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There is an ongoing trend in the European Military a/c industry towards cooperation between nations when purchasing and between manufacturers when developing and producing a/c. Different manufacturers at different locations develop different parts or sub-systems. When using this approach a vital part of a fast and precise system evaluation is the use of simulation models. In order to stay competitive it is not only sufficient to be able to build large simulation models but also to do it fast. This paper describes the conclusions regarding a modeling strategy of large fluid systems drawn from the building of a simulation model of the JAS 39 Gripen fuel system. An overall process is suggested into which the activities of building a model are fitted. This is however not the main objective; it is more important to identify the different issues and activities at the engineering level.

The current work present a simple model to integrate non-linear aerodynamic in conceptual design phase, before wind tunnel testing. A presentation of a simple pitch up maneuver based on three different aerodynamic models is simulated. The simulation indicates different behaviors depending on the aerodynamic model, and shows the importance of including unsteady aerodynamic.

Flow visualization and force and moment measurements were conducted on a number of delta wing planforms and realistic configurations in order to ascertain the existence of Reynolds number effects. The results show the effect of Reynolds number at high angles of attack is insignificant in comparison to other effects such as tunnel blockage and support interference for highly swept lifting surfaces with sharp leading edges. For realistic configurations however the situation is significantly more complicated because of the interaction of vortices shed from the forebody and multiple lifting surfaces. In such cases, it is important to consider such effects carefully when extrapolating to full-scale Reynolds numbers.

In this paper modern optimization techniques are applied to an aircraft sizing problem. The paper starts by discussing how optimization could support the design activity and thereafter different methods of formulating the design problem as an optimization problem is discussed. Finally the problem of aircraft sizing is addressed by combining the presented optimization strategy with a simulation model of an aircraft based on mathematical models gathered from the literature. The outcome of the optimization is for example the optimal layout in order to minimize fuel consumption for a specific mission or the trade-off between the number of passengers and the fuel consumption per passenger.

The design modern aircraft requires integration of multidisciplinary models for analysis in early design phase to increase the chances of a successful project. In this paper, a framework for distributed aircraft analysis in the conceptual design including several domains is presented. The framework is based on so-called Web service standards, allowing integration of distributed models for system simulation and optimization using standardized interfaces. The analysis is controlled by a so-called sequencer which manages the interaction between simulation modules and an XML-based design data repository. This repository includes all design data and an executable process description defining the sequence for execution of the modules. In the paper, the framework with underlying concepts is described. The approach is further illustrated using the design of an Unmanned Aerial Vehicle as an example.

There is a clear risk that system aspects and flight control issues are not dealt with satisfactory in the preliminary design phase. There are several reasons for this. The first is that aircraft are becoming increasingly complex and the second is that there are limited resources available at the preliminary design stage. Therefore it is a risk that preliminary design is handed over that requires a lot more attention in the system and control areas than would otherwise been needed if these matter could have been dealt with more efficiently at the preliminary design phase. With the advent of powerful simulation techniques the resources needed to do this are becoming available. There is, however, a need for tools that can be used to connect the different disciplines with each other. At present designers in different disciplines usually relays, not only on totally different tools, but also different paradigms.

Modelling and simulation is of crucial importance for the understanding of system dynamics. In aircraft, simulation has been strong in the area of flight control. Modelling and simulation of the hydraulic systems has also a long tradition. The rapid increase in computational power has now come to a point where complete modelling and simulation of all the sub systems in an aircraft is not far away. This means new challenges in dealing with very complex multi domain systems. Of all the systems in an aircraft fluid power systems is one of the most difficult to handle from a numerical point of view. They are characterised by difficulties such as discontinuities, very strong non-linearities, stiff differential equations and a high degree of complexity. A considerable effort has therefore been made to develop methods suitable for simulation of such systems.

The design process is an interactive feedback process where the performance of the design is compared with the performance specification. In aircraft design it is very important that the system is optimised with respect to different aspects such as performance and weight. Traditionally, and by necessity, the design procedure has began with some kind of performance specification followed by a conceptual design, and after that the system has been optimised (usually implicitly) with respect to the performance specification. Typically, aircraft design optimisation is characterised by a multitude of objectives that can be difficult to compare to each other, such as low fuel consumption, high speed and passenger comfort. Usually this is where the engineering judgement of the designer comes in. In traditional design it is often difficult to establish what was the result of design decisions and what was the result of pure optimisation.

Mobile hydraulic equipment are today operated manually to a very large extent. There are, however, some applications where substantial benefits would be obtaind if some kind of feedback and more sophisticated control was used. One such application is the control of a crane. Usually the operator controlls the flow to each of the pistons so that the crane tip is moved in the desired direction (Fig. 1). Since many mobile hydraulic valves packages have electronic input and there exists built in position transducers for the pistons, it seems to be rather straightforward to introduce vector control of the crane tip directly. That is, the operator commands controlls the direction and speed of the crane tip. Here, a control algorithm is described that allows the use of mobile electrohydraulic proportional valves while still having accurate vector control of the crane tip.

For a number of years, load-sensing systems have been increasingly used in mobile fluid applications, especially mobile cranes. The high energy saving potential of load-sensing systems is a special advantage; this system type decreases the pressure level of a pump to a value that corresponds to the actuator level. When the configuration includes a variable pump, a decrease in pump flow corresponding to the demand of the load will be a further advantage. Control of a load-sensing system can be enhanced by compensated valves to handle several loads. The paper at hand deals with the theories describing the steady state and dynamic characteristics of load-sensing systems with compensated valves and a variable pump. Two kinds of pressure compensated valves are discussed, the conventional and an interesting alternative with relocated compensators, physically positioned on the outlet side of the control valve instead of the inlet side.