Aeroelasticity
Aeroelasticity is a scientific field focused on the interaction between solid and elastic objects and the forces generated by moving air. It examines how air impacts structures that can deform, such as aircraft and buildings, leading to potential distortions or failures. Since its formal definition in the mid-twentieth century, aeroelasticity has played a crucial role in the design of various objects to ensure their functionality and safety when subjected to aerodynamic forces. Key phenomena studied within this discipline include flutter, divergence, buffeting, dynamic response, load distribution, control effectiveness, and control system reversal.
Divergence can lead to catastrophic twisting of structures when wind forces exceed their capacity, while flutter refers to the instability caused by the elastic movements of components. Both can significantly impact the performance and integrity of vehicles and buildings alike. Engineers utilize wind tunnel tests and simulations to analyze these effects, ensuring that structures can withstand the anticipated aerodynamic forces. The advancements in aeroelasticity contribute to the creation of safer designs in aviation and architecture, enhancing the resilience of these vital infrastructures against the challenges posed by environmental conditions.
On this Page
Subject Terms
Aeroelasticity
Aeroelasticity is a field of science that studies the interaction between an object that is encountering moving air and the forces generated by that air. It specifically looks at what happens when air hits an object that is both solid and elastic, or moveable, and the way the air can bend or distort that object. Since it was first defined in the mid-twentieth century, aeroelasticity has become an important factor in designing aircraft, buildings, and a number of other items for maximum function and safety.
Background
The word aeroelasticity comes from the Greek words aero, meaning "air," and elastikos, meaning "propulsive." In the middle of the seventeenth century, the Latinized form, elasticus, became "elastic," and adopted the meaning of "expanding spontaneously to fill the available space." In 1947, English engineer Arthur Roderick Collar defined a new term, aeroelasticity, as the study of the forces at work when moving air encounters inert and elastic forces.
The forces created by moving air are known as aerodynamics. Aerodynamics can affect an object that is moving through the air, such as a car, airplane, or bird, or an object that is stationary with air moving around it, such as a building, tree, or flagpole. The force exerted by the air can be significant and can be affected by some characteristics of the object. For instance, a sports car that is designed to be low to the ground with a hood angled to allow air to easily flow over it is going to encounter less resistance from the air than a large eighteen-wheeled truck, and a thin flagpole will withstand the forces of a heavy wind better than a large billboard will.
Objects that encounter the forces of air are generally a combination of solid and elastic components. For example, the metal of an airplane body is solid and inert, but the body is made of multiple parts that move in relation to one another, no matter how solid they may appear. The parts themselves may be rigid, but the areas where they connect can flex and move, giving the entire object an elastic quality. Air pushing against the parts in a way that brings them together can compact the object, while air forces that push one of the parts away from the other can cause the object to flex and expand. In either case, the object is distorted by the air from the form that it has when there is no air pushing against it. Aeroelasticity is the study of how these three forces interact with one another. It also encompasses the craft of designing items to withstand the distortion that results in elastic objects as the result of the wind.
Overview
Aeroelasticity is a factor in the design and use of items that have to withstand the effects of moving air. Individuals who study or work with aeroelasticity are concerned with a number of specific aspects of this effect. These include flutter, divergence, buffeting, dynamic response, load distribution, control effectiveness, and control system reversal. Some of these factors affect objects that are moving through the air, such as a plane, while others are also encountered by objects that are stationary with air moving past, such as a skyscraper. These effects can be minor, causing slight, almost imperceptible, vibrations; or they can be serious, resulting in damage to the object. Of these, the two most significant to the study of aeroelasticity are divergence and flutter.
Divergence occurs when the force of the wind is greater than the ability of a structure, such as a plane or building, to overcome that force. This leads to twisting of the structure and can result in structure failure. Divergence can be overcome by adjusting the angle at which the structure encounters the wind (such as angling the wings of a plane) and/or by increasing the stiffness of the structure.
Flutter is instability in the structure that is caused by its elasticity. The movement of the components of the structure will cause slight vibrations as the structure adjusts to the wind forces. Pilots often refer to this as "buzz."
Other phenomena that are considered in the study of aeroelasticity include buffeting, or the forces of variations in air movement, such as the "wake," or air disturbance, left by another aircraft; dynamic response, which are structure distortions that result from wind gusts or sudden movements of an aircraft; load distribution, which refers to how these distortions are spread over the entire surface of a structure; control effectiveness, which addresses how the aerodynamic disturbances affect the handling ability of an aircraft; and control system reversal, which occurs when the aerodynamics outside an aircraft cause the opposite of the expected effect when the controls are used.
Any of these factors can cause structure failure, which is a particular danger in aircraft. To avoid potentially disastrous effects from aeroelasticity, engineers use careful design and extensive product testing. This testing can involve wind tunnels, in which models of a plane or parts of a plane can be exposed to forces of wind that will match and exceed those that will be experienced in use. These tests can also simulate the effects of winds at various temperatures, such as the very cold temperatures experienced by large passenger aircraft flying tens of thousands of feet in the air.
Aircraft models can also be subjected to vibrations that will simulate what they will experience in the air. This testing is conducted while the plane is safely on the ground. Components of buildings, such as beams or wall structures that will be part of a tall skyscraper, can also be tested in this way. Testing can simulate the flutter that could be encountered in certain environmental conditions.
The study of aeroelasticity is helping to create safer buildings and aircraft. These structures can be built to withstand the effects of the maximum aerodynamic forces that can be anticipated during their use. The study of aeroelasticity scenarios can also aid with the development of simulations that will help pilots be prepared to deal with the effects of aeroelasticity they may encounter in actual flight.
Bibliography
"Aeroelasticity: Wing—Flutter and Divergence." Aerodynamics for Students, s6.aeromech.usyd.edu.au/aerodynamics/index.php/sample-page/aeroelasticity/. Accessed 18 Dec. 2017.
Bishop, R.E.D. "Arthur Roderick Collar, 22 February 1908–12 February 1986." Royal Society,1 Dec. 1987, rsbm.royalsocietypublishing.org/content/roybiogmem/33/163. Accessed 18 Dec. 2017. Daglis, Mindaugas. "Aeroelasticity Model for Highly Flexible Aircraft Based on the Vortex Lattice Method." Aerospace, 2023, doi.org/10.3390/aerospace10090801/. Accessed 7 Nov. 2024.
Dimitriadis, G. "Aircraft Design." University of Liege, www.ltas-cm3.ulg.ac.be/AERO0023-1/ConceptionAeroAeroelasticite.pdf. Accessed 18 Dec. 2017.
Lucas, Jim. "What Is Aerodynamics?" Live Science, 20 Sept. 2014, www.livescience.com/47930-what-is-aerodynamics.html. Accessed 18 Dec. 2017.
Moraguez, Matthew. "Aeroelasticity." University of Florida, plaza.ufl.edu/moraguezma/Aeroelasticity.pdf. Accessed 18 Dec. 2017.
Myers, Andrew. "Good Vibrations: Stanford Engineers Put a Damper on 'Aeroelastic Flutter.'" Stanford Report, 24 Mar. 2011, news.stanford.edu/news/2011/march/airplane-aeroelastic-flutter-032411.html. Accessed 18 Dec. 2017.
Names, Ben. "5 Things You Should Know about Flutter." Structural Design and Analysis, structures.aero/blog/5-things-should-know-flutter/. Accessed 18 Dec. 2017.
Roberson, Darryl. "What Is an Aeroelastic Analysis in Aircraft Engineering?" Engre, 15 Aug. 2022, engre.co/blogs/articles/what-is-an-aeroelastic-analysis-in-aircraft-engineering/. Accessed 7 Nov. 2024.
"So Just What Is Aeroelasticity?" Georgia Tech School of Aerospace Engineering, www.msmith.gatech.edu/aeroelasticity. Accessed 18 Dec. 2017.