Structural Aspects of Active Control Technology.

A survey on the structurally relevant applications of Active Control Technology is presented. The benefits and disadvantages of various active control systems for transport aircraft are discussed. The problem of adverse structural coupling is addressed and possible solutions are outlined. Smart Structure Technology offers new applications for active control technology, but, in order to exploit its full potential, multidisciplinary design methods have to be improved

Aeroelastische Entwurfskriterien im Flugzeugbau und Aspekte der Optimierung

Der Vortrag beginnt mit einer kurzen Einführung in aeroelastische Problemstellungen an Flugzeugen, wie z.B. Deformation unter Luftlast von gepfeilten Flügeln, Stabilität von umströmten Strukturen sowie nicht-lineare Effekte im transsonischen Bereich (Amplituden limitierte Schwingungen). Es werden spezielle Beispiele gegeben, an denen gezeigt wird, so noch Forschungsbedarf ist. Weiter wird auf den Entwurfsprozeß für Flugzeuge eingegangen, der ein sehr komplexes multidisplinäres Optimierungsproblem darstellt. Dazu werden Beispiele gegeben, wie z.B. Aeroelastic Tailoring oder Flatteroptimierung. Im Ausblick wird kurz auf die Wechselwirkung zwischen Struktur- und Flugführungssystem eingegangen

The Expanding Domain of Aeroelastic Simulation.

The impact of aeroelasticity and structural dynamics on the design of flight vehicles is apparent when considering the entire time- dependent environment in which these vehicles operate. Aircraft are subjected to maneouvre, gust, and landing loads, and must be freeof flutter and other aeroelastic instabilities throughout the flight envelope. Space vehicles are subjected to release transient loads and aeroacoustic loads at lift-off and must be free of control instabilities. Moreover, they must retarget rapidly and quickly settle from a vibratory condition to a quiet functional state. Rotorcraft, because of their highly-flexible rotating parts, are subjected to strong, periodically unsteady aerodynamic excitations, and also the bladings of advanced turbofan engines may strongly suffer from structural vibrations and aeroelastic instabilities. The ability to predict these effects - which belong to the coupled effects - is essential for the design of safe and economically viable high-performance flight vehicles of the future. In this keynote paper, as an introductory contribution to this Forum, current challenging problem areas in aeroelasticity which deal with coupled problems are pointed out and the impetus of unsteady computational aerodynamics in the development of advanced aeroelastic computational simulation is highlighted. The focus is primarily on aeroelasticity at transonic and separated flows and on computational methods aimed at the study of related unsteady airloads, typically referred to as Computational Fluid Dynamics (CFD)

Dynamics of Flexible Aircraft (DYNAFLEX)

An innovate cooperation between the industry, research establishments, and universities is presented. The program was initiated by the German Ministry of Education and Research (BMBF) and DLR (German Aerospace Center) was tasked to establish together with DASA Airbus (now Daimler Chrysler Aerospace) a multidisciplinary research program focused on the development of key-enabling technologies for the "Megaliner" lead concept. A matrix of interdependent tasks was established by DLR to evoke a multidisciplinary research progress, and five universities were selected to jointly execute the tasks. The organization and work plan of the DYNAFLEX cooperative program is described and results are presented. The program was found to be an effective method for innovative research and should be continued

Status on Strato 2C Flight Flutter Testing Activities.

The STRATO 2C aircraft is currently being developed for manned stratospheric research missions up to 80,000 ft. It is powered by two 330 kW turbocharged piston engines. The requirements for flight endurance, altitude, payload, and operating range can only be met if high aerodynamic quality, high propulsion efficiency, and low empty weight are achieved simultaneously. The large wing span (56.5m)and aspect ratio (21.3) result from aerodynamic optimization. Carbon fibre composites are applied to reduce weight and deflections. Possible aeroelastic problems are dealt with during aircraft deve- lopment. This paper gives an overview on these activities

The Role of Aeroelasticity in Recent German and European Aircraft Research and Development

The increasing performance requirements and the economical pressure to reduce Direct Operational Costs (DOC) of new aircraft designs can no longer be met by applying tradional sequential design methods. This holds especially true when considering aeroelasticity. The impact of its effects on the design of new high-performance transport of fighter aircraft demands the use of multidisciplinary design concepts and optimization strategies even in the preliminary phase. In Germany, a multidisciplinary research program focused on the development of key-enabling technologies for the so-called lead concept Megaliner was initiated as an innovative cooperation between the industry, research establishments, and universities. In this paper, aeroelastic design principles for the passive airframe and for actively controlled advanced aircraft with highly sophisticated fly-by-wire flight control systems are presented. The challenging problems in aeroelasticity are pointed out and the impetus of major disciplines in the development of advanced computational simulation is highlighted. The focus is primarily on the transonic regime and on the study of related nonlinear effects

Flutter Flight Test of the Ranger 2000 Aircraft

The philosophy of a comprehensive flight flutter test using rotating vane exciter and pulse excitation is outlined. Based on the results of the flutter analysis, a lean flight test program was developed and dedicated to wing and T-tail investigations in areas of the flight envelope where low damping was predicted. The implementation of the rotating vane exciter system was well as the sensor installation is described. Emphasis is put on reporting the flight test performance, excitation techniques and quasi online data evaluation. Comparison of test results with analysis is presented

The Changing Role of Aeroelasticity in Aircraft Design

Almost from the beginning of aviation, aeroelasticity was feared for its negative impacts on aircraft stability and performance, which became more and more severe over years. Today however, dramatic changes are expected for the performance and efficiency of future airplanes from new "Active Structures" design concepts, exploiting aeroelastic effects in a beneficial way to reduce aerodynamic drag and design loads, improve manoeuvrability, and enhance aircraft stability. This article is a review of past, on-going, and planned research and development activities where the main objective is an adaptive change of the shape of the airplane by active deformations of the structure. In addition to the intended effects from the structural deformations, these concepts are classified by the types of devices that initiate them: aerodynamic control surfaces, adaptive stiffness systems for the attachment or actuation of an aerodynamic surface, and active structural components. Some of these concepts are mainly concentrating on the creation of large structural deformations - without special considerations about aeroelastic effects, while others are mainly concentrating on the stimulation of deformations by aeroelastic effects. In the first case, the aeroelastic impacts from these concepts and on these concepts will be addressed. The required new analytical design methods will be discussed. Besides the new quality of additional physical properties for the description of structure´s reactions and actions, the field of structural and multi-disciplinary analysis and optimization (MDO) is essential for the effective integration of active elements into an otherwise passive structure. This new design process may also be considered as an extension of "Aeroelastic Tailoring", where the required stiffness distribution of the structure for desired aeroelastic characteristics is achieved by formal structural optimization methods. If properly designed, only a small portion of the total deformation of the structure needs to be carried out actively. This initial step triggers the aeroelastic deformation and aerodynamic load redistribution in the desired way. The major fraction of the required input power can then be taken at no extra costs from the surrounding air. For future designs, an MDO framework is presented to calculate the sensitivities of static aeroelastic and flutter characteristics with respect to the parameters which define the shape and structural layout of a wing. The aerodynamic and structural models are based on one common parametric geometry description which employs the Design Elements Method and is created by a model generator. While the aerodynamic model includes the description for the application of the lifting surface theory the structural model description is based on the Finite Element Method and includes a detailed layout concept with arbitrarily oriented spars and ribs. The characteristics of interest in these studies are the presentation of the model generator with a wide range of geometrical variations defined by small set of parameters and the implementation of the model generator in a design process including the calculation of aerodynamic loads and structural optimization. All of this allows for the study of trim conditions, rolling moment, and induced drag. Shape parameters are the aspect ratio and sweep angle. A wing box layout parameter set includes the position and orientation of spars and ribs defined on the wing planform. A third parameter set consists of structural variables, including element thickness

Multidisciplinary Wing Optimization Using a Wing Box Layout Concept and a Parametric Thickness Model

A concept is presented here for simultaneous optimization of an aircraft wing shape and gauges of the corresponding structural wing box. The approach also follows the concept of a single common parametric description as a basis for structural and aerodynamic modelling. The coordinates of the segment corners or typical planform parameters like the wing sweep angle represent the design variables for planform variation. Control points of parametric Bezier surfaces are used to de¯ne the thickness distribution of the wing box structural elements (skin, ribs, and spars). This concept also takes into consideration common design rules for practicable wing box structures. The parametric description of the gauges of the wing box structural elements guarantees the creation of regular and smooth surfaces and thus supports the generation of practicable thickness distributions from the design engineer's point of view. To improve the optimization e±ciency a lumping of certain stress constraints using the Kreisselmeier/Steinhauser-Function was introduced. A generic wing design is presented as an application and test example for which conventional FE-based thickness optimiza- tions were already performed with various sweep angles. A further example is that of a wing with identical external geometry but with a more realistic wing box structure. Its ribs are perpendicular to the front spar and must be regenerated if the external geometry is modi¯ed