English, c.1920, engraved 'H. HUGHES & SON Ltd LONDON No.228' and above 'THE ADDISON-LAUD COURSE & WIND CALCULATOR, 7 - INCH AIR TYPE B, PAT. No, 253758 BRIT. PAT. 299138, U.S.A. PAT. 1723757' constructed of aluminium with 2 rotating arms, steel linkage, and engraved for WIND, WIND SPEED, AIR SPEED & COURSE, in original fitted pine case with original instructions and advertisement case 20cm wide

The Addison-Luard Course & Wind Calculator 7-Inch Air Type "B" – A Revolutionary Navigational Aid

Among the many ingenious devices developed for navigational calculations in the early 20th century, the Addison-Luard Course & Wind Calculator 7-Inch Air Type "B" stands as a testament to British ingenuity. Patented in the 1920s and produced by the instrument makers H. Hughes & Son Ltd., London, this device provided a rapid and reliable method for determining the impact of wind on an aircraft’s trajectory. Housed in a pine box with a hinged lid and a clasp, the instrument comprises an aluminium disc with degree increments and compass directions, complemented by a mechanical assembly of rulers and a steel concertina linkage.

During the interwar period, advances in aviation and maritime navigation necessitated the development of precise, efficient methods for calculating course adjustments due to external winds. The Addison-Luard Calculator was designed to perform these calculations mechanically, eliminating the need for laborious plotting on paper. This was particularly useful in aviation, where rapid and accurate computations were essential for maintaining course and ensuring safety.

The device was engineered to solve velocity triangles—graphical representations of the relationships between an object’s motion, the influence of wind, and the resulting drift. By setting the known variables—such as an aircraft’s intended course and speed, and the wind’s speed and direction—the calculator mechanically determined the resultant ground speed and true heading, streamlining complex navigational equations.

The Addison-Luard Calculator operates through a mechanical linkage system, integrating three key components:

1. Primary Arm (Course and Speed): The user sets the intended direction of travel and the velocity of the aircraft or vessel using the first arm.
2. Secondary Arm (Wind or Current Data): The second arm is adjusted to reflect the direction and speed of the wind.
3. Resultant Arm (True Heading and Ground Speed): Through the linkage system, the third arm automatically adjusts to display the resultant trajectory and speed, allowing the operator to correct the course accordingly.

Unlike traditional manual plotting methods, this mechanical system ensured rapid computation, reducing the risk of human error and improving navigational efficiency.

The Addison-Luard Course & Wind Calculator found widespread use among aviators, submariners, and surface vessel navigators, particularly before the widespread adoption of electronic navigation aids. In aviation, pilots relied on it to compensate for crosswinds during flight planning and in real-time adjustments, ensuring accurate arrival at their destinations.