2,918 research outputs found

    A method for continuous study of soaring and windhovering birds

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    Avian flight continues to inspire aircraft designers. Reducing the scale of autonomous aircraft to that of birds and large insects has resulted in new control challenges when attempting to hold steady flight in turbulent atmospheric wind. Some birds, however, are capable of remarkably stable hovering flight in the same conditions. This work describes the development of a wind tunnel configuration that facilitates the study of flapless windhovering (hanging) and soaring bird flight in wind conditions replicating those in nature. Updrafts were generated by flow over replica “hills” and turbulence was introduced through upstream grids, which had already been developed to replicate atmospheric turbulence in prior studies. Successful flight tests with windhovering nankeen kestrels (Falco cenchroides) were conducted, verifying that the facility can support soaring and wind hovering bird flight. The wind tunnel allows the flow characteristics to be carefully controlled and measured, providing great advantages over outdoor flight tests. Also, existing wind tunnels may be readily configured using this method, providing a simpler alternative to the development of dedicated bird flight wind tunnels such as tilting wind tunnels, and the large test section allows for the replication of orographic soaring. This methodology holds promise for future testing investigating the flight behaviour and control responses employed by soaring and windhovering birds

    Sensing unsteady pressure on MAV Wings: a new method for turbulence alleviation

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    Experiments at low Reynolds numbers were performed on a pressure tapped NACA2313 wing in a 3 x 2 x 9 meter wind tunnel under nominally smooth (Ti = 1.2%) and turbulent (Ti = 7.2%) flows at a mean flow velocity of 8ms-1 (Re ≈ 120,000). The NACA2313 wing is a replica of a Micro Air Vehicle (MAV) wing of the Flash 3D aircraft used at RMIT University for research purposes. Unsteady surface pressures were measured to understand if the information could be adopted for resolving turbulence-induced perturbations and to furthermore use it in a turbulence mitigation system. Two span-wise locations of chord-wise pressure were acquired when tested under the two different flow conditions. It was discovered that at both span-wise locations, a local Coefficient of Pressure (Cp) held high correlation to the chord-wise Cp integration and allowed for a linear relationship to be formed between the two variables. The defined relationship provided a 95% confidence for angles of attack below stall and was used to estimate the integrated cord-wise pressure coefficient at a particular span wise location. The relationship between a single pressure tap and the integrated Cp of that chord-wise section was valid for the two different span-wise locations with similar defining equations. As one pressure tap is sufficient to adequately estimate the integrated Cp on a chord-wise wing section, a limited amount of pressure taps across the wings span approximates the pressure distribution across the span and eventually approximates the flight perturbations. Being a novel method of sensing aircraft disturbance, applications are not restricted to MAV. The methodology presented could very well be applied to larger aircraft to reduce the effects of turbulence within the terminal area and can provide other means of active stabilization

    Ice Accretion on Fixed-Wing Unmanned Aerial Vehicle—A Review Study

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    Ice accretion on commercial aircraft operating at high Reynolds numbers has been extensively studied in the literature, but a direct transformation of these results to an Unmanned Aerial Vehicle (UAV) operating at low Reynolds numbers is not straightforward. Changes in Reynolds number have a significant impact on the ice accretion physics. Previously, only a few researchers worked in this area, but it is now gaining more attention due to the increasing applications of UAVs in the modern world. As a result, an attempt is made to review existing scientific knowledge and identify the knowledge gaps in this field of research. Ice accretion can deteriorate the aerodynamic performance, structural integrity, and aircraft stability, necessitating optimal ice mitigation techniques. This paper provides a comprehensive review of ice accretion on fixed-wing UAVs. It includes various methodologies for studying and comprehending the physics of ice accretion on UAVs. The impact of various environmental and geometric factors on ice accretion physics is reviewed, and knowledge gaps are identified. The pros and cons of various ice detection and mitigation techniques developed for UAVs are also discussed

    Unsteady pressure sensing on a MAV wing for control inputs in turbulence

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    This thesis presents the results of systematic studies in which the effects of turbulence and how it impacts the aerodynamic performance of a Micro Air Vehicle (MAV) are described. Flow visualization experiments mapping the dynamic nature of the flow over the MAV’s wing lead into the study of pressures on a MAV wing and how this can be used as an input to an autopilot system to mitigate the effects of turbulence. A MAV was tested under two different turbulence conditions (Ti = 1.2% & 7% Lxx = 0.23m) in the RMIT Industrial Wind Tunnel at a Reynolds number of 120,000. Force balance measurements revealed insignificant change in aerodynamic coefficients and derivatives when tested in the two difference turbulence conditions, a result not found in similar low Reynolds number tests involving flat plate airfoils. Force balance data also revealed increased wing performance offering greater lift production at angles of attack where separated flow would normally occur. Unsteady pressures were measured on a pressure tapped 3D NACA2313 wing in the two turbulence flow conditions. The introduction of freestream turbulence improved the time-averaged wing performance by delaying stall for the high turbulence flow condition, a result also found in the force balance data. Smoke flow visualization revealed unsteady flow mechanics at angles of attack greater than 15 degrees with the shear layer undergoing unsteady attachment and detachment at random time intervals. The shear layer was also seen to roll up and form a vortical core, which formed and burst at random intervals. Vortical core formations correlated to time varying pressure data with broad suction peaks formed near the wing leading edge before traversing across the wings chord. The vortical core flow mechanics was assumed to be a result of the oncoming flow vector relative to the wings angle of attack. Despite the unsteady nature of the pressure field, it was discovered that a single chord-wise pressure tap held high correlation (r > 95%) to the chord-wise integration of Pressure Coefficient (Cp) suggesting a linear relationship for angles of attack below stall for frequencies up to 25Hz. Thus a single chord-wise pressure tap can be used to approximate the integrated chord-wise Cp at various span-wise locations. The relationship between local and integrated Cp, per span-wise segment, could also be defined through a low-turbulence flow condition, as differences in the linear equations linking local and integrated pressure were insignificant and fell within the margin of error. With pressure taps placed at various locations across the span, measured pressure can be used to approximate span-wise sectional lift and furthermore be resolved around the aircraft centreline to produce a Turbulence Induced Rolling moment (TIR). TIR signal can be implemented into a control loop feedback system working in tandem with an IMU to form the basis of a MAV roll stabilization system, primarily for MAV flight in turbulent flow conditions

    Air Force Institute of Technology Research Report 2017

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    This Research Report presents the FY18 research statistics and contributions of the Graduate School of Engineering and Management (EN) at AFIT. AFIT research interests and faculty expertise cover a broad spectrum of technical areas related to USAF needs, as reflected by the range of topics addressed in the faculty and student publications listed in this report. In most cases, the research work reported herein is directly sponsored by one or more USAF or DOD agencies. AFIT welcomes the opportunity to conduct research on additional topics of interest to the USAF, DOD, and other federal organizations when adequate manpower and financial resources are available and/or provided by a sponsor. In addition, AFIT provides research collaboration and technology transfer benefits to the public through Cooperative Research and Development Agreements (CRADAs)

    Proceedings of the International Micro Air Vehicles Conference and Flight Competition 2017 (IMAV 2017)

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    The IMAV 2017 conference has been held at ISAE-SUPAERO, Toulouse, France from Sept. 18 to Sept. 21, 2017. More than 250 participants coming from 30 different countries worldwide have presented their latest research activities in the field of drones. 38 papers have been presented during the conference including various topics such as Aerodynamics, Aeroacoustics, Propulsion, Autopilots, Sensors, Communication systems, Mission planning techniques, Artificial Intelligence, Human-machine cooperation as applied to drones

    2016 Annual Report of the Graduate School of Engineering and Management, Air Force Institute of Technology

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    The Graduate School\u27s Annual Report highlights research focus areas, new academic programs, faculty accomplishments and news, and provides top-level sponsor-funded research data and information

    Air Force Institute of Technology Research Report 2014

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    This report summarizes the research activities of the Air Force Institute of Technology’s Graduate School of Engineering and Management. It describes research interests and faculty expertise; lists student theses/dissertations; identifies research sponsors and contributions; and outlines the procedures for contacting the school. Included in the report are: faculty publications, conference presentations, consultations, and funded research projects. Research was conducted in the areas of Aeronautical and Astronautical Engineering, Electrical Engineering and Electro-Optics, Computer Engineering and Computer Science, Systems Engineering and Management, Operational Sciences, Mathematics, Statistics and Engineering Physics
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