Generalized Aerodynamic Modeling of Dynamic Wake Curvature for Open Rotors With Slender Blades

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Ioannis Goulos
Keyword(s):  
Fluid Mechanics ◽  
Vortex Tube ◽  
Flight Test ◽  
Accurate Method ◽  
Flight Mechanics ◽  
Theoretical Development ◽  
Small Scale ◽  
Helicopter Flight ◽  
Transient Control ◽  
Control Response

This paper elaborates on the theoretical development of an analytical approach, capable of modeling the effect of dynamic wake curvature on the aeroelastic response of open rotors with slender blades. The classical solution of incompressible, potential flow derived for a curved vortex tube of uniform vorticity strength is employed. The previously developed curved vortex tube analysis is mathematically generalized to account for arbitrary radial and circumferential variations of circulatory disk loading. An orthogonality analysis is carried out to obtain a finite set of inflow perturbation coefficients that describe the aerodynamic effect of wake curvature in a generalized manner. The end result is a set of integral expressions that provide the interharmonic coupling between the inflow perturbations on the rotor disk due to a curved trailing wake and the corresponding variations of disk loading. The obtained perturbation coefficients are subsequently superimposed upon an existing finite-state induced flow model that assumes a skewed, noncurved cylindrical wake. The developed mathematical approach for fluid mechanics is coupled with an unsteady blade element aerodynamics model, a rotor blade structural mechanics model, and a nonlinear rotor dynamics model. The combined formulation is implemented in an existing helicopter flight mechanics code. The overall method is initially employed to assess the effect of wake curvature on the dynamic response of a small-scale articulated rotor with a flap frequency ratio equal to unity. Subsequently, the integrated model is deployed to investigate the influence of wake curvature and inflow modeling fidelity on the predicted oscillatory blade loads and transient control response of a full-scale helicopter rotor. Comparisons are carried out with flight test measurements as well as with complex free-wake analysis methods. It is shown that including the effect of wake curvature is essential for predicting the transient control response of the investigated rotor. Good agreement is demonstrated between the proposed analytical model and nonlinear predictions carried out by resolving the complex wake geometry. The developed fluid mechanics formulation is a time-accurate method derived from first-principles and is applicable to both axial and nonaxial flow conditions.

scholarly journals Improving a real-time helicopter simulator model with linear input filters

2021 ◽  
Author(s):  
Pavle Šćepanović ◽  
Frederik A. Döring
Keyword(s):  
Feedback Control ◽  
Time Domain ◽  
Flight Test ◽  
Flight Mechanics ◽  
Mean Square ◽  
Qualification Test ◽  
Model Inversion ◽  
Helicopter Flight ◽  
The Time Domain ◽  
Mean Square Errors

AbstractFor a broad range of applications, flight mechanics simulator models have to accurately predict the aircraft dynamics. However, the development and improvement of such models is a difficult and time consuming process. This is especially true for helicopters. In this paper, two rapidly applicable and implementable methods to derive linear input filters that improve the simulator model are presented. The first method is based on model inversion, the second on feedback control. Both methods are evaluated in the time domain, compared to recorded helicopter flight test data, and assessed based on root mean square errors and the Qualification Test Guide bounds. The best results were achieved when using the first method.

scholarly journals Complexity and Simplicity in Doctor–Patient Email Consultations

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Jane Ege Møller ◽  
Antoinette Fage-Butler ◽  
Mathilde Nisbeth Brøgger
Keyword(s):  
Medical Student ◽  
New Technologies ◽  
Theoretical Development ◽  
Small Scale ◽  
Multiple Forms ◽  
Danish Study

New technologies have facilitated doctor–patient email consultations (e-consultations). Guidelines for e-consultation use in Denmark state that they should be used for simple, concrete and non-urgent queries; however, a small-scale Danish study suggested that doctors encounter e-consultations that do not match the guidelines. The purpose of this article is to explore whether e-consultations in Denmark reflect recommendations that they should be simple, short, concrete and well defined, and if not, what forms of complexity are evident. We inductively analysed 1,671 e-consultations from 38 patients aged 21–91 years communicating with 28 doctors, 6 nurses, 1 medical student and 8 secretaries. Results showed both quantitative complexity in terms of number of interaction turns, communicative participants, and questions asked, and qualitative complexity relating to patients’ psychosocial contexts and GPs’ biomedical disease perspective. Thus, despite existing guidelines and the leanness associated with the email medium, multiple forms of complexity were evident. This mismatch highlights the need for theoretical development as well as the value of re-examining existing policies and guidelines regarding expectations for e-consultation use.

Rotorcraft control response using linearised and non-linear flight dynamic models with different inflow models

2017 ◽  
Vol 121 (1238) ◽  
pp. 553-575 ◽  
Author(s):  
T. Sakthivel ◽  
C. Venkatesan
Keyword(s):  
Dynamic Model ◽  
Dynamic Models ◽  
Model Identification ◽  
Flight Test ◽  
Step Size ◽  
Response Characteristics ◽  
Wide Range ◽  
Non Linear ◽  
Steady Level ◽  
Control Response

ABSTRACTThe aim of the present study is to develop a relatively simple flight dynamic model which should have the ability to analyse trim, stability and response characteristics of a rotorcraft under various manoeuvring conditions. This study further addresses the influence of numerical aspects of perturbation step size in linearised model identification and integration timestep on non-linear model response. In addition, the effects of inflow models on the non-linear response are analysed. A new updated Drees inflow model is proposed in this study and the applicability of this model in rotorcraft flight dynamics is studied. It is noted that the updated Drees inflow model predicts the control response characteristics fairly close to control response characteristics obtained using dynamic inflow for a wide range of flight conditions such as hover, forward flight and recovery from steady level turn. A comparison is shown between flight test data, the control response obtained from the simple flight dynamic model, and the response obtained using a more detailed aeroelastic and flight dynamic model.

scholarly journals Design, Development, and Flight Test of a Small-Scale Cyclogyro UAV Utilizing a Novel Cam-Based Passive Blade Pitching Mechanism

2013 ◽  
Vol 5 (2) ◽  
pp. 145-162 ◽  
Author(s):  
Zachary Adams ◽  
Moble Benedict ◽  
Vikram Hrishikeshavan ◽  
Inderjit Chopra
Keyword(s):  
Flight Test ◽  
Small Scale ◽  
Design Development

Distributed Turbulence Model with Rigorous Spatial Cross-Correlation for Simulation of Helicopter Flight in Atmospheric Turbulence

2019 ◽  
Vol 64 (4) ◽  
pp. 1-13
Author(s):  
Honglei Ji ◽  
Renliang Chen ◽  
Pan Li
Keyword(s):  
Atmospheric Turbulence ◽  
Turbulence Model ◽  
Cross Correlation ◽  
Turbulence Models ◽  
Flight Test ◽  
Longitudinal Direction ◽  
Flight Simulation ◽  
Quality Analysis ◽  
Frequency Range ◽  
Helicopter Flight

This paper presents a distributed turbulence model with rigorous spatial cross-correlation for helicopter flight simulation in atmospheric turbulence and for future handling-quality analysis. First, digital filters with longitudinal correlations of the von Kármán turbulence are developed to generate discrete turbulence velocity components. Meanwhile, transverse turbulence correlations are considered by relating the filters in different positions with mathematically rigorous spatial cross-correlation. Then, the distributions of the related filters on the transverse plane in front of helicopter and their velocity components in the longitudinal direction of airspeed, as well as turbulence models of helicopter aerodynamic surfaces, are established. Finally, a flight dynamics model coupled with the turbulence model is developed and validated against the flight-test data. The proposed model can achieve accurate real-time simulations of helicopter response to atmospheric turbulence in the frequency range of interest of handling qualities. The effect of transverse turbulence correlations on helicopter frequency response is also analyzed. The results show that the simulation model regardless of transverse turbulence correlations would aggravate the "rotor-to-body attenuation" effect of the main rotor and therefore underpredict the helicopter roll, pitch, and heave rate responses to atmospheric turbulence in the frequency range of interest.

Real-Time Simulation of Rotor Blade Aeroelasticity for the Multidisciplinary Design of Rotorcraft

2014 ◽  
Author(s):  
Ioannis Goulos ◽  
Vassilios Pachidis
Keyword(s):  
Real Time ◽  
Rotor Blade ◽  
Flight Test ◽  
Flight Mechanics ◽  
Multidisciplinary Design ◽  
Mathematical Approach ◽  
Real Time Simulation ◽  
Analysis Methods ◽  
Time Simulation ◽  
Blade Loads

This paper elaborates on the theoretical development of a mathematical approach, targeting the real-time simulation of aeroelastic rotor blade dynamics for the multidisciplinary design of rotorcraft. A Lagrangian approach is formulated for the rapid estimation of natural vibration characteristics of rotor blades with nonuniform structural properties. Modal characteristics obtained from classical vibration analysis methods, are utilized as assumed deformation functions. Closed form integral expressions are incorporated, describing the generalized centrifugal forces and moments acting on the blade. The treatment of three-dimensional elastic blade kinematics in the time-domain is thoroughly discussed. In order to ensure robustness and establish applicability in real-time, a novel, second-order accurate, finite-difference scheme is utilized for the temporal discretization of elastic blade motion. The developed mathematical approach is coupled with a finite-state induced flow model, an unsteady blade element aerodynamics model, and a dynamic wake distortion model. The combined aeroelastic rotor formulation is implemented in a helicopter flight mechanics code. The aeroelastic behavior of a full-scale hingeless helicopter rotor has been investigated. Results are presented in terms of rotor blade resonant frequencies, airframe–rotor trim performance, oscillatory structural blade loads, and transient rotor response to control inputs. Extensive comparisons are carried out with wind tunnel and flight test measurements found in the open literature, as well as with non-real-time comprehensive analysis methods. It is shown that, the proposed approach exhibits good agreement with flight test data regarding trim performance and transient rotor response characteristics. Accurate estimation of structural blade loads is demonstrated, in terms of both amplitude and phase, up to the third harmonic component of oscillatory loading. It is shown that, the developed model can be utilized for real-time simulation on a modern personal computer. The proposed methodology essentially constitutes an enabling technology for the multidisciplinary design of rotorcraft, when a compromise between simulation fidelity and computational efficiency has to be sought for in the model development process.

Parafoil Flight Mechanics: A Novel Flight Test Facility

2015 ◽  
Author(s):  
Christiaan Redelinghuys ◽  
Arthur Grunwald ◽  
Steven Rhodes ◽  
Jordan L. Adams ◽  
Tracy D. Booysen
Keyword(s):  
Flight Test ◽  
Flight Mechanics ◽  
Test Facility
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