Addison-Luard Course & Wind Calculator type D by H. Hughes and Son Ltd, London. made for the Air Ministry. Circa 1935.
A.M. REF: No: 6B/113 No:1011/35
Diameter: 28 cm.
In original cased numbered: 1011/35 (31 x 32 x 10 cm).
Patented by the British inventors; Herbert Addison and Williams Blaine Luard.
PAT. Nos 264755. 273198.
BRIT. PAT 299138.
U.S.A. PAT. 1723757
For similar Addison-Luard calculators see the collections of:
Science Museum, London. Object number:1956-251
National Museum of Australia, Canberra. Object number: 1989.0009.0039
National Air & Space Museum, Smithsonian Institution. Inventory Number: A19570994001
The Museum of Transport & Technology (MOTAT), Auckland. Accession number 2020.49
The “Addison-Luard” Course and Wind Calculator, Type “D”. The International Hydrographic Review.
This appliance is specially designed for use in transoceanic aircraft flying ; by its means the navigator can solve all velocity triangles concerned with the effect of the wind on his machine without the necessity of actually plotting these triangles. If the wind is already known, the instrument immediately shows the relationship between Course, Air Speed, Track, Ground Speed, etc., while if the wind is unknown, the instrument enables its speed and direction to be quickly calculated from the results of Drift Observations. The instrument consists of a circular base the upturned rim of which is divided from o° to 360°. Four arms, each with a cursor sliding along it, represent the four vectors involved, viz. (1) Air Course and Air Speed ; (2) Track and Ground Speed ;
(3) Wind and Wind Speed ; and (4) Datum Ship Course and Datum Ship Speed.
(1) The Air Course arm, which is formed with a saddle sliding round the upper edge of the upturned flange of the base. The position of the Air Course arm is read by means of the divisions engraved on the inner face of the flange, against which the sighting blade is placed. The cursor representing Air Speed, i.e. the speed of the aircraft through the air, slides on the Air Course arm.
(2) The Track arm is situated in a plane below that of the Air Course arm but is located with respect to the same circumferential degree graduations on the inner face of the flange. The saddle of this arm is graduated in degrees of drift, these being read by
means of the sighting blade carried by the Air Course arm. The Ground Speed cursor slides on the Track arm, and is provided with slots which permit the cursor to be visually linked with the other elements of the apparatus.
(3) The Wind arm is pivoted at the centre of a small independent graduated circle which is itself mounted on the Datum Ship Speed cursor and which is also connected with a sliding member beneath the base in such a way that, although the graduated
circle may be displaced with respect to the axis of the base, it cannot rotate about that axis. The Wind arm carries the Wind Speed cursor.
(4) The Datum Ship Course arm revolves about the centre of the base, and its position is read in conjunction with the reciprocal degree scale engraved on the bottom of the base. The Datum Ship Speed cursor slides, together with the Wind degree scale,
on the Datum Ship Course arm. All the arms are graduated in units of knots. The Air speed and Wind speed cursors are interconnected by linkwork, the main pivot of which has a circular sighting aperture which is, in use, brought exactly over the intersection of the slots of the Ground Speed cursor. Independent clamps are provided for locking respectively the Air Course arm, the Air Speed cursor, and the Track arm. The upper and larger clamp beneath the base simultaneously locks the Datum Ship Course arm and the Datum Ship Speed cursor, while the lower and smaller clamping screw simultaneously locks the Wind arm and Wind Speed cursor.
In addition, a pair of time and distance scales, in the form of circular arcs, respectively engraved Miles and Minutes, are arranged to slide on the upturned flange of the base. These are engraved with scales figured from 20 to 200. The inner Minutes scale
is engraved with a readily distinguished arrow at 60 so that, when the outer scale is moved along till the figure corresponding to the Ground Speed is opposite the arrow, the distance covered in a given number of minutes can be read off on the outer scale opposite the mark corresponding to the number of minutes and vice versa.
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