Abstract:
The present invention provides a tailcone and power assembly mountable to the body of an aircraft using a height adjustable dolly. The tailcone assembly comprises a longitudinal support member, a gas turbine engine mounted to the support member; a firewall; two curved rotatable casings hingeably connected to the support member; an inlet duct extending from an aperture in one of the rotatable casings to the engine inlet; an integral exhaust casing, and interface means for making necessary engine accessory connections to the aircraft. The tailcone is installed on the aircraft by mounting the tailcone in the adjustable dolly, rolling the dolly up to the aircraft, adjusting the dolly until the auxiliary power assembly is properly aligned for attachment to the aircraft, connecting the engine accessories to the aircraft, and bolting the assembly to the aircraft.

Description:
REFERENCE TO COPENDING APPLICATION 
     This is a division of Application Ser. No. 08/892,647, now U.S. Pat. No. 6,039,287 filed Jul. 15, 1997 which claims the benefit of U.S. Provisional Application Nos.: 60/023,080 filed Aug. 2, 1996, and U.S. Provisional Application No. 60/023,202 filed Aug. 5, 1996. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to an aircraft tailcone. More particularly, the present invention relates to a detachable integral aircraft tailcone and power unit assembly configured for quick attachment to and removal from an aircraft. 
     BACKGROUND OF THE INVENTION 
     Modern turboprop and turbofan powered aircraft carry a gas turbine engine known as an auxiliary power unit (APU) in addition to the main propulsion engines. The APU serves two main functions: to provide power to aircraft systems when the main engines are not running, and to enable starting the main engines without need for external power. In many business class aircraft and in aircraft used by smaller regional airlines, the APU is mounted in the tail end of the fuselage generally known as the tailcone. Typically, the engine supplier and tailcone casing supplier coordinate with the aircraft manufacturer in the installation of the APU at the manufacturer&#39;s facility. The APU is custom fit and mounted to the aircraft, and all accessories such as electrical, pneumatic, and fuel, are routed to the APU and connected. The tailcone casing supplier then fits and installs the casing, usually including an openable or removable panel for access to portions of the APU. 
     A problem with this kind of APU installation is the large amount of the time and expense involved in completing an installation. The mounting of the APU and routing and connection of accessories requires substantial effort by skilled technicians and engineers from the aircraft manufacturer and APU supplier. Fitting and attaching the casing requires technical support from the tailcone casing supplier as well. A complete installation can take days or even weeks at the aircraft manufacturers facility resulting in substantial cost and inconvenience. 
     Another problem results from inaccessibility of the APU once the casing is in place. Typically the casing comprises two large panels that are attached to one another and to the aircraft using numerous screws. The casing includes at least one small openable door for providing access to routinely monitored items such as the oil sight glass. However, for anything beyond the routine day to day maintenance it becomes necessary to remove at least one of the large casing panels. Removal of just the screws holding the panels together can take thirty minutes or longer. The time spent on removing and reinstalling the tailcone casing can become particularly inconvenient and costly when it results in unplanned delay to scheduled flights. 
     Accordingly, a need exists for a system that substantially reduces the time and labor required to install and test an APU and tailcone casing onto an aircraft. Another need exists for a tailcone casing that provides quick access to the entire APU mounted therein. 
     SUMMARY OF THE INVENTION 
     In view of the above, it is an object for this invention to provide a system that substantially reduces the time and labor required to install an APU and tailcone casing onto an aircraft, and to provide a tailcone casing giving quick access to the entire APU mounted within. 
     The present invention achieves these objects by providing a detachable integral aircraft tailcone and power assembly mountable to the body of an aircraft using a height adjustable dolly. The tailcone assembly comprises a longitudinal support member having forward and aft axial ends; a gas turbine engine mounted within the tailcone to the support member; a firewall extending from the support member forward of the engine; two curved rotatable casings hingeably connected to the support member and rotatable from a closed position to an open position thereby exposing the engine, the open position being at least 90 degrees from the closed position; an inlet duct extending from an aperture in one of the rotatable casings to the engine inlet; and interface means for making necessary electrical, mechanical, pneumatic, and hydraulic accessory connections between said tailcone assembly and said aircraft body. The forward axial end of the support member includes a flange adapted for quickly and rigidly attaching the entire tailcone assembly to the aircraft body. The integral aircraft tailcone may also include an integrated exhaust muffler. 
     The tailcone assembly is installed on the aircraft by mounting the tailcone in the adjustable dolly, rolling the dolly up to the aircraft, adjusting the dolly until the tailcone assembly is properly aligned for attachment to the aircraft, connecting the engine accessories to the aircraft, and bolting the tailcone to the aircraft. 
     These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a perspective view of the tailcone assembly contemplated by the present invention. 
     FIG. 1A depicts an enlarged fragmented cross-sectional view of an encircled portion of FIG.  1 . 
     FIG. 1B depicts an enlarged fragmented cross-sectional view of a mating edge of the casings and the exhaust cone. 
     FIG. 2 depicts a perspective view of the support member portion of the tailcone assembly of FIG.  1 . 
     FIG. 3 depicts a partially cross sectional partially cutaway side view of the tailcone assembly contemplated by the present invention. 
     FIG. 4 depicts a fragmented cross-sectional view of the integral inlet duct. 
     FIG. 5 depicts an enlarged fragmentary sectional view of an encircled portion of FIG.  1 . 
     FIG. 6A depicts a side view of an integral tailcone and power assembly mounted in an installation dolly as contemplated by the present invention. 
     FIG. 6B depicts an aft looking forward view of the tailcone assembly and installation dolly of FIG.  6 A. 
     FIG. 6C depicts a top looking down view of the tailcone assembly and installation dolly of FIG.  6 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The integral tailcone and power assembly of the subject invention is indicated generally by the numeral  10  in FIG.  1 . The tailcone assembly  10  comprises generally a gas turbine engine  12  mounted from a support member  14 , two rotatable casing halves  18  hingeably mounted to support member  14 , a firewall  17 , and an integral exhaust cone  20  with an open aft end  21 . 
     Referring to FIGS. 2 and 3, primary support for the entire tailcone assembly  10  is provided by the support member  14 . The support member  14  extends longitudinally from a forward end  25  to an aft end  25 . The upper surface of the support member  14  is capped by a fairing  15  contoured to define the top surface of the tailcone between the hinged edges of casing halves  18 . The support member structure is thus entirely enclosed within the tailcone  10 . Alternatively, the upper surface of the support member  14  may be contoured to define the top surface of the tailcone assembly. The support member construction consists of a welded box or I-beam structure preferably made from Inconel 625 sheet and plate stock. Other constructions or materials may be used depending on the particular installation. 
     The support member  14  is adapted for attachment to the rear bulkhead  32  and tail spar  34  of the aircraft. The forward end of support member  14  is tapered at an angle to fit the aircraft bulkhead  32 , and provided with a flange  26  having bolt holes  28  and a locating pin  30 . When the tailcone assembly  10  is installed, the flange  26  is bolted to the aircraft bulkhead  32 , and preferably also to the tail spar  34 , thereby rigidly connecting the tailcone assembly to the aircraft. The connection is designed so that the support member  14  extends roughly horizontally from the aircraft. 
     The support member  14  further includes mounting brackets  36  for connecting to the gas turbine engine main mounts. The engine depicted in the figures has forward and rear main mount pads indicated as  38  and  40  respectively, both located on the top side of the engine. Main mounts  38  and  40  are connected to the mounting brackets  36  through rigid links  42 . It should be noted that the locations and orientations of the engine&#39;s main mounts and the support member mounting brackets  36  shown are illustrative of a typical configuration. The present invention more broadly contemplates mounting any suitable engine to a support member  14  regardless of how the engine mounts may be configured. 
     The engine  12  also includes two secondary mounts  44 . The secondary mounts  44  are connected to the firewall  17  (described below) via struts  48 . Opposite each of the struts  48 , standoffs  50  extend from the firewall  17  to the aircraft. A flange  52  having an alignment pin and bolt holes is defined at the forward end of each standoff  50  for attachment to the aircraft bulkhead  32 . The struts  48  and standoffs  50  are preferably configured to provide a direct load path between the secondary mounts  44  and the aircraft bulkhead  32 . As with the main mounts, the location and orientation of the secondary mounts shown is merely illustrative of a typical installation, and not limiting to the mount configurations contemplated by the invention described and claimed herein. 
     Fire protection and access to the engine&#39;s accessories are provided by the firewall  17 . The firewall  17  is rigidly connected to the support member  14  several inches rearward of flange  26 , and preferably parallel with the aircraft rear bulkhead  32 . A bulb seal  62  is attached to the perimeter of the firewall  17  for sealing off the engine from the aircraft. The seal  62  is itself protected by a seal retainer (not shown) extending from the firewall  17 . When the rotatable casing halves  18  are closed and latched together, the seal  62  is compressed and mates with a seal land (not shown) located on each casing  18 . An access panel  72  is provided in firewall  17  for routing the engine&#39;s accessory connections out of the tailcone assembly  10 . All engine accessory connections may be advantageously made in the cavity between the firewall  17  and the aircraft bulkhead  32 . 
     The rotatable casings  18  enclose almost the entire forward portion of the tailcone assembly  10 . Each casing  18  extends longitudinally from the forward end of the tailcone rearward to a point approximately adjacent the engine exhaust, and wraps circumferentially all the way around to the bottom of the tailcone, abutting one another along their lower longitudinal edges  57 . Four spaced apart latches  58  are used along the lower longitudinal edges  57  to latch the casings  18  to one another. Additional latches on the forward and off edges of the rotatable casings may be used to provide additional support. Preferably latches  58  are flush with the outer surface of the casings  18  when closed and latched. 
     The rotatable casings  18  provide access to the entire APU for performing various engine maintenance by opening one or both sides. The casings  18  are large enough to allow for removal of the APU from the aircraft when required, such as for performing a hot section overhaul, without need for removal of any casing from the aircraft. The aft edges of the casings  18  are undercut to define a lip  64  which overlays a mating step  66  in the forward edge of the exhaust cone  20 , as illustrated in FIG. 1A, thereby creating a lap joint arrangement when the rotatable casings are closed and latched. A similar undercut is provided in the forward edge of the casings  18  for overlaying the perimeter of the aircraft bulkhead  32 . 
     The rotatable casings  18  are hingeably connected to gooseneck hinges  54  and  56  extending from support member  14 . The forward and aft gooseneck hinges  54  are rigidly attached to the sides of support member  14 . A single piece floating hinge  56  is disposed between fixed hinges  54 , and defines the center gooseneck hinge for both casing halves  18 . The floating hinge  56  comprises a single bar formed into the goosenecks at each end, free to slide laterally and vertically in a slot  53  formed in the support member  14 . The floating hinge  56  self aligns with the fixed hinges  54 , thereby ensuring free movement of the casing  18 , and enabling alignment of casings  18  to be controlled solely by adjustment of fixed hinges  54 . Alternative hinging arrangements, for example strip piano type hinges, may be used instead of the gooseneck type depending upon the constraints of the installation. 
     The rotatable casings  18 , are preferably made of a composite skinned honeycomb sandwich construction as shown in FIG.  5 . The core material in the sandwich construction is a honeycomb structure  63  typically made of either Titanium metal or Phenolic—a paper based material. The inner and outer exterior surfaces  65  of the sandwich are made of a carbon fiber reinforced plastic (CFRP). The CFRP consists of carbon fiber and a plastic matrix, where the plastic matrix may be an epoxy, bismaleimide, or polyimide; the latter having higher temperature capability. If an epoxy based CFRP is used, a thermal blanket may be required to shield the doors from engine heat. Such a thermal blanket would typically be made from woven “Teflon” or “Capton” material, and pinned to the inside of the rotatable casings. The outer external surface includes layers of copper foil or nickel mesh  67  for lightning protection. Kevlar plies may be added to the inside surface of the casings  18 , and a higher density honeycomb core used adjacent the turbine and compressor wheels of the gas turbine engine for improved fragment containment. The rotatable casings  18  may alternatively be made of a suitable sheet metal, such as 0.040 inch thick Titanium 6AL-4V with stringer reinforcement. Casings made of Titanium or other metal do not require the addition of copper foil for lightning protection. 
     The tailcone assembly  10  includes means for ducting combustion air to the engine, illustrated in FIG.  4 . One of the rotatable casings  18 , includes an inlet aperture  74  aligned with an integral inlet conduit or duct  76  extending from the inside surface of the casing  18  to an open end adjacent the engine inlet  80 . The inlet conduit  76  includes a gasket  78  at its open end such that when the casings  18  are closed and latched, inlet conduit  76  sealingly mates up with the engine inlet  80 , thereby defining a duct from the engine inlet to the ambient air. Inlet conduit  76  is integral with casing  18  and preferably constructed of the same type of honeycomb composite material. 
     The inner surfaces of the conduit  76  receive an acoustic treatment for suppressing engine noise. The treatment comprises perforating the entire inner composite surface of the honeycomb composite with a plurality of small diameter (approximately {fraction (1/16)} inch) closely spaced holes  77 . Noise abatement may alternatively be achieved by incorporating a wire mesh layer known in the industry as a septum (not shown) into the honeycomb composite structure. The septum may be disposed between the inner composite surface and the honeycomb, or between two layers of honeycomb. A suitable louvered cover plate  79  for directing air into the ducting and filtering out foreign objects is located over aperture  74 . The cover plate  79  may include means for restricting the amount of airflow entering the conduit such as through adjustable louvers or multiple positionable door. 
     Referring to FIG. 3, the aft most portion of the tailcone is an integral exhaust cone  20  rigidly mounted to the aft end of support member  14  by a bracket  85 . The outer surface of the exhaust cone  20  defines the exterior surface of the tailcone aft of the casings  18 . The exhaust cone structure comprises a tapered hollow shell, with an open aft end  21  and a bulkhead  86  at the forward end. The bulkhead  86  defines an aperture  88  adapted for sealingly connecting the exhaust cone  20  to the engine exhaust. Preferably the exhaust cone  20  is constructed of the same type of light weight honeycomb composite as the rotatable casings  18 , namely either epoxy Bismaleimide or Polyimide matrix CFRP covering a honeycomb core; or alternatively a more conventional Titanium sheet and stringer construction. 
     Once attached to the engine exhaust, the exhaust cone  20  functions as a conduit for porting exhaust gas out of the tailcone assembly  10 , taking the place of a conventional tail pipe. The exhaust cone  20  also includes means for suppressing exhaust noise such as a felt metal facesheet  87  and felt metal baffles  89 . Importantly, the exhaust cone  20  acts as the outercasing for the muffler, thereby providing an interested muffler and exhaust case. 
     An adjustable height dolly  11 , shown in FI facilitates installation and removal of the tailcone assembly  10  from an aircraft. The dolly or cart,  11  includes a base portion  90  having steerable adjustable height wheels  92 , and a frame portion  94  extending vertically from and overhanging the base portion. The frame portion  94  includes fittings  97  for suspending the tailcone assembly  10  from suspension points  98  located on the top of the tailcone. 
     With the tailcone mounted in the dolly  11 , the dolly may be rolled up to the rear bulkhead of the aircraft for installation. Any required fine adjustments in mounting alignment are made by adjusting the height of wheels  92 . Alternatively, any other suitable system for final height and angle adjustment of the tailcone assembly  10  may be used, such as adjustable height frame  94  or adjustable fittings  97  thereon. When adequately positioned and aligned, the engine&#39;s accessory connections are made and the tailcone  10  is bolted to the aircraft. 
     Various modifications and alterations of the above described detachable integral aircraft tailcone and power assembly will be apparent to those skilled in the art. Accordingly, the foregoing detailed description of the preferred embodiment of the invention should be considered exemplary in nature and not as limiting to the scope and spirit of the invention as set forth in the following claims.