Behavior Of Aircraft Research Articles

The AutoSOAR autonomous soaring aircraft, part 1: Autonomy algorithms

AbstractAutonomous soaring has the potential to greatly improve both the range and endurance of small robotic aircraft. This paper describes an autonomous soaring system that generates a dynamic map of lift sources (thermals) in the environment and uses this map for online flight planning and decision making. Components of the autonomy algorithm include thermal mapping, explore/exploit decision making, navigation, optimal airspeed computation, thermal centering control, and energy state estimation. A finite state machine manages the aircraft behavior during flight and determines when changing behavior is appropriate. A complete system to enable autonomous soaring is described with special attention paid to practical considerations encountered during flight testing. A companion paper describes the hardware implementation of this system and the results of a flight test campaign conducted at Aberdeen Proving Ground in September 2015.

Design and Development of Control Systems for an Aircraft. Comparison of Performances Through Computational Simulations

The main objective of this paper is to evaluate the technical aspects of the different controllers (PID, MPC and Neural) for the performance of an aircraft's behavior in relation to the longitudinal equations investigated. For this purpose, the behavior of these controllers was developed in a simulator to compare the performance of each one and to be able to decide which is the most advisable according to reference values. The development strategy is to conduct research to determine the various factors such as equations that will help us determine the correct analysis.

Three-Dimensional UAV Routing With Deconfliction

The work presented in this paper relates to the conceptual definition, simulation, and performance analysis of a novel, 3-D graph theory-based routing algorithm. The proposed router is designed to provide path planning with deconfliction, i.e., collision avoidance with other moving objects, for unmanned aerial vehicles (UAV) applications in general and autonomous UAV missions in particular. Thus, novel ways for “sampling” 3-D operating spaces containing hazard areas and other moving objects are presented. The router operates in a way that conforms to the commonly observed behavior of aircraft flying over relatively long periods of time at constant speed and barometric height. Thus, flying is restricted to a number of possible altitude bands, where changes in altitude and/or direction are restricted to values that ensure excessive airframe stress is avoided. The paper attaches considerable emphasis on algorithmic complexity reduction and develops a novel, adaptive, graph search scheme. The proposed router can also be used to support manned aircraft operation, both for pre-flight planning and during the mission as a pilot aid. Computer simulation results are indicative of a routing system which generates realistic flyable routes while algorithmic complexity is suppressed.

Aircraft Flight Modeling During the Optimization of Gas Turbine Engine Working Process

The article describes a method for simulating the flight of the aircraft along a predetermined path, establishing a functional connection between the parameters of the working process of gas turbine engine and the efficiency criteria of the aircraft. This connection is necessary for solving the optimization tasks of the conceptual design stage of the engine according to the systems approach. Engine thrust level, in turn, influences the operation of aircraft, thus making accurate simulation of the aircraft behavior during flight necessary for obtaining the correct solution. The described mathematical model of aircraft flight provides the functional connection between the airframe characteristics, working process of gas turbine engines (propulsion system), ambient and flight conditions and flight profile features. This model provides accurate results of flight simulation and the resulting aircraft efficiency criteria, required for optimization of working process and control function of a gas turbine engine.

Learning Traffic Patterns at Small Airports From Flight Tracks

The majority of reported near-midair collisions that involve a general aviation aircraft occur in the vicinity of nontowered airports. A prior work has investigated the feasibility of creating an automated air traffic control system for these nontowered airports using solutions to a partially observable Markov decision process. Validating such system will require an accurate model of aircraft behavior in the traffic pattern. This paper evaluates the different approaches for deriving traffic pattern models from recorded radar data. The first approach is based on prior trajectory clustering work, where turning points in trajectories are identified and clustered. This method performs well on simulated data, but due to its reliance on noisy heading rates, it has difficulty with real-world data. The second approach uses Bayesian inference techniques to learn the parameters of the traffic pattern model, where a hidden semi-Markov model with a hierarchical Dirichlet process as a prior is investigated. Inference in this model is made computationally tractable using Markov chain Monte Carlo methods. The turning point and Bayesian models are compared with each other using different $f$ - divergence measures, and the latter is found to better represent the observed data.

State Variance-Based Approach to Flight Dynamic Constraints in Multidisciplinary Design Optimization

Traditional flying qualities metrics use first-order descriptors of the “classical” aircraft modes such as the phugoid, short-period, Dutch roll, etc. These modes are often difficult to distinguish from one another in modern aircraft for which the dynamics are usually coupled, leaving designers to develop lower-order equivalent systems as approximations to the behavior of the real aircraft. On the other hand, modern optimal or robust control techniques directly address multiple-input/multiple-output systems, with coupled dynamics, and they function well with higher-order measures of system behavior like state covariances or signal norms. This work presents a new method of approximating the traditional flying qualities requirements for piloted aircraft through a flight condition-dependent recasting of these requirements as upper bounds on the state variances. A linear matrix inequality feasibility problem is developed to compute a control law that stabilizes the system for the given flight condition while satisfying both the state variance and actuator constraints.

Nonlinear aeroelastic scaling of high aspect-ratio wings

The aeronautical industry is currently facing the simultaneous and conflicting demand to enhance flight efficiency while reducing emissions. One potential solution for reducing fuel consumption is to increase the wing aspect-ratio as it improves the lift-to-drag ratio. However, higher aspect-ratio wings result in higher deflections which in turn may lead to nonlinear aeroelastic behavior. In this work, the aeroelastic behavior of a conventional regional aircraft with high aspect-ratio wings is investigated. Aeroelastically scaled models using different scaling methodologies have been evaluated and compared. These methodologies use scaling factors derived from the governing aeroelastic equations of motion to set the target values to be matched through the optimization of the scaled model structure. Two linear scaling approaches were used: the first method consists of a direct modal response matching; while the second method uncouples the mass and stiffness distribution to achieve the modal response. An alternative nonlinear aeroelastic scaling methodology using equivalent static loads is presented, which uses two different optimization routines to match the nonlinear static response and the mode shapes of the full model. The aeroelastic response agreement was found to be considerably better when the nonlinear approach is applied and the accuracy is noticeably better than the results obtained using the traditional linear scaling methods.

Flight tests and flight data analysis - teaching aerospace engineering students

The ability to carry out in-flight tests and to analyse the flight data registered is, in the case of aerospace engineering students, a vital aspect of education. Since aircraft flight tests are very expensive, frequently the funds allocated to them in the process of education are insufficient. The aim of this article is to present a relatively low-cost method of training students to carry out flight tests and to analyse flight data. The method relies on three consecutive steps. At first, simulation tests relying on the mathematical model of an aircraft are carried out. During these simulations, students analyse aircraft behaviour. Next, flight data registered during previously held in-flight tests are analysed. Finally, flight tests are performed by students. As a result, having mastered the ability to analyse real flight data, the students trained will become high-class specialists being able to conduct flight tests and analyse flight data.

Efficient Analysis of HALE Aircraft Structure for Static Aeroelastic Behavior

AbstractIn this work, the static aeroelastic behavior of flexible aircraft with a high aspect ratio wing undergoing large static deformations has been investigated analytically and numerically. Toward this end, a nonlinear structural model based on a simple one-dimensional nonlinear beam theory is used. An efficient evaluation of static deformation of the entire high-altitude long-endurance (HALE) airplane is developed by adopting the single beam model to the wing, the fuselage, the vertical fin, and the tail, and merging all the substructures together. This model can deal with arbitrarily large displacements and rotations of the whole airplane by use of Euler angles and can account for various structural couplings. Static results due to simple external loads are shown for demonstration. Then, the paper discusses coupling the beam model with several aerodynamic models to investigate the static aeroelastic performance of the high aspect ratio wing. Comparisons of the aerodynamic tools are made in terms of ...

Motion Simulation of Transport Aircraft in Extended Envelopes: Test Pilot Assessment

The European research project SUPRA (“Simulation of Upset Recovery in Aviation”) produced an extended aerodynamic model for simulation of a generic transport aircraft, capturing the key aircraft behavior beyond aerodynamic stall. As described in the current paper, a group of 11 test pilots with in-flight experience in stall conditions assessed the validity of this aerodynamic model, in combination with new motion cueing solutions in a conventional hexapod platform as well as a centrifuge-based device. Results showed that the SUPRA model was considered representative outside the normal flight envelope, and on both simulators the enhanced cueing solutions received higher subjective ratings than the comparison condition. The pilots unanimously rejected exercising these conditions without motion. It is concluded that the SUPRA model successfully demonstrates upset conditions, including stall, and that conventional hexapod motion cueing can be improved for the purpose of upset simulation. If available, a ground-based -device is recommended to provide -awareness training.

Computational Aerodynamic Modeling Tools for Aircraft Loss of Control

This paper summarizes the status of ongoing NASA research supported over the past eight years to advance computational capabilities for modeling civil aircraft loss of control due to airframe damage or wing stall. The research is motivated by a desire to exploit the capabilities of computational methods to create augmented flight simulation models that improve pilot training for such loss-of-control scenarios. Flight of aircraft with either airframe damage or operating near and beyond the stall boundary encounters additional nonlinear aerodynamic influences on stability and control from dynamic motions that, if not included in flight simulation models, may lead to incorrect pilot responses. In the present work, both low- and high-fidelity computational methods are explored for analyzing such nonlinearities. The challenge of creating nonlinear reduced-order models from high-fidelity computational data is also addressed. At the beginning, few guidelines were available for computing or modeling the dynamic stability characteristics of civil aircraft in nonlinear stalled flight regimes. To accelerate progress, additional resources were leveraged through participation in two NATO task groups consisting of a diverse international body of computational aerodynamicists and flight simulation experts. As a result, a large body of knowledge has been generated, documenting the state of the art for computing and modeling the highly nonlinear stability characteristics of an unmanned air combat vehicle. This knowledge was infused directly into the NASA loss-of-control work through parallel application studies with the NASA Generic Transport Model. From this, it is concluded that the Reynolds-averaged Navier–Stokes formulation should suffice for capturing the representative behavior of civil aircraft stall for training purposes. Furthermore, promising approaches have been identified for creating nonlinear reduced-order models from computational data that can potentially augment flight simulation models for loss-of-control scenarios.

System analysis of aircraft with natural laminar flow and forward swept wings

The objective of this paper is an enhanced analysis and assessment of a short-to-medium range aircraft configuration with natural laminar flow (NLF) and forward swept wings (FSW) designed by DLR. It is intended to show how the proposed aircraft concept could contribute to a more economic and ecologic operation. By implementing a multidisciplinary simulation and assessment framework, the net-benefit on air transportation system level is evaluated from airline perspective under consideration of realistic airline network conditions. Therefore operational aspects (e.g. stage length) and environmental factors (e.g. insect contamination, cloud encounter) which affect the aircraft effectiveness are included into the assessment. Apart from modeling the technology intended effect of fuel saving on airline economics, the study also aims to determine unintentional repercussions (e.g. change in maintenance effort, emissions, noise) which arise due to the design and the operation of the FSW–NLF concept. The overall goal of the paper is to provide aircraft operators with a better understanding of the behavior of NLF aircraft under realistic operational boundary conditions as well as to demonstrate resulting trade-offs between economical and ecological effectiveness.

Aerodynamic airfoil at critical angles of attack

Aircraft construction experts must not neglect the behavior of aircraft in extreme or closely extreme flight conditions, such as flights at critical angles of attack, where a normal flight can be easily converted into a stall. This paper highlights the essential factors that influence the behavior of aircraft in flight at critical angles of attack. Based on the available experimental results and estimations, the performances of airfoils were analysed depending on air flow conditions (categorized according to Mach and Reynolds numbers), airfoil shapes, dynamics of the transition of angles of attack, description of the flow around airfoils with increasing the angle of attack upon reaching a critical value, and the effect of roughness of airfoil surfaces at critical angles of attack. The paper gives a physical interpretation of a lift decrease and a stall. It minutely describes the origin of flow separation and categorizes airfoil sections by type of separation and their behavior during the flow at the critical angle of attack. Based on modern aerodynamics, this paper aims to show and explain the issues and the most important characteristics of the flow past the body at critical angles of attack and give practical recommendations for airfoil design. As such, it may be of interest to pilots and engineers as well as to educational and research institutions.

A novel design and control solution for an aircraft sidestick actuator based on Halbach permanent magnet machine

This paper is concerned with the design and control of a new sidestick actuators used to handle a civilian aircraft behaviour. Indeed, a discrete robust adaptive sliding mode control for a new designed aircraft sidestick based on synchronous Halbach permanent magnet machine. The main objective is to provide a new design structure and a control solution that ensures maintaining high performance specifications for the actuator and respects the set of constraints required by the considered aeronautical application. Indeed, this study achieved in a partnership with an industrial center of excellence for Fly by Wire Cockpit Controls (side sticks, rudder controls, thrust controls), proposes a novel design that enhances the characteristics of the actuator’s structure and the human machine interface between the pilot and the aircraft. Then, a new control strategy is proposed to optimize the efficiency of this actuator for the considered application. It is based on a discrete optimal adaptive sliding mode control considering time delays and uncertainties in the model by using a delay ahead predictor. The proposed strategy combines an optimal sliding mode surface with the delay ahead predictor in an adaptive control structure. Indeed, a varying parameter is used to achieve an ”on-line” adaption to the varying level of disturbances that affects the system. Then, since the sidestick actuator is designed to handle an aircraft displacement, the proposed control strategy is designed for position tracking. Simulations performed on the previously designed actuator prove the efficiency of the proposed technological solution for aircraft position control.

Control Loss Recovery Autopilot Design for Fixed-Wing Aircraft

In this paper a loop-shaping design approach is investigated for distressed fixed-wing aircraft experiencing control loss due to surface or power failure. An accurate nonlinear model of the aircraft dynamics is utilized to obtain a target aircraft behavior in the emergency situation, for which a loop-shaping controller is designed to balance performance and robustness, and to decouple different command channels. A rudder servoactuator jam scenario is presented as an example where it is seen that the autopilot recovers level flight and responds well to fly-by-wire commands from the operator.

Visualization, Selection, and Analysis of Traffic Flows.

Visualization of the trajectories of moving objects leads to dense and cluttered images, which hinders exploration and understanding. It also hinders adding additional visual information, such as direction, and makes it difficult to interactively extract traffic flows, i.e., subsets of trajectories. In this paper we present our approach to visualize traffic flows and provide interaction tools to support their exploration. We show an overview of the traffic using a density map. The directions of traffic flows are visualized using a particle system on top of the density map. The user can extract traffic flows using a novel selection widget that allows for the intuitive selection of an area, and filtering on a range of directions and any additional attributes. Using simple, visual set expressions, the user can construct more complicated selections. The dynamic behaviors of selected flows may then be shown in annotation windows in which they can be interactively explored and compared. We validate our approach through use cases where we explore and analyze the temporal behavior of aircraft and vessel trajectories, e.g., landing and takeoff sequences, or the evolution of flight route density. The aircraft use cases have been developed and validated in collaboration with domain experts.

Reduced order system identification for UAVs

Abstract Reduced order models representing the dynamic behaviour of symmetric aircraft are well known and can be easily derived from the standard equations of motion. In flight testing, accurate measurements of the dependent variables which describe the linearised reduced order models for a particular flight condition are vital for successful system identification. However, not all the desired measurements such as the rate of change in vertical velocity (Ẇ) can be accurately measured in practice. In order to determine such variables two possible solutions exist: reconstruction or differentiation. This paper addresses the effect of both methods on the reliability of the parameter estimates. The methods are used in the estimation of the aerodynamic derivatives for the Aerosonde UAV from a recreated flight test scenario in Simulink. Subsequently, the methods are then applied and compared using real data obtained from flight tests of the Cranfield University Jetstream 31 (G-NFLA) research aircraft.

Maintenance test flying – an accident waiting to happen?

AbstractThis paper focuses on maintenance test flying as pertaining to commercial jet aircraft. Aircraft maintenance manuals or regulatory prescriptions require aircraft to be test flown prior to being released to service, following specific maintenance, repair, overhaul or modification events. Further, such flights might be conducted to accept or return aircraft as demonstration of their serviceability. Similarly, test flights to verify aircraft performance are at times required.Such maintenance test flights are mostly conducted by pilots rated to fly those aircraft primarily in commercial line operations, typically with no or little training on such specific maintenance or performance test flight procedures or techniques. The international regulatory environment remains in flux with discussion ongoing.In conducting such flights a pilot is exposed to activities outside the normal aircraft standard operating procedures up to the edge of the operational flight envelope. Whilst not intentional, abnormal aircraft behaviour can nevertheless result in inadvertent flight outside the envelope with a consequential potential loss of control. History has shown that the predominant cause of fatal accidents during maintenance test flying result from complex loss of control scenarios not recovered or not recoverable. This raises the question of adequacy of pilot training.Maintenance test flights are a necessary component for the industry to maintain its exceptional safety standards and minimising loss of life. But such flights in themselves remain demonstrably one or two orders of magnitude more risky than commercial flights.

Crash simulations of aircraft fuselage section in water impact and comparison with solid surface impact

Aircraft water landing emergency provisions 14 CFR 25.801 demand requirement of ditching provision if requested in certification. This requires evaluation of the dynamic behaviour and response of aircraft in water impact to analyse the immediate injury to occupants. A correlated finite element model of a narrow-body Boeing-737 fuselage section and smoothed-particle hydrodynamics model of a body of water are coupled and utilised to investigate the structural response of the aircraft fuselage section when subjected to vertical drop test. The vertical drop of the fuselage section onto a body of water is simulated at an impact speed of 9.14 m/s, and also at higher impact speeds of 10.67 and 12.19 m/s. The vertical drop simulations are modelled using the non-linear explicit code, LS-DYNA, to predict the deformation of the fuselage section and acceleration pulses of the cabin floor, as well as the energy absorbed by the fuselage structure. The acceleration pulses from the cabin floor are then utilised as input for the occupant simulation performed using the mathematical code, MADYMO 7.5. The occupant model consists of a MADYMO FAA Hybrid-III 50th percentile dummy, a 2-point lap belt and a rigid seat. The lumbar loads experienced by the occupants in relation to both types of impacts are also presented. The dynamic simulation results from this study suggest that the fuselage section in water impact may be less severe than solid surface impact.

Insect Contamination Impact on Operational and Economic Effectiveness of Natural-Laminar-Flow Aircraft

The objective of this paper is to investigate the effect of insect contamination on operational and economic effectiveness of an aircraft with natural laminar flow wings designed by DLR. It is intended to show how insect debris located close to the wing leading edge influence fuel consumption on single missions as well as economic metrics like net present value. The focus will be on short-to-medium haul operations, i.e., aircraft similar to current state-of-the-art 150 passenger seated aircraft. During the analysis process tools for aircraft design, mission simulation and computation, insect contamination as well as life-cycle cost assessment will be used. The overall goal is to provide aircraft operators with a better understanding of the operational behavior of natural laminar flow aircraft under realistic operational boundary conditions and related economic implications.