Emerald | Aircraft Engineering and Aerospace Technology | Table of Contents

Numerical study on effect of leading-edge tubercles

Fri, 28 Jun 2013 00:00:00 +0100

Abstract

Purpose - The aim of present study is to investigate the effect of spanwise shape of the leading edge on unsteady aerodynamic characteristics of wings during forward flapping and gliding flight. Design/methodology/approach - A computational fluid dynamics approach was conducted to analyze the flow around airfoils with sinusoidal-like protuberances at a Reynolds number of 104. Three-dimensional time-dependent incompressible Navier-Stokes equations are numerically solved by using finite volume method. A multigrid mesh method, which was applied to the situation of fluid across the heaving models is used to simulate this type of flow. The simulations are performed for the wavelength between neighbouring peaks of 0.25c and 0.5c. For each wavelength, two heights of the tubercles,which are 5% and 10% of the chordwise length of wing, are employed on the leading edge of wings. The aerodynamic forces and flow structure around airfoils are presented and compared in detail. Special attention is paid to investigate the effect of leading edge shape on the fluid dynamic forces. Findings - Present results reveal that the wings with leading-edge tubercles have an aerodynamic advantage during gliding flight and also have the potential advantages during flapping forward flight. Originality/value - On the basis of computational study, an improved scenario for flapping wing microaviation vehicle has been originally proposed.

Double-Layer Fusion Algorithm for EGI-Based System

Fri, 28 Jun 2013 00:00:00 +0100

Abstract

Purpose - The Embedded GPS/INS System (EGI) has been used more widely as central navigation equipment of aircraft. For certain cases needing high attitude accuracy, star sensor can be integrated with EGI to improve attitude performance. Since the filtering-correction loop has already built in finished EGI product, centralized or federated Kalman filter is not applicable for integrating EGI with star sensor; it’s a challenge to design multi-sensor information fusion algorithm suitable for this situation.Design/methodology/approach - The alternate fusion algorithms for asynchronous measurements and the sequential fusion algorithms for synchronous measurements are presented. By combining alternate filtering and sequential filtering algorithms, a kind of double-layer fusion algorithms for multi-sensors is proposed and validated by semi-physical test in this paper.Findings - The double-layer fusion algorithms represent a filtering strategy for multiple non-identical parallel sensors to assist INS, while the independent estimation-correction loop in EGI is still maintained. It has significant benefits in updating original navigation system by integrating new sensors.Practical implications - The approach described in this paper can be used in designing similar multi-sensor information fusion navigation system composed by EGI and various kinds of sensors, so as to improve the navigation performance.Originality/value - Compared with conventional approach, in the situation that centralized and federated Kalman filter are not applicable, the double-layer fusion scheme and algorithms give an external filtering strategy for measurements of finished EGI unit and star sensors.

Aerodynamic Parameter Estimation using Adaptive Unscented Kalman Filter

literatinetwork@emeraldinsight.com (Majeed M) — Fri, 28 Jun 2013 00:00:00 +0100

Abstract

Purpose - The purpose of this paper is to estimate aerodynamic parameters accurately from flight data in the presence of unknown noise characteristics.Design/methodology/approach - The introduced adaptive filter scheme is composed of two parallel UKFs. At every time-step, the master UKF estimates the states and parameters using the noise covariance obtained by the slave UKF, while the slave UKF estimates the noise covariance using the innovations generated by the master UKF. This real time innovation-based adaptive unscented Kalman filter (UKF) is used to estimate aerodynamic parameters of aircraft in uncertain environment where noise characteristics are drastically changes.Findings - The investigations are initially made on simulated flight data with moderate to high level of process noise and it is showed that all the aerodynamic parameter estimates are accurate. Results are analyzed based on a Monte Carlo simulation with 4000 realizations. The efficacy of adaptive UKF in comparison with the other standard Kalman filters on the estimation of accurate flight stability and control derivatives from flight test data in the presence of noise, are also evaluated. It is found that adaptive UKF successfully attain better aerodynamic parameter estimation under the same condition of process noise intensity changes.Research limitations/implications - The presence of process noise complicates parameter estimation severely. Since the non measurable process noise makes the system stochastic, consequently, it requires a suitable state estimator to propagate the states for online estimation of aircraft aerodynamic parameters from flight data.Originality/value - This is the first paper highlighting the process noise intensity change on real time estimation of flight stability and control parameters using adaptive unscented Kalman filter.

Effects of characteristic geometric parameters on parafoil lift and drag

literatinetwork@emeraldinsight.com (Yihua Cao, Xu Zhu) — Fri, 28 Jun 2013 00:00:00 +0100

Abstract

Purpose - The purpose of this paper is to describe the effects of characteristic geometric parameters on parafoil aerodynamic performance by using Computational Fluid Dynamics (CFD) technique. Design/methodology/approach - The main characteristic geometric parameters cover the planform geometry, arc-anhedral angle, basic airfoil and leading edge cut. By using the CFD technique, a large number of numerical parafoil models with different geometric parameters are developed to study the correlations between these parameters and parafoil aerodynamic performance.Findings - The CFD technique is feasible and effective to study the effects of characteristic geometric parameters on parafoil aerodynamic performance in three-dimensional (3-D) flowfield condition. The planform geometry can affect the aerodynamic performance obviously. An increase in arc-anhedral angle decreases the lift of a parafoil but has little effect on lift-drag ratio. The model with smaller leading edge radius and thinner thickness of parafoil section achieves larger lift-drag ratio. The leading edge cut has little effect on lift but increase drag dramatically; meanwhile, its effect on flowfield only be confined to the nearby region of leading edge.Practical implications - The presented 3-D numerical simulation results of parafoil models are shown to have good agreement with the tunnel test data in general trend; meanwhile, considering its relatively low-cost, the CFD method could be further used to predict coefficients in pre-research or at non-experimental conditions.Originality/value - It can lay the foundation of the further studies on parafoil aerodynamic performance with different geometric parameters.

Parameters determination for concept design of solar-powered, high-altitude long-endurance UAV

Fri, 28 Jun 2013 00:00:00 +0100

Abstract

Purpose - A methodology to determine the designing parameters for Solar Powered High-altitude, Long-endurance (HALE) UAV is proposed in this paper.Design/methodology/approach - By depicting solar-power distribution on earth, accompanying with the efficiencies analysis of photovoltaic cells (P-cell) and lithium-sulphur battery (LS-battery), the influence of energy to concept design parameters is analyzed firstly. Secondly, the lift efficiency is determined from ground to 20km for HALE UAV. Thirdly, the methodology to determine design parameters for HALE UAV is generalized by analyzing the carrying ability of some famous HALE UAVs, such as Zephyr, Helios.Findings - Energy is the key constraint on designing HALE UAV. The questions about where HALE UAVs are capable to operate and how long they could work can be answered according to power density distribution on earth. The total mass of HALE UAV can be divided into two parts, the one is constant mass, the other is the mass increasing with area of wing, the total mass can be estimated by the former one; the later one plays an important role in estimating wing load in designing process.Practical implications - The only way to enhance carrying ability of HALE UAVs is to redistribute their wing load, the lighter structure materials and better method to fix P-cell with lighter fundus are the key technologies to enhance HALE UAVs’ carrying ability. In current technological level, it is not easy to design a UAV to achieve the aim of high-altitude long-endurance.Originality/value - This paper presents a very efficient and convenient method to determine the designing parameters of HALE UAV.

Contra-rotating propeller for fixed wing MAV. Part I

Fri, 28 Jun 2013 00:00:00 +0100

Abstract

Purpose - Purpose - This is the first of two companion papers presenting the results of research into a contra-rotating propeller designed to drive a super maneuverable Micro Air Vehicle (MAV). It describes the design process and numerical analyses. The second one is devoted to the experimental results verifying the computations. Design/methodology/approach - Design/methodology/approach - Software based on the analytical formulas derived by Theodore Theodorsen was used in the design procedure. Three-dimensional finite-volume simulation, performed with the use of commercial software verified the results. Finally two-dimensional simulation was conducted to explore the effect of the propeller-wing interaction. The meshes applied in these analyses are described. Findings - Findings - Propeller geometry received as a result of the design procedure is presented. The computation results for different turbulence models applied are discussed. Time dependent characteristics of contra-rotating propeller are presented as well as conclusions regarding propeller-wing interaction. Research limitations/implications - Research limitations/implications - Propeller was designed for a fixed wing aeroplane, not for helicopter rotor. Therefore conditions characteristic for fixed wing aeroplane flight are analysed only. Reynolds numbers below 50000 are considered. Practical implications - Practical implications - Designed contra-rotating propeller can be used in fixed wing aeroplane if torque equal to zero is required. Software based on the formulas derived by T. Theodorsen can be used to design other propellers. Originality/value - Originality/value - Software applied in the design procedure was originaly developed by one of authors although it is based on the formulas derived by T. Theodorsen. Contra-rotating propeller simulation results for different turbulence models are discused for the first time. Moreover unique time dependent characteristics of contra-rotating propeller are presented.

Contra-rotating propeller for fixed wing MAV. Part II

Fri, 28 Jun 2013 00:00:00 +0100

Abstract

Purpose - Purpose - This is the second of two companion papers presenting the results of research into a contra-rotating propeller designed to drive a super maneuverable Micro Air Vehicle (MAV), devoted to the experimental results. The first one presented the design process and numerical analyses. Design/methodology/approach - Design/methodology/approach - Most of experiments were conducted in the wind tunnel. Both contra-rotating and conventional propeller were tested. The test procedures and equipment are described first. The attention is focused on the design of an aerodynamic balance used in the experiment. Then, the measurement error is discussed, followed by presentation of the wind tunnel results. Finally an initial flight tests of the MAV equipped with contra-rotating propeller are briefly described. Findings - Findings - Wind tunnel experiment results fall between theoretical results presented in the first part of the paper. The application of contra-rotating propeller allowed to develope the propulsion system with zero torque. Moreover, the efficiency achieved appeared to be a few percent greater than that for a standard conventional propulsion system. The concept was finally proved during the first test flight of the new Micro Air Vehicle MAV. Research limitations/implications - Research limitations/implications - Propeller was designed for a fixed wing aeroplane, not for helicopter rotor. Therefore conditions characteristic for fixed wing aeroplane flight are tested only. Practical implications - Practical implications - Designed contra-rotating propeller can be used in fixed wing aeroplane if torque equal to zero is required. Originality/value - Originality/value - Original design of the balance is described for the first time as well as test procedures applied in this experiment. Most of wind tunnel test results are also new and never published before.

Instrumented Flight Test of Flapping Micro Air Vehicle

Fri, 28 Jun 2013 00:00:00 +0100

Abstract

Purpose - A test is performed using a test measurement system to obtain the real characteristics of flapping vehicles during their flight.Design/methodology/approach - The test is performed in an indoor flight test facility, equipped with a motion capture system and tracking cameras. Spatial position data are obtained from the vehicles with retro-reflective tracking markers attached. A quantitative analysis is carried out through the investigation and interpretation of the test data for the flight performance assessment of the vehicles.Findings - The finding of the analysis addresses that the test enabled the quantitative measurement of vehicles’ flying performance and shows the present vehicles have combined characteristics of both birds and insects.Practical implications - The test metrics attempted in the present study is applicable to the test and evaluation of general flapping MAVs (Micro Air Vehicles). Thus, this testing method will be useful for the development of future MAV (Micro Air Vehicle) system.Originality/value - Full-scale instrumented flight test and measurement of performance parameters of flapping micro vehicles other than visual observation are unprecedented and expected to present the guideline of systematic T&E (Test and Evaluation) of flapping MAVs (Micro Air Vehicles).