ROBUST TRAJECTORY TRACKING FOR A SMALL-SCALE HYBRID AIRCRAFT
By hybrid aircraft, we mean a UAV that can vertically take-off, land and hover like a helicopter, and meanwhile can be converted to a fixed wing airplane to achieve high forward speed and long endurance than normal helicopters. This paper presents our recent work on control of a novel small scale hybrid aircraft. The proposed aircraft should follow a specific trend of trajectory to be able to convert from helicopter to airplane. For such a purpose, we design a robust trajectory tracking controller for helicopter mode of the aircraft. Finally, the simulation results are presented to demonstrate effectiveness of the proposed controller.
Inventing the F-35 Joint Strike Fighter
The F-35 Joint Strike Fighter is a single aircraft developed to meet the multirole fighter requirements of the US Air Force, Navy, Marine Corps, and our allies. The Air Force variant is a supersonic, single engine stealth fighter. The Navy variant has a larger wing and more robust structure in order to operate from an aircraft carrier, while the Marine Corps variant incorporates an innovative propulsion system that can be switched from a turbofan cycle to a turboshaft cycle for vertical take off and landing. This novel propulsion system enabled the X-35 demonstrator to become the first aircraft in history to fly at supersonic speeds, hover, and land vertically. The F-35 program grew out of a design study of a supersonic replacement for the AV-8 Harrier, through the absorption of several other tactical aircraft initiatives. It became an international program with engineers from half a dozen countries developing a replacement for multiple aircraft Types.
Computational Analysis of a Double-Nozzle Crossflow Hydroturbine
The crossflow turbines commonly used in small hydropower systems have a single nozzle. We are unaware of any studies of double-nozzle crossflow turbines which could have twice the power output of the single-nozzle design by doubling the flow through the same runner, with a high maximum efficiency. We present a computational analysis of a double-nozzle crossflow turbine, to determine the turbine efficiency and fundamental flow patterns. This work was based on a single-nozzle crossflow turbine with a maximum efficiency of 88%, one of the highest reported in the open literature through extensive experimental measurements. Previous numerical studies on this turbine have shown that the water flow in the runner was confined to less than half the runner periphery, implying that the other half could be used to double the runner power output by employing a second nozzle. We show that adding a second, identical nozzle without making any other changes to the design achieves a doubling of the power output. The dual-nozzle turbine, therefore, has the same efficiency as the original turbine. We also investigate the use of a slider to control the flow at part-load and show that part-load efficiency of the double-nozzle is very similar to that of the original turbine. This demonstrates the feasibility of using two nozzles for crossflow turbines.