Contents
How to pick a good airfoil based on Cl?
The figure of merit when selecting the airfoil should be the ratio ₂ c L ³ ⁄ ₂ c D; this should reach its maximum at the lift coefficient of minimum energy loss. Enter the lift and drag coefficients into a spreadsheet and create a new column for ₂ c L ³ ⁄ ₂ c D (or c L 3 c D 2; doesn’t matter).
How to determine the required lift for an airfoil?
Determine desired Cl using required lift (weight plus tail download) in the following: where L is lift, Cl is coefficient of lift, A is wing area, r is density and V is Velocity. Explanation is at: Look through your Cl/AoA charts at that Cl then get Cd using the associated AoA.
What to look for in an airfoil design?
₂ c L ³ ⁄ ₂ c D (or c L 3 c D 2; doesn’t matter). Select an airfoil that maximises this value at the calculated optimum lift coefficient. If you only care about efficiency, you want the one that has the highest Cl3/Cd2 for endurance and highest Cl/Cd for range at the design Cl, which may not be zero AoA.
Which is better a real wing or an airfoil?
Since drag due to lift and the drag that is not due to lift have opposite slopes when plotted over velocity, as in the attached graph, the best lift to drag ratio is where the lines cross. That’s why a real wing can never have an L/D better than half of the airfoil 2D cl/cd.
How to describe the circulation of an airfoil?
Figure 11.2 Starting vortex formation from an impulsively started wing in an incompressible flow. Contours distinguish the circulation about the wing and the opposite signed circulation about the starting vortex. 3 The contour about the system never penetrates the vortex sheet separating from the wing trailing edge.
How to calculate the lift coefficient of an airfoil?
Enter the lift and drag coefficients into a spreadsheet and create a new column for ₂ c L ³ ⁄ ₂ c D (or c L 3 c D 2; doesn’t matter). Select an airfoil that maximises this value at the calculated optimum lift coefficient.
How are the coefficients of CD and CL determined?
These tests are used to calculate coefficients of lif and drag versus numbers Reynolds : The coefficient Cd drag and the aerodynamic coefficient Cl lift . The formula for determining these coefficients is that used for calculating the lift and drag.
How is the shape of an airfoil different for each slice?
This airfoil shape can be different if the slice is taken at different locations on the wing. However, for any given slice, we have a given airfoil. We can now think of the airfoil as an infinitely long wing that has the same cross sectional shape. Such a wing (airfoil) is called a two dimensional (2-D) wing.
Which is better a thicker or thinner airfoil?
A thicker airfoil makes for a lighter wing with more internal volume for flaps and fuel. However, if you want to operate your design at high subsonic speeds, thickness needs to be controlled. What is the lowest cruise lift coefficient and the highest lift coefficient for a clean wing and with flaps down?