Journal of Aerospace Engineering

The mixing field in a supersonic cold flow past a set of compression–expansion ramps mounted at the downstream end of a strut, with staged injection at two tandem locations on the strut upstream of the ramps, has been experimentally investigated. Air and helium have been used to inject into a primary stream of air at an inlet Mach number of 2.0. Two test section geometries, one having a flow cross section twice that of the other, have been considered. The larger test section has wall struts as well as a middle strut, whereas the smaller one has the strut only in the middle. Terminal bulk pressure and wall static pressure measurements, and Schlieren visualization have been performed. The Mie scattering technique has been used to obtain the concentration contours of the injectant across the flow cross section at several axial locations downstream of the injection points. The results indicate better mixing with helium injection and less influence of the boundary layer along the test section walls with the larger test section, as expected.

The research used the transonic small disturbance theory to better understand the dynamic aeroelastic phenomena and factors that affect the onset of flutter and store induced limit-cycle oscillations (LCO) in the transonic regime. Several parametric studies of the flutter and LCO of an aircraft wing with underwing store in the transonic regime were conducted, as well as an investigation of the effect of inclusion of store aerodynamics on the onset of flutter. The flutter sensitivity was analyzed for the following store parameters: (1) location of underwing store center of gravity with respect to aerodynamic root chord; (2) location of underwing store along the span of the wing; and (3) underwing clearance (pylon length). The parametric studies indicated that as the store center of gravity is moved fore of the elastic axis, the flutter velocity of the wing increased. Also, as the store is moved towards the aerodynamic tip chord, the flutter velocity of the wing decreased. The research work also concluded that as the underwing clearance is increased, the flutter velocity of the wing decreased. In addition to these results, it also helped in understanding that addition of store aerodynamics had no significant influence on the flutter velocity of the wing. Also, studies were conducted to identify the onset of LCO for different configurations of underwing store and flight regimes (unmatched analysis), thereby identifying the parameters that induce LCO. The sensitive parameters that affect flutter and LCO are identified.

The present study estimates the critical/buckling loads of laminated composite rectangular plates under in-plane uniaxial and biaxial loadings. The formulation is based on the first-order shear deformation theory and von-Karman-type nonlinearity. Chebyshev series is used for spatial discretisation and quadratic extrapolation is used for linearization. An incremental iterative approach is used for estimation of the critical load. Different combinations of simply supported, clamped and free boundary conditions are considered. The effects of plate aspect ratio, lamination scheme, number of layers and material properties on the critical loads are studied.

This paper is concerned with self-powered, self-latching tube hinges, made by cutting three parallel slots in a thin-walled carbon fiber reinforced plastic tube with a circular cross section. Thus, a hinge consists of two short tubes connected by three transversally curved strips of material (known as tape springs). A particular tube hinge design is considered, with a diameter of about one-third that of the hinges used previously; this requires the tape springs to reach strains close to failure when the hinge is folded. Three analyses of the peak strains in a tube hinge are presented. The first analysis obtains general analytical expressions for the longitudinal fold radius of a tape spring and the associated peak fiber strains. The second analysis is a finite-element simulation of the folding of a single tape spring and the third analysis is a simulation of a complete tube hinge. It is found that the largest fiber strains in one- and two-ply hinges can be predicted analytically with very good accuracy. It is also found that the contact and interaction between the three tape springs that form a tube hinge, modeled in the third analysis, do not affect the peak strains significantly.

A genetic algorithm (GA), a well-known numerical method, is widely applied in different areas of optimal studies. It is found that if the solution-search space is wide or if the selected fitness function is highly nonlinear, the GA’s solutions can strongly depend on the set parameters, which include population size, crossover rate, mutation rate, and the remaining size of the parent in the GA. This paper combines the Taguchi experimental method, which serves as a rough search tool, with the GA, which serves as a fine search tool, to find the best combination of the GA parameters for different flight-control problems. The purpose of such a combination is to make control more robust and closer to the optimal solution. To demonstrate this new idea, the writers consider its application to different flight-control problems for the F-16 fighter by using autostabilization, linear quadratic regulator (LQR) and $H_{\infty }$ design. The simulation results not only achieve the expected optimal design for flight-control problems but also justify the reliability and feasibility of the combination of the GA and the Taguchi method.

The orbital motion of tethered satellites is a highly complex nonlinear problem. This investigation formulates a new method that significantly simplifies the dynamic analysis of tethered satellite systems. This is accomplished using the fundamental equation for constrained dynamic systems, which was formulated by Udwadia and Kalaba. As a result of this new method, a study of the periodicity of tethered satellite motion is conducted and an extension to formation flying satellites is made. With varying fixed tether lengths, the system motion seems to transition from periodic to quasi-periodic. The simplified method is also applied to the computation of the control force required for formation flight.