Grid compass

Not to be confused with Grid Compass.

A grid compass known as well as grid steering compass, is a navigational instrument that provides a reference direction (relative to north) in the horizontal plane and allows setting a course (horizontal angle respect to this point), by means of a lockable rotating limb and then, follow that course with a simple sight, by keeping the cross axle within the grid's parallel lines.

The grid compass beats all other types of compasses from the pilot's point of view, because he doesn't need to "observe constantly" the number (or the division mark) of the wanted course. He just has to be concerned to control that the N/S compass needle lies parallel between the two lines of the central grid. It uses a "working principle" similar to the "compass controlled autopilot".

Description

The grid compass has a rotating limb graduated from 0° (north) to 359° ascending in the clockwise direction, with a glass rotating with it, with two centered parallel lines engraved on top. The floating card magnetized circle has four white segments forming a cross with its central part missing.

Prior to start the navigation, the pilot he just needs to set the wanted course, by rotating the limb and locking it with the side lever. After the navigation started, he just has to steer keeping the vertical part of the cross between the two parallel lines to maintain the pre-set course.

The grid steering compasses (Type P8 to Type P11) were fitted in World War II Spitfire aeroplanes, replacing the old P4 series of instruments. They were used for course setting and reading, and as a check compass on aircraft fitted with a remote indicating compass.

See also

• Astrocompass
• Compass
• Solar compass
• Marine sandglass

Bibliography

• Aircraft Instruments

External links

• A Compass for ‘Sandpiper’
• "A Job Thought Impossible", the story of Chrysler Corporation's mass-production of previously hand-made compasses for World War II naval requirements.