Wing Section Profile
Having selected a suitable wing section profile, a set of coordinate points needs to be generated. There are many spreadsheets that can be found on the Web that can generate these coordinates. Figure 17.23 gives an example of an NACA four-digit coordinate calculation, in this case producing the NACA 2412 section that is widely used on light aircraft.
In whatever way the coordinates are produced, it is important that one generates enough points to generate an accurate, smooth curve, which is then going to be imported into Solid- works. The data needs to be formatted into columns of x, y, and z coordinates (even though the z coordinates will all be zero) and saved as a text file. From within Solidworks, this can now be imported as a .txt file to generate a curve using the “Insert/Curve/Curve through XYZ points” command (Figure 17.24).
Figure 17.23 NACA four-digit section coordinate spreadsheet.
Figure 17.24 Curve importing in Solidworks.
In this case, 60 points are used to create an adequately smooth curve. Notice that by zooming enough into the rear edge of the section, it is apparent that it is an open shape. This will be important later on.
This initial curve is reference geometry and cannot be directly used to construct solids and surfaces. The next stage is to create a sketch using this reference curve. To do this, we open a sketch on the XY-plane that the curve sits on.
We then need to carry out the following:
Use the “convert entities” command to convert the reference curve to a sketch curve - the curve turns black when this is carried out to indicate that it is fully defined, Figure 17.25.
• At this stage, it is useful to close the shape (if open), see Figure 17.26. This can simply be accomplished by drawing a line between the two ends of the curve (if it is small; which it should be if we have at least 60 points in the input *.txt file), Figure 17.26.
Figure 17.25 Use of “convert entities” in Solidworks.
Figure 17.26 Closing the 2D aerofoil shape.
Figure 17.27 Deleting sketch relationship with reference geometry.
Next we need to “decouple” the sketched curve from the reference curve so that we can scale it later on - we need to ensure that “view sketch relations” is selected in the view palette and then delete the green “cube” symbol. The sketch curve should turn blue to indicate that it is not fully defined now, Figure 17.27.
- • Then we must construct some reference geometry to constrain the section and allow it to be scaled. Touching vertical and horizontal reference lines therefore need to be defined, Figure 17.28.
- • A number of constraints now need to be defined to tie the section geometry to this reference “scaffold”; the curve needs to pierce the junction point of the lines, and the rear end of the section needs to be tied to the end of the horizontal line. A dimension can now added to the horizontal line to scale the wing section, Figure 17.29.
Figure 17.28 Reference geometry.
Figure 17.29 Constraining curve to reference “scaffold” geometry.
-  A particularly good source of coordinate data can be found at http://airfoiltools.com/plotter/index.