Comparison of Induced Velocity Models for Helicopter Flight Mechanics

2000 ◽  
Vol 37 (4) ◽  
pp. 623-629 ◽  
Author(s):  
R. E. Brown ◽  
S. S. Houston
Keyword(s):  
Flight Mechanics ◽  
Velocity Models ◽  
Helicopter Flight ◽  
Induced Velocity

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.

Dynamic inflow modelling for autorotating rotors

2008 ◽  
Vol 112 (1127) ◽  
pp. 47-53 ◽  
Author(s):  
Y. Murakami ◽  
S.S. Houston
Keyword(s):  
Mass Flow ◽  
First Principles ◽  
Flow Parameter ◽  
Flight Mechanics ◽  
Qualitative Assessment ◽  
Limited Area ◽  
Mode Of Operation ◽  
Scant Attention ◽  
Geometric Relation ◽  
Induced Velocity

Abstract The dynamic inflow model is a powerful tool for predicting the induced velocity distribution over a rotor disc. On account of its closed form and simplicity, the model is especially practical for studying flight mechanics or for designing control systems for helicopters. Scant attention has, however, been paid so far in utilising the dynamic inflow model to analyse an autorotating rotor, which is different from a powered rotor in the geometric relation between the direction of the inflow and the rotor disc. Autorotation is an abnormal condition for helicopters, but for gyroplanes it is the normal mode of operation. Therefore the theoretical discussion on an autorotating rotor is of importance not only to improve the understanding of present gyroplanes, but also in the development of new gyroplanes and to analyse the windmill-brake state of helicopters. Dynamic inflow modelling is reviewed from first principles, and this identifies a modification to the mass flow parameter. A qualitative assessment of this change indicates that it is likely to have a negligible impact on the trim state of rotorcraft in autorotation, but a significant effect on the dynamic inflow modes in certain flight conditions. This is confirmed by numerical simulation, although considerable differences only become apparent for steep descents with low forward speed. It is concluded that while modification of the mass flow parameter is perhaps mathematically accurate, for practical purposes it is required only in a limited area of the flight envelope of autorotating rotorcraft.

High‐Order State Space Simulation Models of Helicopter Flight Mechanics

1993 ◽  
Vol 38 (4) ◽  
pp. 16-27 ◽  
Author(s):  
Frederick D. Kim ◽  
Roberto Celi ◽  
Mark B. Tischler
Keyword(s):  
State Space ◽  
Simulation Models ◽  
High Order ◽  
Flight Mechanics ◽  
Helicopter Flight ◽  
Order State

scholarly journals Actuator Cylinder Theory for Multiple Vertical Axis Wind Turbines

2016 ◽  
Author(s):  
Andrew Ning
Keyword(s):  
Wind Turbines ◽  
Wind Farm ◽  
Vertical Axis ◽  
Total Power ◽  
Velocity Models ◽  
Wake Interference ◽  
Vertical Axis Wind Turbines ◽  
Wake Interactions ◽  
Wake Zone ◽  
Induced Velocity

Abstract. Actuator cylinder theory is an effective approach for analyzing the aerodynamic performance of vertical axis wind turbines at a conceptual design level. Existing actuator cylinder theory can analyze single turbines, but analysis of multiple turbines is often desirable because turbines operate in near proximity within a wind farm. For vertical axis wind turbines, which tend to operate in closer proximity than do horizontal axis turbines, aerodynamic interactions may not be strictly confined to wake interactions. We modified actuator cylinder theory to permit the simultaneous solution of aerodynamic loading for any number of turbines. We also extended the theory to handle thrust coefficients outside of the momentum region, and explicitly defined the additional terms needed for curved or swept blades. It is found that even out of the wake zone, aerodynamic interactions are not negligible at typical separation distances (i.e., 3–6 rotor diameters). If turbines are co-rotating then for the two turbine cases examined in this paper the sum of the total power was effectively constant except within the wake zone. However, if turbines counter-rotate then both beneficial and detrimental changes in power production were observed depending on the relative positions. However, these benefits are on the order of a few percent and unlikely to be advantageous in practice because of wake interference, except for within highly directional wind sites. Limitations of these analyses identified the need for integration with viscous wake models, and potentially with higher-fidelity induced velocity models.

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.

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