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The large, EU Supported ESPOSA (Efficient Systems and propulsion for Small Aircraft) project has developed new small gas turbines for small aircraft. One of the important tasks was the engine - airframe aero-thermal radiation integration that included task of minimizing the infrared radiation of the small aircraft, too. This paper discusses the factors influencing on the aircraft infrared radiation, its possible simulation and measurements and introduces the results of small aircraft infrared radiation measurements. The temperature of aircraft hot parts heated by engines were determined for validation of methodology developed and applied to engine - aircraft thermal integration.
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51
Small Aircraft Infrared Radiation Measurements 2019 47 1
Abstract
The large, EU Supported ESPOSA (Efcient Systems and pro-
pulsion for Small Aircraft) project has developed new small
gas turbines for small aircraft. One of the important tasks was
the engine - airframe aero-thermal radiation integration that
included task of minimizing the infrared radiation of the small
aircraft, too. This paper discusses the factors inuencing on the
aircraft infrared radiation, its possible simulation and measure-
ments and introduces the results of small aircraft infrared radia-
tion measurements. The temperature of aircraft hot parts heated
by engines were determined for validation of methodology devel-
oped and applied to engine - aircraft thermal integration.
Keywords
aircraft, infrared radiation, radiation measurements, engine -
airframe thermal integration
1 Introduction
The infrared is an invisible radiant energy. This electromag-
netic radiation has longer wavelength (starting from nominal
red visible line wavelength 700 nanometers up to 1 mm), than

infrared radiation were developed prior the World War I. During
World War II, the infrared detection was used for tracking, too

(thermal) radiation had been developed for beginning of 1950s,
while, because the success of radar systems, its wide applica-
tion was started about 10 - 15 years later. Titterton (2006) found
from statistics that, the heat-seeking missiles had been respon-
sible for more than 80 % of all the combat losses over 40 years

were responsible for 76% of the neutralized aircrafts, while
during the Kosovo war, the NATO aircraft were not allowed to

et al., 2007). On the same time, since 1987, for 26 years 35
       
that caused more than 500 deaths (Bolkcom et al., 2004). (It is
true, this large number might be less, because some lost civilian
aircraft were used for military purposes, some others or bet-

they may have been perceived as being used for military pur-

 -
ian project for detailing the implementation of an anti-missile
system on a single commercial aircraft (Bolkcom et al., 2004).
The aircraft infrared radiation has investigated by many
researchers, developers for the last 50 - 60 years as it summa-
rized by Mahulikar et al. (2007). The most of research were and
-
mental studies had been focused on the military aircraft infrared
signature measurement and aircraft type recognition, too. Later,
the practical measurement of the civilian large aircraft infrared
radiation signatures (Coiro et al., 2012), the radiation modeling
and countermeasure became to set of important tasks. Parallel,
       
2012) has been developed rapidly, too. The information about
1 

Budapest University of Technology and Economics,
H-1521 Budapest, P.O.B. 91, Hungary
2 Aviation Training Centre,


3 

* Corresponding author, e-mail: jrohacs@vrht.bme.hu
47(1), pp. 51-63, 2019
https://doi.org/10.3311/PPtr.11514
Creative Commons Attribution b

P
P
Periodica Polytechnica
Transportation Engineering



1*, Istvan Jankovics1, Istvan Gal1, Jerzy Bakunowicz2,
Giuseppe Mingione3, Antonio Carozza3

52 Period. Polytech. Transp. Eng. J. Rohacs et al.

in Minkina et al. (2009).
The research can be divided into two major groups: inves-
tigation of the aircraft infrared signature (including the theo-
retical and practical studies) and sensing the infrared radiation.

list the codes using in investigation of the aircraft infrared radi-
ation (Coiro et al., 2012; McGlynn, Auerbach, 1997; Mahulikar
         
can be applied to compute the aircraft infrared signature, espe-
         

 
  
     
Belgium Defence establishment has developed an open-source
        
can be applied to the Arial vehicles, too.
Nowadays, the small and personal air transportation system


developed special small gas turbines for small aircraft. During
optimization of the engine components and airframe integra-
tion the thermal conditions and the infrared radiation had been
taken into account (Buonomo et al., 2013; Carozza et al., 2013;
 
     

This paper shows and discusses the results of the infrared
radiation measurements.
2 The sources of the aircraft infrared radiation
The infrared radiation of aircraft is composed from the dif-
ferent sources (Fig. 1) including the radiation from the aircraft
         
sun-, sky- and earthshines.
The infrared radiation like all electromagnetic radiation
interacts with matter in a variety of ways (White, 2012):

the angle of incidence),
refracts - when the direction of a wave bends when pass-
ing between two transparent media with different propa-

scatters - that occurs (in blue sky) upon interaction with
particles whose size approaches the length of the wave,
diffracts - interaction occurring around the edges of
an obstruction,
interferes - interaction in both a constructive and destruc-
tive manner,
absorbs - when radiation is converted into another form
of energy (mostly to heat),
emits - from matter by conversion from another form
of energy,
transmits - propagation of the infrared radiation through
a transparent medium (or vacuum),


Fig. 1
(Mahulikar et al., 2007)).
3 Governing laws
The aircraft infrared radiation that can be measured or sensed
depends on heat sources, and intensity of sources (initiated by

    
-

3.1 Planck’s radiation law
It describes spectral radiance (L - energy per source unit
parameter-
T ). It can be given

wavelength (λ
LT Lhc
e
ehc kT
λ
λ
λλ
,,
,, /
()
=⋅
21
1
2
5
       -23    
-34
L(λ,T) is W·sr-1·m-3

3.2 Wien’s displacement law
λ) at which the spec-
tral radiance of black body radiation per unit wavelength is

λ
maxmax
,. ,==
⋅⋅
b
TET
1 309 10
75

bmK
2 8977721 10 3
..
(1)
(2)
53
Small Aircraft Infrared Radiation Measurements 2019 47 1
3.3 Stefan Boltzmann radiation law
  
wavelengths (λ      
black body per unit surface area per unit time.
QETd T=
()
=⋅
0
4
λλσ
,,
where σ
σ
=⋅
()
56710
82
4
..
WmK
3.4 Black body

incident radiation to pass into it and absorbs internally all the
       

angles of incidence. Hence the blackbody is a perfect absorber

Blackbody is an ideal of comparison for a body emitting
radiation. A blackbody has two main properties in thermal

emits as much or more energy than any other body at the same
  
the energy is radiated isotopically, independent of direction.
The real body radiation can be given by its emittance or
emissivity that is a ratio of real and black body radiations:
ε
=
E
E
real
black
.
The emissivity varies according to the surface properties,
the material and, for some materials, also according to the tem-
perature of the object. It also depends on the wavelength and
angle of incidence.
For rough surfaces the value is close to unity, for polished
surfaces it is around 0.02.
3.5 Kirchhoff’s law of thermal radiation
The electromagnetic infrared radiation as usually hits the
objects, while the objects absorb some of this energy. The value
of absorptivity (α) is between 0 and 1, where 1 means a black
body, 0 means a perfect white body.
The heated body, having higher temperature emits more
infrared radiation than colder objects.
    
when the temperature of a body is constant, i.e. independent on

this means the body gives off as much energy as much absorbed:
εα
=.
3.6 Conservation of radiation energy
When the incident radiation reaches the surface of a material,
it can act 3 ways depending on the material properties: it can be
α) describes
how much fraction of incidence radiation is absorbed, the trans-
mittance (τ) is a measure of the ability of a material to transmit
 σ) is a mea-

By use of energy conservation law the sum of absorbed,


QQ
QQ
=⋅+⋅ +⋅
ατσ
,
or
1.
As transmission rarely plays a role in practice, the transmis-
sion (τ
ασ
+=1

εσ
+=
1.
    

This short summary of governing rules contains all the
      
radiation simulation, measurements and countermeasures.
The other models are given by special studies and papers. For
   -

-
ing measurement of boundary layer by infrared means might be
found in Boden et al. (2015).
4 Practical aspects
According to the knowledge on (i) material properties, (ii)
    
(Pocket, 2012)) and (iii) our practice with developing the ther-
mographic evaluation methods the following important practi-
cal aspects must be underlined.
There are some aspects according to the emittance: (i) for


concrete, organic substances) have high emissivity in the long-
wave infrared range that is not dependent on the temperature
-

(iv) ε must be set properly for accurate measurement.
       σ
depends on the surface properties, the temperature and the type
        
more strongly than rough, matt surfaces made of the same
        
  

the ambient temperature (mainly in indoor thermography); (iv)
(3)
(4)
(5)
(6)
54 Period. Polytech. Transp. Eng. J. Rohacs et al.

   -

     

Other comments according to the transmittance are (i)
dependence on the type and thickness of the materials and (ii)
the fact, the most materials are not transmissive, i.e. permeable,
to long-wave infrared radiation.
        -

-

  
-
        
are the same. In thermography it means that the heat source
in the background is clearly visible on the surface because of
         


background can be optimized.
Fig. 2
        
roughness of the surface means that each individual ray of inci-
dent radiation reaches a surface which has different orienta-
tion. The normal lines at each point of incidence of rays are
-
ing depending on the surface roughness. It means, with given
accuracy of measurement of incident radiation, the error of
measurement of emitted energy will be proportionately higher

determination of emissivity values.
        

directly proportional to the cosine of the angle between the sur-
face normal and the direction of observer.

at 25 °C) up to 0.94 (glass - 90 °C).
The accuracy of the thermo radiation measurements depends
on the environmental conditions, too. The clouds, precipitation,

The objectives of the thermo radiation measurements are the

possible optimization for reducing the infrared radiation.
Our practice going back to the end of the last century (Oravecz
et al., 2000), and it showed that even relatively simple infrared
cameras (like AGA Thermovision 750 type working with a spe-
   
to measurement, analysis and evaluation of the aircraft infrared
 

a special thermal emittance reducer. The photos were made in
   
the same military helicopter without (upper photo) and with
-
strate that, the infrared radiations origins from all the heated

from the rotor blades that origins from the helicopter itself.
Fig. 3 Infrared radiation of a military helicopter without (upper) and with the
thermal emittance reducer (lower image)
During preparation for measuring the infrared radiation
       
realized several measurements with use of a small gas turbine
research stand and there were analyzed the changes in nacelle
surface temperature and engine airframe integration of a mid-
dle size commercial aircraft.
55
Small Aircraft Infrared Radiation Measurements 2019 47 1
        
radiation of engine nacelles and plumes.
The Fig. 4 and 5 show the changes in temperature of nacelle
surface during the engine tests. As it can be seen, the tempera-
tures measured at the M2 and M3 points are correlated by the
-

Table 1 Engine nacelle and plum radiation
    
rotation speed - revolution per
  
thermal picture is short, with
moderate temperature.
   
    
smooth while its length has
increased, and relatively high
temperatures can be observed
in the core.
    
     
sharp, temperatures in the core
are higher, but not as high as
during the transition.
Fig. 4 Points in which the nacelle surface temperatures are measured (in time
interval with no measured data, the camera was moved to make measurements
from different point of view)
The Fig. 5 shows eight thermo images of the nacelle that
were selected with nearly same time intervals, to show how
changing the temperature of engine nacelle during the 1100
seconds long time period.
Fig. 5 Infrared pictures of an engine nacelle at engine test
(time is sec after starting the test)
5 Radiation simulation
        
     

 -
          
available references all these aspects are investigated.
  -
        



data analysis performed over many years. The vehicle fuselage,
facet, model includes radiation due to aerodynamic heating, inter-
  
combustion gas emissions were calculated for H2O, CO2, CO,
and other gases as well as solid particles. The developed software
56 Period. Polytech. Transp. Eng. J. Rohacs et al.
 
-
ture. This methodology is well applicable today, too.
The early 1990 several general models were developed.

imaging of targets and scenes in a modeling software could be
applied to model targets of a generic aircraft (Miller, 1993).
Already in 1998, Joyner et al. (1998) and his colleague cre-
 -

       

        -
eling using the CFD results as inputs had been developed
(Andersson, 2002).
a) The calculation of the aircraft infrared radiation and sig-
nature simulation depends on the objectives. The most


and Willers, 2012). According to this, there are several
important key considerations and aspects determining
        
methodologies should be taken into account.

(2012) for such an imaging infrared simulation system
are: (i) radiometric accuracy in all spectral bands, (ii)
accurate emitting source surface temperature behavior,
-

 
detailed modeling of signatures and backgrounds, (vi))
accurate atmospheric transmittance and path radiance
models, (vii) realistic rendering of the scene image in
radiometric, spatial and temporal terms, and (viii) com-
prehensive sensor modeling to account for primary and
second order imaging effects.

 
-
ing, (ii) environmental conditions (as humidity) (iii), air-
      

b)    
-
mined for all spectral band.
c)   -
θϕ
(see Fig. 6.a).
d) Distance effect. Generally, the receivers sense the radi-
  Φe     -
ted or received per unit time) in form of radiant inten-
sity (I  
area power density at the receiver, E
   
distance: E = I/R2.
e) Projected area of source. According to the previously
      
-
dian angles, Ω (Fig. 6.b). That means the projected areas

solid body facet model elements that will be perpendicu-
lar to lines connecting them to the sensor elements. The
angle between the normal to sensor plane and connect-
real and spatial position of the surface elements
Aproj.
f) Aircraft position. The measurable radiance depends on
 


aircraft elements. On the other hand, it is easy to under-
   -
shine really depends on the position of aircraft related to
the sensor position.
g)       -
         
      

contained in range of wavelength 3 to 5µm. The measure-

emittance in the given range of wavelength is nearly zero

in range between 4.17 - 4.20 µm and 4.32 - 4.70 µm.
h) -
mined by use of absorptivity of gases. The spectral trans-
missivity and absorptivity in a homogenous isothermal gas
K,
τα
ηη
ηη
==
−−
ee
Ks Ks
,,
1
where s is a thickness of the gas cell. Because the absorp-
         
        -

elements as CO2, H2-

i) Modeling aspects. Actually, the aircraft infrared signature
measuring is based on the radiant intensity or irradiance
measurements (see sub point c)) that are analogous to radar
-
         
Perotoni and Andrade, 2011)). However there is a princi-



For this reason, intensity is actually more closely related to
57
Small Aircraft Infrared Radiation Measurements 2019 47 1
-
mitter power with antenna beam (White, 2012).
j) 
to determining the infrared signature of aircraft. The com-
       


long-range air-to-air detection and tracking engagements.
The code integrated eight standalone modules (Iannarilli,
   -
ing module), (ii) CLOUD (sky background imaging mod-
 

     
      
-
face module).
k)        
(Davis and Thomson, 2002) (i) background information
(geography, date and time, meteorological inputs), (ii) plat-
form characteristics (size, shape, materials, coating, pro-
       -
length band, spatial resolution as scanner, imaging, etc.,
and sensitivity including detector noise). Here the platform
might be the critical elements, because the applied mate-
rials and especial their coating and painting (Mahulikar et
al., 2006) and fuselage skin heated by engine thermal pro-
cesses. The last one can be determined by use of model
developed by Mahulikar and his colleague (Mahulikar et
al., 2001; 2005) that incorporates the radiation interchange
in engine layout, to compute the temperature distribution
of rear-fuselage skin for given engine operating conditions.

plume that is well analyzed by (Mahulikar et al., 2007). Of
 
fuselage play deterministic role in case of military aircraft
and sensing from the real side. During operating the after
burner system, the plume might be longer then the fuselage.
l) Methodology. Most of the simulation methods com-
   
     
(Mahikular et al., 2001; Anderssen, 2002; Jianwei and
Qiang, 2009; Pan et al., 2011).
  
of small aircraft by use of two major methodologies. The theo-
retical investigations had objectives aero-thermal analysis and
evaluation of the engine airframe integration and reducing the
temperature distribution (by this infrared radiation) of the air-
frame elements heated by working engines (Buonomo et al.,

The other program was the practical measurements of the
 
       

The aircraft infrared simulation is based on the coupled
-
fer simulation) and / or multi-disciplinary models (including
       
-
lation methodology.


nacelle wall (conjugate heat transfer analysis) due to the pres-
ence of the engine hot components and taking into account for
nacelle cooling/ventilation system (Buonomo et al., 2013). The
CFD analysis with proper boundary conditions at engine surface
and nacelle wall considers the both convective and radiative heat
transfer. Three-dimensional CFD calculations were performed by

-

       
and nacelle was also taken into account, by using the Discrete
Ordinate model (Buonomo, 2013).
Fig. 6θϕ,
b. (right side) - the sterian angle, Ω and measured surface, Asurf and projection area, Aproj)
a.) b.)
58 Period. Polytech. Transp. Eng. J. Rohacs et al.
Fig. 7 Aircraft infrared radiation simulation methodology
6 Theoretical investigations
   
the developed small gas turbines on several small aircraft dem-


originally designed and built with two piston engine in pusher

       

retractable tricycle landing gear arrangement, and pusher pro-

The another aircraft was a low wing, 4 seated I-31T aircraft
(Fig. 8) designed by the Institute of Aviation in Warsaw and

Fig. 8
   
allowed operational temperatures for the TP-100 are given
in Fig. 9. The Figure shows the hot sections that heat the
nacelle elements.
The Figs. 10 and 11 demonstrate the results of the
theoretical investigations.
The Fig. 10 shows the static temperature distribution on
        
        
with cruise speed 87.445 m/s at 2750 m. At this level the air
  -
    
           

enough from engine and where forced convection effectiveness
prevails, as the combustion air intake, at the lower front face
  K) is
reached close to the engine pipes and gas generator zone. This
 
component materials of nacelle skin (Buonomo et al., 2013).
Fig. 9
(Buonomo et al., 2013)
Fig. 10
(Buonomo et al., 2013)
59
Small Aircraft Infrared Radiation Measurements 2019 47 1
The Fig. 11 shows the wall temperature contours of nacelle

(Carozza et al., 2015). For easier evaluation of the results the idle
condition was chosen as 101325 Pa air pressure and 300 K air
temperature. The propeller effects had been taken into account.
(Carozza et al., 2015). Generally, the propeller may reduce the
skin temperature up to 35 degree (Carozza et al., 2015). This

As it can be recognized from Figs. 10 and 11 difference in
  -

temperatures are very small.
Fig. 11 Wall temperature (K) contours in case of engine idle condition and
taking into the propeller effects (Carozza et al., 2015)
7 Measurements
     
(see Figs. 1 and 8) were applied in practical measurements of
the infrared radiation of engine - airframe sections. The engine
ground tests were measured. A Testo 885-2 thermal imager was
    -

 
       -
peratures under nacelle by use of thermocouples (T1 - put close
to the engine control unit, T2 - near the top of the engine cover,
around the gas generator, near the inner surface of the mask,
            
fuel oil pump (see Fig. 12)) were registered, too, for supporting
the further evaluation of the theoretical studies and practical
measurements.
  -
tion as position of sun, wind direction, humidity, etc., too. The
Fig. 13 shows the position of the investigated aircraft EM-11

Fig. 12 Thermocouples under the nacelle
Fig. 13 Measurement condition
The Fig. 14 presents images recorded during the measure-
ments. The left engine was started at 2:47 PM, i.e. at 46020

included the series of changes in operational condition as it


off, stopping engine regimes.
Table 2 Engine test process
Time Engine operational
condition Time Engine operational
condition
46020 Left engine start 49680 Approach
46200 Left engine warm up 49740 Take-off
46440  49860 Approach
46620  49920 
46920 Idling 50220 Engines stop
47520 Take-off 50280 Cooling
47880  50880 End of measurement
48660 Cruising power
60 Period. Polytech. Transp. Eng. J. Rohacs et al.
Fig. 14
In Fig. 15, there is the same image showing the thermal con-
dition of the left engine nacelle after engine test with use of two
different temperature scales. As it can be seen, the hottest part of

C that is well correlat-
ing with the theoretical calculations (see Figure 10). The investi-
 

pipe has top radiation, because the infrared camera looks into the
pipe (as it can be understood from comparison the pictures of
      

The recorded images had been used for determining the
temperature distribution on the nacelle surface. The changes
in nacelle surface temperature along the chosen reference
lines in case of middle cruise regime are presented in Fig. 17.
     
    
from left end to the right end. P2 and P3 lines are going through
       
inaccurate. However there is a well detectable zone with heat-

Fig. 15 Left side of left engine nacelle radiation with
different temperature scales
Fig. 16 
Fig. 17 Changes in wall temperature along the chosen reference lines
The Fig. 18 demonstrates the real dependence of infrared radi-
ation on engine installation. There are following zones of high
temperature. Upper air intake louvres, which make visible hot
0 5 10 15 20 25 30 35 40 °C
61
Small Aircraft Infrared Radiation Measurements 2019 47 1

    
and ground around and after nose wheel to the temperatures
    
well as for asphalt. Prolonged static operations of the engine set


oil cooler, located in the rear bottom of the cowling with tempera-
tures within the scale. Because the applied temperature scale, the

image, in reality. However, the tube temperature is much greater
(in analogy to Fig. 15), but additional temperature measurement

indicated, that the fumes are not so hot to damage the composite
structure of the hood.
Fig. 18
aircraft demonstrator I-31 T
The Fig. 19 shows the thermal image of the aircraft I-31T noise
section after 63 minutes ground test and 10 minutes cooling.
In Fig. 20 the temperature distribution shown at end of
cruise phase along the chosen reference lines on nacelle wall
of engine mounted in aircraft I-31T. This represents the best
      
        
  
I-31T aeroplane included the measurements of temperature
    
-
ing points concerning engine cooling. The points were located
on the inner and outer surfaces of the cowling in areas of the
        
generator. The analysis revealed that the most critical points
 
gas traces. The temperatures on the inner surfaces of upper
          -
eral. However, recorded values reached temperatures up to 100

noticed in the Figs. 18 and 19, after engine shut down the tem-
peratures in measuring points increased radically.
Fig. 19 Image after engine ground test and 10 minutes cooling
(aircraft I-31 T)
Fig. 20 Changes in nacelle wall temperature along the chosen reference lines
for engine built into aircraft I-31 T
8 Conclusions
        
project developing and implementing a multi physical, namely
aero and thermal optimization in integration of engine into the
airframe. The goal was to minimize the aero-thermal losses for
increasing the engines' effectivities and reducing the infrared
radiations origin from engine - airframe structure. The study
and optimization process were started by theoretical investiga-
tions resulting to development of a CFD methods for aero-ther-
mal integration of engine into airframe. After it a special prac-
tical investigations were organized and realized.
The analysis of previous theoretical investigations and prac-
tical measurements of the aircraft infrared radiations as well as

the condition and methodology for infrared radiation mea-
surements of the aircraft demonstrators. The paper introduced
 
radiation. The full engine ground test was measured. The mea-
       
the possible improvements for reducing the infrared radiation
origin from engine-airframe structure.
62 Period. Polytech. Transp. Eng. J. Rohacs et al.
Acknowledgement
   
   
funded by the 4th call of the FP7 Cooperation Work Programme.
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         
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  -
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          
   

          
 -
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-
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
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   https://www.testo-international.com/media/
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     
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

  


          
       
          
   
 
      
   
           
    
Journal of Quantitative Spectroscopy
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
      
Development of a methodology for infrared aircraft emission estimation.
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
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     
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
of the missile-aircraft engagement. In: P
Technologies for Optical Countermeasures IX (Ed. by Titterton, D. H.,
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https://doi.org/10.1117/12.974801
... According to [18], results obtained on turbojet engine can be used to draw conclusions about non-propulsion power development units, which further enhances the role of turbojets in research applications. In several cases turbojets form the basis of a different development version like turboprop, as found in [19]. Variable nozzles are already being under investigation for turbofan engines as mentioned in [20], which system can also be assessed on turbojet engines ( [21] or [22]). ...
... For this reason, the transfer function of the plant has been established at a specified operating point, this was the nominal. The transfer function is shown in (19). The large magnitudes are due to the fuel supply rate being around 10 −3 kg/s at TPR with a magnitude of 1. ...
... 2.7495 × 10 9 s 3 + 3.612 × 10 3 s 2 + 9.172 × 10 5 s + 1.905 × 10 9 (19) All the PID controllers have been optimized by the integrated tuning tool in MATLAB R Simulink R . All controllers have been obtained as a parallel form, shown in (19), with filtered differential output to reduce the effect of input noise. ...
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The interest in turbojet engines was emerging in the past years due to their simplicity. The purpose of this article is to investigate sliding mode control (SMC) for a micro turbojet engine based on an unconventional compound thermodynamic parameter called Turbofan Power Ratio (TPR) and prove its advantage over traditional linear methods and thrust parameters. Based on previous research by the authors, TPR can be applied to single stream turbojet engines as it varies proportionally to thrust, thus it is suitable as control law. The turbojet is modeled by a linear, parameter-varying structure, and variable structure sliding mode control has been selected to control the system, as it offers excellent disturbance rejection and provides robustness against discrepancies between mathematical model and real plant as well. Both model and control system have been created in MATLAB® Simulink®, data from real measurement have been taken to evaluate control system performance. The same assessment is conducted with conventional Proportional-Integral-Derivative (PID) controllers and showed the superiority of SMC, furthermore TPR computation using turbine discharge temperature was proven. Based on the results of the simulation, a controller layout is proposed and its feasibility is investigated. The utilization of TPR results in more accurate thrust output, meanwhile it allows better insight into the thermodynamic process of the engine, hence it carries an additional diagnostic possibility.
... The aircraft main radiation sources are the hot jet engines (2-3 µm), the exhaust plume (3-5 µm) and the heated fuselage (8-10 µm) [1,2]. The IR radiation from a military helicopter has been presented by Rohacs et al. [3]. IR guided missiles track heat sources emitted by the target and therefore are one of the major threats to military aircraft. ...
... A comparison of the IR emission spectrum of a charge composed of the pyrotechnic composition based on Mg, Teflon ® and Viton (MTV) and target is shown in Figure 1. The thermal signature of the aircraft is shown in Figure 2. [2] MTVs are widely used in infrared decoys [1][2][3][4]. MTV is more radiant at near and medium wavelength bands than traditional pyrotechnic compositions. They are effective against IR missiles, especially of the first generation. ...
... The huge amount of available information confuses pilots during operation, particularly while decision-making in abnormal/emergency situations. While the introduction of new technology brings significant improvements and may solve some problems [25][26][27][28], it often introduces others in all transportation modes [29][30][31][32]. The future working environment of pilots (cockpit and future ground control towers) needs to be designed by taking into account various psychological and human factors. ...
... In this research, the eye blink rate of an experienced pilot was investigated through three flight scenarios. The number of eye blinks (full blink and half blink) of the experienced pilot increased significantly in parallel to the task complexity: (i) 0. 25 Figure 14). In addition to this, it was also noticed that eye flutters (rapid muscle movement in the eyebrow area) also increased. ...
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Due to the introduction of highly automated vehicles and systems, the tasks of operators (drivers, pilots, air traffic controllers, production process managers) are in transition from “active control” to “passive monitoring” and “supervising”. As a result of this transition, the roles of task load and workload are decreasing while the role of the mental load is increasing, thereby the new type of loads might be defined as information load and communication load. This paper deals with operators’ load monitoring and management in highly automated systems. This research (i) introduces the changes in the role of operators and requirements in load management, (ii) defines the operators’ models, (iii) describes the possible application of sensors and their integration into the working environment of operators, and (iv) develops the load observation and management concept. There are some examples of analyses of measurements and the concept of validation is discussed. This paper mainly deals with operators, particularly pilots and air traffic controllers (ATCOs).
... 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 visibility. Research points to the obviousness of the problem but does not provide recommendations for its solution. ...
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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 conducted. Three variants of thermal images were acquired: a helicopter without installation of a thermal visibility 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 intensity of infrared radiation were determined for three variants 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 missiles with infrared homing heads based on reduced radiation 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-exhaust device in the horizontal plane for complete shielding 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 developers of military aviation
... The tail nozzle temperature T p is related to the type of engine, flight speed, altitude, and other factors [17]. The projected area A p (θ ) of the tail nozzle in different detection directions is ...
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To effectively evaluate the detection capability of the infrared search and tracking system (IRST), the mathematical models of target infrared (IR) radiation intensity envelope, atmospheric transmittance, and signal-to-noise ratio (SNR) operating range are improved, respectively. Based on the above three models, the IRST performance evaluation simulation system is designed to analyze the optimal detection point and effective detection area under different conditions (such as target speed, detection angle, detection probability, false alarm probability, and operating range). Meanwhile, in order to verify the validity of the model, the range evaluation method of calibration and cross-validation is proposed. And taking the cross-validation method as the baseline, the error of the optimized mathematical model of IRST in this paper is within 10%. The research results are of reference significance for IRST operating range evaluation, design, and use.
... Due to their huge size and high heat dissipation, the level of infrared energy radiated by these objects is significantly greater than small UAVs (such as an X8 drone). For example, an aircraft radiates large amounts of infrared energy produced by components such as the heated engines and metal body parts, and the reflected energy of the sun and sky [27]. When imaged using an infrared camera from a long distance, even though such objects may occupy small number of pixels in the image, their local contrast is sufficiently bright against the background. ...
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Thermal infrared imaging provides an effective sensing modality for detecting small moving objects at long range. Typical challenges that limit the efficiency and robustness of the detection performance include sensor noise, minimal target contrast and cluttered backgrounds. These issues become more challenging when the targets are of small physical size and present minimal thermal signatures. In this paper, we experimentally show that a four-stage biologically inspired vision (BIV) model of the flying insect visual system have an excellent ability to overcome these challenges simultaneously. The early two stages of the model suppress spatio-temporal clutter and enhance spatial target contrast while compressing the signal in a computationally manageable bandwidth. The later two stages provide target motion enhancement and sub-pixel motion detection capabilities. To show the superiority of the BIV target detector over existing traditional detection methods, we perform extensive experiments and performance comparisons using high bit-depth, real-world infrared image sequences of small size and minimal thermal signature targets at long ranges. Our results show that the BIV target detector significantly outperformed 10 conventional spatial-only and spatiotemporal methods for infrared small target detection. The BIV target detector resulted in over 25 dB improvement in the median signal-to-clutter-ratio over the raw input and achieved 43% better detection rate than the best performing existing method.
... A numerical study was carried out taking into account the geometric dimensions, aerodynamic and gas-dynamic characteristics of the SED with imitation in flight. And the main places of the helicopter's infrared radiation were considered by the authors of [8]. The authors paid great attention to the background of thermal radiation of the fuselage skin elements from the engines located under the hood. ...
... These objects also usually radiate high levels of infrared energy. For example, the infrared energy radiated by an aircraft consists of multiple sources such as those from hot engines, the parts heated by friction and reflections due to the sun and sky [27]. Consequently, although these objects occupy small area in the infrared image, they offer strong thermal signatures and sufficiently high contrast against the background. ...
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Thermal infrared imaging is a promising modality for long-range small target detection. However, low target contrast, high background clutter and sensor noise are some of the key challenges that need to be resolved efficiently for robust detection performance. The spatiotemporal processing in the early stages of the visual pathway of small flying insects has a remarkable ability to simultaneously address such challenges. The first stage of the early visual system corresponds to the adaptive temporal filtering mechanisms of photoreceptor cells. This stage improves the signal-to-noise ratio, enhances target background discrimination and compresses the signal bandwidth. The second stage pertains to the adaptive spatiotemporal filtering in the lamina monopolar cells. This stage removes spatiotemporal redundancy and enhances target contrast. In this paper, we explore such two-stage bio-processing to simultaneously suppress clutter and enhance the contrast of small low-heat-signature targets in real-world infrared imagery. We also propose a simple and efficient spatial contrast operator called center–surround total differential index for target region segmentation. Small moving target detection experiments on real-world high-bit-depth infrared video sequences show that the proposed method significantly outperforms the state-of-the-art spatial and spatiotemporal infrared small target detection methods. Specifically, our method resulted in 59% better detection rate (at 105^{-5} false alarm rate) than the best competing method. Our results show that the bio-inspired spatiotemporal preprocessing is an excellent tool for significantly improving the performance of existing long-range infrared target detection techniques.
... The aircraft noise and IR emissions are greatly affected by propulsion system (Moshkov and Samokhin, 2018;Rohacs et al., 2019). Therefore, a possible modification of the aircraft emissions can be supposed when a hybrid-propulsion systems is used. ...
Article
Purpose This paper aims to present the main results achieved in the frame of the TIVANO national-funded project which may anticipate, in a stepped approach, the evolution and the design of the enabling technologies needed for a hybrid/electric medium altitude long endurance (MALE) unmanned aerial vehicle (UAV) to perform persistent intelligence surveillance reconnaissance (ISR) military operations. Design/methodology/approach Different architectures of hybrid-propulsion system are analyzed pointing out their operating modes to select the more suitable architecture for the reference aircraft. The selected architecture is further analyzed together with its electric power plant branch focusing on electric system architecture and the selected electric machine. A final comparison between the hybrid and standard propulsion is given at aircraft level. Findings The use of hybrid propulsion may lead to a reduction of the total aircraft mass and an increase in safety level. However, this result comes together with a reduced performance in climb phase. Practical implications This study can be used as a reference for similar studies and it provides a detailed description of propulsion operating modes, power management, electric system and machine architecture. Originality/value This study presents a novel application of hybrid propulsion focusing on a three tons class MALE UAV for ISR missions. It provides new operating modes of the propulsion system and a detailed electric architecture of its powertrain branch and machine. Some considerations on noise emissions and infra-red traceability of this propulsion, at aircraft level.
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Along with the diversification and sophisticated development of detection methods in modern warfare, helicopters are increasingly subject to unilateral or simultaneous threats from radar and infrared detectors. In order to improve the survivability and operational effectiveness of the helicopter, a comprehensive stealth approach based on Pareto solution is presented. Considering the geometric constraints and aerodynamic characteristics of the engine intake and exhaust system, the model of the system is established by the full factorial design, the internal, central and external flow fields are constructed, then the high-precision computational fluid dynamics method is used to simulate the total flow field under the rotor downwash airflow in hovering state. The radar cross section of the system is evaluated by the physical optics and physical theory of diffraction. Based on the Monte Carlo and ray tracking method, the infrared signature of the system is calculated and analyzed in detail. Under the comprehensive evaluation and selection of comprehensive stealth approach, the optimization model of the system is continuously established and updated. The ultimate design has achieved good results in both radar cross section reduction and infrared radiation suppression and the proposed method is effective and efficient for radar/infrared integrated stealth of helicopter engine intake and exhaust systems.
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This paper describes a generic approach to generating the IR signature specification of a military platform. A generic naval Frigate is used as a sample platform to demonstrate the process. This paper shows how various simulation techniques can be used to design and specify subsystems that affect the ultimate IR signature of a vehicle. These subsystems can then be specified in detail for the construction of the platform. Once built, the platform performance relative to the contract specification can be evaluated using well defined methods with correction to reference test conditions using available simulation technologies.
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Purpose-Europe has adopted the Flight Path 2050 (FP2050) challenge demanding that by 2050, 90 per cent of the travelers are able to reach door-to-door destinations in Europe within four hours. A hypothesis can be formulated that without the Small Air Transport (SAT) system, optimized for short distances and for multiple but narrow passenger flows, this challenge cannot be met. Design/methodology/approach-This paper defines design goals and necessary research focused on small aircraft concepts, as a required condition to fulfil the FP2050 challenge "90 per cent d2d 4h". Findings-The new small aircraft concepts have been defined as SAT Aircraft Family Program. Three demonstrators with common modules could be proposed: two using the same turboprop engine (first, one engine, 9 passengers; second, two engines, 19 passengers) and third demonstrator could be with a diesel hybrid engine. Research limitations implications-The SAT Aircraft Family Program depends on demand optimized for specific regional features (passenger flows, passenger time value spectrum and infrastructure) and a set of matured technologies as a result of Clean Sky 2 (CS2) devoted to SAT. Practical implications-This practical implications consist of developing on SAT technologies in CS2, deploying the demonstrators by the small aviation industry and launching an SAT system pilot phase. Social implications-FP2050 has changed the approach to a citizen-oriented from an atomized technologies taxonomy-oriented one. The challenge "90 per cent d2d 4h" also covers the needs of remote regions. This niche could be filled by the SAT system using the small aircrafts family. Originality/value-The paper value is in defining entry requirements, answering how to build the SAT Aircraft Family Program satisfying the FP2050 challenge "90 per cent d2d 4h".
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p class="maintext">Reflected background infrared radiation is an important contributor to the aircraft total infrared radiation. A reverse Monte Carlo ray tracing method to compute the infrared radiation signature of aircraft was introduced. The impact of atmospheric and ground radiation on the long wave infrared radiation signature of aircraft at the altitude of 11 km is analysed. The flight speed is Mach 0.8. The horizontal detection directions, downward detection directions and upward detection directions are considered. The results show that in the horizontal plane, the ratio of reflected background infrared radiation to self infrared radiation is about 10 per cent in summer, and 7 per cent in winter; the ratio values distributed in the front and side of the aircraft are bigger than that in the rear; and the existence of atmospheric and ground infrared radiation makes the apparent radiance temperature of the lower part of the aircraft higher than that of the upper part of the aircraft. Defence Science Journal, Vol. 66, No. 1, January 2016, pp. 51-56, DOI: http://dx.doi.org/10.14429/dsj.66.8090 </p
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The gliders exemplify a rare subject of flight test campaigns other than standard certification trials. Therefore, not many examples of research activities may be found worldwide. Nevertheless, the gliders neither have advanced flight controls, nor cruise hypersonic, flight testing might encounter barriers to break. The paper presents one of international measurement campaigns performed within the Advanced In-Flight Measurement Techniques, the collaborative project co-funded by the European Commission, in which several optical measurement methods were developed and enhanced for various industrial flight test applications. Among flying laboratories utilized in the project, the composite training glider, considered as a test-bed, was equipped with instrumentation for two non intrusive metrologies named Image Pattern Correlation Technique and Infrared Thermography. They allow characterizing the wing behavior during flight regarding twist and bending as well as the appearance of transition between laminar and turbulent flow, respectively. The authors focused on challenges regarding a glider as a specific flight test bed for equipment preparation, with limited power supply and limited space. Finally, remarks about measurement accuracy and further applications are included.
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The remote detection of a vehicle requires that some kinds of its emissions are tracked and detected. Usually, electromagnetic emissions are used in the form of radar (electromagnetic waves in the range of radiofrequency and microwaves). Different types of antennas are used as sensors, tailored to the signal frequency band and its polarization, as well as to the target distance (higher gain antennas used for low amplitude signals). For the specific case of radars, the use of computational methods to address the electromagnetic signature (spatial pattern of the scattered energy from the object) has become widespread, given the high costs and complex equipment associated with these respective measurements. Therefore, the use of computer simulation is ideally suited for creating a realistic database of targets and its respective signatures. The same computer-created signatures database can also be used for the thermal range, enabling a complete technology solution for the signature and design of stealth vehicles, with reduced emissions.
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This paper begins with an outline of the procedure for predicting the infrared signature emissions from the airframe, engine casing, and the plume, and their attenuation by the intervening atmosphere. These emissions are contrasted against the background, to obtain the infrared signature levels. The infrared detector's - noise equivalent flux density, is proposed as an operational constraint on the flight envelope. The shift of this newly imposed constraint on the flight envelope for several engine-operating conditions, and for turbojet and turbofan engines is studied. The signature levels from the casing and plume, of a turbofan and equivalent turbojet engine, are compared at different operating points on the flight envelope. Result in the form of a polar plot of infrared signature level variation with aspect is also examined for low flying missions. The results are analysed to direct stealth design and operation.
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A two-dimensional (2D) jet flow and temperature field are simulated by using k-ε T. C. model and compared with other three nontemperature corrected models, which are standard k-ε, RNG k-ε, and SST k-ω model. Then based on the calculated results, the spectral infrared radiation characteristics within 4∼5 μm of the 2D jet flow were calculated. By comparing the computed results of the velocity, temperature field, and infrared radiation with the experimental measurements, it shows that the k-ε T. C. model predicts mean flow mixing more rapidly and the turbulent kinetic energy dissipates earlier than with no temperature correction; the k-ε T. C. model could give a good prediction for the velocity and temperature distributions on the centerline of the 2D hot gas jet, but not on the locations off the centerline. The maximum computation error of the 2D hot jet infrared radiation is decreased from 86% to 26%, and the accuracy of the computation is greatly improved.