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Ill., graph. Darst.

graph. Darst.

Education in engineering design is a challenging task. On the one hand the students have to get a broad theoretical basis and engineering expertise, on the other hand they have to learn how to apply their knowledge and how to face real technical problems [Pulko, 2004]. Since time in University is limited (in Germany a engineering degree at university level takes about 5 years to complete) often an emphasis is put on a sound theoretical education at the expense of practical experience. This paper presents a student competition between four German universities, which provides a practical team-work project for engineering (design) students that nearly spans the whole life-cycle from brainstorming for product ideas to manufacturing and usage of the product. The development task is an aircraft or flight device totally made of steel. Aim of the project is to apply the theoretical knowledge at a practical task.

The EU research Project Power Optimised Aircraft (POA) investigates the approach to replace primary hydraulic supply by extended electric power systems towards a More or All Electric Aircraft. This contribution presents an electrically powered actuation system for nose landing gears using an EHA (electrohydrostatic actuator) approach. One motor pump unit supplies door and gear actuation as well as the steering system. Different control strategies for the individual actuators are introduced. The effects of different control strategies are shown by simulation results.

Regarding the regulation of weakly damped aeroelastic structures by means of the primary flight controls (PFC), the present contribution focusses on a sophisticated robust controller design method, to achieve the required functionality. Generally, the outlined approach is premised on eigenstructure assignment. Enhancements promise effective integration of miscellaneous potentially competing objective specifications either in time or frequency domain as well as parametric requirements. Due to the infinitive set of flight conditions and fuel configurations the underlying aeroservoelastic plant consists of a linear multivariable multi–model system. Technical feasibility, parametric and dynamic uncertainties as well as architectural constraints, e.g. the number of available sensors lead to a robust output feedback controller. Principally the proposed method is well known from flight control design and modal decoupling. But in contrast, the constrained simultaneous robust eigenvalue stabilisation represents the primary objective at the current application. Since the intrinsic controller calculation is implemented as multiobjective optimisation task, proper optimisation criteria are defined, which incorporate the aeroservoelastic performance specifications into the design procedure. The suitability of the resulting low–order static output controller is verified by real time simulation for a completely normal and degraded configuration covering a real PFC actuation system hardware–in–the– loop.

The introduction of variable displacement hydraulic motors to secondary and primary flight actuation offers a considerable potential for power optimization and saving in aircraft hydraulic systems. The application in aircraft systems requires high safety, reliability and availability at the smallest expense possible. Therefore the combination of a variable displacement hydraulic motor with a fixed orifice guarantees fail-passive system behavior. The integration in fly-by-wire flight control architecture leads to digital control structures. Robust controller design is forced because of the influence of several uncertain physical parameters during flight mission. Moreover the significant nonlinear characteristic of the throttled VDHM affects dynamic behavior. An integral discrete-time robust controller design methodology is presented considering specified requirements as dynamic bandwidth, static position accuracy and stationary power drive performance. Here the parameter space approach is used for direct sampled-data controller synthesis. A static linear state feedback controller is chosen. All combinations of uncertain and linearized parameters leads to a multi-model problem which is solved by simultaneous stabilization. Finally simulated and experimental results show typical operation cases and verify expected system dynamics in time- and frequency-domain.

The approach and landing phase is dimensioning for today’s aircraft fluid power systems. In this flight phase, large hydraulic consumers (flaps/slats, landing gear) have to be operated while the available hydraulic power reaches it’s minimum due to the reduced engine speed. During most of the flight the installed resources exceed the hydraulic power requirements by far; resulting in a low overall-efficiency. This paper presents an approach to increase the efficiency of today’s fluid power system by using variable displacement hydraulic motors (VDMHs). Two applications will be introduced: the VDMH driven slat/flap power control unit (PCU) and the bi-directional hydraulic-electrical power conversion unit (HEPCU). The variable displacement PCU reduces the design loads for the fluid power system during take-off and landing. Compared to conventional PCUs used today, a flow reduction of about 50% is expected using the VDHM technique. The HEPCU transfers hydraulic into electrical power and vice versa depending on the current load and flight situation ("hydraulic-electrical power management"). The main benefit from this approach is down sizing the primary power sources (engine driven pumps and generators), a significant increase in reliability and a higher efficiency for both, the hydraulic and the electrical power generation system.

Today’s high lift systems of civil transport aircraft are driven by Power Control Units using valve controlled constant displacement hydraulic motors. This concept leads to complex valve blocks, attended by high power losses to realise discrete speed control, positioning and pressure maintaining functionality. The concept of secondary controlled hydraulic motors with variable displacement offers reduction in flow consumption without pressure losses and decreases the complexity of the valve block design. Instead of controlling flow of the hydraulic motor with valves, torque is adjusted to the load by varying displacement. An electronic control circuit allows flexible digital control concepts e.g. load independent speed control, pressure maintaining functionality, smooth start-up sequences and continuous positioning of the mechanical transmission system. This paper introduces the concept of today’s Power Control Units, the principle and mathematical model of secondary controlled hydraulic motors and the cascade control loop structure. A new hydraulic concept for Power Control Units using secondary controlled hydraulic motors is presented. Theoretical, simulated and experimental results show typical operation sequences under load and a comparison of power requirement to conventional systems.

Since the late 70's, several research and development projects deal with future Power-by-Wire-technology for aircraft flight control systems, aiming to reduce the overall system weight, as well as installation and maintenance effort. The design of appropriate electrically powered actuators still is a key technology. An overview about typical functional and performance requirements on primary flight control actuators is given. With electro-hydrostatic actuators (EHAs), based on an electric motor driven pump directly connected to a hydro-cylinder, safety functions can be realized with low effort by means of small valves. The two basic EHA principles are considered here: the EHA-SM, having a constant displacement pump driven by a speed controlled, electronically commutated brushless DC motor, and the EHA-SP, with an electrically controlled servopump driven by an uncontrolled AC induction motor. A rating method for these EHA-types is proposed to design components very close to the actual requirements, aiming at weight saving solutions. Using characteristic motor torque-speed curves as well as pump performance maps, partly leads to iterative solutions due to interdependencies between the components. Weight and typical dimension envelope estimates were developed as functions of the performance/design values calculated before. Finally, nonlinear dynamic simulation models are set up, thus completing a little 'toolbox' helping the flight control actuation developer, particularly - but not exceptionally - during early project stages.