King post

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Crown posts in the nave roof at Old Romney Church, Kent, England

DFE Ascender III-C ultralight aircraft showing its king post above the wing.

A king post (or king-post or collar beam) is a central vertical supporting post used in architectural or aircraft design applications.

[edit] Architecture

A king post extends vertically from a crossbeam to the apex of a triangular truss. The king post connects the apex of the truss with its base, holding up the tie beam at the base of the truss. King posts were used in roof construction in Medieval architecture, and also appear in Gothic Revival architecture and Queen Anne architecture. A similar structure may be used to construct a simple bridge. The deck of the bridge is supported by a king post, which is held up by a triangular truss.

A development of the king post structure terminates the central post before it reaches the apex of the roof truss. Instead, the king post is held in place by a collar beam, a secondary beam parallel to the tie beam. In this structure, the central post is termed the crown post.

An alternative truss construction uses two queen posts (or queen-posts). These vertical posts, positioned along the base of the truss, are supported by the sloping sides of the truss, rather than reaching its apex. A development adds a collar beam above the queen posts, which are then termed queen struts. A section of the tie beam between the queen posts may be removed to create a hammerbeam roof.

[edit] Aviation

King posts are also used in the construction of wire-braced aircraft, where the king post supports the top cables or "ground wires" supporting the wing.