High Flight Research Articles

Simulation Test of The Aerodynamic Environment of A Missile-Borne Pulsed Laser Forward Detection System at High Flight Speed

When a missile-borne pulsed laser forward detection system flies at supersonic speed, the laser beam will be distorted by the uneven outflow field, resulting in a significant reduction in ranging accuracy. In this paper, the impact of high flight speed on a pulsed laser detection system is studied. First, a new ray tracing method with adaptive step size adjustment is proposed, which greatly improves the computational efficiency. Second, the aerodynamic environment of a munition flying at high speed is simulated by an intermittent transonic and supersonic wind tunnel to obtain the schlieren data of the flow field at various Mach numbers. The schlieren data present a shock wave structure similar to that of the simulation. In addition, the variation patterns of the pulsed laser echo waveform of the model under different aerodynamic conditions are studied to evaluate the detectability and operational stability of the laser detection system under static conditions. The test results match the simulation results well, and the two offer relatively consistent shock wave structures, which verifies the correctness and effectiveness of the flow field simulation model. The test echo waveforms are in good agreement with the simulated echo waveforms; the relative errors between the peak values of test and simulated echo waveforms at various Mach numbers do not exceed 20%, and the correlation coefficients between the test and simulated echo waveforms all exceed 0.7, indicating high correlations between the two.

Matlab sımulatıon of quadcopter dynamıcs and PID attıtude controller

Due to the ever-growing popularity of quadcopters, they are used in various fields such as surveillance, military, surveillance and courier services and are of great importance. Ideal handling of quadcopters is essential for safe maneuvering and high precision flight performance. This research provides simulation of quadcopter control in MATLAB software, development and review of various control principles.
 Dynamic development in unmanned aerial vehicles (UAVs) has led to the rapid spread of quadcopters in many fields, from airspace control to courier services. This research study investigates the Proportional-Integral-Derivative (PID) attitude controller by simulating the quadcopter dynamic object in MATLAB software. The heart of this research is to create and develop a PID attitude controller, which is a critical component for accurate control of quadcopter.

Experimental study of the fuel spray and ignition characteristics in an aeroengine afterburner under subatmospheric pressure

The fuel atomization and ignition characteristics of an afterburner under subatmospheric pressure are important foundations for expanding the operating range of the afterburner at high flight altitudes. In this work, the lean ignition limits of the afterburner at subatmospheric pressure were obtained through experiments, and the fuel droplet size distribution and ignition process in the afterburner were acquired using a laser particle sizer and a high-speed camera. The results showed that the ignition equivalence ratio increased as the inlet pressure decreased and was lowest when the flame stabilizer blockage ratio was 0.3. When the inlet pressure of the combustor decreased from high pressure to subatmospheric pressure, the Sauter mean diameter (SMD) range of the fuel droplets increased from 60∼110 μm to 100∼190 μm due to the increase in the ignition equivalence ratio and the deterioration of the fuel atomization characteristics. Under subatmospheric pressure, the flame residence phase time in the ignition process decreases significantly, while the flame intensity fluctuates more dramatically during the flame growth phase due to the decrease in the equivalence ratio of the gaseous phase, the larger fuel droplet size, and the uneven fuel distribution. When the inlet pressure is high pressure, the flame propagates from the ignition position to the trailing edge of the flame stabilizer first and anchors within the shear layer behind the flame stabilizer, whereas under subatmospheric pressure, the flame does not propagate to the anchoring point in the first place, which is one reason for the difficulty of ignition of combustors under high-altitude conditions.

Thermodynamic analysis of a high Mach number scramjet engine with secondary combustion for thrust enhancement

Intending to augment the thrust of air-breathing vehicles operating at high flight Mach numbers, especially under extreme flight conditions, this study introduced a pioneering methodology predicated on secondary combustion. This innovative scheme uses the product of combustion of hydrocarbon fuel and air to further react with metal fuel to obtain thrust gain. This study was mainly based on theoretical calculation. A preliminary parametric design and performance analysis of a Mach 8 scramjet engine with an afterburner was carried out based on the thermodynamic cycle analysis method, considering the gas component changes. The engine model design with an inward two-dimensional inlet was adopted, along with an oblique injection of hydrocarbon fuel and two combustors in series. In addition, the expansion of gas in a supersonic nozzle was modeled with quasi-one-dimensional flow equations. By maintaining an equivalence ratio of 1.0 for the hydrocarbon fuel in the primary combustor, meticulous exploration of the powder-to-gas ratio in the afterburner, ranging from 0.04 to 0.2, was conducted. Similarly, an investigation into the temperature ratio at the outlet of the inlet, spanning the range of 3.8 to 7, was performed. Through a judicious optimization process involving both the inlet compression temperature ratio and the magnesium powder's powder-to-gas ratio, the engine designed can obtain a maximum thrust gain of 57.3%. The analysis underscores the advantageous correlation between heightened powder-to-gas ratios and augmented thrust production. Setting the upper limit of the powder-gas ratio to 0.16 is recommended to maintain optimal performance. This research also provided a new idea for expanding the application of hydrocarbon fuels in higher flight Mach number scramjet engines.

Cold storage alters the fat-trehalose trade-off, decreases the flight ability, and maintains the high survival rate and flight speed of Osmia excavata (Hymenoptera: Megachilidae).

Osmia solitary bees are important pollinators of various crops worldwide. Refrigeration has been widely used to synchronize the emergence time of Osmia species from cocoons with the blooming time of different crops, but the fitness of Osmia after refrigeration remains unknown. Here, the effects of long-term refrigeration at 0°C on the vitality, flight ability, and metabolism of Osmia excavata, which is known as the "king of pollination" in China, were studied. The survival rate (>90% before 120d), weight loss rate (<15% after 170d), and mean flight speed of O.excavata were not greatly affected after long-term refrigeration. The content of fats, which have antifreeze and energy storage properties, was not significantly altered in O.excavata before 130d of refrigeration, which might explain why the survival rates and flight speed of O.excavata remained high after long-term refrigeration. However, the flight duration and distance decreased significantly (P<0.05), and both were positively correlated with the reduced trehalose levels in O.excavata (r=[+0.69]-[+0.71]; P<0.05). Overall, these findings indicate that the pollination potential of O.excavata for various crops with different flowering periods is high after long-term refrigeration; however, long-term refrigeration may decrease pollination efficiency. Our findings highlight new research directions that could improve the ecological service function of refrigerated O.excavata.

No Signs of Adaptations for High Flight Intensity in the Mitochondrial Genome of Birds.

Mitochondrial genomes are expected to show adaptations for optimizing aerobic respiration in birds that make intense use of flight. However, there is limited empirical evidence of such a relationship. We here examine correlates of several mitochondrial genome characteristics and flight use across a diverse sample of 597 bird species. We developed an index of flight use intensity that ranged from 0 in flightless species to 9 in migratory hummingbirds and examined its association with nucleobase composition, amino acid class composition, and amino acid site allelic variation using phylogenetic comparative methods. We found no evidence of mitochondrial genome adaptations to flight intensity. Neither nucleotide composition nor amino acid properties showed consistent patterns related to flight use. While specific sites in mitochondrial genes exhibited variation associated with flight intensity, there was limited association between specific amino acid residues and flight intensity levels. Our findings suggest a complex genetic architecture for aerobic performance traits, where multiple genes in both mitochondria and the nucleus may contribute to overall performance. Other factors, such as gene expression regulation and anatomical adaptations, may play a more significant role in influencing flight performance than changes in mitochondrial genes. These findings highlight the need for comprehensive genomic analyses to unravel the intricate relationship between genetic variants and aerobic performance in birds.

Predicting aircraft trajectory uncertainties for terminal airspace design evaluation

The terminal airspace that surrounds an airport is the area with high flight density and complex structure. Aircraft are asked to follow the standard arrival and departure routes in terminal airspace, yet the actual trajectories may deviate due to air traffic control (ATC) instructions, pilots' decisions, surveillance and flying performance variations, etc. Predicting aircraft trajectories considering such uncertainties plays a crucial role in evaluating a redesign of the standard routes. Traditional simulation approaches for generating aircraft trajectories in a terminal airspace are cumbersome to use as it requires a detailed setup for each new scenario, while most existing data-driven methods can only be used in an airspace with historical trajectories, not applicable to new structure designs or other terminal areas. To fill in gap, in this paper, we develop a new model based on Multilayer Perceptron Neural Network (MLPNN) to predict aircraft trajectories with uncertainties for terminal airspace design evaluations. A key feature of the proposed model is that it is trained on existing standard routes yet it can be applied to new standard routes to generate trajectories. The enabler of the model's transferability is a novel input-and-output construction method for feature representations of raw trajectory data based on domain knowledge, including trajectory reconstruction, feature engineering, and output designing. After the input-and-output construction, a supervised learning model based on MLPNN is built to predict the standard deviations from the extracted features using historical trajectory data of existing standard routes. Once the model is built, trajectories with uncertainty can be simulated, through applying Gaussian distribution and exponential moving average algorithms, even on newly designed standard routes, where no aircraft have flown yet. Subsequently, new terminal airspace designs could be evaluated for their safety, efficiency, and environmental implications based on the simulated trajectories. The proposed model was tested on real-world operational data. Results showed that the model can quantify the characteristics of aircraft trajectories that are transferable across standard routes, and generate trajectories for new standard routes. We also demonstrated the proposed model on evaluating deficiencies on fuel consumption of actual arrival trajectories compared with the designed arrival routes. The generated trajectories showed 23%–37% more fuel consumption on average than the standard arrival routes in the terminal airspace of Hong Kong International Airport, which was validated with actual flight data.

Discussion on the static-thermal test technology of aircraft

During the high-speed flight of the aircraft, the cabin body will bear aerodynamic loads, engine thrust loads, structural and equipment component mass inertial loads. At the same time, aerodynamic thermal loads will be generated due to high speed flight. With the development of hypersonic aircraft technology, the demand for multi-field coupling test is more and more common. Therefore, it is necessary to carry out the technical verification of the mechanics and thermal composite test on the ground to obtain the structural characteristics. In this paper, a certain type of aircraft cabin as the research object, carried out the research on the combined mechanical and thermal test technology. The results of this paper show that the displacement response of the cabin under the combined action of force and thermal load is consistent with the change trend of the force loading curve, and the force load has obvious influence on the displacement response of the cabin. The strain response is consistent with the trend of temperature curve, and thermal load has obvious influence on cabin deformation. Through this study, we can obtain the static-thermal test technology method, and provide the technical basis for the development of similar test technology.

Small interannual variability in the body mass of a seabird with high flight costs

Small interannual variability in the body mass of a seabird with high flight costs

Safety Assessment for Full Flight between Beidou Radio Determination Satellite Service Airborne Equipment and 5G System

The Beidou Radio Determination Satellite Service (RDSS) is an advantageous service of the Beidou system. However, due to the weak landing power of Beidou RDSS signals and an operating frequency close to the 5G frequency, the system is vulnerable to interference from ground signals. In this paper, from the perspective of civil aviation safety, different evaluation indicators are used for the takeoff and cruise phases, respectively, to study the impact caused by adjacent frequency interference on airborne Beidou RDSS equipment. In the takeoff phase, accurate aircraft position information is obtained by processing real trajectory files. Deterministic analysis methods are used to determine the safety distance for the coexistence of the two systems. During the cruise phase, ground-based 5G base stations have less influence on the airborne RDSS receiver due to the high flight altitude, so the main consideration is electromagnetic compatibility between the airborne Beidou RDSS system and the 5G ATG system. By establishing a Boeing 737–800 simulation model, the antenna isolation degree is used as the evaluation index, and a reasonable antenna layout is given according to the evaluation results. In this study, the theoretical simulation and real flight data are combined to summarise the exact range of adjacent frequency influence during the takeoff phase and a reasonable antenna layout during the cruise phase.

A deep reinforcement learning control approach for high-performance aircraft

This research introduces a flight controller for a high-performance aircraft, able to follow randomly generated sequences of waypoints, at varying altitudes, in various types of scenarios. The study assumes a publicly available six-degree-of-freedom (6-DoF) rigid aeroplane flight dynamics model of a military fighter jet. Consolidated results in artificial intelligence and deep reinforcement learning (DRL) research are used to demonstrate the capability to make certain manoeuvres AI-based fully automatic for a high-fidelity nonlinear model of a fixed-wing aircraft. This work investigates the use of a deep deterministic policy gradient (DDPG) controller agent, based on the successful applications of the same approach to other domains. In the particular application to flight control presented here, the effort has been focused on the design of a suitable reward function used to train the agent to achieve some given navigation tasks. The trained controller is successful on highly coupled manoeuvres, including rapid sequences of turns, at both low and high flight Mach numbers, in simulations reproducing a prey–chaser dogfight scenario. Robustness to sensor noise, atmospheric disturbances, different initial flight conditions and varying reference signal shapes is also demonstrated.

Approximate Analytical Solutions for Launch-Vehicle Ascent Trajectory

Approximate analytical solutions for the ascent trajectory of a solid-fuel launch vehicle are derived. To the best of the authors' knowledge, the solutions are the ones achieving the highest accuracy in ascent-trajectory prediction under the condition of high angle-of-attack (AOA) maneuvers, where the magnitude of AOA can even be greater than 60 deg at high altitudes. As the first step of deriving the solutions, a reduced-order dynamics model with a normalized mass as the independent variable is put forward for longitudinal-plane flight. To further simplify the model, the sine of AOA is chosen as the key parameter for trajectory control and designed as a polynomial of the normalized mass. Meanwhile, an improved aerodynamic model with the sine of AOA as the independent variable is developed. Due to high AOA, the simplified dynamics model is still highly nonlinear and difficult to solve. To overcome this difficulty, by performing force analysis, several approximate polynomials and first-order Taylor series expansions are created to replace some highly nonlinear but relatively small terms in the dynamical equations, while the errors of the approximate formulae relative to the original nonlinear terms are retained and treated as minor perturbations. The benefit is that the modified dynamics model can be divided into two analytically solvable subsystems using a perturbation method. By solving the subsystems, the approximate analytical solutions for downrange, altitude, velocity and flight-path angle (FPA) of the vehicle are obtained successfully. Simulation results verify that the proposed solutions are much more accurate than the existing solutions in the scenario of high AOA flight.

Developlment of a Thermo-Chemical Non-Equilibrium Solver for Weakly Ionized Hypersonic Flowfields

A three dimensional solver for numerical simulation of weakly ionized hypersonic reactive air flows past high speed flight vehicles had been indigenously developed. The two-temperature, seven species, eighteen reactions, thermo-chemical non equilibrium, ionizing, air-chemistry model of Park is implemented in a compressible viscous code CERANS and solved in the finite volume framework. The energy relaxation is addressed by a conservation equation for the vibrational-electron-electronic energy of the gas mixture resulting in the evaluation of its vibrational temperature. The contribution of vibrational-electron-electronic energy of the reactive mixture is accounted in total energy equation as well as in the source terms of the relaxation model. The AUSM-PW+ numerical flux function has been used for modeling the convective fluxes and a central differencing approximation is used for modeling the diffusive fluxes. The code has been characterized for standard test cases involving weakly ionized hypersonic reactive thermo-chemical non equilibrium flows and results obtained are in good qualitative agreement with results available in open literature.

Investigation of Fin Buffet Characteristics of a Developmental Combat Aircraft Through Wind Tunnel Experiments

Airframe buffet is an important dynamic problem associated with combat aircraft flight, especially in the high Angle-of-Attack (AoA) regime. Occurrence of buffet due to flow separation at high angles of attack needs to be structurally cleared and a buffet boundary needs to be established. The methodology adopted to clear the aircraft from buffet during high AoA flight testing of a developmental light combat aircraft is focused in this article. Experimental unsteady pressure data from low speed wind tunnel tests conducted on a scaled down (1:10) model and airframe especially fin vibration data measured from flight tests formed the basis for this methodology. The reference spectrum has been formulated through unsteady pressures measured using pressure transducers mounted on the fin of the wind tunnel model. This spectrum (scaled up to 1:1) i.e. pressure Power Spectral Density (PSD) excitation was used as an input to the FE model of aircraft fin mounted on the rear fuselage. Buffeting response predicted in terms of acceleration PSD on the fin and rudder have been compared with the flight measured acceleration PSD data to validate the numerical model. The validated model is used to predict loads to clear the aircraft for further flight envelope expansion at high AoA.

Compressor and Valve Control Performance Implications on Active Flow Control Aircraft

This study presents the feasibility of implementing commercial-off-the-shelf reciprocating piston compressors for a developed active flow control (AFC) actuation framework to quantify the aerospace relevant performance ramifications of control architecture and compressor operational choices. Three architectures are studied: supply valve metering, exit area metering, and a combined approach. All concepts are studied under varying compressor operation schedules. The analysis framework in this study integrates internal pneumatic actuation and discharge dynamics, an experimentally calibrated compressor pressure and thermal dynamics model, three feedback control architectures, and flight dynamics models. The framework is implemented in simulation to provide a user-friendly tool for linking AFC architecture choices to achievable flight trajectories. Actuator performance is evaluated using actuation time, output, compressor duty cycle, and specific energy consumption. Aircraft tracking performance is evaluated as usable time and slalom centerline deviation. The analysis indicates that a supply-volume-based metering approach is comparatively inefficient concerning an exit-area-based metering, resulting in high flight tracking error. Exit area metering provides the best efficiency and run time with some structural drawbacks, while the combined approach provides the best flight tracking performance at the expense of additional complexity. These results inform the choice of onboard AFC hardware choices.

Static stability study of a model rocket

Relevance. When designing flying models of rockets, one of the difficult tasks is to ensure the static stability of the rocket in flight along a given trajectory. Static stability refers to the ability of a model to return to an equilibrium position disturbed by external forces (wind, model asymmetry, etc.). In this case, the model must be stabilized in terms of the angle between the longitudinal axis of the model and the direction of flight (velocity vector), i.e. maintain a zero angle of attack. The condition for ensuring the static stability of the rocket model is the location of its center of gravity ahead of the center ofpressure. In this case, when the angle of attack is different from zero, the aerodynamic forces will create a stabilizing moment, which will return the model to a zero angle of attack. The purpose of the study is to develop and compare methods for determining the position of the center of pressure of a rocket and determining its static stability. A simplified method, an analytical calculation, a graphical method, and various practical approaches that can be used in rocket modeling are considered. As research methods, an analytical approach, a graphical method and finite element modeling in the SolidWorks Flow Simulation program were used. In addition, a number of approximate calculation methods were considered. The study analyzes the capabilities of the considered methods for determining the static stability of a model rocket and the error of their application. To confirm the results of the calculation, a computer experiment was carried out in the form of blowing a finite element model of a rocket using the SolidWorks Flow Simulation program. The results of computer simulation confirmed the reliability of the proposed methods for determining the static stability of a model rocket. Research results. Simplified methods for determining the static stability of a rocket are the simplest and most reliable when designing model rockets. It is advisable to use it for launching demonstration rockets with an allowable misalignment error of 15% or more. Analytical methods are useful for designing sports models of rockets with high flight requirements, for example, for international competitions. Conclusion. The proposed method for ensuring the static stability of a model rocket makes it possible to simplify the design process of both demonstration and sports models of rockets for reliable demonstration launches.

Development and validation of an assessment index for quantifying cognitive task load in pilots under simulated flight conditions using heart rate variability and principal component analysis

To investigate whether high cognitive task load (CTL) for aircraft pilots can be identified by analysing heart-rate variability, electrocardiograms were recorded while cadet pilots (n = 68) performed the plane tracking, anti-gravity pedalling, and reaction tasks during simulated flight missions. Data for standard electrocardiogram parameters were extracted from the R–R-interval series. In the research phase, low frequency power (LF), high frequency power (HF), normalised HF, and LF/HF differed significantly between high and low CTL conditions (p < .05 for all). A principal component analysis identified three components contributing 90.62% of cumulative heart-rate variance. These principal components were incorporated into a composite index. Validation in a separate group of cadet pilots (n = 139) under similar conditions showed that the index value significantly increased with increasing CTL (p < .05). The heart-rate variability index can be used to objectively identify high CTL flight conditions. Practitioner summary: We used principal component analysis of electrocardiogram data to construct a composite index for identifying high cognitive task load in pilots during simulated flight. We validated the index in a separate group of pilots under similar conditions. The index can be used to improve cadet training and flight safety. Abbreviations: ANOVA: a one-way analysis of variance; AP: anti-gravity pedaling task; CTL: cognitive task load; ECG: electrocardiograms; HR: heart rate; HRV: heart-rate variability; HRVI: heart-rate variability index; PT: plane-tracking task; RMSSD: root-mean square of differences between consecutive R–R intervals; RT: reaction task; SDNN: standard deviation of R-R intervals; HF: high frequency power; HFnu: normalized HF; LF: low frequency power; LFnu: normalized LF; PCA: principal component analysis.

Study on Motion Law of Flyer Driven by Micro-Detonator

In order to provide design parameters for the micro-initiation train of the built-in MEMS Safety and Arming Device, and solve the reliable transmission problem of the micro-initiation train due to the small charge amount. Based on the structure of micro initiating explosive sequence, the test device is designed in the paper. The photon Doppler Velocimeter (PDV) was used to test the velocity of flyer driven by the micro-detonator, and the influence of the parameters of the flyer, acceleration chamber and charge on the flyer velocity was obtained. That is, when the flyer thickness is the same, the charge density is high and the flyer velocity is high; and the specific charge parameters need to match the specific flyer thickness, so as to obtain the flyer with high consistency and stable flight, and then achieve the ideal impact initiation effect. For the effect of the flyer velocity, the charge density is greater than the charge height, and the charge height is greater than the diameter of the charge.

Методы и способы повышения температуры газа перед турбиной газотурбинного двигателя

The paper presents methods and techniques used in increasing gas temperature in front of the turbine blades of the gas turbine engine making it possible in the aggregate to reach the gas temperature of 2300 K. Gas turbine blades made on the basis of the best nickel alloys could operate for a long time without cooling at the temperature of not more than 1300 K. Convective-film cooling today appears to be the most effective method of air cooling the blades, due to which (in combination with the heat-shielding coatings) gas temperature of 2000 K is reached in the fifth-generation gas turbine engines. Significant increase in the efficiency of the turbine blades internal cooling (convective, convective-film, porous) is obtained with using the external cooling, i.e. decreasing the cooling air temperature by the cooling resource of the external environment: atmospheric air (secondary air), water and fuel. External cooling when using the convective-film cooling makes it possible to increase gas temperature in front of the turbine blades by 0.6 ... 1.5 K for each degree in the cooling air temperature decrease. A circulating heat exchanger is proposed, which lowers the cooling air temperature almost to the ambient temperature making it possible in combination with the known methods and techniques for increasing the gas temperature (heat-resistant materials, heat-shielding coatings, convective-film cooling) to increase gas temperature in front of the turbine blades by 300...400 K and bring it up to at least 2300 K. This would allow today to start creating stoichiometric and hyperforced gas turbine engines and to increase the bypass turbojet engines efficiency up to 45%. Air-liquid cooling is a variation of the turbine blades external cooling. The possibility (technical solutions were patented) of introducing the air-liquid cooling in gas turbine engines at the high flight speeds, including the turbojet engines, was studied.

Evaluation of neutron doses in Brazilian aircrew by the Monte Carlo method

The demand for air travel has intensified over the last few decades and, accordingly, studies seeking to assess the levels of exposure to cosmic radiation that aircrew and frequent passengers are subject to have attracted more and more interest. Aircrew, for frequently manning high altitude flights, appear as professionals directly exposed and prone to the risks arising from cosmic radiation. Continuous exposure to particles of cosmic origin can lead to dose levels above the regulatory limits for public exposure, with neutrons being the particles of the highest contribution to the dose. In several countries around the world, aircrew already have regulatory control in terms of radiological protection and are classified as occupationally exposed. In Brazil, however, there is neither a regulatory control nor a specific classification for these professionals. The objective of this work is to estimate both the neutron component of the effective dose and the effective dose of Brazilian aircrew due to cosmic rays using the GEANT4 Monte Carlo toolkit. For the estimation of the effective dose, the EXPACS code was used to estimate the neutron flux and GEANT4 to obtain the doses on the selected flights. The GEANT4 simulations were performed in the flight conditions and with ICRP voxel phantoms. The neutron doses obtained ranged from 0.002 to 3.0 mSv on the different selected flights.The equivalent doses of neutrons, in certain organs, were also estimated. In the end, the total effective doses were presented, with the contribution of neutron doses, and, when compared with the annual dose limits for members of the public and occupationally exposed workers, they showed that aircrew could receive dose levels above the public limit. A comparison was made with experimental dose measurements throughout the Brazilian territory.