Aerodynamic Center: It is that point on an airfoil (or body) about which the aerodynamically generated moment is independent of angle of attack Thin Airfoil Theory:
Symmetric Airfoil: Cambered Airfoil: x A.C .
x A.C . c
4 c 4
Drag Polar Drag Polar : both the Cl and Cd are the
functions of angle of attack thus the drag coefficient is that it depends on lift coefficient and the typical variations on Cl and Cd is called as Drag polar
The Drag polar is very important in performance analysis of aircrafts. For an aircraft with symmetrical airfoil sections the drag polar is given as CD = CDO+KCL2
Lift Curve Slope Lift Curve Slope
Lift Curve for a Normal Wing and NACA 63415 Wing Lift curve for High aspect ratio wing and Delta wing Aircraft
Lift curve for a straight wing and Swept wing Aircraft Maximum Lift Coefficient
Lift coefficient changes with addition of control surfaces Lift coefficient changes with increase in aspect ratio and
also Angle of attack can be decreased Lift coefficient increasing with maximum thickness
Variation of Cl, CD, L/D with AOA Increase in lift coefficient with different control
surfaces or high lift devices Minimum drag coefficient
To obtain minimum drag coefficient 1) we have to streamline the body
2) Increasing the sweep angle Drag coefficient data obtained for a rectangular wing and swept back wing on wing tunnel and lifting line numerical methods
Min drag coefficient for wing section and complete airplane
It gives the maximum possible glide angle Max values of L/D ratios
Effect of Airfoil and wing geometry Airfoil Nomenclature
Reynolds No, Boundary Layer Transition and surface roughness NACA Conventional Airfoils
Laminar Flow Airfoils An airfoil designed for minimum drag
and uninterrupted flow of the boundary layer is called a laminar airfoil. Supercritical Airfoils:
Designed to delay and reduce transonic drag rise, due to both strong normal shock and shock-induced boundary layer separation
Whitchomb supercritical airfoils Drag Reduction And lift Augmentation Methods
Many theories have been developed on how a wing generates lift. The most common one is the Longer Path Theory.
This theory describes how the shape of the aerofoil produces a pressure difference which generates lift. As the aerofoil is designed in such a way that its upper surface is longer than the bottom, and because the molecules that hit the leading edge must meet again at the trailing edge, the ones that travel on the upper surface do so with
greater velocity than the lower Flap system Leading edge devices
Multi element airfoils Circulation control Laminar flow control winglets
Flap systems Flap is an element attached to the aileron
of the wing section It is always possible to reduce stall speed by increasing wing area
Different types of flap system Flaps change the airfoil pressure distribution, increasing the camber of the airfoil and allowing more of the lift to be
carried over the rear portion of the section Leading Edge Devices
Leading Edge Devices Leading edge devices such as nose flaps, Kruger flaps, and slats reduce the pressure peak
near the nose by changing the nose camber. Slots and slats permit a new boundary layer to start on the main wing portion, eliminating the detrimental effect of the initial adverse gradient.
A Wing with slats and Flaps Multi Element Airfoils
Circulation Control Circulation Control Wing technology is one of the most important potential applications of the
Coanda Effect. The objective is to replace the lift devices on the leading and trailing edges of a wing by use of Coanda Surfaces and slot blowing instead.
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