522 research outputs found
Helicopter Noise Footprint Prediction in Unsteady Maneuvers
No full textThis paper investigates different methodologies for the evaluation of the acoustic disturbance emitted by helicopter’s main rotors during unsteady maneuvers. Nowadays, the simulation of noise emitted by helicopters is of great interest to designers, both for the assessment of the acoustic impact of helicopter flight on communities and for the identification of optimal-noise trajectories. Typically, the numerical predictions consist of the atmospheric propagation of a near-field noise model, extracted from an appropriate database determined through steady-state flight simulations/measurements (quasi-steady approach). In this work, three techniques for maneuvering helicopter noise predictions are compared: one considers a fully unsteady solution process, whereas the others are based on quasi-steady approaches. These methods are based on a three-step solution procedure: first, the main rotor aeroelastic response is evaluated by a nonlinear beam-like rotor blade model coupled with a boundary element method for potential flow aerodynamics; then, the aeroacoustic near field is evaluated through the 1A Farassat formulation; finally, the noise is propagated to the ground by a ray tracing model. Only the main rotor component is examined, although tail rotor contribution might be included as well. The numerical investigation examines the differences among the noise predictions provided by the three techniques, focusing on the assessment of the reliability of the results obtained through the two quasi-steady approaches as compared with those from the fully unsteady aeroacoustic solver.Air Transport & Operation
A Finite-State Aeroelastic Model for Rotorcraft–Pilot Coupling Analysis
No full textRotorcraft–pilot coupling (RPC) denotes inter-
play between pilot and helicopter (or tiltrotor) that may
give rise to adverse phenomena. These are usually divided
into two main classes: pilot-induced oscillations driven by
flight dynamics and behavioural processes, and pilot-
assisted oscillations (PAO) caused by unintentional actions
of pilot on controls, owing to involuntary reaction to seat
vibrations. The aim of this paper is the development of
mathematical helicopter models suited for analysis of RPC
phenomena. In addition to rigid-body dynamics, RPCs
(especially PAO) are also related to fuselage structural
dynamics and servoelasticity; however, a crucial role is
played by main rotor aeroelasticity. In this work, the
aeroelastic behaviour of the main rotor is simulated
through a novel finite-state modeling that may conve-
niently be applied for rotorcraft stability and response
analyses, as well as for control synthesis applications.
Numerical results, first are focused on the validation of the
proposed novel main rotor model, and then present appli-
cations of the developed comprehensive rotorcraft model
for the RPC analysis of a Bo-105-type helicopter. Specif-
ically, these deal with the stability of vertical bouncing,
which is a PAO phenomenon caused by coupling of ver-
tical pilot seat acceleration with collective control stick,
driven by inadvertent pilot actions. Further, considering
quasi-steady, airfoil theory with wake inflow correction
and three-dimensional, potential-flow, boundary element method approaches, the sensitivity of PAO simulations to
different aerodynamic load models applied within the main
rotor aeroelastic operator is also investigated
A Finite-State Aeroelastic Model For Rotorcraft Pilot-Assisted-Oscillations Analysis
No full textRotorcraft-pilot couplings denote interactions between pilot and helicopter (tiltrotors) that may
become adverse. They are usually divided into two main classes of phenomena: that including Pilot Induced Oscillations (PIO) phenomena driven by flight dynamics and behavioural processes, and
the one conventionally named Pilot Assisted Oscillations (PAO) which is caused by unintentional actions of pilot on controls, due to his involuntary reaction to seat vibrations. The aim of this paper is the development of mathematical helicopter models suited for analysis of PAO phenomena. PAO are strictly related to the structural dynamics of the fuselage and to aervoelasticity, but a crucial
role is played by main rotor aeroelasticity. This paper presents a finite-state model of main rotor aeroelastic behavior that may conveniently be applied for PAO stability and response analysis, as well as for control applications aimed at PAO alleviation. It is validated, and its sensitivity to the
aerodynamic modeling used within the aeroelastic operator is examined. Further, it is coupled with
fuselage dynamics, servo-elastic and pilot models in order to carry out a numerical investigation
concerning the stability analysis of vertical bouncing, which is a type of PAO instability which might
be caused by the coupling, through the pilot, of vertical acceleration of pilot seat with collective
control stick
Prediction of Rotorcraft-Pilot Coupling Phenomena Through Reduced-Order Aerodynamic Model
No full text
Rotorcraft-pilot coupling analysis through state-space aerodynamic modelling
No full textThe terminology 'rotorcraft-pilot coupling' denotes phenomena arising from interaction between pilot and rotorcraft. Among these, the present work deals with 'pilot-assisted oscillations' that derive from unintentional pilot actions on controls due to seat vibrations, and are strictly related to rotor-aeroelasticity/airframe-structural-dynamics coupling, with involvement of blade control actuator dynamics. Focusing the attention on helicopters, a comprehensive rotorcraft model is developed and applied, with main rotor unsteady aerodynamics described in state-space form. This makes it particularly suited for stability and frequency-response analysis, as well as control applications. Numerical investigations address two critical rotorcraft-pilot coupling aeroelastic issues: stability of vertical bouncing and gust response in hovering. Results from main rotor unsteady aerodynamics modelling are compared with widely-used quasi-steady aerodynamics predictions. These suggest that, for accurate RPC/PAO phenomena predictions, mathematical modelling should include the three-dimensional, unsteady-flow effects, and that the pilot-in-the-loop passive behaviour produces a beneficial effect on the load factor generated by gust encountering
Optimization of oral anticoagulation in patients with atrial fibrillation: The challenge remains open
No full textA novel Nonlinear Model Predictive Controller for Power Maximization on Floating Offshore Wind Turbines
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