Simple blade calculator   Back to Wind Power
Basic info
Blade radius (mm)
From centre to tip
Number of blades
Rated wind speed (m/s)
The wind speed to use when calculating power
Tip Speed Ratio (TSR)
The ratio of the tip speed to the wind speed
Profile data
Profile name
Used for the shape only
Angle of attack (degrees)
Angle of attack for optimun lift:drag ratio
Coeficient of lift (Cl)
at optimum attack angle
Max Cl/Cd
Ratio of lift to drag at optimum attack
Hub radius (mm)
From centre to edge of hub
Root width (mm)
Width of rectangular section of blade root
Number of stations
Show dots
Image size (pixels)
The size of the diagrams
Every profile has a shape, and an angle of attack at which the ratio of lift to drag is the greatest. The default values above are correct for a NACA4412 profile. The bottom two figures are only used for calculating the power and torque in the table below.
The above may be adjusted to change the diagram, but do not affect the performance of the blades.

The ideal blade has a complex 3D shape, and can be difficult to make. A linear approximation for the chord sizes is obtained by choosing two points, and drawing a straight line between those points. This is shown by the green lines in the diagrams. The same can be done for the twist, or blade angle at each station.

A linear approximated blade is very much easier to make, and is surprisingly close to the ideal blade shape in terms of performance. The best points to choose are usually between 0.5 and 0.6 for the first point, and between 0.9 to 1.0 for the second.

Linearisation point 1
The first point to use for the straight line, as a fraction of blade length
Linearisation point 2
The second point to use for the straight line, as a fraction
Ignore linear from
for chords
Ignore linear from
for twists
The root of the blade is usually much wider than the tip, particularly for low TSRs. In some cases, for example when making a mould, it may be desirable to keep the ideal shape near the tip, but to switch to the linear approximation near the root. The two values above can be used to ignore the linearisation from a certain fraction of blade length outwards.

Swept area 3.14 m2
in square metres
Max power (Watts) 1112.12 W
According to the Betz limit
Total blade area 0.388 m2
Area of linear shape, per blade
Power (Watts) 0.0
Rated RPM 477.5 rpm
Revs per minute at rated wind speed
Torque (N/m) 0.00
Tip speed 50.0 m/s

The setting angle is the angle of a line from the front most to the rearmost point of the blade. When measuring or making a blade resting on the flat face, this angle needs to be adjusted by an amount which depends on the shape. For the profile shown here, this adjustment as drawn is 1.94°
         Ideal blade  Using linear approx
  Station   Radius   Speed   Apparent wind   Reynolds   Attack   Setting   Adj set   Chord   Reynolds   Attack   Setting   Adj set   Chord   Setting err   Chord err
10 1000.0mm50.00 50.99m/s @ 7.6° 2.103e+8 5.5° 2.1° 4.0° 62 mm 2.103e+8 5.5° 2.1° 4.0° 62 mm 0.00° 0.0 mm 
900.0mm45.00 46.10m/s @ 8.4° 2.106e+8 5.5° 2.9° 4.9° 69 mm 2.253e+8 4.9° 3.6° 5.5° 73 mm 0.64° 4.8 mm 
800.0mm40.00 41.23m/s @ 9.5° 2.110e+8 5.5° 4.0° 5.9° 77 mm 2.329e+8 4.4° 5.0° 7.0° 85 mm 1.07° 8.0 mm 
700.0mm35.00 36.40m/s @ 10.8° 2.116e+8 5.5° 5.3° 7.2° 87 mm 2.334e+8 4.3° 6.5° 8.4° 96 mm 1.21° 9.0 mm 
600.0mm30.00 31.62m/s @ 12.5° 2.124e+8 5.5° 7.0° 9.0° 101 mm 2.269e+8 4.6° 8.0° 9.9° 108 mm 0.94° 6.9 mm 
500.0mm25.00 26.93m/s @ 14.9° 2.137e+8 5.5° 9.4° 11.4° 119 mm 2.137e+8 5.5° 9.4° 11.4° 119 mm 0.00° 0.0 mm 
400.0mm20.00 22.36m/s @ 18.4° 2.158e+8 5.5° 12.9° 14.9° 145 mm 1.945e+8 7.5° 10.9° 12.8° 130 mm -2.04° -14.3 mm 
300.0mm15.00 18.03m/s @ 24.0° 2.191e+8 5.5° 18.5° 20.4° 182 mm 1.706e+8 11.6° 12.4° 14.3° 142 mm -6.10° -40.4 mm 
200.0mm10.00 14.14m/s @ 33.7° 2.233e+8 5.5° 28.2° 30.1° 237 mm 1.446e+8 19.9° 13.8° 15.8° 153 mm -14.36° -83.5 mm