An Introduction to the Elements of Airplane Stability and Control

Undergraduate Aeronautical Engineering Courses
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source url The study of propulsion is what leads the the engineers determine the right kind of engine and the right amount of power that a plane will need.

Aeronautics (AERN) < Kent State University

Materials and Structures. The choice of materials that are used to make the fuselage wings, tail and engine will affect the strength and stability of the plane. Many airplane materials are now made out of composites, materials that are stronger than most metals and are lightweight.

Stability and Control. The pilot uses these instruments to control the stability of the plane during flight. NASA Engineering Teams consist of many individuals - engineers, technicians, and scientists and various support personal. Scientists are knowledge seekers. They are inquisitive, seeking answers to known questions and finding many more questions.

Engineers are problems solvers. They are the people that make things work and make life interesting, comfortable, and fun.

University Catalog

Technicians are skilled personnel. Their skills are necessary for the research and development activities of Engineers and Scientist. Learning Outcome Demonstrate fundamental understanding of basic concept of flight, aerostructures and propulsion systems together with the important classes of materials used in airframes and aero-engines. Describe basic aircraft systems and its operations and requirements and the Mechanical engineering aspects of aerospace system design and function plus the elements of radar and navigation systems, navigation and landing systems, aircraft electrical power, requirements for radar and actuator systems Recognise the interrelationships underpinning the laws governing these two disciplines.

Define the basic aerodynamics lift and drag forces and general aircraft flight performance and propulsion. Identify the general concept of aerospace engineering and the general aircraft systems and avionics involved in the operation of an aircraft. Execute computer simulations and extract data and perform analyses.

However, it cannot resort to the knowledge gained either from significant operational data or extensive flight test data. As a result it can only rely on a physics based approach and moreover, this approach needs to be modular if it is to assist in the necessary multidisciplinary design process. Within this chapter, a brief review of past methods for modelling and simulation of flexible aircraft is presented before the physics based modular approach is discussed. This is followed by details of the methods needed to integrate aerodynamics, structural dynamics and flight dynamics within a single simulation framework.

Finally, the reader is presented with two test cases that demonstrate the use of such a framework in aircraft design. Traditionally the flight dynamics community has focused on the link between inertial dynamics and aerodynamics and it assumes structural dynamics to occur at far higher frequencies than those of rigid-body dynamics.

Basic Aerodynamics - CG and Stability

The vice versa is true for the structural dynamics community who have mainly focused on specific loads cases for sizing airframe components. The development of aircraft such as the Boeing [ 7 ], which was exceptionally large, and the Rockwell B-1 [ 8 ] with its flexible fuselage made it necessary for flight dynamics and structural dynamics to be integrated.

Aircraft Load and Trim

The approach retains the inertial components of the classical nonlinear six degree of freedom 6-DoF equations [ 1 , 2 ]. However, the aeroelastic effects are introduced by the addition of states related to each aeroelastic mode. Assuming that the free vibration modes are available, these make a set of orthogonal functions. The modal representation of the airframe is often obtained through the use of beam element models of the structure and the use of structural analysis software such as NASTRAN.

The sum of the mode shapes is theoretically infinite but in practice, a finite number of mode shapes are selected in order to investigate the coupling of aeroelastic modes with rigid-body dynamics. The coupling between the rigid-body motion and elastic motion takes place through the forces and moments. This formulation allows the application of stability analysis and flight control methods that have been developed based on traditional aircraft models.

Since the work done by Waszak and Schmidt, modelling frameworks of varying complexity have been developed both in industry and academia. Industrial frameworks are highly complex and aimed at supporting certification activities.

Undergraduate Course Description

Perkins, C. Basic fluid dynamics concepts, conservation laws, potential, airfoil and wing analysis. Topics as applied to dispatch functions include briefing techniques, preflight, weather analysis and flight planning. The aerodynamic forces and moments are modeled using the concept of aerodynamic stability derivatives. Statics and equilibrium of rigid bodies in 2-D and 3-D.

Much research has been carried out to reduce the computational cost and the effort needed to integrate CFD solvers with CSM packages. However, more often the approach has depended on the specific technical challenge faced by the designer.

Table of Contents

The subject of airplane stability and control has advanced much since the elements were first learned just over one hundred years ago. Those who discovered. Find helpful customer reviews and review ratings for An Introduction to the Elements of Airplane Stability and Control at Read honest and.

Academic research has shown the capability to link aeroelasticity with flight control and develop novel approaches to aeroservoelastic analysis of highly flexible configurations [ 13 , 14 , 15 ]. Structural flexibility effects have been modelled through the implementation of a nonlinear structural dynamics formulation and aerodynamic contributions have been captured by means of an Unsteady Vortex Lattice Method UVLM code.

Solving the geometrically-nonlinear beam equations in three different ways, Palacios et al. It has been shown that for certain geometries the intrinsic model required two times less operations per iteration due to simpler algorithms. With regards to aerodynamic modelling Palacios et al. Three models—strip theory, strip theory with wingtip effects correction and UVLM—have been compared for different reduced frequencies and wingtip deflections. It has been shown that at low reduced frequency wingtip effects is of high importance both for low and high aspect ratio wings. However, for the case of increased reduced frequencies there has been no agreement of results for low aspect ratio wing.

On the other hand, for high aspect ratio wing the agreement between the UVLM and the strip theory without wingtip correction has been shown. Such an agreement has been expected as increasing wing aspect ratio tends to reduce the 3D effect over the wing. The dynamic stall effects have not been modelled in the examples, nevertheless they may be of a great importance for a highly flexible wing.

It is important to notice at this point that, if such a dynamic stall model is required by the user, empirical methods are much easier to implement within 2D strip theory than within the UVLM. Integration of both expansions into a single methodology provides a simple alternative to more complex two-dimensional and three-dimensional models for preliminary active aeroelastic analysis of High Aspect Ratio Wings HARW.

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Furthermore, novel concepts for future aircraft, such as those based on blended-wing-body configurations, need detailed stability and control analysis early in the design stage. A real time pilot-in-the-loop simulation environment is therefore needed to identify and solve stability and control problems. The development of such a simulation model requires a trade-off between model fidelity and computational cost. The case for developing physics based simulation models and the motivation to move away from the classical formulations that rely on stability and control derivatives stems from the need for flight dynamic insight at the early conceptual design of highly integrated concepts.

For such concepts, a database of stability and control derivatives such as Heffley and Jewell [ 17 ] does not exist. Moreover, these concepts integrate numerous technologies, such as active folding wingtips for flight and loads control [ 18 ] for which empirical methods also do not exist. The modelling and simulation of airframe aerodynamics alone can be complex, but a further layer of complexity is added when considering flexible aircraft for which, the inertial, aerodynamic and structural models need to be coupled. Multiple calculation points, known as structural nodes and aerodynamic panels, must be defined around the airframe and used to capture local flow physics.

The structural model must be coupled with the aerodynamics model so that aerodynamic forces and moments acting on the structure modify the effective shape of the aircraft. To complete such an aeroelastic coupling, the updated shape is used to compute the aerodynamic loading for the next iteration. This additional layer of complexity and iteration process requires a clear definition of methods used when investigating aircraft flight dynamics. These can be broadly divided into two categories: Low fidelity models used in particular for flight simulation and preliminary design studies.

These allow for a rapid flight dynamic analysis and may allow parameters to be modified for identifying and quantifying possible optimised solutions.

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High fidelity computationally expensive models which are used to consolidate the results obtained via low fidelity simulations and help in the investigation of specific problems where low fidelity simulation is not accurate. For a given problem, multiple approaches can be adopted depending on the needs of the user or the key characteristics of the simulation framework.

Within the latter method, multiple sub-layers of complexity can be added depending on the mathematical formulation being used. A direct solving method, which is the most intuitive as it is based on discrete structural loads and nodes, will also be the most laborious and computationally heavy for a high number of structural elements.

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Alternatively, the modal approach restricted to frequency ranges of interest will be more efficient for linear deformations. Nonlinearities may be relevant only for specific modes and parts of the structure so that optimal solving methods can be identified as well. Similarly, centre of gravity CG position and inertial terms will vary with structural flexibility and displacement.

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Therefore, acceptable or desired fidelity must be identified. For example, assuming a fixed CG and inertia can lead to significant simplifications in the EoM. However, this may be incorrect for HALE configurations where most of the mass lies in the flexible wing that undergoes large deformations. Multiple methods to capture the aerodynamic loads acting on the aircraft have also been developed for different levels of fidelity; from simple lifting line theory, use of Engineering Science Data Unit ESDU to more complex UVLM and further to more expensive CFD based processes.

The desired accuracy and performance can be optimised depending on the purpose of the framework. Dynamic stall models can also be added for a more accurate simulation of high angle of attack or flow detachment scenarios [ 19 ]. CFD simulations are at the higher fidelity end of the spectrum and can be used for construction of the aerodynamic databases [ 20 ]. The objectives and scope of the problem being considered will undoubtedly dictate which mathematical formulation is selected.

For instance, the aerodynamic forces can be calculated using either a Modified Strip Theory MST or a UVLM method [ 21 ] depending on the fidelity requirements and the available computational power. The structural deflection of the wing can be assumed either linear through an Euler-Bernoulli model or nonlinear with a Timoshenko model [ 22 ]. Various atmospheric disturbance models [ 23 ] are also implemented so that flight simulations with or without gusts and turbulence are possible for specific gust loads and flight control research.

Flight control laws and actuation models of a variety of control surfaces can be used if the user wishes to investigate and develop optimal control or loads alleviation laws. The gravity and navigation model allows for trajectory and autopilot if required. So far a number of different modelling approaches towards flight dynamics modelling of flexible aircraft have been introduced. This section focuses on the possible problems and issues that emerge when integrating the various elements of such a framework and discusses the need for modularisation.

The basic components required for building a simulation framework are as follows: A structural dynamics model that outputs airframe deformation. This should require forces and moments acting on the structure as inputs, and provide the corresponding displacements, velocities and accelerations as outputs.

Advanced Flight Dynamics with Elements of Flight Control

An aerodynamic model that provides aerodynamic forces and moments as a function of the flight conditions, rigid-body attitudes and structural deformations. An EoM block which uses the total forces and moments acting on the aircraft to compute the vehicle acceleration, velocity, attitude and position in the various reference frames. This will require a clear definition of aircraft mass properties.

Atmosphere model that outputs parameters such as Reynolds number required to calculate aerodynamic forces and moments. External atmospheric disturbances based on external velocity fields through which the aircraft is flying. Adopting a modular approach allows for a more versatile framework that can be used to study different configurations and scenarios.

Aeronautical Engineering

Moreover, it allows the adoption of multiple approaches to solve particular mathematical or physical problems. The overhead effort required to develop a modular framework, which primarily takes the form of software engineering, is justified by the end result. If carefully managed a versatile framework that allows solvers and models to be treated in a plug-and-play fashion is achievable.