An ultra high vacuum diode laser welding(UHVDLW) system in which a diode laser(DL) welding can be performed in the ISS orbital pressure 10-5Pa was developed for investigating the effect of an environmental pressure on a DL welding phenomenon. The DL welding experiments with power density around 100kW/cm2 were conducted on 304 stainless steel in pressure levels between 105Pa and 10-5Pa. Although a laser-induced plasma plume is observed during welding in the environmental pressure 105Pa and 103Pa, no laser-induced plasma plume is found in the pressure ranging 10Pa to 10-5Pa. A formation of melting process(weld pool shape) with this experimental condition is a keyhole melting type or a transition melting type in the environmental pressure 105Pa and 103Pa. But, a melting process in the pressure lower than 10Pa changes to a heat conduction melting type. The penetration depth showed a decrease with the environmental pressure down to 103Pa and then appears to no change in a pressure lower than 10Pa. Establishment of space DL welding technology needs to develop a suppression technology of a metal vapor deposition to an optical device.
The focus of this study is on PIO to be solved in the development of modern flight control systems. Especially, it is important to investigate the fully-developed PIO as a worst case for the safety of piloted airplanes and to analyze the limit cycle phenomenon including the effects of actuator rate limiting and feedback control loop. Lateral-directional flight control system was taken for instance, this paper proposes a technique to design the feedback control law to have a positive effect on PIO to decrease the amplitude of the oscillation.
Reliability estimation using the dispersive, binominal distribution method has been traditionally used to certify the reliability of liquid rocket engines, but its estimation sometimes disagreed with the failure rates of flight engines. In order to take better results, the reliability growth model and the failure distribution method are applied to estimate the reliability of LE-7A engines, which have propelled the first stage of H-2A launch vehicles.
Wind tunnel tests were conducted to investigate lift to drag ratio improvement by the leading-edge flap the outboard wing on an SST model at transonic regions. Force measurements and surface pressure measurements were performed for the SST model with and without outboard leading-edge flaps of 5 and 12.2 degrees deflection angles. The lift to drag ratio was improved due to a reduction in the drag component when flaps deflected, because the flow was attached to the leading edge surface of the wing. The optimum flap deflection angles to attain the maximum lift to drag ratio at a fixed lift coefficient were estimated using experimental results.
A continuous-thrust guidance algorithm suitable for a formation flying of a large number of spacecraft having electric propulsion systems are discussed. This algorithm generates continuous-thrust transfer trajectory between any two arbitrary states, which can be optimized in term of total fuel consumption for a formation changing. The algorithms are effective not only in term of fuel consumption but also in term of information quantity to be shared among member spacecraft. Moreover taking computational simplicity into consideration, a quasi-optimal continuous-thrust guidance algorithm are derived.
This paper describes the mechanism of the non-slender wing rock that occurs on a 45° delta wing, by focusing on its unsteady aerodynamic characteristics. In free-to-roll test the wing motions showed irregular oscillations the amplitude of which varied with time. In some cases, the wing suddenly changed its trajectory in the middle of the oscillation, and came to stop at roll angle φ=0°. The static rolling moment is quite nonlinear in characteristics, the profile of which has many critical states. The balance test for constant roll rate motion showed that the amount of time lag was not constant for roll angle, and that it is not linear for roll rate. The results of numerical simulation using the experimental data suggest that it is important to take into account the trajectory of the motion for a better understanding about the unsteady aerodynamic characteristics, associated with the non-slender wing rock.
A method to predict the change of the cushion pressure and the bag skirt configuration of ACV in heave is proposed. It is a quasistatic analysis based on the analysis of the skirt configuration in static operation that was proposed by the present authors. The cushion pressure depends on the velocity of motion as well as the hoverheight. It is higher in the downward motion than in the upward motion with the same hoverheight. As the model approaches the ground surface, the bag skirt is pushed outwards and also upwards but the hoverheight still decreases. This produces the increase of the cushion pressure that also flattened the configuration of the bag. The outward displacement of the bag produces the additional increase of the cushion base area and increases the restoring force. The stability is then increased.