Integrated corner for ducted fan engine shrouds

An engine shroud with integral honeycomb panel corners for use in the thrust reverser region of ducted fan gas turbine engines. The integral shroud is useful in a turbine engine having a core engine surrounded by an engine casing and nacelle, with a fan at the inlet directing air flow into the bypass duct between core engine and engine nacelle. The shroud basically consists of right and left ducts each having an approximately semicircular cross-section with radial flanges extending from the duct edges. The flanges permit the halves to be fastened together to produce a tubular shroud adapted to surround a gas turbine engine and form the inner wall of a bypass duct. The disclosed shroud eliminates the prior complex corner fittings connecting the semicircular center portion of the shroud to the extending flanges and provides simple, integral corners.

BACKGROUND OF THE INVENTION 
This invention relates in general to engine shrouds for gas turbine engines 
and, more specifically, to an improved shroud having integral corners. 
Ducted fan jet engines for aircraft applications have come into widespread 
use. Such engines include a core engine within a streamlined shroud, a 
stage of fan blades mounted upstream of the engine and driven thereby, and 
a nacelle surrounding the fan blades and shroud and spaced from the shroud 
to provide a bypass duct between nacelle and shroud through which 
compressed air is forced by the fan blades. 
The shroud which surrounds the engine and forms both the housing for the 
engine and the interior wall of the bypass duct is often formed from two 
halves which are fastened together to form the shroud. This arrangement 
facilitates engine servicing, removal and reinstallation. Each shroud half 
consists of a center section having a generally semicircular cross-section 
which forms half of the tubular shroud around the engiee and two radially 
extending flanges attached to the edges of the each center section to aid 
in supporting the shroud within the engine casing and nacelle and to carry 
means for securing the shroud halves together. 
The intersection between flanges and center section is a rather sharp 
corner, which could not be formed directly in the generally used shroud 
materials. The shroud is ordinarily fabricated from a panel which 
comprises a honeycomb core to which two face sheets are bonded. The panel 
is generally formed from a metal such as aluminum or high strength fiber 
reinforced resin matrix materials such as graphite fibers in an epoxy 
resin matrix. The corners between flanges and center section have in the 
past been made by fastening separate panels together with a variety of 
clamping and fastening fixtures. 
While the prior corner fasteners have been effective, they are cumbersome, 
heavy, require considerable skill to install and are more expensive and 
less reliable than a continuous integral panel would be. Thus, there is a 
continuing need by for shrouds formed as a continuous panel, eliminating 
corner fittings. 
SUMMARY OF THE INVENTION 
The above-noted problems, and others, are overcome by splicing a band of 
lighter, more flexible, honeycomb material having the same thickness as 
the center section and flanges at the sharp corners, so that the entire 
shroud can be formed from honeycomb materials having uniform thickness. 
Face sheets cover all of the varying flexibility, uniform thickness 
honeycomb sections. If desired, pieces or bands of honeycomb material 
having the same thickness but higher densities than those of the center 
section and flanges may be spliced into the honeycomb panels to provide 
local strong areas for the attachment of various fittings or other 
components. The various honeycomb panel pieces are assembled, shaped and 
bent as required, then bonded to suitable face sheets in a conventional 
manner.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is seen a conventional gas turbine engine 10 
of the fan type, mounted by a pylon 12 on an aircraft wing 14. A fan 16 
located just within engine inlet 18 is driven by a core engine within 
engine inner shroud 20. Shroud 20 is ordinarily formed from two 
approximately "C" shaped halves with edge extensions or flanges 22 which 
extend to the inner wall of engine casing 24. An annular space lies 
between shroud 20 and the core engine. 
Engine casing 24 within nacelle 26 forms part of the outer wall of a bypass 
duct 28 between casing 24 and core 20 into and through which fan 16 forces 
a flow of compressed air. In normal engine operation, the compressed air 
flows through bypass duct 28 and out engine outlet 30, adding to engine 
thrust. thrust reversers 32, including turning vane cascades and torque 
ring mounting assembly 34, are provided to reverse engine thrust during 
landing. 
The left hand half of a typical shroud 20 and nearby portions of the thrust 
reverser assembly 32 are shown in greater detail in FIG. 2. A variety of 
components and fittings are typically mounted on or inside the shroud, 
which when assembled surrounds but is spaced from a conventional engine 
(not shown). Typical components and fittings include a precooler duct 36, 
upper and lower bumpers 38 and 40, respectively, various latches 42 for 
fastening the shroud together and to other structures, etc. 
Shroud 20 and flanges 22 are generally formed from a conventionally 
manufactured panel comprising a honeycomb core with two continuous face 
sheets bonded thereto. Typically, the honeycomb core and face sheets may 
be metal such as aluminum or titanium or a fiber reinforced composite, 
such as graphite fibers in an epoxy matrix. While the honeycomb cores can 
be reshaped into shapes having relatively wide curves, sharp corners 
cannot be formed in panels having the thicknesses suitable for use in 
shroud engine shrouds without damaging the panel in the corner regions. 
The prior art method for manufacturing engine shrouds of the sort shown in 
FIG. 2 is illustrated in transverse section in FIG. 3. The widely curved 
shroud center section 20 is fabricated from a honeycomb panel manufactored 
by conventional methods as noted above. Separate pieces of honeycomb are 
cut for flanges 22, including any further extensions 42 as may be desired. 
The honeycomb structure is schematically represented by the parallel lines 
lying perpendicular to the face sheets in FIGS. 3 and 4. Corner fittings 
44, which include splice plates 46 and bolts or rivets 48 are attached to 
the abutting honeycomb pieces along each intersection. In order to 
securely fasten bolts 48 to the honeycomb material, which does not have 
great localized strength, it is necessary to fill the honeycomb cells in 
the region of the bolt with a potting material, typically a synthetic 
resin or to emplace inserts of greater density. The shape of the plates 46 
must be carefully designed for each corner. Thus, it is apparent that 
these corner fittings 44 are heavy, expensive, difficult to fabricate and 
will tend to have less than ideal reliability. 
My improved integral corner structure is best seen in FIGS. 4 and 5. The 
shroud is formed from a honeycomb core with face sheets bonded to both 
surfaces. I have found that the need for complex corner fittings 44 can be 
eliminated and an integral honeycomb shroud can be fabricated by first 
shaping the flanges 22 and 42 and center section 20, leaving gaps at the 
corners. Pieces of lower density, flexible, honeycomb core material 50 are 
shaped to fill the gaps. These pieces are placed in the gaps and face 
sheets 52 are applied and bonded in a conventional manner. Face sheets 52 
may overlap if desired, as shown at 54, or may be doubled around a corner 
as shown at 54, or may be doubled around a corner as shown at 56 to 
provide added local increases in strength if desired. Heat resistant 
layers may also be applied to areas subjected to high temperatures if 
desired, as indicated at 58. 
Where fittings such as bumper 60 on bracket 62 are to be affixed to the 
shroud as shown in FIG. 5, pieces of high density, high strength honeycomb 
64 may be spliced into the basic honeycomb panel. Or, the honeycomb in 
those areas could be filled with potting material or other materials to 
provide mountings for fasteners 66 having sufficient strength. 
This system provides a simple, reliable shroud having a substantially 
uniform thickness and uniformly covered with face sheets to provide a 
versatile light weight structure having strength optimized for the 
requirements of different areas. 
While certain specific materials, dimensions and methods were detailed in 
the above description of preferred embodiments, those can be varied, where 
suitable, with similar results.