Thrust vector control for aircraft

The invention is directed to a thrust vector control for aircraft with one or more jet engines whose thrust nozzles have an adjustable size exist cross-section, each of the jet engines having a ring rudder axially spaced behind the engine and movable about at least one pivot axis extending substantially perpendicular to the engine's longitudinal axis. A substantially planar rudder plate is secured diagonally in the inside cross-section of the ring rudder for each plane defined by each pivot axis and the longitudinal axis of the engine. The rudder plate or plates each consist of a material which is stable at high temperatures without supplementary cooling and which is mechanically loadable, and the connection between the rudder plate or plates and the ring rudder each include a layer of elastic and thermo-insulating material.

BACKGROUND OF THE INVENTION 
The invention relates to a thrust vector control for aircraft with one or 
more jet engines with each of the jet engines having a hrust nozzle with 
an at least approximately round, size-adjustable exit cross-section. More 
specifically, the invention is directed to high-performance fighter planes 
having a ring rudder arranged in an axially spaced position rearwardly of 
each jet engine and movable about at least one pivot axis extending 
substantially perpendicular to the longitudinal axis of the engine. 
Based on currently applicable military principles, modern fighter or 
pursuit airplanes must meet requirements, in particular with regard to 
flight properties, which cannot be fulfilled with conventional technical 
solutions or only insufficiently so. These requirements include, among 
other things, the requirement of great maneuverability at extreme low 
flying speeds. Due to a low aproach velocity and unfavorable approach 
direction (i.e., a high angle of incidence), the effectiveness of control 
surfaces approached aerodynamically, i.e., by ambient air, is very low or 
no longer exists. The only meaningful alternative is, as a rule, a 
controlled deflection of the high-energy engine exhaust jet, of which VTOL 
aircraft are a particularly noteworthy example. But here, too, 
difficulties may arise, as for example, material problems due to the high 
exhaust temperature (to about 2000.about.K.), problems of strength and 
vibration due to the high flow velocities, negative effects on the engine 
throughput (m) due to backpressure effects, etc. 
To avoid temperature problems, it is customary to provide a ring rudder 
having a cross-section which is larger in diameter than the diameter of 
the assooiated jet engine. The ring rudder is spaced axially behind the 
engine nozzle to envelope the exhaust jet with a cooling jacket of ambient 
air sucked in by an ejector effect. The cooling jacket of ambient air 
causes the rudder structure to remain at a relatively low temperature 
(max. about 300.about.C.). The cross-sectional form of the ring rudder is 
adapted to the nozzle form and is usually round or rectangular. Such an 
arrangement is shown, for example, in FIGS. 4 to 6 of DE-AS No. 11 00 385. 
The jet deflection reponse of such ejector ring rudders involves socalled 
dead zones, i.e., the rudder must first be deflected out by a certain 
angle before the exhaust jet is also deflected. The magnitude of this dead 
angle varies according to flight conditions and it varies especially--in 
the case of supersonic engines with adjustable nozzles--with the momentary 
size of the adjustable nozzle cross-section. This rather unpredictable 
behavior makes sensitive control and regulation practically impossible, 
thus ruling out utilization in high-performance aircraft. Alternatively 
the ring rudder could be made so small that it always lies at or in the 
nozzle jet. However, such a small-sized rudder and, possibly, also parts 
of the suspension and actuation mechanism would be continuously exposed to 
the high exhaust temperatures, to the detriment of useful life and 
reliability. 
DE-OS No. 34 20 441 illustrates a jet control wherein a rudder cross with 
movable flaps (11 to 14) is arranged in an engine nozzle of fixed 
diameter. Upon failure or ineffectiveness of the aerodynamic rudders (4 to 
8) the rudder cross permits movement about the pitch, yaw and roll axes, 
thereby increasing flight safety. The flaps (11 to 14) are preferably 
arranged so that they do not lie in the hottest core (17) of the exhaust 
jet. Yet the flaps and parts of their suspension are exposed to relatively 
high temperatures. 
Tests have shown that while with plate or wing type rudders there is no 
occurrence of a dead angle effect in or behind the engine nozzle, only a 
relatively slight jet deflection (max. about 20.about.) is possible. This 
may suffice to increase flight safety, but does not provide a decisive 
improvement in the maneuverability of the aircraft. 
SUMMARY OF THE INVENTION 
It is, therefore, a primary object of the invention to provide a thrust 
vector control for aircraft having adjustable nozzles which is 
structurally straightforward, robust with a long work life, and which is 
especially effective in terms of aerodynamics. Generally, the invention 
comprises a ring rudder arranged in an axially spaced position rearwardly 
of each jet engine of the aircraft and movable about at least one pivot 
axis extending substantially perpendicular to the longitudinal axis of the 
jet engine and wherein a substantially planer rudder plate is secured 
within the cross section of the ring rudder, which rudder plate extends 
within a plane defined by the pivot axis and the longitudinal axis. The 
rudder plate is made from a material which is stable at high temperatures. 
The invention, therefore, combines a known ring rudder operating on the 
ejector principle with one or more rudder plates fixed therein which are 
oriented to coincide with orthogonal planes defined by the pivot axis and 
the longitudinal axis of the aircraft. 
Thus, the ring rudder, including the associated bearings and actuating 
mechanisms, remains cool, with a positive effect on work life and 
reliability. Exposure to hot temperatures is limited to the central part 
of the rudder plates and, accordingly, the resulting problems of service 
life can now be solved without supplementary cooling (coated CFC). 
As tests have shown, through the installation of the rudder plates of the 
invention, a largely linear jet deflection response without dead zones is 
achieved over the entire sphere of operation of the preceding adjustable 
nozzle. The contribution of the ring rudder in terms of aerodynamics is 
that much greater jet deflection angles can be achieved than in 
free-standing rudder plates. 
The mechanical connection between the rudder plates with the ring rudder is 
designed so that unfavorable heat currents and thermostresses are largely 
avoided. 
The invention is explained more specifically below with reference to an 
exemplary embodiment illustrated in the drawing. The figures show in 
simplified form:

DETAILED DESCRIPTION 
Referring now to the drawings and initially to FIG. 1, a thrust vector 
control 1 according to the invention is arranged on a single-jet pursuit 
or fighter plane in "duck" construction. The principles of the thrust 
vector control of the invention are suitable for implementation in 
multi-jet "duck" airplanes (e.g., EFA) and for single and multi-jet 
airplanes with a conventional aerodynamic layout (airfoil wing and 
separate tail elevator unit, delta wing without separate elevator unit). 
Also unmanned, jet-propelled missiles which must be especially 
maneuverable and quick to react (e.g., for flight extremely close to the 
ground) could be equipped with the thrust vector control 1. 
The aircraft 2 shown in FIG. 1 comprises aerodynamic rudder surfaces 8, 9, 
10 customary for such an airplane type. The rudder surfaces 8, 9, 10 may 
consist of several, separately operable partial surfaces (not shown). The 
representation of additional flap systems (e.g., at the front edge of the 
wing) has been dispensed with, for simplification of description. 
For adaption to different modes of operation (with and without reheater, 
Reheat/Dry) and speed ranges, the engine is provided with a thrust nozzle 
3 of adjustable diameter. A ring rudder 4 is arranged coaxially with and 
axially spaced from the thrust nozzle 3. The ring rudder 4 is movable 
about two orthogonal axes Y-Y and Z-Z and has a fixed diameter which is 
larger than the largest adjustable diameter of the thrust nozzle 3 to 
obtain an ejector effect for cooling. For greater clarity, the cardan 
suspension of the ring rudder 4 is not shown. It is meaningful, however, 
to attach the suspension to the airframe of the aircraft 2, in order to 
avoid static and dynamic supplementary loads on the engine and to 
facilitate retrofitting on existing airplane types (no engine alterations 
necessary). The pivot axes Y-Y, Z-Z define, together with the engine's 
longitudinal axis X, two orthogonal planes, in which, pursuant to the 
invention, two rudder plates 5 and 6 are arranged, respectively. The pivot 
axes and hence the rudder plates 5, 6 are parallel to the pitch and yaw 
axes, respectively, of the aircraft 2. It may suffice to provide a single 
pivot axis and hence a single rudder plate for the ring rudder 4. Such a 
single pivot axis may be parallel to either the pitch or yaw axis, or it 
may be in an oblique angle thereto (e.g. in the X-Z plane). 
FIG. 2 illustrates, in cross section, the critical point of the thrust 
vector control 1. This is the point of connection of the rudder plates 5 
or 6 with the ring rudder 4. Because of the extremely different thermal 
stress (ring rudder max. temperature is about 300.about.C., rudder plate 
max. temperature is about 1700.about.C.), it is advisable to make the 
structural parts 4, and 5 and 6 of different materials. Steel, titanium, 
or carbon fiber-reinforced plastic have been found to be suitable for the 
ring rudder 4. As a practical matter, ceramically coated, carbon 
fiber-reinforced carbon is the only material which is, at present, 
feasible for use in the rudder plates 5, 6 without the need for 
supplementary cooling. As a result of the great temperature difference and 
possibly greatly different coefficients of heat expansion (in particular 
for steel/CFC), rather great relative geometric displacements may occur at 
the points of connection. To avoid unduly high tensions in the material, 
the ring rudder 4 is formed so that it encloses the ends of the rudder 
plates 5, 6 in a box-like structure spaced from the rudder plates 5, 6 by 
a predetermined distance. Force transmission between the rudder plates 5, 
6 and the ring rudder 4 is by a rubber-elastic and thermo-insulating 
intermediate layer 7 arranged within the box-like structure between the 
plate 5, 6 and the ring rudder 4. The layer comprises a material such as 
silicone rubber, in which, for better heat removal and with a view to 
higher strength, other components such as fibers of any kind, metal 
particles, carbon particles, etc. may be embedded. As it is expected that 
the rudder plates 5, 6 would have a shorter life than the ring rudder 4, 
it is meaningful to design the former so that they are easy to replace. 
This is easy to achieve in that the box-like concavities of the ring 
rudder 4 are made removable, with the provision, for reasons of strength, 
that the ring rudder 4 should be axially longer than the rudder plates 5, 
6, so that it still forms a closed ring in the region of its front and 
rear edges. 
FIG. 3 clearly shows the improvements which are achieved with the thrust 
vector control according to the invention as compared with prior art 
designs. In the diagram, the qualitative response of the jet deflection 
angle alpha.sub.eff as a function of the angular deflection alpha.sub.geo 
of the rudder is shown. Curve A applies to the invention, that is, for a 
ring rudder with integrated rudder plates 5, 6, curve B illustrates a ring 
rudder without rudder plates, and curve C applies to a free-standing 
rudder plate. It becomes clear that with solution A at a give angular 
deflection alpha.sub.geo the greatest jet deflection alpha.sub.eff is 
obtainable, i.e., A has by far the best efficiency. The slope of each of 
curves A and C is largely linear; this is important for smooth control and 
regulation of the arrangement. Curve B has a "dead zone" or "dead angle", 
i.e., the rudder must first be pivoted by a certain angle before jet 
deflection takes place. This "dead angle" changes in particular as a 
function of the respective thrust nozzle diameter that has been set. Such 
nonlinear processes, however, make it practically impossible to perform as 
a sensitive control. 
Hence, with a comparable linear characteristic as a free-standing rudder 
flap (curve C), the solution according to the invention has a clearly 
higher efficiency (alpha.sub.eff).