aeroanalysis
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Joined: 8/16/2003
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Step by step process for lofting a tapered wing panel in Solidworks.
1. Create your root and tip airfoil coordinate files. Airfoil coordinates can be downloaded from the UIUC airfoil coordinate database website or Hepperle's site etc. Good practice is to leave the airfoil as a unit chord (chord = 1) and scale in Solidworks. If you are truly concerned about precision, normalize the coordinates in Excel by dividing all of the x and y coordinates by the maximum x-value in the file minus the minimum value. Coordinates often are often of a chord of 0.99875 or 1.00031 etc, and start at x=0.00046 or something. If this doesn't make sense to you, ignore it, it's for people who are going to use their CAD files to generate CNC tooling and need precision.
2.Coordinates need to run trailing edge to trailing edge. That means that the first x value in the list should be 1, and drop down to zero at the leading edge, and then increase again back to 1. Coordinates often come as leading edge to trailing edge, then leading edge to trailing edge. Use the "sort" command in Excel to fix it. Plot the airfoil in Excel to make sure it looks right. If there is an extra line joining the trailing edge to the leading edge, you have it wrong.
3. Add a column of zeros between the two columns. Now you have airfoil coordinates located on the xz-plane (aerospace coordinates). Solidworks needs 3 coordinates for each curve point, so even if you insist on working in the XY plane, you need three columns. You can continue to use y as the vertical axis, but you might want to train yourself to use z as vertical, and y the axis in the direction of the right wing). Now save the Excel spreadsheet as a "space delimited" file ( filename.prn). In Excel, go to "File/save as", and in the filetype, select the "space delimited" option. After you have saved it, open the file up in "Notepad" or some other text editor and make sure that there are only spaces between the columns, not tabs. If there are tabs, you will know it because the cursor will jump several spaces when you move it to the right or left across a tab. It should move only one space at a time. There cannot be any header rows. The first line in the file is the first coordinate, no name or anything. There should be three columns, with a couple of spaces between the entries. If everything is okay, save the file. One last thing, Solidworks will only "see" .txt files or *.sldcrv files. So again, using "Notepad", do a "Save as" and change the file type to .txt. That should do it.
4. Open a new part in Solidworks. Get the coordinates in the model set up properly, so that z is up, x is towards the tail, and y is out the right wing. Save this as a template so you don't have to do it again. Create the root and tip planes for your airfoil sketches at each end of your wing panel. Unless your panel has no leading edge sweep, you will need to use a 3D sketch to define the wing leading edge, which you will later need to define the plane at the tip. To generate the 3D sketch, sketch a construction line that defines the planform (top view). Add another construction line at the end point of this first line that defines the front view, (the length sets your dihedral for the panel). Dimension the lines so that you have a defined, parametric sketch. The leading edge line can now be drawn between the origin of the first line (which also should be at the global origin) and the top of the vertical line. IMPORTANT NOTE, draw the line from Root to Tip! I'll explain why later. (You could also do this with two, 2D sketches, but that requires more steps and an additional 2 planes to create, no thanks)
5. Use the "reference geometry/plane" tool to insert a new plane. Check the "normal to curve" box. Check the "set origin on curve" radio button. Select the leading edge line and click okay. Presto, you now have a reference plane in the right place at the right angle, with a local coordinate system at the leading edge. This is why you needed to draw the leading edge line from root to tip. If you draw it from tip to root, the reference coordinate system will be backwards and when you copy your airfoil to this plane, it will come in upside down, doh!
6. Time to bring in the airfoils. Use the "Curves/Curves through XYZ points" tool or use the "Insert/Curves/Curves through XYZ points" command. Hit the browse button and select the file extension type to .txt and browse for your airfoil file. I keep mine in the parts folder so I don't have to go looking all over my files for it. Select the airfoil for the root and a little mini spreadsheet should appear with the columns filled in with your coordinates. Cool, eh? Hit okay and the airfoil is now in the model, and a "curve" is in the the drawing tree. Note that this is not a sketch, and it can't be manipulated like a sketch.
7. For the root airfoil, select the "right" (XZ) plane and start a new sketch. Select the airfoil either in the drawing tree or in the model. Hit "convert entity". Now you have a copy of the airfoil on a sketch. Scale it to your root chord using the "Tools/Sketch tools/Scale-copy" command. Done with the root.
8. Bring the tip airfoil in. You can name the root airfoil curve "root airfoil" so that you can select it from the drawing tree, which might be easier if the root and tip airfoils are similar because they will end up right on top of each other when you import coordinates and will be hard to tell apart when you try to select them in the model. Select the "Right" (XZ) plane and start a new sketch. Apply "Convert entity" to the tip airfoil curve and now you have a sketch of your tip airfoil. Exit the sketch.
9. Now, here's the trick to getting your tip airfoil sketch onto your tip plane. In the drawing tree, select the tip airfoil sketch. Type "Control c" to copy the sketch, select the tip plane, and type "Control v" to paste it onto the plane. This makes a new sketch for the tip airfoil. There is no "copy/paste menu commands. You must use the keyboard short cuts.
10. Almost there. The tip airfoil should be proudly sitting on your tip plane, correctly oriented with the airfoil leading edge at the...leading edge. Open the tip airfoil sketch, scale the tip airfoil to the tip chord, and rotate it if you need to add twist. Exit the sketch. Click the "Lofted boss/base" button, or use "Insert/Boss/Lofted boss/base" command. Select the root airfoil, select the tip airfoil. You don't need the leading edge curve for the loft. Hit Okay. Tah dah! Tapered wing panel!
If I made any errors, or if there is a simpler way to do this (it took way longer to write than to do) let me know. Happy modeling!
-d
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RE: Tips And Tricks for CAD Programs. - 
