Single-skin thrust reverser for aircraft jet engines

Thrust reverser for a jet engine of an aircraft, comprising two symmetrical doors mounted to pivot about an axis which is transverse and substantially diametrical with respect to the jet of the engine and which is disposed downstream of the jet exhaust pipe thereof, the doors being adapted to occupy a folded or stowed position in which they form part of the fairing of the engine or fuselage of the aircraft, or an unfolded or opened out position for which they are disposed transversely with respect to the jet. According to the invention, each of the doors is formed by a single skin which is at least substantially hemi-truncated in shape.

The present invention relates to a thrust reverser for a jet engine, with 
or without by-pass of the main jet, mounted in particular on an aircraft. 
With a view to shortening the distance run by an aircraft between landing 
and stopping or to increasing safety when braking on a damp or icy runway, 
a reverser is known to be used on jet-engined aircraft, which produces a 
braking thrust. 
To this end, a thrust reverser is already known which comprises two 
symmetrical doors pivotally mounted about an axis which is transverse and 
substantially diametrical to the jet of said engine and which is disposed 
downstream of the jet exhaust pipe thereof, said doors occupying a folded 
or stowed position in which they form part of the fairing of said engine 
or fuselage of the aircraft, or an unfolded or opened out position in 
which they are disposed transversely with respect to said jet. 
In this known reverser, each door is "double-skinned", and in stowed 
position the inner skins of the two doors form a convergent duct followed 
by a quasi-cylindrical portion, connected by a ridge, adjacent the edge of 
the nozzle of the engine. 
It is an object of the invention to provide a structure of doors for a 
thrust reverser enabling the dimensions of said doors to be reduced, the 
weight of said reverser to be lightened and the aerodynamic 
characteristics of the reversed jet to be improved. 
According to the invention, this object is attained in that each of said 
doors is formed by a single skin or thin wall which is at least 
substantially hemi-truncated in shape. 
As will be seen hereinafter, such a structure makes it possible to increase 
the critical dimension for the flow of reversed jet, the door dimensions 
being equal, and thus to reduce the length of the doors, the critical 
dimension being equal. This results in a weight saving, an improved 
rigidity of the reverser and a reduction of the drag. 
As used herein, the term "critical dimension" refers to the smallest 
distance separating the exhaust end of the jet tube of the engine and the 
thrust reverser, through which the deflected exhaust gases flow when the 
reverser is in use, which can be used without reducing the mass flow 
through the engine or causing the engine to overheat. A discussion of the 
significance of the "critical dimension" is found in NACA Research 
Memorandum E55E18, "Performance Characteristics in Hemispherical 
Target-type Thrust Reversers", by Fred W. Steffen et al., Sept. 27, 1955. 
Said substantially hemi-truncated skin is advantageously reinforced on its 
concave face, at least near its rectilinear longitudinal edges and its 
circular leading edge, by stiffening sections, taking the shape of said 
concave face and projecting with respect thereto. 
Moreover, said substantially hemi-truncated skin preferably comprises on 
the rear side a crescent-shaped extension, which is separated from the 
rest of said skin, on the concave face thereof, by a stiffening arc. 
In the thrust reverser according to the invention, the concave face of the 
at least substantially hemi-truncated skin is provided, near the 
stiffening arc, with a lining, which, in section through a diametrical 
plane of said skin, is ridged in cross-section, of which ridge the point 
furthest away from said skin is located at the level of said stiffening 
arc, this lining covering, on one side of said arc, said crescent-shaped 
extension, and on the other side, less than half of the length of the 
concave face separating the stiffening arc from the leading edge of the 
door. In this way, the linings of the doors participate, in unfolded 
position, in the division and lateral guiding of the reversed jet. Said 
latter may, moreover, be controlled by the height of the projection of the 
stiffening sections with respect to the concave skin of the door being 
adjusted to perfect the flow of the reversed jet when the doors are in 
unfolded position. 
When the doors are in stowed position, the portions of lining covering the 
crescent-shaped extensions form a cylindrical or slightly divergent 
exhaust pipe. In this latter case, the angle at the vertex of the 
divergent duct is advantageously smaller than six degrees. 
In this way, in the thrust reverser according to the invention, said 
exhaust pipe is separated from the nozzle of the engine by an empty 
annular space, this facilitating the positioning of the doors.

In these Figures, like elements are designated by like references. 
Referring now to the drawings, FIG. 1 shows the rear 1 of an aircraft, 
comprising three jet engines 2, 3 and 4, namely two side engines 2 and 3 
and a central one 4. This engine 4 is to a large extent hidden by a thrust 
reverser, comprising two reverser doors 5, hinged about a pivot 6 enabling 
said doors to pivot about a vertical axis disposed downstream of the fan 
nozzle of the engine 4. This pivot 6 is mounted on the fan channel 7 of 
said nozzle. 
In FIG. 1, the reverser doors are shown in unfolded position, i.e. in a 
position adapted to reverse the jet, whilst in FIG. 3 they are shown to be 
in stowed position. In this latter case, they are in line with the fairing 
8 of the engine 4. 
The reverser doors 5 are identical and interchangeable, so as to be adapted 
to be mounted equally well on the left or on the right. 
As shown in FIG. 2, each door 5 is formed by a thin wall 9, generally 
called a skin, at least approximately in the form of half a frustum of a 
cone. On its concave inner face, the skin 9 is stiffened at its periphery 
by a frame formed of longitudinal beams 10 and 11 along its rectilinear 
edges and arcs 12 and 13 near its leading and rear curvilinear edges. It 
may also comprise additional small longitudinal stiffeners 29. 
The beams 10 and 11 and arcs 12 and 13 are constituted by sections of which 
the cross-section is in the form of a U, a .OMEGA. or the like and are 
fixed on the inner concave face of the skin 9 by their edges. 
The skin 9 and the beams and arcs 10 to 13 may be made of "INCONEL 625" 
(Registered Trade Mark) or any other suitable refractory alloy and these 
different elements of a door 5 may be assembled by riveting. 
Two pivot fittings 14 and 15 are arranged at the rear arc 13, for 
attachment to the hinge device 6. The fittings 14 and 15 are located along 
the rectilinear edges of the door 5. At the leading edge of each door 9, 
stiffening arc 12 and the leading edge of skin 9 adjacent thereto are 
substantially semi-circular and lie in a plane which is generally 
perpendicular to the longitudinal edges of the door. At the trailing edge 
of each door 9, stiffening arc 13 is semi-circular and is also generally 
perpendicular to the longitudinal edges of the door. The trailing edge of 
skin 9 extends rearwardly beyond arc 13 and lies a plane which is oblique 
to the longitudinal edges of the door. Between the trailing edge of the 
skin 9 and stiffening arc 13 there is accordingly defined a 
crescent-shaped section 16 of the skin, having two cusps which lie at 
pivot fittings 14 and 15. The maximum width (i.e., the distance between 
the trailing edge and arc 13) of cresent-shaped section 16 lies in the 
axial plane of symmetry of the skin 9, i.e., the plane including the 
longitudinal axis of the door which divides the skin into symmetrical 
halves. 
Arc 13 is covered by a V-shaped arcuate lining 17 having inclined faces 18 
and 19 which intersect to form a trough, the ridge of arc 13 nesting in 
the trough so formed. Face 18 extends from one side of arc 13 to cover 
substantially the entire inner face of projection 16, while face 19 
extends from the other side of arc 13 to cover only a minor part (less 
than half) of the inner face of skin 9. 
When the doors 5 are in stowed position, the inclined walls 18 come in line 
with the outer edge 20 of the fan duct of the engine 4. (cf. FIG. 3). On 
the other hand, since the inclined face 19 of the lining covers the inner 
concave face of the skin 9 only partially, there is an annular space 21 
between the edge 20 of the fan duct and the ridge 22 (corresponding to the 
arc 13) of the lining 17, which ridge corresponds to the joining of 
inclined faces 18 and 19. 
It will be noted that the aerodynamic loads applied to the doors 5, when 
they are unfolded, are transmitted to the pivot fittings 14 and 15. These 
may be constituted by castings made of a special stainless steel. 
The structure of a door 5 comprising a skin 9 and peripheral stiffeners 10 
to 13 gives this door an excellent rigidity in flexion and in torsion. As 
will be seen hereinbelow, in addition to its structural function of 
rigidification, the frame 10 to 13 allows the reversed jet of the gases 
leaving the engine 4 to be best deflected, due to the optimum choice of 
the height of said frame with respect to the inner concave face of the 
skin 9. 
FIG. 5 shows a known thrust reverser provided with doors 23, also hinged 
about a pivot 6, but of which the structure is a so-called "double-skin" 
structure, since they are constituted by an outer truncated skin 24 and an 
inner ridged skin, composed of a quasi-cylindrical part 25 and a conical 
part 26 connected along a circular ridge 27. In stowed position (FIG. 5), 
the circular ridge 27 is adjacent the edge 20 of the fan and the part 25 
comes in line therewith. There is no annular space 21 in this case. 
The major advantage of the thrust reverser according to the invention over 
the known thrust reverser shown in FIG. 5 is clearly seen on comparing 
FIGS. 4 and 6, in which the two reversers have been shown on the same 
scale, in stowed position. 
The critical dimension L for the reversed flow in the reverser according to 
the invention is thus noted to be substantially larger, for equal 
dimensions of doors 5 and 23, than the corresponding critical dimension L' 
in the known reverser. For critical dimensions L and L' of the same order, 
i.e. for a similar action of the two reversers, doors 5 which are smaller 
than doors 23 may be used, due to the invention. 
This is very important. In fact, apart from the obvious weight saving, this 
reduction in the doors' length beings numerous advantages. A fixed hinge 
element for the doors of the reverser is known to extend the fairing 
downstream of the exhaust plane of the fan channel and such an extension 
is generally known to be accompanied by an increase in the external drag, 
especially in supersonic flight. Further, the thrust reverser according to 
the invention enables the influence on the drag to be reduced. 
Furthermore, the doors being smaller, the hinge 6 thereof is less remote 
from the edge 20 of the fan duct and its support arm or arms 28 can be 
shorter. This results in the hinge system of the doors being more rigid 
and less sensitive to vibrations. 
Moreover, the presence of the annular space 21 between the edge 20 and the 
ridge 22 improves the positioning of the doors. In particular, even when 
the axis of the fairing 8 does not coincide with the axis of the nozzle, 
it enables identical doors 5 to be adapted whilst respecting the 
continuity of the external lines. 
Finally, as a comparison between FIGS. 4 and 7 on the one hand and FIGS. 6 
and 8 on the other hand shows, which Figures schematically show the jets 
leaving the engine, the reverser according to the invention presents 
aerodynamic advantages. 
These FIGS. 4 and 7 show that in the reverser according to the invention, 
the stiffener arc 12 and the longitudinal beams 10 and 11, due to the 
projection that they form with respect to the inner face of the curved 
skin 9, enable the reversed flow to be canalized (avoiding side spillage) 
and to be controlled. By adjusting the height (or projection) h of the arc 
and the beams 10 and 11 with respect to said inner face of the skin 9, it 
is possible to perfect the control of the reversed flow. 
Experience has shown that, on condition that the exhaust section of the jet 
(delimited by the curved inclined faces 18) is slightly larger than the 
section of the nozzle at the edge 20, the presence of the annular space 21 
does not, in direct jet, cause any measurable loss of power of the engine 
4. This is due to the fact that, in operation, a "fluid wall" is 
established between the edge 20 and the ridge 22, the exact form of which 
adapts itself to the conditions of flight and functioning of the engine. 
A good geometric adaptation will thus determine, at low flight velocities 
(take-off and landing in particular), a depression in the annular space 
21, which will cause a small additional flow to be drawn along the front 
arc 12. This depression will progressively fill so that it will be weak or 
nil at cruising speed and that it will never be necessary to install a 
seal along the arc 12. 
However, it is important that the geometry be adapted to each particular 
case. If the faces 18 formed an exhaust pipe which is too small, too large 
or too divergent, noticeable losses of thrust would appear at certain 
speeds. 
Experience has shown that, to this end, the angle of the divergent duct had 
to be smaller than 6.degree..