Should a rotor balance result include its hub and nose cone?

The short answer

It depends on what the balance result claims to cover. A blade-only or bare-hub result cannot automatically represent a completed rotor with additional rotating parts. Define whether the hub, nose cone, attachments and their installed angular positions lie inside the assessed small-wind assembly boundary.

Track mass added after balancing

Any added mass contributes according to its distance from the shaft and its angular position. In a hypothetical illustration, a 0.2 kg item whose centre is 0.1 m off-axis adds 0.02 kg m of eccentric mass moment. Whether that is acceptable requires the actual residual-unbalance criterion. A component centred on-axis can still affect inertia even when it adds no net static eccentricity.

Distinguish component and assembly acceptance

Separately balanced components can assemble differently because fits, keys, fasteners and angular indexing establish their final locations. Conversely, an assembly balance result may only apply when those parts remain in the tested positions. It should not be interpreted as evidence that every replacement nose cone or hub is interchangeable. Balance acceptance also does not establish blade pitch equality, aerodynamic performance or the integrity of the rotor attachment.

Ask which installed boundary the report represents

Request a drawing or parts list identifying the tested rotor boundary and the items added later. If a supplied report excludes the nose cone, ask the designer how its installed eccentricity is covered. Schenck distinguishes rotor/support and correction-plane considerations in balancing; the added-mass example is an original accounting illustration. MARSTON rotor construction and balance practice require actual equipment evidence. Do not undertake improvised field balancing merely because a report’s boundary is incomplete. A report covering the assembled rotor should identify removable covers or accessories whose installation changes mass position. That boundary helps determine whether a later replacement requires a specific balance review rather than automatic acceptance.