At staging of the Two-Stage-to-Orbit aerospace plane, the engine is in the shutdown condition and the intake is in the unstarted condition. Given these conditions, the effect of drag due to the unstarted engine on the flight trajectory was investigated. Then, the effect of the engine operating condition on the pitching moment of the first-stage vehicle was examined. The net drag increased with unstarted intake, and the horizontal distance between the vehicles became larger. The change of the engine operating condition by shutdown affected the pitching moment of the first-stage vehicle.
A new guidance and control system for a spaceplane is presented. The dynamics of the spaceplane has strong nonlinearity, due to which it is difficult to determine the optimal trajectory analytically and to design a stable trajectory tracking system. Therefore, in this study, we attempt to design a guidance and control system using a state-space exact linearization method without any approximation. Then, a minimum acceleration guidance law is derived analytically by solving a two-point boundary-value problem. Lastly, a trajectory control system is designed to track the vehicle with respect to the reference trajectory generated by the guidance system. The numerical simulation results confirm the validity of the linearized model, the optimality of the guidance system and the good tracking property of the developed system.
This paper examines the transfer alignment problem of the StrapDown Inertial Navigation System (SDINS), which is subject to the ship’s roll and pitch. Major error sources for velocity and attitude matching are lever arm effect, measurement time delay and ship-body flexure. To reduce these alignment errors, an error compensation method based on state augmentation and robust state estimation is devised. A linearized error model for the velocity and attitude matching transfer alignment system is derived first by linearizing the nonlinear measurement equation with respect to its time delay and dominant Y-axis flexure, and by augmenting the delay state and flexure state into conventional linear state equations. Then an H∞ filter is introduced to account for modeling uncertainties of time delay and the ship-body flexure. The simulation results show that this method considerably decreases azimuth alignment errors considerably.
This paper investigates the effect of turbulence models on numerical simulation of the vortical flow over a wing-body configuration at low speed and high angles of attack. Numerical simulations are conducted using Reynolds-Averaged Navier-Stokes equations with three popular turbulence models: the Spalart-Allmaras model, the Menter’s shear stress transport model, and the Launder-Sharma k–ε model. Computational results are compared with experiments. The original Spalart-Allmaras model shows excessively large dissipation in the vortical flow away from the surface, but the rotation correction indicates significant improvement in computational results. The Menter’s model predicts reasonable agreement with the experiment in details and capture vortex structures well. The Launder-Sharma k–ε model performs provides results close to those of the Menter’s model at high angles of attack. Although details of the flowfield have been simulated with large differences by different turbulence models, the choice of turbulence models is not important for prediction of aerodynamic forces.
This study applied a Kriging model to optimization of a constrained aerodynamic design problem. The objective function and all constraint functions are considered statistically independent to avoid treating the complicated multivariate normal distribution in the constrained optimization problem. In the Kriging model of objective functions, expected improvements (EI) is calculated and in the Kriging model of constraint function, the probabilities of satisfying the constraints are calculated. Based on these values, an efficient exploration of the global optimum is performed. Two data mining techniques are used to investigate the information of design space such as the relationship between objective function and design variables: Functional Analysis of Variance (ANOVA), and Self-Organizing Map (SOM). ANOVA shows information quantitatively, while SOM shows it qualitatively. Based on the information, elimination of design variables with little effect on objective function is performed. The present method is applied to two-dimensional (2D) transonic airfoil design. The results showed the validity of the present method.
Results of controlling a discharge current oscillation in Hall thrusters at a frequency range of 10–100 kHz are presented. To understand the discharge current oscillation mechanism, the plasma behavior in the acceleration channel was observed with a high-speed camera using a 1-kW class, anode layer type Hall thruster. The emission intensity oscillates equably in the acceleration channel at the same period of the discharge current oscillation; the number density of excited xenon ions oscillates at the same oscillation period and is proportional to the discharge current. These results indicate that the discharge current oscillation is caused by the ionization instability and the number density of plasma oscillates equably in the acceleration channel. Furthermore, the oscillation amplitude was sensitive to the applied magnetic flux density, indicating that this oscillation is affected by electron mobility. The proposed oscillation model based on the experimental results demonstrated that the momentum transfer corresponding to a plasma fluctuation is crucial to achieving stability. Thus, the oscillation amplitude for various acceleration channel configurations—parallel and convergent—was measured, because channel configuration could affect the momentum transfer. The oscillation was successfully suppressed by adopting the convergent configuration, as shown by this model.
The work described here relates to a method for measuring the boundary layer transition in a “low-speed” and “atmospheric” wind tunnel for metallic aircraft model. The objective of the research is to improve the test technique and to clarify the precise procedure for transition measurements, especially for an aircraft model in such a typical wind tunnel. The boundary layer growing on the left wing of the ONERA-Model was investigated at the JAXA 6.5m×5.5m Low-speed Wind Tunnel (LWT1), using two visualizing methods: temperature-sensitive liquid crystal film, and infrared camera. Comparison of the results showed that the IR camera could be more effective using after cooling of the model surface.
A small battery-powered helicopter with a total weight of about 200 g and a rotor diameter of about 35 cm has been developed. Some indoor flights were performed without a human operator using a transmitter. The helicopter is capable of autonomous hovering flight near walls when IR range finders mounted on it are used to measure distances to walls and the floor. Four mounted photodetectors permit two maneuvers. In the first maneuver, the helicopter can follow a moving light. So it can be controlled simply by moving a light, and can follow a robot or a person carrying a light. In the second maneuver, the helicopter flying over a first light can fly towards a second light, when the first light is turned off and the second light is turned on. The position of the helicopter can be controlled by successively switching (on and off) lights in a row.