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Aviation History
1939
1939 - 1709.PDF
564 JUNE I, 1939 CORRESPONDENCE The Editor does not hold himself responsible for the views expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. ALTIMETER CORRECTION A Plea for " Vertical" Pressure-distribution Charts I HAVE often wondered if many of the accidents in the air, both in this country and America, caused through air craft flying into the sides of hills, could have been avoided if the pilots had at their disposal correction charts for their alti meters. Every pilot has at his disposal, on leaving any airport, a chart showing the pressure distribution over th&JSritish Isles and the Continent. From this he can see at a glance whether he is flying into high or low pressure, and is also able to set his altimeter for the level of the airport he is leaving or for sea level. Might I suggest that, in addition to this, the pilot should also be given a plan showing the vertical distribution of pres sure as well as the horizontal, so that at any time during the flight he will be able to see, without having to calculate, the error of his altimeter at any moment during the flight ? Whilst realising that such a plan would not be perfectly accurate, temperature in the upper .air not being exactly known, I feel that a plan sufficiently accurate to within a hundred feet of altitude could be made by an experienced meteorologist in a few seconds and handed to the pilot be fore taking off. The accompanying sketches will illustrate such a scheme in actual practice. The pilot ascends at A on a flight to B. He 400 500 MILES attains an altitude of, say, 1,200 feet by his altimeter. If he maintains that altitude by his altimeter throughout his flight he will, on reaching the point X in the weather chart, be at the danger point, as regards height, on the particular route he is following, and with the prevailing pressure distribution. This point X (located in mountainous country as it is in this case) would, if plotted on a chart, indicate the least safe height to maintain by altimeter over that part of the route in case of misty weather or fog. The pilot could then see at once, without having to make any calculations, his exact height. Pressure decreases at an average of 1 millibar for every 30 ieet of altitude, and some of the depressions passing over the British Isles give a difference on the surface of 30 to 40 milli bars in 300 miles. This means that an aircraft maintaining a height of 2,000 feet by altimeter on a flight from South to North would, on nearing its destination, actually be at an altitude 900 to 1,200 feet less than indicated. Of course, these are extreme conditions, but they show the necessity of very carefully taking into consideration the- vertical distribution. Whilst realising also that pressure is constantly changing —extremely rapidly sometimes—it would be easy to show such a change or forecast change of pressure by indicating the direc tion and velocity of the isobars on the plan by means oi arrows. W. E. A. DUFF. Rugby. POLAND AND BRITAIN Comment on Col. Smallwood's Article MAY I be permitted to comment on Col. Smallwood's recent article in Flight on the inaugural London Warsaw air service ? These comments do not concern the flight itself but the remarks made concerning the education of Polish opinion and ideas, as stated at some length therein. It must obviouslv be difficult for a foreigner to Poland (or any other country 1 to give a really representative viewpoint of the true situation in that country, and a Polish friend of mine, having read the article, expressed disagreement with some of the statements made. He has written as follows: " I have a few remarks concerning the article written by Col. Smallwood, which 1 think might be of some interest. "The author's suggestion that the German language should be used in popularising British ideas in Poland sounds a little paradoxical. Actually the knowledge of German is common only in certain classes of town dwellers (comparatively few in number and found especially in the south and west of Poland). For the overwhelming majority German is no better, say, than English. The best propa ganda could only be carried out effectively in the mother tongue. " Why not give the news in Polish on certain medium waves? " Anything which promotes a better understanding between peoples is a solid contribution to real peace, and this under standing can only come about by the free exchange of opinions —the foreigner's no less than our own. D. F. GEORGE. Hutton, Essex. BLIND APPROACH Future Developments—and a Suggestion AITER reading the article in the issue of May 25 by Mr. A. Robert Edis, I feel gratified to have roused at least some interest and discussion in this subject. I am afraid, however, that, as feared by Mr. Edis. he has been rathei led astray by his lack of technical knowledge. The major diffi culty of his suggestion is the necessity for simultaneous trans mission and reception on the aircraft. Another difficulty is that of mounting a large map together with very delicate instruments in a cockpit. My own feeling in this matter of blind approach is that so far as the final approach and landing are concerned the existing radio guides are sufficient to cope with the minimum visi bilities in which it is possible to land aircraft having present minimum speeds, and that the next advance must be in the way of reducing these speeds. Rather than introduce more complex apparatus along the lines of present radio approach guides, I feel that effort would better be directed to providing '' direct vision,'' which would appear to be possible by an arrangement of a television camera working with infra-red rays coupled directly to a cathode-ray tube receiver similar to that used for television reception. It is patent that the commercial reward which would result from the development of such a scheme would be in no way commensurate with the expense of such development. ™oxv" ever, if, as has been done in the past with such things as heli copters, calculating machines and chronometers, some form ot substantial prize could be offered for the production of a satis factory instantaneous method of direct vision in fog, ™aI?^ technicians with the necessary knowledge would no doubt endeavour to produce such a device. FRANK BRENT. Croydon Aerodrome.
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