Power Balance in Aerodynamic Flows

A control volume analysis of the compressible viscous flow about an aircraft is performed,including integrated propulsors and flow control systems. In contrast to most past analyses which have focused on forces and momentum flow, in particular thrust and drag, the present analysis focuses on mechanical power and kinetic energy flow. The result is a clear identification and quantification of all the power sources, power sinks, and their interactions which are present in any aerodynamic flow. The formulation does not require any separate definitions of thrust and drag, and hence it is especially useful for analysis and optimization of aerodynamic configurations which have tightly integrated propulsion and boundary layer control systems

Habitable Zones and UV Habitable Zones around Host Stars

Ultraviolet radiation is a double-edged sword to life. If it is too strong, the terrestrial biological systems will be damaged. And if it is too weak, the synthesis of many biochemical compounds can not go along. We try to obtain the continuous ultraviolet habitable zones, and compare the ultraviolet habitable zones with the habitable zones of host stars. Using the boundary ultraviolet radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable zones of host stars with masses from 0.08 to 4.00 \mo. For the host stars with effective temperatures lower than 4,600 K, the ultraviolet habitable zones are closer than the habitable zones. For the host stars with effective temperatures higher than 7,137 K, the ultraviolet habitable zones are farther than the habitable zones. For hot subdwarf as a host star, the distance of the ultraviolet habitable zone is about ten times more than that of the habitable zone, which is not suitable for life existence.Comment: 5 pages, 3 figure

Utilising Nonlinear Air Damping as a Soft Mechanical Stopper for MEMS Vibration Energy Harvesting

This paper reports on the theory and experimental verification of utilising air damping as a soft stopper mechanism for piezoelectric vibration energy harvesting to enhance shock resistance. Experiments to characterise device responsiveness under various vibration conditions were performed at different air pressure levels, and a dimensionless model was constructed with nonlinear damping terms included to model PVEH response. The relationship between the quadratic damping coefficient ζ n and air pressure is empirically established, and an optimal pressure level is calculated to trade off harvestable energy and device robustness for specific environmental conditions

Experimental Analysis of Propeller Forces and Moments at High Angle of Incidence

An experimental measurement on propeller forces and moments at high incidence was introduced. Test apparatus and data reduction process was discussed. Two sets of propellers were tested in SaBRe low speed wind tunnel: Graupner E-prop was used to validate the test-bench against known experiment; The second case, consisting of 3D-printed propellers, demonstrated variations in propeller aerodynamic efforts produced at high incidence angle for various advance ratios and blade pitch angles. The test also highlighted the importance of 3 dimensional effects such as stall delay in estimating propeller forces and moments at high incidence angle

A Fixed-Wing Biplane MAV for Low Speed Missions

Practical MAVs missions, such as outdoor urban environment recognitions, simultaneously require a capability of both dashing to escape enemy fire and slowly loitering over a target in order to capture and transmit clear images to a ground station. Since an MAV intrinsically offers better payload and endurance capabilities than a rotorcraft of an equal size, fixed-wing MAVs can be considered as promising platforms to start with. The objective of this study is to investigate the possibility of developing a fixed-wing MAV which can both perform rapid translations and low-speed flights through urban canyons. Alow-speed wind tunnel testing is conducted to compare several powered configurations including monoplane, biplane and tandem wing combinations. The testing also focuses on wing-propeller interactions. Results indicate that a positive stagger biplane configuration powered by counter-rotating propellers placed in pusher position provides the best trade-off between a high-speed performance and a low-speed capability with a limited electric consumption. Consequently, a 30 cm span MAV biplane prototype, named TYTO-30, has been designed and built. TYTO-30 is equipped with a 110g-payload which includes a video camera, navigation and autopilot system and has been flight tested successfully

Conceptual Design for Long-Endurance Convertible Unmanned Aerial System

This research is aimed at analysing the effect of design parameters on critical aerodynamic performance of convertible unmanned aerial vehicle (UAV) with vertical take-off and landing (VTOL) capabilities and providing a sizing tool for its conceptual design. The research was based on new aerodynamic models specifically developed and validated for convertible aircraft, performed using mission-based optimisation techniques. To accommodate a wide range of convertible aircraft configurations, a non-linear lifting-line method was used to efficiently analyse different combinations of lifting surface and propeller arrangements. Propeller loads were calculated using a blade element momentum approach and corrected for high incidence angle conditions according to numerical and experimental studies. Propeller-wing interactions were considered by modifying local boundary conditions at wing sections immersed in propeller slipstream. Previous studies have suggested that the design of convertible aircraft is sensitive to typical mission requirements, notably the endurance breakdown between near-hover flight and cruise flight. A clear sizing law for wing and propeller according to given mission specification could greatly improve the understanding of compromises between hover and high speed flight