For a Hall thruster, the influences of discharge channel wall material on thrust performance and plasma characteristics in the vicinity of the channel wall were investigated. In this study, THT-III 1-kW class Hall thruster was operated with three dielectric channel walls of BN, BNAlN and BNSiN. Discharge current and thrust were measured; specific impulses and thrust efficiencies were evaluated. The plasma potential, channel wall potential, electron temperature and electron number density were measured with an electrostatic single probe. The process of ion generation and acceleration in a Hall thruster was discussed with measured results. The thrust performances were affected by nature of the channel walls. Measured plasma characteristics suggested that the channel wall material affected an ionization region and ion wall losses in the channel, resulting from secondary electron emission. The difference of discharge current between channel materials was considered to be caused by the difference of current density near the inner channel wall.
We have proposed a swirling oxidizer type hybrid rocket engine. In this paper, liquid oxygen (LOX) was used as oxidizer. Combustion tests of a hybrid rocket engine with a swirling LOX flow were conducted by changing the swirl strength. Ignition was rapid and reliable, and combustion of PMMA with swirling LOX was stable. Fuel regression rates, C* efficiency and specific impulse of the hybrid rocket engine with swirling LOX flow were smaller than those with swirling gaseous oxygen (GOX). This low performance may be restraint of atomization and vaporization of LOX by formation of a liquid layer on the PMMA fuel and a decline of angular momentum of the swirling LOX during vaporization. Combustion oscillation occurred when the ratios of differential pressure between injector pressure and chamber pressure to chamber pressure were small. This combustion oscillation was confirmed to be a “Chugging” mode due to combustion time lag of LOX.
The wings formation flight is studied by means of theoretical aerodynamics. Each wing is modeled using the horseshoe vortex. In formation flight each wing flies in an upwash field generated by all other wings of the formation, and consequently its flight power decreases. In V formation flight the wing in a central position has a smaller local flight power reduction, while in U formation flight the local flight power reduction of each wing remains equal. In the case of a long range flight, the optimum shape is not V formation, but U formation flight. It has turned out that the value of a local flight power reduction in V formation flight is equal to that in U formation flight when the leader wing of V formation shifts to the position of a follower wing.
A study on mass flux of water vapor and mist around a cold cylinder (120–250K) was conducted by means of both experimental and numerical methods. The cylinder was placed in a forced convection air flow at a speed of 1m/sec. The experimental study revealed that the mass flux of the cylinder decreases rapidly under the temperature of about 200K. The mass flux at the cylinder temperature of 120K is one-sixth of that of 240K. The numerical study could simulate the mass flux around the cylinder in which we used a new phase change model with considering the transfer of the particles of mist. By this calculation we found some characteristics of the mass transfer of the cold cylinder which is unique when the temperature of the cylinder becomes cold enough to occur condensation.
Japan Aerospace Exploration Agency, JAXA announced a long-term vision recently. In the vision, JAXA aims to develop hypersonic aircrafts. A pre-cooled turbojet engine has great potential as one of newly developed hypersonic air-breathing engines. We also expect the engine to be installed in space transportation vehicles in future. For combustion test in real flight condition of the engines, JAXA has an experimental plan with a small test vehicle falling from a high-altitude balloon. This paper applies numerical analysis and optimization techniques to conceptual designs of the test vehicle in order to obtain the best configuration and trajectory that can achieve the flight test. The results show helpful knowledge when we design prototype vehicles.
The motion of a stabilizer bar of the small coaxial helicopter was analyzed in the previous study. It has been made clear by the measurements on the motion of the stabilizer bar that the following two revisions are required in the analysis. (1) The motion of stabilizer bar is affected by the upper rotor. (2) Neither of the terms in the moment acting on the stabilizer bar at its hinge, kββ+kββ, can be ignored.
A method of evaluating rolling moment for a magnetic suspension model with pair magnets was successfully used when an AGARD-B model was designed. Especially the way is effective at inertia moment adjustment and at control parameters detection. The rolling motion was successfully controlled with the same control method as at the existing 5 D.O.F. control of the JAXA 60cm MSBS. Then the 60cm MSBS got 6 D.O.F. control ability. The model was successfully magnetically suspended from -4 degree to +4 degree in a flow up to 35m/s. Drag coefficient and lift and pitching moment coefficient slopes were measured with the magnetic balance and they showed reasonable values compared with other data set source.