Understanding Aerodynamic Forces: A Lab Guide for Students

UNIV-EN 1131 Student Success Aerodynamic Forces Lab Learning Objectives In this lab, you will learn about the following concepts: - The concept of aerodynamic force in airfoils - Some basic terminology of wings and propellers - Basics of wind energy production - Measuring the aerodynamic lift of a wing section - Measure the electrical output of a wind generator - Using a spreadsheet to compile, calculate, and visualize data sets. - Calculating the statistics of the data taken by all the teams in your section Deliverables - Day A and Day B worksheet filled out as a TEAM but ALL team members must upload a copy - A filled-out Word document of the reflection report (last page), worked on INDIVIDUALLY and uploaded by INDIVIDUALLY by all team members Introduction Aerodynamic forces play an important role in many of the conveniences in modern life, in such areas as airplane propellers and wings, automotive design, wind generation, and the design of building. In this lab, we will seek to explore of aerodynamic forces in a wing section and a propeller. Figure 1. Photo credit: quora.com

In courses such as MAE 3182 (Aerodynamics and Fluids Lab), MAE 3305 Flight Performance, Stability, and Control), CE 3305 (Basic Fluid Mechanics), these concepts as explored in more detail. Wing Airfoils The general shape of symmetric and cambered airfoil types are shown in the Figure 1. Symmetric designs are suited to higher-speed operation and cambered designed work well at lower speeds. The airfoil creates force called lift due the different path taken by the air above and below the wing as shown in Figure 2. The air travels faster on the top (covering a longer distance in the same time) and slower on the bottom causing a higher pressure on the bottom than the top of the wing, pushing the wing up. When looking at the wing, the following figure shows several important parameters. The chord line is drawn from the leading edge of the wing to the trailing edge. The angle between the chord line and the air stream is called the angle of attack. A cambered design can even produce lift at a zero degree angle of attack, whereas a symmetric design requires a positive angle of attack to produce positive lift. Figure 2. Photo credit: uaf.edu Figure 3. Photo credit: aerospaceweb.org

In our lab, we will evaluate a symmetric airfoil section. Each team in the lab will evaluate a custom made airfoil, each with varying properties. Propellers Another application of the airfoil is in the design of propellers. The propeller uses a different set of parameters to describe it, with the concept of angle of attack being replaced by the pitch of the propeller. A way of thinking about pitch is to consider the amount of forward progress a propeller will make for every revolution. For instance, Figure 4 shows a typical RC plane propeller sized 12x6 which indicates a tip to tip distance of 12” and a forward movement of 6” for every rotation: One interesting thing to consider is that there is often a twist in a propeller so that the angle of attack remains constant along the blade from the root to the tips. In other words, the circumferential path taken by a point on the propeller near the root is less a point at the tip so the angle changes from tip to the root. This can be seen in Figure 5: Figure 4. Photo credit: rc-airplane-world.com Figure 5. Photo credit: pilotfriend.com

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In our lab, we will test a small model wind generator using 3 propeller blades which allow the pitch to be changed. Materials For this lab, you will need the following materials: Table 1 Component Count Wing airfoil platform (per team) 1 Wind generator platform (per team) 1 Scale (with 1g resolution to measure wing lift) 1 Voltmeter (to measure wind generator output) 1 Protractor (to measure angle of attack) 1 Fan (per table – per team pair) 1 Letter size paper for 11” separation (one per team) 1 More Information This course was developed by the College of Engineering PI (Program Initiative for New Students) team, with members from each department in the College. The lab was designed by Dr. Jason Losh (CSE Department) and Dr. David Ewing (MAE Department). All members of the Engineering PI group hope that you find this lab interesting and insightful. Please feel to contact your instructor, jlosh@uta.edu , or david.ewing@uta.edu if you have feedback or further questions about this lab. Setup for Wing Airfoil Measurement (Day A)

You will start with an airfoil platform assigned to your group, such as the one shown in Figure 6. The airflow will approach the airfoil from the left. Figure 6 Using the box fan on your table (shared between 2 teams), position the edge of the airfoil platform on a scale approximately 11” (the length of a standard sheet of copy paper) from the front edge of the fan (the length of a piece of letter size paper. The best airflow from the fan is often best when not aligned with the center of the fan. An example setup is shown in Figure 7. Figure 7 One of the key parameters to be measured is the angle of attack. While the angle of attack is defined as the angle between the chord and the airflow. Figure 8 shows a protractor measuring

an approximately 0 degree (left) and 20 degree angle. Note the airfoil platform is designed to lay on its side so the protractor can be easily used to measure the angle. Figure 8

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Setup for Wind Generator Measurement (Day B) Figure 9 The wind generator platform looks similar to the one in Figure 9. When the air flow applies force to the propeller, the propeller spins and turns the DC permanent magnet motor mounted to the hub which acts as a generator. The angle of each of the propeller blade pictured in Figure 9 can be rotated as needed to optimize performance.

f Figure 10 When measuring performance, position the fan and wind generator as shown in Figure 10, with a separation of 11” as in the wing airfoil lab. T he pitch of the propeller can be measured at the tips as shown in Figure 11 showing about a 10 degree angle. Note that the wind generator is leaned on its side supported by a propeller tip. The flat side of the protractor is aligned with the dowel rod.

Figure 11 A multimeter is connected to the generator as shown in Figure 12. The multimeter dial should be rotated to the mV position to measure milliVolts. Insert the red and black leads in the indicated positions on the multimeter. Figure 12 Aerodynamic Forces Lab Instructions for Day A 1. Download the Excel Worksheet from Canvas, in the Modules section. The Module title is “Engineering Lab 2 – Aerodynamic Forces” and the file name is “Aerodynamic Workbook.xlsx”. 2. Navigate to the “Day A – Lift Lab”. This is where you will be recording your readings in the yellow highlighted cells. The green highlighted cells are cells that will automatically calculate things for you. 3. Record the serial number of the wing airfoil platform you used in the appropriate area in the spreadsheet. 4. Setup the fan, scale, and airfoil platform with a separation of 11” as described in the Wing Airfoil Measurement section. 5. Make sure the fan is turned off. Power on the scale and tare (zero) the reading with the airfoil platform on top of the scale. 6. Adjust the airfoil to an angle of attack of zero degrees. You can measure from the bottom side of the airfoil to the bracket as illustrated in Figure 8.

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7. Turn the fan on low. You should notice that the mass displayed on the scale will read as a negative value due to lift. Tweak the position of the fan, maintaining a level air flow and the 11” separation from the fan face to the front of the airfoil platform to maximize the negative value. 8. Record the reading (as a positive value) in the first trial row. 9. Adjust the angle of the airfoil until maximum lift (largest negative mass) is shown on the scale. Record the reading (as a positive value) in the first trial row. 10. Measure the angle using a protractor that resulted in the maximum lift in the first trial row. 11. Reset the airfoil back to zero and repeat steps 7-10 for the second and third trial rows. 12. After filling out the three trials, reset the airfoil back to the 0 degree attack angle. 13. Repeat steps 7-10 for one trial at the medium speed and one trial at the high speed. 14. Share your findings with the other teams in the classroom. 15. Ensure that your area is picked up properly and cleaned. 16. You may want to consider working on the writeup with any time left that you have and during the week (don’t wait until the last minute to complete).

Aerodynamic Forces Lab Worksheet for Day B 1. Open the spreadsheet you saved from Day A and navigate to the “Day B – Turbine Lab” tab. 2. Record the serial number of the wing airfoil platform you used in the appropriate area in the spreadsheet. 3. Setup the fan and wind generator platform with a separation of 11” as shown in the Wind Generator Measurement section. 4. Adjust ALL the propeller blades (as reference in Figure 11 and the procedure describing it) to the pitch that results in the maximum voltage as displayed on the multimeter in the mV range. This will be an iterative process so it may take a few minutes. Start with 10 degrees and adjust all the blades one way or another to find this maximum voltage. 5. Measure the angle of the propeller tip as shown in the Wind Generator Measurement section in Figure 11 corresponding with the voltage in step 4. This will go into the first two highlighted boxes on the spreadsheet (max voltage and angle at maximum voltage). Do NOT adjust the individual propellers for the rest of the experiment. 6. Once you have found the optimal angle of the propeller blades in steps 1-5, we will now look at the output of the wind generator when it is not pointed into the wind (maybe the wind is variable in direction or not perfectly aligned). Use the protractor to vary the angle of the wind generator platform (NOT propellers) relative to the direction of the fan. For reference, 0 degrees is the angle used in steps 4 and 5. Use angles of 0, 15, 30, 45, 60, 75, and 90 degrees and record the voltages in the spreadsheet. 7. You will notice that the graph in the spreadsheet will automatically display your results for you. You will need them for the writeup you will have to turn in later. 8. Clean up your area before leaving the lab. Don’t forget to turn off the multimeter to save the batteries. Offset the propeller blades slightly in preparation for the next section so they start from scratch.

Aerodynamic Forces Lab Reflection Report Homework Assignment (type in your answers after each question. Please italicize your answers to make them distinctive). 1. The experiments on both days explored the application of Aerodynamic forces (forces caused by moving air). In your own words, compare and contrast how these forces were used/applied. Both experiments explored the effects of aerodynamic forces, but they applied them to different devices. In Day A, a wing airfoil was tested to understand how varying the angle of attack affected lift generation. On Day B, a wind generator was tested, focusing on the efficiency of propeller blades' pitch angles for electrical output. Day A emphasized lift for airfoils, while Day B aimed to maximize energy generation in wind turbines . 2. Which experiment caused more fluctuations in the data? What do you think caused these fluctuations? The experiment on Day B, involving the wind generator, caused more data fluctuations. These fluctuations is due to the changing nature of wind and the challenge of finding the optimal blade pitch angle. Changes in wind direction and intensity can lead to variations in airflow, directly impacting the electrical output. Fine-tuning the pitch angle is a difficult process, and minor adjustments can result in significant fluctuations in the measured voltage output due to the sensitivity of the system to angle changes. 3. Look for the teams that had the largest variation in their measurements vs that of the other teams in your section. What could explain these differences -- equipment, measurement technique, or something else? Remember that every team is using a unique airfoil platform. Is there any correlation between these outliers and the standard deviation in the team’s reported measurements? Teams with the most significant variations in measurements compared to others may be affected by several factors. These differences could result from a combination of equipment variations, measurement techniques, and unique airfoil platform characteristics. The differences in airfoil platforms could lead to variations in lift sensitivity or efficiency. Teams might use equipment with different precision levels, affecting the accuracy of measurements. Additionally, teams with higher standard deviations could likely have larger measurement variations, indicating a correlation between outliers and standard deviation within the team's reported measurements. 4. According to your observations and background reading, how would you maximize the airfoil’s performance? To optimize an airfoil's performance, identify the ideal angle of attack, maintain smooth airflow, select the appropriate airfoil shape, ensure surface integrity, and explore control surfaces and aerodynamic enhancements. 5. According to your observations and background reading, how would redesign the wind turbine to maximize its output? Consider wind direction, blade attack angle, etc.

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To redesign a wind turbine for maximum output, one should ensure the turbine is oriented to face the prevailing wind direction

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