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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.

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.

This paper addresses the development of analysis tools for flight loads prediction in the pre-design stage. The analysis tools are embedded in a parametric modelling environment. Emphasis will be on prediction of aerodynamic loads on specific structural parts, like the fin, during dynamic manoeuvres. Principal requirement is that these loads can be computed with low effort, but with sufficient accuracy. In the frame of this work, an availale transport aircraft model has been taken as reference. The aerodynamic loads on the fin are computed using the Vortex Lattice Method (VLM), allowing for comparison with the original aerodynamics data base. For this structural component of the aircraft, a dense panel grid is chosen. In order to account for aerodynamic cross interferences, the remainder of the aircraft geometry is also taken into account, but with a considerably coarser grid. From the comparison with the original database, correction factors and uncertainty bounds are estimated. Next, the geometry of the fin is modified. Based on aerodynamic loads computed with the VLM, the impact on (lateral) manoeuvre loads is analyzed. Hereby the estimated uncertainty levels from the first step are used to predict sensiivities for consideration instructuralsizing.