I have always been interested in flight, so I chose project having to do with engineering and aerodynamics. I chose the idea of dimpling an airfoil (airpllane wing) like a golf ball, in hopes that the dimples would create the same kind of turbulence and vortex generators on the wing that it does on a golfball. After building my own wind tunnel, modeled off the original wright brother's wind tunnel, I hand-crafted around 30 balsa-wook airfoil prorotypes, adding bibi's and shaving them down until each airfoil was the exact same mass and size. I dimpled some10% into the airfoil, starting at the trailing edge, and went up to 20%, 30%,40%,and 50%. I then tested them in my wind tunnel at an angle of attack at 7 degrees (all airplanes fly at an angle, so that they can climb). After canculating the tangent of each degree I recorded the airfoil regressing towards (using tangent because the lift to drag ratio works like a right triangle), I found that the airfoil dimpled at 50% reduced drag by an entire perfent, which is incredibly significant. This means there was turbulence causing the air pressure to attach more closely to the wing rather than creating drag. Reducing drag means saving thousands of dollars in flightfuel! I plan on furthering my research at the college or university I attend, building with real airfoils rather than balsa wood.
Question: Can I make an airplane wing perform like a golf ball in the sense that dimples of the same depth and density will reduce drag for a plane the way it does for the ball, and will I be able to measurably calculate the power of the vortex generators and turbulence acting on the wing?
Hypothesis: Yes, like a golf ball, Bernoulli's principle of fluid dynamics will work the same way on an airfoil, meaning the dimples on the airfoil will allow turbulence and vortex generators that cause the air pressure passing over the wing to conform to the surface area covered in dimples, thus reducing drag. I think I will be ableto soundly record myresulty, and do so accurately my measuring precise degrees in a wind tunnel as I test my dimpled airfoils.
Website: 2.972 How An Airfoil Works, web.mit.edu/2.972/www/reports/airfoil/airfoil.html.
This website describes the baseline for how an airfoil works. It goes into detail about how the curvature, length, and shape of the airfoil accomplishes different tasks for lift. It explains how air passes over the top of the airfoil and circulates down under it, which creates a higher velocity above the wing and lower velocity below the wing. This epitomizes standard lift. Also mentioned is Bernoulli’s Principle, which states that because of the way velocity increases when airflow circulates the airfoil, pressure is higher below the wing than on top of it. Based on this principle, Euler’s equation shows that the actual curvature of the wing forces pressure to be lower on top of the wing to be lower due to the ambient pressures. The website goes further into giving the equations and explaining what each part means.
Website: “How do dimples in golf balls affect their flight?” Scientific American, www.scientificamerican.com/article/how-do-dimples-in-golf-ba/.
This website explores the aerodynamics of a golf ball. Golf balls without dimples travel only half as far as golf balls with dimples, because there is no circulation of air being exerted from the ball. This, as well as the round shape and spin of the ball itself, is what makes it so fast and far-reaching. Like an airfoil, lower pressure is on top of the ball while higher pressure is on top, creating the same principle as a standard airfoil.
website: NASA, NASA, www.grc.nasa.gov/www/k-12/airplane/shape.html.
Lift is determined by the flow of air on the shape and size of an airfoil. The greater the flow of air, the greater the lift. The trailing edge has a huge impact on this, as the shape of the trailing edge controls where the flow goes. Lift can also be depicted by the lift coefficient, which explains how dependencies on shape, inclination, and flow conditions impact lift. The geometry and symmetric relationships of an airfoil also impact the aerodynamics.
The turbulence layers that a golf ball encounteres when flying through unstable air are actually nice for the ball, and the dimples get to play their part. The dimples of the ball rotate the air, creating a backspin, and launching itself through the air. What causes the ball to finally acknowledge Nweton’s Law of Gravity is the fact that there is still drag on the skin of the ball, however little, that slows down the motion. The friction pulls the air to the ball and slows it, though the dimples are able to manipulate it in its favor still.
The research above taught me about the aerodynamic laws involved in how dimples work on a golf ball and how an airfoil works with the lift:drag ratio. This validates my project by teaching me what i needed to know about how both could work together. If i can make these work hand-in-hand, then the world will benefit by the arline industries not having to pay as much for fuel.
1. Print out a cutout of a standard Clark Y airfoil
2. Rubber cement a piece of balsa wood to the paper cutout, and let it dry.
3. Cut out the balsa wood to be roughly the shape of the cutout with a saw table. WEAR SAFETY GLASSES, balsa wood is very soft and shreds easily. Make sure you have a 5-inch width on the balsa wood.
4. After cutting out the balsa wood to roughly the shape of the pasted paper cutout, use a sanding belt to sand the wood right down to the shape of the cutout.
5. Use a hand sander to smooth the surface of each airfoil, and sand them so that each are the exact same height, width, and length.
6. Use a scale, set to measure in grams, to measure the weight of each airfoil.
7. If the airfoils aren’t all the exact same weight, drill a hole in the exact center of the COG and drop in bibi’s until they all weigh as much as the heaviest airfoil. Cover in hot lue and add a lead magnet to keep them all contained.
8. Once each airfoil is the exact same, start to dimple from the trailing edge to 10% into the airfoil. Make sure each dimple is 3.36mm deep, and use graph paper to make sure they are all the same distance apart.
9.Dimple another to 20%, and increase by 10% intervals until you reach 50%. Keep one airfoil plain, that will be your control.
10. Once all of the airfoils are dimpled correctly, test them in the wind tunnel and measure their angle of attack in comparison to the drag after lift is reduced by taking the tangent of the degree recorded minus the initial angle of attack. Set this angle of attack at 7 degrees, because that is the AOA of most Clark Y-winged planes. You reduce lift by pressing back on the airfoil, and measure the angle of attack by letting go of the airfoil and watching what the new degree is.
11.Record your results.
This testing was done at the EAA hangar in Billings Montana, mainly so I would have enough room to do the testing. For safety, goggles and gloves were worn during the entire experiment. I ensured the process was fair and relevant by building every airfoil to be the exact same mass and size, as well as making the wind tunnel a balance-scale, so that results weren't false based on just the wind tunnel.
|Trial 1||Trial 2||Trial 3||Average|
The table above represents 3 trials of the same 5 airfoils being tested at an initial angle of attack at 3 degrees. The numbers recorded are the final degrees of drag. As you cantell, there is no distinct pattern. This trial is not very significant.
|Trial 1||Trial 2||Trial 3||Average|
The second table represents the airfoils tested at an angle of attack at 7 degrees. The numbers recorded also are the final degrees of drag. This table does have a distinct pattern. When it comes to drag, bigger numbers are better, meaning in the wind tunnel, it reads a greater amount of lift. Trials 10%-30% mainly resemble the control in that the numbers are pretty much the same. However, 40%-50% have greater numbers, especially at 50% having an average degree of 10, which means drag is being reduced and lift is increased! After averaging the tangents, there is an entire degree of reduction in drag, which could potentially save thousands of dollars in airline fuel.
After building the airfoils and testing them in the wind tunnel, I found that, when flying at an angle of attack at 7 degrees, airplanes with dimpling up to 50% of their wing, starting at the trailing edge, will actually have a reductionin drag during flight because of how the dimples cause the low air pressure on top of the wing to turbulate, like vortex generators. This answers my question that, yes, dimples on an airfoil will reduce drag, but the wing needs to be covered at LEAST 50% with dimples. Initially I thought that any dimpling would have an effect, which perplexed me when airfoils 10%-30% did not have a change. After researching why this might be, I found that, almost directly in the middle of the wing, there is a center of gravity point where air flows straight back. This means the air flow will never reach parts of the wing where there isonly 10%-30% dimpling. Because the 50% dimpling does reach the center of gravity, air can turbulate instead of flowing straight off the airfoil.
The limitations on this experiment were the supplies I had. Everythig was hand crafted, so of course there is room for human error. This would be fixed If I had access to a lab with a larger wind tunnel and materials such as aluminum or carbon fiber. Carbon fiber airfoils are the one thing I would change, and i would dimple beyond 50% to see if there are greater amounts of reduced drag.
The reason this project hasn't been done yet is because it is not preferable to dimple aluminum. This is why carbon-fiber made planes, which are currently being tested, need to come before my dimpling method, as it is much more malleable of a substance. If dimpling on carbon fiber works, then this could have paramount impacts on the aviation industry. Potentially, this could save thousands, or even hundreds of thousands of dollars in fuel.
This experiment has done wonders in increasing my interest in aviation and the engineering behind it. I hope to progress in my studies and experiment on many types of planes, and maybe someday, even implement it on planes around the world.
Below is a link to a youtube video in which I explain my project to a class.
I have always been interested in aviation. My father is a pilot and I am also taking steps to get my own private-pilot's license. Doing this project not only taught me, but gave me a real sense of who I am. Never before have I been so confident about anything as I was with this project. I was inspired by anaerospace teacher from middle school, Patrick Kenney. His lessons inspired the project.
I have always dreamed of attending the University of Maryland Cllege Park, where I would double major in Aerospace Engineering and politics. Washington D.C. is five minutes away from College Park, and I love Naval History, which makes Maryland perfect.
I'm not going to sugar-coat anything here. I cannot afford to attent this college without scholarships, even after student loans. It terrifies me that, after all the work I've done in high school, I may not even get to attend based on finances alone. Winning this scholarship would mean the difference between me getting the college education of my dreams or not going at all. On top of school, winning would mean all this research would mean it wasn't just some project with no purpose. Others seeing the impoartance of my project will insipre me further.
I greatly thank you for the opportunity to compete for this scholarship in the first place, and I hope my research will inspire you as well in the field of aviation and the great things yet to come.
I worked in the EAA hangar, where I was ablle to use wood-working supplies such as bandsaws and sanders. Safety such as goggles and gloves were used throughout the expeeriment to maximize safety.
Patrick Kenney wasa my mentor. You can contact him at firstname.lastname@example.org
Disclaimer: During this project, there were no major or minor injuries. My mentor had done projects with students before, and knew what sort of safety protection I would need in conducting my experiment.
Websites used for research:
“Aerodynamics - Real-Life Applications.” Science Clarified, www.scienceclarified.com/everyday/Real-Life-
2.972 How An Airfoil Works, web.mit.edu/2.972/www/reports/airfoil/airfoil.html.
“How do dimples in golf balls affect their flight?” Scientific American, www.scientificamerican.com/article/how-do-dimples-in-golf-ba/.
NASA, NASA, www.grc.nasa.gov/www/k-12/airplane/shape.html.
This is an acknoelwdgement of Patrick Kenney, my adult mentor, and all of his guidance in the mathematics, as well as teaching the sciences behind the hand-build wind tunnel and the understanding of balance systems when using the lift;drag ratio.
This is an acknowledgement to the EAA Hangar used, where the project was conducted and supplies were given. Patrick Kenney is the owner of this Hangar.