Journal of Aerospace Engineering

The early detection of cracks, fatigue, corrosion, and structural failure in aging aircraft is one of the major challenges in the aircraft industry. Common inspection techniques are time consuming and hence can have strong economic implications due to aircraft downtime. As a result, during the past decade a number of methodologies have been proposed for detecting structural damage based on variations in the structure’s dynamic characteristics. This paper describes the implementation of the natural excitation technique (NExT) combined with the eigensystem realization algorithm (ERA) to determine the dynamic characteristics of a T-34A Mentor acrobatic category aircraft and a modified DC-3 cargo/transport category aircraft. In-flight acceleration data were processed using NExT-ERA to monitor the predominant natural frequencies and associated mode shapes of the aircraft for varying flight conditions. The results show the effectiveness of this modal identification methodology and the possibility of implementing it in a real-time structural health monitoring system for aircraft.

The purpose of this paper is to present a new systematic procedure for synthesis of nonlinear controllers for single-input multiple-output systems. The procedure is based on several describing function models of the plant, and the nonlinear gains are obtained via an inverse describing function technique. The procedure and associated software are applied to control the bank angle of a cruise missile. The results are compared with a linear controller and another nonlinear controller that was previously reported in the open literature; it is shown that the developed procedure has resulted in a less conservative design (i.e., performance is not sacrificed to assure absolute stability).

For the success of planned missions to the moon in the near future, it is essential to have a thorough understanding of the geotechnical behavior of lunar soil. However, only a limited amount of information is available about geotechnical properties of lunar soils. In addition, the amount of lunar soils brought back to Earth is small. To help the development of new regolith moving machines and vehicles that will be used in future missions, a new lunar soil similant JSC-1A has been developed. A group of conventional geotechnical laboratory tests was conducted to characterize the geotechnical properties of the simulant, such as particle size distribution, maximum and minimum bulk densities, compaction characteristics, shear strength parameters, and compressibility.

Based on momentum conservation principle of space manipulator, this paper presents precapture configuration of space manipulator capturing object. Two unique precapture configurations, “straight-arm capture” (SAC) and “generalized straight-arm capture” (GSAC), were proposed based on the single-arm system; then GSAC was extended to the dual-arm system and the corresponding angular relation was obtained. This configuration satisfies GSAC and can reduce the coupling angular momentum during capture operation and the burden of postimpact control. This avoids the limitation of joint velocity when controlling the compound (manipulator and object) and guarantees the stability of system. The simulation results show the effectiveness of this method.

This review-cum-research paper reports the effects of temperature and time exposure on the material behavior of the aerospace aluminum alloys currently in use in subsonic and supersonic aircraft. The research reported in this paper involves experimental study of the microstructural characterization and temperature effects on the hardness behavior of the age-hardenable 2024-T3 aluminum alloy; the latter was acquired by one of the authors from Royal Malaysian Air Force (RMAF) aerospace industry. The ALCLAD 2024-T3 alloy is being used in C-130 Hercules aircraft by the RMAF. Recent research on various aluminum alloys being used and being considered for application in Concorde is also reviewed.

Mathematical models of a biped and quadruped walking are considered. The planar five-link biped consists of a one-link trunk and two identical two-link legs. In the single support motion (swing phase), the biped has five degrees of freedom and is described by a system of nonlinear ordinary differential equations of the 10th order. These equations are written in a visible matrix form. A seven-link planar biped with massless feet is also considered. In this paper, the swing motion of the biped is assumed a ballistic (passive) one. There are no active torques in the interlink joints during the single support motion—only the gravity force and ground reaction forces are applied to the biped. The problem of design of ballistic swing motion is reduced to the boundary-value problem for the system of nonlinear differential equations with given initial and final configurations and the duration of the half-step. It is assumed that there is no friction in the interlink joints (note that the friction in the human joints is very small). Therefore, in the ballistic swing motion the complete energy of the system (kinetic energy plus potential one) is conserved and the system has the energy integral. Due to this fact some properties of symmetry of ballistic motions are proved. Linearized model can be reduced to the canonical Jordan form. Then the linear boundary-value problem can be solved analytically. Using numerical investigations of the linear model we have animated the biped walking, which occurs “similar” to the human gait: the transferring leg moves over the support, the legs bend with knees forward, and the trunk makes one vibration during one half-step. All these features have not been prescribed beforehand in the statement of the problem. Iteration process is used to solve the nonlinear boundary-value problem. For some cases, several solutions of this nonlinear problem are found numerically. The symmetry properties of the ballistic motions help to find numerically the solutions of this complex nonlinear problem. The ballistic motion is also designed numerically for the three-dimensional biped model with 6, 8, 9, and finally with 11 degrees of freedom. The double-support phase is assumed an instantaneous one. During this phase there is a collision of the transferring (swing) leg and the support. Active impulsive torques are applied in the interlink joints at this instant. These impulsive torques and ground reaction forces are described by delta functions of Dirac. Thus, with this impulsive control, most of the efforts are applied in the double-support phase. Formulas for the energy cost of impulsive control actions have been found. Some problems of optimal distribution of the impulsive actions between the joints are discussed. A planar seven-link model of biped with arms is considered. This model consists of a one-link trunk, two identical one-link arms, and two identical two-link legs with point feet. Ballistic gait of this biped model is studied. The goal of this study is to find the optimal amplitude of the arms swinging, minimizing the energy consumption. We show numerically the existence of the optimal amplitude of the arms swinging. Ballistic walking of a quadruped is investigated too. Three types of quadruped gaits, bound, amble, and trot, are considered. For each kind of the gait, ballistic locomotion is designed and energy consumption is evaluated.

A virtual reality simulation system for a manned maneuvering unit (MMU) and a training system for an astronaut space walk is introduced. The system can simulate an astronaut’s outer space walk by means of manipulating the MMU, and it also can be used as a training environment by taking advantage of virtual reality properties of imagination, interaction, and immersion. As in microgravity space, an astronaut’s moving limbs cause changes in the MMU posture; these changes result in great offsets to correct direction and have a great effect on the MMU’s manipulation performance. A multibody astronaut model is developed by using relative coordinates according to the motion characteristics of an astronaut equipped with MMU. Motion information on the user’s limbs are captured by means of a motion capture subsystem and are mapped to an astronaut in virtual environment to simulate the astronaut’s limb motions while the astronaut is navigating in outer space. It is an open-chain system for an astronaut multibody model. As an astronaut can control his limbs, the whole system dynamics is a hybrid forward and inverse dynamic problem. Recursive dynamic formulations of a previous method are introduced to solve the forward dynamic problem. For the inverse dynamic part, because the system can get motion characteristics of parts of the relative coordinates, unknown generalized driving forces are applied on these known relative coordinates. All the unknown generalized driving forces and unknown relative coordinates can be combined in a set of hybrid dynamic formulations based on a forward dynamic formulation. The motion characteristics of an astronaut multibody model can be obtained by solving the hybrid formulations. Finally, some simulation results for astronaut forward-flying mode with moving limbs are presented; these results show that the movement of an astronaut’s limbs has great effects on astronaut navigation and MMU manipulation performance. The multibody astronaut model has the capability of simulating real space walk with an MMU equipped astronaut.