The purpose of this paper is to discuss the method and accuracy of position determination of a spacecraft at a long distance from the earth like a lunar orbiter. Several very long base-lines which start at a main radio station, spread out in any directions and end at several subordinate radio stations are used to measure differences in the time of arrival of the radio signal transmitted from the spacecraft. Precise measurements of positions and clock offsets of subordinate stations relative to the main station are required to achieve the accurate position determination. The method and the accuracy of the position and clock offset determination of radio stations by using GPS satellites as radio sources of the interferometry measurements are investigated and the following accuracy of the space navigation is shown by simple equations.
This paper proposes two design methodologies for feedback controllers which generate the optimal pathes for the given criterion, for example minimum time, maximum range, minimum fuel and so on. The controllers discussed in this paper include not only guidance laws, but also control laws. Since a large amount of calculation is necessary to solve optimal path problems, it has been difficult to calculate them by onboard computers. The proposed path controllers give inputs using state feedback laws with time-invariant feedback gains. The proposed guidance and control laws does not need much calculation load, therefore they can be used for online controllers. Two types of feedback controllers are proposed in this paper. One uses feedforward inputs given as a function of a state variable, and the other consists of only state feedback inputs. Both controller are designed to minimize the given criterion for uncertain initial conditions. Although the first one has better performance, the second one needs fewer calculation load. Minimum-time turn of aircraft problems are solved as the application. The results show that the pathes which are generated by the proposed controllers are similar to the optimal pathes. The increment in the criterion is less than 1% of the optimal one. The proposed guidance and control laws are effective for online optimal path controller of aircrafts.
Flame holding is an essential technology for Scramjet combustors especially under low Mach flight conditions, under which the airflow temperature is low. An interesting technique for the flame holding is the utilization of shock waves. Experiments in a supersonic wind tunnel showed that the incident shock waves made possible the stable flame holding in Mach 2.5 supersonic airflow within air total temperature of 360K through 900K. The objective of this study was to investigate the flame-holding characteristics depending on air added to hydrogen fuel jet and to understand the mechanism of the flame-holding stabilized by shock wave. The flame-holding limits of hydrogen flow rate with various fuel/air ratio showed that both diffusion- and premixed-type flame-holding existed. In the diffusion-type flame-holding, the hydrogen flow rate of the flame-holding limit decreased as the added air flow rate increased. Increasing the added air flow rate further, the hydrogen flow rate limits turned to increase. To elucidate the mechanism of the flame-holding, visualization of OH species by laser-induced fluorescence and measurements of temperature and hydrogen concentration in the wake were also conducted. They showed that the addition of air suppressed the mixing of fuel and shrank the recirculation flow.
The hot-wire anemometer is now still the most important instrument for measuring turbulent flow. However, the hot-wire output is nonlinear to the wind velocity and is affected by a variation in air temperature. Thus, we have devised the new method of hot-wire calibration by the aid of a computer. There are the following characteristics in this method: First, the calibration curve of the hot-wire output versus the wind velocity is simply determined using a method of three-point interpolation with high accuracy. Second, in place of using analog linearizer, the hot-wire output could be linearized on reference to a table located on computer-memory in real time. Last, the calibration curve could be immediately corrected by remeasuring only the output voltage in the free stream, whenever air temperature varies.
A feedback system for aircraft nonlinear equations of motion is designed in this paper without using linear approximation. The design method is based on inverse dynamics transformation and singular perturbation theory, and enables us to control the nonlinear dynamics directly. This leads to an advantage that the dynamics can be controlled by a single control law through the whole flight envelope. To evaluate and substantiate the design method, ALFLEX (AutoLanding FLight EXperiment) plane is selected, and simulations are given regarding on the time separation between inner and outer loops and on the robustness of modeling errors.
The lift characteristic of blunt trailing edge NACA0012 aerofoil is investigated with a Göttingen type low speed wind tunnel and the results are compared with discrete vortices calculation method. The balance test is performed at Re=3.5×105 and the pressure distributions over the wing surface are measured at Re=4.7×105. The followings are known: (1) the lift slope of a blunt trailing edge aerofoil is greater than the one of the sharp trailing edge NACA0012, (2) the pressure distributions upstream to the trailing edge cutting point are little changed by the cutting, and (3) the lift slope of a blunt trailing edge aerofoil is higher than the sharp trailing edge aerofoil for the same thickness ratio.