This paper attempts to design a guidance law using bifurcating potential fields and velocity field for a swarm of autonomous Unmanned Aerial Vehicles (UAVs). We consider an autonomous flight system that can create different three-dimensional swarming patterns so as to guarantee obstacle and vehicle collision avoidance. The guidance law, which is derived from a steering and repulsive potential field, can express variable geometric patterns for a formation flight of UAVs. The system can transition between different formation patterns by way of a simple parameter change. We also describe the design method for potential field that is flexible enough to respond to a variety of UAV performance and mission. Numerical simulation is performed to verify the validity of the proposed guidance law.
The current paper describes experimental results for a pulsed plasma thruster (PPT) using dimethyl ether (DME) as a propellant. DME is an ether compound, which is neither toxic nor reactive and is stored in the liquid form in tanks because of 6 atm vapor pressure. A coaxial type DME-PPT was designed to evaluate the performance. Main discharges were successfully initiated by an igniter or spontaneous discharge induced by DME injection. The igniter was used in the case that propellant mass was so low that the spontaneous discharge was not initiated by DME feeding. Thrust measurement using a thrust target yielded a specific impulse of 1200s for an igniter type DME-PPT with 1.5μg mass shot and 5J capacitor stored energy, and 620s for spontaneous discharge type with 8.8μg and 13J.
A boomerang thrown properly into the air can fly in an elliptical path and return to the point of origin. In this study, such a motion of the boomerang was numerically simulated to clarify the mechanism of the motion. The simulation was conducted by the double CFD method which is the coupling method of the computational fluid dynamics and the computational flight dynamics. We considered the case that a small flat boomerang was thrown with a translational and a rotational velocity, an angle of the translational velocity from a horizontal plane, and no roll angle. Results showed that the boomerang lifted and traveled in a path with changing roll and pitch angles due to a pressure distribution on its surface, and returned to a point near the origin. Furthermore, an experiment was performed to confirm the validity of the computational results, and the experimental result was qualitatively corresponding to the computational results.
Dual-bell nozzle is one of the altitude compensation nozzle concepts, which consists of two bell-type nozzle with different geometric area ratios. The dual bell nozzle has two operation modes—a low altitude operation mode and a high altitude operation mode. However, the practical transition between these operation modes occurs at lower nozzle pressure ratio (NPR) than the optimum one. In the present study, the effect of introduction of film-cooling flow into the nozzle is examined in order to control the operation mode transition NPR. The experimental and numerical results show that the operation mode transition can be control by injecting the film cooling flow at appropriate inlet pressure and flow rate. By injecting the film cooling flow, the axial momentum near the wall in the extension part becomes small and the separation point movement becomes slower. As a result, the dip of the thrust coefficient during the operation mode transition becomes smaller.