Purpose -The purpose of this paper is to analyze the stability of aeroelastic systems using aeroelastic frequency response function (FRF). Design/methodology/approach -The proposed technique determines the instability boundary of an aeroelastic system based on condition number (CN) of aeroelastic FRF matrix or directly from FRFs data. Findings -Stability margins of typical section and hingeless helicopter rotor blade in the subsonic flow regimes (quasi-steady and unsteady models) are determined using proposed techniques as two case studies. Originality/value -The paper introduces a technique which is applicable not only when aerodynamic and structure analytical models are available but also when there are experimental models for structure and/or aerodynamics, such as impulse response functions data or FRFs data. In other words, the main advantage of the proposed method, besides its simplicity and low memory requirement, is its ability to utilize experimental data.

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In this paper, a full applicable procedure for design, optimization and manufacturing of an operational unmanned helicopter with deep and detailed research basis is presented. 12 The proposed process deals with challenging aspects of manufacturing of the mentioned type of aircraft such as cost, weight, operation ability, reliability, mission justification, stability, performance, etc. To show the applicability of the proposed procedure, a realization of the process in production of an operational unmanned helicopter named as Parvan is described in this paper. Indeed, Parvan is a Remotely Piloted Helicopter (RPH) with 9 kilograms takeoff weight, and main rotor diameter of 1.54 meters which can lift up a 2 kilograms payload and fly in 120 kilometer radius of action for about 1.5 hours.

In the present paper, a complete process from reliability evaluation to design modification is proposed and also applied to a newly designed and manufactured Remotely Piloted Helicopter (RPH) by the authors. First of all, a description of all platform subsystems is presented. After that, function diagram and also product tree of the whole system is depicted for further analysis. Then, the reliability of all parts and components are calculated through standard methods. The procedure is followed by FMEA/FMECA execution and determination of critical components and failures. Then, the reliability of the whole platform is calculated using standard block diagrams. Finally, in order to improve the mission operational reliability of the considered RPH, some modifications are implemented to the platform including configuration and mechanisms design changes.

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