Search

Aircraft environmental performance metrics including fuel burn, takeoff and landing noise, and gaseous emissions are increasingly driving the design and optimization of modern aircraft engines. Gradient-based methods can significantly reduce the computational resources required during their multidisciplinary optimizations. However, current state-of-the art noise modeling tools do not allow for effective computation of sensitivities of acoustic metrics with respect to engine design and control variables, and therefore cannot be easily integrated into multidisciplinary optimization tools. This paper presents the utility of the python Noise Assessment tool (known as pyNA): an aircraft noise estimation model providing sensitivities of acoustic metrics, enabling multidisciplinary optimization and optimal control of engines for low-noise aircraft. The model is used to assess the trades of environmental performance metrics in the clean-sheet engine design for the NASA supersonic technology concept airplane. For the engine examined, if the fan diameter is allowed to change while technology levels are held constant, the takeoff noise levels and emissions are found to be most sensitive to the design fan pressure ratio. For an engine with a fixed fan diameter, takeoff noise levels are found to be insensitive to design variables; whereas nitrogen oxide emissions and cruise thrust-specific fuel consumption are most sensitive to the engine fan and high-pressure compressor pressure ratios. [ABSTRACT FROM AUTHOR]

A generic waverider-type hypersonic aircraft that undergoes an ascent trajectory has been modeled using a first-principles reduced-order model. Two types of operability limits are added that represent boundaries on the aircraft trajectory map (of vehicle altitude versus Mach number). These boundaries are associated with engine unstart and ram-scram transition. The predicted unstart boundary is to be avoided; the ram-scram transition is a condition through which the aircraft must fly, but it is useful for the control system to know when this transition is approached to account for possible sudden changes in thrust and moments. The model shows that unstart occurs if the aircraft flies too high, too slow, or at too great of an acceleration. The unstart limit can be avoided by selecting a trajectory having sufficiently large dynamic pressure or a low vehicle acceleration. Optimizing these factors avoids an excessive value of the fuel-air ratio that is required for trim. The model also identifies an engine inlet geometry that avoids unstart. To assess the model, the computed results are compared to some available experiments. [ABSTRACT FROM AUTHOR]

Air traffic controller workload is considered to be a limiting factor to air traffic growth. Previous research introduced the static solution space approach to assess the difficulty of aircraft merging tasks. In this paper the dynamic, tangent-based solution space will be introduced that includes the future trajectory intent of all aircraft. Metrics derived from the solution space, together with common metrics, were tested for correlations with controller workload. An experiment has been conducted where subjects were required to line up all aircraft in a sector towards a certain waypoint, while periodically rating their workload. High correlations were found between several solution space related metrics and subjective workload ratings. In contrast to the number of aircraft metric, which had the highest correlation with workload, the dynamic solution space may allow for controller workload prediction in real-time. [ABSTRACT FROM AUTHOR]

The article discusses the optimal trajectory optimization for a fixed-wing unmanned aerial vehicles (UAV) in three-dimensional (3-D) space. Details regarding the study including the time-optimal path in 3-D space both in the presence and absence of wind for a constant speed, fixed wing UAV are given. Several methods of the study including path generation using a kinematic model and tracking using a dynamic model, as well as the geometric methods are also explored.

The article presents a study which used of collaborative optimization (CO) with decomposition method in calculating a flight-vehicle trajectory optimization-design problem with constraints of differential equations. The problem is converted into a finite-dimensional nonlinear optimization problem by applying a collocation method and dividing it into 40 uniformly time subintervals, until these are decomposed into only two subproblems and one system-level problem at a half-time point.

Flight-path optimization is designed for minimizing aircraft noise and fuel consumption around airports and for increasing the number of aircraft operations. The main objective of this paper is to provide the optimal flight approach, taking into account noise sources, fuel consumption, constraints, and extreme operational limits of aircraft. This paper introduces a new trajectory generation algorithm based on Hamilton-Jacobi-Bellman considerations, taking into account aircraft jet noise. The shortest and fastest continuous descent approach is obtained as an optimal trajectory reducing aircraft noise (-6 dB) and fuel consumption (-27 % to -15 %). It is a one-segment approach with a soft and short continuous descent, which is better conceived in terms of reduction of environmental impacts of aircraft than the two-segment approach. Results show that this new method is appropriated for aircraft trajectory optimization and could be implemented in avionic systems. It can be interfaced with the in-flight management system respecting constraints of the airspace system regulation and improving its functionalities. Shortest and fastest continuous descent approach could benefit both airlines and conununities. It also could be designed for practitioners to understand the implementation of airport management systems. Shortest and fastest continuous descent approach is considered as a strategy to be used for the final approach. It allows one to avoid difficulties of the flight. It can help the flight crew to make timely and correct thrust settings and approach path corrections. Because this study is limited to one noise source for one aircraft, other research is needed to take into account all noise sources of several aircraft. [ABSTRACT FROM AUTHOR]

A new computational method has been developed that simulates the performance of a civil aircraft and determines the fuel consumption and emissions throughout the flight trajectory by linking the main aircraft aerodynamic characteristics with a model of engine performance. The performance emission simulation of aircraft operations model responds to the needs of the Aviation Integrated Modelling project by delivering a computationally fast and reliable model able to simulate aircraft performance, fuel use, and emissions. The methodology implies that the airframe aerodynamic characteristics and the performance of the engine are modeled by generic nondimensional relationships and related through the equations of motion. These nondimensional characteristics are sufficient to enable accurate determination of the forces acting on the aircraft, the fuel burn of the engine, and the key parameters that determine the emissions of pollutants such as nitrous oxides. Within this paper, this nondimensional approach is demonstrated and validated using comparisons with flight data from commercial aircraft operations. The results show that the model can accurately simulate civil aircraft performance for a range of flight conditions and operating procedures. In future work with the Aviation Integrated Modelling project, the method will be further developed and applied to investigate novel aircraft technologies, new operating procedures, and the use of alternative fuels. [ABSTRACT FROM AUTHOR]

This article discusses findings of a study, which compared the multigroup and multibin methods for the Apollo AS-501 reentry. The study also demonstrated reentry radiation problem with high accuracy for a very low number of bins. The simple arithmetic and the Rosseland means are two obvious possibilities, and these two means were experimented using artificially generated source and opacity functions, and for the unweighted mean opacity, using the Apollo data as well. For this study, the AS-501 flight was chosen because of its flight trajectory.

Discusses a methodology developed for constructing aircraft terrain following/avoidance trajectories incorporating the aircraft actuator constraints. Typical solution to the problem of navigating an aircraft over and through terrain; Significance of terrain-following trajectories to military aircraft; Ways by which aircraft trajectory can be parameterized.

The problem of finding an optimal aircraft trajectory for long-distance flights in three dimensions subject to radar detection constraints is considered. A general point-mass model previously developed is not suitable because the time discretization needs to be very fine to resolve the rigid-body dynamics resulting in very large optimization problems. Different reduced mathematical models are derived and compared to the more general performance model. Finally, a long-range mission involving two subsonic jet trainers approaching a radar target is numerically simulated. The results indicate that the time a hostile radar has an approaching aircraft under surveillance can be greatly reduced by using the proposed methodology. [ABSTRACT FROM AUTHOR]

Coupled computational fluid dynamics with six-degree-of-freedom trajectory predictions using an automated Cartesian method are demonstrated by simulating a GBU-31/Joint Direct Attack Munition store separating from an F/A-18C aircraft. Numerical simulations are performed at two Mach numbers near the sonic speed and compared with flight-test telemetry and photographic-derived data. For both Mach numbers, simulation results using a sequential-static series of flow solutions are contrasted with results using a time-dependent approach. Both numerical approaches show good agreement with the flight-test data through the first 0.25 s of the trajectory. At later times the sequential-static and time-dependent methods diverge, after the store produces peak angular rates; however, both remain close to the flight-test trajectory. [ABSTRACT FROM AUTHOR]

Focuses on a study which developed a radar cross section constraint suitable for three-dimensional flight-path optimization. Performance model; Background on trajectory optimization; Numerical simulation; Conclusions.

Presents a study that examined the application of intelligent cockpit systems to aid air transport pilots in planning and following a safe four-dimensional trajectory to the runway threshold during emergencies. Definition of emergency trajectory generation; Methodology; Results and discussion.

Presents a study which described the development of a tool for the analysis and design of noise abatement procedures at any given airport. Definition of a trajectory optimization problem; Flight-path computation; Numerical examples involving departure trajectories; Effectiveness and flexibility of the tool for analysis of noise abatement procedures.

Provides information on a study which described the development of a balanced field length trajectory optimization approach for a multi-engine helicopter sustaining a single engine failure. Helicopter modeling; Optimal control formulation; Numerical results; Conclusion.

Presents information on a study that deals with the use of beggar code for multiple-body trajectory calculations. Details on grid generation; Specification of the problem; Results; Conclusions.

Presents information on a study which investigated periodic flight trajectories that achieve optimal fuel savings for hypersonic flight. Discussion on optimal time-averaged damped harmonic motion; Optimization results for parameterized altitude profiles; Conclusions.

Presents information on a study which developed an analytical framework to compare the approximate performance of periodic hypersonic cruise (PHC) trajectories for global reach. Performance analysis; Parameters of a periodic hypersonic cruise trajectory; Comparison of flight profiles; Payload mass advantage of vehicles flying a PHC trajectory.

Focuses on the modification of the Snyman-Fatti stochastic multistart trajectory method for global optimization. Distinction between a global and a local phase in the application of the original minimization procedure; Choices of parameter values; Assessment of the performance of the modified algorithm; Applications of the method.

Presents a study which analyzed the predicted trajectories for the fuel tank of airplanes in the full and empty fuel conditions. Iteration of Euler solver and multiblock overset grid scheme; Equation used in expressing time relaxation method; Results and discussion.

Presents a point-mass aircraft model for solving multistage trajectory optimization problems in three dimensions. Performance model; Multistage trajectory optimization; Test case.

Describes a model and numerical implementation used to calculate optimal trajectories for flight path. Calculus of variations as basis of early methods for finding optimal trajectories; Discretization of differential algebraic equations (DAE) as a common approach to calculating optimal trajectories; Robustness of the solution method as one difficulty in solving trajectory optimization problem.

The article discusses a real-time flight trajectory optimization approach and it verification in flight. Several inquiries regarding to real-time flight-path generation have led to a flight path by linking the trim conditions in prestored databases. Using the block diagonal Hessian method, the approach discretizes all of the variables, motion equations and constraint condition equations and changes the trajectory optimization problem into a nonlinear programming problem.

This paper describes the development of a novel tool that calculates environmentally optimized conflict resolutions for two consecutive arrival flights that feature an in-trail separation conflict. This dual-event tool is an extension of a single-event version of the tool that was developed earlier for the analysis and design of noise-abatement procedures around airports. The new tool combines a noise model, an emissions inventory model, a geographic information system, and a dynamic trajectory optimization algorithm. The optimization algorithm generates routings and flight paths that minimize the environmental impact in the residential communities surrounding the airport while satisfying all imposed operational and safety constraints. The environmentally optimized conflict resolutions calculated with the dual-event version of the tool are illustrated in an example scenario based on an approach to one of the runways of Amsterdam Airport Schiphol in The Netherlands. The results indicate that the optimal resolution strategy heavily depends on the considered aircraft types. [ABSTRACT FROM AUTHOR]

The purpose of this study is to apply a multidisciplinary optimization method for the conceptual designs of hypersonic experimental vehicles with advanced airbreathing engines. Using this method, we obtain the necessary vehicle sizes and optimal flight trajectories. The vehicle has a lifting body shape. First, we integrate analytical methods into the optimization problem, the solution of which yields the smallest gross weight of the vehicle. The results indicate a vehicle that is about 12m in total length and 4-5 Mg in gross weight. This information allows us to determine the optimal vehicle configuration and flight trajectory for a highly feasible hypersonic vehicle. In addition, the trajectory optimizations enable the vehicle to glide back to a takeoff point without consuming propellant. This study confirms the effectiveness of the proposed analysis and optimization method. [ABSTRACT FROM AUTHOR]

The flowfields in the tip region of the rotor passage are investigated from a large-scale low-speed axial compressor test at both the design and near-stall conditions by using stereoscopic particle image velocimetry. The characteristics of the tip leakage vortex (TLV) are analyzed based on the variations of its trajectory, concentration, size, streamwise velocity, and the blockage effect, which are extracted from both the ensemble- and conditional-averaged results. According to the ensemble-averaged performance of the TLV, its evolution procedures can be divided into several distinct flow phases. As the flow phase of the TLV changes, its mean flow characteristics also change accordingly. The TLV is inherently unsteady and features unsteady behaviors of vortex wandering, splitting, and breakdown, which have profound effects to its mean flow characteristics. [ABSTRACT FROM AUTHOR]

Methodology for construction and implementation of in-flight trajectory management systems for vehicles participating in future small aircraft transportation systems is considered. The small aircraft transportation systems concept is a modern regional airspace system exploiting integration of key airborne and ground infrastructure technologies to facilitate efficiency and safety improved operations at noncontrolled public-use airports. An area where new trajectory management guidance systems may provide significant benefit is the transition between en route flight and the terminal airspace boundary, or possibly interior terminal airspace navigation fix points, for both approach and departure. Energy state theory and space-time curve geometry are investigated as tools for tailoring time to interface or time to land with traffic constraints. Results imply the trajectory management concepts offer significant design freedom to tailor flight paths and vehicle states for optimum performance and safety in real time. This strategy will also tend to provide practical trajectory profiles while avoiding heavy computational burdens. [ABSTRACT FROM AUTHOR]