Book contents
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Notation
- 3 Hover
- 4 Vertical Flight
- 5 Forward Flight Wake
- 6 Forward Flight
- 7 Performance
- 8 Design
- 9 Wings and Wakes
- 10 Unsteady Aerodynamics
- 11 Actuator Disk
- 12 Stall
- 13 Computational Aerodynamics
- 14 Noise
- 15 Mathematics of Rotating Systems
- 16 Blade Motion
- 17 Beam Theory
- 18 Dynamics
- 19 Flap Motion
- 20 Stability
- 21 Flight Dynamics
- 22 Comprehensive Analysis
- Index
- References
10 - Unsteady Aerodynamics
Published online by Cambridge University Press: 05 May 2013
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Notation
- 3 Hover
- 4 Vertical Flight
- 5 Forward Flight Wake
- 6 Forward Flight
- 7 Performance
- 8 Design
- 9 Wings and Wakes
- 10 Unsteady Aerodynamics
- 11 Actuator Disk
- 12 Stall
- 13 Computational Aerodynamics
- 14 Noise
- 15 Mathematics of Rotating Systems
- 16 Blade Motion
- 17 Beam Theory
- 18 Dynamics
- 19 Flap Motion
- 20 Stability
- 21 Flight Dynamics
- 22 Comprehensive Analysis
- Index
- References
Summary
Two-Dimensional Unsteady Airfoil Theory
Since the aerodynamic environment of the rotor blade in forward flight or during transient motion is unsteady, lifting-line theory requires an analysis of the unsteady aerodynamics of a two-dimensional airfoil. Consider the problem of a two-dimensional airfoil undergoing unsteady motion in a uniform free stream. Linear, incompressible aerodynamic theory represents the airfoil and its wake by thin surfaces of vorticity (two-dimensional vortex sheets) in a straight line parallel to the free stream velocity. For the linear problem the solution for the thickness and camber loads can be separated from the loads due to angle-of-attack and unsteady motion. In the development of unsteady thin-airfoil theory, the foundation is constructed for a number of extensions of the analysis for rotary wings, which are presented in later sections of this chapter.
The airfoil and shed wake in unsteady thin-airfoil theory are modeled by planar sheets of vorticity, as shown in Figure 10.1. An airfoil of chord 2b is in a uniform free stream with velocity U. Since the bound circulation of the section varies with time, there is shed vorticity in the wake downstream of the airfoil.
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- Chapter
- Information
- Rotorcraft Aeromechanics , pp. 366 - 413Publisher: Cambridge University PressPrint publication year: 2013