Aircraft Engineering and Aerospace Technology

Amir H. Hashemian; Mohammad H. Kargarnovin; Jafar E. Jam

doi: 10.1108/00022661111120944pmid: N/A

Purpose – The purpose of this paper is to analyze a squared lattice cylindrical shell under compressive axial load and to optimize the geometric parameters to achieve the maximum buckling load. Also a comparison between buckling loads of a squared lattice cylinder and a solid hollow cylinder with equal weight, length and outer diameter is performed to reveal the superior performance of the squared lattice cylindrical shells. Design/methodology/approach – A cylindrical lattice shell includes circumferential and longitudinal rods with geometric parameters such as cross‐section areas of the rods, distances and angles between them. In this study, the governing differential equation for buckling load which can be presumed as a criterion for designing lattice structures with a specific weight is derived and is used as an objective function in genetic algorithm (GA) method to calculate the optimum geometric parameters of the shell. The optimum parameters were modelled in finite element method (FEM) in order to verify the buckling loads obtained from GA. In another effort, the FEM was applied to analyze the solid hollow cylinders. Findings – The results demonstrate relatively close agreement between the buckling loads obtained from GA and FEM for such shells. It was also shown that latticed cylinders have better performance to carry compressive axial loads than the equivalent solid hollow cylinders with equal weights, lengths and outer diameters. Research limitations/implications – The studies reported in this paper have been carried out for a single squared lattice shell without using two‐side skins. However, using skins can give better performance in carrying compressive axial loads. Practical implications – The results in this paper show that this type of effective, economical lightweight and functional structures could be applied as inter‐stages, inter‐tanks, aircraft fuselage, rocket motor cases, pressure vessels and other elements of civil engineering structures in order to have greater strength and lower weight. Originality/value – Squared lattice cylindrical shell with optimum geometric design could provide the chance for eliminating the stiffeners of shells in aerospace structures in order to decrease the weight and increase the load‐bearing capacity.

Sunil Chandrakant Joshi

doi: 10.1108/00022661111120953pmid: N/A

Purpose – With the advent of micro‐satellites technology, passive thermal controls in the form of surface coatings have become important for onboard thermal management. The thermal coatings, however, suffer outgassing and mass loss due to their direct exposure to harsh thermal environment and high vacuum in space. The purpose of this paper is to discuss testing and evaluation on outgassing of AA6061‐T6 specimen surfaces treated with various types of anodized coatings of different thicknesses and the related mass loss before and after thermal exposure. Design/methodology/approach – Samples of chromic acid, polytetrafluroethylene polymer, and black‐ and brown‐colour anodized aluminum coupons were subjected to high vacuum (∼1×10 −6 mbar), before and after thermal baking at 120°C. Spectrum analysis of the outgassed material to know their quantities and proportion was conducted subsequently using a Quadrupole mass analyzer. Findings – The surface coatings under study complied with the spacecraft requirements for the mass loss of less than 1 percent of the total mass of the coating material used for that surface. The mass spectrum analysis of the outgassed material indicated that the majority of the coating mass loss was on account of water vapours and organic solvents like ethylene. Practical implications – These results provided a good insight into the reliability of the coating materials studied and the bonding between the aluminum substrates and the coatings. Originality/value – The coatings and the technology needed for their application on aluminum are readily available. The present work on outgassing and mass loss in a simulated space environment will provide useful insight on their usage for micro‐satellites.

Jae S. Park; Sung N. Jung; Young H. You; Soo H. Park; Yung H. Yu

doi: 10.1108/00022661111120962pmid: N/A

Purpose – The purpose of this paper is to evaluate the prediction capability of comprehensive structural dynamics (CSD) analysis codes for the higher harmonic control aeroacoustic rotor test (HART) II data. Design/methodology/approach – A nonlinear flexible multibody dynamics analysis code DYMORE, as well as the comprehensive analytical model of rotorcraft aerodynamics and dynamics (CAMRAD) II, are used to perform the task. The predicted results on rotating free vibration analysis, airloads, blade elastic motions, and structural moments are correlated with the measured data for the baseline, minimum noise, and minimum vibration cases. Findings – The DYMORE analysis results with a free wake model show a good performance in capturing blade vortex interaction peaks in the prediction of section normal forces but apparently with a phase shift problem. The high‐frequency behavior in the airloads signal does not affect much on the aeroelastic response and structural moments of the rotor. Originality/value – The present approach uses two separate CSD codes to systematically validate the HART II data. The accuracy of each code on structural dynamic aspects of HART II rotor is assessed using a consistent set of inputs. The effects of blade tip deflections on the interaction of blades and their trailed vortices leading to a reduced noise emission are also investigated.

Mahdi Rezaei; Fariborz Saghafi

doi: 10.1108/00022661111120971pmid: N/A

Purpose – The purpose of this paper is to describe optical flow‐based navigation of a very light fixed‐wing aircraft in flight between obstacles. Design/methodology/approach – The optical flow information of two cameras mounted on the aircraft is used to detect the obstacle. It is assumed that the image processing has been completed and the optical flow vectors have been obtained beforehand. The optical flow is used to detect the obstacles and make a rapid turn manoeuvre for the aircraft. Findings – It is shown that using the optical flow feedback by itself is unable to give a rapid turn to the aircraft and its rate should be employed into the control law. Six degree‐of‐freedom flight simulation showed that the proposed navigation and control strategy give satisfactory results in different flight environments like corridors with parallel and non‐parallel walls and in the L junctions. Simulations also showed that the aircraft flight velocity has little effect on collision avoidance performance. Practical implications – This paper provides a theoretical framework to study the different parameters affect the obstacle detection and avoidance of an aircraft. Originality/value – An analytical equation has been developed to relate the obstacle detection distance to the aircraft manoeuvrability parameters. In addition, an optical flow‐based controller also has been designed to provide rapid turn manoeuvres using the aileron control surface.

Mohammad Rahim; Seyed Móhammad‐Bagher Malaek

doi: 10.1108/00022661111120980pmid: N/A

Purpose – The purpose of this paper is to present a novel approach in terrain following (TF) flight using fuzzy logic. The fuzzy controller as presented in this work decides where and how the aircraft needs to change its altitude. The fast decision‐making nature of this method promises real‐time applications even for tough terrains in terms of shape and peculiarities. The method could always assist to design trajectories in an off‐line manner. Design/methodology/approach – To achieve the aforementioned goal, the method effectively incorporates the dynamics of the aircraft. Basically, the mathematical method employs special relationships among existing slope of the terrain and its derivative together with aircraft flying speed and height above the ground to construct suitable fuzzy rules. The fuzzification method is based on Sugeno and three rule‐sets are used for fuzzy structure. These rules are implemented using Fuzzy Logic Toolbox in MATLAB. Findings – Different case studies conducted for flights in XZ‐plane show the effectiveness of the method as compared to other existing methods available to the authors. The results illustrate a good tracking based on the fuzzy approach while using both 18 and 27 rules with respect to the optimal approach. Furthermore, it is shown that decreasing number of rules from 27 to 18 rules causes only minor changes in the solution. Practical implications – The current work offers a new approach in low‐level flights where maintaining a suitable height above the ground is essential. This is especially important for civil aircraft approaching an airport with low or non‐visibility and during aborted landing manoeuvres. The domain of the current work is however confined to only planning of TF manoeuvres. Nevertheless, the work could be expanded into TF/terrain avoidance and three‐dimensional manoeuvres which are not in the scope of the current work. Originality/value – The current work addresses the problems associated with low‐level flight; such as TF using artificial intelligence and fuzzy logic. The provided intelligence helps the aircraft conduct TF manoeuvres by understanding the general patterns of the existing terrain. The method is fast enough to be applied for real‐time applications.

St. D. Ilcev

doi: 10.1108/00022661111120999pmid: N/A

Purpose – The purpose of this paper is to examine the potential applications of stratospheric communication platforms (SCP), which have been recently introduced as an alternative for satellite communications. Design/methodology/approach – Various applications, solutions and services are planned by using aircraft or airship SCP, which could be classified as digital narrowband or broadband, depending on the broadband required. The platforms as base stations can provide service for fixed and mobile applications, with commercial and military solutions. Subscribers will use uplink to the platform for transmitting and receiving information, where onboard SCP switching devices will downlink to the ground station and route traffic directly to other subscribers within the same platform coverage, to another platform via optical inter‐platform links, trough heterogeneous networks including satellite or to the terrestrial telecommunications network. Each SCP can deploy an antenna for large coverage area or a multibeam antenna capable of projecting numerous spot beams within its potential coverage area. Findings – This paper outlines the findings of fixed and mobile applications, features, testing and some specific development programs of SCP using aircraft solutions, such as SkyTower and airship solutions, such as CRL/TAO/NAL. Research limitations/implications – Particular consideration is given to the use of SCP for delivery of future broadband, broadcast and multimedia wireless communications including research for new communication, navigation and surveillance (CNS) implications. Practical implications – SCP will provide communication facilities that can exploit the best features for both terrestrial and satellite schemes. Originality/value – Emerging solutions of voice, data and video over IP are offered by SCPs operating in the stratosphere at altitudes of up to 25 km.