Retractable head-up displays

Claim 1

A display head for an aircraft head-up display system comprising an optical projector and an image combiner through which an observer can view a distant scene and from which collimated optical images developed by and projected from the optical projector are reflected to the observer wherein: the image combiner is supported from a light obstructive member which intrudes within the observer's field of view of the distant scene in use of the display head, but no intruding part of said member has a width greater than a prescribed interpupillary distance so that notwithstanding the intrusion of said member there is no obstruction by said member of the observer's view of the distant scene, the display head being rotatable about a single axis for displacement between an operational position in which the display head is at a position intercepting the observer's line-of-sight to the distant scene and a stowed position at which the display head is at a position at which it does not intrude into the observer's field of view of the distant scene, and said single axis being inclined with respect to the aircraft orthogonal axes at such an angle, and the display head is so shaped, that in moving the display head from the operational position to the stowed position the initial movement of the display head has a major component parallel to the observer's line-of-sight to the distant scene, and the terminal movement of the display head has a major component to the left or right of said line-of-sight, in a direction at right angles to said line-of-sight towards the stowed position.