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Within the DLR project VicToria various high fidelity-based MDO processes were set-up as applicalble methods for aircraft design. Apart from aerodynamic optimization using high fidelity-based CFD analysis, the sub-processes overall aircraft design synthesis, loads analysis, and structural optimization were part of the MDO processes. The presented paper expounds such MDO sub-processes in order to exhibit their contributions and capabilities for the respected MDO process.

MDO approaches for overall aircraft design based on high-fidelity tools and methods usually go hand in hand with complex computational processes. This is especially the case as the number of the disciplines and the complexity of the disciplinary methods and models increases. Apart from aerodynamic performance analysis of the flexible aircraft using high fidelity CFD analysis, further disciplinary sub-processes were part of three high-fidelity based MDO processes developed and applied within the DLR project VicToria. They were overall aircraft design (OAD) synthesis, loads analysis, structural optimization. In the following, the sub-processes with their simulation models, the analysis and optimizations methods, and the typical responses to be fed into the respective MDO approach are layered out. Furthermore various aspects of the complexity of the simulation models and selected results are presented.

This thesis develops and demonstrates an aircraft pre-design process for loads analysis, load alleviation, structural optimization and fatigue analysis. It is shown that the consideration of maneuver and gust load alleviation in early design stages is a promising concept to reduce wing bending moments, structural mass and extend the fatigue life. The reference aircraft considered are two mid-range configurations: one with a backward and another one with a forward swept wing, respectively. In the loads analysis, quasi-steady maneuvers and dynamic 1-cos gusts are considered. For the load alleviation during maneuvers, the ailerons are deflected symmetrically with precalculated amplitudes. For the gust load alleviation, a feed-forward, proportional control algorithm is set up and the main input for the controller is the gust angle of attack. Analogous to maneuver load alleviation, the ailerons are deflected symmetrically. With the post-processed loads from the simulations, the structure of the wing and horizontal tailplane (HTP) is optimized toward mass minimization. The constraints considered are material strength, buckling stability and static aeroelastic requirements. The steps loads analysis and structure optimization of the developed design process are conducted iteratively until the wing box mass converges. For the reference aircraft, the load alleviation yields a reduction of wing box mass by 2.8% and 6.1%, respectively. Beyond that, a qualitative fatigue analysis is carried out to compare the fatigue behaviors of the active and passive aircraft (with and without load alleviation). In this step, loads due to continuous turbulence and ground-air-ground cycles are considered. For the reference missions, the fatigue life of the active aircraft is improved by 28% and 12% respectively, on top of the mass benefit. However, these numbers of fatigue life improvement are only valid for the considered loads and selected positions. If more loading conditions or structure elements are taken into account, the fatigue benefit may vary. As a conclusion, the proposed process can serve to gain an insight into the benefits of load alleviation for a given aircraft in the pre-design phase, before it advances to the next design stage. In dieser Arbeit wird ein Prozess zur Lastanalyse, Lastabminderung, Strukturoptimierung und Ermüdungsanalyse im Flugzeugvorentwurf entwickelt und demonstriert. Dabei wird gezeigt, dass bei Berücksichtigung von Manöver- und Böenlastabminderung in den frühen Phasen des Flugzeugentwurfs die Biegemomente am Flügel und die Strukturmasse reduziert, und die Lebensdauer der Struktur verlängert werden kann. Die für die Untersuchung verwendeten Referenzflugzeuge sind zwei Mittelstreckenkonfigurationen, jeweils eine mit einem rückwärts und eine mit einem vorwärts gepfeilten Flügel. In der Lastanalyse werden quasistatische Manöver und dynamische 1-cos-Böen berücksichtigt. Die Lastabminderung bei Manövern geschieht durch symmetrisch ausgeschlagene Querruder. Für die Böenlastabminderung wird ein proportionaler Vorsteueralgorithmus entwickelt, dabei stellt der Böenanstellwinkel die Eingangsgröße für die Vorsteuerung dar. Analog zur Manöverlastabminderung werden hierbei die Querruder symmetrisch ausgeschlagen. Mit ausgewählten Lasten aus der Lastanalyse wird die Struktur des Flügels und des Höhenleitwerks hinsichtlich minimaler Strukturmasse optimiert. Die in der Strukturoptimierung berücksichtigten Randbedingungen sind Zugfestigkeit des Materials, Beulstabilität und statische aeroelastische Anforderungen. Die Lastanalyse und Strukturoptimierung im entwickelten Entwurfsprozess wird iterativ durchgeführt, bis die Flügelmasse konvergiert. Bei den Referenzflugzeugen ergeben sich Masseneinsparungen für den Flügelkasten von jeweils 2,8% bzw. 6,1%. Darüber hinaus wird eine Ermüdungsanalyse durchgeführt, um das Ermüdungsverhalten der aktiven und passiven Flugzeuge (mit und ohne Lastabminderung) zu vergleichen. Dabei werden Lasten aufgrund von kontinuierlicher Turbulenz und von Boden-Luft-Boden-Zyklen berücksichtigt. Für die ausgewählten Referenzmissionen erhöht sich die Lebensdauer der Flugzeuge mit aktiver Lastabminderung jeweils um 28% bzw. 12%, zusätzlich zu der Masseneinsparung. Die Werte gelten jedoch nur für die berücksichtigten Lastkonditionen und Positionen. Falls weitere Lastszenarien oder Strukturelemente berücksichtigt werden, kann die Erhöhung der Lebensdauer variieren. Insgesamt ermöglicht der entwickelte Vorentwurfsprozess, den Nutzen der Lastabminderung bei einem gegebenen Flugzeug zu berücksichtigen, bevor dieses in die nächste Entwurfsphase voranschreitet.

The highly parameterized process cpacs-MONA for structural and aeroelastic design of aircraft configurations is presented. The parameterized design process is based on the Common Parametric Aircraft Configuration Schema (CPACS), developed by DLR, where almost all aircraft parameters like mission, geometry, structure, and material are defined. The process stands out for its independent use for structural and aeroelastic design on the one hand and its integration into high fidelity based multidisciplinary optimization tasks on the other hand. The process consists of preliminary mass and loads estimation based on conceptual design methods followed by a parameterized set-up of simulation models and an optimization model. They are used for a comprehensive loads analysis followed by a component wise structural optimization. The latter takes stress, strain, buckling and control surface efficiency as constraints into account. The structural simulation model consist of shell and beam elements for the wing-like component and the fuselage in order to represent the construction of the load carrying structure of the complete aircraft appropriately. Such depth of modelling allows also for the use of well-established structural optimization methods. MONA stands for ModGen, the in-house parametric model generation computer program, and MSC Nastran, used for loads and aeroelastic analysis as well as for structural optimization. cpacs-MONA is also integrated in MDO tasks, where other disciplines like aerodynamics and overall aircraft design are involved. Therein aerodynamic data from high fidelity CFD calculations are used to improve the vortex lattice based aerodynamic method that is applied of the aeroelastic loads analysis. The MDO tasks where cpcas-MONA is integrated can be gradient-free and gradient-based. For the gradient-based MDO task cpacs-MONA delivers to the system optimization level the structural variables, the structural responses the corresponding sensitivities. As structural optimization task alone can deal with a high number of variables and constraints, for the MDO task with other disciplines, like aerodynamics, methods were developed where the number of constraints is reduced that are taken into account on the system level. Two applications are presented for cpacs-MONA. In the first application cpacs-MONA is applied as independent and stand-alone structural and aeroelastic design process. For a long range wide body transport aircraft configuration the design loads case are estimated after a comprehensive loads analysis campaign. For the structural design especially the structural requirements and alternative strategies to achieve sufficient control surface effectiveness within the flight envelope are investigated. In the second application cpacs-MONA is part of a gradient-free optimization task with aerodynamics and the structure to be optimized simultaneously. The presented results show that the aerodynamic optimum lead on the one hand to a heavier wing mass, but investigating the structural optimization results more closely, also local benefits of the new aerodynamic design regarding the wing structure can be found.

This paper presents a modelling scheme suitable for loads analysis of manoeuvres and gusts of a flexible controlled aircraft. In contrast to most ongoing research, the component to be investigated is not the wing but the vertical tail plane (VTP). Critical load conditions for vertical tail plane include yawing maneoeuvre conditions as well as discrete lateral gusts. The resulting design loads are heavily influenced by the flight control system and the associated parameters for yaw damping functions or travel limiter. This poses an interesting problem regarding trade-offs between handling qualities and the structural loads acting on the VTP. This paper investigates the influence of lateral flight control laws on the loads of the different gust and manoeuvre load conditions for certification as specified by the authorities. Sparked by previous incidents, a new load condition was recently introduced: the rudder reversal condition. This new condition features three full reversals of the rudder pedal input instead of just one step input and a mere return to neutral. The loads resulting from the new load condition are considered to be ultimate and not limit loads. The new load condition is assessed and compared to loads envelopes according to the old certification specifications. The introduction of the new rudder control reversal load condition was mainly motivated by wake vortex encounters during which the pilots made excessive or inappropriate use of the rudder. The conjecture is that the loads are primarily caused by pilot action and not the external windfield. Since the present modelling scheme is also capable of simulating position and attitude dependent windfields such as wake vortex encounters, the resulting loads are compared to the new rudder control reversal condition as well.

This paper summarizes an integrated modelling approach for controlled flexible aircraft, applicable for flight loads and flight dynamics analyses. It is particularly suited when numerous repeated design analyses throughout the different design phases of an aircraft development need to be considered. An underrepresented aspect so far is the utilization of active control systems as design parameter already in the early design stages and not merely as mitigation strategy for emerging design deficiencies. An active control system can be beneficial for the reduction of structural weight by the use of load alleviation functions, as well as for improvement of the cruise performance and therefore reducing the fuel consumption. This achieved by appropriately optimizing the lift distribution for different use cases. Regarding the lift distributions with respect to loads analysis: the wing structural weight is driven mainly by the loads it has to sustain. One of the most important load conditions is the 2.5 g vertical pull up manoeuvre. A Manoeuvre Load Alleviation function shifts the center of lift inboard by deflection of the available control surfaces and hence reduces the wing root bending moment, which is in turn the primary driver for structural weight. Another very important load condition to be considered is the Discrete Tuned Gust, which might also be a critical case sizing the wing. An active gust load alleviation (GLA) system needs to redistribute the lift and damp out the structural modes excited by the gust by actively actuating the available control surfaces without introducing undesirable excitation of structural modes by the system itself. In the case of cruise performance, the induced drag depends on the spanwise lift distribution. Due to flexiblity, the wing shape changes during the mission. Active lift adaption by control surface deflections can help to reduce the induced drag. The focus of this paper is on assessing the applicability of the proposed modelling approach for the described use cases.

The DLR project VicToria deals also with high fidelity-based MDO with various approaches. Aside from aerodynamic optimization, further sub-processes are part of the developed MDO processes. They belong to overall aircraft design synthesis, loads analysis, and structural sizing and optimization. The Paper lays out the mentioned MDO sub-processes in order show their contribution and capabilities for the selected MDO process, but also their complexity when dealing with a high fidelity based MDO approach.

This special issue of the CEAS Aeronautical Journal summarizes articles describing results of the work package 'Load Control', which was part of the Smart Fixed Wing Aircraft (SFWA) project, taking place in the framework of the European Clean Sky research programme. The editorial first gives a short overview over the Clean Sky framework and the SFWA project. Second, the articles of the special issue are shortly introduced.

The article describes the use of the Multi-Body Dynamics (MBD) models, the Finite Element Analysis (FEA) and the CAD-modelling process in the automotive suspension development. Automation of maximum quasi-static loads calculation with the automatic two-way geometry update between MBD/CAD-models and automatic load transfer to the finite element analysis allows performing numerous analysis of suspension during development without significant time consumption, and, hence, provides an increased accuracy and reliability of stress analysis results.

Loads analysis and structural design are core steps of the aircraft design process. To reduce wing loads and with it the wing structural mass, methods of passive and active loads alleviation have been researched in recent years. However, those methods are currently implemented without the consideration of dynamic simulations or unsteady aerodynamics in the optimization process in aircraft predesign. The purpose of this research is to investigate the influence of passive and active loads alleviation methods on the structural mass in aircraft preliminary design. The methods have been applied on the wing of a Generic Mid-Range (GMR) aircraft configuration. The models have been created with ModGen, an in-house program at DLR Institute of Aeroelasticity. The models comprise FE-models for the structure and masses, as well as DLM (Doublet-Lattice-Method) model for the aerodynamics. For the investigation of the influence of the loads alleviation systems, a loop of loads analysis and subsequent structure optimization has been conducted. The loads analysis consists of gust and maneuver simulations. For the passive loads alleviation, an aeroelastic tailoring of the wing structure has been implemented, whereas for the active loads alleviation the ailerons are deflected to redistribute lift during maneuvers and to partially compensate lift increment during gust encounters. With the implemented methods, a first quantification of the influence of loads alleviation methods on the structural mass in aircraft predesign is possible.

An integrated modelling approach for gust and manoeuvre loads analysis is presented. Typically, the unsteady aerodynamics for gust loads are computed by the Doublet Lattice Method. However, this method does not account for effects, which are important from a flight dynamics and manoeuvre loads perspective. E.g., the roll-yaw coupling, also responsible for the flight mechanical eigenmodes like the dutch roll mode, are unaccounted for by the DLM. Since, the dutch roll mode might also be excited by lateral gusts, this might have an influence on the loads response. In this paper, the unsteady aerodynamics are computed by a 3D panel method, capable of capturing the flight dynamics accurately and provide complex Aerodynamics Influence Coefficients for gust loads analysis as a function of reduced frequency similar to the DLM. The aerodynamics of the panel method are validate by comparison with CFD results. Differences in the flight mechanics between the DLM and the panel methods are assessed for a parametric variation of the wing dihedral of an aircraft model. Finally, results from a frequency domain gust loads analysis of a lateral gust for the DLM and the 3D panel method are compared.

In the work package “Adaptive Wing” in the Clean-Sky “Smart Fixed Wing Aircraft” (SFWA) project, design processes and solutions for aircraft wings have been created, giving optimal response with respect to loads, comfort and performance by the introduction of passive and active concepts. Central activity of the work was the design and optimization of adaptive wing structures, for complete wings as well as for special components. This process, often called "aeroelastic tailoring", formed the backbone of the work package. Other important contributions have encompassed the development and improve-ment of methods for loads analysis, by extending the classical linear tool set by fast non-linear approach-es. Partners from industry and research involved in the work package contribute with special expertise to the process.The paper gives an outline of the objectives and the work done in the work package, as well as an over-view of the integration of the “Adaptive Wing” activi-ties in the framework of the SFWA project.

This work gives an overview of Reduced Order Model (ROM) applications employed within the context of the DLR Digital-X project. The ROM methodology has found widespread application in fluid dynamics. In its direct application to CFD it seeks to reduce the computational complexity of a problem by reducing the number of degrees of freedom rather than simplifying the physical model. Here, parametric aerodynamic ROMs are used to provide pressure distributions based on high-fidelity CFD, but at lower evaluation time and storage than the original CFD model. ROMs for steady aerodynamic applications are presented. We consider ROMs combining proper orthogonal decomposition (POD) and Isomap, which is a manifold learning method, with interpolation methods as well as physics-based ROMs, where an approximate solution is found in the POD-subspace or non-linear manifold by minimizing the corresponding steady or unsteady flow-solver residual. The issue of how to train the ROM with high-fidelity CFD data is also addressed. The steady ROMs are used to predict the static aeroelastic loads in an MDO context, where the structural model is to be sized for the (aerodynamic) loads. They are also used in a process where an a priori identification of the critical load cases is of interest and the sheer number of load cases to be considered does not lend itself to high-fidelity CFD. We also show an approach combining correction of a linear loads analysis model using steady, rigid CFD solutions at various Mach numbers and angles of attack with a ROM of the corrected Aerodynamic Influence Coefficients (AICs). This integrates the results into a complete loads analysis model preserving aerodynamic nonlinearities while allowing fast evaluation across all model parameters. Thus, correction for the major nonlinearities, e.g. depending on Mach number and angle of attack combines with the linearity of the baseline model to yield a large domain of validity across all flow parameters at the expense of a relatively small number of CFD solutions. The different ROM methods are applied to 3D test cases and in particular to a transonic wing-body transport aircraft configuration.

The estimation of loads acting on an aircraft structure is an indispensable task ranging from conceptual, preliminary, and detail design to loads flight testing when an aircraft is already in service. Work package 4 of the DLR project iLOADS covers the range broadly. Physics-based loads and aerodynamic performance analysis methods in pre-design are presented using a parameterized and automatized process nested in an overall aircraft design loop. Such process can be used for conventional an unconventional configurations. Covering the complete design process, a parametric set-up for structural modeling, estimation of loads and loads flight testing for the DLR HALO, a modified Gulfstream G550, is also shown. Finally the in-flight system identification activities including flight tests for the DLR Discus-2c are described.

The determination of loads acting on the aircraft is one of the main tasks during aircraft development. The knowledge of loads is important for aircraft design, e.g. for the sizing of the airframe structure, and also for certification. The definition of realistic loads assumptions is important, as well as the generation of loads from simulation and experiment. DLR is involved in a large number of aircraft design activities, and operates a fleet of research aircraft; thus DLR requires in-depth expertise for the definition and the determination of relevant and crucial load cases. The aim of the project iLOADS is the development of an internal DLR loads process, comprising expertise from different DLR institutes. The goal of the process is to strengthen the assessment capabilities of DLR with respect to the influence of loads on new aircraft configurations, and to support certification capabilities for the DLR aircraft fleet. The loads process will be investigated towards the influence of different analysis approaches on aircraft structural design, and it will be subject to verification and validation on different air-craft configurations. The paper will give an overview of the background of the iLOADS project, as well as of the work performed in the project. The definition of the loads process as well as the implementations for different applications investigated in the project will be presented in more detail.

Baigiamąjame darbe pateikiamas bandymo stendo, skirto sraigtasparnio Mil Mi-17 nešančio sraigto stabdžio bandymui, projektavimo procesas. Darbe apžvelgiamos sraigtasparnio Mil Mi- 17 techninės skrydžio bei transmisijos charakteristikos, analizuojama nešančiojo sraigto stabdžio konstrukcija ir stabdžio kokybės patikrinimo procedūros. Atsižvelgiant į dideles laiko sąnaudas stabdžio kokybės įvertinimui, projektuojamas stendas, leisiantis kokybės įvertinimo procedūras atlikti efektyviau. Darbe atliktas nešančiojo sraigto stabdymo sistemos jėgų tyrimas, leidęs įvertinti stabdžio bandymo metu veikiančias apkrovas. Sudarytas bandymo stendo modelis ir atlikti stipruminiai skaičiavimai. Suprojektuotas stendas leidžia atlikti visas stabdžio kokybės įvertinimo procedūras. Taip pat numatyta galimybė patikrinti stabdymo momento atitikimą normoms., This bachelor final project presents the process of engineering the test stand for helicopter Mil Mi-17 main rotor brake. In this work it is surveyed the technical flight and transmission characteristics of helicopter Mil Mi- 17, analysed main rotor brake construction and brake quality test procedures. Considering the fact that quality examination of brake takes a long time, there was designed the test stand will that helps to accomplish the procedures of examination with less time expenses. Due to accomplishement of analysis of main rotor braking system forses, loads which are working while testing brake can be estimated. The test stand model has been composed and calculations of strength has been done. It is possible to accomplish all necessary procedures to exam brake quality by this test stand, as well as to test if braking force momentum is within the normal range.

This paper demonstrates how the robust performance analysis framework can be used to determine worst case loads of flexible aircraft due to 1-cos gusts. This framework is a part of control theory and is used to characterize a system by input-output norms: e.g. the induced L2-L∞ norm represents the worst case energy-to-peak gain. Two very efficient ways to compute this norm are presented. Based on the physical interpretation of this norm, an aircraft model is weighted such that the induced L2-L∞ norm of the weighted system represents a close but guaranteed upper bound for 1-cos gusts and similar excitations. The analysis results are compared to simulations. Since the energy-to-peak gain can be computed in a very efficient way for LTI models, the norm is used to quickly obtain an upper bound for loads and to identify critical flight conditions. In a second example, the analysis is additionally performed on an uncertain mode