Aircraft Shape Research Articles

OPTIMAL GEOMETRICAL DESIGN OF AIRCRAFT USING GENETIC ALGORITHMS

With the advent of computers and search and optimization tools such as the genetic algorithm, the ability to manipulate numerous aircraft design parameters in a reasonable amount of time is feasible. From this angle, the lengthy time and effort spent creating and integrating aerodynamics codes, sizing routines, and performance modules, can be mitigated by the use of a genetic algorithm. Consequently, a genetic algorithm has been created and employed as a cost effective tool to explore possible aircraft geometries in the conceptual design process of the aircraft. A program has been developed to address most aspects of aircraft design such as aircraft sizing and configuration, performance, and propulsion, to name a few. These codes have been integrated into a genetic algorithm, which performs the task of searching and optimizing. The adaptive penalty method has been employed to handle all constraints imposed on the design. In addition, adjustments for varying degrees of selection and crossover intensities and types have been studied. A design study has also been carried out to compare an existing aircraft shape with the genetic algorithm optimized aircraft shape and configuration. Results indicate that the genetic algorithm is a powerful multi-disciplinary optimization and search tool, capable of simultaneously managing and varying numerous aircraft design parameters. Moreover, the genetic algorithm is capable of finding aircraft geometries and configurations that are both efficient and cost effective.

Identification of large aircraft

Large commercial aircraft are much more easily identified by radar than are fighter aircraft, because the former's two-dimensional images have sufficient details to let one recognize the aircraft's shape. The usual problem with identification based on shape is lack of knowledge of the aspect angle. As an indication of the relative ease with which commercial aircraft can be identified, this note describes a shape-based identification method that does not require knowledge of the aspect angle.

Putting Four Dimensions in “Perspective” for the Pilot

A novel concept for a cockpit decision aid was designed from an analogy with the future cone of the Minkowski “space-time” diagram (Hawking, 1988). For this purpose, a volume of airspace around ownship was theoretically selected and projected in future time. Aircraft flight parameters consisting of three dimensions of space, and one dimension of time, were treated as “events in space-time”. Aircraft shapes depicted all “events” having a probability of occurrence within the pre-defined region of “space-time”, with collision threats marked by vectors. The resulting display provided an ‘out-the-window’ pilot-centric perspective of the predicted situation, demarcated by pre-defined time-intervals. This concept was tested in two experimental studies. Overall results suggest that such a presentation of predictive spatio-temporal air traffic information would likely aid pilot decision-making, especially in a Free Flight (FF) environment.

Exact modal analysis of an idealised whole aircraft using symbolic computation

AbstractExact expressions for the frequency equations and mode shapes of an idealised whole aircraft are derived using the symbolic computation package REDUCE. The aircraft is idealised as a bending-torsion coupled beam for the wing with the associated mass and inertia of the fuselage, tail-plane, fin and rudder assembly being concentrated at the root. The governing differential equation of motion of the aircraft is then solved in its most general form. The analysis is split into symmetric and anti-symmetric cases to formulate the equations from which the natural frequencies and the corresponding mode shapes of the unrestrained aircraft are derived. The analytical approach used here is of great significance, particularly from an aeroelastic optimization point of view, for which repetitive calculations of natural frequencies and mode shapes are often required. The application of the theory is demonstrated by numerical results. These results have been compared with those obtained from the dynamic stiffness and finite element methods.

Efficient aerodynamics for a second-generation supersonic transport aircraft

The EUROSUP Project, supported by the European Union, has investigated the use of advanced techniques for simulation of viscous flows in combination with algorithms for modifying aircraft shape to realise efficient aerodynamic designs of a conceptual second-generation supersonic aircraft. This paper describes the work performed and concludes that these methods are capable of yielding highly efficient results.

Parabolic equation techniques for scattering

Parabolic equation techniques for scattering are outlined for both acoustic and electromagnetic waves. Angular limitations are overcome by rotating the paraxial direction and solving for scattered fields that are accurate in sectors centered about the paraxial direction. These fields are then combined to obtain a scattered field that is accurate in all directions. This approach is efficient for bistatic scattering by objects that can be large compared to the wavelength. Parabolic equation techniques are applied to electromagnetic scattering by a finitely conducting sphere and a large idealised aircraft shape and to acoustic scattering in the presence of an interface.

Integrated Design of Aerodynamics and Control System for Micro Air Vehicles.

Technology on Micro Air Vehicles (MAVs) has been attracting the attention for aircraft's researchers. Multidisciplinary optimization is expected to achieve the higher performances and the stability for MAVs. This paper proposes the simultaneous optimization methods of the aerodynamics based on the aircraft shape and the control system. The purpose of the optimization is to reduce the control energy and the roll angle under the constraints with respect to the robust stability. The control system is composed of the H2 and the mixed H2/H∞ controllers. Efficient optimization procedures based on a two step procedure for the H2 optimization and LMI solver for the H2/H∞ control are developed in this study. Both aircraft shape and control design variables are simultaneously optimized by the proposed methods. Effectiveness of the proposed approaches is verified with some numerical applications.

Platform for Multi-Model Design

This paper introduces a global platform for the simulation and the design of multi-model configurations. Fluid-structure interaction and optimization procedures are coupled with turbulent incompressible and compressible flow solvers in order to treat complex aerodynamics problems. First, the equations used in modeling the fluid and the structure are presented, as well as the numerics used in the solvers. Then follows the description of our optimization framework, the gradient approximation and several optimization methods we employed. The applications concern shape optimization for turbomachinery blades and aircraft airfoils and shape optimization coupled with aeroelasticity in aeronautics. The platform is dedicated to the treatment of realistic problems and serves as a powerful tool for design in industrial environments.

The viscous optimal shape design, via spectral solutions

The shape of a flying configuration is globally optimized if its camber, twist, thickness and the similarity parameters of its planform are determined in order to obtain a minimum drag at cruising Mach number. The optimum–optimorum (OO) theory of the author solves this problem by using a lower limit hyper-surface for the drag functional. A multipoint design is realized by using movable leading edge flaps. The iterative OO theory is used for the computation of the friction drag, for the determination of the viscosity effect in the optimal shape of the flying configuration and to perform the multidisciplinary design by including structure and thermal auxiliary conditions. A proposal of a fully-optimized shape of supersonic transport aircraft with twin integrated fuselages is also made. Copyright © 1999 John Wiley & Sons, Ltd.

The viscous optimal shape design, via spectral solutions

The shape of a flying configuration is globally optimized if its camber, twist, thickness and the similarity parameters of its planform are determined in order to obtain a minimum drag at cruising Mach number. The optimum–optimorum (OO) theory of the author solves this problem by using a lower limit hyper-surface for the drag functional. A multipoint design is realized by using movable leading edge flaps. The iterative OO theory is used for the computation of the friction drag, for the determination of the viscosity effect in the optimal shape of the flying configuration and to perform the multidisciplinary design by including structure and thermal auxiliary conditions. A proposal of a fully-optimized shape of supersonic transport aircraft with twin integrated fuselages is also made. Copyright © 1999 John Wiley & Sons, Ltd.

Parametric study of supersonic aircraft shape for reduced boom

For future supersonic commercial aircraft it is important to know the strength of their sonic booms and to search for ways to reduce levels. This paper discusses: (1) the method of sonic boom calculation, (2) the effect of aircraft parameters on sonic boom magnitude, and (3) the design of an aircraft shape to reduce sonic boom. The pressure field near an aircraft is calculated using a finite-difference marching procedure in conjunction with a linear-theory panel method. With use of Zhilin’s integral, the near field is transformed to a Whitham F-function, which is the initial data for the wave propagation. The problem of wave propagation in the nonuniform stratified atmosphere is solved by a system of nonlinear equations to obtain the sonic boom signature at the ground. A global parametric study was conducted to include the influence of approximately 16 aircraft parameters, such as dihedral and sweep angle, wing location, canard, etc. Also, for a given wing and fuselage volume distribution, the sonic boom level was minimized by adjusting the wing mean camber surface. This solution was obtained by the inverse aerodynamic method based on linear (panel method) and nonlinear (Euler equation) algorithms.

Multilevel parametrization for aerodynamical optimization of 3D shapes

We introduce and discuss a combination of methods and options that aim at the aerodynamical optimization of a flow around an arbitrary aircraft shape. The flow is governed by the Euler equations, discretized by a mixed element-volume method on a fixed unstructured tetrahedrization. The shape parametrization relies on the skin of the above mesh through a hierarchical representation. Descent-type and one-shot algorithms are devised and adapted to the solution of a few model problems.

Radar cross-section computations using the parabolicequation method

Two-way parabolic equation (PE) techniques are used to compute the radar cross-section of two-dimensional objects. A finite-difference implementation of a wide angle PE in combination with non-local boundary conditions allows fast execution times on a desktop computer. The technique is applied to scattering by a cylinder and by an idealised aircraft shape. Numerical results are in good agreement with calculations using other methods.

Robust partial shape classification using invariant breakpoints and dynamic alignment

A system for classifying partially occluded noisy shapes in varying positions, orientations, and dimensions is described. An iterative algorithm derived from the colinearity principle is developed to locate invariant breakpoints on a shape contour. The set of invariant breakpoints partitions the contour into a sequence of contour segments. Each contour segment is described by an ordered sequence that represents the Euclidean distance between the pixels in the contour segment and the centroid of the region formed by connecting the end-points of the contour segment by a straight line. Two stages of dynamic alignment with the appropriate constraints are formulated to determine shape similarity. The first stage gives a distance measure of contour segment similarity, and in the second stage, the intersegment distances are used to optimally align contour segments so that a final measure of shape similarity is obtained. The performance of the system is demonstrated by considering the classification of aircraft shapes belonging to four classes and classification results are presented as functions of noise and occlusion levels. The results indicate that reasonable classification is obtained for noisy shapes with 0 to 30% occlusion.

Shape description by time series

Time series modeling techniques are adapted to represent or describe two-dimensional closed contours. Both linear and nonlinear models are fitted. It is found that to detect small changes in shape nonlinear modeling is necessary, even though linear models may be sufficient to differentiate between shapes which differ widely. A nonlinear model called the noncausal quadratic Volterra model is developed for the purpose. Implementation is illustrated with shapes of aircraft.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mesh generation by a sequence of transformations

A sequence of transformations is used to map a three-dimensional aerodynamic shape into a simplified configuration. Coordinate surfaces are generated in the mapped space and the transformation sequence is inverted to produce a three-dimensional mesh that conforms with solid boundaries. The method has been used to generate meshes about typical aircraft shapes consisting of a wing, body, tail and fin.

Air Flow and Particle Trajectories around Aircraft Fuselages. I: Theory

Abstract A potential-flow sink-source technique is used to model the flows around fuselage shapes. It is shown that the flow in any plane can be approximated reasonably well using an axisymmetric model of similar shape and that at a few fuselage radii from the nose the flow is determined principally by the size of the fuselage radius. Departures from the free-stream velocity are typically less than 10% and vary as the inverse square of the scaled distance from the nose. Analyses of water drop trajectories around three different aircraft shapes show that two of the more important features of the trajectories, the width of the shadow zone and the concentration enhancement factors, can be described quite generally in terms of a scaled fuselage radius and a parameter similar to the Stokes number. Thus the maximum width of the shadow zone is shown to be about one-fifth of the fuselage radius and occurs for a combination of particle size and aircraft speed for which the modified Stokes parameter has a value of ...

Forces exerted by a weak shock wave on a wing of complicated shape in plan at supersonic velocities

A method is presented for calculating the supersonic distributed and total aerodynamic characteristics of a wing of complicated shape in plan, including a wing having the shape of an aircraft in plan which encounters a weak shock wave of arbitrary orientation. The problem is solved in the linear formulation.

A Subsonic Panel Method for Iterative Design of Complex Aircraft Configurations

An iterative-design method for the generation of wing geometries with specified surface-pressure distributions is described. The design method is an adaptation of the well-known surface-transpiration technique for approximating boundary-layer effects. A velocity distribution normal to the aircraft surface is sought which minimizes the difference between computed and desired pressures. The transpiration distribution for a given initial wing geometry is determined by numerical optimization and is then used to reloft the configuration. The use of this iterative procedure with a subsonic surface-singularity panel method is illustrated for several example design problems. I. Introduction D URING the past decade, several panel methods16 have been developed which can be used to determine the potential flowfield about realistic aircraft shapes. These computational methods provide the needed capability for accurately modeling the aerodynamic interference effects of arbitrary geometries such as multiple lifting surface and/or wing-body configurations. Viscous effects for weak interaction flow conditions can also be approximated by the incorporation of suitable boundary-layer computational methods.1

The shapes of things to come—an introduction to the capabilities of the British Aerospace Numerical Master Geometry system

The purpose of this paper is to give a brief introduction to the scope, flexibility and power of the British Aerospace Numerical Master Geometry (NMG) System, which is a computer aid for the design and manufacture of complicated three-dimensional curved surfaces. NMG is currently used at all ex-BAC sites within the Aircraft Group of British Aerospace for the purpose of generating and storing master computer models of the external shapes of aircraft or components. These master models may then be interrogated using a simple command language to derive information about the external shape for such diverse uses as aerodynamic analysis, detail structural design, numerically controlled machining and inspection. The use of such models means that everyone has access to the same basic information, and consistency is assured.