Unmanned Aerial Vehicles are used generally at low levels and speeds. The research reported in this article investigates the possible use of twin-wing designs for higher altitudes with a focus on the possible lift capable for either short runways or high payloads. The wing aerofoil and unique Angles of Attack, AoA, are set 5o on the upper wing and 10o on the lower. There is a positive upper wing stagger of 50% of the chord length at height separation of 1 chord. These parameters have been established from previous research and this research investigates how they generate lift at take-off and what lift and drag properties exist. It also determines if these parameters are in-line with those for high altitude flight

McAndrew, Ian R.

Vishnevskaya, Elena

Witcher, Kenneth L.

English

Embry-Riddle Aeronautical University

Publications 2018 Take-off Characteristics for NACA 4612 Aerofoil in a Twin-Wing Configuration With Optimum Angles of Attack Elena Vishnevskaya Embry-Riddle Aeronautical University Kenneth L. Witcher Embry-Riddle Aeronautical University Ian R. McAndrew Embry-Riddle Aeronautical University Follow this and additional works at: https://commons.erau.edu/publication  Part of the Aeronautical Vehicles Commons, and the Propulsion and Power Commons Scholarly Commons Citation Vishnevskaya, E., Witcher, K. L., & McAndrew, I. R. (2018). Take-off Characteristics for NACA 4612 Aerofoil in a Twin-Wing Configuration With Optimum Angles of Attack. MATEC Web of Conferences, 189(). https://doi.org/10.1051/matecconf/201818910029 This Article is brought to you for free and open access by Scholarly Commons. It has been accepted for inclusion in Publications by an authorized administrator of Scholarly Commons. For more information, please contact commons@erau.edu. Take-off characteristics for NACA 4612 aerofoilin a twin-wing configuration with optimumangles of attackKenneth L. Witcher1, Ian R.McAndrew2, *, and Elena Vishnevskaya31Embry Riddle Aeronautical University – Worldwide, Florida USA2Embry Riddle Aeronautical University – Worldwide, Earnley, UK3Embry Riddle Aeronautical University – Worldwide, Bitburg, GermanyAbstract. Unmanned Aerial Vehicles are used generally at low levels andspeeds. The research reported in this article investigates the possible use oftwin-wing designs for higher altitudes with a focus on the possible liftcapable for either short runways or high payloads. The wing aerofoil andunique Angles of Attack, AoA, are set 5o on the upper wing and 10o on thelower. There is a positive upper wing stagger of 50% of the chord length atheight separation of 1 chord. These parameters have been established fromprevious research and this research investigates how they generate lift attake-off and what lift and drag properties exist. It also determines if theseparameters are in-line with those for high altitude flight.1 Introduction and backgroundUnmanned Aerial Vehicles, UAV, are used for many things nowadays and theirpossibilities are increasing. One area they are not classically designed to operate is at highaltitudes above current commercial aircraft operational levels. The research reported herebuilds upon the use of twin-wing UAV to achieve high altitudes at relatively low speedsand applies the principles learned to review the requirements for take-off [1]. UAVs areusually low based technology including the power units and control surfaces. Most havefixed pitched propellers and no high-lift devices. This research effort aims to determine ifhigh altitude twin-wings are equally practical for other stages of flight [2].Take-off can be classified in three ways: shortest runway length needed; maximumtake-off weight, MTOW; and stall conditions at take-off speed. Whilst the first two can beaccommodated, the third condition is critical to ensure safety and reliability. UAVs beingremotely piloted cannot have instantaneous feedback to respond when emergencies occur;thus, take-off stability is a significant part of design [3].2 Literature and theory* Corresponding author: McAnd4f1@erau.edu© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).MATEC Web of Conferences 189, 10029 (2018)  https://doi.org/10.1051/matecconf/201818910029MEAMT 2018Take-off has different aerodynamic considerations than other stages of flight. Lift needs tobe generated quickly, as this happens the drag increases proportionally. At low speeds thedrag is not significant and this is why acceleration can happen quickly [4]. Drag and liftcombined influence stall, and it is stall that is critical when taking-off. Stall will beindependent of speed as the Angle of Attack, AoA, increases and loss of lift will result inaircraft departure of controlled flight at take-off [5]. Lift generated on twin-wing aircrafthas separate airflow consideration, here, combined with the flow between the underneath ofthe lower wing and the runway. The influences of the runway and the twin-wings arecomplex with many different inputs that may interact with others to compound theinfluences [6].Previous research has been based on using a NACA 6214, shown below in figure 1,which is in a twin-wing configuration. This aerofoil is used for gliders needing high lift andhas many benefits; in particular the thickness is indicative for higher lift at low speeds. Thisaerofoil would not be ideal for higher speeds in the transonic range; and this is one of theprincipal reasons it has been used in previous research.Fig. 1. NACA 4612 aerofoil section.3 MethodologyA Computational Fluid Dynamics, CFD, simulation will be used with MicroCDF ® 2D.Simulation needs verifying, this has been covered in previous research, see reference 1.Wind tunnel length of 12.5 m; model length 3.84 m and resolution 1250 x 800. Take-offconfigurations are accommodated by setting the ground effects on the model [7]. Modelsimulated set as smooth and the different speeds range from Mach 0.06 to 0.2 and shown intable 1 below. These take-off speeds are empirically set to cover a range below, at take-offand in excess of take-off to determine the Lift, Drag, and potential stability [8]. The AoA ofthe upper wing is set at 5o and the lower at 10o as these were established for optimum flightconditions.4 Results and discussionsEach simulation used the same parameters as discussed with the exception of changes toMach numbers. Results for each speed were recorded in Mach; density; pressure andtemperature. Additionally, the stream lines and force lines were recorded and the significantdata are shown and discussed below.Table 1. Simulation data for twin-wing at various Mach speeds.Mach 0.06 0.09 0.1 0.11 0.12 0.13 0.15 0.22D Lift Force N/m 1.78E5 2.3E3 3.2E3 41E3 4.9E3 5.9E3 8.3E3 1.6E42D Drag Force N/m 1.49E4 3.6E2 3.6E2 4.2E2 4.8E2 5.4E2 6.8E2 1E32D Coefficient Lift 1.8 1.18 1.18 1.18 1.2 1.3 1.35 1.472D CoefficientDrag1.5 0.13 0.13 0.13 0.13 0.12 0.11 0.1Pitch 1.5 0.11 0.11 0.11 0.13 0.11 0.12 0.132MATEC Web of Conferences 189, 10029 (2018)  https://doi.org/10.1051/matecconf/201818910029MEAMT 2018Take-off has different aerodynamic considerations than other stages of flight. Lift needs tobe generated quickly, as this happens the drag increases proportionally. At low speeds thedrag is not significant and this is why acceleration can happen quickly [4]. Drag and liftcombined influence stall, and it is stall that is critical when taking-off. Stall will beindependent of speed as the Angle of Attack, AoA, increases and loss of lift will result inaircraft departure of controlled flight at take-off [5]. Lift generated on twin-wing aircrafthas separate airflow consideration, here, combined with the flow between the underneath ofthe lower wing and the runway. The influences of the runway and the twin-wings arecomplex with many different inputs that may interact with others to compound theinfluences [6].Previous research has been based on using a NACA 6214, shown below in figure 1,which is in a twin-wing configuration. This aerofoil is used for gliders needing high lift andhas many benefits; in particular the thickness is indicative for higher lift at low speeds. Thisaerofoil would not be ideal for higher speeds in the transonic range; and this is one of theprincipal reasons it has been used in previous research.Fig. 1. NACA 4612 aerofoil section.3 MethodologyA Computational Fluid Dynamics, CFD, simulation will be used with MicroCDF ® 2D.Simulation needs verifying, this has been covered in previous research, see reference 1.Wind tunnel length of 12.5 m; model length 3.84 m and resolution 1250 x 800. Take-offconfigurations are accommodated by setting the ground effects on the model [7]. Modelsimulated set as smooth and the different speeds range from Mach 0.06 to 0.2 and shown intable 1 below. These take-off speeds are empirically set to cover a range below, at take-offand in excess of take-off to determine the Lift, Drag, and potential stability [8]. The AoA ofthe upper wing is set at 5o and the lower at 10o as these were established for optimum flightconditions.4 Results and discussionsEach simulation used the same parameters as discussed with the exception of changes toMach numbers. Results for each speed were recorded in Mach; density; pressure andtemperature. Additionally, the stream lines and force lines were recorded and the significantdata are shown and discussed below.Table 1. Simulation data for twin-wing at various Mach speeds.Mach 0.06 0.09 0.1 0.11 0.12 0.13 0.15 0.22D Lift Force N/m 1.78E5 2.3E3 3.2E3 41E3 4.9E3 5.9E3 8.3E3 1.6E42D Drag Force N/m 1.49E4 3.6E2 3.6E2 4.2E2 4.8E2 5.4E2 6.8E2 1E32D Coefficient Lift 1.8 1.18 1.18 1.18 1.2 1.3 1.35 1.472D CoefficientDrag1.5 0.13 0.13 0.13 0.13 0.12 0.11 0.1Pitch 1.5 0.11 0.11 0.11 0.13 0.11 0.12 0.13Above, the values of both lift and drag forces, in N/m, and coefficients for lift and dragare shown for each Mach value. Figure 2, below, shows the Mach speed variations forMach at 0.09. The key to the speeds shown is on the left of the figure. Nominal speed ofMach 0.09 and the range seen is from Mach 0.032 to 0.136. Theory of lift relates to thespeed: the faster the speed, the lower the static pressure [9]. The faster the speed on theupper surface in relationship to the lower surface, then the greater the lift. Interestingly, thelift on the lower wing is not significantly lower than the upper, showing the two wings arenot significantly causing compound flow problems. In the wake of the lower wing is a highspeed section that is trailing and clearly on the runway surface. This would wash-upanything on the runway and might affect the airflow of any UAV taking off immediatelybehind. It also would induce more drag than expected. The downwash and trailing highspeed on the runway will have practical concerns for the use on airfields with a non-standard surface.Fig. 2.Mach 0.09 simulation results.Figure 3 shows the Mach number distribution, on the left, at a forward speed of Mach0.2. This is expected to be substantially greater than take-off speed. There is no downwashcausing the high speeds passing over the runway. This might be as the speed increases theresulting pressure on the runway creates a higher static pressure slowing any passing air.Leading edge speeds at Mach 0.2 are more influenced and create a generally more stabledistribution [10]. On the right are the pressure profiles. The lower wing is generatinggreater differential pressure with a humongous distribution on the whole of the underside.On the upper wing the lower side is split in two pressure levels and the lowest differentialpressure is approximately at the maximum chord thickness.Fig. 3.Mach 0.2 simulation results for Mach and pressure.3MATEC Web of Conferences 189, 10029 (2018)  https://doi.org/10.1051/matecconf/201818910029MEAMT 2018Streamlines for the Mach 0.2 shows in figure 4, below, the leading edge disturbance, onthe right, and how far behind the trailing edge where laminar flow returns [11]. Thesematch and support the results of pressure distribution in figure 3. All the main influences ofthe lower wing are directly under the length of the chord; and, in this case, add to thepressure differential. On the left side is the temperature profile, lower temperatureapproximately relates to density and, thus, pressure [12]. The higher AoA on the lowerwing influences the temperature above its horizon, and directly underneath. Theaforementioned is less likely if the ground effect was removed. Trailing edges at themidpoint soon revert to normal temperature and then those directly behind these edges.Fig. 4.Mach 0.2 laminar flow lines at lading and trailing edges.Results shown in table 1 shows the principal results for all the speeds simulated at thetake-off speeds regardless of the actual speed when take-off is capable. Clearly, Mach 0.2exceeds what was expected and the influences of lift and drag are shown in figure 5. Liftand drag are plotted for the forces in N/m. The primary axis shows the forces for the lift andthe secondary vertical axis, right those for drag. At lower speeds the lift to drag ration is atits greatest, which is not surprising given drag is negligible at lower speeds, especiallybelow Mach 0.07 (50 mph) where aerodynamic streamlining does not add advantage, table1 at 0.06 M values are ignored here as potentially spurious. As the speeds increase, so dothe lift and drag, and increases proportionally until Mach 0.13, when this increase isnotably higher and approximately follows an exponential increase. Between Mach 0.15and 0.2 the increase in drag exceeds the rate of change for lift and is indicative on stallsymptoms; suggesting this configuration is where stall is occurring. Further research anddata analysis would be needed to verify and relate all the parameters. Determining an AoAnot within the stall zone will enable optimum take-off speed to be established.Fig. 5. Lift and drag at various Mach speeds.4MATEC Web of Conferences 189, 10029 (2018)  https://doi.org/10.1051/matecconf/201818910029MEAMT 2018Streamlines for the Mach 0.2 shows in figure 4, below, the leading edge disturbance, onthe right, and how far behind the trailing edge where laminar flow returns [11]. Thesematch and support the results of pressure distribution in figure 3. All the main influences ofthe lower wing are directly under the length of the chord; and, in this case, add to thepressure differential. On the left side is the temperature profile, lower temperatureapproximately relates to density and, thus, pressure [12]. The higher AoA on the lowerwing influences the temperature above its horizon, and directly underneath. Theaforementioned is less likely if the ground effect was removed. Trailing edges at themidpoint soon revert to normal temperature and then those directly behind these edges.Fig. 4.Mach 0.2 laminar flow lines at lading and trailing edges.Results shown in table 1 shows the principal results for all the speeds simulated at thetake-off speeds regardless of the actual speed when take-off is capable. Clearly, Mach 0.2exceeds what was expected and the influences of lift and drag are shown in figure 5. Liftand drag are plotted for the forces in N/m. The primary axis shows the forces for the lift andthe secondary vertical axis, right those for drag. At lower speeds the lift to drag ration is atits greatest, which is not surprising given drag is negligible at lower speeds, especiallybelow Mach 0.07 (50 mph) where aerodynamic streamlining does not add advantage, table1 at 0.06 M values are ignored here as potentially spurious. As the speeds increase, so dothe lift and drag, and increases proportionally until Mach 0.13, when this increase isnotably higher and approximately follows an exponential increase. Between Mach 0.15and 0.2 the increase in drag exceeds the rate of change for lift and is indicative on stallsymptoms; suggesting this configuration is where stall is occurring. Further research anddata analysis would be needed to verify and relate all the parameters. Determining an AoAnot within the stall zone will enable optimum take-off speed to be established.Fig. 5. Lift and drag at various Mach speeds.Pitch, shown in table 1, is shown for all Mach numbers and the effective lift of eachstage is seen to be identical and consistent, a summary of this is shown in figure 6 below..This suggests no natural pitch up at take-off speed, it will ‘drift’ with the lift generated, andthis is indicative of stability.Fig. 6. Effective pitch at various Mach speeds.5 Conclusions and future workThis research reported has simulated the take-off speeds for a twin-wing configuration withthe upper wing at an AoA 5o and the lower at 10o. Mach, density, pressure and temperaturesvariations were determined and thus, lift and drag values. The ground effects and influenceson drag have shown the lift is considerably greater in the ranges of AoA that would be bothpractical and acceptable for take-off. Pitch is not changing as speed increases through allthe speeds. What is not known is the AoA during the start and range of stall velocities.Future work will concentrate on this and also how a particular wing profile will be effectedby the form at a fuselage and wing tip vortices.References1. McAndrew, I, Vishnevskaya, E. and Carruthers, A. (2017) TWIN-WING DESIGNOPTIONS USED FOR UNMANNED AERIAL VEHICLES TO ACHIEVE HIGHALTITUDES AT LOW SPEEDS, International Journal of Research & DevelopmentOrganisation, Nov issue, p11-20.2. McAndrew, I. R, Navarro, E. & Witcher, K (2017), INTERNATIONAL JOURNALOF MATERIALS, MECHATRONICS AND MANUFACTURING, Propeller DesignRequirements for Quadcopters Utilizing Variable Pitch Propellers, Volume 6, Number1.3. Anderson, J., Fundamentals of Aerodynamics, McGraw-Hill Education, 2010,9780073398105.4. Roskin, J., (1997) Airplane Aerodynamics and Performance, Darcorporation.5. Houghton, E., Carpenter, P., Collicott, S., and Valentine, D., (2016) Aerodynamics forEngineering Students, 7th Ed., Butterworth Hill.6. Witcher, K., McAndrew, I. R., and Vishnevskaya, E, (2017) Aerodynamic Analysis ofLow Speed Wing Design using Taguchi L9 Orthogonal Array, InternationalConference on Mechanical and Aerospace Engineering, Yokohama, Japan, 29th – 31stDec.7. Moran, J (2003). An introduction to theoretical and computational aerodynamics.Dover. p. 7. ISBN 0-486-42879-6.8. Halliday, D., (2014) Fundamentals of Physics, Wiley, UK9. McAndrew, I. R., Carruthers, A. & Navarro, E. (2014). HYPERSONIC UNMANNEDAERIAL VEHICLES: A CASE FOR RAPID DEPLOYMENT OF SPECIALISEDCARGO. International Journal of Unmanned Systems Engineering (Vol. 2, No. 3, pp.5MATEC Web of Conferences 189, 10029 (2018)  https://doi.org/10.1051/matecconf/201818910029MEAMT 201880-85). ISBN: 978-1-907980-06-0. World Congress on Unmanned SystemsEngineering, University of Oxford, Oxford, UK. 30th July – 1st August.10. Clarke, M., Norman, N., Smith, S., (2015), Construction and Analysis of SubsonicAirfoils for Wind Tunnel Testing, ASME 2015 International Mechanical EngineeringCongress & Exposition, ASME International Undergraduate Research and DesignExpo.11. Sareen, A., Deters, R.W., Henry, S.P., & Selig, M.S. (2014). Drag reduction usingriblet film applied to airfoils for wind turbines. ASME Journal of Solar EnergyEngineering, 136(2), 021007-1 – 021007-8. doi:10.1115/1.4024982.12. Sumwalt, R., Cross, D., & Lessard, D. (2015). Examining how breakdowns in pilotmonitoring of the aircraft flight path can lead to flight path deviations. InternationalJournal of Aviation, Aeronautics, and Aerospace, 2(3), Article 8. Retrieved fromhttp://commons.erau.edu/ijaaa/vol2/iss3/8.6MATEC Web of Conferences 189, 10029 (2018)  https://doi.org/10.1051/matecconf/201818910029MEAMT 2018

Take-off Characteristics for NACA 4612 Aerofoil in a Twin-Wing Configuration With Optimum Angles of Attack

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Take-off Characteristics for NACA 4612 Aerofoil in a Twin-Wing Configuration With Optimum Angles of Attack

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