2 Aerodynamics
93
Fig. 2.24 Joukowsky airfoil
disturbance. It is concluded that for the ideal incompressible flow around a
thin airfoil at a small angle of attack, the disturbance velocity potential, the
boundary conditions of the material surface, and the pressure coefficient can
be superposed linearly. The lift and moment acting on the thin airfoil can be
regarded as the sum of the effects of curvature, thickness, and angle of attack.
Therefore, the flow around a thin airfoil can be superposed by three simple
flows.
During World War I, the belligerent countries have found some airfoils
with better performance in practice, for example, Joukowsky airfoil,
Gottingen airfoil in Germany, RAF airfoil in Britain (Royal Air Force, later
changed to RAE airfoil), Clark-y in the United States; after the 1930s, NACA
airfoil (National Advisory Committee for aeronautics, later NASA, National
Aeronautics and Space Administration) in the U.S.A. and cAI airfoil
(central air fluid Research Institute in Russia). In the late 1930s, the National
Aeronautical Advisory Council of the United States (NACA, now NASA)
made a systematic study on the performance of airfoil (as shown in Fig. 2.25)
Fig. 2.25 Lift coefficient and drag coefficient of airfoil
93
Fig. 2.24 Joukowsky airfoil
disturbance. It is concluded that for the ideal incompressible flow around a
thin airfoil at a small angle of attack, the disturbance velocity potential, the
boundary conditions of the material surface, and the pressure coefficient can
be superposed linearly. The lift and moment acting on the thin airfoil can be
regarded as the sum of the effects of curvature, thickness, and angle of attack.
Therefore, the flow around a thin airfoil can be superposed by three simple
flows.
During World War I, the belligerent countries have found some airfoils
with better performance in practice, for example, Joukowsky airfoil,
Gottingen airfoil in Germany, RAF airfoil in Britain (Royal Air Force, later
changed to RAE airfoil), Clark-y in the United States; after the 1930s, NACA
airfoil (National Advisory Committee for aeronautics, later NASA, National
Aeronautics and Space Administration) in the U.S.A. and cAI airfoil
(central air fluid Research Institute in Russia). In the late 1930s, the National
Aeronautical Advisory Council of the United States (NACA, now NASA)
made a systematic study on the performance of airfoil (as shown in Fig. 2.25)
Fig. 2.25 Lift coefficient and drag coefficient of airfoil