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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.

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Presentation on theme: "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."— Presentation transcript:

1 Stall Speeds - Fact or Fiction?

2 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. Stall Speeds - Fact or Fiction?

3 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. Stall Speeds - Fact or Fiction?

4 At stall in steady state flight, maximum Lift equals Weight: Lmax = W = (Clmax) (q) (S) Clmax = W / q S q = (Vi) (Vi) Std conditions, in MPH Clmax = W / (Vstall)² ( ) (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. Stall Speeds - Fact or Fiction?

5 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 Stall Speeds - Fact or Fiction?

6

7 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 Stall Speeds - Fact or Fiction?

8 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 Stall Speeds - Fact or Fiction?

9 What parameters affect a wing’s Clmax? Aspect Ratio - Span ² / S Higher AR => Steeper lift curve slope Higher AR => Slightly increased Clmax Stall Speeds - Fact or Fiction?

10 Lift Curve

11 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. Stall Speeds - Fact or Fiction?

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

13 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 Stall Speeds - Fact or Fiction?

14 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 Stall Speeds - Fact or Fiction?

15 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 Stall Speeds - Fact or Fiction?

16 High Lift Devices Effect on a Clark Y airfoil Clark YClmax Basic section 1.3 Plain flap1.8 Slotted flap, w optimum slot 2.0 Slotted + Leading Edge Slat2.2 Stall Speeds - Fact or Fiction?

17 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 ° Flower, 30% C, 40°3.18° L.E. + Fowler3.815° L.E. + Fowler + VGs4.015° Stall Speeds - Fact or Fiction?

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

19 Circulation Stall Speeds - Fact or Fiction?

20 Circulation Stall Speeds - Fact or Fiction?

21 Circulation Stall Speeds - Fact or Fiction?

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

23 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil63/2 A415Roncz2412 Airfoil Clmax Plan formRectangularTaperedTapered FlapsPlainSlottedFowler Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

24 AirplaneSundownerCirrusCessna ModelC23SR-22Skylane 182T HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil63(2) A415Roncz2412 Airfoil Clmax Plan formRectangularTaperedTapered FlapsPlain ?Slotted ?Fowler Aspect Ratio Wing Clmax Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

25 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil mod ? Airfoil Clmax ? Plan formRectangularRectangularRectangular FlapsSlotted?Slotted?None Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

26 AirplaneBeaverBeaverZodiac ModelCH 601 HD HP light80 Gross Weight (under) Stall Speed Max. Speed Wing Span Wing Area Airfoil mod Airfoil Clmax Plan formRectangularRectangularRectangular FlapsSlotted?Slotted?None Aspect Ratio Wing Clmax Fact or Fiction?FictionFactFact Stall Speeds - Fact or Fiction?

27 Airplane Model HP Gross Weight Stall Speed Max. Speed est.. Wing Spa Wing Area AirfoilUSA35B64A-21262(1)-412 Airfoil Clmax Plan formRectangularTaperedRectangular FlapsNonePlainPlain Aspect Ratio Wing Clmax some power Fact or Fiction? Stall Speeds - Fact or Fiction?

28 AirplaneLegend CubBushbyThorp Model-100 LSAMustang IIT-18 CAFE HP Gross Weight Stall Speed Max. Speed est. Wing Spa Wing Area AirfoilUSA35B64A-21262(1)-412 mod Airfoil Clmax Plan formRectangularTaperedRectangular FlapsNonePlainPlain ? Aspect Ratio Wing Clmax some power Fact or Fiction?FictionFactFact Stall Speeds - Fact or Fiction?

29 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil Dykins Airfoil Clmax est1.50 Plan formRectangular Tapered+WORectangular FlapsPlain ?Plain Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

30 AirplaneTeam RocketEuropaVan's ModelF-1 StdClassic CAFERV-4 HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil Dykins Airfoil Clmax1.50?1.50 Plan formRectangular Tapered+WORectangular FlapsPlain ?Plain Aspect Ratio Wing Clmax Fact or Fiction?FictionFactFact Stall Speeds - Fact or Fiction?

31 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil64(2)-415NLF(1) 0416MS(1)-313 Airfoil Clmax Plan formSplitTaperedTapered FlapsPlain?FowlerSlotted Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

32 AirplaneBarracudaSwearingenTeam Rocket ModelSX-300F-1 Evo HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil64(2)-415NLF(1) 0416MS(1)-313 Airfoil Clmax Plan formSplitTaperedTapered FlapsPlain?FowlerSlotted Aspect Ratio Wing Clmax Fact or Fiction?FactFactFiction Stall Speeds - Fact or Fiction?

33 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilNLF1-0215FGC10/11GC10/11 Airfoil Clmax1.50 est.?? Plan formTapered TaperedTapered FlapsPlainFowlerFowler Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

34 AirplaneLancair LancairLancair Model320 CAFE LegacyLegacy CAFE HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilNLF1-0215FGC10/11GC10/11 Airfoil Clmax1.50 est.?? Plan formTapered TaperedTapered FlapsPlainFowlerFowler Aspect Ratio Wing Clmax Fact or Fiction?FactLoCFact Stall Speeds - Fact or Fiction?

35 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilRoncz Roncz LS(1)-0413 mod Airfoil Clmax??1.60 Plan formRectangular Rectangular Rectangular FlapsSlottedSlottedFowler + Vortex Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

36 AirplaneVan’sVan’sGlastar ModelRV-9ARV-9A CAFEGlastar HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilRoncz Roncz LS(1)-0413 mod Airfoil Clmax??1.60 Plan formRectangular Rectangular Rectangular FlapsSlottedSlottedFowler + Vortex Aspect Ratio Wing Clmax Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

37 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilLS(1)-0413 modLS(1)-0413 modLS(1)-0413 mod Airfoil Clmax Plan formRectangularTaperedTapered FlapsFowler + VortexSlottedSlotted Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

38 AirplaneGlastarGlasairGlasair ModelGlastar CAFESII- FT shortIII short HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilLS(1)-0413 modLS(1)-0413 modLS(1)-0413 mod Airfoil Clmax Plan formRectangularTaperedTapered FlapsFowler + VortexSlottedSlotted Aspect Ratio Wing Clmax Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

39 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilLS(1)-0413 modLS(1)-0413 mod Airfoil Clmax Plan formTaperedTaperedRectangular FlapsPlainPlainPlain Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

40 AirplaneGlasairGlasairVan's ModelIII short CAFE III long CAFE RV-7 HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilLS(1)-0413 modLS(1)-0413 mod Airfoil Clmax Plan formTaperedTaperedRectangular FlapsPlainPlainPlain Aspect Ratio Wing Clmax Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

41 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilRonczRoncz Airfoil Clmax??1.50 Plan formRectangularRectangularRectangular FlapsSlottedSlottedPlain Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

42 AirplaneVan'sVan'sVan's ModelRV-9ARV-9A CAFERV-8A HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area AirfoilRonczRoncz Airfoil Clmax??1.50 Plan formRectangularRectangularRectangular FlapsSlottedSlottedPlain Aspect Ratio Wing Clmax Fact or Fiction?FactFactLoC Stall Speeds - Fact or Fiction?

43 Airplane Model HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil Airfoil Clmax Plan formRectangularRectangularRectangular FlapsPlainPlainPlain Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

44 AirplaneVan'sVan'sVan's ModelRV-8A CAFERV-7ARV-10 HP Gross Weight Stall Speed Max. Speed Wing Span Wing Area Airfoil Airfoil Clmax Plan formRectangularRectangularRectangular FlapsPlainPlainPlain Aspect Ratio Wing Clmax Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

45 Airplane Model HP Gross Weight Stall Speed Max. Speed ? Wing Span Wing Area AirfoilLS(1)-0413 mod? / 12 Airfoil Clmax1.60?1.60 Plan formTaperedTaperedTapered FlapsSlottedSlottedPlain Aspect Ratio Wing Clmax Fact or Fiction? Stall Speeds - Fact or Fiction?

46 AirplaneGlasairColumbiaBeechcraft ModelSII - RG short350G36 HP Gross Weight Stall Speed Max. Speed ? Wing Span Wing Area AirfoilLS(1)-0413 mod? / 12 Airfoil Clmax1.60?1.60 Plan formTaperedTaperedTapered FlapsSlottedSlottedPlain Aspect Ratio Wing Clmax Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

47 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 Stall Speeds - Fact or Fiction?

48 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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