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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.
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| Linearisation point 1
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| The first point to use for the straight line, as a fraction of blade length
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| Linearisation point 2
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| The second point to use for the straight line, as a fraction
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| Ignore linear from
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| for chords
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| Ignore linear from
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| for twists
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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.
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