M. Voskuijl

Rotorcraft simulation modelling and validation for control law design

This paper describes the development and validation of a high fidelity simulation model of the Bell 412 helicopter for handling qualities and flight control investigations. The base-line model features a rigid, articulated blade-element formulation of the main rotor, with flap and lag degrees of freedom. The Bell 412 HP engine/governor dynamics are represented by a second-order system. Other key features of the base-line model include a finite-state dynamic inflow model and lag damper dynamics. The base-line model gives excellent agreement with flight-test data over the speed range 15-120kt for on-axis responses. Prediction of off-axis responses is less accurate. Several model enhancement options were introduced to obtain an improved off-axis response. It is shown that the pitch/roll off-axis responses in transient manoeuvres can be improved significantly by including wake geometry distortion effects in the Peters-He finite-state dynamic inflow model.

Automated Control Surface Design and Sizing for the Prandtl Plane

This paper presents a methodology for the design of the primary flight control surfaces, in terms of size, number and location, for fixed wi ng aircraft (conventional or unconventional). As test case, the methodology is a pplied to a 300 passenger variant of the Prandtl Plane. This box wing aircraft is deemed to have low induced drag compared to conventional aircraft. The methodology is completely physics based and includes an aerodynamic analysis, followed by a control allocat ion algorithm and an analysis of the flight mechanics. The design has to fulfill a set of hand ling qualities requirements with a minimum total control surface area. An optimizatio n algorithm is used to find the best design. Results indicate that this is possible with ailerons outboard on both wings, elevators inboard on both wings and conventional rudders in the vertical tail. The configuration allows for pure torque control and also direct lift control in the longitudinal axis. These features can potentially enhance airfield performan ce. Nomenclature

Distributed Propulsion featuring Boundary Layer Ingestion Engines for the Blended Wing Body Subsonic Transport

The blended wing body aircraft is one of the promising contenders for the next generation large transport aircraft. This aircraft is particularly suitable for the use of boundary layer ingestion engines. Results published in literature suggest that it might be beneficial to have a large number of these engines (distributed propulsion). A conceptual design study is therefore performed to determine the potential benefits of boundary layer ingestion engines for a conventional number of engines increasing to a large number of engines. A gasturbine performance tool is combined with a weight prediction tool and a mission analysis tool to analyze aircraft-engine combinations. A genetic algorithm is used to find engine specifications that result in minimum fuel consumption for a given configuration (e.g. 8 engines). Results show that the potential of distributed propulsion systems relies heavily on a weak dominance of beneficial effects over negative effects of similar magnitude. From a performance point of view it is better to abandon the distributed propulsion concept and to focus on a small number of large boundary layer ingestion engines instead since they do not suffer high internal losses. A propulsion system with three boundary layer ingestion engines is shown to have a 5% performance improvement in terms of fuel consumption over a conventional strut mounted propulsion system.

Model Generation for the Verification of Automatically Generated Mechatronic Control Software

The development of embedded control software for mechatronic systems is mainly a non-automated process, requiring the intervention of a human programmer. A project has been started with the intention to develop a set of prototype tools and a framework with which an interdisciplinary product development team can automatically generate control software for mechatronic systems. This paper will discuss the development of a Control Model Generator as part of this project, which is envisioned to be able to generate system dynamics models at various levels of detail, which can be used to verify the automatically generated code at software level. Using SysML and Modelica, a model based view can be maintained throughout the model generation process.

Simulation of automatic helicopter deck landings using nature inspired flight control

The landing of a helicopter on a ship is one of the most dangerous of all helicopter flight operations. The Bell 412 advanced systems research aircraft is subject to a torque oscillation issue which increases pilot workload significantly when operating with low power margins and/or whilst performing tasks that require accurate torque control. This makes the deck landing task with this helicopter even more difficult. An automatic deck landing system was therefore developed. This system makes use of a novel control strategy for vertical control based on optical flow theory. Furthermore, it incorporates a torque envelope protection system. A successful automatic landing was performed in the flight simulator at the University of Liverpool. The novel control strategy created a very natural motion of the helicopter, similar to how a real pilot would fly it. The same control technique was subsequently applied to the simulation of an automatic lateral repositioning of a UH60 like helicopter in order to prove the generality of the technique. This manoeuvre was simulated successfully within level 1 handling qualities boundaries.

Development and Implementation of a Novel Parametrization Technique for Multidisciplinary Design Initialization

A new parametrization method for aircraft shapes is presented to enhance shape optimization for aircraft design. This parametrization method was implemented in a tool that creates feasible initial solutions for multidisciplinary design optimization problems. The tool combines all aspects of the aerodynamic design process: parametrization, aero-dynamic analysis and optimization. The novel parametrization method presented in this paper makes use of the Class-Shape-Refinement-Transformation (CSRT) method. This method employs a combination of Bernstein polynomials and B-splines to allow for both global and local control of the shape. Additionally, the use of B-splines makes it possible to efficiently handle volume constraints, which are very common in aircraft design. The parametrization method was coupled to two different aerodynamic analysis tools. The commercial panel method code VSAERO was used for the low-speed regime and an in-house Euler code was used for transonic and supersonic flight conditions. Various different optimization schemes were investigated and compared. A number of test cases were performed. For the first set of test cases, a three-dimensional geometry was optimized for subsonic conditions, using VSAERO and various optimization algorithms. For the second set of test cases, an airfoil was optimized for transonic and supersonic conditions, using the in-house Euler solver and a gradient-based optimizer. From this work it can be concluded that a combination of stochastic and gradient-based optimization algorithms works best together with the CSRT method. Additionally, refining the shape using B-splines proved to be an efficient way of increasing the design freedom, while the design space remained smooth enough to employ gradient-based optimization.

Cruise Range in Formation Flight

A new set of analytical range equations (a modification of the traditional Breguet range equation) suitable for formation flight at transonic flight speeds under realistic operating conditions (constant Mach number and altitude) is derived. Formations of two aircraft of the same type are analyzed to determine the effects of 1)xa0weight differences between the aircraft, 2)xa0altitude, and 3)xa0the formation flight range on the potential fuel benefits and the associated optimum Mach number. In the case of a weight difference, the lightest aircraft should lead the formation to realize the largest fuel benefits. Overall, fuel savings of 6 to 12% for the total formation can be realized at the expense of a reduction in cruise Mach number from 0.85 to 0.80. The fuel benefit is much less (2 to 8%) when the formation is flown at the original design cruise Mach number. In terms of fuel benefits and Mach number, it is beneficial to fly in formation at higher altitudes. Formation flight step climb procedures are possible, ...

Helicopter load alleviation using active control

This paper discusses how structural load objectives can be included in a rotorcraft flight control system design in an efficient and straightforward way using multivariable control techniques. Several research studies have indicated that pitch link loads for various rotorcraft types can reach high or even unacceptable values, both in steady state and maneuvering flight. This is especially the case for high-speed aggressive maneouvers. Pitch link loads at high-speed flight are therefore taken as a case study. A novel longitudinal control system is presented, designed to reduce helicopter pitch-link loads during high-speed longitudinal manoeuvres whilst providing a pitch attitude command attitude hold response type. The design is based on a high-order model of a helicopter representative of the UH-60 Black Hawk. New metrics are presented for the analysis of structural loads that can be used in combination with ADS-33 handling qualities requirements.

Environmental Impact Evaluation of Aircraft at System-of-Systems Level

Next generations of civil transport aircraft will need to be evaluated not only against their behaviour as an aircraft system but also as a part of the larger air transport system. In addition to this are the sustainability issues related to for instance noise and emissions, represented by environmental impact. Both issues mandate the incorporation of complex stakeholder behaviour in the design and evaluation of future aircraft. A framework is proposed in extension of existing Design and Engineering Engines to perform such evaluations. For this extension a combination of agent based modelling and simulation approach, value engineering and multi-level optimization is suggested to quantitatively implement quality function deployment. As an illustration of the complexity in evaluating new aircraft concepts, the Prandtl Plane study case is used. From this study case it is found that, when evaluated using the current DEE, the Prandtl Plane shows a potential for alternative use at systems level. But no conclusion can be drawn on the environmental impact effect on the air transport system without addressing the system-of-systems considerations. This includes the unknown stakeholder response with respect to the new opportunities provided by the Prandtl Plane. One of the great challenges for future design is the increasing complexity, not only in the proposed solutions, e.g. Prandtl Plane, but also in the measures of desirability, e.g. global emissions. This requires the integrated approach addressing the complexities at both system-of-systems and system level, proposed in extension to the current design and engineering engine.