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 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:

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. 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. 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. 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 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 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 Stall Speeds - Fact or Fiction?

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?

Lift Curve

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?

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?

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?

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?

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?

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?

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 1.5516° Flower, 30% C, 40°3.18° L.E. + Fowler3.815° L.E. + Fowler + VGs4.015° Stall Speeds - Fact or Fiction?

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?

Circulation Stall Speeds - Fact or Fiction?

Circulation Stall Speeds - Fact or Fiction?

Circulation Stall Speeds - Fact or Fiction?

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

Airplane Model HP180310230 Gross Weight245034003100 Stall Speed597056 Max. Speed147228173 Wing Span32.7538.5036.00 Wing Area146.0149.9174.0 Airfoil63/2 A415Roncz2412 Airfoil Clmax1.601.501.60 Plan formRectangularTaperedTapered FlapsPlainSlottedFowler Aspect Ratio7.39.97.4 Wing Clmax1.881.812.22 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneSundownerCirrusCessna ModelC23SR-22Skylane 182T HP180310230 Gross Weight245034003100 Stall Speed597056 Max. Speed147228173 Wing Span32.7538.5036.00 Wing Area146.0149.9174.0 Airfoil63(2) A415Roncz2412 Airfoil Clmax1.601.501.60 Plan formRectangularTaperedTapered FlapsPlain ?Slotted ?Fowler Aspect Ratio7.39.97.4 Wing Clmax1.881.812.22 Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

Airplane Model HP45045080 Gross Weight510035001050 Stall Speed455044 Max. Speed158158125 Wing Span48.0048.0027.00 Wing Area250.0250.0130.0 Airfoil64-41564-41565-018 mod ? Airfoil Clmax1.51.5 ? Plan formRectangularRectangularRectangular FlapsSlotted?Slotted?None Aspect Ratio9.29.25.6 Wing Clmax3.942.191.63 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneBeaverBeaverZodiac ModelCH 601 HD HP450450 light80 Gross Weight510035001050 (under) Stall Speed455044 Max. Speed158158125 Wing Span48.0048.0027.00 Wing Area250.0250.0130.0 Airfoil64-41564-41565-018 mod Airfoil Clmax1.51.5 Plan formRectangularRectangularRectangular FlapsSlotted?Slotted?None Aspect Ratio9.29.25.6 Wing Clmax3.942.191.63 Fact or Fiction?FictionFactFact Stall Speeds - Fact or Fiction?

Airplane Model HP100160180 Gross Weight132014831600 Stall Speed386459 Max. Speed95211207 est.. Wing Spa35.5024.3420.83 Wing Area180.097.186 AirfoilUSA35B64A-21262(1)-412 Airfoil Clmax1.501.501.5 Plan formRectangularTaperedRectangular FlapsNonePlainPlain Aspect Ratio7.06.15.0 Wing Clmax1.981.462.09 some power Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneLegend CubBushbyThorp Model-100 LSAMustang IIT-18 CAFE HP100160180 Gross Weight132014831572 Stall Speed386459 Max. Speed95211207 est. Wing Spa35.5024.3420.83 Wing Area180.097.186 AirfoilUSA35B64A-21262(1)-412 mod Airfoil Clmax1.501.501.5 Plan formRectangularTaperedRectangular FlapsNonePlainPlain ? Aspect Ratio7.06.15.0 Wing Clmax1.981.462.03 some power Fact or Fiction?FictionFactFact Stall Speeds - Fact or Fiction?

Airplane Model HP26080180 Gross Weight200013001500 Stall Speed545054 Max. Speed250172212 Wing Span21.8326.1023.00 Wing Area104.095.0110.0 Airfoil23013.5Dykins23013.5 Airfoil Clmax1.501.50est1.50 Plan formRectangular Tapered+WORectangular FlapsPlain ?Plain Aspect Ratio4.67.24.8 Wing Clmax2.582.141.83 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneTeam RocketEuropaVan's ModelF-1 StdClassic CAFERV-4 HP26080180 Gross Weight200013001500 Stall Speed545054 Max. Speed250172212 Wing Span21.8326.1023.00 Wing Area104.095.0110.0 Airfoil23013.5Dykins23013.5 Airfoil Clmax1.50?1.50 Plan formRectangular Tapered+WORectangular FlapsPlain ?Plain Aspect Ratio4.67.24.8 Wing Clmax2.582.141.83 Fact or Fiction?FictionFactFact Stall Speeds - Fact or Fiction?

Airplane Model HP260300295 Gross Weight230024002100 Stall Speed658650 Max. Speed225295265 Wing Span24.7524.4024.83 Wing Area120.071.5104.0 Airfoil64(2)-415NLF(1) 0416MS(1)-313 Airfoil Clmax1.501.401.50 Plan formSplitTaperedTapered FlapsPlain?FowlerSlotted Aspect Ratio5.18.36.0 Wing Clmax1.771.773.22 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneBarracudaSwearingenTeam Rocket ModelSX-300F-1 Evo HP260300295 Gross Weight230024002100 Stall Speed658650 Max. Speed225295265 Wing Span24.7524.4024.83 Wing Area120.071.5104.0 Airfoil64(2)-415NLF(1) 0416MS(1)-313 Airfoil Clmax1.501.401.50 Plan formSplitTaperedTapered FlapsPlain?FowlerSlotted Aspect Ratio5.18.36.0 Wing Clmax1.771.773.22 Fact or Fiction?FactFactFiction Stall Speeds - Fact or Fiction?

Airplane Model HP170310310 Gross Weight177522002217 Stall Speed716568 Max. Speed233285292 Wing Span23.7025.5025.50 Wing Area76.082.582.5 AirfoilNLF1-0215FGC10/11GC10/11 Airfoil Clmax1.50 est.?? Plan formTapered TaperedTapered FlapsPlainFowlerFowler Aspect Ratio7.47.97.9 Wing Clmax1.812.472.27 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneLancair LancairLancair Model320 CAFE LegacyLegacy CAFE HP170310310 Gross Weight177522002217 Stall Speed716568 Max. Speed233285292 Wing Span23.7025.5025.50 Wing Area76.082.582.5 AirfoilNLF1-0215FGC10/11GC10/11 Airfoil Clmax1.50 est.?? Plan formTapered TaperedTapered FlapsPlainFowlerFowler Aspect Ratio7.47.97.9 Wing Clmax1.812.472.27 Fact or Fiction?FactLoCFact Stall Speeds - Fact or Fiction?

Airplane Model HP160160160 Gross Weight175017581960 Stall Speed504949 Max. Speed194193167 Wing Span28.0028.0035.00 Wing Area124.0124.0128.0 AirfoilRoncz Roncz LS(1)-0413 mod Airfoil Clmax??1.60 Plan formRectangular Rectangular Rectangular FlapsSlottedSlottedFowler + Vortex Aspect Ratio6.36.39.6 Wing Clmax2.212.312.49 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneVan’sVan’sGlastar ModelRV-9ARV-9A CAFEGlastar HP160160160 Gross Weight175017581960 Stall Speed504949 Max. Speed194193167 Wing Span28.0028.0035.00 Wing Area124.0124.0128.0 AirfoilRoncz Roncz LS(1)-0413 mod Airfoil Clmax??1.60 Plan formRectangular Rectangular Rectangular FlapsSlottedSlottedFowler + Vortex Aspect Ratio6.36.39.6 Wing Clmax2.212.312.49 Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

Airplane Model HP160180300 Gross Weight195021002400 Stall Speed476873 Max. Speed158228290 Wing Span35.6723.3023.30 Wing Area128.081.381.3 AirfoilLS(1)-0413 modLS(1)-0413 modLS(1)-0413 mod Airfoil Clmax1.601.601.60 Plan formRectangularTaperedTapered FlapsFowler + VortexSlottedSlotted Aspect Ratio9.96.76.7 Wing Clmax2.692.182.16 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneGlastarGlasairGlasair ModelGlastar CAFESII- FT shortIII short HP160180300 Gross Weight195021002400 Stall Speed476873 Max. Speed158228290 Wing Span35.6723.3023.30 Wing Area128.081.381.3 AirfoilLS(1)-0413 modLS(1)-0413 modLS(1)-0413 mod Airfoil Clmax1.601.601.60 Plan formRectangularTaperedTapered FlapsFowler + VortexSlottedSlotted Aspect Ratio9.96.76.7 Wing Clmax2.692.182.16 Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

Airplane Model HP300300180 Gross Weight240025001800 Stall Speed807458 Max. Speed282281209 Wing Span23.3027.0025.00 Wing Area88.097.2121.0 AirfoilLS(1)-0413 modLS(1)-0413 mod23013.5 Airfoil Clmax1.601.601.50 Plan formTaperedTaperedRectangular FlapsPlainPlainPlain Aspect Ratio6.27.55.2 Wing Clmax1.661.831.73 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneGlasairGlasairVan's ModelIII short CAFE III long CAFE RV-7 HP300300180 Gross Weight240025001800 Stall Speed807458 Max. Speed282281209 Wing Span23.3027.0025.00 Wing Area81.397.2121.0 AirfoilLS(1)-0413 modLS(1)-0413 mod23013.5 Airfoil Clmax1.601.601.50 Plan formTaperedTaperedRectangular FlapsPlainPlainPlain Aspect Ratio6.27.55.2 Wing Clmax1.801.951.73 Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

Airplane Model HP160160200 Gross Weight175017581800 Stall Speed504958 Max. Speed194193219 Wing Span28.0028.0024.00 Wing Area124.0124.0116.0 AirfoilRonczRoncz23013.5 Airfoil Clmax??1.50 Plan formRectangularRectangularRectangular FlapsSlottedSlottedPlain Aspect Ratio6.36.35.0 Wing Clmax2.212.311.80 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneVan'sVan'sVan's ModelRV-9ARV-9A CAFERV-8A HP160160200 Gross Weight175017581800 Stall Speed504958 Max. Speed194193219 Wing Span28.0028.0024.00 Wing Area124.0124.0116.0 AirfoilRonczRoncz23013.5 Airfoil Clmax??1.50 Plan formRectangularRectangularRectangular FlapsSlottedSlottedPlain Aspect Ratio6.36.35.0 Wing Clmax2.212.311.80 Fact or Fiction?FactFactLoC Stall Speeds - Fact or Fiction?

Airplane Model HP200180260 Gross Weight166818002700 Stall Speed585863 Max. Speed220207208 Wing Span24.0025.0031.75 Wing Area116.0121.0148.0 Airfoil23013.523013.523013.5 Airfoil Clmax1.501.501.50 Plan formRectangularRectangularRectangular FlapsPlainPlainPlain Aspect Ratio5.05.26.8 Wing Clmax1.671.731.80 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneVan'sVan'sVan's ModelRV-8A CAFERV-7ARV-10 HP200180260 Gross Weight166818002700 Stall Speed585863 Max. Speed220207208 Wing Span24.0025.0031.75 Wing Area116.0121.0148.0 Airfoil23013.523013.523013.5 Airfoil Clmax1.501.501.50 Plan formRectangularRectangularRectangular FlapsPlainPlainPlain Aspect Ratio5.05.26.8 Wing Clmax1.671.731.80 Fact or Fiction?FactFactFact Stall Speeds - Fact or Fiction?

Airplane Model HP180310300 Gross Weight210034003650 Stall Speed686668 Max. Speed238219+? Wing Span23.3035.8033.50 Wing Area81.3141.2180.7 AirfoilLS(1)-0413 mod?23016.5 / 12 Airfoil Clmax1.60?1.60 Plan formTaperedTaperedTapered FlapsSlottedSlottedPlain Aspect Ratio6.79.16.2 Wing Clmax2.182.161.71 Fact or Fiction? Stall Speeds - Fact or Fiction?

AirplaneGlasairColumbiaBeechcraft ModelSII - RG short350G36 HP180310300 Gross Weight210034003650 Stall Speed686668 Max. Speed238219+? Wing Span23.3035.8033.50 Wing Area81.3141.2180.7 AirfoilLS(1)-0413 mod?23016.5 / 12 Airfoil Clmax1.60?1.60 Plan formTaperedTaperedTapered FlapsSlottedSlottedPlain Aspect Ratio6.79.16.2 Wing Clmax2.182.161.71 Fact or Fiction?FactFactFact 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 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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