bluuebunny/crossref_metadata_2025_split huggingface dataset:
A calculation method for parametric design studies of V/STOL aircraft
Authors: Gologan C. , Broichhausen K. , Seifert J. 
Published: February 2016

AbstractThis paper provides a method that helps the aircraft designer to develop a performance constraint chart (PCC) for vertical/short takeoff and landing (V/STOL) aircraft that produce hybrid lift (static lift in combination with aerodynamic lift). The PPC provides a first estimation for the thrust-to-weight ratio (T0/MTOW) and wing loading (MTOW/S). The method is applicable to concepts, where static lift and main-engine thrust are coupled (e.g. the F-35B system, turbojet and lift-fan, coupled by a shaft) and to concepts, where static lift is produced by separate devices (e.g. lift-engines or other concepts for static lift). It includes thrust vectoring of the main engine.The method includes the evaluation of certain flight stages, or segments, as short take-off and landing (STOL), vertical landing (VL), one engine inoperative (OEI) climb (for civil aircraft concept applications) and cruise, all these have to be considered. For each of these five segments, standard flight mechanics equations are extended by a static lift component, an augmentation ratio (a factor that describes the dependency of the thrust and the static lift, if coupled) and the thrust vectoring angle. Hence these equations are modified in a way that the aircraft designer can directly calculate T0/MTOW and MTOW/S for the performance requirements of each segment. Thus, an optimum design point can be selected. Inputs are aerodynamic coefficients, maximum lift coefficient of the wing, mass fraction from take-off to landing, additional static lift during take-off and landing, number of engines, augmentation ratio of the propulsion system and required take-off and landing field length.A performance constraint chart for a JSF F-35B type aircraft is modelled to show the application of the method. As an application to civil aircraft a PCC and a parameter optimisation for the civil regional jet ‘HyLiner’ is presented.
Flight structures fundamental research trends and directions
Authors: Giurgiutiu Victor 
Published: February 2016

AbstractThe paper presents an overview of the fundamental research performed in the US in the field of flight structures under the sponsorship of the Air Force Office of Scientific Research (AFOSR). After presenting a general overview of AFOSR, the paper focuses on the structural mechanics program. Three large applications areas are considered: (a) future flight structures; (b) structural sustainment; (c) structural dynamics and vibration control. These three broad areas are covered at various levels of complexity and detail. Currently supported topics are presented and major funding and results are discussed. The paper ends with summary and conclusions.
In-situ impact-induced damage assessment of woven composite laminates through a fibre Bragg grating sensor network
Authors: Garrett R. C. , Peters K. J. , Zikry M. A. 
Published: February 2016

AbstractWoven composite specimens with embedded fibre Bragg grating (FBG) sensor networks were impacted at low velocities, while global measurements of contact forces and dissipated energies were obtained from drop tower measurements, and local residual, post-impact strain values were obtained from the FBG sensors. Critical damage events were identified in the global data for these specimens and damage signatures in the residual strain data corresponding to these critical damage events were correlated. The results indicate that the full spectral scan information from the sensor network, although obtainable at a lower scan rate, provide more reliable residual lifetime information than average residual strains.
Flight control system design with H∞ loop-shaping approach through non-diagonal weights
Authors: Panesi R. , Mengali G. 
Published: February 2016

AbstractThis paper deals with the design methodology of multi-variable flight control systems through a H∞ loop-shaping technique. A new procedure for the design of non-diagonal pre-and post-compensators is described. In particular, important improvements over existing methods are introduced to both make the selection of weights easier and to contain the order of the resulting controller. The new procedure can be easily managed through suitable Matlab commands and functions, thus simplifying the whole algorithm implementation and providing an effective control system design with a minimum effort. Two typical design problems are addressed: a pitch pointing control system and a lateral controller for coordinated turns. In both cases, a good decoupling between existing channels is obtained by means of a non-diagonal pre-compensator which shapes the plant transfer function, and provides the desired response settling time. The design approach is particularly effective even for nominal plants with strong cross-coupling between channels. The design procedure is illustrated with the aid of a Matlab/Simulink model of a single seat fighter aircraft. We show that a trade-off between the conflicting requirements of fast response and moderate use of control surfaces can be easily managed by varying the constant terms of the diagonal post-compensator.
Increasing persistence of UAVs and MAVs through thermal soaring
Authors: Cowling I. D. , Willcox S. , Patel Y. , Smith P. , Roberts M. 
Published: February 2016

AbstractThis work looks to harness atmospheric energy through thermal soaring to optimise the flight persistence of Micro Air Vehicles (MAVs) and Unmanned Air Vehicles (UAVs). There are two key challenges when considering thermal soaring, the first being the locating of thermals and the second being the extraction of the maximum potential energy from the thermals. Thermal location is by no means an exact science with experienced glider pilots needing to consider many factors to improve the probability of encountering a thermal. As thermals are caused by the uneven heating of the Earth’s surface it is, however, possible to predict likely thermal locations. With the application of a suitable guidance algorithm which considers these ‘hot spots’ it is possible to increase the likelihood of encountering a thermal. Once a thermal is found it is important to attempt to extract the maximum energy from the thermal. To do this the vehicle needs to move quickly to the centre of the thermal. There are many potential techniques for thermal centring, some of which appear to be entirely contradictory to each other, the crucial factor determining the success of such a technique has been found to be the response time of the onboard sensors. This paper considers the many aspects of thermal soaring such as locating thermals, thermal detection and thermal centring. Five different thermal models are presented which are used to demonstrate the thermal centring techniques. Finally a commercial glider simulation package is used to demonstrate the control architecture and simulate a fully autonomous flight.
An aviation approach to space transportation
Authors: Ashford D. 
Published: February 2016

AbstractThis paper presents a strategy for developing the first orbital spaceplane soon and at low cost and risk. The paper then shows how this vehicle will introduce an aviation approach to orbital space transportation to replace the present missile paradigm, leading to far lower costs and improved safety.To illustrate the potential benefits, the paper presents preliminary sizing and cost estimates of a simple lunar base. Even including the cost of developing the spaceplanes and other vehicles required, the total cost is about ten times less than that of present plans that use large new expendable launch vehicles. Timescales need not be greatly affected.
A methodology for optimisation design and analysis of stratosphere airship
Authors: Wang Q. , Chen J. , Fu G. , Duan D. , Zhao H. 
Published: February 2016

AbstractThis paper presents a methodology for studying the feasibility of stratosphere airship for high altitude long endurance missions and arriving at the baseline specifications of conventional configuration of stratosphere airship, given the performance and operational requirements. Based on this methodology, the AODAP platform (Airship Optimisation Design and Analysis Platform) was developed. Some innovative concepts used in AODAP that are different from previous methods and codes are presented. The shape optimisation of airship was introduced into the design process, and several optimum objectives can be selected including minimum drag, minimum weight and composite objective based on MDO (Multidisciplinary Design Optimisation). The methodology was validated for other design concepts previously developed for similar missions and also was compared to a low altitude vehicle. The baseline specifications of stratosphere airships designed for various shapes using this methodology are presented. The results of sensitivity analyses for a specified airship are discussed, and the sensitivity of airship length with some critical parameters including area density of envelope fabric, area density of solar cell, efficiency of solar cell and efficiency of fuel cell for the specified shape is also provided.
Analysis of helicopter vibratory hub loads alleviation by cyclic trailing-edge blade flap actuation
Authors: Gennaretti M. , Molica Colella M. , Bernardini G. 
Published: February 2016

AbstractThe aim of the present work is the investigation about the use of blade trailing-edge flaps for the reduction of vibratory loads arising at the hub of helicopter main rotors in forward flight. The alleviation of these loads is achieved through multicyclic higher harmonic actuation of the blade flaps, which is related to measured vibratory loads amplitude. The feedback control law is obtained by an optimal control process based on the minimisation of a cost function, under the constraint of compatibility with the nonlinear equations governing blade aeroelasticity. In the numerical investigation concerning a four-bladed rotor in level flight conditions, a computationally efficient local controller methodology is applied, with the attention focused on the effectiveness of the control algorithm, along with its robustness with respect to differences (existing in real applications) between the aeroelastic models used for control law synthesis and validation.
Extreme short take–off and landing regional jets – economic motivation and technological challenges
Authors: Gologan C. , Kelders C. , Kuhlmann A. , Seifert J. 
Published: February 2016

AbstractA predominant problem in the US as well as in Europe is the imminent capacity shortage of major hub airports: Air traffic is assumed to increase significantly worldwide, while further runway extensions of airports are difficult because of residents’ resistance and limited land space availability. However, the increasing market size also provides a potential for new aircraft concepts. What type of aircraft will meet best the future market requirements is a question arising.We show that currently discussed solutions to airport capacity problems are mostly not in line with market requirements and have therefore not the potential to alleviate the increasing capacity problems. We analyse to what extend an aeroplane with extreme short takeoff and landing (ESTOL) capability might be able to overcome these capacity problems and discuss resulting technical requirements. Subsequently we present some of the current technological challenges in this area of research and give an overview on ESTOL regional jet concepts that are currently investigated at Bauhaus Luftfahrt.
Systems and certification issues for civil transport aircraft flow control systems
Authors: Liddle S. C. , Jabbal M. , Crowther W. J. 
Published: February 2016

AbstractThe use of flow control (FC) technology on civil transport aircraft is seen as a potential means of providing a step change in aerodynamic performance in the 2020 time frame. There has been extensive research into the flow physics associated with FC. This paper focuses on developing an understanding of the costs and design drivers associated with the systems needed and certification. The research method adopted is based on three research strands:1. Study of the historical development of other disruptive technologies for civil transport aircraft,2. Analysis of the impact of legal and commercial requirements, and3. Technological foresight based on technology trends for aircraft currently under development.Fly by wire and composite materials are identified as two historical examples of successful implementation of disruptive new technology. Both took decades to develop, and were initially developed for military markets. The most widely studied technology similar to FC is identified as laminar flow control. Despite more than six decades of research and arguably successful operational demonstration in the 1990s this has not been successfully transitioned to commercial products. Significant future challenges are identified in cost effective provision of the additional systems required for environmental protection and in service monitoring of FC systems particularly where multiple distributed actuators are envisaged. FC generated noise is also seen as a significant challenge. Additional complexity introduced by FC systems must also be balanced by the commercial imperative of dispatch reliability, which may impose more stringent constraints than legal (certification) requirements. It is proposed that a key driver for future successful application of FC is the likely availability of significant electrical power generation on 787 aircraft forwards. This increases the competitiveness of electrically driven FC systems compared with those using engine bleed air. At the current rate of progress it is unlikely FC will make a contribution to the next generation of single-aisle aircraft due to enter service in 2015. In the longer term, there needs to be significant movement across a broad range of systems technologies before the aerodynamic benefits of FC can be exploited.
Control laws for a formation of autonomous flight vehicles
Authors: Chiaramonti M. , Mengali G. 
Published: February 2016

AbstractThis paper investigates the performance of a flight control system, based on nonlinear dynamics inversion theory, whose aim is to maintain a given geometry of a formation of unmanned aerial vehicles. A fundamental aspect is the complete three dimensionality of the formation geometry that provides a substantial improvement over existing two-dimensional control laws. The designed control system has been implemented in a Simulink® environment and its effectiveness has been tested with a campaign of numerical simulations.
Computational fluid dynamics application to aerospace science
Authors: Shang J. S. 
Published: February 2016

AbstractA brief narration on significant accomplishments in computational fluid dynamics (CFD) for basic research and aerospace application is attempted to highlight the outstanding achievements by scientists and engineers of this discipline. To traverse such a vast domain, numerous and excellent contributions to CFD will be unintentionally overlooked by the author’s limited exposure. Nevertheless it is an ardent hope that the present abridged literature review will aid to reaffirm excellence in research and to identify knowledge shortfalls both in aerodynamics and its modeling and simulation capability. The future modeling and simulation technology needs, as well as potential and fertile research areas, are humbly put forth for consideration.
Optical space telescope structures: The state of the art and future directions
Authors: Santer M. J. , Seffen K. A. 
Published: February 2016

AbstractFuture space telescopes will be required to have significantly greater aperture and lower areal density than is currently achievable. Gossamer spacecraft structures have been proposed as a means of achieving this, but the technologies are far from mature. A state-of-the-art review is timely and necessary as new structural paradigms are being considered for the next generation of space telescopes. There is, however, a knowledge gap between the structural engineering community and the additional fields involved in the complete telescope system, leading to the proposal of structures which are unlikely to be launched. It is hoped that, by providing a resource by which structural engineers are made aware of the wider issues in telescope design, this review will serve to overcome this knowledge gap to facilitate productive collaboration.
A correction to sonic boom theory
Authors: Cain T. 
Published: February 2016

AbstractCurrent sonic boom theory is based on linear midfield solutions coupled with acoustic propagation models. Approximate corrections are made within the theory to account for non-linearities, in particular for the coalescence of compression waves and the formation of weak shocks. A very large adjustment is made to account for the increasing acoustic impedance that the waves encounter as they propagate from the low density air at cruise altitude to the high density air at sea level. Typically this correction reduces the calculated over pressure levels by a factor of three. Here the method of characteristics (MOC) is used to prove that the density gradient within a hydrostatic atmosphere has no direct effect on the propagation or intensity of the wave. However gravity and ambient temperature both affect the wave propagation and the combined pressure level attenuation is not dissimilar to that previously attributed to acoustic impedance. Although the flawed acoustic theory has given reasonable predictions of measured sonic booms, the omission of gravity from the equation of motion and the inclusion of a false impedance modification, makes the model unreliable for prediction of future designs, particularly those focused on boom minimisation. As an aid to quiet supersonic aircraft design, Whitham’s theory is extended to include gravity and ambient temperature variation and shown to be in good agreement with a MOC solution for the real atmosphere.
Material state changes as a basis for prognosis in aeronautical structures
Authors: Reifsnider K. L. , Fazzino P. , Majumdar P. K. , Xing L. 
Published: February 2016

AbstractThe long-term performance of aeronautical structures is typically discussed in terms of concepts such as structural integrity, durability, damage tolerance, fracture toughness, etc. These familiar concepts are usually addressed by considering balance equations, crack growth relationships, and constitutive equations with constant material properties, and constant or cyclically applied load conditions. Loading histories are represented by changing stress (or strain) states, only. But for many situations, especially associated with high performance aircraft, the local state of the material may also change during service, so that the properties used in those equations are functions of time and history of applied conditions. For example, local values of stiffness, strength, and conductivity are altered by material degradation to create ‘property fields’ that replace the global constants, and introduce time and history into the governing equations. The present paper will examine a small set of such problems and offer a construct for using related solutions to estimate future performance based on history of use and current material state, a concept typically called prognosis.
Using deformation modes to identify cracks in turbine engine compressor disks
Authors: Brockman R. A. , John R. , Huelsman M. A. 
Published: February 2016

AbstractRecent studies show that analytical predictions of crack growth in rotating components can be used in conjunction with displacement measurement techniques to identify critical levels of fatigue damage. However, investigations of this type traditionally have focused on the detection of damage at known flaw locations. This paper addresses the related problem of estimating damage associated with flaws at unknown locations, through the combined use of analytical models and measured vibration signatures. Because the measured data are insufficient to identify a unique solution for the location and severity of fatigue cracks, the function of the analytical model is to bound the extent of damage occurring at life-limiting locations. The prediction of remaining life based on estimates of worst-case fatigue damage and crack locations also is discussed.
Load transportation system based on autonomous small size helicopters
Authors: Bernard M. , Kondak K. , Hommel G. 
Published: February 2016

AbstractThis paper is devoted to modelling and control algorithms for a slung load transportation system composed of one or multiple helicopters, where the load is coupled by the means of flexible ropes (see Fig. 1). The coupled helicopter system overcomes the payload limitation of a single small size helicopter, while keeping most of its advantages: small costs of operation, low maintenance costs and increased safeness. Therefore, the system can be utilised whenever the use of full size helicopters is impossible, too expensive or prohibited by law. We focus on the deployment and repairing of distributed sensor networks, using a transportation system based on multiple small size helicopters. A possible real world application is the deployment of fire fighting equipment, where space limitation of the fire trucks prohibits the application of bigger UAVs and using full size helicopters is too dangerous. The problem of load transportation using one or two full size helicopters (twin lift helicopter system), connected to the load by means of flexible ropes, has been discussed in the aerospace research community at least since 1960. We have shown in our previous work that there is a fundamental difference in the mathematical description between small and full size helicopters. Therefore, also the control design for the case of small size helicopters needs to be different. To our knowledge, the control of a slung load transportation system composed of multiple small size helicopters has not been studied until now. In this paper, the complete mechanical setup of the slung load transportation system based on one or more small size helicopters is presented. This includes a short description of the used UAVs, the additionally required sensors, and how the load is mounted. A model of one/multiple helicopters transporting a load is introduced. This model is used in a simplified form for the controller design and in full form for simulation. The controller for one and two helicopters, which is based on a state feedback controller, as well as the controller for three and more helicopters, which is based on a non linear controller, are explained in detail. Both controllers utilise an underlying non-linear orientation controller. We propose a feedback loop, based on forces measured in the ropes, to compensate for the influence of the rope. The controllers were tested in simulation and in real flight experiments. The world wide first flight experiment with three coupled helicopters was successfully conducted at the end of 2007.