Journal of Aerospace Engineering

Future lunar explorations require a thorough understanding of the geotechnical properties of lunar soils. However, the small amount of lunar soil that was brought back to earth cannot satisfy the needs. A new lunar soil simulant, NU-LHT-2M, has been developed to simulate lunar regolith in the lunar highlands region. It is characterized to help the development of regolith-moving machines and vehicles that will be used in future missions to the moon. The simulant’s particle size distribution, specific gravity, maximum and minimum densities, compaction characteristics, shear strength parameters and compressibility have been studied; and the results are compared with the information about lunar regolith provided in the Lunar Sourcebook.

Benchmark stacking sequence configurations with up to 21 plies are presented for laminates with properties similar to conventional materials, and against which new forms of coupled laminate behavior can be assessed. The benchmark configurations include fully uncoupled extensionally isotropic laminates and fully isotropic laminates, together with a special class of uncoupled laminate, possessing matching elastic properties in both extension and bending; more commonly referred to as a quasi-homogeneous orthotropic laminate. The concept of an equivalent isotropic laminate is also introduced as a universally applicable datum, useful for characterization of ply number groupings for which no benchmark configurations exist. Most of the benchmark configurations are found to possess nonsymmetric stacking sequences, which also serves to demonstrate that stacking sequence symmetry is neither sufficient nor necessary for fully uncoupled laminate designs. Finally, dimensionless parameters are provided for each stacking sequence, from which the $\mathbf{A}\mathbf{B}\mathbf{D}$ matrix is shown to be readily derived.

The flutter analysis of swept aircraft wings carrying a powered engine is presented. Because of the powered engine, both concentrated engine mass and the thrust force terms are combined in the governing equations which are obtained using Hamilton’s principle. Heaviside and Dirac delta functions are used to precisely consider the location and properties of the engine mass and the thrust force. The wing performs as a classical beam; and the structural model, which incorporates bending-torsion flexibility, is used. Also, Peter’s unsteady aerodynamic pressure loadings are considered and modified to take the sweep effects into account. The Galerkin method is subsequently applied to convert the partial differential equations into a set of ordinary differential equations. Moreover, the numerical results are compared with published results and excellent agreement is observed. Numerical simulations indicating the significant effects of the sweep angle, the thrust and the design parameters such as the mass ratio and the engine attached locations on the flutter boundaries are presented.

In this work, a mathematical model to study the dynamic behavior of a trike ultralight aircraft is developed. This is done because, to the best of the writers’ knowledge, no specific theories are available for powered hang gliders. To do that, in order to take into account the engine thrust, the necessary changes have been made on models developed for hang gliders. The trike, which is a particular case of powered hang glider, is modeled as a compound system made of a wing and an undercarriage. The case of rigid wing, made of composite materials, is considered in the present work. Equilibrium governing equations are written, the trim conditions are evaluated, and the fixed control dynamic stability is investigated for both longitudinal and lateral motion. After that a modified wing configuration, with two additional vertical fins, is investigated and compared. The dynamic response to pilot controls is evaluated to complete the analysis.

In this paper, a new nonlinear control strategy is proposed for hovering control of planar vertical takeoff and landing (PVTOL) aircraft. The control of this typical nonlinear, nonminimum-phase system is treated as a robust control problem. The robust control design is then converted to an equivalent optimal control design so that both stabilization and performance can be guaranteed. The primary contribution of this work is to provide a closed-form solution to the resultant nonlinear optimal control problem by employing a recently emerging nonlinear control approach, called the $\theta -D$ technique. The $\theta -D$ technique is based on optimal control theory and derived from an approximate solution to the Hamilton-Jacobi-Bellman equation via a perturbation process. This formulation will not only enhance the system performance but also simplify the design process in that robustness and optimality are integrated in one unified optimal control framework. Furthermore, the closed-form control law is very suitable for onboard implementation. The effectiveness of the proposed method is demonstrated by simulation results and comparison studies with a similar linearization based optimal control formulation.

A single component accelerometer-based force balance is developed, calibrated, and used for high enthalpy applications. Functionality of this force balance, for such applications, is demonstrated for the first time during high enthalpy tests in a newly established free piston- driven shock tunnel, HST3, using a 60° apex angle blunt cone model at 0° angle of incidence. Usefulness of this force balance is also confirmed, for much complicated high enthalpy flow situations, during the drag reduction studies with counterflow supersonic jet from the stagnation point.

Aerospace, aviation particularly, need, in any era, the strongest and most thermostable materials available, often at nearly any price. The space elevator, space ships (especially during atmospheric reentry), rocket combustion chambers, thermally challenged engine surfaces, hypersonic aircraft materials are better now than any available, with undreamed performance as the reward if obtained. As shown in this research, the offered new material allows to greatly improve all characteristics of space ships, rockets, engines, and aircraft, and design new types space, propulsion, and aviation systems. At present the term “nanotechnology” is well known—in its ideal form, the flawless and completely controlled design of conventional molecular matter from molecules or atoms. Such power over nature would offer routine achievement of remarkable properties in conventional matter, and creation of metamaterials where the structure not the composition brings forth new powers of matter. But even this yet unachieved goal is not the end in material science possibilities. The writer herein offers the idea of design of new forms of nuclear matter from nucleons (neutrons, protons), electrons, and other nuclear particles. He shows this new “AB Matter” has extraordinary properties (for example, tensile strength, stiffness, hardness, critical temperature, superconductivity, supertransparency, zero friction, etc.), which are up to millions of times better than corresponding properties of conventional molecular matter. He shows concepts of design for space ships, rockets, aircraft, sea ships, transportation, thermonuclear reactors, constructions, and so on from nuclear matter. These vehicles will have unbelievable possibilities (e.g., invisibility, ghostlike penetration through any walls and armor, protection from nuclear bomb explosions and any radiation flux, etc.). People may think this as fantasy. But 15 years ago most people and many scientists thought nanotechnology was fantasy. Now many groups and industrial laboratories, even start-ups, spend hundreds of millions of dollars for development of nanotechnological-range products (precise chemistry, patterned atoms, catalysts, metamaterials, etc.) and we have nanotubes (a new material which does not exist in nature) and other achievements are beginning to come out of the pipeline in prospect. Nanotubes are stronger than steel by a hundred times—surely an amazement to a 19th century observer if he could behold them. Nanotechnology, in near term prospect, operates with objects (molecules and atoms) having the size in nanometer $\left({10}^{-9}\text{m}\right)$ . The writer here outlines perhaps more distant operations with objects (nuclei) having the size in the femtometer range ( ${10}^{-15}\text{m}$ , millions of times smaller than the nanometer scale). The name of this new technology is femtotechnology.

A method and facilities for delivering payload and people into outer space are presented. This method uses, in general, engines located on a planetary surface. The installation consists of a space apparatus, power drive stations, which include a fly-wheel accumulator (for storage) of energy, a variable reducer, a powerful homopolar electric generator, and electric rails. The drive stations accelerate the apparatus up to hypersonic speed. The estimations and computations show the possibility of making this project a reality in a short period of time (for payloads that can tolerate high $g$ forces). The launch will be very cheap at a projected cost of $3–$5/lb. The authors developed a theory of this type of the launcher.

This paper presents a new navigation guidance law for a pursuer to intercept a moving target with a prescribed impact direction in space. The proposed guidance law makes the pursuer follow a relatively circular trajectory with respect to the target. The performance of the proposed law does not depend on initial arrangement geometry and the magnitude of acceleration command is essentially bounded even at impact time. Numerical simulations confirmed technical soundness of mathematical developments and good performance of our new law even for maneuvering targets.

The nose cap demonstrator named Nose_2 has been tested for the second time in the plasma wind tunnel (PWT) facility which is part of the sharp hot structure (SHS) technology project, focused on the assessment of the applicability of ultrahigh temperature ceramics (UHTC) to the fabrication of high performance vehicles and SHS for reusable launch vehicles. In this paper the FEM based thermal analyses, carried out for the rebuilding of this PWT test, are presented. Experimental data measured in the PWT have been compared with numerical ones in order to validate the FEM model and to help in interpreting the experimental test itself. The knowledge on the physical phenomenon under investigation has been greatly improved, thanks to the synergy between numerical and experimental activities. In particular, a qualitative study of the modeling of the tip-dome interface has been performed in order to estimate the thermal contact resistance that heat flux encounters in passing through the demonstrator. The correlation between numerical and experimental temperature curves has been found to be satisfactory for both internal and surface temperature distribution, and the FEM model was found reliable in reproducing the thermal behavior of the nose cap.

Flutter control of smart composite plates under subsonic airflow is investigated in hygrothermal environment. The active fiber composite (AFC) which is more effective and adaptive than the conventional monolithic piezoelectric material is used in the present analysis to control the undesirable response due to hygrothermal effect. The velocity and displacement feedback control algorithm are subsequently established to reduce actively the response of the plate. Numerical examples of isotropic and laminated composite plates with or without hygrothermal effect are presented. It is observed that the structures become weak in the presence of hygrothermal load in the form of reduced flutter boundary. The flutter boundary can be enhanced with the help of AFC. The parametric study is performed and it is observed that the flutter boundary can be enhanced with the help of a feedback-control system activating the AFC. Therefore, one can say that the AFC is effective to enhance the flutter boundary of the present aeroelastic structure in the hygrothermal environment.

Flutter-critical velocity is usually estimated from deterministic analyses by assuming that physical and geometrical parameters are perfectly known. However, aleatory and epistemic uncertainties, especially those associated with the definition of material properties, are intrinsically present partly because of the random nature of every physical system and partly because those properties are evaluated from a finite number of observations. The paper focuses on the combination of structural reliability analysis with aeroelastic simulation to give a correct flutter speed evaluation for design purposes. Two typical aeronautical test cases have been considered: (1) an isotropic material structure and (2) a composite material structure. Different computational methodologies (classical and developed by authors) have been coupled with a simple two-dimensional aeroelastic model to study the qualitative consequences of uncertainty in determination of critical flutter speed and to provide a comparison between different reliability methods such as Monte Carlo (MC) simulation, first-order reliability method (FORM), second-order reliability method (SORM), and response surface by fixed or adaptive order regressor coupled with FORM and MC. For the isotropic case best prediction of MC results is always obtained with high-order response surface (HORS) (coupled with both MC and FORM) above all for low levels of coefficient of variation (C.V.) (10% or under) for which results are basically equivalent. FORM and SORM give acceptable results only above cumulative distribution function values of 35–40%. Only response surface with a fixed polynomial order always gives totally misrepresentative results even for very low variability of basic physical quantities. For the composite case, no generic conclusion can be made about the influence of physical quantities on uncertainty propagation because it strongly depends on layup configuration. From a design point of view, variability in composite materials is even more important because, in a general sense, more variables are involved. The flutter speed reductions reveal greater slope of the linear regressors with respect to the isotropic counterpart, with stronger differences when the uncertainty afflicting the basic random variables is higher.

The reconfigurable flight control system was developed, applying a nonlinear aircraft model following control algorithm to support the autopilot. The model of a six degrees of freedom airplane with nonlinear aerodynamics and second-order dynamics of control system actuators was supplemented by aircraft autopilot based on classical control laws. The autopilot commands the aircraft in normal operations. In failure cases, the control system reconfiguration is performed using comparison of control external loads on damaged aircraft with loads in undamaged aircraft operation. Fuzzy logic method produces the control signals preventing the consequences of failures. The objective of reconfiguration is to continue the performed flight, including maneuvers, and, if this is not possible, to obtain the steady flight. The aircraft simulation model was tested for consistency with the expected flight performance. The selected autopilot functions were validated and reconfiguration applied in selected cases of failures. The final simulations proved the efficiency of reconfiguration.