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82-539: Development of the initial concept was done with wind-tunnel testing in the mid 1980s under Air Force contract. The designation "X-52" was skipped in sequence to avoid confusion with Boeing's B-52 Stratofortress bomber. The pre-production version of the F/A-18 was an ideal aircraft for proving AAW technology, a relatively high wing aspect ratio for a fighter, with adequate strength, but no additional stiffness needed to be added to change its twisting behaviour. The X-53 F/A-18

164-402: A thermodynamic system is equal to the energy gained as heat, Q {\displaystyle Q} , less the thermodynamic work, W {\displaystyle W} , done by the system on its surroundings. where Δ U {\displaystyle \Delta U} denotes the change in the internal energy of a closed system (for which heat or work through

246-448: A change in the internal energy of the system need to be accounted for in the energy balance equation. The volume contained by the walls can be the region surrounding a single atom resonating energy, such as Max Planck defined in 1900; it can be a body of steam or air in a steam engine , such as Sadi Carnot defined in 1824. The system could also be just one nuclide (i.e. a system of quarks ) as hypothesized in quantum thermodynamics . When

328-451: A clamped-free beam (i.e., a cantilever wing) are which yields the solution As can be seen, for λL = π /2 + nπ , with arbitrary integer number n , tan( λL ) is infinite. n = 0 corresponds to the point of torsional divergence. For given structural parameters, this will correspond to a single value of free-stream velocity U . This is the torsional divergence speed. Note that for some special boundary conditions that may be implemented in

410-470: A concise definition of thermodynamics in 1854 which stated, "Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency." German physicist and mathematician Rudolf Clausius restated Carnot's principle known as the Carnot cycle and gave to the theory of heat a truer and sounder basis. His most important paper, "On

492-433: A continuous stream of vortices known as a Kármán vortex street , which can induce structural oscillations. Strakes are typically wrapped around chimneys to stop the formation of these vortices. In complex structures where both the aerodynamics and the mechanical properties of the structure are not fully understood, flutter can be discounted only through detailed testing. Even changing the mass distribution of an aircraft or

574-582: A conventional wing during maneuvering. So this change, which can be accomplished in software, benefits overall performance. To test the AAW theory, NASA and the USAF agreed to fund development of a single demonstrator, based on the F/A-18. Work started by taking an existing F/A-18 airframe modified with a preproduction wing, and added an outboard leading edge flap drive system and an updated flight control computer. Active aeroelastic wing control laws were developed to flex

656-417: A correlation between pressure , temperature , and volume . In time, Boyle's Law was formulated, which states that pressure and volume are inversely proportional . Then, in 1679, based on these concepts, an associate of Boyle's named Denis Papin built a steam digester , which was a closed vessel with a tightly fitting lid that confined steam until a high pressure was generated. Later designs implemented

738-400: A description often referred to as geometrical thermodynamics . A description of any thermodynamic system employs the four laws of thermodynamics that form an axiomatic basis. The first law specifies that energy can be transferred between physical systems as heat , as work , and with transfer of matter. The second law defines the existence of a quantity called entropy , that describes

820-430: A few. This article is focused mainly on classical thermodynamics which primarily studies systems in thermodynamic equilibrium . Non-equilibrium thermodynamics is often treated as an extension of the classical treatment, but statistical mechanics has brought many advances to that field. The history of thermodynamics as a scientific discipline generally begins with Otto von Guericke who, in 1650, built and designed

902-469: A large increase in steam engine efficiency. Drawing on all the previous work led Sadi Carnot , the "father of thermodynamics", to publish Reflections on the Motive Power of Fire (1824), a discourse on heat, power, energy and engine efficiency. The book outlined the basic energetic relations between the Carnot engine , the Carnot cycle , and motive power. It marked the start of thermodynamics as

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984-403: A looser viewpoint is adopted, and the requirement of thermodynamic equilibrium is dropped, the system can be the body of a tropical cyclone , such as Kerry Emanuel theorized in 1986 in the field of atmospheric thermodynamics , or the event horizon of a black hole . Boundaries are of four types: fixed, movable, real, and imaginary. For example, in an engine, a fixed boundary means the piston

1066-662: A modern science. The first thermodynamic textbook was written in 1859 by William Rankine , originally trained as a physicist and a civil and mechanical engineering professor at the University of Glasgow . The first and second laws of thermodynamics emerged simultaneously in the 1850s, primarily out of the works of William Rankine, Rudolf Clausius , and William Thomson (Lord Kelvin). The foundations of statistical thermodynamics were set out by physicists such as James Clerk Maxwell , Ludwig Boltzmann , Max Planck , Rudolf Clausius and J. Willard Gibbs . Clausius, who first stated

1148-424: A physical or notional, but serve to confine the system to a finite volume. Segments of the boundary are often described as walls ; they have respective defined 'permeabilities'. Transfers of energy as work , or as heat , or of matter , between the system and the surroundings, take place through the walls, according to their respective permeabilities. Matter or energy that pass across the boundary so as to effect

1230-419: A required motion, which, in turn, will reduce aileron drag and its associated unwanted tendency to cause the aircraft to yaw . If the controls can be used to eliminate the twisting and its negative effects on control input, the next step is to deliberately introduce some twisting which adds to the effect of the control deflection. When applied correctly, the wing will twist less and in an opposite direction to

1312-475: A role in a wide variety of topics in science and engineering . Historically, thermodynamics developed out of a desire to increase the efficiency of early steam engines , particularly through the work of French physicist Sadi Carnot (1824) who believed that engine efficiency was the key that could help France win the Napoleonic Wars . Scots-Irish physicist Lord Kelvin was the first to formulate

1394-441: A set number of variables held constant. A thermodynamic process may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. It can be described by process quantities . Typically, each thermodynamic process is distinguished from other processes in energetic character according to what parameters, such as temperature, pressure, or volume, etc., are held fixed; Furthermore, it

1476-439: A steam release valve that kept the machine from exploding. By watching the valve rhythmically move up and down, Papin conceived of the idea of a piston and a cylinder engine. He did not, however, follow through with his design. Nevertheless, in 1697, based on Papin's designs, engineer Thomas Savery built the first engine, followed by Thomas Newcomen in 1712. Although these early engines were crude and inefficient, they attracted

1558-529: A sudden impulse of load increasing. It is a random forced vibration. Generally it affects the tail unit of the aircraft structure due to air flow downstream of the wing. The methods for buffet detection are: In the period 1950–1970, AGARD developed the Manual on Aeroelasticity which details the processes used in solving and verifying aeroelastic problems along with standard examples that can be used to test numerical solutions. Aeroelasticity involves not just

1640-401: A system on its surrounding requires that the system's internal energy U {\displaystyle U} decrease or be consumed, so that the amount of internal energy lost by that work must be resupplied as heat Q {\displaystyle Q} by an external energy source or as work by an external machine acting on the system (so that U {\displaystyle U}

1722-497: A theory of wing divergence, leading to much further theoretical research on the subject. The term aeroelasticity itself was coined by Harold Roxbee Cox and Alfred Pugsley at the Royal Aircraft Establishment (RAE), Farnborough in the early 1930s. In the development of aeronautical engineering at Caltech , Theodore von Kármán started a course "Elasticity applied to Aeronautics". After teaching

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1804-467: A third, they are also in thermal equilibrium with each other. This statement implies that thermal equilibrium is an equivalence relation on the set of thermodynamic systems under consideration. Systems are said to be in equilibrium if the small, random exchanges between them (e.g. Brownian motion ) do not lead to a net change in energy. This law is tacitly assumed in every measurement of temperature. Thus, if one seeks to decide whether two bodies are at

1886-474: A wide variety of topics in science and engineering , such as engines , phase transitions , chemical reactions , transport phenomena , and even black holes . The results of thermodynamics are essential for other fields of physics and for chemistry , chemical engineering , corrosion engineering , aerospace engineering , mechanical engineering , electrical engineering , cell biology , biomedical engineering , materials science , and economics , to name

1968-547: A wind tunnel test of an airfoil (e.g., a torsional restraint positioned forward of the aerodynamic center) it is possible to eliminate the phenomenon of divergence altogether. Control surface reversal is the loss (or reversal) of the expected response of a control surface, due to deformation of the main lifting surface. For simple models (e.g. single aileron on an Euler-Bernoulli beam), control reversal speeds can be derived analytically as for torsional divergence. Control reversal can be used to aerodynamic advantage, and forms part of

2050-413: Is a principal property of the thermodynamic state , while heat and work are modes of energy transfer by which a process may change this state. A change of internal energy of a system may be achieved by any combination of heat added or removed and work performed on or by the system. As a function of state , the internal energy does not depend on the manner, or on the path through intermediate steps, by which

2132-399: Is at equilibrium, producing thermodynamic processes which develop so slowly as to allow each intermediate step to be an equilibrium state and are said to be reversible processes . When a system is at equilibrium under a given set of conditions, it is said to be in a definite thermodynamic state . The state of the system can be described by a number of state quantities that do not depend on

2214-647: Is determining the spontaneity of a given transformation. Equilibrium thermodynamics is the study of transfers of matter and energy in systems or bodies that, by agencies in their surroundings, can be driven from one state of thermodynamic equilibrium to another. The term 'thermodynamic equilibrium' indicates a state of balance, in which all macroscopic flows are zero; in the case of the simplest systems or bodies, their intensive properties are homogeneous, and their pressures are perpendicular to their boundaries. In an equilibrium state there are no unbalanced potentials, or driving forces, between macroscopically distinct parts of

2296-558: Is known as aerothermoelasticity , and its synthesis with control theory is known as aeroservoelasticity . The second failure of Samuel Langley 's prototype plane on the Potomac was attributed to aeroelastic effects (specifically, torsional divergence). An early scientific work on the subject was George Bryan 's Theory of the Stability of a Rigid Aeroplane published in 1906. Problems with torsional divergence plagued aircraft in

2378-415: Is locked at its position, within which a constant volume process might occur. If the piston is allowed to move that boundary is movable while the cylinder and cylinder head boundaries are fixed. For closed systems, boundaries are real while for open systems boundaries are often imaginary. In the case of a jet engine, a fixed imaginary boundary might be assumed at the intake of the engine, fixed boundaries along

2460-425: Is recovered) to make the system work continuously. For processes that include transfer of matter, a further statement is needed: With due account of the respective fiducial reference states of the systems, when two systems, which may be of different chemical compositions, initially separated only by an impermeable wall, and otherwise isolated, are combined into a new system by the thermodynamic operation of removal of

2542-403: Is said to be in a state of thermodynamic equilibrium . Once in thermodynamic equilibrium, a system's properties are, by definition, unchanging in time. Systems in equilibrium are much simpler and easier to understand than are systems which are not in equilibrium. Often, when analysing a dynamic thermodynamic process, the simplifying assumption is made that each intermediate state in the process

Boeing X-53 Active Aeroelastic Wing - Misplaced Pages Continue

2624-437: Is the elastic twist of the beam, GJ is the torsional stiffness of the beam, L is the beam length, and M ’ is the aerodynamic moment per unit length. Under a simple lift forcing theory the aerodynamic moment is of the form where C is a coefficient, U is the free-stream fluid velocity, and α 0 is the initial angle of attack. This yields an ordinary differential equation of the form where The boundary conditions for

2706-399: Is the point at which the structure is undergoing simple harmonic motion —zero net damping —and so any further decrease in net damping will result in a self-oscillation and eventual failure. "Net damping" can be understood as the sum of the structure's natural positive damping and the negative damping of the aerodynamic force. Flutter can be classified into two types: hard flutter , in which

2788-420: Is used to model exchanges of energy, work and heat based on the laws of thermodynamics . The qualifier classical reflects the fact that it represents the first level of understanding of the subject as it developed in the 19th century and describes the changes of a system in terms of macroscopic empirical (large scale, and measurable) parameters. A microscopic interpretation of these concepts was later provided by

2870-426: Is −273.15 °C (degrees Celsius), or −459.67 °F (degrees Fahrenheit), or 0 K (kelvin), or 0° R (degrees Rankine ). An important concept in thermodynamics is the thermodynamic system , which is a precisely defined region of the universe under study. Everything in the universe except the system is called the surroundings . A system is separated from the remainder of the universe by a boundary which may be

2952-490: The First World War and were solved largely by trial-and-error and ad hoc stiffening of the wing. The first recorded and documented case of flutter in an aircraft was that which occurred to a Handley Page O/400 bomber during a flight in 1916, when it suffered a violent tail oscillation, which caused extreme distortion of the rear fuselage and the elevators to move asymmetrically. Although the aircraft landed safely, in

3034-451: The Kaman servo-flap rotor design. Dynamic aeroelasticity studies the interactions among aerodynamic, elastic, and inertial forces. Examples of dynamic aeroelastic phenomena are: Flutter is a dynamic instability of an elastic structure in a fluid flow, caused by positive feedback between the body's deflection and the force exerted by the fluid flow. In a linear system , "flutter point"

3116-404: The energy , entropy , volume , temperature and pressure of the thermodynamic system in such a manner, one can determine if a process would occur spontaneously. Also Pierre Duhem in the 19th century wrote about chemical thermodynamics. During the early 20th century, chemists such as Gilbert N. Lewis , Merle Randall , and E. A. Guggenheim applied the mathematical methods of Gibbs to

3198-546: The inertial , elastic , and aerodynamic forces occurring while an elastic body is exposed to a fluid flow. The study of aeroelasticity may be broadly classified into two fields: static aeroelasticity dealing with the static or steady state response of an elastic body to a fluid flow, and dynamic aeroelasticity dealing with the body's dynamic (typically vibrational ) response. Aircraft are prone to aeroelastic effects because they need to be lightweight while enduring large aerodynamic loads. Aircraft are designed to avoid

3280-532: The stiffness of one component can induce flutter in an apparently unrelated aerodynamic component. At its mildest, this can appear as a "buzz" in the aircraft structure, but at its most violent, it can develop uncontrollably with great speed and cause serious damage to the aircraft or lead to its destruction, as in Northwest Airlines Flight 2 in 1938, Braniff Flight 542 in 1959, or the prototypes for Finland's VL Myrsky fighter aircraft in

3362-471: The Moving Force of Heat", published in 1850, first stated the second law of thermodynamics . In 1865 he introduced the concept of entropy. In 1870 he introduced the virial theorem , which applied to heat. The initial application of thermodynamics to mechanical heat engines was quickly extended to the study of chemical compounds and chemical reactions. Chemical thermodynamics studies the nature of

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3444-415: The analysis of chemical processes. Thermodynamics has an intricate etymology. By a surface-level analysis, the word consists of two parts that can be traced back to Ancient Greek. Firstly, thermo- ("of heat"; used in words such as thermometer ) can be traced back to the root θέρμη therme , meaning "heat". Secondly, the word dynamics ("science of force [or power]") can be traced back to

3526-497: The attention of the leading scientists of the time. The fundamental concepts of heat capacity and latent heat , which were necessary for the development of thermodynamics, were developed by Professor Joseph Black at the University of Glasgow, where James Watt was employed as an instrument maker. Black and Watt performed experiments together, but it was Watt who conceived the idea of the external condenser which resulted in

3608-644: The basic ideas of the second law in his paper "On the Moving Force of Heat", published in 1850, and is called "one of the founding fathers of thermodynamics", introduced the concept of entropy in 1865. During the years 1873–76 the American mathematical physicist Josiah Willard Gibbs published a series of three papers, the most famous being On the Equilibrium of Heterogeneous Substances , in which he showed how thermodynamic processes , including chemical reactions , could be graphically analyzed, by studying

3690-467: The course for one term, Kármán passed it over to Ernest Edwin Sechler , who developed aeroelasticity in that course and in publication of textbooks on the subject. In 1947, Arthur Roderick Collar defined aeroelasticity as "the study of the mutual interaction that takes place within the triangle of the inertial, elastic, and aerodynamic forces acting on structural members exposed to an airstream, and

3772-413: The determination of entropy. The entropy determined relative to this point is the absolute entropy. Alternate definitions include "the entropy of all systems and of all states of a system is smallest at absolute zero," or equivalently "it is impossible to reach the absolute zero of temperature by any finite number of processes". Absolute zero, at which all activity would stop if it were possible to achieve,

3854-462: The development of statistical mechanics . Statistical mechanics , also known as statistical thermodynamics, emerged with the development of atomic and molecular theories in the late 19th century and early 20th century, and supplemented classical thermodynamics with an interpretation of the microscopic interactions between individual particles or quantum-mechanical states. This field relates the microscopic properties of individual atoms and molecules to

3936-862: The direction, thermodynamically, that a system can evolve and quantifies the state of order of a system and that can be used to quantify the useful work that can be extracted from the system. In thermodynamics, interactions between large ensembles of objects are studied and categorized. Central to this are the concepts of the thermodynamic system and its surroundings . A system is composed of particles, whose average motions define its properties, and those properties are in turn related to one another through equations of state . Properties can be combined to express internal energy and thermodynamic potentials , which are useful for determining conditions for equilibrium and spontaneous processes . With these tools, thermodynamics can be used to describe how systems respond to changes in their environment. This can be applied to

4018-508: The early 1940s. Famously, the original Tacoma Narrows Bridge was destroyed as a result of aeroelastic fluttering. In some cases, automatic control systems have been demonstrated to help prevent or limit flutter-related structural vibration. Propeller whirl flutter is a special case of flutter involving the aerodynamic and inertial effects of a rotating propeller and the stiffness of the supporting nacelle structure. Dynamic instability can occur involving pitch and yaw degrees of freedom of

4100-452: The external aerodynamic loads and the way they change but also the structural, damping and mass characteristics of the aircraft. Prediction involves making a mathematical model of the aircraft as a series of masses connected by springs and dampers which are tuned to represent the dynamic characteristics of the aircraft structure. The model also includes details of applied aerodynamic forces and how they vary. The model can be used to predict

4182-437: The flutter margin and, if necessary, test fixes to potential problems. Small carefully chosen changes to mass distribution and local structural stiffness can be very effective in solving aeroelastic problems. Methods of predicting flutter in linear structures include the p-method , the k-method and the p-k method . For nonlinear systems , flutter is usually interpreted as a limit cycle oscillation (LCO), and methods from

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4264-417: The following aeroelastic problems: Aeroelasticity problems can be prevented by adjusting the mass, stiffness or aerodynamics of structures which can be determined and verified through the use of calculations, ground vibration tests and flight flutter trials . Flutter of control surfaces is usually eliminated by the careful placement of mass balances . The synthesis of aeroelasticity with thermodynamics

4346-433: The influence of this study on design". In an aeroplane, two significant static aeroelastic effects may occur. Divergence is a phenomenon in which the elastic twist of the wing suddenly becomes theoretically infinite, typically causing the wing to fail. Control reversal is a phenomenon occurring only in wings with ailerons or other control surfaces, in which these control surfaces reverse their usual functionality (e.g.,

4428-405: The lifting surface to move in the same direction and when it comes to point of divergence the structure deforms. Divergence can be understood as a simple property of the differential equation (s) governing the wing deflection . For example, modelling the airplane wing as an isotropic Euler–Bernoulli beam , the uncoupled torsional equation of motion is where y is the spanwise dimension, θ

4510-472: The macroscopic, bulk properties of materials that can be observed on the human scale, thereby explaining classical thermodynamics as a natural result of statistics, classical mechanics, and quantum theory at the microscopic level. Chemical thermodynamics is the study of the interrelation of energy with chemical reactions or with a physical change of state within the confines of the laws of thermodynamics . The primary objective of chemical thermodynamics

4592-615: The net damping decreases very suddenly, very close to the flutter point; and soft flutter , in which the net damping decreases gradually. In water the mass ratio of the pitch inertia of the foil to that of the circumscribing cylinder of fluid is generally too low for binary flutter to occur, as shown by explicit solution of the simplest pitch and heave flutter stability determinant. Structures exposed to aerodynamic forces—including wings and aerofoils, but also chimneys and bridges—are generally designed carefully within known parameters to avoid flutter. Blunt shapes, such as chimneys, can give off

4674-498: The other laws. The first, second, and third laws had been explicitly stated already, and found common acceptance in the physics community before the importance of the zeroth law for the definition of temperature was realized. As it was impractical to renumber the other laws, it was named the zeroth law . The first law of thermodynamics states: In a process without transfer of matter, the change in internal energy , Δ U {\displaystyle \Delta U} , of

4756-399: The process by which the system arrived at its state. They are called intensive variables or extensive variables according to how they change when the size of the system changes. The properties of the system can be described by an equation of state which specifies the relationship between these variables. State may be thought of as the instantaneous quantitative description of a system with

4838-489: The propeller and the engine supports leading to an unstable precession of the propeller. Failure of the engine supports led to whirl flutter occurring on two Lockheed L-188 Electra aircraft, in 1959 on Braniff Flight 542 and again in 1960 on Northwest Orient Airlines Flight 710 . Flow is highly non-linear in the transonic regime, dominated by moving shock waves. Avoiding flutter is mission-critical for aircraft that fly through transonic Mach numbers. The role of shock waves

4920-407: The rates of approach to thermodynamic equilibrium, and thermodynamics does not deal with such rates. The many versions of the second law all express the general irreversibility of the transitions involved in systems approaching thermodynamic equilibrium. In macroscopic thermodynamics, the second law is a basic observation applicable to any actual thermodynamic process; in statistical thermodynamics,

5002-513: The role of entropy in the process of chemical reactions and has provided the bulk of expansion and knowledge of the field. Other formulations of thermodynamics emerged. Statistical thermodynamics , or statistical mechanics, concerns itself with statistical predictions of the collective motion of particles from their microscopic behavior. In 1909, Constantin Carathéodory presented a purely mathematical approach in an axiomatic formulation,

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5084-446: The rolling direction associated with a given aileron moment is reversed). Divergence occurs when a lifting surface deflects under aerodynamic load in a direction which further increases lift in a positive feedback loop. The increased lift deflects the structure further, which eventually brings the structure to the point of divergence. Unlike flutter, which is another aeroelastic problem, instead of irregular oscillations, divergence causes

5166-459: The root δύναμις dynamis , meaning "power". In 1849, the adjective thermo-dynamic is used by William Thomson. In 1854, the noun thermo-dynamics is used by Thomson and William Rankine to represent the science of generalized heat engines. Pierre Perrot claims that the term thermodynamics was coined by James Joule in 1858 to designate the science of relations between heat and power, however, Joule never used that term, but used instead

5248-400: The same temperature , it is not necessary to bring them into contact and measure any changes of their observable properties in time. The law provides an empirical definition of temperature, and justification for the construction of practical thermometers. The zeroth law was not initially recognized as a separate law of thermodynamics, as its basis in thermodynamical equilibrium was implied in

5330-494: The scope of currently known macroscopic thermodynamic methods. Thermodynamics is principally based on a set of four laws which are universally valid when applied to systems that fall within the constraints implied by each. In the various theoretical descriptions of thermodynamics these laws may be expressed in seemingly differing forms, but the most prominent formulations are the following. The zeroth law of thermodynamics states: If two systems are each in thermal equilibrium with

5412-443: The second law is postulated to be a consequence of molecular chaos. The third law of thermodynamics states: As the temperature of a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value. This law of thermodynamics is a statistical law of nature regarding entropy and the impossibility of reaching absolute zero of temperature. This law provides an absolute reference point for

5494-534: The study of dynamical systems can be used to determine the speed at which flutter will occur. These videos detail the Active Aeroelastic Wing two-phase NASA - Air Force flight research program to investigate the potential of aerodynamically twisting flexible wings to improve maneuverability of high-performance aircraft at transonic and supersonic speeds, with traditional control surfaces such as ailerons and leading-edge flaps used to induce

5576-529: The subsequent investigation F. W. Lanchester was consulted. One of his recommendations was that left and right elevators should be rigidly connected by a stiff shaft, which was to subsequently become a design requirement. In addition, the National Physical Laboratory (NPL) was asked to investigate the phenomenon theoretically, which was subsequently carried out by Leonard Bairstow and Arthur Fage . In 1926, Hans Reissner published

5658-407: The surface of the case and a second fixed imaginary boundary across the exhaust nozzle. Generally, thermodynamics distinguishes three classes of systems, defined in terms of what is allowed to cross their boundaries: As time passes in an isolated system, internal differences of pressures, densities, and temperatures tend to even out. A system in which all equalizing processes have gone to completion

5740-486: The system arrived at its state. A traditional version of the second law of thermodynamics states: Heat does not spontaneously flow from a colder body to a hotter body. The second law refers to a system of matter and radiation, initially with inhomogeneities in temperature, pressure, chemical potential, and other intensive properties , that are due to internal 'constraints', or impermeable rigid walls, within it, or to externally imposed forces. The law observes that, when

5822-470: The system boundary are possible, but matter transfer is not possible), Q {\displaystyle Q} denotes the quantity of energy supplied to the system as heat, and W {\displaystyle W} denotes the amount of thermodynamic work done by the system on its surroundings. An equivalent statement is that perpetual motion machines of the first kind are impossible; work W {\displaystyle W} done by

5904-448: The system is isolated from the outside world and from those forces, there is a definite thermodynamic quantity, its entropy , that increases as the constraints are removed, eventually reaching a maximum value at thermodynamic equilibrium, when the inhomogeneities practically vanish. For systems that are initially far from thermodynamic equilibrium, though several have been proposed, there is known no general physical principle that determines

5986-859: The system. A central aim in equilibrium thermodynamics is: given a system in a well-defined initial equilibrium state, and given its surroundings, and given its constitutive walls, to calculate what will be the final equilibrium state of the system after a specified thermodynamic operation has changed its walls or surroundings. Non-equilibrium thermodynamics is a branch of thermodynamics that deals with systems that are not in thermodynamic equilibrium . Most systems found in nature are not in thermodynamic equilibrium because they are not in stationary states, and are continuously and discontinuously subject to flux of matter and energy to and from other systems. The thermodynamic study of non-equilibrium systems requires more general concepts than are dealt with by equilibrium thermodynamics. Many natural systems still today remain beyond

6068-462: The term perfect thermo-dynamic engine in reference to Thomson's 1849 phraseology. The study of thermodynamical systems has developed into several related branches, each using a different fundamental model as a theoretical or experimental basis, or applying the principles to varying types of systems. Classical thermodynamics is the description of the states of thermodynamic systems at near-equilibrium, that uses macroscopic, measurable properties. It

6150-518: The twist. Thermodynamics Thermodynamics is the branch of physics that studies heat , work , and temperature and their relation to energy , entropy , and the physical properties of matter and radiation . The behavior of these quantities is governed by the four laws of thermodynamics , which convey a quantitative description using measurable macroscopic physical quantities , but may be explained in terms of microscopic constituents by statistical mechanics . Thermodynamics plays

6232-427: The wall, then where U 0 denotes the internal energy of the combined system, and U 1 and U 2 denote the internal energies of the respective separated systems. Adapted for thermodynamics, this law is an expression of the principle of conservation of energy , which states that energy can be transformed (changed from one form to another), but cannot be created or destroyed. Internal energy

6314-402: The wing leading edge to provide more lift during certain portions of flight. By deploying the slats at the same time as the ailerons their twisting effect on the main structural parts of the wing, oppose one another which eliminates the twisting. This improves the ability of the ailerons to produce large rolling moments on the aircraft. This means that less aileron deflection is needed to produce

6396-590: The wing, and flight instrumentation was used to accurately measure the aeroelastic performance of the wing planform . Flight software was then modified for flight testing, and the aircraft first flew in modified form on November 15, 2002. The aircraft successfully proved the viability of the concept in full scale during roll maneuver testing in 2004–2005. The test aircraft was re-designated X-53 on August 16, 2006, per memo by USAF Deputy Chief of Staff, Strategic Plans and Programs. General characteristics Performance Avionics The leading edge flap drive system

6478-511: The world's first vacuum pump and demonstrated a vacuum using his Magdeburg hemispheres . Guericke was driven to make a vacuum to disprove Aristotle 's long-held supposition that 'nature abhors a vacuum'. Shortly after Guericke, the Anglo-Irish physicist and chemist Robert Boyle had learned of Guericke's designs and, in 1656, in coordination with English scientist Robert Hooke , built an air pump. Using this pump, Boyle and Hooke noticed

6560-527: Was first analyzed by Holt Ashley . A phenomenon that impacts stability of aircraft known as "transonic dip", in which the flutter speed can get close to flight speed, was reported in May 1976 by Farmer and Hanson of the Langley Research Center . Buffeting is a high-frequency instability, caused by airflow separation or shock wave oscillations from one object striking another. It is caused by

6642-410: Was modified at McDonnell Douglas (now Boeing Phantom works) using an outboard actuation unit developed by Moog Inc . AAW flight control laws were programmed into a research flight control computer modified to include independently actuated outboard leading edge control surfaces. Aeroelasticity Aeroelasticity is the branch of physics and engineering studying the interactions between

6724-440: Was modified to allow two leading edge control surfaces to work together with its two trailing edge surfaces to control wing aeroelastic twist and provide excellent high speed rolling performance. AAW was developed from the knowledge that the aeroelasticity of the wing, caused by deflecting one control surface, can be offset by deflecting other control surfaces. In particular, almost all modern aircraft use some form of slat along

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