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Eastern-European Journal of Enterprise Technologies ISSN 1729-3774 3/1 ( 129 ) 2024
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ENGINEERING TECHNOLOGICAL SYSTEMS
DETERMINING
INFRARED RADIATION
INTENSITY
CHARACTERISTICS
FOR THE EXHAUST
MANIFOLD OF GAS
TURBINE ENGINE
ТВ3-117 IN МІ-8МSB-B
HELICOPTER
Mykhailo Kinashchuk
Assistant*
Ihor Kinashchuk
Corresponding author
PhD*
E-mail: kinaschuk@gmail.com
*Department of Aviation Engines
National Aviation University
Liubomyra Huzara ave., 1, Kyiv, Ukraine, 03058
The object of this study is the screen-exhaust device
in the TV3-117 engine of the Mi-8MSB-B helicopter.
To reduce visibility in the thermal range, a system of
mixing hot engine exhaust gases with ambient air is used;
this technique makes it possible to reduce the infrared
radiation of engines. For this purpose, a new sample of
screen-exhaust device was designed for testing.
A thermal imaging survey of the helicopter was con-
ducted. Three variants of thermal images were acquired:
a helicopter without installation of a thermal visibili-
ty reduction system, a helicopter with standard exhaust
shields installed, and a helicopter with newly developed
shield exhaust devices installed. Based on the obtained
experimental results, the characteristics of the intensi-
ty of infrared radiation were determined for three va-
riants of research in the range of thermal waves of 3–5 μm.
The study uses a comprehensive approach to solving the
tasks, which includes a statistical analysis of known and
promising ways to protect a helicopter from guided mis-
siles with infrared homing heads based on reduced radi-
ation forces and a theoretical method for calculating flow
and temperature fields. The advantages of placing the
section of the exhaust channel of the designed screen-ex-
haust device in the horizontal plane for complete shield-
ing of infrared radiation in the lower hemisphere have
been experimentally proven. The benefits of directing the
flow of exhaust gases from the screen-exhaust device into
the space above the helicopter propeller and dividing this
flow into four separate flows were shown. The results of
experimental research could be used to design new or
improve existing screen-exhaust devices by the develo-
pers of military aviation
Keywords: gas turbine engine, screen-exhaust device,
thermal visibility, intensity of infrared radiation
UDC 629.735.03(02)
DOI: 10.15587/1729-4061.2024.303472
How to C ite: Kinashchuk, M., Kinashchuk, I. (2024). Deter mining infrared radiation intensity characteristics for the exhaust
manifold of gas turbin e engine ТВ3-117 in М І-8МSB-B helicopter. Easte rn-European Journal of Enterprise Tech nologies,
3 (1 (129)), 6–13. https://doi .org/10.15587/1729-4061.2 024.303472
Received date 02.02.2024
Accepted date 29.04.2024
Published date 16.05.2024
1. Introduction
The development of aviation science and technology, the
construction of complex multi-mode aerial vehicles (AV) re-
quires intensive scientific research into the development and
construction of both gas turbine engines (GTE) and their
individual elements. Increasing requirements for the efficien-
cy of power plants and ensuring a small external resistance
during their integration with the airframe led to the need
for detailed studies of the output device as one of the most
important elements of GTE.
The characteristics of output devices significantly affect
GTE operation, the level of thrust, predetermine the thermal
visibility and dependence of an aerial vehicle on a possibility
being hit by missiles with infrared homing heads. Output
devices, as one of the main elements of GTE, perform the
following functions:
– provision of noise absorption;
– removal of exhaust gases under the mode of maximum
efficiency of their energy use;
– lowering the temperature of exhaust gases;
– discharge of outgoing gases in the desired direction
with minimal losses;
– reducing the concentration of harmful emissions into
the atmosphere.
Military helicopters perform many different tasks, and
the scope of their use is constantly expanding. The history
of the development of military equipment shows that any
means of armed struggle (including a helicopter) is charac-
terized by three generalized properties: combat power, mo-
bility, and survivability.
The survivability of a helicopter is defined as the ability
to perform the assigned task after a single exposure to the
means of destruction. The work of specialists is often related
to the improvement of the following four elements of the
system [1, 2], which affect survivability:
1. Conspicuity – inability to prevent visual, acoustic, or
radar detection.
2. Perception – inability to prevent or evade means of
damage.
Engineering technological systems: Reference for Chief Designer at an industrial enterprise
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3. Vulnerability – inability to withstand damage.
4. Recoverability – associated with taking into account
the long-term impact of various factors after exposure, dam-
age control, fire safety, restoration of functional properties,
or in extreme cases, emergency abandonment of the aircraft.
Accordingly, a high level of survivability is ensured by the
use of any tactical techniques, procedures, and methods, as well
as specialized equipment or its possible combination, which
makes it possible to increase the probability of aerial vehicle
survival when operating under conditions of enemy resistance.
Portable anti-aerial vehicle missile systems (MANPADs)
have become one of the most effective and widespread means
of combating aircraft, helicopters, and other aerial objects
during hostilities. However, their widespread use for terrorist
purposes has greatly aggravated the problem of the safety
of civil aircraft and helicopter flights, making it one of the
most acute and relevant under current conditions. Therefore,
a new and promising area of ensuring the safety of air trans-
port is the design of aerial vehicle protection systems against
possible damage by missiles with infrared homing heads.
Scientific research into this area is important. Conduct-
ing theoretical and experimental studies of subsonic gas
ejectors of various schemes and with various active gas flow
parameters is an urgent scientific task. Solving this problem
will make it possible to increase the effectiveness of the use of
existing and promising aviation equipment when performing
combat tasks.
2. Literature review and problem statement
In modern warfare, air superiority is required to dominate
air combat. Portable shoulder-based air defense systems, other
surface-to-air missiles with infrared (IR) guidance, and air-to-
air missiles pose a deadly threat to helicopter survivability [3].
Heat-seeking missiles with infrared detection systems use tech-
niques to acquire and intercept airborne targets by passively
detecting the target’s IR radiation. The growing importance
of infrared signatures and the constant increase in sensitivity
of missile detectors in the form of multispectral and multicolor
thermal imaging systems have increased the ability to detect
infrared guided missiles. These factors indicate the need for
detailed research into characteristics of infrared radiation in
order to prevent the destruction of modernized and new types
of missile weapons with infrared target detection systems.
Summarizing the experience of armed conflicts that have
occurred in the world in recent years convincingly shows
that the greatest losses of the fleet of aerial vehicle and he-
licopters were caused by the use of guided missiles. These
missiles belong to the «air-to-air» and «ground-to-air» clas-
ses, equipped with homing heads [4]. In this regard, the task
of protecting aerial vehicle from damage by guided missiles
is one of the most important for aviation. The theoretical
aspects of detecting (selecting) an object from the surround-
ing background in the IR range are sufficiently studied. But
there is a need for further studies of IR radiation covering the
ranges of 1–3 μm, 3–5 μm, and 8–14 μm.
Paper [5] presents a model of the screen-exhaust de-
vice (SED), which is integrated into the tail part of the
helicopter; mathematical modeling of the thermal radiation
of the helicopter using SED was performed. It is shown how
the exhaust gases heat the tail part of the helicopter and how
this process increases the thermal visibility of the helicopter.
However, such a solution cannot be implemented for heli-
copters of the Mi-8 family due to the design features of this
aerial vehicle. Such a feature for Mi-8 and Mi-24 helicopters
requires further research.
Thus, IR-guided missiles have become one of the most
powerful threats to the survivability of combat helicopters.
In paper [6], only a numerical study and analysis of the
thermal radiation of the helicopter were carried out. The
1.9–2.9 μm and 3–5 μm ranges are shown to be mainly used
to detect hot engine parts, while the rear fuselage emits more
heat in the 8–12 μm range. The analysis of the radiation
ranges of 2.7 μm, 4.3 μm, 5.5 μm, 6.5 and 15 μm due to the
emission of CO2, CO, and H2O present in exhaust gases is
performed in more detail in [7]. Numerical studies carried
out by the authors have scientific value but do not provide an
opportunity to obtain reference data that could be used for
design calculations of SED for a specific type of helicopter.
With an increase in the speed of direct flight, the ejec-
tion coefficient increases and the average temperature of the
initial mixed flow decreases, which leads to a decrease in the
intensity of infrared radiation. exhaust flow in the range of
3–5 μm [8]. However, the effect of the forward flight speed
on the total radiation intensity of the helicopter from SED
is not monotonic due to the complex interaction between the
forward flow and the washover flow. It is necessary to carry
out numerical studies with verification of experimental stu-
dies to determine the functional dependence.
Taking into account the effect of solar radiation on the
total thermal radiation of the helicopter is reported in [9].
This aspect is very important because the side of the helicop-
ter, the elements of which are heated by solar radiation, has
a greater thermal visibility. The study proved that the time of
year has an effect on the thermal visibility of the helicopter,
on the days of the autumn and spring equinoxes and the sum-
mer solstice, the thermal radiation of the helicopter increases
by about 7 %, 11 %, and 21 %, respectively. The results of the
research were determined by numerical modeling and require
experimental confirmation.
Screen-exhaust devices are used to minimize the level of
IR radiation of the helicopter engine, thereby increasing its
thermal invisibility. The results of numerical modeling are giv-
en in [10]. It is shown that masking the hot parts of the engine
and reducing the temperature of the visible part of the exhaust
pipe by cooling it with air is effective in reducing the thermal
visibility of the helicopter. The reduction of the peak tempera-
ture of exhaust gases occurs by increasing the mixing of exhaust
gases with ambient air. A comparative analysis of the results ob-
tained by the authors with the characteristics of screen-exhaust
devices existing in operation was not carried out.
Sources of the infrared signature of a helicopter in flight
are given in work [11]; schematic structural solutions of SED
used by leading manufacturers of combat helicopters are
described. The effectiveness of the use of SED for shielding
the heated surfaces of the output devices of the gas tur-
bine has been proven. The results of numerical modeling of
gas-dynamic flow and thermal radiation when using SED are
represented in a generalized form, which makes it impossible
to compare them with known SED designs.
The temperature distribution on the fuselage is regulated
by heat transfer between the skin and internal hot elements
and between the skin and the external environment. The
temperature distribution is affected by many factors, namely:
disturbances caused by the rotation of the helicopter blades,
radiation from the internal elements of the engines, convec-
tion heat exchange between the fuselage and the atmosphere,
Eastern-European Journal of Enterprise Technologies ISSN 1729-3774 3/1 ( 129 ) 2024
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solar irradiation of the fuselage. Of particular value are the
results of work [12], in which simulations of the zones of im-
pact of aerial vehicle by thermal missiles are given.
The mixing of the exhaust gases reduces the velocity of
the flow to the extent that the velocity of the gases becomes
too low to escape far from the fuselage of the helicopter. This
leads to the formation of hot zones on the rear part of the
fuselage [13], and accordingly to an increase in thermal visi-
bility. Research points to the obviousness of the problem but
does not provide recommendations for its solution. The solu-
tion to the above problem should also be taken into account
when designing new structures of SED.
In order to ensure complete thermal invisibility of the
infrared system of the release of helicopter exhaust gases,
in [14], a project of a model for reducing thermal visibility,
a model of protection against infrared radiation based on
a secondary ejector is given. But the structure of the above
design will not be able to protect the helicopter from being
hit by air-to-air missiles when attacking the helicopter from
higher altitudes than the helicopter’s flight.
Taking into account the experience of previous studies
and the current state of thermal visibility of helicopters, there
is a task of further improvement of the thermal visibility re-
duction system. Weapons of defeat by missiles with infrared
homing heads are constantly being modernized and improved.
As before, the main technique for protecting helicopters from
such weapons is the development of means of reducing the
level of infrared radiation and reducing the temperature of
the outgoing gases. It is necessary to study the mechanisms of
the IR signature emitted by a helicopter under different flight
modes. This should be taken into account for different types
of helicopter designs, and should also take into account their
modernization, which may make certain changes to improve
the means of protection against thermal visibility.
3. The aim and objectives of the study
The purpose of our work is to experimentally determine
the characteristics of the IR radiation of the exhaust mani-
fold of the TV3-117 gas turbine engine in the Mi-8 helicopter
using various SED sets. This will make it possible to inves-
tigate the thermal visibility of the helicopter in the specified
ranges using the developed system of mixing hot engine ex-
haust gases with ambient air with the newly designed SED.
To achieve the goal, the following tasks must be solved:
– to design a new full-scale sample of SED;
– to investigate the theoretical method of calculating
the flow fields and temperature of subsonic gas ejectors of
screen-exhaust devices in GTE, to analyze the geometric and
gas-dynamic parameters of the ejector mixing chambers;
– to conduct full-scale experimental studies of the de-
signed screen-exhaust device.
4. The study materials and methods
4. 1. The object and hypothesis of the study
The object of our study is the screen-exhaust device in
the TV3-117 engine of the Mi-8MSB-B helicopter.
The subject of research is the internal aerodynamics of
screen-exhaust devices of gas turbine engines, which deter-
mines their efficiency and cooling efficiency of the exhaust
jet and hood housing.
The hypothesis of this study was to prove that the SED,
fabricated according to the new technology, could lead to
a decrease in the thermal visibility of the helicopter. The new
structural solutions used in the newly designed screen-ex-
haust device would outperform standard old SED samples in
terms of their parameters.
Assumptions were adopted that additional shielding of
SED with ejection-cooled blades could reduce the thermal
radiation of the emission zone of the helicopter’s exhaust
gases mixed with air.
The use of spot welding of metal structural elements with-
out riveting and the use of cheaper heat-resistant structural
elements can be considered a simplification of SED design.
4. 2. Experimental model
The exhaust manifold is used on helicopter GTEs to divert
exhaust gases in the desired direction, as well as to increase the
efficiency of the engine, which is achieved by a certain diffu-
sivity of the exhaust channel. Such a structural solution allows
part of the kinetic energy of the exhaust gases to be converted
into compression work and increase the pressure drop on the
free turbine, and accordingly, the power of the gas turbine.
Under a number of engine operating modes, the gas flow at
the entrance to the exhaust channel may have a significant
twist. Therefore, the quality of the exhaust manifold, its charac-
teristics, affect the characteristics of the entire engine.
The above-mentioned features of the exhaust manifold were
taken into account when designing a new screen-exhaust device.
Fig. 1 shows a new screen-exhaust device for left and
right TV3-117 engines of all types installed on Mi-8MSB-B,
Mi-8MT, Mi-14, Mi-24 helicopters. The designs of SED for
the left and right engines are completely identical, differing
only in mirror images of each other.
The principle of operation of this screen-exhaust device
is described in [15]. For conducting experimental studies, the
SED set was installed on the Mi-8MSB-B helicopter, Fig. 2.
Fig. 1. Screen-exhaust device of a helicopter
Fig. 2. Screen-exhaust device installed on the Mi-8 helicopter
for experimental tests
Engineering technological systems: Reference for Chief Designer at an industrial enterprise
9
At the stage of flight tests, we experimentally determined
the characteristics of IR radiation of the helicopter with
a SED kit to assess the degree of reduction in the strength of
IR radiation of the engine output devices. The methodology
for conducting these studies is given in [16].
The SED kit is designed to reduce the infrared visibility
of helicopters equipped with TV3-117 type turboshaft en-
gines of all modifications for Mi-8MSB-V, Mi-8MT, Mi-14,
and Mi-24. The designs of the screen-exhaust devices for
the right and left engines of the helicopter are completely
identical, in a mirror image, they are performed by measur-
ing and constructing a circular indicator of the power of IR
radiation. In order to exclude the influence of reflected solar
radiation and infrared radiation of the helicopter, the work
was performed in cloudy weather in the absence of rain, snow,
and fog. There should be no natural or artificial sources of IR
radiation (the Sun, powerful electric lamps, heating applian-
ces, etc.) in the direction of the ground-based equipment for
measuring the magnitude of the IR radiation within an angle
of ±20° vertically and horizontally.
Ground equipment for measuring the magnitude of IR ra-
diation was located at a distance of 300 m from the helicopter.
The indicator of the strength of IR radiation was taken
in five positions of the ground equipment for measurement
relative to the helicopter:
– at angles of orientation of the helicopter to the ground
equipment for acquiring the magnitude of IR radiation force
of 30°, 45°, 90°, 135°, 180°;
– in each position, the engine was brought to modes:
cruising, maximum duration, take-off.
During the tests, synchronization (time binding) of the
data received from the measuring equipment was ensured.
Determining the compliance of the tactical and technical
characteristics of the SED set during testing is carried out
under the specified conditions of influence of external factors
of a natural nature, as well as under the specified modes of
operation of the test object.
When conducting tests, the following methods are used
to assess the compliance of the SED set with the require-
ments of TT:
1. At the stage of ground tests:
– calculations – when evaluating changes in the charac-
teristics of the range and flight duration of the helicopter,
which are associated with the installation of the SED kit;
– engineering analysis – when assessing the sufficiency
of the provided materials, which confirm the strength of the
design of the SED experimental set (calculations, references,
conclusions);
– evaluation of the technical level of the SED set.
2. At the stage of flight tests:
– experimental determination of traction characteristics of
a helicopter with an SED kit to estimate engine power losses;
– experimental determination of the characteristics of
the IR radiation of a helicopter with an SED kit to assess the
degree of reduction in the power of the IR radiation of the
output devices of the engines.
4. 3. Theoretical method for calculating the current
and temperature fields
The equations for the flow fields and the temperature of
the helicopter are very complex. The external flow around
the attack helicopter body resulting from propeller rotation
and the internal flow inside the exhaust nozzles from the
petal nozzles are computed under a coupled mode to deter-
mine the temperature distribution on the helicopter skin and
in the exhaust plume. The governing equations include the
conservation equations of mass, momentum, and energy, as
well as the mass transport and radiation transport equations.
These equations will take the following form:
∇⋅
()
=ρν 0,
(1)
ρν ντ⋅∇
()
=−∇+∇⋅p,
(2)
∇⋅
+
()
=∇⋅∇−
∑
νρ λEp
Th
J
ef
fj
j
j
,
(3)
∇⋅
()
=−∇⋅ρν
YJ
jj
,
(4)
∇⋅
()
+
()
=Lrss Lrs
T
,,,αα
σ
π
4
(5)
where ρ is gas density; ν is the velocity vector; p – static
pressure; τ is the tension tensor; E – total energy; λeff – ef-
fective conductivity (λeff = λ+λt); λ is thermal conductivity,
λt is turbulent thermal conductivity); T – temperature;
hj and Jj represent the enthalpy and diffusion flux for
species J, respectively; Yj is the local mass fraction of
species j and L; (r, s) – radiation; s is the direction vector;
α – absorption coefficient; σp is the Stefan-Boltzmann
constant.
A significant number of factors affect the maximum flight
range of an anti-aircraft missile guided by IR. This maximum
range is determined by the formula:
D
IS D
mF
THD
aa
n
=
()
ατητ
00
,
(6)
where Iα is the radiation power of the target in the spectral
sensitivity range λ1–λ2 of the IR GOS radiation receiver
in the direction of the guided missile attacking the target,
which is specified by the sighting angle α; S0 is the working
area of the IR GOS lens; τ0 is the transmission coefficient of
the IR optical system of the target radiation in the range of
wavelengths λ1–λ2; ηа is the efficiency factor of the image
analyzer used in the IR GOS; τα(D) is the transmission
coefficient of atmospheric radiation of the target in the
range λ1–λ2, which is a function of the distance D between
the missile and the target; m is the signal/noise ratio, which
is necessary for reliable target detection; Fn is the sensitivity
threshold of the IR GOS radiation receiver.
A number of well-known and promising ways of protect-
ing a helicopter from guided missiles with IR GOS are based
on reduced radiation force Iα. The power of radiation is pro-
portional to the product:
IkST
iiiiiαeη=4,
(7)
where ei is the radiation coefficient; ηi is a coefficient that
indicates how much of the radiation of the target helicop-
ter belongs to the range of wavelengths λ1–λ2, in which
the radiation receiver of the thermal head of the homing
missile works; ki is a coefficient that indicates how much
of the radiation of the target helicopter, which is in the
range of wavelengths λ1–λ2, is used by the radiation re-
ceiver of the thermal homing head of the missile; Si is the
area of the sensitive emitter head; Ti is the temperature
of the emitter.
Eastern-European Journal of Enterprise Technologies ISSN 1729-3774 3/1 ( 129 ) 2024
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5. Results of the thermal imaging examination
of the helicopter
5. 1. Structural construction of the newly designed gas-
dynamic circuit of the screen-exhaust device
A new full-scale SED sample was designed (Fig. 3). The
rotary gas-dynamic circuit of the SED, through which the ex-
haust gases of the engine are diverted, structurally consists of
the main nodes: receiver (1); the front part of the contour (2);
power belts (3, 4); the rear part of the contour (5); seal (6).
All the above nodes are made of sheet heat-resistant
stainless steel with a thickness of 0.6...1 mm and are connec-
ted to each other by spot welding.
Fig. 3. Rotating gas-dynamic circuit
of the screen-exhaust device
A seal made of heat-resistant rubber (6) is bolted to the
front edge of the receiver (1). On the power belts (3, 4),
brackets for SED suspension are fixed with bolts on the
fastening nodes. In the flow part of the gas-dynamic circuit,
straightening blades are fixed by welding. The blades are
made of sheet heat-resistant stainless steel with a thick-
ness of 0.6...0.8 mm, they have slots for the organization of
ejection processes when the engine exhaust gases flow along
the circuit.
5. 2. Results of a numerical study of the organization of
the gas-dynamic flow in the screen-exhaust device
The theoretical method of calculating the flow fields
and temperature of subsonic gas ejectors of screen-ex-
haust devi ces in GTE was studied, and the geometric and
gas-dynamic parameters of the ejector mixing chambers
were analyzed.
The quality of the flow, the absence of secondary flows,
the inspection of injection phenomena along the path in the
structure of the SED and the nozzles of the engine under
the same boundary conditions using the exhaust nozzle were
determined.
Fig. 4 shows the current lines in the regular nozzle with
the SED attached. The nature of the flow has a complex spa-
tial structure with a small number of vortex zones, which are
concentrated in the zone of attachment of SED to the side of
the helicopter around the exhaust nozzle [15].
The shortcomings revealed in the process of numeri-
cal studies regarding the organization of the gas dynamic
flow in SED were taken into account during the further
structural optimization of the SED. The results of our
study could be used in the verification of the results of the
numerical study by comparison with the results of further
experimental studies and field tests under the conditions of
a helicopter flight.
Fig. 4. Flow lines in a standard nozzle with an attached
screen-exhaust device
5. 3. Experimental studies of the designed screen-ex-
haust device
We have conducted research during the thermal imaging
examination of the Mi-8 helicopter. The indicatrix of the
magnitude of the IR radiation force was taken in five positions
of the ground equipment for measurement relative to the heli-
copter at the orientation angles of the helicopter to the ground
equipment for the measurement of the IR radiation force of
180°, 190°, 200°, 210°, 220°, 230°, 240°, 270°, 300°, 330°, 0°.
Three variants of thermal images were obtained: a heli-
copter without installing a thermal visibility reduction
system (Fig. 5), a helicopter with installed standard screen-
exhaust devices (Fig. 6), a helicopter with installed screen-ex-
haust devices of a new development (Fig. 7). These figures
show the results of measuring the magnitude of the IR radia-
tion force at an angle of 180°.
According to the results of our research, diagrams of tem-
perature distribution in percentage value were constructed.
Fig. 8 shows a diagram of temperature distribution in per-
centages with the installed old system of reducing thermal
visibility. Fig. 9 shows a diagram of temperature distribution
in percentage values without installing a system for reducing
thermal visibility. Fig. 10 shows a diagram of the temperature
distribution in percentages with the installed new system for
reducing thermal visibility.
Fig. 5. Thermal images of a helicopter without a thermal
visibility reduction system installed
Fig. 6. Thermal images of a helicopter with an old thermal
visibility reduction system installed
Engineering technological systems: Reference for Chief Designer at an industrial enterprise
11
Fig. 7. Thermal images of the helicopter with
the new thermal visibility reduction
system installed
Based on the results of thermal imaging surveys, the
characteristics of the infrared radiation intensity of the he-
licopter body were constructed. Fig. 11, 12 show a compa-
rison of the intensity of thermal radiation of standard and
new screen-exhaust devices.
As can be seen from Fig. 11, 12, the radiation power Iα
during the study of the newly designed screen-exhaust de-
vices is lower at angles of 180–270 °C than the radiation
power of regular SEDs.
Fig. 11. Characteristics of the intensity of infrared
radiation of the helicopter body: – helicopter without
installation of a thermal visibility reduction system;
– helicopter with installed standard screen-exhaust
devices; – helicopter with installed newly
developed screen-exhaust devices
Fig. 12. Characteristics of the infrared
radiation intensity of the helicopter body:
– helicopter with installed standard
screen-exhaust devices; – helicopter
with installed newly developed screen-
exhaust devices
6. Discussion of results of investigating
the characteristics of infrared radiation
intensity of the helicopter exhaust
manifold
A new full-scale sample of SED has
been designed. Additional shielding of the
SED with blades with ejection cooling is
proposed, which can reduce the thermal
radiation of the emission zone of the helicop-
ter’s exhaust gases mixed with air (Fig. 3).
The metal body and elements made of sheet
heat-resistant stainless steel with a thickness
of 0.6...0.8 mm have slots for the organiza-
tion of ejection processes when the exhaust
gases of the engine flow through the circuit.
Previous resource tests of SED on the bench
showed the effectiveness of structural and
technological solutions adopted in terms
Fig. 8. Temperature distribution diagram in percentage with the old thermal
reduction system installed
Fig. 9. Diagram of temperature distribution in percentage values without
installation of the thermal visibility reduction system
Fig. 10. Temperature distribution diagram as a percentage with the new thermal
visibility reduction system installed
Eastern-European Journal of Enterprise Technologies ISSN 1729-3774 3/1 ( 129 ) 2024
12
of strength. We proposed vertical separation of the high-tem-
perature core of helicopter exhaust gases into three streams.
Based on the results of numerical modeling of the flow
and temperature fields of the newly designed screen-exhaust
device of the gas turbine engine based on real structural di-
mensions (Fig. 4), the gas-dynamic parameters of the ejector
mixing chambers were obtained. Verification of injection
phenomena along the tract in the design of the SED is de-
fined. The results are given in more detail in [15]. In further
experimental studies, these results will be compared with the
aim of introducing correction factors and adopted models
during further numerical modeling and improving the me-
thod for calculating the zazodynamic flow in SED.
Three variants of thermal imaging studies were obtained:
a helicopter without installation of a thermal visibility reduc-
tion system, with installed standard screen-exhaust devices,
and a helicopter with installed screen-exhaust devices of
a new development.
As can be seen from the diagram shown in Fig. 11, the
helicopter will remain vulnerable in the absence of shield-
ing of heated surfaces. Because the radiation from a small
visible part of the metal surface of the exhaust manifold, on
the contrary, is more noticeable than the radiation from the
entire uncooled exhaust gas. Fig. 8 shows the temperature
distribution in percent, the maximum visible temperature at
a measurement angle of 180° was more than 210 °C, while the
radiation power Iα was 27.25 W/sr. During the thermal im-
aging examination of a regular SED, Fig. 9, the temperature
range was 50–130 °C. When examining the temperature as
a percentage with the new system installed, the percentage
value of the reduction in thermal visibility was 30–50 °C.
The highest radiation power was recorded at angles of
240–300° – 75 W/sr, which is shown in Fig. 11.
A shortcoming of this study worth noting is that the ef-
fect of solar radiation on the overall thermal radiation of the
helicopter was not taken into account. This aspect is very
important because the side of the helicopter whose elements
are heated by solar radiation has greater thermal visibility.
Modern missile guidance heads operating in the spectral
range with wavelengths of 3–5 μm can receive weaker signals
from less heated radiating surfaces. The use of a new screen-ex-
haust device reduces thermal visibility by almost 9 times.
The value of the radiation power Iα is in the range of 13 W/sr.
When using a standard SED, the maximum radiation power
was 17.3 W/sr. Smaller indicators of the radiation power Iα
in the newly designed screen-exhaust device are achieved
by placing the section of the exhaust channel in a horizontal
plane and dividing the flow of exhaust gases in the section of
the exit from the SED into four separate streams. The use of
ejector systems in the new screen-exhaust device contributed
to the effective mixing of cold ambient air with the exhaust
stream, which reduces the CO2 concentration and tempera-
ture and reduces the visibility of the helicopter.
The works of our colleagues [6, 10] make it possible to
resolve the issue of numerical modeling of SED, calculation
of their design parameters. Methods of calculation of output
devices of the ejector type for various applications have been
developed, as well as highly effective experimental samples of
output devices of the ejector type. And there are no methods
for solving the task of determining the parameters and tac-
tical-technical characteristics in the study of full-scale SED
samples as part of a helicopter with working engines in the
literature available to the author, which predetermines the
prospects of our research.
The results of our research make it possible to partially
compare the simulation results of the simulation of the zones
of impact of aerial vehicle by thermal missiles, modeled in
paper [12] with the real indicators of the radiation power Iα.
Determining the conformity of the tactical and technical
characteristics of the SED set during the tests should be car-
ried out under the given conditions of the influence of external
factors of a natural nature, as well as under the given modes
of operation of the test object. However, it was not possible
to fully conduct such experimental studies. Only the stage of
ground tests was used to the fullest and possible extent.
But the limitations inherent in this study did not affect
the results obtained. Experimental studies gave an oppor-
tunity to practically check the application of the proposed
solutions regarding the new structure of SED and to compare
with standard SEDs.
The ranges of input data within which the results are
obtained are adequate and can be reproduced, leading to the
claimed effects and characteristics of SED. Experimental
studies were carried out according to the methodology given
in [16]. The tests were carried out in accordance with the
tactical and technical characteristics of the SED set under
the given conditions of influence of external factors of a na-
tural nature, as well as under the given modes of operation
of the test object. Work [16] reports available and standard
means of on-board measurement of information and their
characteristics used in research.
It is advisable to carry out further experimental studies in
order to verify the results of numerical studies by comparing
them with the results of further experimental studies and
field tests under the conditions of a helicopter flight.
7. Conclusions
1. We have designed a new full-scale SED sample, the
structural scheme of which is more effective in terms of
hydraulic losses and more technological in production com-
pared to regular screen-exhaust devices. Compared to stan-
dard SEDs, the newly designed structure of a screen-exhaust
device has a more perfect aerodynamic shape, which led to
a decrease in total pressure losses. The application of the
connection of metal parts and structural elements using
spot welding instead of riveting can lead to the possibility of
cheaper production and the manufacture of more aerodyna-
mically perfect parts of SED.
2. The applied theoretical method for calculating the flow
fields and temperature of subsonic gas ejectors of screen-ex-
haust devices of gas turbines and the gas-dynamic parameters
of the ejector mixing chambers obtained by the method of
numerical modeling based on the geometric dimensions of
the newly designed SED was analyzed. This was necessary
for comparison with the results of field tests. In further
experimental studies, these results are compared with the
purpose of introducing correction coefficients of the models
during further numerical modeling and improving the me-
thod for calculating the gas-dynamic flow in the SED of other
designs and schemes.
3. Experimental studies of the designed screen-exhaust
device were carried out. It was found that placing the section
of the exhaust channel of the designed SED in the horizontal
plane compared to the standard SED ensures a reduction of
IR radiation in the lower hemisphere. Directing the flow of ex-
haust gases from the SED into the space above the helicopter
Engineering technological systems: Reference for Chief Designer at an industrial enterprise
13
propeller, the desired effect of mixing them with the surround-
ing air is achieved. As a result, the temperature of the exhaust
gases and the total infrared radiation of the helicopter itself
decrease sharply. The distribution of the flow of exhaust gases
at the SED section into four separate streams allows for their
rapid mixing with air in the surrounding atmosphere.
Conflicts of interest
The authors declare that they have no conflicts of interest
in relation to the current study, including financial, personal,
authorship, or any other, that could affect the study and the
results reported in this paper.
Funding
The study was conducted without financial support.
Data availability
The data will be provided upon reasonable request.
Use of artificial intelligence
The authors confirm that they did not use artificial intel-
ligence technologies when creating the current work.
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