Flight Dynamics Analysis Research Articles

Interplay of unsteady aerodynamics and flight dynamics of transport aircraft in icing conditions

Airframe icing causes significant degradation of aerodynamic characteristics and influences the flight safety. Wind tunnel study of longitudinal steady and unsteady aerodynamic characteristics of a transport aircraft in icing conditions is carried out in order to develop mathematical model of aerodynamics in the extended flight envelope. The wind tunnel results are validated through flight tests conducted for the real aircraft. Large, glaze-horn ice shapes, corresponding to holding flight phase, are considered. Influence of an ice protection system as well as its failure is examined. Effect of icing on the unsteady aerodynamics characteristics is studied not only through wind tunnel tests but also via analysis of subsequent influence on the flight dynamics of the aircraft. The conducted study shows that the ice shapes of the holding phase lead to reduced stall angle of attack (AoA), maximum lift, and longitudinal damping. Flight dynamics analysis demonstrates that dangerous aircraft behaviour in the form of high AoA departure and limit cycle oscillations (LCO) can be observed at smaller elevator deflections for the iced aircraft. The account for icing influence on the unsteady aerodynamics in the flight dynamics simulations revealed degradation of the dynamic response and deterioration of phase portraits of the system. Even for small AoA and elevator deflection, the aircraft might be trapped into the basin of attraction of high-AoA LCO. In addition, incorporating icing effects in unsteady aerodynamics manifest larger amplitude of LCO.

Nonlinear modeling of composite wing with application to UAV flight dynamic analysis

Wings have obvious nonlinear vibrations such as buffeting and flutter during the flight of the aircraft, the nonlinear vibrations are harmful to the safety of wing structures and stability of aircraft flight. Thereby, studying nonlinear dynamic characteristics of wings is extremely important, which makes the accurate nonlinear dynamic model urgently needed. For composite wings, traditional modeling theory cannot accurately predict the variability caused by manufacturing process, machining behavior and operating condition. Therefore, this paper used a numerical-experimental method to establish the dynamic model of a composite wing, considering geometric nonlinearity. In the method, the nonlinear dynamic model of the composite wing was predicted by an experimental modal analysis with a frequency response function, and a nonlinear static test with the nonlinear least squares method. Then, the nonlinear modeling was applied to a UAV flight dynamic simulation and a flight test was also conducted. The results of the simulation are in good agreement with those of the test, which shows that the nonlinear modeling is perfectly suited for the nonlinear dynamic analysis of the composite wing.

Debris collision avoidance by means of attitude control-in-flight demonstration with TET-1

Collision avoidance is more and more of importance due to the growing amount of space debris posing a threat not only on satellites in orbit but also on upcoming missions. To avoid a collision between space debris and functioning satellites or even between two functioning satellites collision avoidance manoeuvres can be induced if one of the satellites has a working propulsion system. An alternative method of collision avoidance operations is presented in this study. By changing the satellites attitude, it is possible to obtain an increase or decrease in the semi-major axis in relation to its nominal orbital decay. The change in the semi major axis together with the time until closest approach provokes a change in the relative geometry of the object orbits resulting in a decreasing collision risk. This method enables collision avoidance manoeuvres for satellites in Low Earth Orbits featuring active attitude control and drag-susceptible geometries. Additionally, the probability of a collision can be reduced by changing the satellite attitude so that the minimum effective area is perpendicular to the relative velocity vector at the time of closest approach. Both methods can be applied to satellites without propulsion, which otherwise would be defenceless. A test run for verification of collision avoidance by means of drag-minimization was performed in June 2018 with the Technology Experiment Carrier (TET-1) satellite of the FireBIRD constellation. The experiment planning and results are presented along with the initial flight dynamics analysis and representative examples for collision avoidance scenarios.

Flight Dynamics Modeling and Dynamic Stability Analysis of Tilt-Rotor Aircraft

The tilt-rotor aircraft has often been proposed as a means to increase the maximum speed of the conventional helicopter. The tilt-rotor aircraft consists of three primary flight modes that are the helicopter flight mode in low forward speed flight, airplane flight mode in high forward speed flight, and conversion flight mode. The aim of this paper is to develop a nonlinear flight dynamics mathematical modeling method of tilt-rotor aircraft and investigate the dynamic stability characteristics of tilt-rotor aircraft. First, a nonlinear tilt-rotor aircraft flight dynamics model is developed. The trim and linearized results are present to verify the model. Then, using a numerical differentiation technique, the dynamic stability of the tilt-rotor aircraft is assessed. The results show that the flight speed and nacelle angle would affect the magnitude and the trend of the aerodynamic derivatives. The damping of the pitch short period mode and the Dutch roll mode is insensitive to flight speed while they could be affected by nacelle angle. In all flight modes, as flight speed increases, the natural modes become more stable.

Coupled Simulations of Atmospheric Turbulence-Modified Ship Airwakes and Helicopter Flight Dynamics

The influence of a neutral atmospheric boundary layer on a one-way coupled dynamic interface simulation is evaluated. The effort is performed within the context of time-accurate large-eddy simulations of Simple Frigate Shape 2, which is immersed into a turbulence-resolving atmospheric inflow that emulates the dynamics of a realistic atmospheric boundary layer. Several baseline cases are used to represent a traditional approach of modeling the incoming wind as a constant, uniform inflow. When comparing the atmospheric boundary layer-resolving to the baseline simulations, it is observed that the velocities in a ship airwake are considerably different when formed from an atmospheric boundary layer. The unsteady computational fluid dynamics solution is then saved as a database and used as external disturbances for flight dynamics analysis. Such an approach is common in piloted flight simulation. The pilot workload is evaluated using a helicopter approach scenario and multiple hover locations. Such cases are evaluated, and it is found that the large scales present in the atmospheric boundary layer notably disturb the helicopter. The disturbances result in increased controls input and aircraft movement. Frequency-domain analysis of the increased stick movement suggest that the atmospheric boundary layer impacts the 0.1–2 Hz stick controls, which comprise the frequency range known to affect pilot workload.

Propeller control strategy for coaxial compound helicopters

The coaxial compound configuration has been proposed as a concept for future high-performance rotorcraft. The co-axial rotor system does not require an anti-torque device, and a propeller provides axial thrust. A well-designed control strategy for the propeller is necessary to improve the performance and the flight dynamics characteristics. A flight dynamics model of coaxial compound helicopter is developed to analyze these influences. The performance and the flight dynamics characteristics in different propeller strategies were first investigated. The results show that there is an improvement in the performance in high-speed flight when the propeller provides more propulsive forces. It also illustrates that a reasonable allocation of the rotor and the propeller in providing thrust can further reduce the power consumption in the mid speed range. In other words, the propeller control strategy can be an effective method to improve the cruise-efficiency. The flight dynamics analysis in this paper includes trim and handling qualities. The trim results prove that the propeller strategy can affect the collective pitch, longitudinal cyclic pitch, and the pitch attitude. If the control strategy is designed only to decrease the required power, it will result in a discontinuity in the trim characteristics. Handling qualities are investigated based on the ADS-33E-PRF requirement. The result demonstrates that the bandwidth and phase delay results and eigenvalue results in various speed at different propeller strategies are all satisfied. However, some propeller control strategies lead to severe inter-axis coupling in high-speed flight. Based on these results, this paper proposes the propeller control strategy for the coaxial compound helicopter. This strategy ensures good trim characteristics and handling qualities, which satisfy the related requirements, and improves the flight range or the performance in high-speed flight.

MATHEMATICAL MODELLING OF THE UNMANNED AERIAL VEHICLE DYNAMICS

The article gives a classification of the main components of unmanned aerial vehicle (UAV) systems, gives the areas in which the application of UAVs is actual in practice today. Further, the UAV is considered in more detail from the point of view of its flight dynamics analysis, the equation necessary for creating a mathematical model, as well as the model of an ordinary dynamic system as a non-stationary nonlinear controlled object, is given. Next, a description of the developed software for modeling and a description of program algorithm are given. Finally, a conclusion describes the necessary directions for further scientific researches.

Flight dynamic coupling analysis of a bio-inspired elastic-wing aircraft

ABSTRACTIt is a challenge for small, fixed-wing aerial vehicles to maintain flight stability under gusts. Inspired by the geometric features and the structural dynamic characteristics of the gliding bird wing, an elastic wing with similar characteristics was designed and optimised for use as part of unmanned aerial vehicle. A flight dynamic model, which includes the coupling of the longitudinal flight modes and the aeroelastic modes of the flexible wing, was built to analyse the mechanisms of specific coupling for the structural characteristics of the wing design, and how these specific couplings affect flight dynamics. The results showed that the bio-inspired elastic wing effectively allows alleviation of the gust response of the prototype through coupling effects of the short period and the first aeroelastic mode, even with a considerable frequency gap. These effects become more significant when the airspeed becomes larger. The conclusions of this research can facilitate further development of bird-sized unmanned aerial vehicles to extend their applications and make these vehicles more adaptive for flight in complex atmospheric environments.

Impact of Adverse Environmental Conditions on Rotorcraft Operational Performance and Pollutant Emissions

It is anticipated that the contribution of rotorcraft activities to the environmental impact of civil aviation will increase in the future. Due to their versatility and robustness, helicopters are often operated in harsh environments with extreme ambient conditions. These severe conditions not only affect the performance of the engine but also affect the aerodynamics of the rotorcraft. This impact is reflected in the fuel burn and pollutants emitted by the rotorcraft during a mission. The aim of this paper is to introduce an exhaustive methodology to quantify the influence adverse environment conditions have in the mission fuel consumption and the associated emissions of nitrogen oxides (NOx). An emergency medical service (EMS) and a search and rescue (SAR) mission are used as case studies to simulate the effects of extreme temperatures, high altitude, and compressor degradation on a representative twin-engine medium (TEM) weight helicopter, the Sikorsky UH-60A Black Hawk. A simulation tool for helicopter mission performance analysis developed and validated at Cranfield University was employed. This software comprises different modules that enable the analysis of helicopter flight dynamics, powerplant performance, and exhaust emissions over a user-defined flight path profile. For the validation of the models implemented, extensive comparisons with experimental data are presented throughout for rotorcraft and engine performance as well as NOx emissions. Reductions as high as 12% and 40% in mission fuel and NOx emissions, respectively, were observed for the “high and cold” scenario simulated at the SAR role relative to the same mission trajectory under standard conditions.

Fluid–structure interaction and flight dynamics analysis of parachute–payload system during uncontrolled airdrop process

The coupling behaviors of a special parachute’s inflation incorporating fluid–structure interaction and flight dynamics are investigated based on the multibody dynamic model and LS-DYNA nonlinear analysis code. A new coupling model is developed to predict both the opening phase of parachute and the trajectory of payload during airdrop mission in low attitude. The moving mesh technology is introduced to realize the finite mass inflation simulation. A simplified integration platform is built by coupling the fluid–structure interaction and flight dynamics model, and solved based on two-way data transfer to efficiently replicate the dynamic characteristics of parachute finite mass inflation. Finally, the opening performances of the parachute at different airdropping velocities are analyzed and compared with the experimental results. The unsteady flow dynamics is simulated and the wake re-contacts phenomenon occurred. Taking consideration of the periodical disturb of wind gust, the trajectory of parachute–payload system is simulated and compared with the real airdrop test results. In conclusion, the results show that this coupling model is efficient to simulate and predict the dynamics behaviors of parachute–payload system in a finite mass inflation scenario, which will be beneficial for airdrop missions.

An innovative route from wind tunnel experiments to flight dynamics analysis for a highly swept flying wing

A flying wing configuration with highly swept leading edges and low aspect ratio such as the generic UCAV configuration DLR-F19 is very attractive for military applications due to its very favorable stealth capabilities. As the assurance of good flying qualities, however, is a critical aspect for such a configuration, it should be considered early in the design process. This paper presents an innovative way to derive a flight dynamics model from wind tunnel experiments by applying a system identification approach, normally employed for flight test. This allows the modelling of nonlinear aerodynamic effects and provides a model which can be directly integrated into flight dynamics simulations. New wind tunnel maneuvers are applied which significantly reduce the time of the wind tunnel experiments and improve the quality of the aerodynamic dataset generation. The aerodynamic model is then integrated into a 6-DoF simulation environment in order to perform a flight dynamics analysis of the UCAV configuration. The purpose of this analysis is to compare the flying qualities as derived from wind tunnel data with the results determined on the basis of data from VSAERO, a low-fidelity aerodynamic tool used in preliminary aircraft design.

Aerodynamic shape study of supersonic surface to surface missiles with continuous flexible nose

The aerodynamic characteristics of nine configurations of supersonic continuous deflectable nose guided missiles have been investigated. The optimized geometry was achieved based on the accuracy of confliction with constant target in ground to ground mission. The studied configurations consist of a spherical nose tip, a tangent ogive, one set of stabilizing tail fines and a cylindrical body whose midsection is flexible to form an arc of a circle. So the cylindrical body consists of a fixed part in the vicinity of the nose, middle flexible part and main body with stabilizers. The effects of fixed length (Fix = 0, 1.5, 3Cal) and flexible length (Flex = 1, 2.5, 5Cal) parameters on the aerodynamics and flight dynamics of guided missile have been studied. A code has been developed to solve full Navier-Stokes equations using finite volume and Runge-Kutta time stepping techniques and modified Baldwin-Lomax turbulence model. Multi-block technique was also used to solve the main body and fin parts flow fields. Further, a 3 degree of freedom code along with a pure pursuit guidance subroutine was developed to compare planar flight dynamics of missiles. It was found that although the missiles with bigger lengths for fixed and flex parts show more maneuverability, but this is not favorable for all missile missions as sometimes it decreases the confliction accuracy. Flight dynamic analysis shows that a change in initial launch angle may shift the favorite configuration. This means only the aerodynamic defined aim functions cannot completely supersede flight dynamic analysis in geometric optimization. Further, the thrust vector moment is an important portion of total control moment as it enhances the hitting accuracy and also decreases the importance of geometry.

Dynamics Simulation and Analysis of Transition Stage of Tilt-Rotor Aircraft

This paper presents the flight dynamics simulation and analysis of a tilt-rotor vertical takeoff and landing (VTOL) aircraft on transition phase, that is conversion from vertical or hover to horizontal or level flight and vice versa. The model of the aircraft is derived from simplified equations of motion comprising the forces and moments working on the aircraft in the airplane's longitudinal plane of motion. This study focuses on the problem of the airplane's dynamic response during conversion phase, which gives an understanding about the flight characteristics of the vehicle. The understanding about the flight dynamics characteristics is important for the control system design phase. Some simulation results are given to provide better visualization about the behaviour of the tilt-rotor. The simulation results show that both transition phases are quite stable, although an improved stability can give better manoeuver and attitude handling. Improvement on the simulation model is also required to provide more accurate and realistic dynamic response of the vehicle.

Rosetta lander Philae: Flight Dynamics analyses for landing site selection and post-landing operations

On the 12th of November 2014, The Rosetta Lander Philae became the first spacecraft to softly land on a comet nucleus. Due to the double failure of the cold gas hold-down thruster and the anchoring harpoons that should have fixed Philae to the surface, it spent approximately two hours bouncing over the comet surface to finally come at rest one km away from its target site. Nevertheless it was operated during the 57h of its First Science Sequence. The FSS, performed with the two batteries, should have been followed by the Long Term Science Sequence but Philae was in a place not well illuminated and fell into hibernation. Yet, thanks to reducing distance to the Sun and to seasonal effect, it woke up at end of April and on 13th of June it contacted Rosetta again. To achieve this successful landing, an intense preparation work had been carried out mainly between August and November 2014 to select the targeted landing site and define the final landing trajectory. After the landing, the data collected during on-comet operations have been used to assess the final position and orientation of Philae, and to prepare the wake-up. This paper addresses the Flight Dynamics studies done in the scope of this landing preparation from Lander side, in close cooperation with the team at ESA, responsible for Rosetta, as well as for the reconstruction of the bouncing trajectory and orientation of the Lander after touchdown.

A multidisciplinary design and analysis environment and its application to aircraft flight dynamics analysis

Abstract Complex engineering problems have to be jointly solved by many disciplinary teams with multitudinous computational software packages and physical experiment systems. Thus, the efficiency and effectiveness of solving complex engineering problems largely depend on effective collaboration among specialist engineers, seamless integration of disparate cyber-physical systems, and transparent interoperations of heterogeneous data sources. This paper presents a multidisciplinary design and analysis (MDA) environment in conjunction with its application to aircraft flight dynamics analyses. The MDA infrastructure builds a cybernetic platform that integrates structure analysis and flow computation systems with wind tunnel experiment systems; reconciles and interoperates diverse data sources generated by the cyber-physical systems. It is demonstrated that application of the MDA environment cost-effectively enhances work efficiency, team collaboration, and solution optimality in aircraft flight dynamics engineering processes.

A method for nonlinear aeroelasticity trim and stability analysis of very flexible aircraft based on co-rotational theory

Very flexible aircraft with high aspect ratio wings subjected to aerodynamic loads undergoes large deformation, which will lead to distinct changes on the mass distributions, stiffness characteristics and aerodynamic characteristics of the complete aircraft. The aeroelasticity and flight dynamics of such aircrafts are nonlinear and the linear elastic theory model cannot be used. A new method is developed for the analysis of nonlinear aeroelasticity and flight dynamics of very flexible aircraft through combining the co-rotational beam theory with the modified ONERA dynamic stall model. Based on a form of co-rotational technique which is external to the element, a spatial two-node beam element, which depicts the geometrically nonlinear dynamic characteristics of the flexible wing, is developed. Both tangential stiffness matrix and mass matrix of the beam element are formulated to establish the nonlinear dynamic equations. In addition, the modified ONERA dynamic stall model is adapted to evaluate the unsteady nonlinear aerodynamic loading of the very flexible wing. Using the present method, the nonlinear aeroelastic response, trim and stability characteristics of a very flexible aircraft are predicted in this paper. The obtained results show a good agreement to the literature, which indicates that the present method is accurate and efficient.

Rosetta lander Philae – Landing performance and touchdown safety assessment

This paper describes the simulation and analysis work on Rosetta lander Philae׳s touchdown dynamics which was done to support its Landing Site Selection Process. The simulation part consists of a numerical multi-body simulation to describe Philae׳s touchdown dynamics. Suitable performance metrics in conjunction with Monte Carlo trajectory data from the flight dynamics analysis yields landing area specific landing gear performance and safety figures. These were then incorporated into the site selection process with regard to landing system performance margins and touchdown safety. While Philae finally made a nearly successful landing the actual flight data were used to review and discuss the applicability of the presented simulation and analysis scheme.

Conceptual Design for the Performance Optimization of Compound Coaxial Helicopter

The purpose of this paper is to study the conceptual design and optimization of a compound coaxial helicopter. At the conceptual design phase, the compound coaxial helicopter design work was based on the conventional helicopter and fix-wing aircraft design method. The intersection of these aspects makes the design work more complex, thus, a program for the sizing and performance optimization was developed for the aircraft. The program included the total weight design, aerodynamic analysis, flight dynamics analysis, performance calculation and particle swarm optimization analysis. Under the restricted condition of the flight performance requirements, optimize the design parameters which make the weight efficiency factor decrease. Therefore, the study of optimum design process was warranted.

MATLAB-Based Flight-Dynamics and Flutter Modeling of a Flexible Flying-Wing Research Drone

A relatively low-order linear dynamic model is developed for the longitudinal flight-dynamics analysis of a flexible flying-wing research drone, and results are compared to previously published results. The model includes the dynamics of both the rigid-body and elastic degrees of freedom, and the subject vehicle is designed to flutter within its flight envelope. The vehicle of interest is a 12–lb, unmanned flying-wing aircraft with a wingspan of 10 ft. In the modeling, the rigid-body degrees of freedom are defined in terms of motion of a vehicle-fixed coordinate frame, as required for flight-dynamics analysis. As a result, the state variables corresponding to the rigid-body degrees of freedom are identical to those used in modeling a rigid vehicle, and the additional states are associated with the elastic degrees of freedom. Both body-freedom and bending–torsion flutter conditions are indicated by the model, and it is shown that the flutter speeds, frequencies, and genesis modes suggested by this low-order model agree very well with the analytical predictions and flight-test results reported in the literature. The longitudinal dynamics of the vehicle are characterized by a slightly unstable phugoid mode, a well-damped pitch-dominated elastic-short-period mode, and the stable or unstable aeroelastic modes. A classical rigid-body short-period mode does not exist.

Analysis of flight dynamics for large-scale morphing aircraft

Purpose This paper aims to clarify the flight dynamics characteristics and improve the flight performance for large-scale morphing aircrafts. With specific focus on the effects of morphing on mass distribution, aerodynamics and flight stability, the study aims to develop the dynamic model, outline the morphing strategies design and evaluate the flight stability in transient stage of morphing.