The pre-cooled turbojet (PCTJ) engine which will be installed in a hypersonic transport has been studied in the Japan Aerospace Exploration Agency. The takeoff noise reduction is one of the most important technical issues in the development of a high-speed propulsion. Engine/airframe integration is quite important in terms of not only the propulsion performance but also the acoustics radiation. In this study, the effect of the engine number, engine spacing and ramp length on the noise radiation characteristics from the multiple jet is investigated. Acoustic data for the ramp, sidewall and cowl directions are acquired. For sidewall direction cases, the sound intensity is not proportional to the number of engines; smaller than simple expectation since nearby jet shields the noise from the far side jet. For cowl direction cases, the sound intensity is also smaller than simple expectation since turbulent kinematic energy generation is hindered between the neighboring jets.

In multi-cycle operation of Microwave Rocket, the influence of the density non-uniformity formed in a thruster on the resulting propulsive impulse remains unclear. In order to analyze the thrust performance in a thruster containing a hot residual gas, a new millimeter-wave discharge propagation model was developed. By coupling it with a reed-valve's fluid-structure interaction model, a full-scale analysis up to the second cycle operation was performed changing the thruster radius from 16 mm to 40 mm with the fixed millimeter-wave beam radius of 20.4 mm. As a result, the partial filling rate monotonically decreased with the thruster radius, while the hot residual gas at the center of the thruster was most prominent in the case with the radius of 24 mm. With a smaller radius, the inflow gas from the reed valve directly reached the center, and with a larger radius the inlet gas was transfered by vortices formed inside the thruster. During the second cycle, the decrease in the propulsive impulse was most noticeable for the case with the radius of 24 mm, illustrating that the thrust performance was strongly associated with the residual gas density at the center of the thruster, rather than the partial filling rate.

Aircraft maintenance costs are the third largest component after fuel and equipment costs. Maintenance costs must be managed without compromising safety and must not be excessive. The structure of maintenance costs is complex, as they are affected by many variables, such as aircraft size, operating type, and aircraft age, and studies focusing on maintenance costs have been limited. This study proposes an econometric model of maintenance costs using panel data analysis and describes the structure of aircraft maintenance costs, focusing on airline homogeneity and heterogeneity. Maintenance cost data from 2006 to 2018 for U.S. airlines are used. We constructed a model using panel data analysis and decomposed the parameters into homogeneous and heterogeneous elements. Defining three common variables and using their coefficients as the homogeneity parameter, we showed that more than 90% of the variation in airline maintenance costs can be explained. We also analyzed heterogeneity by applying our original two-dimensional fixed effects estimation matrix. The results show that the heterogeneity of airline maintenance costs depends on factors that depend on the type of aircraft in operation and the number of aircraft in the fleet.

The authors have proposed the evaluation methodology in early design phase for the feasibility of novel instrument layout to be applied for the next generation aircraft, based on the MIL-HDBK guideline. However, the methodology has not been widely evaluated for its effectivity yet whether it could facilitate the critical design issue findings and mitigates the risk for late issue finding. This paper evaluated the effectivity of proposed methodology by applying it for the novel instrument layout design and comparing the result with (1) the one of the conventional layout design, and (2) with pilots' eye trajectory data measured by camera through simulated flight, and with (3) the result of conventional methodology which is typically conducted under early design phase. The results showed that the methodology (1) identified the critical design issue and the idea for solution, (2) had a data which is consistent with the measured data, and (3) improved bias and coverage than the one of conventional methodology. Therefore, it confirmed that proposed methodology is potentially effective to facilitate the critical design issue findings and mitigates the risk for late issue finding, in order not to bring the potential issue over in service but to keep flight safety.

One-degree-of-freedom (1 DOF) thrust stands, which measure only one direction of thrust, have been mainly used for the evaluation of propulsion systems in microspacecraft. Since actual spacecraft may generate an unintentional thrust vector and a torque vector, there has been previous research on a magnetic levitation thrust stand with 6 DOF. However, there is a limit to the weight that could be levitated. In the 6 DOF thrust stand of this study, the weight limit was relaxed by suspending the spacecraft mounting plate with 3 springs. The simple cold gas jet module was used to evaluate its performance by measuring all forces and torques in 6 directions. As a result of the experiment, the measurement uncertainties of the thrust stand were evaluated as 0.520mN force in the main thrust direction, 0.221mN force in the transverse direction, and 0.289mN・m torque. The main thrust was measured at 43.5mN, which was in good agreement with the theoretical value.