Aerospace Systems最新文献

This paper studies the reliability modeling of civil aircraft engine nacelles. Based on the fault record data of an aircraft over the years, the two-parameter Weibull model and the Cox proportional hazards model are used respectively. On MATLAB and SPSS software, reliability modeling was carried out for several important equipment of this type of aircraft. And it was tested in the fault prediction to verify the feasibility of the model and prediction method.

In this paper, the patterns of fatigue damage accumulation for a stringer panel and a panel with lattice reinforcement made of a polymer composite material (PCM) were studied using the Wim Van Paepegem calculation method. Both panels have the same overall dimensions, are made of the same material and are designed to carry the same compressive load. Based on the results of the calculations, the zones were determined in which the greatest loss of stiffness occurs in one of the components for both types of panels. The number of cycles to complete loss of stiffness for these components for each of the zones was obtained. It was found that in the stringer panel, the greatest loss of stiffness occurs in the layers of the stringer web and in the panel with lattice reinforcement in the zone where the diagonal ribs intersect. At the same time, it was found that in a lattice panel, these fatigue damage occurs under a smaller number of applied cycles than in a stringer panel.

Onboard measurement system, the function of which is to collect, record and process measurement information, performs these tasks by obtaining information from the sensors. However, the sensors are noisy, so it is necessary to combine multiple pieces of information to give a good accuracy to the signals provided by the onboard measurement system. The extended Kalman filter, which is one of the most widely used data fusion methods, is also one of the derivatives of the standard Kalman filter used for non-linear problems. On the other hand, the spline approximation, especially the cubic and Hermitian splines provide a very good and smooth estimate. It is known that the implementation of spline method is simpler than Kalman filtering. This paper describes an empirical comparative analysis of the extended Kalman filter and spline method. The impressive result is that a simple spline approximation in many cases performs better than a sophisticated Kalman filter.

Designers of small UAVs are often faced with a hurdle in the propeller selection stage in preliminary design due to the lack of simple yet accurate models to estimate small propellers’ performance (thrust coefficient, power coefficient, and efficiency variation with advance ratio). It might even seem impossible to have accurate propeller performance models as the performance depends on the propeller geometry, and small propellers have complex geometries that are not readily available. Nonetheless, by analyzing the performance data of over 170 propellers (diameters ranging from 2 to 18 inches) from different manufacturers, we show that: (a) the thrust and power coefficient curves can be approximated as second and third-order polynomials in advance ratio, respectively, and (b) the coefficients of these polynomials depend predominantly on the pitch ratio. Leveraging this observation, we develop novel empirical relations that determine the coefficients of the polynomial performance curves as functions of the propeller pitch ratio alone. The efficacy of the proposed performance estimation models is demonstrated by accurately predicting the performance curves of several propellers that were not used to construct the empirical relations. Further, using the developed empirical relations, we propose a method to select a suitable propeller that provides high efficiency for a given set of preliminary UAV design parameters like the required thrust and operating velocity.

This paper investigates a novel compound control scheme combined with the advantages of trajectory linearization control (TLC) and alternative enhanced composite nonlinear extended state observer (ECNESO) in presence external and internal disturbance. First, an improved generalized tracking differentiator (IGTD) is applied to realize differentiation and filtering for the reference command. Second, ECNESO are constructed to estimate the uncertainties acting on the LTV. In addition, combining the novel observer with TLC strategy, a method is developed to force the controlled output to track the reference signal, rather than just stabilizing it around zero. Moreover, for the first time, this paper gives a rigorous proof of enhanced extended state observer (EESO) for nonlinear systems. The proposed TLC- ECNESO strategy is guaranteed the robustness of closed-loop system in the presence of parametric uncertainties and internal and external disturbances, in addition, the simplicity of the proposed strategy can meet the real-time computational requirement in practical air vehicle control systems. Stability analysis verifies that all signals in the closed-loop system are uniformly ultimately bounded. Finally, numerical simulation studies demonstrate the feasibility and efficacy of the proposed method.

Arbitrary flange connection with metal seal, which has one or more wedge-shaped edges in its construction, is estimated in the article irrespectively of construction of flange connection and its parts. Raised question is about obtaining a method for choosing the optimal wedge angle according to the criterion of minimal leak of the sealed substance through the contact of the wedge-shaped edge of the seal with the flange. The scientific problem is solved by means of derivation and exploration of the permeability function of the contact of the wedge-shaped edge of the seal with the flange a function, showing the dependence of the leak of the sealed substance in conditional flow units on the angle of the wedge-shaped edge. Results of the research make it possible to increase the tightness of flange connections, mentioned before, without increasing of tightening force, and, as a result, without increasing of the mass of flange connection, and this is especially important in modern flying vehicles.

The use of composite materials for the smooth load-bearing wing box panels of low-capacity aircraft can increase their weight efficiency. The present study considers thin smooth load-bearing panels of anisotropic structure, which can be used as the upper load-bearing wing box panels of forward-swept wings. The case of the maximum bending moment acting on the wing is considered, with wing box panels primarily subjected to compression at insignificant torque shear forces. The paper aims to develop a procedure for determining the thickness of thin anisotropic panels while allowing for the post-buckling behaviour under the action of near-expected compressive and shear flows. In accordance with the methodology for designing load-bearing panels for the post-buckling state, an analytical solution to a geometrically nonlinear problem was considered for anisotropic rectangular panels with hinged support; a procedure was proposed for designing panels that relies on the limiting static stresses of the composite cover exhibiting post-buckling behaviour. The obtained analytical expression was analysed to determine normal membrane stresses, and an expression was presented to ascertain the minimum thickness of the panel. A special attention was paid to the problem of determining the potentially critical points of an anisotropic panel exhibiting post-buckling behaviour, in which stresses can reach the maximum absolute values. The proposed procedure can be used to ascertain the thickness of thin load-bearing anisotropic panels under compressive and shear forces.

A methodology and results of fatigue life assessment of a structure containing continuous welding joint under random kinematic loading taking into account the influence of residual welding stresses have been presented. Realizations of random stress processes in the welding joint area and dependences for amplitude repeatability of reduced regular stress cycles have been constructed on the basis of numerical simulation. Characteristics of durability of the structure by two theories of accumulation of fatigue damages have been determined. Significant influence of residual welding stress levels on durability is shown.

The coupled effect of dynamics and nucleation during supercooled droplet’s collision on superhydrophobic surface plays an important role in the anti-icing capability of different superhydrophobic surface, however, without any method to evaluate it. In this work, the impact-freezing behaviors of supercooled droplets on surfaces with different wettability, including two typical hydrophobic surfaces, were investigated experimentally. The morphology, size, velocity, and nucleation rate of freezing on each surface at different temperatures were extracted, based on which emphasis was put on discussing the discrepancy of freezing processes and the formation mechanism of freezing morphologies on different superhydrophobic surfaces. The main findings are: (1) The freezing morphology on superhydrophobic surface was independent of contact angle and supercooling degree, but depended on the surface roughness; (2) the interaction between the fast motion of unfrozen water and the generation of ice nucleus dominates in the formation of freezing morphology, while the ice growth process has less influence. On smooth surface, multiple ice nucleus generating before bounce impeded the fast retraction of droplet, forming irregular-hill freezing shape whose size enlarged with decreasing temperature. On rough surface, because of the later nucleation after retraction process finished, the freezing morphology showed convergent sphere shape with supercooling-independent freezing size; (3) considering more complicated impact dynamics, including breaking and bouncing, on different superhydrophobic surfaces, an impact-freezing model was established and could be used to estimate the average frozen spreading ratio.

This paper introduces and investigates several methods of filtering and delay synchronization in incremental control law structures. It is shown that proper filter and delay synchronization is of great importance for both the performance and stability of the control laws. It is derived how to synthesize complementary filters in case of sensor dynamics, sensor delays and internal control law filtering such as roll-off filters and notch filters. The complementary filters are compared to common synchronization approaches previously applied in incremental control laws. It is shown that the proposed methods are beneficial for Multiple Input Multiple Output (MIMO) systems in case that different delays and filtering is present in the different measurement signals. In case of strongly coupled input effectiveness, the synchronization on the actuator feedback may become even unstable, where the complementary filter approach recovers the design closed-loop behavior. In addition, it is derived how to initialize the complementary filters for a transient-free engagement in non-steady-state conditions. The results are compared in simulation with a roll rate control law for a fixed wing aircraft.