Brian Johansen, Mechanical Engineering
The purpose of an airplane wing is to provide lift by creating a pressure gradient between the top and bottom of the wing. However, this pressure gradient causes some inherent problems at the wing tip. A vortex forms when the high pressure from the bottom side of the wing flows around the wig tip to the top side of the wing. This vortex is detrimental not only to the lift that the wing can produce but to the fuel efficiency of the airplane.
In order to alleviate this problem engineers have turned to the winglet. A winglet is a vertical fin placed at the tip of a wing. It acts like a dam preventing the flow of air from the bottom of the wing to the top. Presently, winglets are being used on airplanes such as the Boeing 747-400 and many small business jets. The purpose of my research was to determine whether or not the winglet would be beneficial to smaller wings at speeds below fifty miles per hour. In order to conduct the experiment I designed several different winglets as well as a wing made out of fiberglass.
The wing was mounted in a wind tunnel in such a way that the angle of attack (the angle that the wing makes with the oncoming wind) could be changed. Strain gages were attached to the aluminum bar that the wing was mounted on. The readings from the strain gages were then converted to lift and drag forces as well as moment forces. From this I was able to determine what effect the various winglets were having on the wing.
The results of the experiment showed that the use of a winglet does in fact enhance the aerodynamic properties of a small wing at low speeds. Figure 1 shows the results for one of the wind speeds used in the experiment. It compares the results of the wing without a winglet, a winglet that has no airfoil built into it (flat plate), and a winglet with an airfoil built in (winglet). The graph compares the lift vs. drag ratio of the various configurations to the angle of attack of the wing. At the low angles of attack the winglet does not seem to enhance the performance of the wing. This is due to the weak pressure gradient that is being produced. But as the angle of attack increases, the strength of the pressure gradient also increases. At approximately 1.5 degrees the winglet begins to help the performance of the wing. Under normal flight conditions the wing would be flying at an angle of attack between 2 and 6 degrees. By using a winglet, the overall aerodynamic characteristics of the wing are enhanced by 11%.
This research project has been the most beneficial experience that I have had here at Brigham Young University. It has taught me many things that I would not have been able to learn under any other circumstance. It has also helped me apply theories I have learned in the classroom. However, the most important thing it has given me is the confidence to carefully plan out and take the necessary preparations to see a research project to a successful conclusion. I would and do recommend this experience to anyone who is willing to work and wants to have a good learning experience.