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Article
Publication date: 1 October 1999

Yihua Cao

The details of predicting the aerodynamic forces of maneuvering helicopter rotors are discussed in this paper. A new approach to modeling the unsteady rotor aerodynamic…

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Abstract

The details of predicting the aerodynamic forces of maneuvering helicopter rotors are discussed in this paper. A new approach to modeling the unsteady rotor aerodynamic forces is presented based on the insight into nonuniform induced velocity distribution, inflow dynamics and unsteady airfoil behavior. For a specified maneuver, the rotor control inputs and helicopter flight attitudes during the maneuvering are first obtained using inverse solution technique, and then the unsteady rotor forces are numerically simulated by synthetically applying the vortex theory, dynamic inflow theory and unsteady airfoil aerodynamic models. Good results of the sample calculations of lateral jink and pop‐up maneuvers are obtained.

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Aircraft Engineering and Aerospace Technology, vol. 71 no. 5
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 August 2003

Yihua Cao and Yuan Su

An analytical method to predict the effects of rotor downwash on engine jet was proposed to investigate the flow pattern of helicopter engine jet. First, free wake…

Abstract

An analytical method to predict the effects of rotor downwash on engine jet was proposed to investigate the flow pattern of helicopter engine jet. First, free wake analysis was carried out to calculate the rotor wake geometry and the downwash around the engine jet space. Then the engine jet path, cross section shape and physical variants were calculated and analyzed. Finally, an example was given to show the typical results for an insight into the influence of engine jet upon the temperature distribution around a helicopter. The method developed here can be used to predict rotor wake, engine jet and temperature distribution of a helicopter.

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Aircraft Engineering and Aerospace Technology, vol. 75 no. 4
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 April 1999

Yihua Cao

A new method for predicting rotor wake in low speed and hovering flight is described to investigate the motion of the helical tip vortex. Beginning with the generalized…

Abstract

A new method for predicting rotor wake in low speed and hovering flight is described to investigate the motion of the helical tip vortex. Beginning with the generalized wake model, a semi‐empirical correction for the vortex core effect on rotor wake is made and free wake calculation is carried out. As an example of its engineering application, the calculated downwash velocity field along the rocket launch line is presented and simply analysed. In terms of theory, the method developed here may provide of a referable basis for further study the formation mode of the tip vortex and vortex core interior structure.

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Aircraft Engineering and Aerospace Technology, vol. 71 no. 2
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 December 2002

Yuan Su and Yihua Cao

As compared with the maneuvering flight studies for single main rotor helicopters, the corresponding studies for coaxial rotor helicopters are relatively poor. In this…

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Abstract

As compared with the maneuvering flight studies for single main rotor helicopters, the corresponding studies for coaxial rotor helicopters are relatively poor. In this paper, the maneuvering flight governing equations for coaxial rotor helicopters is established. By introducing induced velocity interference factor analysis, the coaxial rotor aerodynamic interference can be taken into account. With the combination of coaxial rotor helicopter control features and nonlinear inverse simulation technique, the governing equations for maneuvering flight can be solved so as to determine helicopter control input, control force and moment, and helicopter body attitudes which are needed for performing a specified maneuver. Good results of the sample calculations of level turn and lateral jink maneuvers are obtained and simply analyzed.

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Aircraft Engineering and Aerospace Technology, vol. 74 no. 6
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 February 2005

Yihua Cao, Ke Chen and Jian Wang

To establish a method for the calculations in the field of rotor aerodynamics.Design/methodology/approach – The calculations of the lift‐drag characteristics of OAF and…

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Abstract

Purpose

To establish a method for the calculations in the field of rotor aerodynamics.Design/methodology/approach – The calculations of the lift‐drag characteristics of OAF and NACA63A312 airfoils at low speed are made using Jameson/TVD mixed scheme. By means of finite volume approach for numerical discretization and Runge‐Kutta time‐stepping advance, Euler/Navier‐Stokes equations are solved. Furthermore, a model based on circular tiny segment momentum theory and blade element theory is established to study the thrust and power of ducted tail rotor.Findings – The results of the calculation demonstrate the feasibility of the established method for analyzing ducted tail rotor aerodynamic characteristics.Research limitations/implications – Although the global thrust and power of ducted tail‐rotor could be obtained using current method, the exact flow filed (such as shroud pressure field and the flow over fan blade) calculations still rely on the complex three‐dimensional CFD technique that should be studied in future.Practical implications – A very useful method for the preliminary design of the ducted tail rotor.Originality/value – By comparing the calculated results with those of relevant experiment, it is proved that the method developed here is suitable for the calculations in the field of rotor aerodynamics.

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Aircraft Engineering and Aerospace Technology, vol. 77 no. 1
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 April 2004

Yihua Cao, Guangli Zhang and Yuan Su

This paper describes the typical maneuvering courses of helicopters with mathematics systematically and presents the formulas and approaches for calculating the dynamics…

Abstract

This paper describes the typical maneuvering courses of helicopters with mathematics systematically and presents the formulas and approaches for calculating the dynamics characteristics. A set of generalized equations which govern the kinematics and dynamics of helicopters in maneuvering flight is given. Three aerobatic maneuvers for loop, roll and turn are specially analyzed in detail and the sample calculations are presented. The method established in this paper is of practical significance for aerobatic employment and design of helicopters.

Details

Aircraft Engineering and Aerospace Technology, vol. 76 no. 2
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 30 January 2007

Yuan Su, Yihua Cao and Kungang Yuan

This paper aims to present a theoretical method for analyzing the stability and control of a hingeless helicopter in the presence of windshear.

Abstract

Purpose

This paper aims to present a theoretical method for analyzing the stability and control of a hingeless helicopter in the presence of windshear.

Design/methodology/approach

In this paper, the stability and control of a hingeless helicopter in the presence of windshear are investigated. First, the rotary wing dynamic model considered is the one of flap‐pitch (including the elastic deformation of the control system)‐torsion coupling. The induced velocity nonuniform distribution derived from vortex theory is taken into account. Then, as for atmospheric turbulence, the linear windshear model is used for modeling the variation of wind field. Finally, according to the calculated results of the stability characteristic roots and the control response of the helicopter, the helicopter performance in wind shear field is analyzed, and some conclusions are obtained.

Findings

Some useful conclusions are obtained through sample analysis.

Research limitations/implications

Although the analyses for stability and control of a hingeless helicopter in the presence of windshear could be obtained using the current method, the model of complex wind field will still be expected in future studies.

Practical implications

A very useful method for analyzing helicopter stability and control.

Originality/value

The proposed method is valid and available for the analysis of helicopter flight dynamics.

Details

Aircraft Engineering and Aerospace Technology, vol. 79 no. 2
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 October 2000

Yihua Cao, Guocai Hu and Jifei Wang

Labyrinth seals have been used extensively in industrial production. Better prediction of the performance of a labyrinth seal requires that these mechanisms be understood…

Abstract

Labyrinth seals have been used extensively in industrial production. Better prediction of the performance of a labyrinth seal requires that these mechanisms be understood. This cannot be achieved except by investigating the flowfield details. Therefore, a total variation diminishing (TVD) finite volume scheme is applied to the Navier‐Stokes equations to obtain gas seal flowfield characteristics of axially staggered configuration in this paper. The calculation results here show the evolution process from unsteady flowfield characterization to steady flow pattern. Also, these new flowfield details may provide referable basis for understanding seal mechanisms.

Details

Aircraft Engineering and Aerospace Technology, vol. 72 no. 5
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 6 September 2011

Yihua Cao, Kungang Yuan and Guozhi Li

The purpose of this paper is to describe a methodology for predicting the effects of glaze ice geometry on airfoil aerodynamic coefficients by using neural network (NN…

Abstract

Purpose

The purpose of this paper is to describe a methodology for predicting the effects of glaze ice geometry on airfoil aerodynamic coefficients by using neural network (NN) prediction. Effects of icing on angle of attack stall are also discussed.

Design/methodology/approach

The typical glaze ice geometry covers ice horn leading‐edge radius, ice height, and ice horn position on airfoil surface. By using artificial NN technique, several NNs are developed to study the correlations between ice geometry parameters and airfoil aerodynamic coefficients. Effects of ice geometry on airfoil hinge moment coefficient are also obtained to predict the angle of attack stall.

Findings

NN prediction is feasible and effective to study the effects of ice geometry on airfoil performance. The ice horn location and height, which have a more evident and serious effect on airfoil performance than ice horn leading‐edge radius, are inversely proportional to the maximum lift coefficient. Ice accretions on the after‐location of the upper surface of the airfoil leading edges have the most critical effects on the airfoil performance degradation. The catastrophe of hinge moment and unstable hinge moment coefficient can be used to predict the stall effectively.

Practical implications

Since the simulation results of NNs are shown to have high coherence with the tunnel test data, it can be further used to predict coefficients at non‐experimental conditions.

Originality/value

The simulation method by using NNs here can lay the foundation of the further research about the airfoil performance in different ice cloud conditions through predicting the relations between the ice cloud conditions and ice geometry.

Details

Aircraft Engineering and Aerospace Technology, vol. 83 no. 5
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 22 May 2007

Yihua Cao and Chongwen Jiang

This paper aims to provide a preliminary method for the numerical simulation of the flow field around a parachute.

Abstract

Purpose

This paper aims to provide a preliminary method for the numerical simulation of the flow field around a parachute.

Design/methodology/approach

With the rise of computational fluid dynamics and structural finite element method, it is possible to accurately describe the dynamic characteristics of a parachute. In order to simulate the flow field around the parachute during terminal descent, a finite volume method and Spalart‐Allmaras turbulence model are used to solve the incompressible Navier‐Stokes equations.

Findings

The calculated results for flow field show good agreement with the experimental data.

Research limitations/implications

Although a preliminary analysis for the flow field around the parachute could be obtained using current method, the exact flow field (such as involving the canopy flexibility and weave porosity) calculations still rely on the complex fluid‐structure interaction analytical techniques that should be studied in future.

Practical implications

A very useful method for the preliminary analyses of the parachutes.

Originality/value

By comparing the calculated results with those of relevant experiment, it is proved that the proposed method is valid and available to parachute analyses.

Details

Aircraft Engineering and Aerospace Technology, vol. 79 no. 3
Type: Research Article
ISSN: 0002-2667

Keywords

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