Select an Airfoil

Overview

Select profiles that work well at low speeds (low Reynolds Number).

• Browse the Collegiate Wind Turbine Challenge Reports for tested designs that have worked for others.

• IMPORTANT: record the design(s) you choose.

• Visit the Airfoil Tools site and locate your chosen design(s).

Expected Wind Speed

Ms. Dooley and Mr. Willis measured the wind speed in Willow Bend’s wind tunnel, which will likely be used at the competition.

At the center of the tunnel (24 inches from the front, 24 inches off the ground, and centered left-to-right), we measured 4.1 meters per second with the fans on medium speed (the speed we tested our kits at) and 4.0 meters per second with the fans on high speed (yes, it was slower!).

Collect Performance Data

We are only interested in performance data for low wind speeds (low Reynolds numbers). On the Airfoil Tools site:

1. Uncheck boxes for any Reynolds numbers above 100,000 and click the Update plots button.
   
2. Create a screenshot of the Cl v Alpha plot for your team’s documentation.
   

A CL vs. alpha (α) plot shows how much lift an airfoil produces at different angles.

• CL (coefficient of lift) \= how much lift the blade makes
• Alpha (α) \= the angle between the wind and the blade

Steps to Use the Plot

1. Find the peak (before stall)
   Look for the highest point on the graph before it drops off.
   This is where the airfoil makes the most efficient lift.

2. Choose a good operating angle
   Don’t pick the very top—choose a slightly lower angle (often \~4°–8°).
   This avoids stall and keeps the blade stable.

3. Set your blade pitch
   Use that angle to decide how much to twist your blade in your design.

4. Adjust from root to tip

5. Near the hub (root): larger angle

6. Near the tip: smaller angle
   This helps the whole blade work efficiently.

Key Idea

You are using the graph to pick the best angle for your blade to “slice” through the air and generate lift without stalling.