Showing papers in "Journal of Aircraft in 2013"
TL;DR: Early morphing aircraft history is reviewed to identify inventions and innovations that led to both successes and failures, and recent government-sponsored activities in the United States are discussed.
Abstract: The term ‘morphing aircraft’ describes a broad range of air vehicles and vehicle components that adapt to planned and unplanned multipoint mission requirements. Adaptation or morphing requires changing system features including vehicle ‘states,’ such as vehicle shape, during in-flight operation. The term morphing can be applied to almost any activity in which in-flight vehicle features are changed. As such, morphing has become a buzzword loosely applied to a wide variety of activities, some of which are disconnected from air vehicle morphing development. This has led to three myths: 1) morphing shape change is too expensive, 2) morphing aircraft must weigh more than nonmorphing aircraft, and 3) morphing requires exotic materials and complex systems. This paper attempts to dispel these myths by reviewing early morphing aircraft history to identify inventions and innovations that led to both successes and failures. The review also discusses recent government-sponsored activities in the United States: in par...
291 citations
TL;DR: In this article, the stiffness optimization of the upper and lower skins of an aircraft was studied for the purpose of reducing the anisotropic anisotropy of composite composite materials.
Abstract: The drive for ever more efficient aircraft structures stimulates the research to use the full potential of anisotropy of composite materials. The stiffness optimization of the upper and lower skins...
120 citations
TL;DR: In this article, the authors considered the problem of the fast computation of forced periodic motions using the Euler equations and evaluated three methods: time domain, frequency domain, and harmonic balance method.
Abstract: Dynamic derivatives are used to represent the influence of the aircraft motion rates on the aerodynamic forces and moments needed for studies of flight dynamics. The use of computational fluid dynamics has potential to supplement costly wind-tunnel testing. The paper considers the problem of the fast computation of forced periodic motions using the Euler equations. Three methods are evaluated. The first is computation in the time domain, which provides the benchmark solution in the sense that the time-accurate solution is obtained. Two acceleration techniques in the frequency domain are compared. The first uses a harmonic solution of the linearized problem, referred to as the linear frequency-domain approach. The second uses the harmonic balance method, which approximates the nonlinear problem using a number of Fourier modes. These approaches are compared for the ability to predict dynamic derivatives and for computational cost. The NACA 0012 aerofoil and the DLR-F12 passenger jet wind-tunnel model are the test cases. Compared to time-domain simulations, an order of magnitude reduction in computational costs is achieved and satisfactory predictions are obtained for cases with a narrow frequency spectrum and moderate amplitudes using the frequency-domain methods.
101 citations
TL;DR: In this article, a linear model, obtained from the generic nonlinear equations of motion for aircraft, is used as a basis for system identification, and the parameters of the linear model are identified by fitting the model to frequency responses extracted from the data.
Abstract: This paper describes a practical system identification procedure for small, low-cost, fixed-wing unmanned aircraft. Physical size and cost restrictions limit the sensing capabilities of these vehicles. The procedure is demonstrated on an Ultra Stick 25e, therefore emphasizing a minimum complexity approach compatible with a low-cost inertial sensor. A linear model, obtained from the generic nonlinear equations of motion for aircraft, is used as a basis for system identification. This model is populated with results from a first principles analysis to form a baseline model. Flight experiments are designed using the baseline model and operational constraints to collect informative data. Parameters of the linear model are identified by fitting the model to frequency responses extracted from the data. The parameters are integrated into the nonlinear equations of motion, and both linear and nonlinear models are validated in the time domain. Verification of model accuracy is extended with a sensitivity and resid...
99 citations
TL;DR: In this article, the optimal shape of flying wings for subsonic and transonic speeds is examined using a suite of tools developed around a three-dimensional, time-spectral, Euler computational fluid dynamics solver.
Abstract: The optimal shape of flying wings for subsonic and transonic speeds is examined using a suite of tools developed around a three-dimensional, time-spectral, Euler computational fluid dynamics solver. The first result in the study is a lift-constrained drag minimization, performed on an unswept, rectangular wing. When the spanwise twist distribution of the wing is varied, the elliptic optimum predicted by the low-speed inviscid theory can be reproduced. With this result as a reference, three different optimization formulations are explored. These formulations consider the addition of bending moment constraints, static-stability constraints, and dynamic-stability constraints. In each case, the design space of the problem is explored using both planform and shape variables to determine the optimal shape. These techniques are used to show that the addition of stability constraints has a significant impact on the optimal surface shape of the wing. In particular, it is shown that at lower speeds, the airfoil sha...
92 citations
TL;DR: The first publicly charted optimized profile descent procedure was implemented at Los Angeles International Airport in December 2007 and was designed so that aircraft could conduct arrival and approach operations with the engines remaining at or near minimum idle power settings.
Abstract: The optimized profile descent is an example of one of the many NextGen technologies under development to modernize and increase the efficiency of the national airspace system. The first publicly charted optimized profile descent procedure was implemented at Los Angeles International Airport in December 2007. This new flight procedure was designed so that aircraft could conduct arrival and approach operations with the engines remaining at or near minimum idle power settings; thereby, saving an average of 25 gal of jet fuel per flight when compared to the various aircraft types conducting an arrival and approach along the same lateral path at Los Angeles International Airport. This optimized profile descent translates into annual reductions of approximately 2,000,000 gal of jet fuel and 41,000,000 lb of carbon dioxide emissions. Given the positive environmental benefits of an optimized profile descent, there are several projects underway to increase the use of environmentally friendly arrival procedures wit...
83 citations
TL;DR: In this article, a method for estimating the airspeed, angle of attack, and sideslip without using a conventional, pitot-static air data system is presented, which relies on measurements from Global Positioning System, an inertial measurement unit, and a low-fidelity model of the aircraft's dynamics, which are fused using two cascaded extended Kalman filters.
Abstract: A method for estimating the airspeed, angle of attack, and sideslip without using a conventional, pitot-static air data system is presented. The method relies on measurements from Global Positioning System, an inertial measurement unit, and a low-fidelity model of the aircraft’s dynamics, which are fused using two cascaded extended Kalman filters. In the cascaded architecture, the first filter uses information from the inertial measurement unit and Global Positioning System to estimate the aircraft’s absolute velocity and attitude. These estimates are used as the measurement updates for the second filter in which they are fused with the aircraft dynamics model to generate estimates of the airspeed, angle of attack and sideslip. Methods for dealing with the time and interstate correlation in the measurements coming from the first filter are discussed. Simulation and flight-test results of the method are presented. Simulation results show that the root mean square error of the airspeed estimate is less than...
81 citations
TL;DR: In this paper, the flow fields around NACA0012 and NACA0002 airfoils at Reynolds number of 23,000 and the aerodynamic characteristics of these flowfields were analyzed using implicit large-eddy simulation and laminar-flow simulation.
Abstract: In this study, the flowfields around NACA0012 and NACA0002 airfoils at Reynolds number of 23,000 and the aerodynamic characteristics of these flowfields were analyzed using implicit large-eddy simulation and laminar-flow simulation Around this Reynolds number, the flow over an airfoil separates, transits, and reattaches, resulting in the generation of a laminar separation bubble at the angle of attack in a certain degree range Over an NACA0012 airfoil, the separation point moves toward its leading edge with an increasing angle of attack, and the separated flow may transit to create a short bubble On the other hand, over an NACA0002 airfoil, the separation point is kept at its leading edge, and the separated flow may transit to create a long bubble Moreover, nonlinearity appears in the lift curve of the NACA0012 airfoil, but not in that of NACA0002, despite the existence of a laminar separation bubble
72 citations
TL;DR: In this article, the effects of engine placement and sweep on the flutter characteristics of an aft-swept flying wing resembling the Horten IV are investigated using the Nonlinear Aeroelastic Trim and Stability of HALE Aircraft.
Abstract: The effects of engine placement and sweep on the flutter characteristics of an aft-swept flying wing resembling the Horten IV are investigated using the Nonlinear Aeroelastic Trim and Stability of HALE Aircraft. The analysis was validated against the published results for divergence and flutter of swept wings and found to be in excellent agreement. Moreover, the modal frequencies and damping obtained for the Goland wing were found in excellent agreement with published results based on a new continuum-based unsteady aerodynamic formulation. This aircraft exhibits a nonoscillatory yawing instability, expected in aircraft with neither a vertical tail nor yaw control. More important, however, is the presence of a low-frequency “body-freedom flutter” mode. The aircraft center of gravity was held fixed during the study, which allowed the aircraft controls to trim similarly for each engine location and minimized flutter speed variations along the inboard span. The maximum flutter speed occurred for engine placem...
65 citations
TL;DR: In this paper, a large-eddy simulation of a single aircraft wake-vortex evolution in ground proximity is investigated numerically by means of largeeddy simulations and the simulation is performed either with a flat ground or with different modifications to the ground surface to trigger rapid vortex decay.
Abstract: Aircraft wake-vortex evolution in ground proximity is investigated numerically by means of large-eddy simulations The simulations are performed either with a flat ground or with different modifications to the ground surface to trigger rapid vortex decay The impact of environmental turbulence in terms of turbulent wind is taken into account, where wall-resolved and wall-modeled large-eddy simulation are performed for low- and high-Reynolds-number cases, respectively To understand wake-vortex decay mechanisms in ground proximity, the interaction of primary and secondary vortices is carefully investigated We find that vortex decay can be initiated at an earlier time and substantially accelerated with obstacles at the ground We explain the fundamental vortex dynamics describing five characteristics of the phenomenon and quantify the decay We demonstrate that similar effects can be achieved, employing relatively small plate lines as opposed to the original large block-shaped barriers The obstacles trigg
60 citations
TL;DR: In this article, the authors presented linear parameter varying modeling and simulation of a folding-wing morphing aircraft in the wing-folding process, and derived the decoupled longitudinal dynamic equation of the morphing process by simplification, and numerically simulated by the quasi-steady aerodynamic assumption.
Abstract: The purpose of this paper is to present linear parameter varying modeling and simulation of a folding-wing morphing aircraft in the wing-folding process. Morphing aircraft can alter the shape to adapt to mission environment changing. When the wing shape is varying, the dynamic responses of the morphing aircraft will be dependent on the time-varying aerodynamic forces and moments, which will be a function of the wing shape change by the morphing command. The folding-wing morphing aircraft is regarded as a variable geometry rigid body, and the six-degree-of-freedom nonlinear dynamic model in the wing-folding process is founded. The decoupled longitudinal dynamic equation of the morphing process is deduced by simplification, and the longitudinal dynamic responses of the wing morphing process are numerically simulated by the quasi-steady aerodynamic assumption. Furthermore, using the Jacobian linearization approach, the longitudinal nonlinear dynamics equations of morphing aircraft are linearized, and the lon...
TL;DR: In this article, the authors used bifurcation analysis and time-history simulations to understand the flight dynamics of the open-loop NASA generic transport model by identifying the attractors of the dynamical system that govern upset behavior.
Abstract: Despite the significant improvement in safety linked to the fourth generation of airliners, the risk of encountering upset conditions remains an important consideration. Upset, which may arise from faults, external events, or inappropriate pilot inputs, can induce a loss-of-control incident if the pilot does not respond in the correct manner. Any initiative aimed at preventing such events requires an understanding of the fundamental aircraft behavior. This paper presents the use of bifurcation analysis, complemented by time-history simulations, to understand the flight dynamics of the open-loop NASA generic transport model by identifying the attractors of the dynamical system that govern upset behavior. A number of drivers for potential upset conditions have been identified, including nonoscillatory spirals and oscillatory spins. The analysis shows that these spirals and spins are connected in two-parameter space and that, by an inappropriate pilot reaction to the spiral, it is possible to enter the oscil...
TL;DR: In this article, the authors investigated the feasibility of flying over a large vertical extent over open fields using a point-mass sailplane model and a full six degree-of-freedom (6-DOF) piloted sailplane.
Abstract: Dynamic soaring of a sailplane in the earth’s atmospheric boundary layer was computationally investigated over a range of conditions to explore the feasibility of flying over a large vertical extent over open fields. A point-mass sailplane model was studied as well as a full six degree-of-freedom (6-DOF) piloted sailplane model. For the point-mass model, parameter sweeps were performed around a baseline 3-m (9.58-ft) wingspan sailplane having a weight of 15 kg (33 lb) and aspect ratio of 20. Results from the point-mass model show that in certain high wind conditions, dynamic soaring energy-conserving orbits are possible for flight trajectories extending from the ground to 185 m (607 ft) aloft. A 6-DOF piloted flight simulator was used, and it produced similar results that showed dynamic soaring over open fields for large vertical extents. Together these results support the conclusion that it is possible to perform dynamic soaring in high wind conditions through the full extent of the atmospheric boundary layer to high altitudes over open land with model-scale unpowered sailplanes having both high wing loadings and high lift-to-drag ratios.
TL;DR: In this article, the nonlinear normal modes of the Morane-Saulnier Paris aircraft were computed from a reduced-order nonlinear finite element model using a numerical algorithm combining shooting and pseudo-arclength continuation.
Abstract: Nonlinear normal modes, which are defined as a nonlinear extension of the concept of linear normal modes, are a rigorous tool for nonlinear modal analysis. The objective of this paper is to demonstrate that the computation of nonlinear normal modes and of their oscillation frequencies can now be achieved for complex, real-world aerospace structures. The application considered in this study is the airframe of the Morane–Saulnier Paris aircraft. Ground vibration tests of this aircraft exhibited softening nonlinearities in the connection between the external fuel tanks and the wing tips. The nonlinear normal modes of this aircraft are computed from a reduced-order nonlinear finite element model using a numerical algorithm combining shooting and pseudo-arclength continuation. Several nonlinear normal modes, involving, e.g., wing bending, wing torsion, and tail bending, are presented, which highlights that the aircraft can exhibit very interesting nonlinear phenomena. Specifically, it is shown that modes with ...
TL;DR: In this article, closed-form relations for the induced-drag and lift coefficients acting on a wing in ground effect to those acting on the same wing outside the influence of ground effect are presented.
Abstract: Closed-form relations are presented for estimating ratios of the induced-drag and lift coefficients acting on a wing in ground effect to those acting on the same wing outside the influence of ground effect. The closed-form relations for these ground-effect influence ratios were developed by correlating results obtained from numerical solutions to Prandtl’s lifting-line theory. Results show that these influence ratios are not unique functions of the ratio of wing height to wingspan, as is sometimes suggested in the literature. These ground-effect influence ratios also depend on the wing planform, aspect ratio, and lift coefficient.
TL;DR: The correlation-based γ-Reθt model was implemented in a hybrid Reynolds-averaged Navier-Stokes solver and validated on various test cases as mentioned in this paper.
Abstract: The correlation-based γ-Reθt transition transport model was implemented in a hybrid Reynolds-averaged Navier–Stokes solver and validated on various test cases. The γ-Reθt model predicts two-dimensional transition phenomena such as transition due to Tollmien–Schlichting instabilities and separation-induced transition. The present work includes results for the application of the γ-Reθt to two three-dimensional test cases, which are the 6∶1 inclined prolate spheroid and the ONERA M6 wing. Depending on the flow conditions, the computational results are in good agreement with the experimental data. Once the given flow conditions lead to three-dimensional transition phenomena, the transition prediction with the γ-Reθt model is not reliable, because the model is based on the characteristics of two-dimensional boundary layers and three-dimensional transition mechanisms are not taken into account. To close this gap, the γ-Reθt model was extended by an approach that accounts for transition due to crossflow instabil...
TL;DR: In this paper, a combination of the quasi-steady aerodynamics and the calculus of variations was used to obtain true optimality for the kinematics optimization of a flapping-wing micro-aircraft.
Abstract: The weight and power constraints imposed on flapping-wing micro air vehicles necessitate optimal design of the flapping kinematics. To date, the approach adopted for kinematics optimization has been to assume specific functions for the Euler angles describing the wing motion with respect to the body. Then, optimization is performed on the parameters of these functions. In another approach, a number of instants over the flapping cycle are selected, and optimization is performed on the magnitude of the Euler angles at these instants. This latter approach provides more freedom for the variations of the Euler angles rather than confining them to certain patterns. Yet, in both approaches, finite-dimensional optimization is adopted and, as such, additional constraints are imposed. Considering that the problem is an infinite-dimensional optimization problem, we use in this work the calculus of variations to obtain true optimality. The combination of the quasi-steady aerodynamics and the calculus of variations ap...
TL;DR: A Williams International FJ44-3A turbofan engine was used to demonstrate the high-speed fan noise reduction potential of a foam-metal liner installed in close proximity to the fan rotor as mentioned in this paper.
Abstract: A Williams International FJ44-3A turbofan engine was used to demonstrate the high-speed fan noise reduction potential of a foam-metal liner installed in close proximity to the fan rotor. The engine was tested in the NASA Glenn Research Center’s Aeroacoustic Propulsion Laboratory. Two foam-metal liner designs were tested and compared to the hardwall baseline. Traditional single degree-of-freedom liner designs were also evaluated to provide a comparison to the state-of-the art design. This report presents the test setup and documents the test conditions. Far-field acoustic levels and limited engine performance results are also presented. The results show that the foam-metal liner achieved up to 5 dB of attenuation in the forward-quadrant radiated-acoustic power levels, which is equivalent to the traditional single degree-of-freedom liner design. Modest changes in engine performance were noted.
TL;DR: In this article, an aerostructural analysis using a proper orthogonal decomposition with a neural network is proposed for accurate and efficient aerostructureural wing design optimization using the reduced-order model.
Abstract: In this study, an aerostructural analysis using a proper orthogonal decomposition with a neural network is proposed for accurate and efficient aerostructural wing design optimization using the reduced-order model. Because reduced-order-model basis weighting estimation has a limitation in that its robustness cannot be guaranteed by various design variables and wing deformation due to fluid structure interaction, this study employs the neural network, which is capable of perceiving the relationship between the input variables and reduced variables for the proper orthogonal decomposition to complement the defects. To construct the proper orthogonal decomposition with a neural network, the neural network is learned using pairs of design variables and reduced variables from snapshot data obtained from the aerostructural analysis. Because the proposed aerostructural analysis using a proper orthogonal decomposition with a neural network is applied to validation cases and its results are compared to those of the ...
TL;DR: In this paper, the aerodynamic effects of the application of Gurney flaps of different heights and chordwise locations to five airfoils have been investigated in the Pennsylvania State University low-speed, low-turbulence wind tunnel.
Abstract: The aerodynamic effects of the application of Gurney flaps of different heights and chordwise locations to five airfoils have been investigated in the Pennsylvania State University low-speed, low-turbulence wind tunnel. The effectiveness of each Gurney flap/airfoil combination is measured by the change in the maximum lift coefficient of the airfoil. When grouped by flap height and plotted against chordwise location, there is considerable scatter in the data, indicating that the effectiveness of the Gurney flap is strongly influenced by airfoil shape. Two anomalous cases are considered in detail. In the first case, the increase in cl,max is considerably different for two airfoils with the addition of a Gurney flap having the same height and mounted at the same chordwise location. The second case is one in which a Gurney flap of a specific height and mounting location is found to increase cl,max on one airfoil and decrease it on another. For these cases, pressure distributions, lift curves, and drag polars ...
TL;DR: In this paper, experimental investigations have been carried out with the two-dimensional DLR-F15 high-lift wing-section model in the Cryogenic Wind-tunnel Cologne DNW-KKK to differentiate between the influence of Mach and Reynolds numbers on the stall behavior.
Abstract: Experimental investigations have been carried out with the two-dimensional DLR-F15 high-lift wing-section model in the Cryogenic Wind-tunnel Cologne DNW-KKK to differentiate between the influence of Mach and Reynolds numbers on the stall behavior. Because of the cryogenic environment, Mach and Reynolds numbers have been varied independently between M=0.1–0.25 and Re=1.4×106−15.6×106. The investigation covers two- and three-element configurations at various slat and flap settings and two different slat shapes. The focus of the investigation is to identify conditions of turbulent leading-edge stall, shock-related lift limitations, and flap separations and their influence on achievable maximum lift coefficient.
TL;DR: In this article, a theoretical analysis implies that speed profile has an impact as substantial as, if not more than, vertical profile on the fuel consumption in the terminal area, and design guidelines for the continuous-descent-approach procedures are derived.
Abstract: The continuous-descent approach is among the key concepts of the Next Generation Air Transportation System. Although a considerable number of researchers have been devoted to the estimation of potential fuel savings of the continuous-descent approach, few have attempted to explain the fuel savings observed in field tests from an analytical point of view. This paper focuses on the evaluation of the continuous-descent approach as a fuel-reduction procedure. This research gives insights into the reasons why the continuous-descent approach saves fuel, and design guidelines for the continuous-descent-approach procedures are derived. The analytical relationship between speed, altitude, and fuel burn is derived based on the base of aircraft data total-energy model. A theoretical analysis implies that speed profile has an impact as substantial as, if not more than, vertical profile on the fuel consumption in the terminal area. In addition, the continuous-descent approach is not intrinsically a fuel-saving procedu...
TL;DR: A novel procedure for solving the related optimization problem is described that addresses the implementation of a difficult state constraint: the flight path must belong to the surface of the vertical cylinder whose base is the closed ground path.
Abstract: This paper considers the optimization of flight trajectories for solar-powered aircraft. This work is unique relative to past work because flight path is constrained to repeatedly traverse a specified closed ground path. Constraints of this form are of interest in a variety of missions where the goal is to loiter near a fixed point on the ground. The performance index to be maximized is the average input power to the battery over each cycle of the ground path. It is advantageous to allow the periodic flight path to have altitude variations because during both ascent and descent there are opportunities to increase the angle of sun exposure to the aircraft solar array. A novel procedure for solving the related optimization problem is described that addresses the implementation of a difficult state constraint: the flight path must belong to the surface of the vertical cylinder whose base is the closed ground path. Results for a wide collection of optimization examples are described, which lead to an importan...
TL;DR: In this paper, the authors proposed an underactuated parallel mechanism, which can be set up in a modular fashion, offering controlled motion in all six spatial degrees of freedom while providing multiple degrees of fault tolerance with only four actuators.
Abstract: The ability to vary the geometry of a wing to adapt to different flight conditions can significantly improve the performance of an aircraft. However, the realization of any morphing concept will typically be accompanied by major challenges. Specifically, the geometrical constraints that are imposed by the shape of the wing and the magnitude of the aerodynamic and inertia loads make the usage of conventional mechanisms inefficient for morphing applications. This paper presents the design of a novel underactuated parallel mechanism, which addresses such concerns. This mechanism, which can be set up in a modular fashion, offers controlled motion in all six spatial degrees of freedom while providing multiple degrees of fault tolerance with only four actuators. The main feature of the design is the usage of active and passive linearly adjustable members to replace the structure of a conventional wing box. These members provide the necessary stiffness and load-bearing capabilities for the wing. With the excepti...
TL;DR: In this paper, the authors derived the equations for the evaluation of range and endurance of battery operated electrical aircraft, keeping into account the effects of Peukert's law on the battery discharge process.
Abstract: T HE interest in electrically-driven propeller airplanes has been steadily increasing over the last 15 years with applications ranging from small electric remotely piloted vehicles [1] up to large high-altitude/long-endurance aircraft [2], passing through general aviation size airplanes powered by means of hydrogen fuel cells [3]. The art and science of preliminary sizing of conventional aircraft has been the subject of many textbooks over the years [4,5] and, in this framework, reasonably accurate range and endurance prediction against design performance requirements plays quite obviously a crucial role. Unfortunately, the extension of the results valid for conventional configurations to electrically powered aircraft is not always straightforward. In a recent paper, [6] the equations for the evaluation of range and endurance of battery operated electrical aircraft are derived, keeping into account the effects of Peukert’s law on the battery discharge process [7]. Wilhelm Peukert performed tests on lead–acid batteries and discharging them with a constant current. His analysis proved that the discharge time Δt and the discharge current i satisfy the law [7]
TL;DR: In this article, a comparative study of two airfoils at low Reynolds numbers using the transitional unsteady Reynolds-averaged Navier-Stokes shear-stress transport γ-Reθ model and the ANSYS CFX computational fluid dynamics suite is proposed.
Abstract: A comparative study of two airfoils at low Reynolds numbers using the transitional unsteady Reynolds-averaged Navier–Stokes shear-stress transport γ-Reθ model and the ANSYS CFX computational fluid dynamics suite is proposed. The NACA 0012 and Selig–Donovan 7003 airfoils were selected and exposed to chord-based Reynolds numbers ranging from 4.8×104 to 2.5×105 at angles of attack ranging from 0 to 8 deg. The adopted numerical model and setup were shown to accurately predict the main flow features. Specifically, both laminar separation without reattachment and laminar-separation-bubble flow modes were observed depending on the airfoil geometry and orientation, Reynolds number, and freestream-turbulence intensity. In general, with increasing angle of attack or Reynolds number, laminar-separation bubbles shrank and receded toward the leading edge while vortex-shedding periodicity and coherency degraded. In all cases, the Selig–Donovan 7003 proved of superior aerodynamic performance when compared to the NACA 00...
TL;DR: This paper documents the prediction of UH-60A Black Hawk aerodynamic loading using the multisolver Computational Fluid Dynamics/Computational Structural Dynamics analysis framework for rotorcraft Helios for a range of critical steady forward flight conditions.
Abstract: This paper documents the prediction of UH-60A Black Hawk aerodynamic loading using the multisolver Computational Fluid Dynamics/Computational Structural Dynamics analysis framework for rotorcraft Helios for a range of critical steady forward flight conditions. Comparisons with available flight test data are provided for all of the predictions. The Helios framework combines multiple solvers and multiple grid paradigms (unstructured and adaptive Cartesian) such that the advantages of each paradigm is preserved. Further, the software is highly automated for execution and designed in a modular fashion to minimize the burden on both the users and developers. The technical approach presented herein provides details of all of the participant modules and the interfaces used for their integration into the software framework. The results composed of sectional aerodynamic loading and wake visualizations are presented. Solution-based adapative mesh refinement, a salient feature of the Helios framework, is explored fo...
TL;DR: An efficient solution algorithm is developed by modifying the simultaneous perturbation stochastic approximation method to account for limits on optimization parameters in the simultaneous helicopter and control system design approach.
Abstract: This article proposes simultaneous helicopter and control system design and illustrates its advantages. First, the traditional, sequential approach in which a satisfactory control system is designed for a given helicopter is applied. Then, a novel approach, in which the helicopter and control system are simultaneously designed, is applied to redesign the entire system. This redesign process involves selecting certain helicopter parameters as well as control system parameters. For both design procedures the key objectives are to minimize control energy and satisfy prescribed variance constraints on specific outputs. In order to solve the complex optimization problem corresponding to the simultaneous design approach, an efficient solution algorithm is developed by modifying the simultaneous perturbation stochastic approximation method to account for limits on optimization parameters. The algorithm is applied to redesign helicopters using models generated in straight level as well as maneuvering flight condi...
TL;DR: This paper presents a procedure for reliable and robust optimization of an aircraft at the conceptual design phase, where uncertainties on model and design variables are taken into account in a probabilistic setting.
Abstract: Low-fidelity analytical models are often used at the conceptual aircraft design stage Because of uncertainties on these models and their corresponding input variables, deterministic optimization may achieve under-design or over-design Therefore it is important to already consider these uncertainties at the conceptual design stage in order to avoid inefficient design and then costly time over runs due to re-design This paper presents a procedure for reliable and robust optimization of an aircraft at the conceptual design phase Uncertainties on model and design variables are taken into account in a probabilistic setting More precisely, at each point of the optimization process uncertainties are modeled by an adaptive normal law strategy in order to fit the historical aircraft database The statistical parameters are adjusted depending on the available information at the current point of the optimization process To improve computational cost, response surface approximations are constructed to represent
TL;DR: In this model, the wing rotates about its root in a propeller-like motion at a fixed angle of attack, and the spanwise velocity and pressure gradients that exist on an insect wing due to forward/aft sweep about the wing root are preserved, along with the threedimensionality induced by the root and tip vortices.
Abstract: T HE flow produced by a bio-inspired flapping wing is unsteady, three-dimensional, and dominated by separated flow and strong vortices. To better understand which structures in this complicated flow are most responsible for the production of lift and drag, several canonical problems have been designed to model portions of a natural wing stroke. These include both twoand threedimensional transient, reciprocating, and quasi-steady variations of pitching, plunging, translating, and rotatingwings. The rotatingwing model is designed to represent the translational phase of an insect wing stroke. In this model, the wing rotates about its root in a propeller-likemotion at a fixed angle of attack. The spanwisevelocity and pressure gradients that exist on an insect wing due to forward/aft sweep about the wing root are preserved, along with the threedimensionality induced by the root and tip vortices. The result is a relatively simple flowfield that preserves the most important characteristics of the translational phase of an entomological wing stroke. Some of the earliest rotating-wing experiments were performed by Usherwood and Ellington on hawkmoth wings at Reynolds numbers O 10 [1,2]. In these experiments, the wing’s lift coefficient was found to decrease as Reynolds number increased from 10,000 to 50,000, and it was postulated that this change in lift production was due to the formation of aweaker leading-edge vortex (LEV) at higher Reynolds numbers. Later, Ozen and Rockwell used particle image velocimetry (PIV) to characterize the steady-state flow structure on a low-aspect-ratio rotating plate at fixed angles of attack between 30 and 75 deg. They observed a stable LEV for a range of Reynolds numbers between 3600 and 14,500 [3]. However, other experiments focusing on the start of a rotating wing accelerating to Reynolds numbers between 10,000 and 60,000 revealed an LEV that formed and shed early in the wing stroke, resulting in a high-lift transient, after which lift dropped to about half of themaximum value [4–6]. At lower Reynolds numbersO 1000 , flow visualizations and PIV have demonstrated spanwise flow on a rotatingwing, and an attached LEV during wing acceleration that later burst over the outboard half of the wing during deceleration [7–9]. The objective of the work presented here is to identify the formation, structure, and possible separation of the leading-edge vortex at the beginning of thewing stroke (i.e., within the first 90 deg of wing rotation) as well as after long convective times (i.e., for wing strokes greater than 90 degrees including multiple revolutions). To this end, flow visualization is performed for threewing revolutions to analyze the vortex structure and the location of the burst point. In addition, unsteady lift and drag measurements are acquired for two revolutions to relate the flow structure to the aerodynamic forces produced by the wing.