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Detection and control of ground resonance using phase of fuselage attitude rates
Salini S. Nair,Ranjith Mohan +1 more
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In this article, the phase relations between the fuselage states corresponding to the least damped mode (regressive lag mode) and its correlation with frequency coalescence were analyzed for ground resonance.Abstract:
Ground resonance is a type of aeromechanical instability that occurs when the helicopter is in contact with the ground. It may occur due to coalescence between frequencies of two modes of the system if damping is insufficient. In this paper, we analyze the phase relations between the fuselage states corresponding to the least damped mode (regressive lag mode) and its correlation with frequency coalescence. The phase of fuselage states (attitude or attitude rates), which are easily measurable, is observed to exhibit certain trends with variation in parameters like rotor speed and landing gear stiffness. The phase data can aid in the design of a stability augmentation system for ground resonance. It can serve as a parameter to detect the possibility of instability and in systems with uncertainties in parameters, like landing gear stiffness, it can aid in selecting the appropriate feedback gain for stabilization. The model we have primarily considered has isotropic rotor and anisotropic hub, hence multiblade coordinate transformation is used and the stability analysis is done in fixed frame. The analysis is further extended to incorporate dynamic inflow effects and anisotropy in rotor blades, where Floquet method is used for stability analysis. Air resonance instability is also investigated on similar lines and the proposed method is found to be good for its detection.read more
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Influence of contact points of helicopter skid landing gears on ground resonance stability
TL;DR: In this article, a ground resonance test environment was created for soft-in-plane rotor systems with flexible landing gear models using direct finite-element models and applying modal reduction to embed CAD-derived landing gear model.
References
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Book
Principles of Helicopter Aerodynamics
TL;DR: A history of helicopter flight can be found in this paper, where the basic helicopter aerodynamic properties are discussed and a detailed analysis of the rotor blade motion is presented, as well as a detailed discussion of the rotor wakes and tip vortices.
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Finite-State Induced-Flow Model for Rotors in Hover and Forward Flight
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TL;DR: In this article, the authors present an analysis of nonlinear systems for aerodynamic and aerodynamic stability analysis of rotors in a single-rotor-pylon system, with a focus on the effects of vibration and flutter of the rotors.
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