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The interest in electric and hybrid electric power system has been increasing, in recent times, due to the benefits of this technology, such as high power-to-weight ratio, reliability, compactness, quietness, and, above all, elimination of local pollutant emissions. One of the key factors of these technologies is the possibility to exploit the synergy between powertrain, structure, and mission. This investigation addresses this topic by applying multi-objective optimization to two test cases&mdash, a fixed-wing, tail-sitter, Vertical Take-off and Landing Unmanned Aerial Vehicle (VTOL-UAV), and a Medium-Altitude Long-Endurance Unmanned Aerial Vehicle (MALE-UAV). Cruise time and payload weight were selected as goals for the first optimization problem, while fuel consumption and electric endurance were selected for the second one. The optimizations were performed with Non-dominated Sorting Genetic Algorithm-II (NSGA-II) and S-Metric Selection Evolutionary Multiobjective Algorithm (SMS-EMOA), by taking several constraints into account. The VTOL-UAV optimization was performed, at different levels (structure only, power system only, structure and power system together). To better underline the synergic effect of electrification, the potential benefit of structural integration and multi-functionalization was also addressed. The optimization of the MALE-UAV was performed at two different levels (power system only, power system, and mission profile together), to explore the synergic effect of hybridization. Results showed that large improvements could be obtained, either in the first test case when, both, the powertrain design and the aircraft structure were considered, and in the optimization of the hybrid electric UAV, where the optimization of the aircraft flight path gave a strong contribution to the overall performances.

The ducted fan propulsion systems provide attractive solutions for manned and unmanned aerial vehicles, with potential applications in general aviation and military missions. They provide higher power-to-thrust ratios over their free-rotor counterpart. However, ducted fans currently implemented in vertical takeoff and landing (VTOL) type aerial vehicles have an inherent duct lip separation and inlet flow distortion problem in edgewise flight. This problem is severe when the flight direction of the VTOL vehicle and the rotor axis of rotation are normal to each other. Separation at the leading edge duct lip for this high angle of attack situation disallows flow from effectively entering the fan rotor causing unwanted inlet flow distortion. Discussed here will be optimized design solutions to controlling and/or eliminating this flow separation at the leading edge duct lip. The designed were three types of lip-s: parametric, detached duct lip, and double duct. The parametric lip-spoilers consisted of inner-face and outer-face duct lip-spoilers. Inner-face duct lip-spoilers predominantly contributed to increased control over the negative nose-up pitching moment while the outer face and detached duct lip-spoilers predominantly controlled the increase in the mass flow rate through the ducted fan rotor. The double-ducted fan (DDF) was successful in eliminating duct lip separation through its added second duct. The main purpose of this study is to design and test various duct lip-spoilers that improves the ducted fan aerodynamic performance in edgewise flight. The conceptual design, analysis and flow visualization for a number of novel lip-spoilers are discussed in detail.

This paper briefly describes a novel ducted fan inlet flow-conditioning concept that will significantly improve the performance and controllability of ducted fans operating at high angle of attack. High angle of attack operation of ducted fans is very common in VTOL (vertical take- off and landing) UAV systems. The new concept that will significantly reduce the inlet lip separation related performance penalties in the edgewise/forward flight zone is named double-ducted fan (DDF). The current concept uses a secondary stationary duct system to control inlet lip separation related momentum deficit at the inlet of the fan rotor occurring at elevated edgewise flight velocities. The DDF is self-adjusting in a wide edgewise flight velocity range and its corrective aerodynamic effect becomes more pronounced with increasing flight velocity due to its inherent design properties. In this manuscript, after a comprehensive discussion of VTOL inlet flow distortion issues, a conventional baseline duct without any lip separation control feature is compared to two different double-ducted fans named DDF CASE-A and DDF CASE-B via 3D, viscous and turbulent flow computational analysis. Both hover and edgewise flight conditions are considered. Significant relative improvements from DDF CASE-A and DDF CASE-B are in the areas of vertical force (thrust) enhancement, nose-up pitching moment control and recovery of fan through-flow mass flow rate in a wide horizontal flight range.

This paper discusses trajectory tracking control for Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) using the command filtered backstepping technique. Quaternions are used to represent the attitude of the vehicle to ensure the global attitude tracking without singularities. Since the quaternions have their own unique algebra, they cannot be filtered by a vector-based command filter; therefore, a second-order quaternion filter is developed to filter the quaternion and automatically compute its derivative, which determines the commanded angular rate vector. A quadrotor vehicle is used as an example to show the performance of the proposed controller.