The Effect of Winglet Design on Weight of Aircraft Due to Lift and Drag
Winglets are a type of wingtip device attached to the tip of aircraft wings, which serve the purpose of reducing drag, increasing fuel efficiency, and increasing safety. Winglets have to be incorporated perfectly into the whole design of the wing, so there are many winglet designs, with different sizes, shapes, and upward and outward angles. The purpose of the experiment was to determine the effect of winglet design on the weight of an aircraft, as a result of reduced drag. Based upon previous research, it was believed that if an Advanced Technology winglet was used, then that aircraft would have the least amount of drag and weigh the least.
A wind tunnel was constructed, and five aircraft and an aircraft stand were 3d printed. The wingtips on the aircraft included a wingtip fence, no winglet, classic winglet, AT winglet, and an original winglet design, which was designed based upon previous experiments. Each aircraft was weighed and placed inside the wind tunnel on the stand and scale. The wind tunnel fan, 50.8 CM in size, was turned on and the weight of the aircraft was documented and compared to the previous weight. The results indicated that the original design winglet, with a mean weight decrease of 17.454 grams performed the best, as compared to the other designs with mean weight decreases of 16.702 grams, 15.93 grams, 15.05 grams, and 12.432 grams. The standard deviation for all of the levels of IV were between 0.305 and 0.905, which indicated precise results. The mean weight loss was greatest for dual feather winglet designs. While the AT winglet performed the best of the winglets currently in production, the results did not support the hypothesis that the AT winglet would have the least amount of drag and the largest weight decrease, as the original design performed better. Future considerations could include angle of attack.
Winglets are small vertical fins attached to the tip of the wing on an aircraft. They serve the purpose of reducing drag (the force, or resistance, acting opposite of the motion through the air) to save fuel, and have been around since the 1970's, as a result of the oil crisis (Larson, 2001). Many experiments have been conducted to determine the benefits of winglets, including Richard Whitcomb who determined at NASA that winglets could result in a 7% increase in fuel savings (Hossain, et.al., 2011). Whitcomb analyzed the air flow at the tip of the wing and determined that an angled surface at the tip could reduce drag, resulting in improved aerodynamics, increased flight distance, and fuel efficiency (Guerrero, et.al., 2012). There are now several types of winglets, with different sizes, shapes, and upward and outward angles.
Winglets save fuel by turning wasted energy into thrust and they reduce the wingtip vortex trails, which are the rotating air trailing behind the wing. Wingtip vortex trails are usually greatest when landing and taking off, and are safety concerns for airplanes flying behind other airplanes. Winglets reduce the takeoff distance of airplanes, as a result of a reduction of drag. However, even with these benefits, not all airplanes have winglets, as some manufacturers question the benefit of installing winglets when estimated fuel savings does not justify the cost of the winglet (Arvai, 2012). This is especially true on commuter aircraft, where winglets may result in the use of more fuel, or save marginal amounts of fuel (less than 0.5% of fuel needed without winglets). These aircraft do not maintain a long cruising altitude (about 10,000 meters), which is where winglets are most effective (Arvai, 2012). Winglets also come at a cost, including the manufacturing cost of the winglet, the added weight, and a slower climb rate (Aravi, 2012).
There are four forces that act upon an airplane, weight, lift, thrust, and drag. The weight of an airplane is the downward force that gravitation puts upon the airplane. Lift opposes weight and is what keeps an airplane in the air. Lift is created by the motion of an airplane as it moves through the air. On a level flight with constant altitude, the total of upward forces are equal to downward. An increase in angle of attack (AOA), which is the angle between the flowing air and the chord (the line between the leading and trailing edges of the airfoil) can increase lift, but it increases drag too. Engines on airplanes provide the thrust that moves the airplane. Drag opposes that motion and is caused by friction and air pressure differences. Induced drag is drag caused by lift that varies along the wing. At the tip of the wing, vortices form and create the induced drag.
Airfoils are designed to generate lift by creating lower pressure above the wing than the air pressure below. For an airfoil to be efficient, the lift to drag ratio (lift divided by drag, or L/D), must be high (Hall, 2015). The shape and size of an airfoil impacts the amount of drag, and short wide wings have more induced drag, the downward force produced by the swirling air behind the wing, which is strongest at the wingtips. Winglets are used to minimize the induced drag at the tip of the wings (Hall, 2015). The type of winglet affects the weight of the airfoil, and each have a different impact on the aerodynamics of the wing. Winglets have to be incorporated perfectly into the whole design of the wing, which is why many different winglet designs exist.
The interest in this subject came out of an air crash in 2005, and the determined probable cause of the crash. Research began on what could have been done to prevent it from happening again. The resulting knowledge sparked an additional interest in aviation. This project could be helpful in the future in becoming an aeronautical engineer. This project will be helpful to the community because of how it could help reduce fuel costs for airlines, reduce pollution, increase safety, and lower the overall operating costs for airlines.
In this investigation, the independent variable was the different types of winglets used on the airfoil. The dependent variable was the weight of the airfoil due to lift and drag. The control was no winglet. Previous research showed that the Advanced Technology winglet was one of the best winglets in the single aisle airplane market, which gave customers who used this type of winglet a 1.5% fuel burn reduction (Boeing, 2012). Due to this research, it was believed that if an Advanced Technology winglet was used, then that aircraft would have the least amount of drag and have the largest weight decrease.
Methods and Materials
The fuselage and tail of a scale aircraft, a Gulfstream G500 was 3d printed using a Makerbot Mini Plus, generation five, with 1.75 mm PLA filament (Appendix A, Diagram 7 - Pre-assembly Aircraft). The wings were 3d printed with an Advanced Technology winglet attached (Appendix A, Diagram 2 - AT Winglet). While using extreme caution, the wing was glued to the fuselage with cyanoacrylate adhesive, while wearing gloves in proper ventilation (Appendix A, Diagram 6 - Post-assembly Aircraft). The previous steps were then repeated with the remaining four levels of the independent variable, which were no winglets (the control), wingtip fence, normal winglet (on the Gulfstream G500, the manufacturer uses a modified version of the normal winglet), and an original design (Appendix A, Diagrams 1-5). The original design winglet was based on a combination of previous successful winglets to incorporate both a dual-feather winglet and raked wingtip benefits. While being careful to prevent accidental cuts and burns, plexiglas (.32 cm thick), three 0.47 cm thick boards, and a 50.8 centimeter fan were combined to produce a wind tunnel (Appendix A, Diagram 8 - Wind tunnel). A airplane stand was then 3d printed in order for the aircraft to stand on its own (Appendix A, Diagrams 9-10). The scale, airplane stand, and the aircraft were then placed inside of the wind tunnel, 20.32 cm from the end of the wind tunnel. All of these, except for the winglet, remained constant during the experiment. The aircraft was weighed and the weight, in grams, was recorded. The weight of the aircraft was the dependent variable. The wind tunnel fan was turned on, and the aircraft was observed for one minute. The weight of the aircraft was measured using the scale, the fan was turned off, and the aircraft was then removed from the wind tunnel. The data was then recorded on a data table. The previous steps were repeated 49 times for the Advanced Technology winglet and 50 times for the remaining four levels of independent variables.
The effect of winglet design on the weight of aircraft due to lift and drag is summarized in Appendix B, Table 1. While the AT winglet had the largest decrease in weight of the winglets currently in production, the original design winglet outperformed the AT winglet. The original design winglet had a mean weight decrease of 17.454 grams and the AT winglet had a mean weight decrease of 16.702 grams, only 0.752 grams less than the original design winglet. The wingtip fence had a mean weight decrease of 15.93 grams, slightly better than the normal winglet, which had a mean weight decrease of 15.05 grams. The no winglet design had the least mean weight decrease, which was 12.432 grams. The AT winglet had a standard deviation of 0.516, indicating that the results are precise. The standard deviation for the original design winglet was 0.692, indicating precise results. The standard deviation for the normal winglet was 0.761, wingtip fence was 0.905, no winglet design was 0.305, all indicating precision. The data did not support the research hypothesis that the AT winglet would have the least amount of drag and the largest weight decrease.
The purpose of the experiment was to determine the effect of winglet design on the weight of an aircraft due to lift and drag. When using dual feather winglets, the means for weight loss were higher. The original design winglet had a mean weight loss of 17.454 grams and the AT winglet had a mean weight loss of 16.702 grams. These were significantly higher than the normal winglet mean weight loss of 15.05 grams and the wingtip fence mean weight loss of 15.93 grams, both of which were single feather winglets. Another finding was that aircraft with winglets performed better than aircraft without winglets, as the aircraft with normal winglets had a mean weight loss of 15.05 grams as compared to a mean weight loss of 12.432 grams with no winglet.
The results of the experiment did not support the hypothesis but the results were consistent with the majority of previous experiments. Boeing, the manufacturer of the winglet, found that the Advanced Technology winglet performed much better than the other wingtip devices, as well as the no winglet airfoils, in testing (Boeing, 2012). This also held true in the experiment conducted, as the AT winglet performed better than the other winglets, with an average of 0.772 grams more weight loss than the next best winglet currently in use. Dual feather winglets reduce the strength of the vortices much more than the other winglets, as was found in this experiment. The AT winglet may have also performed the best of those that have been in production because of the way the AT winglet implements the properties of a raked wingtip, which was known to lower the amount of induced drag (Brady, 2013). This also could have been the reason for the original design winglet outperforming the other winglets, as it incorporates the properties of both a raked wingtip, a dual feather winglet, and a winglet. Airfoils with winglets have performed better than the airfoils with no winglet, as winglets decrease induced drag, and make vortices (the twin tornadoes at the end of a wing) weaker (Hall, 2015).
In another experiment conducted by NASA, which tested whether winglets would benefit an airplane or not, the winglet design outperformed the no winglet design (Hall, 2015). This also held true in this experiment, as the normal winglet out preformed the no winglet design by over 120%. However, this experiment contradicted an article online, which stated that winglets are just good for marketing and do not actually help the airline industry (Arvai, 2012).
Air speed could be a further consideration in future experiments, as during cruising speeds, the induced drag can account for up to 40% of the entire drag, and 80-90% of drag during take-off (Guerrero, et.al., 2012). For this reason, performance improvements that winglets provide are the most at low air speeds. As airspeed increases, induced drag decreases, but profile drag (drag caused by friction) increases, so the benefit of the winglets is impacted by air speed (Maughmer, et.al., 2002). Further consideration could also be given to the angle of attack in future experiments, as there have been conflicting results in previous experiments, resulting in concerns in handling qualities in instances of high angle of attack, where the combination of wing and winglet can result in a potential degrade in handling (van Dam, et.al., 1981). Given these factors, even when some planes operate for the longest period of time (30 years), they may have marginal fuel savings. For that reason, some airplanes use raked wingtips instead of winglets, as the raked wingtips are better for short distance flights where climb performance is more important than reducing drag.
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