MULTIFUNCTIONAL AIRCRAFT WITH REDUCED VISIBILITY TO RADAR
Field of technology
The invention relates to aircraft industry, in particular to
tactical'aircrafts used to detect and defeat air, sea and land
targets.
, Background art
A multifunctional aircraft (Fomin A.V. Su-27. History of
Fighter, Moscow, RA Intervestnik, 1999, pp. 208-251) comprises
an airframe, a power plant, general aircraft equipment, a
display/control system, complex of weapons, active and passive
countermeasures, target sight equipment (radar sighting system,
optronic' sighting system), parameters monitoring and recording
system, inter-aircraft and control center communication system,
flight and navigation system, countermeasures system, a weapons
and passive countermeasures control. system, which provide
navigation, piloting in manual and automatic control modes,
integrated control of systems, inter-aircraft navigation and ingroup
exchange by tactical information, guidance from control
command centers, radar surveillance of airspace and land
surface,'airspace location, detection and support of land and
air targets, target designation to weapons, active radar
jamming, use of uncorrected weapons and aircraft weapons (ACW)
with passive heat, passive and active radar seekers for land,
air and sea targets, use of passive countermeasure means.
A disadvantage of the. known technical solution is that it
has a high value of radar cross-section (RCS) which defines the
characteristics of the aircraft detection by enemy radar means.
RCS of the known aircraft is about 10-15 sq. m (average value
for selected aspect).
Summary of the invention
The technical result to be achieved by the invention is to
reduce the amount of aircraft visibility to radar to an average
of about 0,l-1 sq. m.
Sais technical result is achieved by the fact that in a
multifunctional aircraft comprising an airframe, a power plant,
onboard equipment set, wherein air weapons are accommodated
inside the airframe; an air intake duct is S-shaped and has
radar-absorbing coatings applied on walls of the air intake
duct; a device is mounted in the air intake duct to divide the
geometrical section of the air intake duct in front of inlet
guide vanes into a number of separate cavities defined by
cylindrical or flat surfaces, and swept lips of the air intake
duct entrance form a parallelogram; the sweep of leading and
trailing edges of lifting surfaces, air intakes, and door flaps
is restricted to two or three directions; fuselage sidewalls in
the cross section and all-moving vertical empennage are inclined
from the vertical plane in the same direction; air intake and
exhaust devices are shielded; a compartment of flight refueling
probe is closed by a flap; furthermore, spaces between
individual structural and access elements of the airframe are
filled with conductive sealants; canopy glazing is metallized;
antenna radomes are made of frequency selective structures;
optical sensors are able to be turned in the idle state with a
badk side coated with a radar-absorbing coating facing
illuminating radars; antenna compartments are closed by
shielding diaphragms; antenna planes are deflected from the
vertical plane; at least part of the antennas are structures of
airframe units, and antenna feed system is based on radar
wavelength low reflective antennas.
Brief description of the drawings
The invention is illustrated by the drawings, where:
fig.1 shows a plan view of an aircraft having integral
aerodynamic layout;
fig.2 is a bottom view of an aircraft having integral
aerodynamic layout;
fig.3 is a front view of an aircraft having integral
aerodynamic layout;
fig.4 shows section A-A of fig.2;
fig.4 shows section B-B of fig.2.
Reference numerals in the drawings:
1 - Fuselage
2 - Wing panels
3 - Panels of all moving vertical empennage (AMVE)
4 - Panels of all moving horizontal empennage (AMHE)
5 - Cockpit canopy
6 - Horizontal lips of engine air intakes
7 - Fine-meshed screens closing air exhausts
8 - Lateral inclined lips of engine air intakes
9 - Power plant RCS reducing device
10 - Flaps of flight refueling probe compartment.
Description of embodiment
Complex of on-board aircraft equipment includes: general
aircraft equipment; display/control system; a complex of
weapons,' active and passive countermeasures; target sight
equipment (radar sighting system, optronic sighting system); a
system for monitoring and recording parameters; inter-aircraft
and control center communication system; flight and navigation
system; countermeasures system; a system to control weapons and
passive countermeasures, to provide navigation, piloting in
manual and automatic control modes, integrated control of
systems, inter-aircraft navigation and exchange by tactical
information in group; guidance from command control centers,
radar surveillance of airspace and land surface, airspace
location, detection and support of land and air targets, active
radar jamming, use of uncorrected weapons and aircraft weapons
with passive heat, passive and active radar seekers for land,
air and sea targets, passive countermeasure means.
Aircraft RCS is composed of RCSs of the following
constituent parts: airframe; power plant; optical and antenna
systems of on-board equipment; suspended and extendable in
flight equipment.
RCS magnitude of an airframe and a power plant is determined
by three factors:
- shape of theoretical contours and layout of the airframe,
including air intake and air duct;
- design of airframe units, technological and operational
joints of skins, doors, holes and joints between moving and
fixed pafts of the airframe;
- use of radar absorbing and shielding materials and
shape of theoretical contours and layout of the airframe
have enabled the reduction in the energy of reflected EM waves
in certain aspects owing to redistribution of backscattering
chart maximums to a minimum number of directions and to .least
dangerous sectors.
Strdctural measures
Positioning air weapons (AW) inside the airframe has enabled
thq reduction in overall RCS due to elimination of reflection of
electromagnetic waves of illuminating .radars from AW and their
launchers.
S-shaped intake duct ,in combination with radar-absorbing
coatings (RAC) provides for reduction of RCS in near axial
directions. In other sectors of forward hemisphere (FHS), RCS is
reduced 'due to shielding the engine inlet guide vanes (IGV)
whose elements basically reflect electromagnetic (EM) waves of
illuminating radars, which is a substantial portion (up to 60%)
of the RCS of the airframe/engine system in FHS. RAC applied on
the walls of the air intake (AI) duct reduces the magnitude of
electromagnetic signals reflected from the IGV and re-reflected
to the duct walls, thus the overall A1 RCS in FHS is reduced..
The device 9 in the air intake duct for reducing engine RCS
in the fbrward hemisphere can be mounted in a duct of any shape
upstream of IGV, but preferably it is mounted in "straight"
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ducts. The device 9 acts as a shield partially closing the IGV
in near axial directions against EM waves. In addition to
shielding, the device 9 divides the geometric section of the
intake duct upstream of the IGV into a series of separate
cavities defined by cylindrical (or concentric or . nonconcentric)
or flat surfaces, where flat surfaces can be
parallel* or intersecting. Each cavity has a smaller cross
sectional area than that of the air intake duct in that zone.
Such segmentation together with RAC coating of the segment walls
allows reducing the magnitude of EM signals reflected from the
IGV and re-reflected to the walls of cavities of the device 9,
thus the overall A1 RCS level in FHS reduces.
Restricting the sweep of leading and trailing edges of
lifting surfaces, air intake, door flaps to two or three
directions (sweep angles) different from the axial direction can
bring global maxima of backscattering pattern (BSP) to these
dir-ections. Such BSP causes a decrease in the overall RCS level
in FHS.
Inclination of sidewalls of the fuselage 1 in cross section,
inclination of vertical aerodynamic surfaces (vertical empennage
4, lateral lips 8 of air intake) to the same direction in crosssection
can reduce RCS in lateral hemisphere (LHS) by virtue of
multiple~reflections of EM wave hitting the inclined surface of
the airframe to the side different from the direction of
il1,uminating radar.
Shielding the air intake and exhaust devices by structural
elements and by fine-mesh screens can reduce or eliminate the
RCS component caused by airframe "irregularities" (such as hole,
slit, cavity) due to the fact that the linear cell size of the
mesh closing the irregularity is less than 1/4 the length of the
EM wave illuminating the aircraft. In such a situation the fine
mesh acts as EM wave shield, thereby reducing the component of
irregularities in RCS.
Closing the flight refueling probe compartment by a flap 10
eliminates the compartment and probe component in the total
aircraft RCS.
Use of all moving vertical empennage 4 reduces the total
vertical empennage area and, as a consequence, reduces the level
of signal reflected from vertical empennage, which in turn
reduces the magnitude of RCS in the LHS.
Use of conductive sealants provides for electrical
conductivity between individual structural and access elements
of the airframe, which in turn eliminates the component of
"irregularities" (such as slit, junction) in the aircraft RCS
due to the fact that in the absence of electrical irregularities
there is no scattering of surface electromagnetic waves.
Use-of RAC can significantly reduce RCS global maxima due to
the fact that the operation principle of RAC relies on partial
absorption of energy of EM wave hitting the material, hence
provides for reduction in the level of .reflected radar signal.
Making the canopy glazing metallized provides for EM
impermeability such that the glazing is substantially formed by
impermeable sloping wall, which reflects incident EM wave,away
from illuminating radar.
Basic measures for reducing the on-board equipment component
in RCS are the following.
Use of frequency selective structures in antenna radomes
that are radio transparent in the operating frequency range of
own antenna, and radio opaque in other frequency bands (of
illuminating radars). Thus, electromagnetic waves incident on
the radomes from illuminating radars are re-reflected (due to
the radome shape formed by surfaces inclined to the vertical
plane) away from illumination direction.
Rotation of optical part of optical sensors in the idle
state and application of RAC on the back side. Therefore, in
idle (passive) state of sensors (minimum RCS state) the sensor
faces the direction of illuminating radars with the side coated
by RAC, thus providing for partial absorption of incident EM
waves, thereby reducing RCS.
Use of shielding diaphragms in antenna compartments to
eliminate the traveling wave effect, when incident wave, having
been repeatedly reflected in closed compartment, is amplified
and radiated into outer space. Shielding diaphragm is mounted
around the antenna post to border th,e post periphery. RAC is
applied on the diaphragm wall facing the illuminating radar.
Upon illumination the shielding diaphragm prevents the EM wave
from penetrating the antenna compartment and absorbs some of the
incident wave energy thereby lowering RCS.
Deflection of the antenna plane from the vertical plane, and
hence deflection of the antennas normal from the horizontal
plane changes the direction of reflected EM waves away from the
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illuminating radar, thereby reducing RCS of the antennas.
Reduced total number of antennas and use of airframe units
as antennas (e.g. use of vertical empennage as a communications
antenna). Reducing the total number of antennas decreases the
overall RCS as each antenna adds a certain component to the RCS.
Using the existing airframe unit (vertical empennage) as an
antenna makes it possible to omit a separate antenna, which
naturally reduces the RCS compared with the embodiment
comprising a separate antenna.
Use of antenna-feeder system based on antennas that are low
reflective in radar wavelengths. Low reflective properties of
antennas are provided by the fact that they don't extend beyond
the aircraft external contours and do not bring a component to
the aircqaft RCS due to direct reflection of EM waves.
Complex implementation of the aforementioned measures
provides for maximum reduction in the visibility to radar with
minimal negative impact on aerodynamic, weight, process,
operational and other characteristics of the aircraft.
CLAIM
1. Multifunctional aircraft comprising an airframe, a power
plant, onboard equipment set, characterized in that air weapons
are accommodated inside the airframe; an air intake duct is Sshaped
and- has radar-absorbing coatings applied on walls of the
air' intake duct; a device is mounted in the air intake duct to
divide the geometrical section of the air intake duct in front
of inlet guide vanes into a number of separate cavities defined
by cylindrical or flat surfaces, and swept lips of the air
intake duct entrance form a parallelogram; the sweep of leading
and trailing edges of lifting surfaces, air intakes, door flaps
is restricted to two or three directions; fuselage sidewalls in
the cross section, and all-moving vertical 'empennage are
indlined from the vertical plane in the same direction; air
intake and exhaust devices are shielded; a flight refueling
probe compartment is closed by a flap; furthermore, spaces
between individual structural and access elements of the
airframe are filled with conductive sealants; canopy glazing is
metallized; antenna radomes are made of frequency selective
structures; optical sensors are able to be turned in the idle
state with a backside coated with a radar-absorbing coating
fac'ing illuminating radars; antenna compartments are closed by
shielding diaphragms; antenna planes are deflected from the
vertical plane, wherein at least part of the antennas are
structures of airframe units, and antenna feed system is based
on radar wavelength low reflective antennas.
Dated this the 25th day of July 20 14.
(H. SUBRAMANIAM)
Of SUBRAMANIAM & ASSOCIATES
Attorneys for the applicants ,
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