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.
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.
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.
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
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?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
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
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
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?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?
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?
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?
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?
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?
Stall Speeds - Fact or Fiction?
High Lift Devices
Effect on a Clark Y airfoil
Clark Y Clmax
Basic section 1.3
Plain flap 1.8
Slotted flap, w optimum slot 2.0
Slotted + Leading Edge Slat 2.2
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-1 Clmax 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°
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.
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Circulation
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Circulation
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Circulation
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Bernoulli or Newton?
a.k.a.
Pressures or Momentum?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 180 310 230Gross Weight 2450 3400 3100Stall Speed 59 70 56Max. Speed 147 228 173Wing Span 32.75 38.50 36.00Wing Area 146.0 149.9 174.0Airfoil 63/2 A415 Roncz 2412Airfoil Clmax 1.60 1.50 1.60Plan form Rectangular Tapered TaperedFlaps Plain Slotted FowlerAspect Ratio 7.3 9.9 7.4Wing Clmax 1.88 1.81 2.22
Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Sundowner Cirrus CessnaModel C23 SR-22 Skylane 182THP 180 310 230Gross Weight 2450 3400 3100Stall Speed 59 70 56Max. Speed 147 228 173Wing Span 32.75 38.50 36.00Wing Area 146.0 149.9 174.0Airfoil 63(2) A415 Roncz 2412Airfoil Clmax 1.60 1.50 1.60Plan form Rectangular Tapered TaperedFlaps Plain ? Slotted ? FowlerAspect Ratio 7.3 9.9 7.4Wing Clmax 1.88 1.81 2.22
Fact or Fiction? Fact Fact Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 450 450 80Gross Weight 5100 3500 1050Stall Speed 45 50 44Max. Speed 158 158 125Wing Span 48.00 48.00 27.00Wing Area 250.0 250.0 130.0Airfoil 64-415 64-415 65-018 mod ?Airfoil Clmax 1.5 1.5 ?Plan form Rectangular Rectangular RectangularFlaps Slotted? Slotted? NoneAspect Ratio 9.2 9.2 5.6Wing Clmax 3.94 2.19 1.63Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Beaver Beaver ZodiacModel CH 601 HDHP 450 450 light 80Gross Weight 5100 3500 1050 (under)Stall Speed 45 50 44Max. Speed 158 158 125Wing Span 48.00 48.00 27.00Wing Area 250.0 250.0 130.0Airfoil 64-415 64-415 65-018 modAirfoil Clmax 1.5 1.5 Plan form Rectangular Rectangular RectangularFlaps Slotted? Slotted? NoneAspect Ratio 9.2 9.2 5.6Wing Clmax 3.94 2.19 1.63Fact or Fiction? Fiction Fact Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 100 160 180Gross Weight 1320 1483 1600Stall Speed 38 64 59Max. Speed 95 211 207 est..Wing Spa 35.50 24.34 20.83Wing Area 180.0 97.1 86Airfoil USA35B 64A-212 62(1)-412Airfoil Clmax 1.50 1.50 1.5Plan form Rectangular Tapered RectangularFlaps None Plain PlainAspect Ratio 7.0 6.1 5.0Wing Clmax 1.98 1.46 2.09 some powerFact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Legend Cub Bushby ThorpModel -100 LSA Mustang II T-18 CAFEHP 100 160 180Gross Weight 1320 1483 1572Stall Speed 38 64 59Max. Speed 95 211 207 est.Wing Spa 35.50 24.34 20.83Wing Area 180.0 97.1 86Airfoil USA35B 64A-212 62(1)-412 modAirfoil Clmax 1.50 1.50 1.5Plan form Rectangular Tapered RectangularFlaps None Plain Plain ?Aspect Ratio 7.0 6.1 5.0Wing Clmax 1.98 1.46 2.03 some powerFact or Fiction? Fiction Fact Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 260 80 180Gross Weight 2000 1300 1500Stall Speed 54 50 54Max. Speed 250 172 212Wing Span 21.83 26.10 23.00Wing Area 104.0 95.0 110.0Airfoil 23013.5 Dykins 23013.5Airfoil Clmax 1.50 1.50est 1.50Plan form Rectangular Tapered+WO RectangularFlaps Plain ? PlainAspect Ratio 4.6 7.2 4.8Wing Clmax 2.58 2.14 1.83Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Team Rocket Europa Van'sModel F-1 Std Classic CAFE RV-4HP 260 80 180Gross Weight 2000 1300 1500Stall Speed 54 50 54Max. Speed 250 172 212Wing Span 21.83 26.10 23.00Wing Area 104.0 95.0 110.0Airfoil 23013.5 Dykins 23013.5Airfoil Clmax 1.50 ? 1.50Plan form Rectangular Tapered+WO RectangularFlaps Plain ? PlainAspect Ratio 4.6 7.2 4.8Wing Clmax 2.58 2.14 1.83Fact or Fiction? Fiction Fact Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 260 300 295Gross Weight 2300 2400 2100Stall Speed 65 86 50Max. Speed 225 295 265Wing Span 24.75 24.40 24.83Wing Area 120.0 71.5 104.0Airfoil 64(2)-415 NLF(1) 0416 MS(1)-313Airfoil Clmax 1.50 1.40 1.50Plan form Split Tapered Tapered Flaps Plain? Fowler SlottedAspect Ratio 5.1 8.3 6.0Wing Clmax 1.77 1.77 3.22Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Barracuda Swearingen Team RocketModel SX-300 F-1 EvoHP 260 300 295Gross Weight 2300 2400 2100Stall Speed 65 86 50Max. Speed 225 295 265Wing Span 24.75 24.40 24.83Wing Area 120.0 71.5 104.0Airfoil 64(2)-415 NLF(1) 0416 MS(1)-313Airfoil Clmax 1.50 1.40 1.50Plan form Split Tapered Tapered Flaps Plain? Fowler SlottedAspect Ratio 5.1 8.3 6.0Wing Clmax 1.77 1.77 3.22Fact or Fiction? Fact Fact Fiction
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 170 310 310Gross Weight 1775 2200 2217Stall Speed 71 65 68Max. Speed 233 285 292Wing Span 23.70 25.50 25.50Wing Area 76.0 82.5 82.5Airfoil NLF1-0215F GC10/11GC10/11Airfoil Clmax 1.50 est. ? ?Plan form Tapered Tapered TaperedFlaps Plain Fowler FowlerAspect Ratio 7.4 7.9 7.9Wing Clmax 1.81 2.47 2.27 Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Lancair Lancair LancairModel 320 CAFE Legacy Legacy CAFEHP 170 310 310Gross Weight 1775 2200 2217Stall Speed 71 65 68Max. Speed 233 285 292Wing Span 23.70 25.50 25.50Wing Area 76.0 82.5 82.5Airfoil NLF1-0215F GC10/11GC10/11Airfoil Clmax 1.50 est. ? ?Plan form Tapered Tapered TaperedFlaps Plain Fowler FowlerAspect Ratio 7.4 7.9 7.9Wing Clmax 1.81 2.47 2.27Fact or Fiction? Fact LoC Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 160 160 160Gross Weight 1750 1758 1960Stall Speed 50 49 49Max. Speed 194 193 167Wing Span 28.00 28.00 35.00Wing Area 124.0 124.0 128.0Airfoil Roncz Roncz LS(1)-0413 modAirfoil Clmax ? ? 1.60Plan form Rectangular Rectangular RectangularFlaps Slotted Slotted Fowler + Vortex Aspect Ratio 6.3 6.3 9.6Wing Clmax 2.21 2.31 2.49Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Van’s Van’s GlastarModel RV-9A RV-9A CAFE GlastarHP 160 160 160Gross Weight 1750 1758 1960Stall Speed 50 49 49Max. Speed 194 193 167Wing Span 28.00 28.00 35.00Wing Area 124.0 124.0 128.0Airfoil Roncz Roncz LS(1)-0413 modAirfoil Clmax ? ? 1.60Plan form Rectangular Rectangular RectangularFlaps Slotted Slotted Fowler + Vortex Aspect Ratio 6.3 6.3 9.6Wing Clmax 2.21 2.31 2.49Fact or Fiction? Fact Fact Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 160 180 300Gross Weight 1950 2100 2400Stall Speed 47 68 73Max. Speed 158 228 290Wing Span 35.67 23.30 23.30Wing Area 128.0 81.3 81.3Airfoil LS(1)-0413 mod LS(1)-0413 mod LS(1)-0413 modAirfoil Clmax 1.60 1.60 1.60Plan form Rectangular Tapered TaperedFlaps Fowler + Vortex Slotted SlottedAspect Ratio 9.9 6.7 6.7Wing Clmax 2.69 2.18 2.16Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Glastar Glasair GlasairModel Glastar CAFE SII- FT short III shortHP 160 180 300Gross Weight 1950 2100 2400Stall Speed 47 68 73Max. Speed 158 228 290Wing Span 35.67 23.30 23.30Wing Area 128.0 81.3 81.3Airfoil LS(1)-0413 mod LS(1)-0413 mod LS(1)-0413 modAirfoil Clmax 1.60 1.60 1.60Plan form Rectangular Tapered TaperedFlaps Fowler + Vortex Slotted SlottedAspect Ratio 9.9 6.7 6.7Wing Clmax 2.69 2.18 2.16Fact or Fiction? Fact Fact Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 300 300 180Gross Weight 2400 2500 1800Stall Speed 80 74 58Max. Speed 282 281 209Wing Span 23.30 27.00 25.00Wing Area 88.0 97.2 121.0Airfoil LS(1)-0413 mod LS(1)-0413 mod 23013.5Airfoil Clmax 1.60 1.60 1.50Plan form Tapered Tapered RectangularFlaps Plain Plain PlainAspect Ratio 6.2 7.5 5.2Wing Clmax 1.66 1.83 1.73Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Glasair Glasair Van'sModel III short CAFE III long CAFE RV-7HP 300 300 180Gross Weight 2400 2500 1800Stall Speed 80 74 58Max. Speed 282 281 209Wing Span 23.30 27.00 25.00Wing Area 81.3 97.2 121.0Airfoil LS(1)-0413 mod LS(1)-0413 mod 23013.5Airfoil Clmax 1.60 1.60 1.50Plan form Tapered Tapered RectangularFlaps Plain Plain PlainAspect Ratio 6.2 7.5 5.2Wing Clmax 1.80 1.95 1.73Fact or Fiction? Fact Fact Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 160 160 200Gross Weight 1750 1758 1800Stall Speed 50 49 58Max. Speed 194 193 219Wing Span 28.00 28.00 24.00Wing Area 124.0 124.0 116.0Airfoil Roncz Roncz 23013.5Airfoil Clmax ? ? 1.50Plan form Rectangular Rectangular RectangularFlaps Slotted Slotted PlainAspect Ratio 6.3 6.3 5.0Wing Clmax 2.21 2.31 1.80Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Van's Van's Van'sModel RV-9A RV-9A CAFE RV-8AHP 160 160 200Gross Weight 1750 1758 1800Stall Speed 50 49 58Max. Speed 194 193 219Wing Span 28.00 28.00 24.00Wing Area 124.0 124.0 116.0Airfoil Roncz Roncz 23013.5Airfoil Clmax ? ? 1.50Plan form Rectangular Rectangular RectangularFlaps Slotted Slotted PlainAspect Ratio 6.3 6.3 5.0Wing Clmax 2.21 2.31 1.80Fact or Fiction? Fact Fact LoC
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 200 180 260Gross Weight 1668 1800 2700Stall Speed 58 58 63Max. Speed 220 207 208Wing Span 24.00 25.00 31.75Wing Area 116.0 121.0 148.0Airfoil 23013.5 23013.5 23013.5Airfoil Clmax 1.50 1.50 1.50Plan form Rectangular Rectangular RectangularFlaps Plain Plain PlainAspect Ratio 5.0 5.2 6.8Wing Clmax 1.67 1.73 1.80Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Van's Van's Van'sModel RV-8A CAFE RV-7A RV-10HP 200 180 260Gross Weight 1668 1800 2700Stall Speed 58 58 63Max. Speed 220 207 208Wing Span 24.00 25.00 31.75Wing Area 116.0 121.0 148.0Airfoil 23013.5 23013.5 23013.5Airfoil Clmax 1.50 1.50 1.50Plan form Rectangular Rectangular RectangularFlaps Plain Plain PlainAspect Ratio 5.0 5.2 6.8Wing Clmax 1.67 1.73 1.80Fact or Fiction? Fact Fact Fact
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
AirplaneModelHP 180 310 300Gross Weight 2100 3400 3650Stall Speed 68 66 68Max. Speed 238 219+ ?Wing Span 23.30 35.80 33.50Wing Area 81.3 141.2 180.7Airfoil LS(1)-0413 mod ? 23016.5 / 12Airfoil Clmax 1.60 ? 1.60Plan form Tapered Tapered TaperedFlaps Slotted Slotted PlainAspect Ratio 6.7 9.1 6.2Wing Clmax 2.18 2.16 1.71Fact or Fiction?
Stall Speeds - Fact or Fiction?
Stall Speeds - Fact or Fiction?
Airplane Glasair Columbia BeechcraftModel SII - RG short 350 G36HP 180 310 300Gross Weight 2100 3400 3650Stall Speed 68 66 68Max. Speed 238 219+ ?Wing Span 23.30 35.80 33.50Wing Area 81.3 141.2 180.7Airfoil LS(1)-0413 mod ? 23016.5 / 12Airfoil Clmax 1.60 ? 1.60Plan form Tapered Tapered TaperedFlaps Slotted Slotted PlainAspect Ratio 6.7 9.1 6.2Wing Clmax 2.18 2.16 1.71Fact or Fiction? Fact Fact Fact
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
Stall Speeds - Fact or Fiction?
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.