FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1937
1937 - 2257.PDF
AUGUST 12, 1937- FLIGHT. T/T PRIVATE FLYING Topics of the Day Qone Marine W E who pride ourselves on making long dead-reckoning cross-country flights and arriving vertically over our terminal aerodrome hardly know how complicated real navigation can he. Disregarding the very slight changes in magnetic variation, there is only one exterior factor—wind speed and direction —to be dealt with when we plot our courses. Last week I spent, by way of a change, doing a little amateur ocean sailing and fell more or less naturally into the job of navigator, thereby learning a very great deal. All my previous sailing had been done while in sight of land. For getting the ordinary business of chart-reading, which came fairly naturally to me, the navigator of a sailing vessel has tides and lee-way for which to account, and it is, fur thermore, not usually possible to sail in a straight line towards an objective. Apart from the necessity of avoid ing sundry obstructions in the way of sharp recks, one's track must be adjusted according to the direction of the wind, which has an annoying habit of changing just when a complete plan of action has been plotted. It is not, in fact, possible to arrange any plan in advance and without the use of such things as D/F radio and sextants a certain amount of intelligent guessing is essen tial. For instance, on the crossing between St. Catherine's Point (I.O.W.) and Alderney, with tides running in alter nate directions across our course, it was permissible to ignore their effect. Nevertheless, if a landfall was to be expected (accord ing to the trailing log) in an " extra '' tide one way or another, some allowance would have had to be made for it, and this allowance could only be guessed. In fact, after sixteen hours of fog we hit Alderney spot on and pretty well sailed straight into the harbour at Braye ; in another hour considerable allowance would have had to be made for an additional westerly tide and for the tidal race which rushes past the north coast of the island. People who think that the tides simply go up and down would be surprised to learn that seven- and eight-knot currents are to be expected around the Channel Islands. New Methods VTONE of which has much direct connection with fiy- 1 ' ing, though the sound of two Jersey Airways' D.H.86s during the Channel crossing provided a comforting check on- our movements. Fortunately, I remembered that neither Exeter nor Brighton services ran on Thursday. When there is anything at all to be seen a bearing com pass can be used very successfully at sea, since, however good the visibility, it is very difficult to estimate distances and one's consequent position. All marine charts have a compass rose laid out according to the magnetic variation at the time of publication. This variation changes very siowly and the quickest way of obtaining the actual mag netic bearing of any particular track is to use a parallel *Lufe—"marching" this, if necessary, across the chart. Usually it is posible to reach a rose on one extension. Unfortunately, our four-mile aviation maps are merely printed with a variation arrow. Most of one's tracks are, nowever, drawn first on ten-mile maps and on these a com plete compass rose is printed. I shall immediately equip myself with a parallel rule for such plotting work ; the method of using a protractor against a convenient meridian now appears to be a trifle crude. Though the printed roses are only correct for the particular part of the map or chart on which they appear, and the variation alters slightly year by year, the parallel rule method leaves less possi bility of vital error. Our present flying maps are, how ever, not laid out on Mercator's projection, and I may find that there is rarely a convenient rose available to give a correct bearing. Between Great Yrrmouth and Land's End on a ten-mile map with Cassini's projection the angles of the meridians vary six degrees in relation to one another.' Since our compasses have verge rings or cards calibrated through 360 deg. it was not possible to become accus tomed immediately to the marine type, the card on which is calibrated in thirty-two points (each of 11.25 deg.) with degrees marked up to ninety East or West of North and South. A magnetic bearing of 300 deg., for instance, is indicated as 60 deg. W. of N. (or about three points N.W of W.), while one of 100 deg. is shown as So deg. E. of S. (cr about one point S.E. of E.). The " point " methrd of indication is very necessary in marine work, as it is usually impossible to read the actual figures on a compass card from one's position beside the wheel—particularly in rough weather. The ninety-degrees scheme of calibration has one considerable advantage: a reciprocal bearing can be obtained at once simply by reversing the reading. The reciprocal of 80 deg. E. of S., for instance, is 80 deg. W. of N. I never can do a three-figure sum in my head. Ignorance IT has always been surprising to me that anybody ever • manages to find out about air services, even if he or she prefers to travel by such means. People in general simply do not know of the existence of such things. Somehow or other I had got to get back from Alderney to the mainland in the quickest possible manner, yet I wandered from one steamship company and travel agent to another in Guernsey and ran up against a blank wall every time. Yet I was in the exceptional position of knowing that Jersey Airways ran between Alderney and Jersey, and between Jersey and the mainland. What of the ordinary mortals who do not even know that? Eventually I found the agent for Jersey Airways, and he got through to Jersey Airport, and we fixed every thing up. But let it be placed on record that the ordinary agent and steamship enquiry man knew nothing and cared less. INDICATOR.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
