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Stall Speeds - Fact or Fiction?

Stall Speeds - Fact or Fiction?. Stall Speeds - Fact or Fiction?. Stall Speeds - Fact or Fiction?. What is stall speed? The speed at which the maximum lift equals the weight is the stall speed. (We will ignore the lift component required to offset trim.)

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Stall Speeds - Fact or Fiction?

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  1. Stall Speeds - Fact or Fiction?

  2. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? What is stall speed? The speed at which the maximum lift equals the weight is the stall speed. (We will ignore the lift component required to offset trim.) How can we evaluate claimed stall speeds? By calculating the coefficient of lift required to produce the claimed stall speed, and comparing it to known parameters, such as the airfoil’s ideal properties and the known performance of similar airplanes.

  3. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? How can we calculate the Coefficient of lift? The lift equation: L = Cl q S L = Lift, in Lbs. Cl = Wing Coefficient of lift q = Dynamic Pressure, in Lbs. per Ft.² S = Wing area, in Ft.² W = Weight, in Lbs.

  4. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? At stall in steady state flight, maximum Lift equals Weight: Lmax = W = (Clmax) (q) (S) Clmax = W / q S q = (Vi) (Vi) (0.00256) @ Std conditions, in MPH Clmax = W / (Vstall)² (0.00256) (S) Note: This is the Clmax for the wing as a whole. It will always be less than the airfoil can generate in 2-D flow.

  5. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? What parameters affect a wing’s Clmax? Basic airfoil section design Higher speed airfoils are designed for delayed separation (more laminar flow) => lower Clmax at speeds less than cruise

  6. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction?

  7. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? What parameters affect a wing’s Clmax? Reynolds number = VL/ Lower Rn = lower Clmax Hard to find test data between Rn of 500,000 and 3,000,000 Most airfoil data is at Rn higher than most homebuilt Rn at stall speed Example: 48” chord, 2000 Ft altitude, 50MPH => Rn of 1,800,000

  8. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? What parameters affect a wing’s Clmax? Lift Distribution - Elliptical is best Wing Plan form Elliptical is best Tapered - Tips stall first Wing Twist - Washout Most Certified Light A/C use it Airfoil section verses Span

  9. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? What parameters affect a wing’s Clmax? Aspect Ratio - Span² / S Higher AR => Steeper lift curve slope Higher AR => Slightly increased Clmax

  10. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Lift Curve

  11. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? What parameters affect a wing’s Clmax? High Lift Devices Plain Flaps Slotted Flaps Fowler Flaps Leading Edge Devices Boundary Layer Control Devices Vortex Generators etc.

  12. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Plain Flaps Simple to build Less costly Add lift Used to create drag Potential to increase Clmax by approximately 60%

  13. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Slotted Flaps More complicated to build More costly Add lift Typically => greater change in  => more nose down Potential to increase Clmax by 80% or more Wide variation in performance based on flap shape and slot geometry

  14. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Fowler Flaps Most complicated trailing edge flaps to build Most costly Potential to increase section Clmax by more than 100% Also add effective wing area Wide variation in performance based on configuration

  15. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Leading Edge Devices Complex Costly Used for special purpose and complex aircraft Add lift Raise the nose / offset the nose down effect of T.E. flaps

  16. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? High Lift Devices Effect on a Clark Y airfoil Clark YClmax Basic section 1.3 Plain flap 1.8 Slotted flap, w optimum slot 2.0 Slotted + Leading Edge Slat 2.2

  17. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? High Lift Devices Effect on a GAW-1 airfoil, 2-D in wind tunnel 18%, design Cl = 0.4, Rn ~ 2,500,000 GAW-1Clmax stall Basic section 1.55 16° Flower, 30% C, 40° 3.1 8° L.E. + Fowler 3.8 15° L.E. + Fowler + VGs 4.0 15°

  18. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? What parameters affect a wing’s Clmax? Parameter Parameter Clmax Design Speed   Rn   Lift Dist. Less than elliptical  Taper Ratio   Aspect Ratio   Flaps, etc. 

  19. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Circulation

  20. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Circulation

  21. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Circulation

  22. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Bernoulli or Newton? a.k.a. Pressures or Momentum?

  23. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 180 310 230 Gross Weight 2450 3400 3100 Stall Speed 59 70 56 Max. Speed 147 228 173 Wing Span 32.75 38.50 36.00 Wing Area 146.0 149.9 174.0 Airfoil 63/2 A415 Roncz 2412 Airfoil Clmax 1.60 1.50 1.60 Plan form Rectangular Tapered Tapered Flaps Plain Slotted Fowler Aspect Ratio 7.3 9.9 7.4 Wing Clmax 1.88 1.81 2.22 Fact or Fiction?

  24. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Sundowner Cirrus Cessna Model C23 SR-22 Skylane 182T HP 180 310 230 Gross Weight 2450 3400 3100 Stall Speed 59 70 56 Max. Speed 147 228 173 Wing Span 32.75 38.50 36.00 Wing Area 146.0 149.9 174.0 Airfoil 63(2) A415 Roncz 2412 Airfoil Clmax 1.60 1.50 1.60 Plan form Rectangular Tapered Tapered Flaps Plain ? Slotted ? Fowler Aspect Ratio 7.3 9.9 7.4 Wing Clmax 1.88 1.81 2.22 Fact or Fiction? Fact Fact Fact

  25. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 450 450 80 Gross Weight 5100 3500 1050 Stall Speed 45 50 44 Max. Speed 158 158 125 Wing Span 48.00 48.00 27.00 Wing Area 250.0 250.0 130.0 Airfoil 64-415 64-415 65-018 mod ? Airfoil Clmax 1.5 1.5 ? Plan form Rectangular Rectangular Rectangular Flaps Slotted? Slotted? None Aspect Ratio 9.2 9.2 5.6 Wing Clmax 3.94 2.19 1.63 Fact or Fiction?

  26. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Beaver Beaver Zodiac Model CH 601 HD HP 450 450 light 80 Gross Weight 5100 3500 1050 (under) Stall Speed 45 50 44 Max. Speed 158 158 125 Wing Span 48.00 48.00 27.00 Wing Area 250.0 250.0 130.0 Airfoil 64-415 64-415 65-018 mod Airfoil Clmax 1.5 1.5 Plan form Rectangular Rectangular Rectangular Flaps Slotted? Slotted? None Aspect Ratio 9.2 9.2 5.6 Wing Clmax 3.94 2.19 1.63 Fact or Fiction? Fiction Fact Fact

  27. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 100 160 180 Gross Weight 1320 1483 1600 Stall Speed 38 64 59 Max. Speed 95 211 207 est.. Wing Spa 35.50 24.34 20.83 Wing Area 180.0 97.1 86 Airfoil USA35B 64A-212 62(1)-412 Airfoil Clmax 1.50 1.50 1.5 Plan form Rectangular Tapered Rectangular Flaps None Plain Plain Aspect Ratio 7.0 6.1 5.0 Wing Clmax 1.98 1.46 2.09 some power Fact or Fiction?

  28. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Legend Cub Bushby Thorp Model -100 LSA Mustang II T-18 CAFE HP 100 160 180 Gross Weight 1320 1483 1572 Stall Speed 38 64 59 Max. Speed 95 211 207 est. Wing Spa 35.50 24.34 20.83 Wing Area 180.0 97.1 86 Airfoil USA35B 64A-212 62(1)-412 mod Airfoil Clmax 1.50 1.50 1.5 Plan form Rectangular Tapered Rectangular Flaps None Plain Plain ? Aspect Ratio 7.0 6.1 5.0 Wing Clmax 1.98 1.46 2.03 some power Fact or Fiction? Fiction Fact Fact

  29. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 260 80 180 Gross Weight 2000 1300 1500 Stall Speed 54 50 54 Max. Speed 250 172 212 Wing Span 21.83 26.10 23.00 Wing Area 104.0 95.0 110.0 Airfoil 23013.5 Dykins 23013.5 Airfoil Clmax 1.50 1.50est 1.50 Plan form Rectangular Tapered+WO Rectangular Flaps Plain ? Plain Aspect Ratio 4.6 7.2 4.8 Wing Clmax 2.58 2.14 1.83 Fact or Fiction?

  30. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Team Rocket Europa Van's Model F-1 Std Classic CAFE RV-4 HP 260 80 180 Gross Weight 2000 1300 1500 Stall Speed 54 50 54 Max. Speed 250 172 212 Wing Span 21.83 26.10 23.00 Wing Area 104.0 95.0 110.0 Airfoil 23013.5 Dykins 23013.5 Airfoil Clmax 1.50 ? 1.50 Plan form Rectangular Tapered+WO Rectangular Flaps Plain ? Plain Aspect Ratio 4.6 7.2 4.8 Wing Clmax 2.58 2.14 1.83 Fact or Fiction? Fiction Fact Fact

  31. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 260 300 295 Gross Weight 2300 2400 2100 Stall Speed 65 86 50 Max. Speed 225 295 265 Wing Span 24.75 24.40 24.83 Wing Area 120.0 71.5 104.0 Airfoil 64(2)-415 NLF(1) 0416 MS(1)-313 Airfoil Clmax 1.50 1.40 1.50 Plan form Split Tapered Tapered Flaps Plain? Fowler Slotted Aspect Ratio 5.1 8.3 6.0 Wing Clmax 1.77 1.77 3.22 Fact or Fiction?

  32. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Barracuda Swearingen Team Rocket Model SX-300 F-1 Evo HP 260 300 295 Gross Weight 2300 2400 2100 Stall Speed 65 86 50 Max. Speed 225 295 265 Wing Span 24.75 24.40 24.83 Wing Area 120.0 71.5 104.0 Airfoil 64(2)-415 NLF(1) 0416 MS(1)-313 Airfoil Clmax 1.50 1.40 1.50 Plan form Split Tapered Tapered Flaps Plain? Fowler Slotted Aspect Ratio 5.1 8.3 6.0 Wing Clmax 1.77 1.77 3.22 Fact or Fiction? Fact Fact Fiction

  33. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 170 310 310 Gross Weight 1775 2200 2217 Stall Speed 71 65 68 Max. Speed 233 285 292 Wing Span 23.70 25.50 25.50 Wing Area 76.0 82.5 82.5 Airfoil NLF1-0215F GC10/11 GC10/11 Airfoil Clmax 1.50 est. ? ? Plan form Tapered Tapered Tapered Flaps Plain Fowler Fowler Aspect Ratio 7.4 7.9 7.9 Wing Clmax 1.81 2.47 2.27 Fact or Fiction?

  34. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Lancair Lancair Lancair Model 320 CAFE Legacy Legacy CAFE HP 170 310 310 Gross Weight 1775 2200 2217 Stall Speed 71 65 68 Max. Speed 233 285 292 Wing Span 23.70 25.50 25.50 Wing Area 76.0 82.5 82.5 Airfoil NLF1-0215F GC10/11 GC10/11 Airfoil Clmax 1.50 est. ? ? Plan form Tapered Tapered Tapered Flaps Plain Fowler Fowler Aspect Ratio 7.4 7.9 7.9 Wing Clmax 1.81 2.47 2.27 Fact or Fiction? Fact LoC Fact

  35. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 160 160 160 Gross Weight 1750 1758 1960 Stall Speed 50 49 49 Max. Speed 194 193 167 Wing Span 28.00 28.00 35.00 Wing Area 124.0 124.0 128.0 Airfoil Roncz Roncz LS(1)-0413 mod Airfoil Clmax ? ? 1.60 Plan form Rectangular Rectangular Rectangular Flaps Slotted Slotted Fowler + Vortex Aspect Ratio 6.3 6.3 9.6 Wing Clmax 2.21 2.31 2.49 Fact or Fiction?

  36. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Van’s Van’s Glastar Model RV-9A RV-9A CAFE Glastar HP 160 160 160 Gross Weight 1750 1758 1960 Stall Speed 50 49 49 Max. Speed 194 193 167 Wing Span 28.00 28.00 35.00 Wing Area 124.0 124.0 128.0 Airfoil Roncz Roncz LS(1)-0413 mod Airfoil Clmax ? ? 1.60 Plan form Rectangular Rectangular Rectangular Flaps Slotted Slotted Fowler + Vortex Aspect Ratio 6.3 6.3 9.6 Wing Clmax 2.21 2.31 2.49 Fact or Fiction? Fact Fact Fact

  37. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 160 180 300 Gross Weight 1950 2100 2400 Stall Speed 47 68 73 Max. Speed 158 228 290 Wing Span 35.67 23.30 23.30 Wing Area 128.0 81.3 81.3 Airfoil LS(1)-0413 mod LS(1)-0413 mod LS(1)-0413 mod Airfoil Clmax 1.60 1.60 1.60 Plan form Rectangular Tapered Tapered Flaps Fowler + Vortex Slotted Slotted Aspect Ratio 9.9 6.7 6.7 Wing Clmax 2.69 2.18 2.16 Fact or Fiction?

  38. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Glastar Glasair Glasair Model Glastar CAFE SII- FT short III short HP 160 180 300 Gross Weight 1950 2100 2400 Stall Speed 47 68 73 Max. Speed 158 228 290 Wing Span 35.67 23.30 23.30 Wing Area 128.0 81.3 81.3 Airfoil LS(1)-0413 mod LS(1)-0413 mod LS(1)-0413 mod Airfoil Clmax 1.60 1.60 1.60 Plan form Rectangular Tapered Tapered Flaps Fowler + Vortex Slotted Slotted Aspect Ratio 9.9 6.7 6.7 Wing Clmax 2.69 2.18 2.16 Fact or Fiction? Fact Fact Fact

  39. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 300 300 180 Gross Weight 2400 2500 1800 Stall Speed 80 74 58 Max. Speed 282 281 209 Wing Span 23.30 27.00 25.00 Wing Area 88.0 97.2 121.0 Airfoil LS(1)-0413 mod LS(1)-0413 mod 23013.5 Airfoil Clmax 1.60 1.60 1.50 Plan form Tapered Tapered Rectangular Flaps Plain Plain Plain Aspect Ratio 6.2 7.5 5.2 Wing Clmax 1.66 1.83 1.73 Fact or Fiction?

  40. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Glasair Glasair Van's Model III short CAFE III long CAFE RV-7 HP 300 300 180 Gross Weight 2400 2500 1800 Stall Speed 80 74 58 Max. Speed 282 281 209 Wing Span 23.30 27.00 25.00 Wing Area 81.3 97.2 121.0 Airfoil LS(1)-0413 mod LS(1)-0413 mod 23013.5 Airfoil Clmax 1.60 1.60 1.50 Plan form Tapered Tapered Rectangular Flaps Plain Plain Plain Aspect Ratio 6.2 7.5 5.2 Wing Clmax 1.80 1.95 1.73 Fact or Fiction? Fact Fact Fact

  41. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 160 160 200 Gross Weight 1750 1758 1800 Stall Speed 50 49 58 Max. Speed 194 193 219 Wing Span 28.00 28.00 24.00 Wing Area 124.0 124.0 116.0 Airfoil Roncz Roncz 23013.5 Airfoil Clmax ? ? 1.50 Plan form Rectangular Rectangular Rectangular Flaps Slotted Slotted Plain Aspect Ratio 6.3 6.3 5.0 Wing Clmax 2.21 2.31 1.80 Fact or Fiction?

  42. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Van's Van's Van's Model RV-9A RV-9A CAFE RV-8A HP 160 160 200 Gross Weight 1750 1758 1800 Stall Speed 50 49 58 Max. Speed 194 193 219 Wing Span 28.00 28.00 24.00 Wing Area 124.0 124.0 116.0 Airfoil Roncz Roncz 23013.5 Airfoil Clmax ? ? 1.50 Plan form Rectangular Rectangular Rectangular Flaps Slotted Slotted Plain Aspect Ratio 6.3 6.3 5.0 Wing Clmax 2.21 2.31 1.80 Fact or Fiction? Fact Fact LoC

  43. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 200 180 260 Gross Weight 1668 1800 2700 Stall Speed 58 58 63 Max. Speed 220 207 208 Wing Span 24.00 25.00 31.75 Wing Area 116.0 121.0 148.0 Airfoil 23013.5 23013.5 23013.5 Airfoil Clmax 1.50 1.50 1.50 Plan form Rectangular Rectangular Rectangular Flaps Plain Plain Plain Aspect Ratio 5.0 5.2 6.8 Wing Clmax 1.67 1.73 1.80 Fact or Fiction?

  44. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Van's Van's Van's Model RV-8A CAFE RV-7A RV-10 HP 200 180 260 Gross Weight 1668 1800 2700 Stall Speed 58 58 63 Max. Speed 220 207 208 Wing Span 24.00 25.00 31.75 Wing Area 116.0 121.0 148.0 Airfoil 23013.5 23013.5 23013.5 Airfoil Clmax 1.50 1.50 1.50 Plan form Rectangular Rectangular Rectangular Flaps Plain Plain Plain Aspect Ratio 5.0 5.2 6.8 Wing Clmax 1.67 1.73 1.80 Fact or Fiction? Fact Fact Fact

  45. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Model HP 180 310 300 Gross Weight 2100 3400 3650 Stall Speed 68 66 68 Max. Speed 238 219+ ? Wing Span 23.30 35.80 33.50 Wing Area 81.3 141.2 180.7 Airfoil LS(1)-0413 mod ? 23016.5 / 12 Airfoil Clmax 1.60 ? 1.60 Plan form Tapered Tapered Tapered Flaps Slotted Slotted Plain Aspect Ratio 6.7 9.1 6.2 Wing Clmax 2.18 2.16 1.71 Fact or Fiction?

  46. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Airplane Glasair Columbia Beechcraft Model SII - RG short 350 G36 HP 180 310 300 Gross Weight 2100 3400 3650 Stall Speed 68 66 68 Max. Speed 238 219+ ? Wing Span 23.30 35.80 33.50 Wing Area 81.3 141.2 180.7 Airfoil LS(1)-0413 mod ? 23016.5 / 12 Airfoil Clmax 1.60 ? 1.60 Plan form Tapered Tapered Tapered Flaps Slotted Slotted Plain Aspect Ratio 6.7 9.1 6.2 Wing Clmax 2.18 2.16 1.71 Fact or Fiction? Fact Fact Fact

  47. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Possible reasons for the unsubstantiated claims: Equating indicated airspeed to calibrated airspeed Too rapid deceleration into stall Testing with some power on Testing at other than standard conditions Testing at less than gross weight Self-certify = right to claim ignorance

  48. Stall Speeds - Fact or Fiction? Stall Speeds - Fact or Fiction? Observations and Conclusions: Several kit manufacturers list neither maximum speed nor red line speed. It is not clear that all manufacturers list stall speeds at gross weight. It is not clear that all manufacturers use calibrated airspeed. Some manufacturers quote stall speeds with power above idle. Most pilot reports do not include measured, calibrated, performance data. There are many misperceptions about airfoils. There is no magical airfoil. CAFE performs an excellent service.

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