Moscow Aviation Institute

All modern aircraft are designed in accordance with the requirements of the certification basis (CB). FAR.25 contains numerous clauses that impose requirements on the strength of the main landing gear (MLG) hinge structure. In this paper, two typical landing gear hinge configurations were identified, an analytical analysis was conducted, and the main analytical formulas for determining reactions at the landing gear hinge nodes were derived, with the goal of creating a simple mathematical model. Trivial algebraic methods, such as solving statically indeterminate frames, were used to determine the main reactions. This model allows for the creation of a model for optimizing the landing gear hinge design, the main goal of which is to identify hazardous areas that do not meet the requirements for safe MLG failure when the airframe load is exceeded. At the same time, this mathematical model is planned to be used to determine reactions for the design of durable structures in the early stages of aircraft design.

An Erratum to this paper has been published: https://doi.org/10.1134/S1063785026010013

The work is devoted to numerical simulation of the problems of flowing around moving bodies. The main equations of heat and mass transfer of a viscous compressible gas are provided. To describe the flow over the object with moving boundaries, a motion velocity vector is introduced into the numerical scheme of the finite-volume method. The computation method on meshes with overlapping (or overset grids) was considered as a simulation approach. Key stages of the proposed computation technology are given. To reduce the computational complexity of generating an interpolation stencil, the use of hierarchical data structures is proposed. Reconstruction methods described in the work are based both on well-known algorithms for interpolating computed values, and original methods based on the use of gradients of computation fields and on the use of a four-point stencil. To demonstrate the operability of the algorithms, the problem of subsonic flow around the two-link airfoil section and the task of separating the store from the wing with the pylon in the transonic flow of a compressed gas are considered. The primary objective of this work is to develop an efficient numerical model based on unstructured overset grids for solving applied problems of fluid-moving body interaction in the interests of the aviation industry. The analysis of the obtained results for the separation problem has shown the advantage of the proposed reconstruction approaches with respect to standard interpolation methods, which made it possible to increase the accuracy of prediction of aviation angle dynamics by more than 15

The paper proposes an approach for fast tuning the nonlinear attitude control system applied for a quadcopter. First, a mathematical model of quadcopter’s motion is estimated by a simple identification process using a low-cost test bench. After that, the controllers’ parameters are computed via optimization-based synthesis using simulation-in-loop framework. The proposed approach therefore does not require the development of a complex mathematical model built on the theories of aerodynamics, flight dynamics and DC motors, as well as geometry and mass/inertial properties of a quadcopter. There is also no need to apply any algorithm for nonlinear control system analysis. Due to its simplicity, the proposed approach can be used for quick synthesis of new control systems or adjusting the existing ones. The adequacy of the proposed approach is confirmed by bench studies of identification accuracy and control performance. Besides this, the paper also firstly describes the mathematical principle of the square-root controller implemented in well-known flight controller software like Ardupilot.

Testing the Kerr spacetime solution of general relativity (GR) has increasingly become a requirement with the recent observations of black hole shadows and gravitational waves. In this context, we examine the physical properties of the shock cone formed by Bondi-Hoyle-Lyttleton (BHL) accretion around a black hole or a naked singularity using the Johannsen-Psaltis (JP) metric, and compare them with those of the Kerr metric solution. We demonstrate how these properties vary with the metric's deviation parameter (eta). We find that when a/M = 0.9 and a black hole is formed for eta < 0, as the deviation parameter decreases, the opening angle of the resulting cone becomes smaller, leading to a shift of the resulting quasi-periodic oscillations (QPOs) from low to high frequencies. On the other hand, for eta > 0, it is observed that the shock cone forms around the naked singularity at small values of eta. Furthermore, at large eta values, the cone evolves into a torus-like structure under the influence of the strong gravitational field. In the case of |eta|similar to 8, perfect harmonicity is observed, along with possible resonances such as the 3:2 ratio, consistent with observations. Additionally, for the case of a slowly rotating black hole (a/M = 0.4), a behavior resembling the bending of the shock cone due to the curvature of spacetime in the presence of a strong gravitational field is also observed at large n values, similar to what is observed when the spin parameter of the Kerr black hole is a/M >= 0.9. Finally, we have calculated fundamental frequencies to investigate QPOs around rotating JP black holes. We use Markov Chain Monte Carlo (MCMC) analyses to obtain constrained values for the black hole mass, spacetime deformation, and QPO orbits around black hole candidates at the center of the Milky Way and M82 galaxies, and microquasars XTE J1550, GRO J1655-40,& GRS 1915-105, using QPO data observed in them. Overall, the JP metric with moderate deviation (|eta| approximate to 8) is more consistent with the observed QPO frequencies and resonance structures than the pure Kerr metric, suggesting that small deviations from Kerr spacetime may more accurately describe strong field gravity around astrophysical black holes.