A quasi-continuous method is developed for solving thin-wing problems. For the purpose of satisfying the wing boundary conditions, the spanwise vortex distribution is assumed to be stepwise-constant, while the chordwise vortex integral is reduced to a finite sum through a modified trapezoidal rule and the theory of Chebyshev polynomials. Wing-edge and Cauchy singularities are acounted for. The total aerodynamic characteristics are obtained by an appropriate quadrature integration. The two-dimensional results for airfoils without flap deflection reproduce the exact solutions in lift and pitching moment coefficients, the leading edge suction, and the pressure difference at a finite number of points. For a flapped airfoil, the present results are more accurate than those given by the vortex-lattice method. The three-dimensional results also show an improvement over the results of the vortex-lattice method. Extension to nonplanar applications is discussed.

A Quasi-Vortex-Lattice Method in Thin Wing Theory

At the end of the e rst century of manned, powered e ight, it is worthwhile to look backward to understand how innovation in airplane design required developments in aeroelasticity and how aeroelasticity has played a role in shaping the e rst 100 years of aircraft design. The insights gained will help to predict how and where aeroelasticity and aeroservoelasticity will ine uence the future development of efe cient, more capable, innovative air vehicles, and dee nethe needs fortechnology and tools to enable this future. By dee nition, all new aircraft begin as unconventional to a certain extent. Designs that never see universal use remain curiosities, but still help our questforbettervehiclesandguidethedevelopmentofanalysis, design, and testing tools. Innovative, nontraditional designsaffected by aeroelasticconsiderations haveincluded obliquewing aircraft, forward-swept wing aircraft,Xwings,e ying wings, andlargejoined wings. Designsthat wereunusually innovativeat thetimeoftheirintroduction but later became widespread include the swept-back wing jet, the T-tail, and the e y-by-wire control cone gured vehicle. Control and exploitation of aeroelasticity depends on the continued development of new materials, new structuralandaerodynamicconcepts,sensors,actuators,andactivecontroltechniques.Suchdevelopmentsmustbe accompanied by properintegratedanalysis/designtools,and,most importantly, by thesamehumaninquisitiveness and creativity that has driven aircraft design for over a century. This paper uses the history of nonconventional airplane cone gurations to review some of the steps taken during the past century to establish aeroelastic effects as integrated design features that must be anticipated, controlled, and exploited. The paper goes on to discuss the potential impact of past lessons on emerging airplane cone gurations currently in various stages of study and development.

Aeroelasticity of Nonconventional Airplane Configurations-Past and Future

Active flutter suppression, which is a part of the group of flight vehicle technologies known as active controls, is an important contributor to the effective solution of aeroelastic instability pr...

https://arc.aiaa.org/doi/pdf/10.2514/1.C034442

Aircraft Active Flutter Suppression: State of the Art and Technology Maturation Needs

The interactions of lightweight flexible airframe structures, steady and unsteady aerodynamics, and wide-bandwidth active controls on modern airplanes lead to considerable multidisciplinary design challenges. More than 25 years of mathematical and numerical methods' development, numerous basic research studies, simulations and wind-tunnel tests of simple models, wind-tunnel tests of complex models of real airplanes, as well as flight tests of actively controlled airplanes, have all contributed to the accumulation of a substantial body of knowledge in the area of aeroservoelasticity. A number of analysis codes, with the capabilities to model real airplane systems under the assumptions of linearity, have been developed. Many tests have been conducted, and results were correlated with analytical predictions. A selective sample of references covering aeroservoelastic testing programs from the 1960s to the early 1980s, as well as more recent wind-tunnel test programs of real or realistic configurations, are included in the References section of this paper. An examination of references 20-29 will reveal that in the course of development (or later modification), of almost every modern airplane with a high authority active control system, there arose a need to face aeroservoelastic problems and aeroservoelastic design challenges.

Integrated Aeroservoelastic Optimization: Status and Direction

Stability in Aviation. By Prof. G. H. Bryan, F.E.S. Pp. X + 192. 5S. net. 1911. (Macmillan.)

Application of oscillatory aerodynamic theory to estimation of dynamic stability derivatives

Spanwise distribution of induced drag in subsonic flow by the vortexlattice method

behavior is that a minimum interval corresponding to two turns of the main rotor is required to allow the transient engine dynamics to settle down toward a new steady state following each application of the controls. The time constant associated with a  rst-order approximation to the engine governormodel is typically 0.397 s. This is more than double the time interval of 0.1755 s that corresponds to one full turn of the main rotor. This explanation can be veri ed by reducing the engine model time constants s e1, s e2 , and s e3 to 1% of their nominal values. The results improve, and a control application interval of once per revolution produces smooth control time histories and engine states.

William P. Rodden

Papers

Application of oscillatory aerodynamic theory to estimation of dynamic stability derivatives

Spanwise distribution of induced drag in subsonic flow by the vortexlattice method

Structural Dynamics and Quasistatic Aeroelastic Equations of Motion