Wing buttock line
Wing buttock line (WBL) (also referred to as butt line ) is a term used in aircraft construction for an axis of the coordinate system in which information on the position of structural elements of an aircraft is made.
definition
The WBL specification is used to describe the position of components (e.g. wing ribs or the position of the engine mount) relative to the aircraft's longitudinal axis . The WBL counts in the direction of the transverse axis of an aircraft. The number in the WBL designation indicates the distance from the longitudinal axis in inches .
The designation of the coordinate axis in the direction of the longitudinal axis is center line , and water line is used to describe the height of the position .