Drag Reduction of MAV by Biplane Effect Chinnapat THIPYOPAS Graduate student, Department of Aerodynamics and Jean-Marc MOSCHETTA Associate Professor of Aerodynamics, Department of Aerodynamics Ecole Nationale Supérieure de l’Aéronautique et de l’Espace (SUPAERO) 10 Av. Ed. Belin, Toulouse, France P1/29

Department of Aerodynamics SUPAERO Contents Introduction Part 1 Optimization - (Experimental) - (Numerical) Part 2 Biplane Combinations Part 3 Propeller Influence Conclusions Department of Aerodynamics SUPAERO P2/29

Department of Aerodynamics SUPAERO Contents Introduction Part 1 Optimization - (Experimental) - (Numerical) Part 2 Biplane Combinations Part 3 Propeller Influence Conclusions Department of Aerodynamics SUPAERO P3/29

Monoplane MAV concepts Minus-Kiool 57g - 20.6 cm Plaster 64g - 23 cm Department of Aerodynamics SUPAERO P4/29

Total Drag = Parasite Drag + Induced drag Department of Aerodynamics SUPAERO Monoplane-MAVs Plaster, SUPAERO Maxi-Kiool, SUPAERO Induced Drag 76%* Drenalyne, SUPAERO Biplane Concept !! Total Drag = Parasite Drag + Induced drag 100 % 20-30 % 70-80 % * J.L’HENAFF, SUPAERO 2004 P5/29

Department of Aerodynamics SUPAERO Monoplane vs. biplane wing drag = Parasite Drag + Induced Drag Parasite drag is a function of Skin-Friction which depends on Wing Chord Induced Drag is very strongly effected by Aspect Ratio Constant lift, speed & overall dimension - Why interest biplane plane concept ? - high parasite drag (skinfriction drag) due to boundary layer - Low induced drag because of higher aspect ratio Biplanes were most successfully marketed in the early days of aviation when the wing sections used were very thin and consequently the wing structure needed to be strengthened by external bracing wires. The biplane configuration allowed the two wings to be braced against one another, increasing the structural strength. The big disadvantage of the biplane layout was that the two wings interfered with one another aerodynamically, each reducing the lift produced by the other. P6/29

Department of Aerodynamics SUPAERO Contents Introduction Part 1 Optimization - (Experimental) - (Numerical) Part 2 Biplane Combinations Part 3 Propeller Influence Conclusions Department of Aerodynamics SUPAERO P7/29

Department of Aerodynamics SUPAERO Optimization process Design Constraints Maximum overall dimension : 20 cm Lift at 10 m/s = Weight = 80 grams Manoeuvrability : 20 grams min. for payload Cost function Minimum Drag at cruise condition Department of Aerodynamics SUPAERO P8/29

Department of Aerodynamics SUPAERO Experimental setup Wind tunnel Test Section 45cm x 45cm Velocity 10 m/s Measurement 3-component balance Models 16 flat-plate wing models Aspect ratio 1 – 4 Taper ratio 0.2 – 1.0 Sweep angle 0 - 50° Reference surface/length For comparison, every model is referenced by same area, length AR1, Taper 1, No Swept Strut 20cm. AR2.5, Taper0.6, Swept25° Department of Aerodynamics SUPAERO P9/29

Model’s Drag Correction Strut Model is not attached to strut Model Strut Department of Aerodynamics SUPAERO P10/29

Department of Aerodynamics SUPAERO Results No. Model Name Area * * * (cm.) Disc 314.2 2.8223 0.0232 0.0147 1.997 0.3578 8.32 0.127 5.052 8.56 0.055 5.871 4.6 1 A1S0T0.2 144.0 2.1647 0.0146 0.0202 0.887 0.5127 6.176 0.293 2.209 23 0.085 3.803 12.3 2 A1S0T1 200.0 2.5556 0.0219 0.0214 1.449 0.3888 5.336 0.189 3.399 14.6 0.073 4.39 8.56 3 A1S25T0.6 224.8 2.4667 0.0112 0.01 1.621 0.3857 8.926 0.164 3.953 13.5 0.058 5.532 7.56 4 A1S50T0.2 144.0 2.4114 0.0163 0.0224 1.046 0.4178 9.967 0.256 2.530 21 0.078 4.128 11.3 5 A1S50T1 130.2 2.4902 0.0183 0.0281 0.944 0.3738 7.633 0.252 2.552 21.8 0.081 3.967 12.2 6 A2,5S0T0.6 146.7 3.7786 0.02 0.0273 0.627 0.2814 3.099 - - - 0.055 6.036 6.38 7 A2,5S0T1 137.9 3.556 0.0112 0.0162 0.572 0.2966 2.43 - - - 0.054 5.899 7.44 8 A2,5S25T0.6 146.7 3.6615 0.0172 0.0234 0.619 0.3032 4.904 - - - 0.052 6.288 6.38 9 A2,5S25T1 137.9 4.0961 0.02 0.029 0.601 0.2683 4.503 - - - 0.061 5.227 6.5 10 A2,5S50T1 102.9 3.0513 0.0067 0.0131 0.535 0.319 5.766 - - - 0.071 4.552 11.5 Only AR1 wings have lift enough for 80 grams. Approximated 50% produced by each wing for biplane, some of AR2.5 wings have lift enough to fly. Biplane has L/D more than monoplane (4 and 6) All configuration that best in L/D have maximum wing area. 11 A4S0T0.2 99.3 4.3273 0.0166 0.0326 0.355 0.2413 2.453 - - - 0.060 5.404 8.46 12 A4S0T1 94.1 4.5539 0.0167 0.0345 0.381 0.2455 1.497 - - - 0.074 4.386 9.83 13 A4S25T0.6 96.6 4.9468 0.0133 0.0275 0.418 0.2363 3.261 - - - 0.058 5.613 7.6 14 A4S50T0.2 84.1 3.3926 0.0124 0.0295 0.481 0.2943 5.221 - - - 0.092 3.499 14.3 15 A4S50T0.6 79.5 3.4883 0.0095 0.0239 0.442 0.3056 5.95 - - - 0.091 3.533 14.9 16 A4S50T1 76.7 3.5983 0.0141 0.0368 0.424 0.2781 5.311 - - - 0.091 3.508 15.1 Red color is a value referenced by wing’s area P11/29

Department of Aerodynamics SUPAERO Numerical method Vortex lattice method : code TORNADO v126b [T. Melin; KTH] Drag evaluation Parasite Drag = 1.5 of equivalent flat plate skin friction drag (Blasius Eq. + Thwaites formula) + Induced drag (TORNADO) Various models : aspect ratio taper ratio sweep angle Department of Aerodynamics SUPAERO P12/29

Department of Aerodynamics SUPAERO Results Triplane Biplane Monoplane An approximate stall angle curve L/D at cruise cond. increases with AR Poor manoeuvrability of monoplane wings with AR 2 and higher greater L/D for biplanes L/D of Triplane AR4 is smaller than biplane because of high parasite drag. Biplane AR2-3 is suitable for flight Department of Aerodynamics SUPAERO P13/29

Department of Aerodynamics SUPAERO Biplane vs. monoplane -50 50 100 150 200 250 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 Drag Mass Monoplane Biplane 60 grams 80 Department of Aerodynamics SUPAERO P14/29

Department of Aerodynamics SUPAERO Contents Introduction Part 1 Optimization - (Experimental) - (Numerical) Part 2 Biplane Combinations Part 3 Propeller Influence Conclusions Department of Aerodynamics SUPAERO P15/29

Department of Aerodynamics SUPAERO Other planforms Zimmerman Planform Area (m2) CL (max) CD (min) L/D (max) Zim1 0.0264 1.251 0.0533 4.03 Zim2 0.0173 0.586 0.0419 5.21 Zim1Inv 0.986 0.0538 3.75 Zim2Inv 0.605 0.0344 4.96 Plaster1 0.0245 0.909 0.0411 4.92 Plaster2 0.0166 0.0354 5.47 Drenalyne1 0.0273 1.260 0.0528 4.46 Drenalyne2 0.585 0.0375 4.81 Plaster Drenalyne Department of Aerodynamics SUPAERO P16/29

Inverse Zimmerman Torres et al., Univ. Florida, 1999 Calculation Inverse Zimmerman Torres et al., Univ. Florida, 1999 Plaster wing Reyes et al., SUPAERO, 2001 Department of Aerodynamics SUPAERO P17/29

Department of Aerodynamics SUPAERO Scale 1 (SUPAERO) Scale 3 (S4, ENSICA) End-plates Decalage angle Parameters Gap Stagger Decalage angle Upper Wing Stagger The difference in the angle of incidence of the two wings of a biplane is called the decalage Gap U Lower Wing Side View Department of Aerodynamics SUPAERO P18/29

Department of Aerodynamics SUPAERO Gap Reduced an influence between both wings Increase lift slope and maximum lift Not change position of aerodynamics center Increase drag from the structure  L/D not change P19/29

Department of Aerodynamics SUPAERO Stagger Increase lift slope and maximum lift Aerodynamics center is between two wing No stagger has more L/D Local AoA of fore-wing is bigger Department of Aerodynamics SUPAERO P20/29

Department of Aerodynamics SUPAERO Decalage Angle Done with positive stagger model Strongly effect to stall angle and L/D Negative decalage give highest wing performance Department of Aerodynamics SUPAERO P21/29

Department of Aerodynamics SUPAERO Visualisation S4, ENSICA Department of Aerodynamics SUPAERO P22/29

Department of Aerodynamics SUPAERO Contents Introduction Part 1 Optimization - (Experimental) - (Numerical) Part 2 Biplane Combinations Part 3 Propeller Influence Conclusions Department of Aerodynamics SUPAERO P23/29

Department of Aerodynamics SUPAERO Propeller Effect (S4) Upper Wing Lower Wing U Motor Side View 7 4 6 5 1 2 3 Front View Half Span Center line Upper wing 7 motor positions were observed. Lower wing stall at 22° Lower wing not stalled The stall angle is delayed, lower wing is still not stall at AoA 22° Upper wing stalls At pre-stall regime, lift is increased due to propeller. Lift increases Motor & propeller Test section Power supply Moveable system Tube Lift, maximum lift and L/D are increased. Department of Aerodynamics SUPAERO P24/29

Propeller Effect (Scale 1) Zim2 wing planform scale 1 (20cm. Max dim.) Monoplane Wing Motor in front of wing gives highest performance. The motor countering / encountering wingtip vortex effects are very small. P25/29

Effect of induced flow to model Attach Motor to the model Propeller Effect Motor sting Model struts Effect of induced flow to model -2 -1 1 2 3 4 5 6 7 -10 -5 10 20 25 Incidence B = mid position R = upper wing G = lower wing L/D 15 Motor on upper and lower wing have the same effect Middle position is poorest Attach Motor to the model Attached on upper and lower wing Same efficiency Delay stall phenomena, increase maximum lift P26/29

Department of Aerodynamics SUPAERO Contents Introduction Part 1 Optimization - (Experimental) - (Numerical) Part 2 Biplane Combinations Part 3 Propeller Influence Conclusions Department of Aerodynamics SUPAERO P27/29

Conclusions On-going developments Department of Aerodynamics SUPAERO Conclusions Biplane is better than monoplane for this design criteria Wind tunnel measurements and numerical calculations confirm the interest for biplane MAV wings. AR 2.5 to 3 are appropriate for biplane MAV concepts. On-going developments More accuracy measurement Further optimization of motor position (wingtip) Optimizing biplane-connecting structure Pototype of Biplane MAV P28/29

Thank you for your attention P29/29

Drag Reduction of MAV by Biplane Effect Chinnapat THIPYOPAS Graduate student, Department of Aerodynamics and Jean-Marc MOSCHETTA Associate Professor of Aerodynamics, Department of Aerodynamics Ecole Nationale Supérieure de l’Aéronautique et de l’Espace (SUPAERO) 10 Av. Ed. Belin, Toulouse, France

Parasite and Induced Drag Department of Aerodynamics SUPAERO Parasite and Induced Drag 55 - Why interest biplane plane concept ? - high parasite drag (skinfriction drag) due to boundary layer - Low induced drag because of higher aspect ratio The zone which biplane has total drag less than monoplane configuration (when Induced drag > 45% total drag)

Parasite and Induced Drag Airplane drag = Parasite Drag + Induced Drag Parasite drag is a function of Skin-Friction which depends on Wing Chord Induced Drag is very strongly effected by Aspect Ratio The zone which biplane has total drag less than monoplane configuration (when Induced drag > 45% total drag) case a.) AR1 b.) AR2 c.) 2 x AR2 total Surface S S/2 Lift for each wing W W/2 Max. Lift L L/2 Lift coef. CL 2CL Skin friction drag Df Df/1.414 1.414Df Induced drag coef. CDi 2CDi CDi/2 Induced drag Di Di/4 Di/2 Total drag 1.5Df + Di 1.5Df /1.414 + Di 1.5*1.414Df + Di/2 55 - Why interest biplane plane concept ? - high parasite drag (skinfriction drag) due to boundary layer - Low induced drag because of higher aspect ratio

Results Reynolds number effect on L/D Winglet can improve wing performance Gap increases the lift slope and maximum lift L/D increased by positive stagger Stall angle and maximum lift changed by decalage angle Parasite drag from the strut between two wing is very important The induced drag is independent of the stagger angle (Munk's stagger theorem). If the system is unstaggered then D_ij = D_ji. which is Munk's reciprocity theorem. The induced drag of a multiplane system does not change if the elements are translated in a direction parallel to the direction of flight.

Propeller-induced lift Increasing in lift

Why are these 16 models ? The Taguchi method was used in the first experimental design table. But an interaction between each parameters is very strong. To determine the optimizing model, some interpolation was formed to complete the experimental table.

Gap effect

Stagger effect

Decalage effect

Scale 1 Sweptm Plaster and Inv-Zim planeform Connected with strut Biplane parameters Gap Stagger Decalage angle The difference in the angle of incidence of the two wings of a biplane is called the decalage

Swept Planform

Inverse-Zimmerman

Visualisation Smoke generation Tuft method

Motor-Propeller Effect Attached on upper and lower wing Same efficiency Delay stall phenomena, increase maximum lift

GEOBAT