An improved algorithm is proposed to manage with the huge computation burden of the quaternion particle filter in aircraft attitude estimation. Based on the particle filtering frame, the new filter provides robust performance for nonlinear and non-Gaussian stochastic systems. And the posterior distribution of the new estimator is approximated as a new quaternion distribution to realize parallel computation. In addition, similar to the extended Kalman filter, this new method implements time update by replacing particles update with linear transformation to reduce computational complexity. Numerical simulations are carried out to compare the new algorithm to the extended Kalman filter and to quaternion particle filter in simulation results. The simulation results indicate that this estimation technique has faster convergence rate than the extended Kalman filter and takes less computation times than quaternion particle filter under the same accuracy as quaternion particle filter.

In this study, the basic aerodynamic characteristics of a Busemann biplane model in a low-speed wind tunnel were clarified by the wake survey technique. A low-speed wind tunnel of the blowdown type was used, and it had an exit nozzle size is in 1.5 m × 1.5 m. A wake measurement system and six-component balance system were installed in the test section. A five-hole probe was used in the wake measurement system to measure the velocity distribution. The Busemann biplane model was designed to cruise at Mach 1.7. The total length of the model was 742 mm, and the width was 556 mm. The shape of the fuselage was 76 mm square on a side, and the nose had a double-conical shape. The flow velocity was 20 m/s, and the Reynolds number derived from the mean chord length was 1.4 × 10⁵. The results of the study are summarized as follows. Based on the visualization of the wake flow, vortices were generated from the tips of the upper and lower wing elements of the biplane at an attack angle of α = 0°, but the vortices had an opposing rotation direction. Analysis of the wake data showed that locally induced drag was not generated at the wing tip. At α = 6° and 8°, the profile drag increased, probably due to the influence of the flow separation from the upper surface of the upper wing element. However, the total lift coefficient increased with an increasing angle of attack, even at α > 8°. Therefore, it can be concluded that the biplane lift is mainly generated by the lower wing elements.

Two types of wing geometries imitating wings of birds in gliding flight are analyzed with the vortex lattice method in terms of lift-drag ratio and root bending moment while varying the joint positions and joint angles under the constant lift coefficient and constant flight velocity conditions. One geometry is, what is sometimes called, a gull wing which has a dihedral inner wing and horizontal outer wing, named “DH wing.” On the contrary, the other geometry is a drooped wing which has a horizontal inner wing and anhedral outer wing, named “HA wing.” The lift-drag ratio of the HA wing becomes larger when the joint of the anhedral outer wing is closer to the wing tip with a larger anhedral angle, while the root bending moment of the HA wing becomes smaller when the joint of the anhedral outer wing is closer to the wing root with a larger anhedral angle. In contrast, the DH wing has no combination of a joint position and joint angle to improve the lift-drag ratio, and it is found that the HA wing effectively contributes to the reduction of the root bending moment and the lift-drag ratio compared with the DH wing.

The penetration of sonic booms into the ocean and an estimation of the extent of their influence are important topics for supersonic and hypersonic aviation. Most prior studies were conducted assuming a flat-water surface. However, it is known that the effect of the surface waviness is not negligible in the case of real ocean environments. In the present study, the numerical method analyzes the two-dimensional flow field of sonic boom propagation across the air and water is proposed. When the flight Mach number of an aircraft is higher than 4.4, the underwater flow field becomes supersonic, and a sonic boom is generated there. The numerical results show that, in the underwater subsonic regime, the penetrating waves have the form of evanescent waves under either flat or wavy water surface, but the waviness-induced ripples with the smaller decay rate are responsible for deeper penetration. In contrast, in the supersonic underwater flow, the surface waviness hardly affects the penetration depth of underwater sonic booms, although it can slightly weaken the boom intensity. The effect of the amplitude of surface waviness on the underwater penetrating wave was also investigated.