By Vale Rasmussen Class of 2022
This study seeks to exam the potential benefits of a novel winglet by testing an augmented winglet design. Specifically, the study will test whether a wing with a winglet that has been curved 180 degrees– the augmented winglet - will show the benefits of reduced drag and incresed lift when compared to a wing with no winglet and a conventional winglet.
The flat edge of a conventional wing with a winglet absent creates high amounts of drag in the form of vortices. With a winglet “blended” into a wing, the vortices become smaller, reducing drag.
The results were expected to validate the hypothesis that an increase in winglet size will provide a proportionate benefit in increased lift and decreased drag. The winglets were examined using both wind tunnel testing and computer simulation testing using computational fluid dynamics (CFD).
The results of CFD testing include the unexpected finding that in terms of efficiency, the wing with no winglet(used as a control) was best, the tested augmented winglet was next, and the control with a conventional winglet was last; the wind tunnel tests showed the control with a conventional winglet slightly more efficient than the tested augmented winglet, but much more efficient than the control with no winglet. It is concluded that the results were inconclusive to confirm the hypothesis that increasing the size of a winglet will increase the beneficial effects on lift and drag, although data from the experiment suggests this may in fact be the case, such that additional study is needed to ei ther confirm or negate the hypothesis, and to determine if other effects of winglets should be considered in the overall design of an aircraft.
Introduction The flat edge of a conventional wing with a winglet absent creates high amounts of drag in the form of vortices. With a winglet “blended” into a wing, the vortices become smaller, reducing drag. Reducing drag is a top concern when designing an aircraft. The less drag present, the smoother the aircraft files through the air. This translates to less power needed when accelerating to cruising speed. This, in turn, reduces the amount of fuel used on a particular flight. Fuel costs have always been a large concern in the air line industry.
High fuel costs led to the downfall of the Concorde, and are now threatening to stop service of the Airbus A380. The importance of fuel efficiency on aircraft has led to many designs now seen on modern aircraft including winglets. Because of the wide variation of winglets, study is needed to determine whether new or expanded forms of winglets will produce greater efficiencies in the form of increased lift and reduced drag.
Drag is a force that opposes the forward motion of the aircraft, and can come from many sources, both on and off of the aircraft, such as the air density or engines protruding from the aircraft. Another type of drag, called induced drag, is created at the edge of a wing where air moving past the wing can form a vortex, or multiple vortices, which can generate considerable drag (see Figure 1).
Figure 1
The flat edge of a conventional wing with a winglet absent creates high amounts of drag in the form of vortices. With a winglet “blended” into a wing, the vortices become smaller, reducing drag. Reducing drag is a top concern when designing an aircraft.
The less drag present, the smoother the aircraft files through the air. This translates to less power needed when accelerating to cruising speed. This, in turn, reduces the amount of fuel used on a particular flight. Fuel costs have always been a large concern in operating aircraft. High fuel costs led to the downfall of the Concorde and are now threatening to stop service of the Airbus A380. The importance of fuel efficiency on aircraft has led to many designs now seen on modern aircraft. These include the flexible wing on the Boeing 787, improved engine design, and winglets. The simple design of the winglet has allowed it to be put in place on most aircraft produced today. According to Airbus, the winglets on their aircraft “improve aerodynamics, reducing fuel burn by up to 4 per cent”(PC et al. 4154).
Throughout the years, winglets have changed shape drastically. Variations of the winglet include, a simple 90-degree sharp edged triangle winglet as seen on a Boeing 767, to acute angled winglets on the Airbus A350, to winglets on the top and bottom of the wing as seen on the Boeing 737 Max. Because of the wide variation of winglets, further tests are needed to see how the modern design can be improved. The results of the present study will inform future studies to determine the point at which winglets become ineffective due to size.
The efficiency of winglets has been explored in many areas of past research. The variety of winglets has led to comparisons of differing winglets. In one study, winglet angles were compared to each other and to a wing with no winglet. A 30-degree, 60 degree, and 90 degree winglet were selected to be tested (PC et al. 4156). The results were done through an advanced computer simulation which models wingtip vortices, drag, and other factors. The authors concluded that a 60-degree winglet can be assumed to be the most efficient winglet. However these results are only relevant in the case of a NACA 4412 airfoil type, which was used in the simulation. In designing a full-scale aircraft, different winglets can be selected to fit the needs of the particular aircraft.
In an additional study, a “spiroid” winglet design was tested against a wing without a winglet. The spiroid design was influenced by observing natural fliers, such as birds (Raj, et al. 1141). The small triangles at the edges of birds with span wings were the reason this type of winglet was chosen for testing. The winglet’s shape starts with a conventional triangle winglet and then loops forward, down, and reconnects to the wing. This creates a hollow, box-like winglet.
In this experiment, the wing chosen for testing was a Boeing 737 airfoil, the BAC 449. (Raj, et al. 1142). CAD software was used to design the wing and winglet and were placed into a computer simulation. Their results showed that the L/D efficiency factor for the wing without winglet was 5.388, while the wing with spiroid winglet yielded a 5.700. (Raj, et al. 1146). Yet another radical design has yielded a positive result. Thanks to the observation of birds, this efficient winglet was able to be put into place. However, the spiroid winglet was not compared to a conventional winglet and cannot be put into perspective with the others. This further shows that more testing is needed for a clear picture of winglet efficiency. In the case of the spiroid winglet, the design is now being used on test aircraft to see if it demonstrates its efficiency at full scale.
Each past study addressed specific wings, winglet designs, and testing methods. Future studies are necessary to manipulate many of these variables in order to provide aircraft designers with a better understanding of how various types of winglets will be most useful for their aircraft designs. The present study will test the expectation that a wing with a split winglet will show the benefits of reduced drag and increased lift when compared to a wing with no winglet. The results will assist in future planned studies of winglet design and performance in other applications, particularly in firefighting aircraft.
Figure 2
Hypothesis
Increasing the size of a winglet at the end of a wing, from no winglet, to a typical winglet, to a large spiroid winglet, will increase the wing’s efficiency in terms of increasing lift and decreasing drag.
Variables
Independent: Winglet size/design will change, starting with no winglet, to a typical winglet, to a large spiroid winglet.
Dependent: Lift and drag of the wing, measured directly and as expressed by a ratio of Lift/Drag.
Controlled: Controlled variables which will be maintained constant in all experiments include the wing size and design,
temperature, humidity, altitude, and testing equip-ment. All experiments will use the same range of airspeeds.
Materials
• Computer aided design (CAD) program “Solidworks 2018”
• Lulzbot Taz 6 3D printer on IC3D ABS plastic
• Three 3-D printed wings con-sisting of 2 control wings, one with no winglet, and one with a conventional winglet. The third is the test winglet with the 180 degree rotation, each with a chord length of the rectangular wing remained at 210 millime-ters scale length . Wings conformed to a standardized airfoil, NACA 2412. Figure 3 depicts each of the wings, with winglet where applicable.
• Jetstream 500 wind tunnel and measurement software
• Mounting bracket with hook and loop tape
• CFD features of the Solidworks 2018 software.
Procedures
1. CAD software was used to design three wings
2. The three model wings were created by 3-d printing.
3. For wind tunnel tests, the models were placed on a mounting bracket with hook and loop tape attached to the bracket and part.
4. Wind tunnel integrated software (Jetstream 500) measured the lift and drag forces at varying wind speeds from 20-70 mph) and recorded these to computer files which were imported into Excel spreadsheets.The mounting bracket allowed for a free pitching motion of the parts to see how effective the lift force was relative to pitch. The parts pitched to a higher angle of attack (AOA) at high wind speeds.
5.The Solidworks 2018 computational fluid dynamics(CFD) simulator was used to conduct simulated wind tunnel tests and to measure lift and drag with a constant AOA. In the simulation, the preset “air”was selected as the fluid with a constant humidity factor in both simulations. The test was run at 20, 30, 40, 50, 60, and 70 mph to compare the results with those of the wind tunnel. The positive y-forces and negative x-forces, lift and drag respectively, were placed in an excel spreadsheet. The two forces were plotted on a graph with wind speed on the x-axis to create a similar graph to the wind tunnel tests.