In future mobile communications satellites, it is important to increase the transmitting and receiving performance of the satellite to permit the use of small and economical earth terminals. This paper analyzes the relationships between the effective mass of the communications system and the number of antenna beams and transponders. We present a configuration that minimizes the mass of a multi-beam mobile communications satellite by using elliptical beams, with more beams for receiving than for transmitting. We optimize the transponder output power, the size of the elliptical antennas, and the number of transmitting and receiving beams. The minimum mass achieved is smaller than the effective mass of conventional communications equipment using multi-circular beams.
A computer-aided design system is developed for the preliminary design of aircraft by integrating the various design operations with an object-oriented programming approach. The design process of aircraft consists of determining the values of principal particulars, evaluation of the estimated performance of the designed object, and the re-design process based on the evaluation. In the system, various kinds of knowledge and data used in the preliminary design and their manipulations are modularized as objects and their methods, and they are integrated for supporting designer's handling of a design. The integration include the functions of geometric modeling and data retrieve. Moreover, the system has a function of interactive optimization for supporting designers especially in the phase of re-design. The system is applied to the design of a commuter aircraft in order to check its effectiveness.
This paper concerns with the results of an experimental study on dynamic load characteristics in parachute inflation at a subsonic speed. The unsteady drag of the parachutes in the process of inflation is measured in a wind tunnel at M=0.2, and the opening shock load is examined in detail with emphasis on the effects of porosity and size of the models. It is shown that the circular vents near the edge of the canopy are more effective than the slit vents to reduce the opening shock load without considerable decrease of drag in the steady-state. Detailed examination reveals that the model geometry as well as descending speeds has no serious influence on the coefficients of the opening shock load Cm and the opening time Ct, if both Cm and Ct are defined by use of the effective references calculated from the concept of an equivalent parachute, which has a circular plane canopy with the reduced area obtainable by subtracting porous area from the geometric one.
The purpose of this study is to establish the method for decisions on proper inspection intervals needed to maintain reliability of aircraft structures using the parameter values estimated from inspection results in service by Bayesian theorem. Attention is focused on only fatigue damage in this study, and inference is made for uncertain factors related to the probability of detection and initiation of cracks. It is demonstrated that the reliability is possibly kept above a predetermined level, by updating inspection schedule according to the already performed inspections. Applying the model to the economical consideration for maintenance procedures, a preliminary study is attempted to evaluate the effect of nonrepaired crack length. Numerical examples are carried out to demonstrate the application of the present analysis.