Modern Military Aircraft Research Articles

A COMMERCIAL TURBOFAN ENGINE MODELING AND EXERGY ANALYSIS

Turbofan engines are one of the most common types of engines used in modern commercial and military aircraft due to their efficiency and performance characteristics. In this study, a thermodynamic model is generated using GasTurb 14 software for a commercial two-spool, unmixed flow, and booster turbofan engine (CFM56-5A3) used in Boeing A320-212. Besides, an exergy analysis of the modeled turbofan engine is performed. Exergy performance criteria such as exergy efficiency, exergy development potential, exergy destruction ratio, productivity lack ratio, and fuel depletion ratio are evaluated for the engine components. In addition, how bypass ratio (BPR) affects net thrust and specific fuel consumption (SFC) for the modeled turbofan engine is investigated. As a result, the net thrust and SFC values of the modeled engine and the actual engine are overlapped with 14.0% and 7.2% deviation, respectively. The maximum exergy efficiency occurs at the high-pressure turbine as 0.992. When the bypass ratio is minimum, the maximum net thrust and SFC occur as 62.24 kN and 24.08 g kN-1 s-1, respectively. High pressure turbine has the minimum exergy development potential of 1528.5 kW.

Leading-Edge Vortex Controller (LEVCON) Influence on the Aerodynamic Characteristics of a Modern Fighter Jet

The purpose of this paper is to assess the influence of a novel type of vortex creation device called the leading-edge vortex controller (LEVCON) on the aerodynamic characteristics of a fighter jet. LEVCON has become a trending term in modern military aircraft in recent years and is a continuation of an existing and widely used aerodynamic solution called the leading-edge root extension (LERX). LEVCON is designed to operate on the same principles as LERX, but its aim is to generate lift-augmenting vortices, i.e., vortex lift, at higher angles of attack than LERX. To demonstrate the methodology, a custom delta wing fighter aircraft is introduced, and details about its aerodynamic configuration are provided. The LEVCON geometry is designed and then incorporated into an existing three-dimensional (3D) model of the aircraft in question. The research is conducted using OpenFOAM 8, a high-fidelity computational fluid dynamics (CFD) open-source software. The computational cases are designed to simulate the aircraft’s flight at stall velocities within a high range of angles of attack. The results are assessed and discussed in terms of aerodynamic characteristics. A conclusion is drawn from the analysis regarding the perceived improvements in fighter jet aerodynamics. The analysis reveals that both lift and critical angle of attack can be manipulated positively. With the addition of LEVCON, the average lift gain in the high angle of attack (α) range is between 8.5% and 10%, while the peak gain reaches 19.4%. The critical angle of attack has also increased by 2°, and a flatter stall characteristic has been achieved.

Effectiveness of water spray in infrared signature suppression of engine plumes

In modern military aircraft, reducing the Infrared (IR) signature is critical for stealth. However, the IR signature from the engine plume is particularly challenging to address due to its link with engine operation and its unique, non-continuous characteristics. In this study, a novel approach using a water spray cloud to attenuate the IR signature from the engine plume was proposed, and it is experimentally verified by employing a micro-turbine engine. Six water nozzles generated the water spray cloud, and IR signature reduction was quantitatively measured using an IR spectrometer. Variations in water injection pressure and observation angles were used as experimental conditions. The results revealed that the IR signature was reduced with higher water injection pressure, attributed to the increased thickness of the water spray cloud. The IR signature from the engine plume was effectively attenuated by the water spray cloud in overall, with a more pronounced effect observed at lower observation angles due to the extended path within the cloud. The potential of water spray clouds for enhancing the IR stealth of military aircraft is underscored by this research.

Methodology for thermal calculation of the heat exchanger for cooling the air at the intake of the aerospace plane engine compressor

The tasks performed by modern military aircraft are currently expanding, as they are solved both in the air and in the aerospace, at high altitudes and at high flight speeds. However, in this case, the use of turbojet engines operation on aviation kerosene is not possible because of the high temperatures of aircraft structural elements due to aerodynamic heating that leads to the destruction of kerosene and the impossibility of using it as fuel. It is necessary to search for alternative fuel options, one of which is cryogenic fuel. This article substantiates the possibility of using cryogenic fuel, in particular hydrogen, for aerospace plane engines. Hydrogen has higher energetic qualities compared to aviation kerosene. The necessity of cooling the air before it enters the engine at high flight speeds of the aircraft has been proved. A design of the heat exchanger for cooling the air entering the compressor is proposed, and a method for its thermal calculation is developed, which is necessary when designing the structural layout of aerospace plane propulsion system.

A Dynamic Aircraft Response Model for Determining Roughness Limits

Runway roughness poses significant risks to aircraft and aircraft personnel. Roughness irregularities can be found in both civilian and military airfields, from rutting to bomb-damaged repairs. Various methods exist for determining roughness criteria, such as discrete surface deviation evaluation and dynamic response models. Although validated dynamic response models such as TAXI-G were used extensively in the HAVE BOUNCE program from the 1970s up to the late 1990s, modern military aircraft have not undergone the same formal analysis. This paper presents the mathematical formulation and validation of the WESTAX dynamic response model. The computer program is capable of simulating the responses of different critical aircraft components while trafficking over idealized runway profiles. The validation results showed that the numerical model was capable of closely matching field data over single- and double bump events. The findings suggest that the WESTAX dynamic response model is a capable candidate for establishing aircraft roughness limits.

Numerical study on adjustment of the main flow field with guide vanes in transition zone for an S-duct

A 30°/30° S-duct is often employed by a modern civil and military aircraft. Due to the vortex generators have poor control effect on the flow separation in the large curvature S-duct, so a new method adjusting the direction of the main flow in the transition zone for S-duct is proposed in the present study. These studies are carried out by solving Navier-Stokes equations with SST k-ω turbulence model. In order to explore the control mechanism of guide vanes on the flow field for S-duct, the internal flow field of S-duct with/without guide vanes is analyzed and compared in detail, including the velocity distribution on the symmetry plane, the secondary vortex intensity at different cross sections, turbulent kinetic energy on different cross sections, total pressure distribution on different cross sections, three-dimensional streamline, and so on. The results show that guide vanes can not only effectively adjust the direction of the main flow, but also restrain the flow separation, reduce the total pressure loss, and improve the uniformity of flow field.

Tehnički aspekti bezbednosti letenja vojnih vazduhoplova

Introduction/purpose: The use of modern military aircraft requires an extraordinary effort of human and material potential to ensure the conditions for the execution of specific tasks. Complex technology, different spatial and temporal conditions of aircraft use impose the need to create organizational and technical conditions to assist the pilot during flight with the aim of safely and completely accomplishing the flight task. The aim of this paper is to identify possible problems in the organization of the flight safety system through the description of the influence of technical factors on flight safety and to find the best solutions for overcoming problems during the life cycle of the aircraft. Methods: In the research of the subject area, first of all, the analysis of the regulations regulating the field of flight safety was carried out, and then a description of the technical means and their impact on flight safety was carried out. Results: On the basis of the performed analysis, the activities to ensure the reliability of the aircraft during development and production were defined, and directions for improving flight safety were proposed through the amendments of regulations, organizational and technical as well as technological measures. Conclusion: The results of the analysis confirm the assumptions about the possible directions of development and improvement of flight safety of military aircraft through improvement and installation of technical systems (devices and equipment), both aviation and ground.

Experimental simulation methodology and spatial transition of complex distortion fields in a S-shaped inlet

The S-shaped inlet of the modern military aircraft propulsion system suffers from severe inlet distortion during flight maneuvering. The complex distorted flow field is generally decomposed into total pressure and swirl distortion, both of which could substantially degrade the performance and stability of an aero-engine. In the ground test of fans and low-pressure compressors, how to simulate the complex inlet distortion occurring in flight is non-trivial. In this paper, a subsonic S-shaped inlet test rig was constructed, and eight configurations of curved-edge plate-type distortion generators were installed in the intake channel to create a complex distorted flow field downstream. Results show that the distorted flow field is dependent on the circumferential position of the blocking plate due to the duct curvature. Prominent vortex structures caused by the pressure gradient and the cross secondary flow exist between the main flow and separated flow. Conventional distortion indices DC, CDI/RDI, and the SAE AIR1419/SAE AIR 5686 standard system are implemented to represent the total pressure distortion and swirl distortion and the effects of the size and location of the curved-edge plate on distortion intensity and distribution are investigated. Additionally, this paper also studied the spatial variation of the total pressure and swirl distortion between the duct circular exit section and the annular section, termed as spatial transition characteristics. This spatial transition process can be used in the future to specify a real inlet flow condition for stability assessment of a fan or low-pressure compressor. According to the experimental results, the circumferential total pressure distortion index is approximately unaltered along the contraction duct, while the radial index reduces by 62% on average. The spatial transition of the swirl distortion differs for bilaterally symmetrical and asymmetric swirling fields. The overall swirl intensity index decays by 37%∼70% only for bilaterally symmetrical modes, while being the same for bilaterally asymmetric approximately. At last, the generation and evolution mechanism of the above complex distorted flow field is analyzed theoretically.

Injuries associated with the use of ejection seats: a systematic review, meta-analysis and the experience of the Israeli Air Force, 1990-2019

IntroductionAll modern military jet aircraft are equipped with rocket-assisted ejection systems. Jet aircraft operate in the majority of the conflict regions throughout the world, and in nearly all modern countries during peacetime. Civilian and military emergency services may be called upon to treat aircrews that have ejected and should be familiar with the common injury patterns associated with aircraft ejection. MethodsA systematic review and meta-analysis of the literature were undertaken using the preferred reporting for systematic reviews and meta-analyses (PRISMA) methodology. Peer-reviewed journal and conference papers published between 1 January 1971 and 15 June 2019 were included. Our primary outcomes of interest were mortality and major injury rates. The I2 test was used to assess heterogeneity among the included studies, and data were pooled under random effects models. In addition, all ejection cases in the Israeli Air Force (IAF) between 1990 and 2019 were studied. The data were manually extracted from the accident records and the electronic medical records system. ResultsWe identified 14 studies that included 1710 aircrew ejections. Heterogeneity was high (I2>75%). Pooled mean mortality and major injury rates were 10.5% (95% CI 6.8-14.8%) and 29.8% (95% CI 20.1-40.6%), respectively. The major injuries included spinal fractures (61.6%), extremity trauma (27.3%), and head trauma (8.9%). During the IAF study period, a total of 37 aircrew ejected from 26 IAF aircraft. The fatality rate was 5.4% and 18.9% suffered major injuries. ConclusionsAlthough ejection is lifesaving, it is associated with unique injury patterns that should be addressed during clinical evaluation. Because of their high prevalence, spinal precautions are paramount until spinal injury can be ruled out, generally by advanced imaging. Looking forward, injury patterns will continue to evolve in parallel with improving ejection seat systems.

William M Smith

As a medical student, William M Smith (“Bill”) was an enthusiastic member of the University Air Squadron and after graduation served with the Royal Air Force both at home in...

Independent Temporal Integration of ARINC653 Conformed Architecture — A Search Based Solution

ARINC653-based integrated modular avionics (IMA) architecture has been widely adopted in the design of modern civil and military aircraft. IMA imposes various requirements on the underlying operating system, of which the temporal and spatial separation requirements are essential to task allocation. In practice, finding the optimal allocation configurations of tasks to enable processing modules to satisfy various temporal constraints is one of the greatest challenges. For that purpose, hundreds of tasks must be mapped into given processing modules, which has been proven to be a nonpolynomial problem. This paper introduces a search-based approach to aid in finding effective solutions for the task allocation problem in polynomial time. Two search techniques based on both population search (genetic algorithm) and neighbor search (simulated annealing), along with their multicore versions, are presented. A heuristic is designed specifically to validate whether candidate solutions fulfill various constraints implied by IMA, and thus to evaluate the fitness. Furthermore, the multicore version is designed to reduce the time delay of obtaining a new optimized configuration. The results show that both algorithms can ultimately find optimized solutions with utility rates above 90% in all configurations and can support the optimization over 100 tasks, which is an outstanding result. The result also reveals that simulated annealing can produce a better solution under limited resources, while the genetic algorithm will determine a valid solution within a shorter time period. Moreover, simulated annealing outperforms the genetic algorithm in terms of both effectiveness and efficiency with respect to solving this allocation problem with complicated constraints.

CONCEPT OF INTEGRATED AIRBORNE SYSTEMS FOR PROVIDING AIRCRAFT OPERATIONS SAFETY, INCLUDING SYSTEMS FOR MONITORING THE FUNCTIONAL STATE OF THE OPERATOR

The development of modern civil and military aircraft is characterized by a rapid increase in the degree of functionality due to the requirements of today and the expansion of the scope of tasks to be solved. In military aviation, this feature is due to a significant expansion of the area of combat employment in terms of the enemy's active opposition, and in civil aviation, it can be explained by a large-scale implementation of technical means of flight control automation and landing under the conditions of high flights traffic in urban areas. In this regard, there was a fundamentally important transition from the separate design of airframes and components to the design of aircraft systems (AS) which represent a single complex system that solves many interdependent and interrelated tasks. Of course, such systems need technical diagnostics, real-time performance testing, and forecasting the remaining resource. This paper presents and describes the main scientific and technical ways to develop and create integrated airborne systems for providing flight safety of aircraft, including systems for monitoring the functional state of the pilot. The article considers the main methods and means for diagnostics and prognostics of the technical condition of an airframe and the critical units of aircraft. Their comparative analysis is carried out and a block diagram of an integrated diagnostic system is proposed. The essence of this system is to implement the procedure for accumulating flight data on the parameters of critical components and units on board aircraft and using a rapid-analysis method that involves monitoring the dynamics of changes in the trend of the controlled parameters in relation to limit values in real-time mode.

CRITERIA AND APPROACHES FOR ASSESSMENT OF THE USE OF AIRSPACE OF THE MEMBER STATES OF EUROCONTROL BY MILITARY AIRCRAFTS

Sustainable development of civil aviation is associated with the end of the block confrontation between East and West, which is directly related to the reduced use of military aviation. The modern military aircrafts are engaged in international air traffic in strict compliance with the requirements of each member state of the EU and Eurocontrol. Ensuring enough freedom to fly through the airspace of European countries depends on the equipment of the military aircrafts, the available military air traffic management infrastructure, the adopted rules and procedures for flight operations, and the training of the pilot and navigational staff. By providing adequate freedom to use airspace creates prerequisites for successful implementation of tasks in overcoming the consequences of disasters, accidents and catastrophes.With the use of area navigation and implementation of new airspace structures was put into action the concept proposed by Eurocontrol - the Concept of Flexible Use of Airspace (FUA). Combined with facilitating access to the aeronautical information of member states of Eurocontrol, opportunities are being created to conduct research into the use of airspace by military aircrafts. Through comparative study may identify best practices to inspire the creation of conditions for improving the interaction between civil air traffic service units and controlling military units in coordinating the use of airspace by military aircrafts.This study proposes criteria and approaches to assess the possibilities of using the airspace of member states of Eurocontrol by military aircrafts. Based on the results obtained, recommendations can be made to improve the legislation in determining the conditions for use of the national airspace by military aircrafts. The analysis stands conclusion that there are conditions to improve the possibilities of using the airspace of Bulgaria by military aircraft.

Computational Analysis of Straight Nozzle: Technical Note

Most of the modern aircraft and military aircraft are powered by the modern gas turbine engine. They have nozzles to produce the required speed. Depending upon the required exit Mach number, a nozzle can be designed to be used for subsonic and supersonic flows. For the sonic flows, the convergent nozzle is used and for supersonic flows a convergent–divergent (CD) nozzle is used. In a CD nozzle, a straight nozzle flow is accelerated from low subsonic to sonic velocity at the throat and further expanded to supersonic velocities at the exit. This paper focuses on designing a straight nozzle to attain super-sonic flow and optimizing it to achieve maximum thrust without flow separation due to shock waves. This research also confirms that at which angle of deflection on the divergent portion produces more speed. The flow conditions were selected in view of the pressure, temperature and gases that are accessible at the exit of the combustion chamber. At the exit of the nozzle, the shock induced flow separation due to, over, under and optimum expansion conditions were studied.

English

English

Electrochemical Corrosion of the Stainless Steel 15-5PH and 17-4PH Passivation in Citric Acid

Corrosion, the product of the oxidation-reduction reactions of a metallic material with its environment, generates in modern military aircraft manufactured mainly with titanium and stainless steels: deterioration, maintenance and even impact on safety. Within the methods of protection against corrosion are the coatings. The passivation is a conversion coating for stainless steels to increase the surface oxide layer that reduces the effects of corrosion. The objective of this work is to study the formation of a passive layer in steels 15-5 and 17-4PH using the electrochemical technique of potentiodynamic polarization curves (PPC), using as a passivating agent citric acid at a temperature of 25 ° C with a time of immersion of 30, 60 and 90 min and exposed in a sodium chloride medium. The passive layer was evaluated by the technique of X-ray photoelectron spectroscopy (XPS). The results obtained by PPC indicate a mixed activation control for both steels. Passive layers with corrosion current density (Icorr) of the order of 10-5mA / cm2 for 15-5PH while for the 17-4PH the passive layer presents Icorr 10-4mA / cm2 at a time immersion of 30min. The corrosion kinetics indicates a passivation mechanism for the 15-5PH steel while for the 17-4PH passivation-pseudopassivation, which indicates less stable passive layers for the latter steel. The XPS technique allows to define passive layers of up to 12.5nm, constituted by Cr2O3.

Experimental and Modeling Studies of Heat Transfer, Fluid Dynamics, and Autoxidation Chemistry in the Jet Fuel Thermal Oxidation Tester (JFTOT)

Modern military aircraft use jet fuel as a coolant before it is burned in the combustor. Prior to combustion, dissolved O2 and trace heteroatomic species react with the heated fuel to form insoluble particles and surface deposits that can impair engine performance. For safe aircraft operation, it is important to minimize jet fuel oxidation and resultant surface deposition in critical fuel system components. ASTM D3241, “Standard Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels” (ASTM International: West Conshohocken, PA, 2014), defines the standard test method for evaluation of the thermal oxidation stability of aviation turbine fuels. The JFTOT is a thermal stability test that measures the tendency for fuel to form deposits via heated tube discoloration and/or an increased pressure drop across an outlet filter. It is used to discriminate between fuels of poor and acceptable thermal stability. However, the fluid dynamics, heat transfer characteristics, extent of oxidation, and corresp...

Significance of Geometric Nonlinearity in the Design of Thermally Loaded Structures

In reality, all structures exhibit some degree of nonlinearity; however, in many cases, its effects are negligible to the overall structural response and it is common to treat them as such in analysis and design optimization. Due in large part to this practice, severe consequences and structural failures may arise when this nonlinearity cannot be neglected. Currently, this occurs with increasing frequency as designers continue to explore innovative aircraft concepts that push the limits of existing design tools and industry standards. In this research, such a case is investigated where geometrically nonlinear effects result from an elevated temperature environment. The thermoelastic response of characteristic aerospace structures is investigated by comparison of linear and nonlinear analysis results. Results indicate that geometric nonlinearity, which manifests as stress stiffening behavior and deformation-dependent load contributions, plays a significant factor in properly predicting the structural response for structures found in modern military aircraft with embedded engines. In addition, parametric studies present the influence of geometry parameters and boundary fixivity, or how components are attached to adjoining structures, on the nonlinearity in order to identify features that make it critical. Based on these observations, some guidelines regarding when geometric nonlinearity should be included in the structural analysis of thermally loaded structures are provided. These guidelines are useful to the structural analyst or designer faced with the analysis of components in a thermal environment due to engine heat, aerodynamic effects, or other sources.

Acoustic measurements of models of military style supersonic nozzle jets

Modern military aircraft jet engines are designed with variable-geometry nozzles to provide optimal thrust in different operating conditions, depending on the flight envelope. However, acoustic measurements for such nozzles are scarce, due to the cost involved in making full-scale measurements and the lack of details about the exact geometries of these nozzles. Thus the present effort at Pennsylvania State University (PSU) in partnership with GE Aviation and the NASA Glenn Research Center is aiming to study and characterize the acoustic field produced by supersonic jets issuing from converging-diverging military style nozzles, and to identify and test promising noise reduction techniques. An equally important objective is to develop methodology for using data obtained from small- and moderate-scale experiments to reliably predict the full-scale engine noise. The experimental results presented show reasonable agreement between small-scale and medium-scale jets, as well as between heated jets and heat-simulated ones.

Statistical modelling for prediction of axis-switching in rectangular jets

Rectangular nozzles are increasingly used for modern military aircraft propulsion installations, including the roll nozzles on the F-35B vertical/short take-off and landing strike fighter. A peculiar phenomenon known as axis-switching is generally observed in such non-axisymmetric nozzle flows during which the jet spreads faster along the minor axis compared to the major axis. This might affect the under-wing stores and aircraft structure. A computational fluid dynamics study was performed to understand the effects of changing the upstream nozzle geometry on a rectangular free jet. A method is proposed, involving the formulation of an equation based upon a statistical model for a rectangular nozzle with an exit aspect ratio ( AR e) of 4; the variables under consideration (for a constant nozzle pressure ratio ( NPR)) being inlet aspect ratio ( AR i) and length of the contraction section. The jet development was characterised using two parameters: location of the cross-over point ( X c) and the difference in the jet half-velocity widths along the major and minor axes (Δ B30). Based on the observed results, two statistical models were formulated for the prediction of axis-switching; the first model gives the location of the cross-over point, while the second model indicates the occurrence of axis-switching for the given configuration.