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Aviation History
1913
1913 - 1119.PDF
OCTOBER 18, 1913. j/yggf] DETERMINING POSITION AT SEA. By "DOVORIAN.' A PARAGRAPH which appeared in FLIGHT some little time ago ur.der the heading " Determining Position at Sea," calls, I think, for comment, as it tends to give a wrong impression of the accuracy with which the position of an aeroplane may be determined at sea. It is quite impossible for even the best navigating officer to determine the position of a ship to within one quarter of a mile of its true and actual position on the chart, so that in the case of an aeroplane the difficulties would be even greater. I am of course presuming that the position has been determined by two observations or " sights " of some celestial body, and not by bearings of points of land, whose positions are already accurately known on the chart. The conditions under which these observations are made, viz , being "at sea " or being " in the air," personal errors in actually taking the sights and working them by either the " OLD or the NEW NAVIGATION " methods, both of which are equally accurate, •do not permit of such accuracy. Perhaps the chief reasons that preclude any great accuracy in taking " sights " in an aeroplane are :— 1. The tremendous vibration as compared to that on board ship. 2. The height of eye above sea-level (H.E.) must be known to nearest foot, to obtain good results, and this is not easy to obtain accurately in an aeroplane, as the aneroid is a very delicate instru ment, and susceptible to the smallest change of atmospheric con ditions, which small change would at once render the H.E. wrong by at least 6 ft. 3. At any great height the horizon obtainable would be a very unsatisfactory one. Probably what Mr. Rainey did was to get an " intercept" of one quarter of a mile in one or the other or both of his observations of the sun, that is to say, the difference between the calculated and the observed Zenith distance of the sun was one quarter of a mile. This does not necessarily mean that the position thus determined was only one quarter of a mile out. On the contrary, it was probably two or three miles out. This sounds a lot, but in practice an intercept of three miles is not considered much out, and the sights obtained to get as close as that would be excellent ones. The only other explanation is that Mr. Rainey must have been •exceptionally lucky in obtaining a couple of magnificent sights in order to get his observed position so close to the actual position of the machine at the time—an occurrence which would be extraor dinary in itself, if it happened once in a hundred such observations. A short description of the procedure of determining one's position at sea might be of interest to readers of FLIGHT. Let us suppose that an aviator is commencing the " Trans-Atlantic flight " to New York. He leaves the land at X (say Queenstown), and plots his true course S. 40 W., having previously corrected the compass course he is steering (say S. 59J VV.) for Variation, and the Deviation of the compass. Let us suppose again that the speed of the machine is 50 m.p.h. After flying for four hours and covering 200 miljs, he takes his first observation of the sun, and finds its true bearing to be, let us say, S. 60 E. (at 10 a.m.), and on working out the sight he obtains an intercept of one quarter of a mile " further " from the sun. He plots his true course, true bearing of the sun, and the intercept, on the chart, placing his first position line at right-angles to the true bearing of the sun, and one quarter of a mile from his DEAD RECKONING POSITION at io a.m. Now he knows that he is somewhere on the position line, and as he has no other position line until he takes his second sight, he presumes that he is at the position point A. He therefore lays off his course, which remains as before, from the point A instead of from the D.R. position. After flying for another four hours and covering another 200 miles, he takes his second sight at 2 p.m. The sun has ROYAL FLYING CORPS (MILITARY 'WING). OFFICIAL summary of work for week ending October 10th :— No. 1 Squadron (Airship).—" Beta" "Delta" and "Eta" were each out most days during the week. " Eta " made two good trips on the 6th and 9th respectively. " Delta," piloted by Capt. Waterlow, satisfactorily passed an eight hours' test on the roth, going to Canterbury, on to the coast, and thence down the coast over Chatham and Sheerness, up the Thames and back to Farn borough, via Redhill and Petersfield. No. 2 Squadron.—Most of the machines are in process of being thoroughly overhauled after their participation in the Irish Command manoeuvres. Capts. Becke, MacLem and Todd, and Lieuts. Dawes and Lawrence have taken over machines at Farnborough. The three first named officers are now on their way to Montrose by air. The remainder will start early next week. No. 3 Squadron.—The machines of A, B and C flights were out most days throughout the week. On the 3rd the majority of the officer pilots proceeded to Farnborough by air to attend a conference on the work carried out on Army manoeuvres. The work of over hauling machines after manoeuvres was carried on. No. 4- and 5 Squadron.—The pilots of these squadrons were up on numerous occasions on BE's and Maurice Farrnans, but the greater part of the week has been confined to the work of overhaul ing the aeroplanes after manoeuvres. ~Flying DepcH.—Experimental work was continued after the break necessitated by manoeuvres. r (OUEENSTOV/N < ^T'Sg^^ POSITION LINE OF f 5I6HT TRANSPOSED TO D.R POUT ION OF B°- SIGHT INTERCEPT^Mlt , FURTHER S.tO' W' D.R. POSITION OF I Sl&HT AT 10 AM coutee at conWii STeincc BY tmrat is 5 59*30 W. , UWIAT/m 1011/ JO'.Y DCVIATIOHWSWl'M'W < COHMW CttOf IH'JJi) „ THtmORt THC TRUC TRUE COURSE coumc M Piomn av THC CHART BY /WW,? 5 S.WW 7M3 a 08TAIHCO Br USC OF 7HC roaemm, FIOJK MAGNETIC N\ " 5tr- TRUE BLARINC, 5.60° £. TRUE NORTH OF SUN •VARIATION 18 soV/. (113 now passed the Meridian, and its true bearing is found to be, let us say, S. 60 W. We will now presume that the aviator, on working out his second sight, obtains the same intercept as before (one quarter of a mile " further "), and draws his second position line. Where this second position line intersects the first position line, which has been transposed from the first sight to the D.R. position of the second sight, is the aviator's FIX or position observed by two sun-sights. This FIX is probably four or five miles out. The aviator then alters his course, as the course which I have started him on would not take him to New York, but was merely chosen for convenience in explanation. ® ® ® ® General News.—A proportion of officers, n.c.o.'s, and men have proceeded on winter leave. Nos. 3 and 4 Squadrons will move into a completed portion of the new barracks at Netheravon on Monday next. THE ROYAL FLYING CORPS. The following appointments were announced by the Admiralty on the 10th inst. :— Lieuts. A. J. Miley and E. Osmond, to the " Hermes," additional, as Flying Officers for Isle of Grain Naval Air Station, to date October 2nd. Capt. A. C. Barnby, R.M.L.I., to the " Hermes," as Flying Officer, Isle of Grain Naval Air Station, to date October 2nd. The following appointments were announced in the London Gazette of the 14th inst..-— R.F.C.—Military Wing.—The undermentioned to be Flying Officers and to be seconded: Lieut. Reginald G. D. Small, the Prince of Wales's Leinster Regiment (Royal Canadians). Dated September Qth, 1913. Lieut. Maurice W. Noel, the King's (Liverpool Regiment). Dated September nth, 1913. Second Lieut. William C. K. Birch, Alexandra Princess of Wales's Own (Yorkshire Regiment). Dated September nth, 1913. Lieut. Edward R. L. Corballis, the Royal Dublin Fusiliers. Dated September 13th, 1913. Second Lieut. George F. Pretyman, Prince Albert's (Somerset Light Infantry). Dated September 15th, 1913. Lieut. Gordon Adams, the Prince of Wales's Volunteers (South Lancashire Regiment). Dated September 24th, 1913. 1145
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