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Angle-of-Attack (AOA) and angle-of-sideslip (AOS) are critical flight parameters affecting the flight safety, and their accuracy and reliability directly impact the operating status and performance of some significant airborne systems. To enhance the redundancy and accuracy of AOA and AOS, this article investigates the problem of the airflow angles estimation and complementary filter design for civil aircraft. Specifically, an extended Kalman filter based AOA and AOS estimation method considering acceleration correction is developed to increase the redundancy. Subsequently, a novel inertial AOA and inertial AOS calculation method using attitude angles, azimuth angle, and flight path angle is introduced, and two schemes for designing the discrete complementary filter based on Tustin transform are presented to improve the accuracy. Through simulations, the developed algorithms are verified, and the results illustrate that the AOA estimation error is within ± 0.6°, and the AOS estimation error is within ± 0.3°. • A novel AOA and AOS estimation method based on extended Kalman filter is introduced. • A novel inertial AOA and inertial AOS calculation method is developed. • Two schemes for designing discrete AOA/AOS complementary filter are presented. [ABSTRACT FROM AUTHOR]

Adverse meteorological conditions often contribute to the formation of ice on aircraft wing section, engine nacelle and other parts leading to the loss of lift coefficient and increase in drag coefficient affecting aircraft control and stability. This paper addresses the problem of in-flight icing on an asymmetric aerofoil under three different ambient and cloud conditions. The study involves prediction of the leading-edge ice thickness using a numerical model developed from the mass and energy conservation law and Messinger freezing fraction model at the same Reynolds number. Later on, degradation in the aerodynamic performance of the iced aerofoil was also investigated using the computational fluid dynamics (CFD) technique, taking the flow field around a 2D aerofoil geometry into account. The aerodynamic study indicates that cumulus clouds embedded with stratified clouds contribute to the formation of mixed ice on aerofoil leading edge and causes the worst icing scenario reducing the lift coefficient to 90% and increasing the drag coefficient to 800% for the same ambient conditions. [ABSTRACT FROM AUTHOR]

This paper investigates the aerodynamics of a wing under figure-of-eight flapping motion based on Fluid–Structure Interaction (FSI) Computational Fluid Dynamics (CFD) simulations. The kinematic of a wing under figure-of-eight motion creates a condition with a variable angle-of-attack. The effect of using different angles of attack at an initial condition, namely initial pitch angles, for the wing and the spatial size of the figure-of-eight pattern, namely the input link angle, is investigated. The initial pitch angles input is varied from 0° to 330° in steps of 30°, and the input link angles used are 30°, 45°, and 60°. The Young's modulus of the wing is 3.4 GPa spanwise, which is the elastic modulus of balsa wood material. In comparison with an initial pitch angle of 0°, the 90° initial pitch angle shows much better flight performance in terms of lift generated and stability. The results show that the maximum average lift coefficient of 0.393 occurs at the 90° initial pitch angle. The maximum lift-induced moment for the 90° initial pitch angle is only 5.55% of the maximum lift induced moment for the 0° initial pitch angle. A higher input link angle generates a greater lift force. The pressure distribution in the vicinity of the wing area and the von Mises stress of the wing are also presented. [ABSTRACT FROM AUTHOR]

Control programs and flight paths of the hypersonic first stage of an aerospace system in climb with acceleration to hypersonic velocity are analyzed. Two approaches to determining the control programs and flight paths are identified: the "traditional" approach and the "optimization" one. The "traditional" approach implies specifying a typical mission profile with max-q and peak heat flux. In the case of the "optimization" approach the problem of propellant mass minimum is stated and solved using the method of Pontryagin’s maximum principle. It concerns the mass of propellant consumed in hypersonic acceleration for various terminal flight path angles. Optimal control programs and optimal flight paths are determined. Those meeting the max-q and peak heat flux requirements are selected. The results of modeling the motion of a hypersonic booster with typical and optimal angle-of-attack schedules corresponding to the "traditional" and "optimization" approaches are presented and discussed. It is established that less propellant is consumed in the case of optimal control, which is accounted for by more efficient use of the hypersonic booster's aerodynamic performance due to direct control of the angle of attack.

This work deals with the safety analysis of an air data system (ADS) partially based on synthetic sensors. The ADS is designed for the small aircraft transportation (SAT) community and is suitable for future unmanned aerial vehicles and urban air mobility applications. The ADS's main innovation is based on estimation of the flow angles (angle-of-attack and angle-of-sideslip) using synthetic sensors instead of classical vanes (or sensors), whereas pressure and temperature are directly measured with Pitot and temperature probes. As the air data system is a safety-critical system, safety analyses are performed and the results are compared with the safety objectives required by the aircraft integrator. The present paper introduces the common aeronautical procedures for system safety assessment applied to a safety critical system partially based on synthetic sensors. The mean time between failures of ADS's sub-parts are estimated on a statistical basis in order to evaluate the failure rate of the ADS's functions. The proposed safety analysis is also useful in identifying the most critical air data system parts and sub-parts. Possible technological gaps to be filled to achieve the airworthiness safety objectives with nonredundant architectures are also identified. [ABSTRACT FROM AUTHOR]

Based on the missiles with adjustable thrust, a distributed synergetic guidance law for multiple missiles with angle-of-attack constraint is designed to achieve a cooperative attack by multiple missiles on a moving target. Divide the guidance law into two parts: the line of sight (LOS) direction and the normal direction of LOS. The guidance law is designed in LOS direction based on the multi-agent system cooperative control theory and super-twisting algorithm, which can control missiles' time-to-go converging in finite time. In the normal direction of LOS, the other guidance law is designed to control missiles hitting the target with impact angle constraint based on zeroing LOS rate thought and finite-time sliding mode control theory. The two non-homogeneous disturbance observers are designed to estimate the target manoeuvring information in the two parts of the guidance law. The simulation results show that the guidance law designed by this paper can complete the cooperative attack task while suppressing the chattering phenomenon effectively. [ABSTRACT FROM AUTHOR]

Aircraft handling qualities may be influenced by wing-tip flow separations and horizontal tail (HT) reduced efficiency caused by loss of local dynamic pressure or local tailplane flow separations in high angle-of-attack manoeuvres. From the flight tester's perspective, provided that the test aircraft presents sufficient longitudinal control authority to overcome an uncommanded nose-up motion, this characteristic should not be a safety factor. Monitoring and measuring the local airflow in the aircraft's HT provides information for safe flight-test envelope expansion and data for early aerodynamic knowledge and model validation. This work presents the development, installation and pre-flight calibration using computational fluid dynamics (CFD), flight-test calibration, results and benefits of differential pressure based local angle-of-attack and total pressure measurements through 20 static pressure ports and a Kiel pitot. These sensors were installed in a single-aisle, four-abreast, full fly-by-wire medium-range jet airliner with twin turbofan engines and conventional HT (low vertical position). [ABSTRACT FROM AUTHOR]

In this paper, we present an adaptive mesh refinement method that is used in conjunction with local direct collocation methods for solving Mars entry trajectory optimization problems with a maximum parachute deployment altitude. The study focuses on the capability of the mesh refinement method to solve Mars entry trajectory optimization problems and the potential benefits of enabling angle-of-attack control. The numerical results show that Mars entry trajectory optimization problems can be solved accurately and efficiently using the proposed method. The accuracy is found to be comparable to that of indirect methods, and the computational time is on the order of several seconds, depending on the complexity of the problem. Furthermore, it is found that parachute deployment altitude gains of 2.2–3.1 km over pure bank control are possible if angle-of-attack control is enabled for a Mars Science Laboratory-type vehicle. Efforts are also made to investigate the influences of bank angle limits on entry trajectories, and it is found that the structure of the optimal bank angle profiles are generally similar for different bank angle limits, but a larger bank angle range allows an higher maximum parachute deployment altitude. • Mars entry trajectory optimization problems are solved accurately and efficiently. • The influence of bank limits on the terminal altitude can be as large as 1.4 km. •The terminal altitude can be increased by 2.2-3.1 km if AOA control is enabled. [ABSTRACT FROM AUTHOR]

This work deals with the safety analysis of an air data system (ADS) partially based on synthetic sensors. The ADS is designed for the small aircraft transportation (SAT) community and is suitable for future unmanned aerial vehicles and urban air mobility applications. The ADS’s main innovation is based on estimation of the flow angles (angle-of-attack and angle-of-sideslip) using synthetic sensors instead of classical vanes (or sensors), whereas pressure and temperature are directly measured with Pitot and temperature probes. As the air data system is a safety-critical system, safety analyses are performed and the results are compared with the safety objectives required by the aircraft integrator. The present paper introduces the common aeronautical procedures for system safety assessment applied to a safety critical system partially based on synthetic sensors. The mean time between failures of ADS’s sub-parts are estimated on a statistical basis in order to evaluate the failure rate of the ADS’s functions. The proposed safety analysis is also useful in identifying the most critical air data system parts and sub-parts. Possible technological gaps to be filled to achieve the airworthiness safety objectives with nonredundant architectures are also identified.

The effects of sound pressure level at two observation positions of a fixed and varied blade pitch angle at Low-Mach unsteady incompressible Reynolds-Average Navier-Stokes flow approach, on an H-rotor Vertical Axis Wind Turbine. The objective of the study is to compare the noise dissipation and output power/energy of the airfoil blades design of the vertical axis wind turbine in residential zones. The Ffowcs Williams-Hawkings (FHWH) techniques were applied to validate the output noise and vortex shedding of the different angles of attacks (AoA). The study postulated that the time history of the calculated sound pressure level at two observers positions: the aeroacoustic, blade vortex interaction noise, flow separations, dynamic stall experience from varied angled of attacks are found to produces less noise and vortex shedding compared to the fixed angle of attack.

The physics of ballistic penetration mechanics is of great interest in penetrator and countermeasure design. The phenomenology associated with these events can be quite complex, and a significant number of studies have been conducted ranging from purely experimental to "engineering" models based on empirical and/or analytical descriptions to fully coupled penetrator/target, thermomechanical numerical simulations. Until recently, however, there appears to be a paucity of numerical studies considering "non-ideal" impacts (Goldsmith, 1999, "Non-Ideal Projectile Impact on Targets," Int. J. Impact Eng., 22, pp. 95-395). The goal of this work is to demonstrate the SHISM algorithm implemented in the ALEGRA multimaterial arbitrary Lagrangian Eulerian code (Boucheron, et al., 2002, ALEGRA: User Input and Physics Descriptions, Version 4.2, SAND2002-2775, Sandia National Laboratories, Albuquerque,, NM). The SHISM algorithm models the three-dimensional continuum solid mechanics response of the target and penetrator in a fully coupled manner. This capability allows for the study of nonideal impacts (e.g., pitch, yaw, and/or obliquity of the target/penetrator pair). In this work predictions using the SHISM algorithm are compared with previously published experimental results for selected ideal and nonideal impacts of metal penetrator-target pairs. These results show good agreement between predicted and measured maximum depths-of-penetration (DOPs), for ogive-nose penetrators with striking velocities in the 0.5-1.5 km/s range. Ideal impact simulations demonstrate convergence in predicted DOP for the velocity range considered. A theory is advanced to explain disagreement between predicted and measured DOPs at higher striking velocities. This theory postulates uncertainties in angle-of-attack for the observed discrepancies. It is noted that material models and associated parameters used here were unmodified from those in literature. Hence, no tuning of models was performed to match experimental data. [ABSTRACT FROM AUTHOR]

In the area of synthetic sensors for flow angle estimation, the present work aims to describe the verification in a relevant environment of a physics-based approach using a dedicated technological demonstrator. The flow angle synthetic solution is based on a model-free, or physics-based, scheme and, therefore, it is applicable to any flying body. The demonstrator also encompasses physical sensors that provide all the necessary inputs to the synthetic sensors to estimate the angle-of-attack and the angle-of-sideslip. The uncertainty budgets of the physical sensors are evaluated to corrupt the flight simulator data with the aim of reproducing a realistic scenario to verify the synthetic sensors. The proposed approach for the flow angle estimation is suitable for modern and future aircraft, such as drones and urban mobility air vehicles. The results presented in this work show that the proposed approach can be effective in relevant scenarios even though some limitations can arise. [ABSTRACT FROM AUTHOR]