Sliding throat gas turbine engine nozzle

Exit area control panels 18 are supported for movement at an angle with respect to the nozzle axis 12. A varying exit area is formed as actuator 26 axially positions the panels 18. In each exit area control panel 18, there is slidably supported a throat area control panel 28, driven by actuator 32. A sliding throat is achieved as the two panels 18,28 are moved in each quadrant. Yaw and pitch vectoring is accomplished with selective positioning of the two panels.

TECHNICAL FIELD 
The invention relates to convergent/divergent nozzles for aircraft gas 
turbine engines, and in particular to an arrangement for controlling the 
shape and size of the nozzle. 
BACKGROUND OF THE INVENTION 
Maximum thrust and efficiency of a gas turbine engine is achieved when the 
exhaust passes through a discharge nozzle which controls expansion, and 
maximizes the discharge velocity. When an aircraft operates at both 
subsonic and supersonic speeds the exhaust nozzle pressure ratio varies 
over a substantial range. 
Under subsonic flight conditions the pressure ratio is relatively small and 
a nozzle having a substantially convergent shape is desirable. At 
supersonic flight conditions when the nozzle pressure ratio is high the 
appropriate geometry is achieved by a nozzle having a convergent portion 
followed by a divergent portion. This is referred to as a 
convergent/divergent nozzle. 
Many designs have been made which provide the variable geometry which will 
effect proper operation at both subsonic and supersonic speeds. For the 
subsonic condition where only the convergent nozzle is desired there is 
only a nominal divergence, this being selected to assure that the throat 
area remains upstream of the divergent flaps. At supersonic speeds, means 
are supplied to effect the appropriate divergent flowpath downstream of 
the throat. Many of these designs require additional structure and weight 
to achieve the actuation of the divergent flaps. It is apparent that for 
an aircraft engine light weight and simplicity are desirable features. It 
further is useful to have a structure which may be easily sealed against 
leakage. 
In modern military aircraft additional maneuverability is desirable. This 
may be achieved by using pitch and yaw vectoring which requires 
discharging the exhaust gas selectively with a velocity component other 
than straight back. Again simplicity and lightweight is desirable in 
achieving this vectoring. It is also desirable that the structure used 
have a minimum impact on the external configuration of the nozzle and 
aircraft. 
SUMMARY OF THE INVENTION 
In the preferred embodiment the engine achieves throat area and discharge 
area control as well as pitch and yaw vectoring. This is all accomplished 
by the simple mechanism of using four exit area control panels which slide 
substantially axially, but at an angle with respect to the axis so that 
the area is reduced on aft movement of the panels. Each of the panels 
carries within it a throat area control panel, which moves with respect to 
the exit area control panel to set the relative location of the throat 
with respect to the exit area control panels. 
Rather than skewing the walls of the divergent nozzle to obtain pitch 
control, the nozzle is manipulated to obtain a throat area plane 
perpendicular to the desired flow direction and at an angle with the 
vertical. This being the sonic restriction of the nozzle, the flow is 
established perpendicular to this plane thereby achieving pitch control. 
The throat area plane is further modified by having a swept throat. Here 
the plane established by the throat restriction is swept to an angle 
toward the side of the aircraft and away from perpendicular to the axial 
flow through the nozzle. This provides a discharge having a thrust in a 
horizontal direction. Manipulation of the two sides of the nozzle to 
obtain differential flow, and thus a differential thrust achieves yaw 
operation. 
Limited portions of the preferred embodiment could be used to obtain a 
controllable convergent/divergent nozzle without pitch or yaw control, or 
a nozzle having only pitch or yaw control. 
The gas turbine engine has a static structure with an opening for an axial 
flow of gas therethrough. At least one, and preferably four, area control 
panel extends into the flowpath and is slidingly supported from the static 
structure. It is driven for axial movement at an angle with the axis. 
A throat area control panel is slidably supported in each exit area control 
panel, The throat area control panel extends into the flowpath and is 
located on the gas side of the exit area control panel, This throat area 
control panel is driven along a flowpath relative to the throat area 
control panel into the flowpath preferably along a slightly arcuate path.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 the static structure 10 has an axis 12 and an opening 
for the flow of exhaust gas 14 through the nozzle 16. 
Four exit area control panels 18 are each supported on two bearings, 20 and 
22. These bearings are supported on the static structure 10 and fit within 
slots 24 on the panels. These slots are positioned for axial movement of 
the panels at an angle with respect to the axis 12. Accordingly when the 
exit drive means in the form of actuator 26 drives the panels with respect 
to the static structure they move into or out of the flowpath, thereby 
effecting a sliding action with axial relocation of the throat of the 
nozzle. 
A throat area control panel 28 is slidably supported in slot 30 of each 
exit area control panel. A throat drive means in the form of actuator 32 
drives the panel for movement into or out of the gas stream with respect 
to the exit area control panel 18. The slot 30 is arcuate in shape to 
maintain the opening 34 between the throat area control panel and the exit 
area control panel at a uniform minimum distance. 
FIG. 2 is a sectional end view through FIG. 1 showing the four exit area 
control panels 18 and four throat area control panels 28. It can be seen 
that the flow area 34 is of a diamond shape with a width to height ratio 
of about 3 to 1. The opening shown in FIG. 1 is the opening towards the 
center of the nozzle, while the panels are touching at the wall. This is 
accomplished by establishing the structure such that each of the panels 
has a gas side surface extending transverse to the flowpath at an angle 
with respect to a horizontal line 36 forming the top and bottom sides of 
the diamond. The diamond shape more conveniently fits within an air frame 
design than other shapes. It should be noted that as the panels are 
withdrawn in the forward direction the gas sides 38 of the panels move 
apart and a truncated diamond opening is obtained with flat sides formed 
by the walls 40 of the static structure 10. 
FIG. 3 shows an exploded isometric view of one throat area control panel 
and one exit area control panel. The throat area control panel 28 has a 
break point line 42 which is shaped to form a flow restricting throat at 
an angle other than perpendicular with the axis 12. Flow passing through 
this throat will therefore be skewed from the axial direction to a 
direction perpendicular to the throat plane. The sharp demarkation of line 
42 is illustrated here primarily for discussion purposes. It is not 
essential that there be such a sharp demarkation, although this would 
facilitate stabilizing the throat location. 
FIGS. 4 and 5 are side and top sections respectively of the nozzle at 
maximum afterburning condition without vectoring. The exit area control 
panel 18 is moved forward at or near the limit of it's forward movement. 
The throat area control panels 28 are still located aft with respect to 
the exit area control panel. Opening 44 against the wall 40 of the nozzle 
can be seen since this represents the truncated portion of the diamond 
occurring with the nozzle open to this condition. 
The particular location of the control panels is selected as showing a 
typical unvectored, high expansion ratio setting for the nozzle. The 
angular orientation of line 42 can better be seen in these two views than 
in the isometric view. 
FIGS. 6, 7 and 8 illustrate side sectional, top sectional and end views of 
the nozzle at intermediate power. The exit area control panels 18 are 
moved aft near the limit of their travel while throat area control panels 
28 are moved forward toward intermediate position within the exit area 
control panels. At this minimum flow condition the opposing faces 38 of 
the panels are touching at the outboard location. The particular location 
of the panels under this condition is for an unvectored low expansion 
ratio setting. 
FIG. 9 is a sectional side view showing the vector down position at the 
afterburning or maximum flow area position. The two upper exit area 
control panels 46 are moved to a more aft position than the two lower exit 
area control panels 48. Furthermore within the upper panels the two upper 
throat area control panels 28,50 are moved aft slightly less than the two 
lower throat area control panels 28,52. This sets the lines 42 at 
different axial positions resulting in the throat plane 54 being at an 
angled down position with respect to the axis 12. Since the sonic flow 
must pass through this plane at a direction perpendicular to the plane, 
the gases are ejected along a line 56 with the downward component to 
achieve pitch control. 
FIGS. 10 and 11 are a top sectional view and an end view respectively of 
the yaw position at intermediate power. Exit area control panels 18 are 
moved near the full aft position as they were in FIG. 6, 7 and 8. The 
throat area control panels 28 are however located differently on the two 
sides of the nozzle. Viewed in the direction of the gas flow, panel 28 on 
the lefthand side, now designated as panel 60 is moved full aft while the 
righthand panel 28 now designated as panel 62 is moved more toward the 
forward position. 
The flow nozzle area 34 is now skewed with a lesser area 64 on the lefthand 
side compared to the larger area 68 on the righthand side. Because of the 
swept flow established by lines 42 the flow 64 from the left side of the 
nozzle has a leftward component while the flow 66 from the righthand side 
of the nozzle has a rightward component. With the different flow areas 
there are different flow quantities. This results in the flow 66 
dominating, providing a rightward component to effect yaw control of the 
aircraft. Aerodynamic model testing has shown this method of yaw vectoring 
to be effective to thirteen degrees. 
Even during vectoring maneuvers, the external nozzle surfaces remain in a 
constant position. This would presumably be selected at the minimum loss 
boatail angle. Variable convergent/divergent control as well as vectoring 
thrust are accomplished without interfering with the optimum design of the 
aircraft in the nozzle area. 
Seals are always required between the moving parts of the nozzle and the 
surrounding static structure. Since all movement in this nozzle is 
substantially linear between two components, all internal seal surfaces 
have a constant clearance. They also have sealing surfaces at a constant 
angle during all modes of operation. Simple low leakage rate straight line 
seals can be used, reducing the complexity and increasing the efficiency 
of the overall system. 
The internal surface area is at a minimum during the maximum temperature 
afterburning operation, since the panels are fully withdrawn at this time. 
The external nozzle surface approaches the simplicity of a fixed shroud 
nozzle with only four suitably angled seal lines which are constant during 
all modes of operation. The overall complexity of external fairings is 
reduced because the number of fairings is minimized, as well as the 
hardware required to move the fairings. This also leaves the overall 
impression of desirable smoothness on the exterior of the airplane.