Current Issue : January - March Volume : 2018 Issue Number : 1 Articles : 5 Articles
Aerodynamic characteristics of helicopter engine side air intakes are investigated.\nThe experimental data set is obtained by wind tunnel testing of a full-scale helicopter fuselage\nsection model. For the simulation of realistic engine operation, engine mass flow rates are reproduced.\nFive-hole pressure probe data of the aerodynamic interface plane as well as local surface pressure\ndistributions are compared for different geometries and operation conditions. Previous investigations\nindicate that unshielded, sideways-facing air intakes yield lowest distortion and highest total pressure\nlevels in low speed conditions. In fast forward flight condition, however, forward-facing intake\nshapes are more beneficial. On this basis, the current research assesses the optimization potential\nof retrofit modifications such as a rear spoiler (small scoop) and an intake guide vane. Two optimal\nconfigurations of retrofit modifications are identified, combining benefits of the various basic intake\nand plenum chamber shapes....
Effects of swirling oxidizer flow on the performance of a HTPB/N2O Hybrid rocket motor were studied. A hybrid propulsion\nlaboratory has been developed, to characterize internal ballistics characteristics of swirl flow hybrid motors and to define the\noperating parameters, like fuel regression rate, specific impulse, and characteristics velocity and combustion efficiency. Primitive\nvariables, like pressure, thrust, temperature, and the oxidizer mass flow rate, were logged. A modular motor with 70mm outer\ndiameter and variable chamber length is designed for experimental analysis. The injector module has four tangential injectors and\none axial injector. Liquid nitrous oxide (N2O) as an oxidizer is injected at the head of combustion chamber into the motor. The\nfeed system uses pressurized air as the pressurant. Two sets of tests have been performed. Some tests with axial and tangential\noxidizer injection and a test with axial oxidizer injection were done. The test results show that the fuel grain regression rate has\nbeen improved by applying tangential oxidizer injection at the head of the motor. Besides, it was seen that combustion efficiency of\nmotors with the swirl flow was about 10 percent more than motors with axial flow....
Gasoline engines are increasingly popular for use in small unmanned aircraft\nrequiring endurance due to the specific energy of gasoline (47.3 MJÃ?·kgâË?â??1) and\nits cost effectiveness. However, gasoline is volatile and it poses a health hazard.\nIn this work, isopropanol is proposed and investigated as viable fuel for\nsmall gasoline engines. Isooctane is used as a benchmark for performance\ncomparison. The field testing reveals that isopropanol offers similar running\nperformance and ease of starting. The maximum output power of isopropanol\nis surprisingly found to occur at a more advanced ignition timing compared\nwith isooctane. The significant outcome of this study is that isopropanol can\nreadily be used as a replacement fuel for existing engines without the need for\nany modifications to the ignition module or the engine itself....
Displaced solar orbits for spacecraft propelled by electric sails are investigated. Since the propulsive thrust is induced by the sail\nattitude, the orbital and attitude dynamics of electric-sail-based spacecraft are coupled and required to be investigated together.\nHowever, the coupled dynamics and control of electric sails have not been discussed in most published literatures. In this paper, the\nequilibriumpoint of the coupled dynamical system in displaced orbit is obtained, and its stability is analyzed through a linearization.\nThe results of stability analysis show that only some of the orbits aremarginally stable. For unstable displaced orbits, linear quadratic\nregulator is employed to control the coupled attitude-orbit system. Numerical simulations show that the proposed strategy can\ncontrol the coupled system and a small torque can stabilize both the attitude and orbit. In order to generate the control force and\ntorque, the voltage distribution problem is studied in an optimal framework. The numerical results show that the control force and\ntorque of electric sail can be realized by adjusting the voltage distribution of charged tethers....
The implementation of advanced guidance laws with bearings-only measurements requires estimation of the range information.\nTo improve estimation accuracy and satisfy the impact angle constraint, this paper proposes a two-phase optimal guidance law\nconsisting of an observing phase and an attacking phase. In the observing phase, the determinant of Fisher information matrix is\nmaximized to achieve the optimal observability and a suboptimal solution expressed by leading angle is derived analytically. Then,\na terminal sliding-mode guidance law is designed to track the desired leading angle. In the followed attacking phase, an optimal\nguidance law is integrated with a switching termto satisfy both the impact angle constraint and the field-of-view constraint. Finally,\ncomparison studies of the proposed guidance law and a traditional optimal guidance law are conducted on stationary targets and\nmaneuvering targets cases. Simulationresults demonstrate that the proposed guidance law is able to improve the rangeobservability\nand achieve better terminal performances including impact angle accuracy and miss distance....
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