Aircraft Engineering and Aerospace Technology

Holzäpfel, Frank ; Stephan, Anton ; Heel, Tobias ; Körner, Stephan

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0045

Purpose – From pilot reports, field measurements and numerical simulations, it is known that wake vortices may persist within the glide path in ground proximity, leading to an increased encounter risk. This paper aims to investigate wake vortex behaviour during final approach and landing to understand why landings can be safe nevertheless. Further, it is investigated whether and to which extent the installation of plate lines beyond the runway tails may further accelerate wake vortex decay and thus improve safety by reducing the number of wake vortex encounters. Design/methodology/approach – A hybrid numerical simulation approach is used to investigate vortex evolution from roll-up until final decay during the landing manoeuvre. The simulations are complemented by field measurement data accomplished at Munich Airport and at Special Airport Oberpfaffenhofen. Findings – During touchdown, the so-called end effects trigger pressure disturbances and helical vortex structures that appear to ensure vortex decay rates in ground proximity needed to guarantee the required safety targets of aviation. Light detection and ranging (LIDAR) measurements indicate that vortex decay indeed can be accelerated by a plate line installed on the ground surface. The lifetime of the most safety relevant, long-lived and strongest vortices can be reduced by one-third. Practical implications – The installation of plate lines beyond the runway tails may improve safety by reducing the number of wake vortex encounters and increase the efficiency of wake vortex advisory systems. Originality/value – The novel numerical simulation technique and the acquired insights into the wake vortex phenomena occurring during landing as well as the demonstration of the functionality of the patented plate line provide high originality and value for both science and operational application.

Gagnon, Louis ; Morandini, Marco ; Quaranta, Giuseppe ; Muscarello, Vincenzo ; Masarati, Pierangelo

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0047

Purpose – Few modeling approaches exist for cycloidal rotors because they are a prototypal technology. Thus, the purpose of this study was to develop new models for their analysis and validation. These models were used to analyze cycloidal rotors and a helicopter that uses them instead of a tail rotor. Design/methodology/approach – Three different models were developed to study the aerodynamic response of cycloidal rotors. They are a simplified analytical model resolved algebraically; a multibody model resolved numerically; and an unsteady computational fluid dynamics (CFD) model. The models were validated using data coming from three different experimental sources, each with rotor spans and radii of roughly 1 m. The CFD model was used to investigate the influence of rotor arms. The efficiency and the stability of the rotor in different configurations were studied. An aeroelastic multibody simulation was used to verify the influence of flexibility on the rotor response. Findings – The analyses suggested that cycloidal rotors can increase the efficiency of a helicopter at high velocities while flexibility reduces it and may lead to instabilities. Research limitations/implications – These models do not consider the effect of boundary layer friction on the trailing vortices generated by the rotor blades. Practical implications – These models allow a four-step aerodynamic optimization procedure. First, a range of optimized configurations is obtained by the analytical model. Second, the multibody model refines that range. Third, the CFD model detects eventual problematic blade interactions. Originality/value – The models presented should serve researchers and industrials looking for a means to measure the performance of cycloidal rotors concepts. The results presented also guide an initial cycloidal rotor design.

Leger Monteiro, Jakson Augusto ; Páscoa, José C ; Xisto, Carlos M.

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0051

Purpose – Cycloidal rotors, also known as cyclogyros, are horizontal axis rotary-wing machines with potential for Vertical Take-Off and Landing aircraft applications. The paper aims to devise and validate a new semi-empirical analytical model that is capable of assisting in the structural and aerodynamic design of cyclogyros. Design/methodology/approach – The analytical model comprises a purely analytical kinematic sub-component that is used for analyzing the structural feasibility of the rotor. Several geometrical parameters are assessed, e.g. the oscillation schedule of the blades as a function of the properties of the pitching mechanical system. The dynamic sub-component of the model is used for estimating the rotor thrust production and power consumption. This sub-component is semi-empirical and uses a calibration function that was devised using the available experimental data. Findings – For a set of initial conditions and geometrical parameters, the model is capable of providing a real animation of the cyclogyro operation. It is shown that the motion of the blades does not comply with the requirements of a perfect cycloidal curve. The study concerning the simulation of the virtual camber effect on the drum blades, with and without the pitch effect, shows that the virtual camber strongly depends on the chord-to-radius ratio and on the aircraft advance velocity. Originality/value – A new analytical model capable of assisting in the geometrical and aerodynamic design of cyclogyros is here proposed. The model is capable of providing approximate estimations of the cyclogyro thrust production and power consumption under operating design conditions.

Ageev, Nikita ; Pavlenko, Alexander

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0052

Purpose – This study aims to decrease the aerodynamic drag of the body of revolution at supersonic speeds. Supersonic area rule is widely used in modern supersonic aircraft design. Further reduction of the aerodynamic drag is possible in the framework of Euler and Reynolds averaged Navier–Stokes (RANS) equations. Sears–Haack body of revolution shape variation, which decreased its aerodynamic drag in compressible inviscid and viscous gas flow at Mach number of 1.8 under constraint of the volume with lower bound equal to volume of initial body, was numerically investigated. Design/methodology/approach – Calculations were carried out in two-dimensional axisymmetric mode in the framework of Euler and RANS with SST model with compressibility correction equations at structured multiblock meshes. Variation of the radius as function of the longitudinal coordinate was given as a polynomial third-order spline through five uniformly distributed points. Varied parameters were increments of the radius of the body at points that defined spline. Drag coefficient was selected as an objective function. Parameter combinations corresponding to the objective function minimum under volume constraint were obtained by mixed-integer sequential quadratic programming at second-order polynomial response surface and IOSO algorithm. Findings – Improving variations make front part of the body become slightly blunted, transfer part of volume from front part of the body to back part and generate significant back face. In the framework of RANS, the best variation decreases aerodynamic drag by approximately 20 per cent in comparison with Sears–Haack body. Practical implications – The results can be applied for the aerodynamic design of the bullets and projectiles. The second important application is knowledge of the significance of the difference between linearized slender body theory optimization results and optimization results obtained by modern computational fluid dynamics (CFD) optimization techniques. Social implications – Knowledge about the magnitude of the difference between linearized slender body theory optimization results and optimization results obtained by modern CFD optimization techniques can stimulate further research in related areas. Originality/value – The optimization procedure and optimal shapes obtained in the present work are directly applicable to the design of small aerodynamic drag bodies.

Bijewitz, Julian ; Seitz, Arne ; Isikveren, Askin T. ; Hornung, Mirko

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0053

Purpose – Motivated by the potential of gaining noticeable improvements in vehicular efficiency, this paper aims to investigate the benefits attainable from introducing a more synergistic propulsion/airframe integration. In previous work, the concept of a boundary layer ingesting propulsor encircling the aft section of an axisymmetric fuselage was identified to be particularly promising for the realisation of aircraft wake filling, and hence, a significant reduction of the propulsive power required. Design/methodology/approach – After reviewing the theoretical principles of the propulsive fuselage concept, a book-keeping and model matching procedure is introduced, which is subsequently used to incorporate the numerically computed aerodynamic characteristics of a propulsive fuselage aircraft configuration into a propulsion system (PPS) sizing and performance model. As part of this, design heuristics for important characteristics intrinsic to propulsive fuselage power plants are derived. Thereafter, parametric study results of the PPS are discussed, and the obtained characteristics are compared to those of a conventionally installed power plant. Finally, the impact of the investigated PPS on the integrated performance of a propulsive fuselage aircraft concept is studied, and the results are compared and contrasted to previously conducted analyses based on semi-empirical characteristics. Findings – It was found that the aircraft-level benefit originally predicted based on semi-empirical methods could be confirmed using the numerically derived PPS design heuristics, specifically an improvement in vehicular efficiency of 10.4 per cent over an advanced conventional reference aircraft. Practical implications – The approach presented in the paper may serve as a guideline when incorporating the results of high-fidelity aerodynamic methods into a PPS sizing and performance model suitable for aircraft-integrated assessment of a propulsive fuselage concept. The vehicular efficiency potentials offered through the synergistic PPS integration approach are highlighted. Originality/value – The paper contributes to a deeper understanding of the characteristics of a boundary layer ingesting fuselage fan (FF) power plant relative to a conventionally installed PPS. In addition, a set of PPS design correlations are presented allowing for the integrated sizing of a FF power plant.

Führer, Tanja ; Willberg, Christian ; Freund, Sebastian ; Heinecke, Falk

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0054

Purpose – To obtain a good start configuration in the early design phase, simulation tools are used to create a large number of product designs and to evaluate their performance. To reduce the effort for the model generation, analysis and evaluation, a design environment for thin-walled lightweight structures (DELiS) with the focus on structural mechanics of aircrafts has been developed. Design/methodology/approach – The core of DELiS is a parametric model generator, which creates models of thin-walled lightweight structures for the aircraft preliminary design process. It is based on the common parametric aircraft configuration schema (CPACS), which is an abstract aircraft namespace. DELiS facilitates interfaces to several commercial and non-commercial finite element solvers and sizing tools. Findings – The key principles and the advantages of the DELiS process are illustrated. Also, a convergence study of the finite element model of the wing and the fuselage and the result on the mass after the sizing process are shown. Due to the high flexibility of model generation with different levels of detail and the interface to the exchange database CPACS, DELiS is well suited to study the structural behaviour of different aircraft configurations in a multi-disciplinary design process. Originality/value – The abstract definition of the object-oriented model allows several dimensions of variability, such as different fidelity levels, for the resulting structural model. Wings and fuselages can be interpreted as finite beam models, to calculate the global dynamic behaviour of a structure, or as finite shell models.

Goetzendorf-Grabowski, Tomasz ; Antoniewski, Tomasz

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0055

Purpose – Unconventional configuration aircrafts are not often designed because of many problems, mainly with stability and trim. However, they could be very promising. The problems can be compensated by extraordinary performance and some flying characteristics. The three-surface aircraft, presented in the paper, is such a configuration – problems and profits are both present, but advantages seem to be more prevalent. This paper aims to present main assumptions for a new, three-surfaces aircraft design, its evaluation according to flying quality requirements and the discussion on selected performance characteristics. The paper completes with the first experimental results of flight tests of a 40 per cent scaled model. Design/methodology/approach – Aerodynamic computations were made using panel method code (KK-AERO, PANUKL). Stability analysis was done using SDSA package, developed within the SimSAC project. Findings – Initial design assumptions and numerical analysis results were proven during flight tests. Practical implications – The paper contains results of numerical analysis, which were crucial in designing the layout of the new, three-surface aircraft. Originality/value – This paper presents an original approach to design a new, unconventional aircraft. The approach and results could be useful in other projects.

Romeos, Alexandros ; Giannadakis, Athanasios ; Perrakis, Konstantinos ; Panidis, Thrassos

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0071

Purpose – The purpose of this paper is to study the structure and dynamic development of a pair of co-rotating trailing vortices, during their formation, interaction and merging, using detailed experimental measurements of the velocity and vorticity fields. Design/methodology/approach – The vortices were generated using two half wings (NACA0030) positioned at equal and opposite angles of attack at the entrance of the test section of an open-circuit, subsonic, wind tunnel. Velocity vector measurements were obtained at Re c = 133,000, on cross-plane grids at several distances from the trailing edges of the wings, using an in-house developed four-sensor hot wire anemometer probe. Findings – The results include cross-plane contour plots of the mean and fluctuating velocity as well as mean vorticity fields. Each of these variables is affected in a different way, providing complementary information on the development of the flow field. After shedding, the two vortices are swept along the stream-wise direction and spiral around each other, thereby developing a braid of two vortices, which then deforms the external flow field. Gradually, the interaction with the external flow field links both vortices together until the final merging and the formation of a new stable linear vortex emerges. Practical implications – Trailing vortices have been rendered particularly important during the past decades, because of increasing traffic density of very heavy aircrafts and several plane “incidents”, which were attributed to the action of the vortex wake. Originality/value – The presented results provide information on the evolution and merging of a pair of vortices formed by a closely spaced differential wing configuration. The vortices interact almost immediately after shedding as expected in flap–flap or flap–wing vortices interaction.

Scherer, Julian ; Kohlgrüber, Dieter

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0056

Purpose – This paper aims to summarize the main features of the fuselage structure description within the Common Parametric Aircraft Configuration Schema (CPACS) data format. Design/methodology/approach – The CPACS fuselage structure description includes the definition of arbitrary sheets and structural profiles which can be combined with a variety of material definitions to so-called structural elements. Besides the definition of these structural elements, the definitions of structural members, such as stringers, frames, floor structures and pressure bulkheads, as well as the definitions of the complex load introduction regions that transfer loads from the wings and the empennage into the fuselage shell are introduced. Finally, exemplary models generated with different mesh generation tools developed at the DLR Institute of Structures and Design are presented. These models are suitable for subsequent static or dynamic structural analyses. Findings – The CPACS fuselage structure description is suitable for defining standard fuselage configurations including complex load introduction regions suitable for different types of structural analysis. Practical implications – The work shows exemplary fuselage models generated from the introduced CPACS fuselage description suitable for subsequent static and dynamic structural analyses. As the CPACS standard is available for download, the described definitions may be used by universities, research organizations or the industry. Originality/value – The work presents the definitions of the fuselage structure within the CPACS schema that were mainly developed by the authors employed at the DLR Institute of Structures and Design. The exemplary applications show models generated completely on the basis of the definitions described in this paper.

Bach, Tobias ; Führer, Tanja ; Willberg, Christian ; Dähne, Sascha

2016 Aircraft Engineering and Aerospace Technology

doi: 10.1108/AEAT-02-2015-0057

Purpose – The purpose of this paper is to present a structural design and optimization module for aircraft structures that can be used stand-alone or in a high-fidelity multidisciplinary design optimization (MDO) process. The module is capable of dealing with different design concepts and novel materials properly. The functionality of the module is also demonstrated. Design/methodology/approach – For fast sizing and optimization, linear static finite element (FE) models are used to obtain inner loads of the structural components. The inner loads and the geometry are passed to a software, where a comprehensive set of analytical failure criteria is applied for the design of the structure. In addition to conventional design processes, the objects of stiffened panels like skin and stringer are not optimized separately and discrete layups can be considered for composites. The module is connected to a design environment, where an automated steering of the overall process and the generation of the FE models is implemented. Findings – The exemplary application on a transport aircraft wing shows the functionality of the developed module. Originality/value – The weight benefit of not optimizing skin and stringer separately was shown. Furthermore, with the applied approach, a fast investigation of different aircraft configurations is possible without constraining too many design variables as it often occurs in other optimization processes. The flexibility of the module allows numerous investigations on influence of design concepts and failure criteria on the mass and layout of aircraft wings.