Actual Flight Conditions Research Articles

Numerical Study on Heat Transfer and Thermal–Mechanical Performance of Actively Cooled Channel of All-Movable Rudder under Supercritical Pressure

The utilization of an actively cooled thermal protection system is widely recognized as an effective approach to decrease the temperature of components exposed to severe aerodynamic heating. In this study, two cooling schemes with different flow paths and structural configurations were proposed, and six cooling channel designs were developed by modifying the leading-edge details. A numerical analysis on the heat transfer and thermal–mechanical performance was conducted under actual flight conditions (30 km altitude, Mach 8). The results highlight an optimal design scheme that balances temperature control and minimized coolant flow rates. The channel flow field demonstrated its superiority by effective convective heat transfer and improved fluid mixing facilitated through recirculation zones and turbulence at the bends. Structural assessments showed that the optimal scheme not only provided better cooling but also preserved the structural integrity. Overall, the study offers a practical and effective thermal protection approach for air rudders subjected to severe heat.

Enhancing pilot vigilance assessment: The role of flight data and continuous performance test in detecting random attention loss in short IFR flights

Situational awareness (SA) and fatigue management are crucial aspects of aviation safety, particularly during demanding flight phases. This study introduces an innovative approach employing flight data, machine learning, and Continuous Performance Test (CPT) metrics to predict pilot performance and SA during instrument approaches under Instrument Meteorological Conditions (IMC). Data were collected from over 10 pilots across more than 40 flights in a high-fidelity Cessna 172 analog flight simulator.Significant correlations were observed between dynamic cognitive performance parameters and the exceedance shape factor, a novel measure of pilot sustained attention introduced in this research. Key variables identified through correlation analysis included variability, interstimulus change, and reaction time standard deviation.Importantly, commission scores and reaction time standard deviation emerged as key predictors in the machine learning model, specifically the Optimizable Gaussian Process Regression (GPR) model with a radial basis function kernel. The model achieved a validation R-squared of 0.90 and a test R-squared of 0.70. These systems could incorporate additional data sources, such as eye-tracking and scan pattern analysis, for a better assessment of pilot SA and fatigue levels. While post-flight measurements are inherently reactive, they are effective for monitoring the degradation of pilot CPT scores after each leg of high-frequency, short-duration flights.Notable limitations include the need to understand individual cognitive differences among pilots, such as age, experience, and cognitive style. The predictive model also requires validation in actual flight conditions to determine its ecological validity. Future research should aim to address these limitations, generalize the findings, and integrate CPT data with other sensor inputs to provide a more comprehensive understanding of pilot performance.

Detection of Pilot's Mental Workload Using a Wireless EEG Headset in Airfield Traffic Pattern Tasks.

Elevated mental workload (MWL) experienced by pilots can result in increased reaction times or incorrect actions, potentially compromising flight safety. This study aims to develop a functional system to assist administrators in identifying and detecting pilots' real-time MWL and evaluate its effectiveness using designed airfield traffic pattern tasks within a realistic flight simulator. The perceived MWL in various situations was assessed and labeled using NASA Task Load Index (NASA-TLX) scores. Physiological features were then extracted using a fast Fourier transformation with 2-s sliding time windows. Feature selection was conducted by comparing the results of the Kruskal-Wallis (K-W) test and Sequential Forward Floating Selection (SFFS). The results proved that the optimal input was all PSD features. Moreover, the study analyzed the effects of electroencephalography (EEG) features from distinct brain regions and PSD changes across different MWL levels to further assess the proposed system's performance. A 10-fold cross-validation was performed on six classifiers, and the optimal accuracy of 87.57% was attained using a multi-class K-Nearest Neighbor (KNN) classifier for classifying different MWL levels. The findings indicate that the wireless headset-based system is reliable and feasible. Consequently, numerous wireless EEG device-based systems can be developed for application in diverse real-driving scenarios. Additionally, the current system contributes to future research on actual flight conditions.

Combustion characteristics of a supersonic combustor model for a JAXA flight experiment

JAXA is conducting a flight-ground test comparison program to clarify the “facility effect” on hypersonic aerodynamics and combustion phenomena and to develop a CFD tool for predicting flight data from ground test data. The aim is a flight experiment to obtain data on aerodynamic heating and supersonic combustion under actual flight conditions and to validate the CFD tool using flight data and the corresponding ground test data. This study aimed at determining a flow-path geometry and a fuel injector configuration for a supersonic combustor suitable for clarifying the influence of the different test flow compositions between flight and ground test conditions on combustion. The candidate configurations proposed by the CFD study were evaluated by direct-connect combustion tests using ethylene fuel. The results showed that a combustor flow was symmetric when the fuel equivalence ratio was low and asymmetric when the equivalence ratio and the pressure in the combustor were high. Because an asymmetric flow is unsuitable for validating CFD based on steady RANS, the total equivalence ratio was limited to 0.44. The combustor model uses two-stage fuel injectors and cavity flame holders to combust ethylene fuel. The depth of the cavity flame holder had little influence on combustion. However, the number of injection holes for the injector located downstream of the cavity affected the combustor pressure. The combustor flow-path design was finalized based on the combustion test results. In addition, an ethylene fuel ignition method using pilot hydrogen injection, adopted for the flight experiment, was also demonstrated successfully.

Research on operating characteristics of single-spool turbojet enginewith the afterburner AL-21F

The single-spool, single-thread, turbojet engine with afterburner AL-21F has been used on fighter aircraft for a long time, but there are few studies on this engine in Vietnam. This article uses the theoretical approach, calibrates according to the technical description and actual operation, combined with specialised software such as GasTurb and GSP to calculate engine thermodynamic parameters in some actual flight conditions. The obtained results showed that, when the flight speed increases, the specific fuel consumption increases linearly, while the initial engine thrust decreases and reaches the minimum value at M=0.3÷0.5, then continue to increase and reach the maximum at the speed limit. When increasing the height, the speed and regulating spool speed of the engine remain the same, the engine thrust decreases as well as the specific fuel consumption increases. When increasing the rotor rotation speed, the engine thrust increases linearly but the specific fuel consumption decreases gradually and remains almost the same at engine rpm above 85%. The results allowed for a better understanding of the operating process of the AL-21F engine in particular and turbojet engines in general or used to build simulation models operating close to reality.

Design and Control of a Hand-Launched Fixed-Wing Unmanned Aerial Vehicle

In order to address the flexible requirements on load, flight speed, and maneuverability in actual flight conditions, a hand-launched fixed-wing unmanned aerial vehicle (UAV) is designed with high performance in portability, lightweight, and maneuverability. On this basis, a novel system-decomposition-based robust control method is proposed to achieve a satisfactory control performance for this designed UAV under internal/external uncertainties. First, considering the feature that the coupling terms are usually small in most flight conditions and may be regarded as disturbance, the complex flight system is decomposed into a group of simple subsystems with disturbance, namely, roll–yaw subsystem, pitch–altitude subsystem, and airspeed subsystem. Since the complexity of each subsystem is much smaller than the original system, this will reduce the difficulty of the controller design and complexity of the controller. Besides, to improve the tracking performance and robustness to disturbances, an extended state observer based robust control method is proposed for each subsystem. The stability and robustness of the proposed control method are effectively demonstrated by the theoretical analysis and the actual flight experiments on the designed UAV.

Numerical Investigation of the Intercooler Performance of Aircraft Piston Engines Under the Influence of High Altitude and Cruise Mode

Abstract Multistage supercharging is an effective way to solve the problems of low volumetric efficiency and combustion deterioration of piston engines under high altitude conditions. As a critical component of the supercharger system, the high-altitude intercooler performance is challenged to meet the heavy heat load caused by the large boosting ratio. The purpose of this study was to add more knowledge on the high-altitude intercooler performance to the limited existing studies. The intercooler experimental tests were conducted in a high-altitude simulation system, allowing for simultaneous pressure and temperature reductions. A 3D computational fluid dynamics (CFD) model was developed and validated against experimental results to investigate the intercooler performance, including the heat exchange and pressure drop characteristics. The results indicated that the atmospheric conditions and cruising speed significantly affected the intercooler performance. For example, the weighting of the effects of the temperature difference and air density on heat exchange performance varied with altitude. The altitude of 11 km was the turning point of the heat transfer rate because it is the junction of the troposphere and stratosphere. Based on this finding, this study further investigated whether a higher cruise speed could compensate for heat transfer deterioration with increasing altitude, more consistent with actual flight conditions. The simulation results showed that the variation of cruise speed directly affected the effectiveness of the heat exchanger, resulting in a different trend with altitude. Furthermore, the heat exchange of the intercooler fluctuated less with altitude under variable speed conditions. Overall, these findings support more fundamental research on high-altitude intercoolers, which may benefit the design and optimization of high-altitude engines and turbocharged systems.

Numerical Assessment of Camphor Ablation Flight Relevance in Hypersonic Wind-Tunnel Testing

Designing thermal protection systems (TPS) for ballistic reentry capsules requires both reliable numerical tools and experimental facilities to evaluate surface ablation and its shape change. Low-temperature ablators, such as camphor, can be employed in low-enthalpy wind tunnels to overcome limitations of standard hypersonic experimental facilities, which cannot induce the actual TPS ablation due to limits in inflow total enthalpy, velocity, or test time duration. However, the flight relevance of such an experiment needs to be accurately assessed, as both the capsule dimension and the ablative material during the test differ from the flying ones. The main goal of this work is to perform numerical simulations in order to assess the flight relevance of the ground tests. Computational fluid dynamics (CFD) simulations have been performed for both low-enthalpy wind-tunnel conditions for a camphor scaled-down capsule and actual reentry flight conditions, assuming a carbon-based heat shield. Moreover, numerical analyses have been improved by coupling the CFD solver with a material response code named PATO, which models the heating transient process. The obtained results show how the CFD/material response coupling has a more important effect for the on-ground testing conditions considered, resulting in a more favorable agreement with the available experimental data. Finally, the shape change relevance of the analyzed low-temperature ablator has been verified by providing a similitude criterion between the on-ground and in-flight capsule recession. In particular, a few seconds of exposure are sufficient to generate the same shape change that is expected in flight.

Improving the Methods of Assessing the Quality of Aircrew Piloting Technique

The article presents aircraft flight data in the landing approach mode, which was obtained on an integrated flight simulator and in actual flight conditions, processed by various probabilistic-statistical methods. These data were used to assess the quality of flight crew piloting techniques. We have reviewed the methods based on the Neyman–Pearson criterion, and the optimal Bayesian criterion is considered. When using them, we revealed the presence of a deterministic sinusoidal component in the flight parameters. We also used the method of analyzing autocorrelation functions and the method of analyzing the spectra of flight parameters of normalized and unnormalized autocorrelation functions. In a comparative analysis of these methods, we have shown that the most informative approach is the analysis of the spectra of flight parameters of normalized and unnormalized autocorrelation functions. This paper shows that the successful completion of the landing stage largely depends on the accuracy of the aircraft entry to the glidepath intercept point.

Quadcopter Precision Landing on Moving Targets via Disturbance Observer-Based Controller and Autonomous Landing Planner

Unmanned aerial vehicles, especially quadcopters, play key roles in many real-world applications and the related quadcopter autonomous control algorithms have attracted a great deal of attention. In this paper, we address the vision-based autonomous landing problem of a quadcopter on a ground moving target. Firstly, we propose a disturbance observer-based control algorithm, consisting of a nonlinear disturbance observer and robust altitude and attitude controllers. This algorithm is based on the quadcopter dynamics model, and its stability is strictly proved using Lyapunov’s theory. Secondly, we develop an autonomous landing planner which we test for various landing scenarios to deliver improved reliability and accuracy of the landing mission. These theoretical studies are complemented by a numerical feasibility study, before demonstrating the effectiveness of our approach under actual flight conditions with an experimental quadcopter platform.

Effect of Componential Camouflage on Aircraft's IR Multiband Susceptibility

Aircraft's infrared (IR) signature modeling considering thermal-flow characteristics and emissivity control for IR camouflage have been recently studied. However, there are few studies trying to analyze the camouflage effect by applying IR camouflage material to the aircraft surface based on the surface temperature distributions or to find suitable surfaces for effective camouflage. In this study, we describe the effect of componential signature reduction on aircraft's susceptibility to IR-guided missiles considering multiband detection. We analyzed the thermal-fluid characteristics of aircraft using coupled simulations of computational fluid dynamics with a conduction and radiation solver. We calculated IR signature levels from the surface temperature distribution in the mid-wavelength (3–5 μm) and long-wavelength (8–12 μm) bands for the multiband susceptibility analysis. Based on the surface temperature distribution and IR signature level, the aircraft surface was classified according to surface temperature and heating cause. Consequently, we determined that the zone highly heated by the external flow or plume has the dominant impact on the IR signature. We expect that this study will be helpful for advancing and realizing IR camouflage in actual flight conditions.

UAV Recognition Based on Micro-Doppler Dynamic Attribute-Guided Augmentation Algorithm

A micro-Doppler signature (m-DS) based on the rotation of drone blades is an effective way to detect and identify small drones. Deep-learning-based recognition algorithms can achieve higher recognition performance, but they needs a large amount of sample data to train models. In addition to the hovering state, the signal samples of small unmanned aerial vehicles (UAVs) should also include flight dynamics, such as vertical, pitch, forward and backward, roll, lateral, and yaw. However, it is difficult to collect all dynamic UAV signal samples under actual flight conditions, and these dynamic flight characteristics will lead to the deviation of the original features, thus affecting the performance of the recognizer. In this paper, we propose a small UAV m-DS recognition algorithm based on dynamic feature enhancement. We extract the combined principal component analysis and discrete wavelet transform (PCA-DWT) time–frequency characteristics and texture features of the UAV’s micro-Doppler signal and use a dynamic attribute-guided augmentation (DAGA) algorithm to expand the feature domain for model training to achieve an adaptive, accurate, and efficient multiclass recognition model in complex environments. After the training model is stable, the average recognition accuracy rate can reach 98% during dynamic flight.

System design and experimental verification of an internal insulation panel system for large-scale cryogenic wind tunnel

With the rapid development of aerodynamics for high speed aircraft, the flight experiments need to be carried out under ultra-high Reynolds number condition to simulate actual high-speed flight conditions, which puts forward higher requirements for the wind tunnel. Reynolds number increases rapidly as the decrease of the flow temperature because the viscosity of the working gas decreases and the density increases. As a result, a pressurized tunnel at cryogenic temperature can provide real-flight Reynolds numbers. Therefore, cryogenic wind tunnel is one of the best testing facilities to rech ultra-high Reynolds number. The thermal insulation system is crucial for the design and operation of the cryogenic wind tunnel. In this paper, the features of an internal insulation system for the cryogenic wind tunnel are firstly highlighted in comparison with traditional insulation systems. The internal thermal insulation system for the cryogenic wind tunnel is discussed. In order to evaluate the thermal insulation performance, the heat transfer calculation for a typical wind tunnel region with the diameter of two meters is carried out using finite element method based on the analyses of the heat transfer conditions. The averaged heat load from the environment is obtained to optimize the liquid nitrogen consumption during the wind tunnel operation. The thickness of the panel should be 150 mm to reach the design target of averaged heat flux 60 W/m2. Meanwhile, the typical region is constructed according to the new internal insulation system. Cryogenic test is conducted and it is proven that the new internal insulation system could efficiently prevent the environment heat flow and ensure the normal operation of the cryogenic wind tunnel.

Thermal performance affected by the mesoscopic characteristics of the ceramic matrix composite for hypersonic vehicle

The rigorous thermal environment brought by long-time high-speed flight is imposed severe requirements on the structural bearing capacity and structural thermal safety of the aircraft. The integrated non-ablative thermal protection system based on continuous fiber-reinforced ceramic matrix composites is becoming a hot spot on the design of aircraft structures. However, the multi-scale, non-linear, non-uniform features of such materials, as well as complex thermal and mechanical characteristics, pose serious challenges to structural design and evaluation. Under the aero heating environment, the non-uniform temperature rising and thermal matching between different components in the continuous fiber-reinforced ceramic matrix composites are extremely complicated, which has a significant influence on the thermal safety performance of the structure. In this paper, based on the commonly used 3D orthogonal weaving process and the thermal characteristics prediction method of fiber bundles considering the effect of PyC interface layer, the fluid-structural strong thermal coupling characteristics of different woven parameters in typical aircraft structure is carried out. Quantitatively characterizing the heat transfer characteristics of this new material under the actual flight condition of the aircraft can further to improve the accuracy of the thermal property parameters obtained based on the ground test. The analysis results show that increasing the proportion of fiber bundles in a certain direction is the most effective method to increase the thermal conductivity in this direction. At the same time, the arrangement of the coupling yarns will also have a greatly influence on the thermal conductivity of the material. These results is of great significance for the design of the materials.

Influences of accelerating states on supercritical n-decane heat transfer in a horizontal tube applied for scramjet engine cooling

Supercritical n-decane is applied in the regenerative cooling system of scramjet engines while scramjets are always in various irregular movements. With the desire to explore heat transfer performance of supercritical n-decane under actual flight conditions, numerical simulations and analysis of different states during the accelerated flight process are carried out under three different heat fluxes and eight varying acceleration states. Specific flow and heat transfer mechanisms are explored by analyzing the temperature and flow fields affected by acceleration. Results show that acceleration weakens the intensity of the first abnormal heat transfer state but does not affect its appearance location, and there are almost no effects on the second heat transfer state. Another important conclusion is that the external factors have a great influence on supercritical n-decane heat transfer. The overall average surface heat transfer coefficient could be even up to 27.5% higher than for an ordinary horizontal tube. It is indicated that more attention should be paid to the external factors when investigating supercritical flow and heat transfer in the research and development of scramjet engine cooling.

Transient Performance Analysis of an Aero Gas Turbine Cooled Cooling Air Heat Exchanger

Abstract Aviation faces several challenges to maintain growth while adapting to an environmentally viable footprint. Increasing efficiency, which in the past induced a steady rise in the turbine entry temperatures, requires successful cooling of critical components to relieve the combined effects of higher temperatures and pressures. Starting with a conceptual design that alters the flow path of the secondary air system to divert bled air into a heat exchanger, this research focuses on assessing the effects of actual flight conditions on a cooled cooling air (CCA) system. In particular, the study undertakes a transient analysis of the CCA heat exchanger under a stressful temperature increase. The performance of the unit from idle to max take off (MTO) conditions required a unique facility for experimental testing, also capable of reaching and sustaining the necessary specifications. The novelty of the concept compelled the development of numerical models to aid the design and evaluation of the experiment. These models use one- and three-dimensional techniques to perform preemptive analysis of the test range, to ensure safety during the actual test, and to provide valuable information about the facility system and the inner flow structure of the heat exchanger. The study completed successful experiments using numerically generated procedures. A back-to-back configuration, representative of multiple installations, offers evidence about the cross-influence of each heat exchanger. The research also examined the dynamic effects to provide the bases for further studies focusing on this topic.

Experimental investigation of pressure drop of feeding pipes of liquid oxygen in a five-way distribution cavity under different working states

The uniform distribution of liquid oxygen is essential for design of feeding system in multi-engines of cryogenic rockets. Aiming at a cryogenic launch vehicle with four engines in parallel, a five-way spherical cavity structure was used to evenly distribute liquid oxygen in the multi-branch pipes. These cryogenic rocket engines need to be controlled by opening or closing states for multi-branch pipes to adapt different flight conditions. To study effect of working states on pressure drop in the four branch pipes with the five-way spherical cavity, a large-scale test system was constructed to carry out discharging flow of liquid oxygen. The feeding pipes of full-scale model were adopted, and forty-nine sensors were arranged in the pipes to measure pressure and temperature of liquid oxygen. The constant discharging flow was maintained by a feedback system of tank pressure. The opening or closing states of branch pipes were controlled by cut-off valves at the end of each branch pipe. The liquid oxygen tests were carried out under different actual flight conditions. The results shown that the opening or closing states for four branch pipes had a dramatic effect on the pressure drop in the multi-branch pipes. When the branch pipes all drained at the same time, there was a large pressure drop in two symmetrical branch pipes which enhanced linearly with the increase of Reynolds number. The pressure drop of two branch pipes on the symmetrical sides could exceed 0.1 MPa which was far greater than the normal flow resistance, when the Reynolds number was 5.0 × 106. It was found that there was a regular swirling flow formed in the five-way spherical cavity by using CFD method. When two branch pipes were turned off, whether symmetrical sides or adjacent sides, the large pressure drop still existed, and was positively correlated with the varying Reynolds number. The maximum pressure drop in the branch pipes was close to 0.09 MPa, when the Reynolds number was 3.3 × 106. When three branch pipes were closed, the large pressure drop disappeared, and the flow resistance related positively with the Reynolds number, which accorded with the normal flow resistance. Moreover, according to data of six hot test runs and two verification tests, it was found that the inlet pressure in the main pipe had greatly influence on the pressure drop, which raised sharply as the inlet pressure increased. These results could help to provide a design reference for feeding system of multi-engines in cryogenic rockets.

Analysis of Nonlinear Transient Energy Effect on Thermoelectric Energy Storage Structure.

In complex flight conditions, due to the large amount of unusable heat generated by aerodynamic heating, the thermal protection system of an aircraft needs to withstand a large temperature shock, which brings great challenges to the design of the structure. In order to effectively utilize the irregular aerodynamic heat, and improve structural heat conduction, a composite structure is formed by using phase change energy storage materials on the basis of the thermoelectric structure, which transforms the aerodynamic waste heat into stable electric energy for the internal system. Through the study of the response of nonlinear transient energy, it is found that the thermoelectric and mechanical properties of the new structure can be improved by adding phase change energy storage materials. Under actual flight conditions, the new structure can reduce the maximum temperature by 180 K and the maximum thermal stress by 110 Mpa. The mechanical properties of the structure are effectively improved, the service life of the structure is prolonged, and the waste heat can be converted into stable electrical energy output to improve the thermoelectric output performance. On the premise of ensuring conversion efficiency, the output power of the new structure has been improved by 64.8% through structural optimization under actual flight conditions.

Cognitive Workload Analysis of Fighter Aircraft Pilots in Flight Simulator Environment

Maintaining and balancing an optimal level of workload is essential for completing the task productively. Fighter aircraft is one such example, where the pilot is loaded heavily both physically (due to G manoeuvering) and cognitively (handling multiple sensors, perceiving, processing and multi-tasking including communications and handling weapons) to fulfill the combat mission requirements. This cognitive demand needs to be analysed to understand the workload of fighter pilot. Objective of this study is to analyse dynamic workload of fighter pilots in a realistic high-fidelity flight simulator environment during different flying workload conditions. The various workload conditions are (a) normal visibility, (b) low visibility, (c) normal visibility with secondary task, and (d) low visibility with secondary task. Though, pilot’s flying performance score was good, the physiological measure like heart rate variability (HRV) features and subjective assessment (NASA-TLX) components are found to be statistically significant (p<0.05) between tasks. HRV features such as SD2, SDNN, VLF and total power are found to be significant at all task load conditions. The features LFnu and HFnu are able to differentiate the effect of low visibility and secondary cognitive task, which was imposed as increased task in this study. This result benefits to understand the pilot’s task and performance at each flying phase and their cognitive demands during dynamic workload using HRV, which could assist pilot’s training schedule in optimal way on simulators as well as in actual flight conditions.

Air Pollutant Emission Inventory from LTO Cycles of Aircraft in the Beijing-Tianjin-Hebei Airport Group, China

Based on the International Civil Aviation Organization's standard emission model, this survey collected the actual flight conditions of the nine airports in the Beijing-Tianjin-Hebei airport group, fully considered the impact of the height of the atmospheric mixed layer, and revised the operating time using the US Environmental Protection Agency method to accurately estimate the 2018-2019 shipping season (364 days) landing and take-off cycle (LTO) air pollutant emissions list for Beijing-Tianjin-Hebei airport group aircraft. The results show that the total emissions of NOx, CO, SO2, HC, and PM in the LTO cycle of the Beijing-Tianjin-Hebei airport group in the 2018-2019 season are 10720.5, 3972.2, 407.8, 508.0, and 53.7 t, respectively. Within these, the winter and spring season emissions are 4290.2, 1646.7, 168.3, 220.1, and 22.4 t, respectively; and the summer and autumn season emissions are 6430.3, 2325.5, 239.5, 287.9, and 31.3 t, respectively. From the perspective of spatial distribution, Beijing Capital Airport is the airport in the group with the largest amount of air pollutants discharged. Regarding time distribution, the highest peak is at 07:00-08:00, there is a medium-high emission level from 12:00-20:00, and the emissions are relatively low after 21:00. The aircraft emit more NOx and CO in the LTO cycle, with PM accounting for the least amount of emissions. The discharges of different pollutants under different working modes are significantly different. Of all the aircraft in the airport group, the B777 unit LTO discharges the most pollutants, that of the B737 is the least, and the B787 unit LTO circulation HC is the lowest.