One of the fundamental problems preventing commercial transport aircraft from supersonic flight is the creation of strong shock waves. Here, a biplane concept is proposed that will enable a significant reduction of shock waves: Introduce a second wing nearly parallel to the conventional wing, creating a biplane configuration. The interaction between the two wings will cancel or reduce the shock waves created by the individual wings. Several simple two-dimensional biplane configurations are currently under study, using CFD (computational fluid dynamics) codes, Euler calculations for inviscid flow analysis and inverse-problem analysis for wing design, to demonstrate our biplane concept.
The effects of magnetic field strength and shape on thrust efficiency of a Hall thruster were examined experimentally using the THT-IV 1-kW-class Hall thruster. Thrusts were measured with varying magnetic field and channel geometry. Exhaust ion beam measurement was also implemented to evaluate internal efficiencies of propellant utilization efficiency, acceleration efficiency, voltage utilization efficiency and beam focusing efficiency. Spatial ion current profiles were measured with a Faraday probe and ion energy distribution functions were estimated from data with a retarding potential analyzer. Stable operation was obtained over the wide range of operational condition, and voltage utilization efficiency and beam focusing efficiency were estimated suitably. Acceleration efficiency and propellant utilization efficiency, however, were not able to be evaluated experimentally because the total ion current calculated by integrating the ion current density over the measured area was very small. Using obtained results, the relationships between each internal efficiency and thrust performance and between magnetic field characteristics and thrust efficiency were discussed. Consequently, it was expected that the change of magnetic field strength mainly affected acceleration efficiency and voltage utilization efficiency, and that the change of magnetic field shape affected voltage utilization efficiency in long discharge channel case and beam focusing efficiency in short channel case.
The effectiveness of fuzzy logic control law for automatic landing of aircraft, which cover both of control to lead aircraft from level flight at an altitude of 500m to the flight on the glide-path course near the runway and control for the aircraft to land smoothly on a runway, was studied. The control law of the automatic landing was designed to match the design goals of leading from the horizontal flight to the flight on the glide-path course quickly and smoothly and of landing smoothly on a runway. Because there is the ground effect at landing, design of control law and evaluation of control performance were done in consideration of the ground effect. As a result, it was confirmed that the design objective was achieved. Even if the characteristics of the plant changes greatly, this control law was able to maintain the control performance. Moreover, it was confirmed to be able to land safely when there was air turbulence. This paper shows that fuzzy logic control is an effective and flexible method when applied to control law for automatic landing and the design method of control law using fuzzy logic control was obtained.
To repair a malfunctioning satellite or de-orbit a space debris object, capturing free-flying, non-cooperative objects in orbit is required. These objects could be in complicated attitude motions, such as spin, nutation and tumbling, which are obstacles to capturing a non-cooperative object. This paper discusses a fuzzy control applied to reduction of tumbling motion of the non-cooperative object by the repetitive impulses produced by projecting small particles to the non-cooperative object. The purpose of this study is to tune the parameters of the fuzzy controller which determines the direction and velocity of the projection by means of learning algorithm. It is shown that the proposed method has advantage in robustness to variation of motion and geometry of the target.
This paper presents a control design of gain scheduling controllers for active flutter suppression (AFS) in which the closed loop system is stabilized in the operating region specified in advance. The AFS system of a high-aspect-ratio wing is represented by a linearly interpolated polytopic model whose varying parameter is the dynamic pressure. The gain scheduling controller in this paper consists of a regulator and a full-order observer which are scheduled by the varying parameter. Linear matrix inequalities for designing the gains of the regulator and the observer are separately derived in the frame of the H2 optimization. The control performance and the characteristics of the designed gain scheduling controllers are evaluated in comparison with fixed H2 controllers which are designed with the same design parameters. As the result, the gain scheduling controllers may be inferior to the fixed controller at local regions, but are superior to the fixed controllers for the entire operating region.
Breakdown of diffuser flow was often observed in our scramjet engine tests. This facility operation may damage the engine wind-tunnel and should be prevented. An one-dimensional analysis was applied to the diffuser flow to identify the causes of the flow breakdown. All the losses and gains by engine and friction loss in the diffuser were represented by point-sources of mass, momentum and energy. The thermal choking condition was calculated by uses of a chemical equilibrium code. The fuel rates causing the flow-choking successfully reproduced the limit fuel rates observed in our tests. Inlet-unstart of engine lost the ejector-pumping effect in the diffuser system to trigger the flow choking. The choking was also promoted by the drag of the gas sampling rakes. The choking in diffuser flow and the engine unstart may couple each other to cause hysteresis in the diffuser breakdown, which was also experienced in our tests. A rocket-based, combined-cycle (RBCC) engine will be tested under the Mach 4 condition. The engine easily causes the choking of diffuser because of the large propellant supply rates and the relatively-low specific impulse. Operation of the wind-tunnel was discussed to control the flow choking in the tests.
A semi-empirical model to estimate the location of the region where high aerodynamic heating occurs due to shock-wave/laminar-boundary-layer interaction around compression ramps in hypersonic flow is presented. To develop the behavioral formula, the scale of upstream influence and the free interaction characteristic are examined numerically. A flat plate/ramp configuration is used in the study and the following is obtained. A parametric model to evaluate the effects of ramp angle, wall temperature, Mach and Reynolds numbers on the scale is developed. The deflection angle of a boundary layer edge is estimated using a free interaction similarity rule. All model coefficients required are defined from numerical results. It is shown that the predicted position agrees with experimental data available. Finally, limitations concerning the model are discussed.