Parametric study for optimizing winglet efficiency and comparative analysis of aerodynamic performance of a wing with no winglet and with different types of winglets for lighter aircraft

Aircraft performance is highly affected by induced drag caused by wingtip vortices. Winglets are wing tip extensions and are used to minimise vortices formation to improve fuel effi ciency. They are usually used in heavier transport aircraft due to higher operation costs and higher fuel consumption due to higher range missions. The research conducted for this thesis was used to investigate if the use of winglets in lighter low speed aircraft is benefi cial in any way in terms of aerodynamic effi ciency. This project includes a subsonic wind tunnel experiment used for validation of Computational Fluid Dynamics (CFD) analysis, performed on a fi xed rectangular wing of a NACA 653218 aerofoil and a 3D printed blended winglet. The objectives of the analysis were to compare the aerodynamic characteristics of rectangular wing with different types of winglets and perform a parametric study to modify the winglets in order to optimise effi ciency and reduce fuel consumption, as well as investigate the effects of surface roughness on the turbulent boundary layer. The wind tunnel experimental analysis was performed at sea-level conditions. The CFD simulations were performed at low subsonic fl ow in ANSYS CFX using Finite Volume Method, replicating the wind tunnel closed-loop conditions. The cfd fi ndings were compared to existing data and to wind tunnel results. The investigation results indicate that the modifi ed winglets designed for optimization, signifi cantly affect the aerodynamic effi ciency compared to traditional winglets or no winglets and were estimated to produce an approximate increase in lift to drag ratio of 40% using a modifi ed winglet. A specifi c shape of curved winglet was found to be very effective at redirecting fl ow away from the wing and further research is recommended in this type of curved winglet .The effects of the surface roughness on the turbulent boundary layer are recommended for investigation as were not able to be completed due to campus laboratories lockdown. Literature Review Parametric study for optimizing winglet effi ciency and comparative analysis of aerodynamic performance of a wing with no winglet and with different types of winglets for lighter aircraft


Introduction
By 1950, oil had become one of the main energy sources in the United States and was the only fuel source used in air transportation. During the 1970s, oil embargo and oil price had soared thus causing aircraft manufacturers, to fi nd new ways of reducing fuel consumption due to the new high cost.
Winglets have been studied long before the oil embargo in the late 70s by many scientists. However, the fi rst researcher that fi rst developed wingtip devices was Whitcomb, whose breakthrough research managed to lead many aircraft manufacturers to incorporate winglets and to this day, remains one of the most innovative ideas in aviation, considering most of the transport aircrafts nowadays use wingtip devices. Airplane wings are shaped in a particular way, to make air move faster over the top of the wing and slower over the bottom, like shown in Figure 1. When air moves faster, the pressure of the air decreases according to Bernoulli's principle and therefore the pressure on the top of the wing is less than the pressure on the bottom of the wing. The high pressure at the bottom pushes the wing upwards creating what is known as Lift. However, the inequality of pressure causes the air particles to move towards the low-pressure area, consequently causing air to swirl at the wingtips, which creates a wingtip vortex.
This phenomenon is called induced drag or downwash, which causes energy loss, increases drag and creates a downward force on the top of the wing, thus requiring more lift to counteract the downward force and more thrust to counteract the induced drag, resulting in higher fuel consumption. Winglets increase the aspect ratio of the wing while keeping the surface area relatively low which increases lift generation, and redirect the surrounding fl ow minimising vortices. Since using winglets reduces the intensity of the wingtip vortices, less energy is lost from the air rotating outwards, which results in more thrust being available, while using the same amount of fuel. Improved winglet effi ciency enables more payload capacity, reduces fuel consumption while increases cruising range which all result to lower operating costs. The research conducted in this thesis, could have a potential impact on environmental sustainability, since fuel effi ciency will result to reduced harmful greenhouse emissions.
Global pollution caused by aviation, only accounts for a small percentage of global pollution levels however, what is causing concern is not the amount of carbon emission that is released during fl ight, but the way that the emissions are released, which is mid-air while fl ying therefore, polluting the atmosphere both locally and globally .Besides greenhouse gas emission, aircrafts also release air vapor, which is composed of air in the form of ice crystals. The air vapour by its very nature is not harmful, However as aircrafts fl y up to the stratosphere which is a dry air region, air vapour emissions are polluting the atmosphere by contaminating the dry air particles with moist particles that turn into long exhaust plumes [2]. This phenomenon is called contrail, and it worsens the climate change, by trapping heat inside the atmosphere. Therefore, there is a great concern about how aviation is involved in the increase of global warming the last decades. Various winglet effi ciency experiments have been conducted over the last couple of decades but mainly for transport aircraft due to the higher costs affi liated with heavier aircrafts. Currently there is a trend on research for development of lighter air vehicles like automated unmanned aerial vehicles (quadcopters) or electric aircrafts. But according to studies, electric or fully automated air vehicles will probably take decades of studying and testing until they are commercially used .Therefore, there is potential improvement in increasing effi ciency of current light aircrafts like gliders or four seated fi xed-winged aircraft like the Cessna 172. Typical glider and Cessna cruising speeds range from 30 to 65 m/s, respectively. Therefore, this research is conducted to fi ll this gap in current research concerning the use of winglets for optimized performance and fuel effi ciency for light, low speed air vehicles. Different angles of attack will be tested as well as different speeds ranging from 30 to 65 m/s in order to test the applicability of this research on the aircrafts mentioned. Project methodology, data gathering and results analysis will be discussed in detail over the next chapters.

Research questions
• This project was conducted to investigate the following research questions.What are the effects of different winglets on lighter aircraft effi ciency?
• Which winglet parameters have the greater impact on overall effi ciency?
• How does surface roughness affect the turbulent boundary layer?
In order to properly answer the research questions both experimental and numerical approaches were used in order to identify the most effi cient winglet that could be used in lighter aircrafts.

Aims and scope
The main objectives of this project were to identify the key parameters that infl uence winglets' effi ciency through comparative and quantitative analysis of different types of winglets in order to provide better aerodynamic performance for lighter aircrafts. If aerodynamic effi ciency will be achieved then consequently fuel effi ciency will also be achieved resulting in lower operating costs and lower environmentally harmful emissions. This research was not conducted for heavier type aircrafts like Boeing or Airbus but for gliders or low speed aircrafts like Cessna 172. This study is mainly concerned in lift to drag ratio because of the tendency of Drag to increase with lift. Therefore, higher lift does not always signify better performance as could produce very high drag as well. Hence, the optimum measurement of greater performance is lift to drag ratio and this would be referred to as aerodynamic effi ciency in this thesis.
To answer the research questions, the project was divided into stages involving CFD simulation and Wind tunnel testing.

P roject management
This project was managed over a 7 month period from September 2019 to April 2020 and was fi rst managed according  proper risk management plan was not developed as a risk of unavailable computer was low and hence the risk assessment has not changed from the initial one submitted in November (Appendix A), which mainly consists of wind tunnel risks like proper usage of wind tunnel equipment as well as usage of protective gears for the ears . Ultimately, a part of the simulation as well as testing was not completed in campus, due to the current unforeseen pandemic of coronavirus outbreak.
Although, even if a proper risk assessment plan was developed at an early Stage, it would not have been suffi cient to mitigate the problem of campus lockdown since these unforeseen circumstances are a global issue.

L iterature review
The work involved in this project is focused on decreasing harmful gas emissions by increasing the aerodynamic effi ciency of low speed light aircraft using winglets. This involves understanding the nature of winglets as well as possible factors effecting the aerodynamic behaviour of the wings during fl ight . The aerodynamic behaviour i3s usually studied through two methods, experimental testing as well as numerical modelling using mathematical modelling. These two methods were researched as well as winglets and fl ow behaviour in order to answer the research questions and aims that were set out to be achieved.

W inglet studies
Comprehension of fl ow behaviour around aerofoils is critical in using CFD for analysing and designing winglets. Bodies that move fast enough, create separation of the surrounding fl ow as well as turbulent wakes. These affect the aerodynamic capability of an aircraft and hence why is vital to understand these fl ow mechanisms.
Blended winglets are modern upward curved wingtips that are usually used in civilian transport heavy aircrafts. A study was conducted in which he optimised a winglet designed and performed a parametric study and found that the most dominant parameters effecting the aerodynamic behaviour of the winglet were the cant angle as well as the span [3]. Another study was conducted on the effects of winglet parameters on the overall effectiveness of the in which it was found that the aerodynamic effi ciency reduction was linked with cant angle increase while toe angle had no effect in aerodynamic behaviour winglet [4]. An investigation was conducted for raked winglets which are small swept wingtips. The fi ndings of this study [5] resulted in increase in lift to drag ratio of 25 using RANS and S-A turbulence models.

B oundary layer separation
The aerodynamic capability of an object is linked to the boundary layer formed around the object and its point of separation.
The shape of the boundary layer is highly affected by pressure gradient. The pressure gradient changes over an objects body due to fl ow moving over different curvatures at the body's surface, in this case, a wing's maximum thickness to the initial project Gantt chart that was submitted on November with the Initial project concept proposal. That was prepared in the early stages of the project summarizing all the required tasks and meetings and their respective timescale estimation to successfully complete this project. However, as the project progressed some of the tasks that were listed in the initial plan were no longer feasible. Some implications were revealed in some point of this project which resulted in changes being added to the fi nal project plan. The updated and fi nal version of the project Gantt chart was produced in March 2020 (Appendix A). It includes the critical path in which the co-dependent tasks can be observed as well as the project milestones. All the tasks were successfully completed, which are in green colour, except the tasks which are in light blue colour. 3D printing the modifi ed winglet was not completed due to student budget limitations (around £300). The cost of 3D printing a winglet with the chosen dimensions was not taken into consideration in the initial project plan. Consequently point. In this region, as the mainstream fl ow is accelerating up to the point of maximum thickness, the curvature of the body causes the fl ow lines to curve, and in order to equilibrate the centripetal forces, the fl ow accelerates and the fl uid pressure drops. Up to this point the pressure gradient is negative, which is called favourable pressure gradient [6]. Once the fl ow moves beyond the point of maximum thickness, the curvature of the body is less effective at directing the fl ow in curved streamlines due to the open space downstream. Hence, the curvature in the fl ow reduces and the fl ow decelerates, the pressure gradient becomes positive as the pressure increases, turning the previously favourable pressure gradient into what is known as adverse pressure gradient. If the adverse pressure gradient acts over an extended distance, the deceleration in the fl ow near the wall will be suffi cient to reverse the direction of fl ow in the boundary layer. The boundary layer develops a point of infl ection as shown in fi gure 2, known as the point of boundary layer separation. For aircraft wings, boundary layer separation can cause signifi cant consequences ranging from rise in pressure drag to lift loss, known as aerodynamic stall.

Effects of Re in separation
Reynolds number is a dimensionless quantity that measures the ratio of inertial forces to viscous forces of a fl uid. This is used in fl uid mechanics to predict fl ow behaviour. When the viscous forces are stronger than the inertial forces , they are enough to keep all the fl uid particles in smooth lines resulting in parallel looking lines with no interchange of fl uid particles between individual streamline layers, then the fl ow is laminar as seen in fi gures 3,4. This usually occurs at very low fl uid speeds that result in Reless than 50 000 [8]. However, when the inertial forces dominate, the fl uid particles are moving in irregular patterns creating eddies. This occurs at relatively high fl uid speeds, resulting in Re higher than 100,000.
The process at which the fl ow patterns interchange can be explained using Figure 5 [9]. When the fl uid speed becomes signifi cantly high reaching a Re higher than 100 000, then the wake region moves forward as fl ow lines separate from the body's surface following the turbulent boundary layer resulting low pressure difference and low pressure drag as seen in Figure  5, example E [10].
Separation can occur at either laminar or turbulent fl ow however, one of the two fl ow patterns delays the point of separation due to the pressure gradient which is one of the main factors infl uencing the point of separation. When a turbulent boundary layer enters a region of adverse pressure gradient, it can persist for a longer distance without separating compared to a laminar fl ow. This is due to the higher existing momentum near the wall and its continuous replenishing by turbulent mixing. Therefore, some winglets and wings are often design in such way that would result in higher Re number and hence turbulent fl ow because of laminar boundary layer's inability to damp out disturbances and therefore inability to delay separation. A study was found (Syahmi & Hakim, 2018) which investigated the fl ow separation at three different Reynolds numbers which are 1E+6, 3 E+6 and 4E+6 using pressure distribution method and fl ow visualization. The experiment was conducted in Low Speed Tunnel. The pressure distribution is done on three different wingspan, which are 40%, 50% and 70%m of span and was measured and plotted to observe the fl ow characteristic at angle of attack from 0° to 35° for all three     separates at 20°.This was used as a guidance to use Re higher that 4E+6 so that it resists adverse pressure gradient as angles of attack up to 20 degrees will be used.

Compu tational fl uid dynamics
The best performing CFD code for low subsonic speeds of M lower that 0.2 has proven to be the Spalart-Allmaras turbulence model as suggested in studies (ES & OE, 2016) and was found to be slight more accurate than standard k - models. For lift coeffi cient, it is found maximum error by Spalart-Allmaras model about 12% lower than other turbulence models. For drag coeffi cient, it is found maximum error by Spalart-Allmaras model about 25% lower than other turbulence models. K- models ,are easier to converge and don't have any restrictions in CFX.
Another study that analysed different winglet types using different turbulence models suggest that k- model was the better one in terms of lower power intensity as other models were found to be more power intensive requiring signifi cantly greater computational time while both provide similar fl ow resolution [11]. It also concluded that the winglets performed better at cruising aoa with cant angles ranging from 45˚ to 60˚.
A study conducted on different winglet aspect ratio has found that all winglets provide improved aerodynamic effi ciency , but winglets with high and low aspect ratios performed averaged as opposed to the one winglet with optimum aspect ratio which performed signifi cantly better [12]. It was also suggested to used multi-tip end on the winglets as they improve lift generated.
A study investigating the difference between grit size in lift and drag coeffi cient results of a NACA653218, in which grit size ranged from 500 000 elements to a million. It was concluded that while higher number of elements resulted in greater accuracy of results, the suggested minimum element size was found to be around a million. It also tested different turbulence models resulting in error of S-A model around 25% less then other models like standard k- or RNG k- models [13].
A simulation analysis on raked winglets of 30˚ and 45˚ swept angles resulted in an average of 15% increase in lift coeffi cient at low angles of attack as well as considerable reduction in wing tip vortex [14].
According to (Tuling ,2019) the structure of the turbulent BL categorised into three areas .One the viscous sub-layer, in which molecular viscosity is higher then other forces .The buffer region, in which molecular viscosity and Reynolds stresses are equal and fully turbulent region, in which Reynolds stresses In the latter case the height of the wall is of magnitude of 50 to 100. Therefore, the wall height that was used for the cfd simulation was 100.

Stage 1: Numeric al simulation
Computational Fluid Dynamics or CFD in Ansys, was used to conduct a comparative analysis between the rectangular wing as well as the different types of winglets by simulating their aerodynamic performance .Other software could have been used like STRAR CCM+, but Ansys was preferred due to previous experience as well as literature review fi ndings. The main objectives of the simulation are pressure plots showing pressure distribution over the wing as well as lift to drag ratio, representing the aerodynamic effi ciency. These are used in order to assess the aerodynamic effi ciency as well as the downward force applied on the top surface of the wing.
The different models that were used for the simulation were Re number is preferable. For this reason, the wing needed to be as big as possible since the university's wind tunnel is subsonic and the maximum speed that can be achieved is 45 m/s, therefore the chord needed to be as big as possible but considering the wind tunnel test section space limitations, the maximum dimensions chosen for the wing were 400 mm for chord and 900 mm for span . These were the initial dimensions chosen for the models used both for manufacturing and cfd dimensions. However, these were changed a few times due to other limitations like 3d printer could only print maximum 290mm in height or the model could be split and printed in parts using a dovetail joint. However due to budget limitations this was not possible, therefore the fi nal dimensions were changed to 290mm chord which is considered as the maximum height in 3D printing software. A wind tunnel testing the modifi ed winglet was not conducted due to budget limitations as second winglet could not be manufactured due to budget limitations. Another wind tunnel test would was also planned for investigating the effects of surface roughness using the same winglet for the fi rst test ,but modifi ed in order to make the surface as smooth as possible ,but was not conducted due to campus laboratories closure due to national lockdown [15][16][17][18][19][20].

Long term implication s of project
The technical aspects of this research involved 3D printing thermoplastic which is manufactured from non -renewable sources and releases toxic gases in the process. It is also non-biodegradable and can only be recycled under specifi c conditions. Other materials could have been used like PLA since it is made from corn starch and hence is compostable and more environmentally friendly but was not available to use. ABS printing also involved high costs. However, other manufacturing methods would be used for light aircraft winglets which would involve higher costs, nonetheless the fuel costs savings due to better performing wings, would certainly overcome the manufacturing costs over a time period. This investigation could have a substantial impact in environmental sustainability well as cost effi ciency in lighter aircraft as higher aerodynamic performance means less fuel is used for the same range mission. Higher aerodynamic effi ciency is mathematically represented as higher Cl to Cd ratio, therefore increased range missions could be achieved using the same or less amount of fuel, which results in lower polluting greenhouse gas emissions. This is based on Breguet's formula seen in fi gures 5,6, in which Range is directly proportional to Cl to Cd ratio. Pre-processing is the fi rst stage and involves geometry setup for mesh generation, computation involves turbulence modelling using energy conservation which is applied using a controlled volume approach. The energy equation is primarily derived from the fi rst law of thermodynamics as seen in

Technical content
. Energy conservation

Design
The cad models were designed in Solid works using a NACA Following the analysis, the modifi ed winglets were designed based on the best performing winglet which was found to be the blended, modifying the cant angle into 60 ˚and 70 ˚ as well as changing vertical distance and back shape (as seen in fi gures

Pre-processing
Geometry: The CAD models were imported in CFX Design Modeler in order to create a certain geometry around the CAD model to simulate the wind tunnel, as CFD simulation was planned to be experimentally validated in this facility.
Therefore, an enclosure was used to create a replica of the wind tunnel testing section according to the wind tunnel's           The quality of the mesh was also assessed using the quality function under mesh metric. There are two ways to check the quality. These are using skewness and orthogonal quality which describe the asymmetry of cells and the closeness between element edges respectively. Figure

Solver control
For this study k- turbulence model was used which was successfully implemented as this model is less demanding in terms of mesh quality and stability. Other models were also

Manufacturing process
Winglet manufacturing: Two separate geometries were created for the original prototype that was used for the wind tunnel test, one for the main rectangular wing and the other geometry was the blended winglet of 45 degrees cant angle (fi gure 23). It represents the initial winglet design through the 3D printing software, in which clearly exceeds the maximum height that the machine can print at once. This caused two problems, one of them was that the winglet needed to either scaled down or be printed into two smaller parts and assembled back into one piece after the printing process by using a dovetail joint. The other problem was that even if the part would be hollowed out, it would still be very expensive and would exceed the budget limitations. Although the winglet was scaled down to 290mm chord, the cost of printing had used up the student budget, therefore the other winglets that were initially planned to be tested were not printed.
The winglet was hollowed using a shell function in Solid works keeping 4 mm of layer to avoid printing failure as well as ensure material durability during wind tunnel testing. An additional 5cm were added at the winglet's chord edge to create a "lip" which would help with the wing assembly. The fi nal CAD model and STL fi le that was used for printing are illustrated in fi gure 32, and the predicted printed version can be seen in fi gure 33. The actual printed winglet is shown in fi gure 33 which was printed very successfully. However, the surface of the 3d printed part was quite rough as seen in fi gure 33 but could be smoothed by following a certain procedure in order to avoid affecting the wind tunnel results. In order to do this the winglet would need to be smoothed and painted to create a smoothed surface. A new wing would also have to be manufactured to be used for the second wind tunnel experiment investigating the effects of the surface roughness on the turbulent boundary layer.

Wing manufacturing:
The wing shown in fi gure 14 was design with a hole of 12.5mm diameter cutting through the wing , merging the two sides . This was done in order to mount the wing on the rod of the wind tunnel's symmetry wall. The wing was manufactured from foam with fi nal dimensions of 500mm span and 283mm in order to be able to slide into the winglet. The assembly shown in fi gure 34, validates that both components were accurately designed creating the perfect fi t.
Wind tunnel experimental setup: The winglet as it is made from foam, has a rough surface which would greatly    The model was mounted to a rod, fi xed to the measuring sting in the high-speed section of the wind tunnel, by sliding the wing over using the 12.5mm diameter cut out section. A big sized ruler was used to measure the vertical distance from the fl oor to each side of the wing, in order to make sure that the wing was parallel to the ground. This is a simple calibration method to ensure the accuracy of the aoa starting from exactly 0 degrees. Next, three screws were placed strategically one side of the wing to ensure stability during the wind tunnel. Firstly, the rectangular wing was tested as seen in fi gure 35 ranging the aoa from 0 to 15 degrees for 37 and 30 m/s , recording all data channels (lift,drag,aoa, speed). The speed did not exceed 37m/s due to wing movement during the test. The same procedure followed for testing the blended winglet, after a fi lm was attached at the top opening to reduce drag due to rough edges as seen in fi gure 36.

Result analysis
CFD Post-processing results: Data gathered from cfd computation of the different types of winglets were used in order to assess each winglets effi ciency which is related to L to D drag or Cl to Cd ratio and how pressure is distributed over the upper surface of the wing. CFX-post was used to calculate lift and drag coeffi cients by using equation 4. However, lift and drag forces were calculated using in-built expressions to describe force on y and x axis respectively as seen in equation 5, in which a variable wing was created that is located at the named selection that was previously named at pre-processing as "wing". The ratio was found using the absolute value of lift divided by drag.   The contour plots seen in fi gures 40,41 illustrate the pressure distribution over the top and bottom surfaces of the wings as well as front and back sides. As mentioned, when the pressure of the air particles is higher at the bottom than on the top, these tend to move towards the top surface creating wing tip vortices and downwash. Therefore, the winglet with less downwash according to the pressure contour plots was the back curved 60˚ due to lower pressure levels at the winglet upper surface which is indicated from the light blue colour, while the blended 70˚winglet seemed to produce more downwash indicated from the intense green colour.
Furthermore, the winglet that produces less wing tip vortices seems to be the back curved 60˚ as opposed to the blended 70˚ which seemed to have slightly better pressure      unevenly, creating higher levels of wing tip vortices. This is also validated as seen in fi gures 42 in which the 70˚blended winglet's vortex is signifi cantly more intense compared to the front curved winglet 50˚ or the blended 45˚.

Aerodynamic effi ciency analysis
Lift and drag values were evaluated using CFX-post calculators and using the values generated, graphs were plotter in order to easily analyse the results. Firstly, the CFD results were validated using existing results found from literature review. The dimensions that were originally supposed to be used, were similar to those from the lit review and were used for cfd validation before the wind tunnel testing. However, the dimensions were scaled up for the wind tunnel testing preparation, in order to achieve higher Re but were scaled down slightly later on, due to printing limitations. Therefore, validation from existing data was only used in early stages of cfd investigation for only 2 winglet confi gurations as seen in fi gure 46 to assess the validity of the initial setup and mesh settings. Existing data were obtained from literature review with smaller wing dimensions and averaged to use for comparison.
However, since the fi nal values were signifi cantly bigger than the ones used previously , higher values of effi ciency were expected in later results.     The initial comparative analysis between 3 models is illustrated in fi gure 47 were results found suggest that the simulation setup and mesh settings were correct, therefore producing similar results with existing data. The latest simulation results for comparison of the effects of winglets on overall effi ciency can be seen in fi gure 48, where the lift to drag ratio was almost doubled with a blended winglet, compared to a rectangular wing with no winglet. The comparative analysis of the effects of blended and raked winglets on effi ciency can be seen in fi gures 49, in which clearly the blended winglet was the most effi cient with maximum lift to drag ratio of around 70, while raked and rectangular around 30 and 20 respectively.
The lift to drag ratio for all winglets including the modifi ed ones can be seen in fi gures 50-54. The most effi cient winglets seemed to be the curved ones as expected, due to their ability to redirect the surrounding fl ow, while the least effi cient was found to be the raked which is probably due to the straight shape of the winglet. All of the winglets seemed to be more effi cient at the highest speed of 45 m/s and the stall angle was found to be 10 degrees in the initial simulation with smaller dimensions, while in the latest simulation was found to be around 14 for the modifi ed winglets. This indicates that winglet confi gurations do not provide optimum aircraft performance at all stages of fl ight.     m/s and hence, an investigation was done to investigate the winglets' behaviour in such speed. The best performing winglet at this speed was found to be the back curved 60˚ with 43.8491 and blended winglet of 45 ˚with slight difference at 43. 339.The accuracy of the simulation was also assed using control volume approach. Theoretically the amount of air mass fl ow entering the controlled volume shall equal the amount of air mass fl ow exiting the controlled volume. Therefore, a calculator was used in CFD-post to estimate the amount of air mass fl ow entering and leaving the controlled volume, ranging from 5% error to 15% depending on the intensity of the model's cad geometry. An overall increase in lift to drag ratio of 40% was calculated from cfd results, between a wing with no winglet and the most effective winglet which was the back curved 60˚ winglet. Therefore, the dominant parameters affecting drag reduction were found to be the cant angle with optimum cant angle of 60˚, as well as the shape of the winglet.
The same cant angle (60˚) but with higher vertical distance was found to produce more drag, while higher cant angles were found to be ineffective.