49, 51 is connected to the upper fitting 31 at the second upper connection location 39b, which is located inwardly of the first upper connection location 39a. The hole in the outer end of the second arm 51 is connected to the engine casing 71 at the third lower connection location 75c, which is located inwardly of the second lower connection location 75b. All of the second link connections are pin-and-clevis joints. The third link 53 also has a dog leg shape and includes a first arm 55 and a second arm 57. The arms 55, 57 are of the same general length and define an angle of roughly 105°. Three link holes are provided, one at the intersection of the two arms 55, 57 and one at each of the outer ends of the arms. The hole in the outer end of the first arm 55 is connected to the upper fitting 31 at the third upper connection location 35c, which is located inwardly of the second upper connection location 35b. The hole at the intersection of the two arms 55,57 is connected to the upper fitting 31 at the fourth upper connection location 39d, which is located inwardly of the third upper connection location 39c. The hole in the outer end of the second arm 57 is connected to the engine casing 71 at the fourth lower connection location 75d, which is located inwardly of the third lower connection location 75c. All of the third link connections are pin-and-clevis joints. One particular embodiment of the relative locations of the upper and lower connections on such a prior art engine mount is described in the table of FIGURE 3. The values in FIGURE 3 are for use with a C.F.M.I.56-7 underwing aft engine mount, as used on (but not limited to) a Boeing 737 Next Generation aircraft (-600/-700/-800). As will be understood by those skilled in the art, slight variations may be made to this particular embodiment if the engine mount is to be used on an engine other than the C.F.M.I.56-7 underwing engine. The x and y coordinate system is shown in FIGURE 2 centered at the first lower connection location 75a. The locations listed in FIGURE 3 will vary depending on the particular engine application to which a mount is being applied. The following description of the pin-and-clevis joint of the first arm 49 of the second link 47 is illustrative of all of the pin-and-clevis joints at both the upper and lower connection locations. Exceptions are noted. FIGURE 4 is a cross-sectional side view of the second arm 51 of the second link 47 taken along line 4-4 of FIGURE 2. The pin-and-clevis joint at the second upper connection location 39b comprises the two previously described clevis tines 42a, 42b within which the second link 47 is held by a clevis pin 43. The clevis pin 43 passes through a circular clevis hole 44a located in one of the clevis tines 42a, through a hole 61 in the second link 47, and a circular hole 44b located in the other clevis tine 42b. The third lower connection location pin-and-clevis joint is configured similarly. Each link hole 61 in the links 45, 47, 53 includes a spherical bearing 63. The spherical bearing comprises a bearing ball 65 and a bearing race 67. The bearing race 67 is swaged onto the link hole 61 by means of a lip 69. The bearing ball 65 is positioned in the bearing race 67 and includes a bearing ball hole 68 through its center. The clevis pins 43 pass through the bearing ball holes 68. The spherical bearings 63 allow the link to rotate relative to the clevis. As shown in FIGURE 4, bushings 91 are located in the pin holes 44a, 44b located in the clevis tines 42a, 42b. The bushings 91 extend from the bearing ball 65 to almost the outer surface of the clevis 41. The bushings 91 reduce the vibration of the link and clevis pins. The clevis tines 42a, 42b; bearing ball 65; bearing race 67; and bushings 91 of all of the clevis assemblies are sized to fit closely together. The clevis pins 43 include a head 93 located at one end and threads 95 located at the other end. When inserted in the clevis tines 42a, 42b, the size of the clevis pin 43 is long enough to allow the threaded portion 95 to extend past the clevis tines 42a, 42b. An end cap 97 and nut 99 attached to the threaded end of the clevis pin 43 firmly secure the clevis pin 43 in the clevis 41. In this engine mount 19, the diameter of the clevis pin 43 and the diameter of the bearing hole 68 are substantially the same for the clevises 41 at the first, second, and fourth upper connection locations 39a, 39b, 39d and at the first, second, and fourth lower connection locations 75a, 75b, 75d. At the third upper connection location 39c and the third lower connection locations 75c, the diameter of the bearing ball hole 68 is slightly larger than the radius of the clevis pin 43. In this embodiment of the invention the diametric gap between the clevis pin 43 and bearing ball hole 68 of the third lower connection location 75c is approximately 7.87 mm (0.310 inch). The diametric gap between the clevis pin 43 and bearing ball hole 68 of the third upper connection location 39c is approximately 5.08 mm (0.200 inch). As discussed in more detail below, the diametric gaps ensure that the links will float around the clevis pin and will not contact the clevis pin during normal operation. Obviously, these dimensions are to be taken as exemplary, since other dimensions may be better for other applications. All of the link holes 61 are circular and are formed about an axis normal to the outer surface of each of the links 45, 47, 53. The link holes 61 are sized to fit closely against the bearing race 67, which is designed to fit closely about the bearing ball 65. The links are positioned within the clevises 41 at a slight tilt. The precise tilt amount will depend upon the amount of movement expected due to thermal expansion at a particular connection location during flight. Even though the links 45, 47, 53 may be tilted at a different angle, during the cruise phase of flight, the movement of the engine 11 will cause all links to become generally vertically oriented and transversely aligned relative to the longitudinal axis 13 of the engine 11. FIGURE 5 is a schematic view of the failsafe aft engine mount 19 of FIGURE 2, showing the position of the links 45, 47, 53 during normal operations. As shown in FIGURE 5, the links 45, 47, 53 and clevis pins 43 are sized and placed within the aft engine mount 19 so that under normal loading conditions, the first link 45 and the second arm 57 of the third link 53 carry substantially all of the vertical loads, first arm 49 of the second link 47 carries substantially all of the horizontal loads, the second arm 51 of the second link 47 carries no loads, and the first arm 55 of the third link 53 carries no loads. The upper and lower connection locations are shown by a dot in the center of each of the circles of FIGURE 5. The dots also indicate the general axial center of the clevis pin 43. A single circle surrounds the first, second and fourth upper connection locations 39a, 39b, 39d and the first, second, and fourth lower connection locations 75a, 75b, 75d indicating that the clevis pin 43 and bearing ball hole 68 at that connection location are sized to fit one another closely, as described above. At the third upper connection location 39c and the third lower connection location 75c there are two circles indicating that the bearing ball hole diameter is larger than the clevis pin radius. The large circle represents the bearing ball hole 68 and the smaller circle represents the clevis pin 43 diameter. The lines 77 connecting the connection locations of the links 45, 47, 53 are straight and show that the loading between two connection locations follows a straight path through a link. Therefore, no link is subjected to a bending load in a non-failure condition. FIGURE 6 is a schematic view of the aft engine mount 19 of FIGURE 2, showing the position of the second and third links 47, 53 during a failed first link 45 condition. If the first link 45 fails, then the bearing ball 65 of the second arm 51 of the second link 47 will be forced into contact with the clevis pin 43 at the clevis joint of the third lower connection location 75c (as shown in FIGURE 6). This allows the second link 47 to work with the remaining third link 53 to absorb the loads previously carried by the failed first link 45. The clevis pin 43 of the clevis joint at the third upper connection location 39c moves closer to the bearing ball hole 68 in the first arm 55 of the third link 53 (as shown in FIGURE 6). However, a connection is not made. FIGURE 7 is a schematic view of the aft engine mount 19 of FIGURE 2, showing the position of the first and third links 45, 53 during a failed second link 47 condition. If the second link 47 fails, then the bearing ball 65 of the first arm 55 of the third link 53 will be forced into contact with the clevis pin 43 at the clevis joint of the third upper connection location 39c. The third link 53 works with the first link 45 to absorb the loads previously carried by the failed second link 47. FIGURE 8 is a schematic view of the aft engine mount 19 of FIGURE 2, showing the position of the first and second links 45, 47 during a failed third link 53 condition. If the third link 53 fails, then the bearing ball 65 of the second arm 51 of the second link 47 will be forced into contact with the clevis pin 43 at the clevis joint of the third lower connection location 75c. This allows the second link 47 to work with the remaining first link 45 to absorb the loads previously carried by the failed third link 53. FIGURES 9-13 illustrate a failsafe aft engine mount formed in accordance with the present invention. This novel engine mount is similar to the mount described with reference to FIGURES 2-8, with the exception of changes to the third link 53, its connection to the upper fitting, and the manner in which the mount operates during failure conditions. In particular, referring to FIGURE 9, the novel third link 153 also has a dog leg shape formed by a peg 155 and a substantially straight arm 157. The peg 155 and arm 157 define an angle of roughly 115 degrees. The peg 155 extends inwardly (i.e., toward the mount middle portion) from an upper region of the third link 153. Still referring to FIGURE 9, the upper fitting 31 includes a hole 159 within which the peg 155 is inserted. The hole is formed through the structural webbing of the upper fitting. Both the peg and the hole are cross-sectionally circular or ovoid, with the hole cross-sectional shape being larger than the peg cross-sectional shape. During normal operations, the peg does not contact the hole surfaces. In preferred arrangements the peg is spaced in the range of about 2.54 mm to 7.62 mm (0.100 inches to 0.300 inches) from its side surfaces to the upper fitting hole surfaces during normal operations. The preferred distance being about 6.4 mm (¼ inch) between the peg side surfaces and the upper fitting hole surfaces during normal operations. FIGURE 10 is a schematic view of the novel failsafe aft engine mount of FIGURE 9, showing the position of the links 45, 47, 53 during normal operations. In such circumstances, the first link 45 and the third link arm 157 carry substantially all of the vertical loads, the first arm 49 of the second link 47 carries substantially all of the horizontal loads, the second arm of the second link 47 carries no loads, and the peg 155 of the third link carries no loads. Operation of the mount during a failed link condition is shown schematically in FIGURES 11-13. Just as in FIGURES 5-10, the upper and lower connection locations are shown by a dot or cross in the center of each of the circles. The dots also indicate the general axial center of the clevis pin 43. FIGURE 11 is a schematic view of the aft engine mount of FIGURE 9, showing the position of the second and third links 47, 153 during a failed first link 45 condition. If the first link 45 fails, then the bearing ball of the second arm 51 of the second link 47 will be forced into contact with the clevis pin 43 at the clevis joint of the third lower connection location 75c. This allows the second link 47 to work with the remaining third link 153 to absorb the loads previously carried by the failed first link 45. The third link peg 155 moves closer to the upper fitting hole 159 surfaces as shown in FIGURE 11, however, a connection is not made between the peg 155 and the hole 159 at this time. FIGURE 12 is a schematic view of the aft engine mount of FIGURE 9, showing the position of the first and third links 45, 53 during a failed second link 47 condition. If the second link fails, then the third link peg 155 is forced into contact with the upper fitting hole 159. Because the peg is acting as an anti-rotation member, the peg (and the hole) may be oriented from the other third link portions (and the upper fitting) in any one of a number of directions. What is important to the present invention is that the peg and hole are configured to limit the movement of the third link during a second link failure condition. The third link 153 thus works with the first link 45 to absorb the loads previously carried by the now failed second link 47. FIGURE 13 is a schematic view of the aft engine mount of FIGURE 9, showing the position of the first and second links 45, 47 during a failed third link 153 condition. As in FIGURE 8, if the third link 153 fails, then the bearing ball 65 of the second arm 51 of the second link 47 is forced into contact with the clevis pin 43 at the clevis joint of the third lower connection location 75c. While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the scope of the invention.

Claims: A failsafe engine mount (19) for attaching an engine casing (71) of a jet engine (11) to a support structure (17) on an airplane, comprising: an upper fitting (31) attachable to the airplane support structure (17), the upper fitting (31) including a lower edge having first, second, and third upper connection locations (39a,39b,39d) located in a plane lying generally transverse to the longitudinal centerline of the engine (11); a clevis strip (73) attached to the outer periphery of the engine casing (71) in a plane lying generally transverse to the longitudinal centerline of the engine (11), the clevis strip (73) including first, second, third, and fourth lower connection locations (75a,75b,75c,75d) located in a plane lying generally transverse to the longitudinal centerline of the engine (11) ; a substantially straight first link (45) connecting to the upper fitting (31) at the first upper connection location (39a) and connecting to the clevis strip (73) at the first lower connection location (75a); a second link (47) including a first arm (49) and a second arm (51), the first arm (49) connecting to the clevis strip (73) at the second lower connection location (75b) and connecting to the upper fitting (31) at the second upper connection location (39b), the second arm (51) connecting to the clevis strip (73) at the third lower connection location (75c); and a third link (153) connecting to the upper fitting (31) at the third upper connection location (39d) and connecting to the clevis strip (73) at the fourth lower connection location (75d), characterized in that , the third link (153) includes a peg (155) extending from an upper region of the third link (153), the peg (155) being insertable into a hole (159) formed in the upper fitting (31). The failsafe engine mount (19) according to claim 1, characterized in that, the connections of the links (45,47,153) to the upper connection locations (39a,39b,39d) of the upper fitting and to the lower connection locations (75a-d) of the clevis strip (73) are pin-and-clevis joints (41-44). The failsafe engine mount (19) according to claim 2, characterized by spherical bearings (65,67) at the pin-and-clevis joints (41-44), positioned so that all links (45,47,153) lie in generally the same transverse plane relative to the longitudinal centerline of the engine (11) during the normal cruise operation of flight. The failsafe engine mount (19) according to any of the prceding claims characterized in that the upper fitting (31) further comprises structurally reinforced portions (35). The failsafe engine mount (19) according to any of the preceding claims characterized in that the upper fitting (31) further comprises a mounting platform (33) suitable for connection to the airplane support structure (17). The failsafe engine mount (19) according to any of the preceding claims characterized in that the second arm (51) of the second link (47) is arranged to be unloaded during normal airplane operation and/or is arranged to work with the first link (45) to carry the engine loads should the third link (153) fail. The failsafe engine mount according to any of the preceding claims characterized in that the peg (155) of the third link (153) is positioned to be unloaded during normal airplane operation and/or is positioned to be unloaded during a failure of the first link (145). The failsafe engine mount (19) according to any of the preceding claims characterized in that the peg (155) of the third link (153) and the upper fitting hole (159) are arranged to work with the first link (45) to carry the engine loads should the second link fail (47). The failsafe engine mount (19) according to any of the preceding claims characterized in that the peg (155) of the third link (153) is cross-sectionally ovoid in shape. The failsafe engine mount according to claim 9, characterized in that the peg (155) is spaced in the range of about 2,54 mm to 7,62 mm (0.100 inches to 0.300 inches) about its side surfaces from the surfaces of the upper fitting hole (159) surfaces during normal operations, and is preferably spaced about 6,4 mm (1/4 inch) at its side surfaces from the surfaces of the upper fitting hole (159) during normal operations.

Inventors: DUNSTAN KENT W, HEY KENNETH E, DUNSTAN, KENT W., HEY, KENNETH E.
Applicants: BOEING CO, THE BOEING COMPANY
Application year: 1998
Main classification: B64D27
IPC codes: B64D27