The paper describes the system developed and used by the United States Hydrographic Office for selecting the optimum track for transoceanic crossings by applying long-range predictions of wind, waves and currents to a knowledge of how the routed vessel reacts to these variables. Over a period of two years, over 1000 optimum ship routes were provided to one authority, with an average reduction in travel time of 14 hours.

In 1955, following certain discussions within the Technical Committee, arising largely from a suggestion put forward by Mr. A. J. Moline, a member of the Australian Institute of Navigation, the Institute decided to set up a Working Party to go into the philosophy underlying current practices of fuel reserve calculation for aircraft. Because it would have been inappropriate for the Institute to attempt to lay down any sort of recommended code of practice, the Council paid particular attention to the precise terms of reference of the Working Party. It was agreed that its function would be: ‘To examine the requirement for reserve fuel and the factors governing its determination; to ascertain whether common parameters obtain, and to assess their application to future aircraft operation’.

The Chairman of the Working Party, and author of the following report, which has been discussed and agreed by the other members, was Mr. Jack Vivian, of British European Airways Corporation. The other members were Captain R. C. Alabaster (British Overseas Airways Corporation), Wing Commander D. Bower (Royal Air Force), Wing Commander M. C. Bunting (Royal Air Force), Mr. D. O. Fraser (English Electric Aviation Limited), Mr. J. P. Meade (Meteorological Office), Mr. J. E. D. Williams (then of El Al Airlines), and Mr. D. A. Blake (Ministry of Aviation). All members served in a personal, not an official capacity.

The report has been forwarded to the Aeronautical Research Council of the Ministry of Supply.

In a previous paper (Journal, 11, 180), the author gave assessments of the forecast wind errors likely to be met with at any point on the globe by an aircraft flying for one hour. The present paper follows this up by giving the probable errors of 24-hour wind forecasts over routes of any length, and thereby assesses the probable unpunctuality of aircraft owing to wind forecast errors.

After the radar altimeter came into use at the end of the second world war, the combination with a pressure altimeter made it possible to measure horizontal pressure gradients, which enabled the navigator to estimate the geostrophic wind. The pressure gradient is directly related to the component of the wind at right angles to the track by means of the geostrophic relation and the navigator is thus provided with a method of evaluating one component of the drift. A position line of pressure combined with another position line (Loran, astro, &c.) enables the position of the aircraft to be determined.

This paper describes and discusses some of the techniques by which a moving inertial platform may be aligned by using external velocity measurements and also presents some of the major problems and error sources affecting such alignment. It is based upon the results of a 3-year study, of inertial and doppler-inertial navigation at the Naval Ordnance Test Station, China Lake, California, and, in general, applies to inertial navigation systems which erect to either the local level or the mass-attraction vertical. Although rudimentary derivations are made of the alignment techniques, the paper is largely nonmathematical for ease of reading. Emphasis is placed upon the major errors affecting the alignment. This paper describes and discusses some of the techniques by which a moving inertial platform may be aligned by using external velocity measurements and also presents some of the major problems and error sources affecting such alignment. It is based upon the results of a 3-year study, of inertial and doppler-inertial navigation at the Naval Ordnance Test Station, China Lake, California, and, in general, applies to inertial navigation systems which erect to either the local level or the mass-attraction vertical. Although rudimentary derivations are made of the alignment techniques, the paper is largely nonmathematical for ease of reading. Emphasis is placed upon the major errors affecting the alignment.

Both the argument and the geometry in this paper require careful study before they can be appreciated; it is hoped that the following notes, which are restricted to purely geometrical considerations, will assist readers to understand them.

The author's fundamental argument is that it is geometrically impossible for ships A and B, at distance r apart and moving with constant speeds v and u, to approach each other more closely than distance d (less than r) if the courses of ships A and B are each restricted to a semi-circular anti-collision sector, depending only on the angle δ sin δ = d/r, and on an agreed universal convention. This is illustrated in Fig. 1 in which the two sectors are indicated by vv' for ship A and uu' for ship B. Adopting the convention that the ships pass ‘port to port’, the permissive anti-collision sector for each ship is, relative to the bearing of the other ship, from δ to starboard, increasing to 180° and to port from 180° to 180° −δ . This is equivalent to restricting the course so that the other ship bears more than δ to port or more than 180°−δ to starboard.

Much has been written from time to time about the disaster which befell the fleet under Sir Clowdisley Shovel (or Shovell) among the rocks of the Scilly Islands on 22/23 October 1707. Although many writers have discussed the cause of the catastrophe I have come across no one who has examined the D.R. positions of the various vessels involved, and it is these which I propose to consider here.

It may be as well to recapitulate the story of the disaster. (At this time, it should be noted, the day at sea was measured from noon to noon and began twelve hours earlier than the civil day. Consequently, the afternoon at sea had a later date to that ashore. Noon positions logged were those at the end of the sea date.)

The following discussion took place at an Ordinary Meeting of the Institute held at the Royal Geographical Society in London on 19 February 1960, with the President, Wing Commander E. W. Anderson, O.B.E., D.F.C, A.F.C, in the Chair. Dr. J. G. Porter is at the Royal Greenwich Observatory, Herstmonceux, Mr. D. J. Cashmore and Mr. T. McClymont are both with English Electric Aviation Limited.

Doppler-operated computers which perform plane D.R. navigation are currently offered to the airlines. A datum track and distance to go are set; from the time of selecting ON, the computer resolves small elements of distance run (input doppler and heading reference) as follows:

Change in across-track dist. = element of dist. run × sin (actual tr. − set tr.)

Change in along-track dist. = element of dist. run × cos (actual tr. − set tr.)

These relations are true for a plane Earth.

IN the Meteorological Office, great accuracy is not usually attainable in determining or forecasting the position of significant weather features. Special projections of charts are therefore not often required; the normal conic projection with two standard parallels or (near the equator) the mercator projection is quite adequate. However, in the radiolocation of thunderstorms a chart drawn on a gnomonic projection is required. The bearings of each lightning flash within one or two thousand miles are recorded from a small number of special stations (SFERICS stations). When these bearings are plotted on a gnomonic chart by straight lines drawn from the appropriate observing station the coordinates of the source of the lightning can be quickly determined and reported through normal meteorological channels. Speed is essential and therefore the charts on which the bearings are drawn are specially designed with the SFERICS stations grouped more or less evenly about the tangential point of the projection plane of the gnomonic chart.

Mr. J. F. Green, in an article on gyro failure (this Journal, 13, 78). draws. attention to a principle that is of direct importance whenever navigators are dependent, for their information, on an equipment which, though normally serviceable, can develop a gross error. His principle is the triplication of instrumentation: the agreement between the two supposed serviceable equipments is a control on the possible malfunctioning of the third.

The following comments have been received on Mr. E. S. Calvert's paper, published in the last number of the Journal. A further selection of comment, including a note by Captain F. J. Wylie, and possibly a reply by Mr. Calvert, will be published in the next number.

The platform shown in Fig. I is one of a series of miniature platforms developed for inertial guidance and weighs only 28 lb. It is a three-axis, four-gimbal platform permitting complete freedom of manœuvre without gimbal lock. Three miniature integrating gyroscopes are used for stabilizing the gimbal system (Fig. 2) and three miniature pendulous accelerometers provide voltage outputs proportional to accelerations experienced by the platform.