Activity 1.2.7 Airfoil ConstructionIntroduction

Computer simulation is an excellent tool for predicting performance; however, it is not perfect. Engineers and technologists test physical models to verify a simulation prediction.

In this activity you will construct a physical airfoil model for wind tunnel testing.

Equipment PC with Autodesk Inventor software Engineering notebook Pencil Styrofoam Foam cutter Aluminum flashing Scissors 6d x 2” Finish Nails Drill bit sized for finish nail Fine grit sandpaper e.g. 220 grit Spray adhesive Model profile data from airfoil simulation

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Procedure1. Open the FoilSim model created in the previous activity. Select the Geometry tab

and highlight the Coordinates and press Crtl-C to copy the data.

Airfoil Coordinates

2. Open a spreadsheet such as Microsoft Excel. Paste the data into a worksheet. Place labels at the top of each column for X and Y.

3. The data is scaled to represent one unit along the x-axis beginning at the trailing edge. Find the coordinates representing the leading edge and insert a row. Place labels for the upper and lower surfaces. The physical model will be approximately 4 in., therefore the data must be scaled by a factor of 4. Create two columns labeled X-Scale and Y-Scale. Use a formula function to scale the data. Below is an example.

Spreadsheet Showing Formula

4. Engineers frequently perform quality checks of their work. A quick data quality verification can be done by creating a scatter plot with the data to confirm that it resembles the airfoil.

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Scatter Plot to Verify Data

5. Highlight the scaled coordinate columns. Open a new excel file and click Paste Special and select values to import the calculated values. Save this file.

6. Start a new Autodesk Inventor part file and start a sketch on the front plane (XY Plane)

7. Select the Sketch tab on the ribbon. Click Points in the Insert menu and select the Microsoft Excel file saved previously. The text labels

Insert Points

Data Points Imported

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8. Select spline and use the existing points to draw the airfoil starting at the trailing edge. Ensure that the actual points are selected indicated when the select position turns to the color green. Misplaced points can be corrected after the spline is created by ending the spline function, left clicking the point and dragging it to the correct position.

Spline Drawn

9. Add a 5 in. x 2 in. rectangle around shape keeping the airfoil approximately in the center. Add two 0.125 in. diameter holes in a large part of the airfoil forward and aft. These holes will serve as future template alignment guides. Add forward and aft tangent lines to guide hot wire entry. See the example below.

Airfoil Template

10.Save the file.

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11.Open a new .IDW file.

12.Edit the sheet size to be an A-size and delete the title block.

13.Select Base, select Front orientation and confirm that the file is the .IPT file saved earlier. Place the view towards the top of the page. Select Base again, select Back orientation and confirm that the file is the .IPT file saved earlier. Place the view towards the bottom of the page. An example is shown below. Print three copies of this page.

Airfoil Templates

14.Print two copies of the template and label the templates for cutting.

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Airfoil Templates with Guides

15.Cut a 5 in. x 2 in. rectangle of aluminum and adhere the template to the aluminum. It is typically more efficient to apply the adhesive to the back of the paper then placed the paper on the aluminum.

Transfer the template to the Aluminum

16.Use the template guide to cut the aluminum flashing. Drive a finish nail through the eight alignment holes using a block of wood for backing. The final templates should resemble images below.

Templates on Aluminum

17.Prepare a piece of Styrofoam to be 2 in. x 5 in. x 5 in.

18.Adhere the top templates to the right and left sides of a Styrofoam block. Push finish nails into the four alignment holes.

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19.Use the foam cutter to cut the top of the Styrofoam block. See image below.

Styrofoam Cutter

20.Remove the top templates from the Styrofoam. Adhere the bottom templates carefully positioning these using the previously punctured nail holes.

21.Rest the top shell on the top of the airfoil to allow a better grip on the airfoil. Cut Styrofoam using the bottom template. The airfoil will resemble the image below.

Airfoil Shells

22.Prepare the airfoil for mounting to the testing. Adhere a metal mounting tab to the airfoil lower surface. Ensure that the tab is aligned parallel to the cord and approximately at the midpoint of the cord.

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Airfoil with Mounting Tab

23.Congratulations. You have a physical airfoil ready to test in a wind tunnel.

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Conclusion

1. Explain how you might expect construction imperfections to impact airfoil performance.

2. Explain how the construction process coulbe improved.

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