Browsing by Author "Halefom, Mekonen H."

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    Tailoring an Airworthiness Document to Unmanned Aircraft Systems: A Case Study of MIL-HDBK-516C
    Halefom, Mekonen H. (Virginia Tech, 2020-03-17)
    With the popularity of unmanned aircraft systems (UAS), there is a growing need to assess airworthiness for safe operations in shared airspace. In the context of this thesis, shared airspace implies the introduction of UAS into airspace designated for manned aircraft. Airworthiness guidelines are generally statements that state safety requirements to prevent unwanted consequences, such as aircraft accidents. Many governmental agencies such as the U.S. Federal Aviation Administration (FAA) analyzed the risks of UAS to third-parties, all personnel and properties exterior to the aircraft. This thesis concerns the adaptation of existing airworthiness documents written for manned aircraft to UAS. The proposed method has three stages that are applied in sequence to identify relevant and irrelevant airworthiness statements, the building blocks of an airworthiness document, with regard to UAS. This method is applied to MIL-HDBK-516C, used as a case study; however, the proposed methodology can be applied to any airworthiness document developed for manned aircraft. This thesis presents a list of all MIL-HDBK-516C airworthiness statements that are directly relevant, indirectly relevant, and irrelevant to UAS; additionally, the indirectly relevant airworthiness statements to UAS are provided along with suggested modification.
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    A Tutorial Review of Indirect Wind Estimation Methods Using Small Uncrewed Air Vehicles
    Ahmed, Zakia; Halefom, Mekonen H.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2024-08)
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    Unsteady Aerodynamics in Model-Based Wind Estimation from Fixed-Wing Aircraft Motion
    Halefom, Mekonen H.; Hopwood, Jeremy W.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2024-08)
    This paper examines the value of incorporating unsteady aerodynamics in a model-based wind estimator for a small, fixed-wing aircraft and presents results of an experimental implementation. An extended Kalman filter is designed for two motion models identified from flight data: one that includes unsteady effects and another that does not. An air data unit with wind vanes and a Kiel probe is used to reconstruct the local wind velocity for validation. Analysis of time histories of the wind estimates and the wind estimate error relative to the reconstructed wind velocity shows that the two model-based estimators perform equally well. The power spectral densities of the reconstructed wind and the estimated wind, computed using either estimator, follow Kolmogorov’s −5/3 law.