If you would like to write for this, or any other Emerald publication, then please use our Emerald for Authors service information about how to choose which publication to write for and submission guidelines are available for all. Please visit www.emeraldinsight.com/authors for more information. About Emerald www.emeraldinsight.comEmerald is a global publisher linking research and practice to the benefit of society. The company manages a portfolio of more than 290 journals and over 2,350 books and book series volumes, as well as providing an extensive range of online products and additional customer resources and services.Emerald is both COUNTER 4 and TRANSFER compliant. The organization is a partner of the Committee on Publication Ethics (COPE) and also works with Portico and the LOCKSS initiative for digital archive preservation. AbstractPurpose -This paper aims to focus on mathematical model development issues, necessary for a better prediction of dynamic responses of articulated rotor helicopters. Design/methodology/approach -The methodology is laid out based on model development for an articulated main rotor, using the theories of aeroelastisity, finite element and state-space represented indicial-based unsteady aerodynamics. The model is represented by a set of nonlinear partial differential equations for the main rotor within a state-space representation for all other parts of helicopter dynamics. The coupled rotor and fuselage formulation enforces the use of numerical solution techniques for trim and linearization calculations. The mathematical model validation is carried out by comparing model responses against flight test data for a known configuration. Findings -Improvements in dynamic prediction of both on-axis and cross-coupled responses of helicopter to pilot inputs are observed. Research limitations/implications -Further work is required for investigation of the unsteady aerodynamics, a state-space representation, within various compatible dynamic inflow models to describe the helicopter response characteristics. Practical implications -The results of this work support ongoing research on the development of highly accurate helicopter flight dynamic mathematical models. These models are used as engineering tools both for designing new aerial products such as modernized agile helicopters and optimization of the old version products at minimum time and expense. Originality/value -Provides further information on the mathematical model development problems associated with advanced helicopter flight dynamics research.

Purpose -The purpose of this paper is to examine the cross-coupled responses of a coupled rotor-fuselage flight dynamic simulation model, including a finite-state inflow aerodynamics and a coupled flap-lag and torsion flexible blade structure. Design/methodology/approach -The methodology is laid out based on model development for an articulated main rotor, using the theories of aeroelastisity, finite element and finite-state inflow formulation. The finite-state inflow formulation is based on a 3D unsteady Euler-based concepts presented in the time domain. The most advantages of the model are the capability of modeling dynamic wake effects, tip losses and skewed wake aerodynamics. This is, in fact, a special type of the inflow model relating inflow states, to circulatory blade loadings through a set of first-order differential equations. A non-iterative solution of the differential equations has practically altered the model into a simple and direct formulation appending properly to the rest of the helicopter mathematical model. A non-linear distribution of the induced velocity over the rotor disc is finally obtained by the use of both Legendre polynomials and higher-harmonic functions. Ultimately, validations of the theoretical results show that the on-axis response, direct reaction to the pilot input, has a good accuracy both quantitatively and qualitatively against flight test data, and the off-axis response, cross-coupled or indirect reaction to the pilot input are improved by this approach of modeling. Findings -Improvements in dynamic prediction of both trim control settings and dynamic cross-coupled responses of helicopter to pilot inputs are observed.Research limitations/implications -Further work is required for investigation of the augmented finite state inflow model, including the wake rotation correction factors to describe helicopter maneuvering flight characteristics. Practical implications -The results of this work support the future researches on design and development of advanced flight control system, incorporating a high bandwidth with low-phase delay to control inputs and also high levels of dynamic stability within minimal controls cross coupling. Originality/value -This paper provides detailed characteristics on the mathematical integration problems associated with the advanced helicopter flight dynamics research.

Purpose The effects of rotor blade design variables and their mutual interactions on aerodynamic efficiency of helicopters are investigated. The aerodynamic efficiency is defined based on figure of merit (FM) and lift-to-drag responses developed for hover and forward flight, respectively. Design/methodology/approach The approach is to couple a general flight dynamic simulation code, previously validated in the time domain, with design of experiment (DOE) required for the response surface development. DOE includes I-optimality criteria to preselect the data and improve data acquisition process. Desirability approach is also implemented for a better understanding of the optimum rotor blade planform in both hover and forward flight. Findings The resulting system provides a systematic manner to examine the rotor blade design variables and their interactions, thus reducing the time and cost of designing rotor blades. The obtained results show that the blade taper ratio of 0.3, the point of taper initiation of about 0.64 R within a SC1095R8 airfoil satisfy the maximum FM of 0.73 and the maximum lift-to-drag ratio of about 5.5 in hover and forward flight. Practical implications The work shows the practical possibility to implement the proposed optimization process that can be used for the advanced rotor blade design. Originality/value The work presents the rapid and reliable optimization process efficiently used for designing advanced rotor blades in hover and forward flight.

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