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Theoretical and numerical aspects of aerodynamic efficiency of propulsion systems are studied. Focus is on types of propulsion that closely couples to the aerodynamics of the complete vehicle. We discuss the effects of local flow fields, which are affected both by conservative flow acceleration as well as total pressure losses, on the efficiency of boundary layer immersed propulsion devices. We introduce the concept of a boundary layer retardation turbine that helps reduce skin friction over the fuselage. We numerically investigate efficiency gains offered by boundary layer and wake interacting devices. We discuss the results in terms of a total energy consumption framework and show that efficiency gains offered depend on all the elements of the propulsion system.

The development of a wingtip-mounted electric lift propeller concept to enable quiet, efficient VTOL aircraft has yielded a promising UAV design employing two-bladed propellers that lock into a fixed position during horizontal flight to become wingtip extensions, resulting in a low-drag cruise configuration. The desire to reduce dependence on high-fidelity computational simulations which would increase the development timeframe for this concept led to the adoption of a spiral development model in which a series of six increasingly large and complex subscale prototypes were built and tested. Results from these tests were used to validate and update the computational models and led to various modifications of the aircraft configuration. A fully-functional 55-pound airframe designed to demonstrate mechanical feasibility, desired aerodynamic properties, full mission profiles including quiet VTOL and efficient forward flight operations, automatic stabilization, pilot workload mitigation and fully autonomous control was also constructed and is undergoing early stage testing. Static and flight test results as well as conceptual design studies are presented, including aerodynamic and structural simulations. The impact of these results on the design of the aircraft is examined. The feasibility and current performance predictions of this concept as applied to larger scale UAV systems is also touched upon.

ight, becoming lifting surfaces. The design of these blades and their integration onto an airframe pose many challenges, including performing this blade repositioning with a mechanism that is adequately simple, reliable, lightweight, and aerodynamic; determining a blade geometry that strikes the right compromise between performance as a rotor blade and as a wingtip; and providing sucient pitch and yaw control in vertical and transitional ight without resorting to overly complex and heavy mechanisms, such as rotor cyclic. A spiral development model is employed in which a series of increasingly large and complex subscale prototypes are built and tested. Results from these tests demonstrate the strengths, weaknesses, and design tradeos of this conguration. Conceptual design is aided by an aerodynamic and structural mission analysis code. Detailed aerodynamic analysis of these designs is performed in CFD, which illuminates the unusual aerodynamics of this design in vertical and horizontal ight and the eects of these aerodynamics on overall performance. Compelling applications of this concept to the personal air vehicle and on-demand aviation markets are examined.