An ejector nozzle comprising an axially translatable member on which is mounted an axisymmetric array of first flaps 36 and hinged seal plates 39 which serve to define a variable area convergent nozzle. The first flaps have cam followers 38 that co-operate with cams 35 to determine the attitude of the first flaps 36. A plurality of second flaps 40 and second seal plates 43 are mounted on the first flaps. The upstream end of the second flaps 40 are spaced from the downstream ends of the first flaps 36 to form an air inlet. An axisymmetric array of third flaps 50 surround the first and second flaps 36,40. The third flaps 50 are pivotally connected at their downstream ends to the downstream ends of the second flaps 40, and are connected at their upstream ends to fixed structure 32,45,47 by pivotal links 49. A fixed ring 46 carrying rollers 51 surrounds the second flaps 40 at a region intermediate their upstream and downstream ends. The rollers 51 provide a fulcrum about which the second flaps 40 rock. Axial movement of the member 28 causes the first second and third flaps 36,40,50 to take up different positions and open up an air inlet that allows ambient air to mix with the hot gases flowing through the nozzle.

This invention relates to nozzles for gas turbine aero-engines and is 
particularly concerned with variable geometry nozzles and the suppression 
of the infra red radiation emitted by the hot exhaust plume of such 
engines. 
Modern combat aircraft require the flexibility of being able to fly at 
subsonic or supersonic speeds and to perform a variety of roles. In some 
roles it is necessary to augment the basic thrust produced by the engine 
in the "dry" mode by burning additional fuel downstream of the engine's 
turbines, utilizing the unburnt oxygen in the exhaust gases to support 
combustion. This mode is known as reheat or afterburning. During reheat it 
is necessary to increase the area of the nozzle to accommodate the 
increased volume of gases so as not to impair the efficient functioning of 
the engine. In other roles such as supersonic cruise, it is desirable to 
vary the geometry of the exhaust nozzle of the engine from a convergent 
geometry for subsonic speed to a configuration having an increased area 
throat (compared to that required during the "dry" mode or at subsonic 
cruise) formed between a convergent and divergent part of the 
nozzle--often referred to as a con-di nozzle. 
There are times during the flight envelope of an aircraft when reheat is 
not required and when the prime requisite is to reduce the infra red 
emission of the exhaust plume and thereby reduce or avoid detection by 
heat seeking missiles directed towards the aircraft. These missiles 
usually detect the infra red radiation of the hot exhaust gas plume and 
once the plume is located, home in on the hot parts of the engine to 
destroy the aircraft. 
There is a need for a nozzle design that not only caters for dry and reheat 
modes of operation, but also enables one selectively to reduce the 
infrared emission of the engine. 
An object of the present invention is to provide a variable geometry nozzle 
which is capable of use both in the dry and reheat modes of operation and 
also capable of reducing the infra red emission of the hot exhaust gas 
plume. 
The invention as claimed enables one to vary the geometry of the nozzle to 
cope with dry and reheat modes of operation by moving the flaps and 
enables one to reduce the infra red emission by opening additional air 
inlets which admit ambient air to cool and shield the hot exhaust plume. 
The nozzle of the present invention may be installed on a fixed jet pipe or 
on a vectorable jet pipe. Furthermore, the nozzle of the present invention 
may be installed on the vectorable front nozzles of an engine such as the 
Rolls-Royce Limited Pegasus engine which discharge cold or reheated 
by-pass air.

Referring to FIG. 1 there is shown schematically a gas turbine aero engine 
10 of the by-pass type. The engine comprises in flow series, an axial flow 
low pressure compressor 11, an axial flow high pressure compressor 12, a 
combustion chamber 13, a high pressure turbine 14 which drives the H.P. 
compressor 12, a low pressure turbine 15 which drives the L.P. compressor 
11, and a jet pipe 16 terminating in a vectorable variable area nozzle 17. 
The L.P. compressor 11 supplies compressed air to the H.P. compressor 12 
and to a plenum chamber 18 which forms part of the by-pass duct 19 and 
which terminates in two vectorable nozzles 20. The nozzles 20 are mounted 
in bearings 25 for rotation through an angle of approximately 110.degree. 
about an axis 21. 
Additional combustion equipment 22 is provided in the plenum chamber 18 so 
that additional fuel can be burnt in the air stream ejected through the 
nozzles 20 to increase the thrust. To enable the engine to run efficiently 
the nozzles 17 and 20 are provided with variable-area, variable-geometry 
outlets. 
For convenience the invention will be more particularly described with 
reference to nozzle 17 but it is to be understood that the mechanism for 
varying the area and geometry may be similar for all the nozzles 17 and 
20, and may also be used with nozzles for fixed jet pipes. 
The nozzle 17 is of the type in which a scarfed rotatable duct 17(a) is 
mounted in bearings 23 on the downstream end of the jet pipe 16, and a 
second scarfed duct 17(b) is mounted in bearings 24 for rotation in the 
opposite direction to that of duct 17(a). The bearing 24 is, in turn, 
rotatable bodily on trunnions 26 which extend transverse to the axis of 
duct 17(b). This type of nozzle is described in more detail in co-pending 
U.S. Patent Application Ser. No. 376,388 entitled Vectorable Nozzles for 
Turbomachines naming Gary Frank Szuminski as the inventor. In operation, 
the bearing 24 is rotated about the axis of the trunnions 26 by means of a 
screw jack (shown schematically by the numeral 56) which pushes on the 
brackets that support the bearing 24 in the trunnions 26. As the bearing 
24 is swung about the axis of the trunnions 26 the ducts 17(a) and 17(b) 
are rotated in opposite directions by means of a motor 52 and sprockets 
53, chain drives 54 and flexible drive shaft 55 as explained in the 
above-mentioned U.S. patent application. 
The nozzle 17 has at its downstream end a duct 17(c) which is carried by 
the fixed race of the bearing. It is this duct 17(c) that is provided with 
the mechanism for varying the geometry and area of the outlet of the 
nozzle 17 in accordance with the present invention, as shown in FIGS. 2 
and 3. 
Referring to FIGS. 2 and 3, the mechanism for varying the geometry and area 
of the outlet nozzle comprises an annular member 28 which is translatable 
axially and on which is carried three sets of flaps as will be described 
below. The member 28 is mounted to slide axially inside the downstream end 
duct 17(c) and the member 28 comprises an annular hollow box structure. 
The member 28 slides inside the bore of the duct 17(c) and a heat shield 
liner 29 is provided to protect the duct 17(c) and the member 28 from the 
hot gases flowing through the nozzle when the reheat combustor 30 in the 
jet pipe is ignited. 
The member 28 is supported on axially extending tubes 31 which carry an 
annular cam-ring assembly 32. 
Located between the tubes 31 are lead screw 33 of a screwjack which engages 
a nut 34 (of the recirculating ball type) fixed to the member 28. Rotation 
of the lead screws 33 by a motor drive through gearboxes pushes and pulls 
the member 28 to and fro in the axial direction. 
The cam ring assembly 32 comprises two polygonal frameworks of tubes 34 
interconnected by which a plurality of cams 35 facing inwards (only one of 
which is shown). The cams 35 are equispaced around the axis of the duct 
17(c). 
A set of first primary flaps 36 is pivotally attached to the member 28. 
Each first primary flap 36 is pivotally attached at its upstream end to 
the downstream inner circumferential end of the member 28 and has a web 37 
projecting from its outer facing side. The web 37 carries a cam follower 
38, in the form of a roller, that engages one of the cams 35 to define and 
vary the attitude of the flaps 36 relative to member 28 as member 28 is 
moved in axial directions. 
The flaps 36 comprise a hollow structure with spaced walls which are made 
from a carbon-carbon material such as Pyrocarb (Registered US Trade Mark) 
material as manufactured by Hitco of USA. Pyrocarb materials comprise a 
carbon matrix in which is embedded a woven cloth of carbon fibres. The 
material is projected from oxidation either by overcoating it with a 
non-oxidising protective layer or by impregnating silicon into it and 
converting the silicon to silicon carbide. Adjacent flaps 36 are 
interconnected by means of pairs of sealing plates 39 located between 
adjacent flaps 36. The sealing plates 39 are connected to the side edges 
of the flaps 36 by means of axially extending hinges. Each pair of plates 
39 are also connected together by hinges 39(a) which extend axially. The 
hinged attachments of the plates 39 to the flaps 36 permit the flaps 36 to 
assume different diameters to vary the area of the nozzle formed by the 
flaps 36. 
A second flap 40 is pivotally attached at its upstream end to each flap 36. 
Each flap 40 is a hollow structure of spaced carbon-carbon walls similar 
to flaps 36, and each flap 40 is provided with a flange 41 projecting 
forwards of the upstream end of the flaps 40. The flanges 41 are pivotally 
connected to lugs 42 on the outside surface of flaps 36 at a position 
intermediate the upstream and downstream ends of the flaps 36. 
The second flaps 40 are spaced circumferentially and the gaps between them 
are closed-off by thin carbon-carbon seal plates 43. The upstream ends of 
the seal plates 43 are located on the inward-facing side of the flaps 40 
and are constrained from falling inwards by rollers 44 which are mounted 
on flanges that project through the gaps between flaps 40 to engage the 
outer surface of the flaps 40. The seal plates 43 allow the flaps 40 to 
assume different positions where they define a divergent part of the 
nozzle by sliding relative to the flaps 40. 
The cam ring assembly 32 also includes two fixed rings 45,46 located 
downstream of the cams 35. The fixed rings are connected back to the fixed 
structure of the cam ring assembly 32 by struts 47. The fixed ring 45 has 
spaced around its outer diameter a number of lugs 48 on each of which is 
mounted a pivotal link 49. 
A set of third flaps 50 made of a carbon fibre reinforced polyimide 
material are pivotally mounted at an upstream end on the links 49. Each of 
the flaps 50 is pivotally attached at its downstream end to the downstream 
end of one of the second flaps 40. The flaps 50 overlap each other to 
accommodate different positions of the flaps 50 and form a seal 
therebetween. 
The fixed ring 46 is located at a position intermediate the upstream and 
downstream ends of the flaps 40 and is provided with circumferentially 
spaced rollers 51 each of which is arranged with its axis of rotation 
tangential to the circumference of the ring 46. Each roller 51 engages the 
outside surface of one of the flaps 40 and allows the flaps to move in 
axial directions relative to the ring 46. 
In operation of the nozzle, with the member 28 moved rearwards to the fully 
rearwards position (shown in FIG. 2), the cams 35 and cam followers 38 
push the flaps 36 inwards to define a convergent throat. Simultaneously 
the flaps 40 are moved bodily rearwards and, because they are pivotally 
connected at their downstream ends to the flaps 50, they pull the flaps 50 
rearwards. This in turn compresses the links 49 and, because they are 
constrained by the ring 46, the outer ends of the links 49 push the 
upstream end of the flaps 50 outwards to open up an air intake. Ambient 
air flows into the intake and exits into the hot gas flowing through the 
nozzle through the gap between the downstream ends of the flaps 36 and 
sealing plates 39 and the upstream ends of the flaps 40 and seal plates 
43. 
Axial movement of the flaps 36,40 and 50 causes the flaps 40 to rock about 
the fulcrum provided by the rollers 51 to define the proper divergent exit 
area of the nozzle downstream of the throat defined by the flaps 36. 
The colder ambient air mixes with the hot turbine exhaust gases to cool the 
plume and reduce the infra red emissions thereof. 
Pulling the member 28 forwards to the position shown in FIG. 3 causes the 
cam follower 38 to follow the cam 35 and pulls the flaps 36 outwards to 
define a maximum area throat as would be required during the reheat mode. 
The length of flange 41 is chosen so that in this position of flap 36 the 
upstream edges of the flaps 40 and seal plates 43 seal against the 
downstream ends of flaps 36 and seal plates 39. Forward movement of the 
flaps 40 pulls the flaps 50 forwards and simultaneously closes off the air 
intake. 
Clearly, at intermediate positions between those shown in FIGS. 2 and 3 
various combinations of convergence and divergence with different throat 
areas can be obtained.