Small wind / Buyer questions
Mechanical interfaces
Does a swept blade's physical length equal the rotor radius?
The short answer
Not necessarily. Curved blade length follows a chosen path, whereas rotor radius is a distance from the rotation axis to the rotating envelope. A swept blade can therefore have a physical length that should not simply be doubled to obtain wind-rotor diameter.
Define the measurement path
A tape following the leading edge, a blade reference-axis length and a straight root-to-tip distance can all give different results. None includes an unspecified hub offset automatically. For capture-area calculations, identify the actual radial extent about the shaft axis. For transport, the packed three-dimensional envelope may matter instead. Using one convenient length for both decisions can misstate swept area and shipping clearance simultaneously.
Use coordinates rather than a silhouette
For a point expressed in a plane normal to the shaft, radial distance is the square root of the sum of the two transverse coordinates squared. Its axial coordinate does not add directly to that radius. A hypothetical point at transverse coordinates 1.2 m and 0.5 m has radius 1.3 m. This geometric example describes one point; the complete blade envelope still needs all relevant sections and their finite width.
Request the assembly diameter definition
Ask whether the quoted diameter represents the maximum undeformed envelope, an aerodynamic modelling radius or another documented dimension. Include root placement, sweep, cone and the reference operating/measurement state where relevant. OpenFAST separately records span and sweep offsets, supporting that distinction. Do not infer a MARSTON rotor diameter from a standalone blade length, and do not treat the static geometry as proof of deflected clearance, annual energy yield or compatibility with a different hub. Distinguish a blade tip coordinate from the maximum radial outline of a wide section. The point used by the designer to define rotor diameter should remain explicit when transferring geometry into a purchasing comparison.
Sources
Examples are illustrative. Confirm product-specific performance, compatibility and supply scope in the applicable documents.