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Aviation History
1951
1951 - 1932.PDF
21.'September 1951 401 CORRESPONDENCE The Editor of "Flight" does not hold himself responsible for the views expressed by correspondents in these columns; the names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. Electric De-icing WITH reference to the article, "The Icing Problem," byS. S. Schaetzel, in your issue of August 31st, one statement is open to criticism. Speaking of the advantages of the electrical system, the author cites its "ability to deal with any icing condition, no matter how severe." He continued, "It is immaterial to the system how much ice is accumulated on the heating pads; the same small quantity of ice had only to be melted, from under- neath, to ensure the breakaway of the deposit." This implies that any "cycling" electrical de-icing system will function satisfactorily whatever may be the applied intensity of icing. This is not so. The time taken to raise the temperature of the inner ice surface from "switch on" of the system is dependent upon the thickness of the layer of ice—which increases, often sub- stantially, the thermal capacity of the aircraft skin. Conditions are aggravated by the fact that, once the temperature of the ice surface is raised above ambient, the electrical system has to "make good" the heat lost to the air. This latter quantity is dependent on the position and structure of the surface protected. It follows, then, that the temperature-rise of the innermost ice film obeys a logarithmic law and it is quite possible for the "on" period of the de-icing system to be of insufficient duration for satisfactory operation. Also, of course, the density of heating may prove to be inadequate for low ambient temperatures. Thus it is necessary to design an electrical thermal de-icing system for each specific installation, and no overall formula as to cycling time or power density can be laid down. The above details are no doubt well known to your contribu- tor but I have thought to emphasize them so that your readers would not gain the impression that any electrical system of thermal de-icing is bound to prove satisfactory in service. St. Albans, Herts. P. C. «ODGE. Unhappy DesignationsW ITH regard to the squadron identification letters "US", it is possible that your correspondents of August 3rd and 17th are both correct. Indeed, I can visualise that those un- fortunate letters were offered to, and cold-shouldered by, a number of squadron commanders. I can certainly vouch for the fact that, at some time in 1940, they were painted on the Hawker Audax army co-operation aircraft of No. 28 Squadron, then stationed at Kohat, N.W.F.P., India, alongside the Westland Wapitis of the one-and-only No. 27 ("pregnant elephant") squadron. Let me hurriedly repeat, that this was in 1940, not 1914; India was like that! As I remember the story, some pretty caustic correspondence must have passed between the Air Ministry and the house-proud squadron-commander. At any rate, a few weeks later, red-faced mechanics were painting out "US" and substituting "BF", so the poor chap got the worst of it in the end. Incidentally, it seems a pity that such squadrons as No. 27, with a wonderful record in the 1914-1918 war, and an active- service record between the wars, should be reduced to ferrying soldiers and whatnot around the earth. Tradition dies easy that way. Nairobi, East Africa. F. FENTON, F/O. Facing Which Way? TN the currently fashionable argument on backward- or forward- ••• facing seats many people espouse one form or the other without considering the argument sufficiently deeply. It seems to me that the case in which we are interested is that of the aircraft which hits the ground and/or an obstacle whilst in a normal horizontal position when taking off, in flight or landing; tiie arrangement of seats to face forward or backwards is nullified if the aircraft strikes while falling vertically, groundlooping or somersaulting. If it disintegrates, the argument again has no force, since the arrangement of the seats and their occupants relative to the force imposed by a head-on collision is immedi-at ey and radically changed. We are therefore left with the case jn which the aircraft does not disintegrate, but may or may not be damaged. In either case the important point is whether or not the seats break loose. If they do, they and their contents will normally pile up in the forepart of the fuselage; and fatalities are then likely to occur, regardless of the position of the seats before thev begin to move. I would be glad if anyone could produce evidence on this point, as distinct from opinions. My own view is based on observation of the results of accidents to aircraft with forward-facing seats; so far I have seen nothing to suggest that backward-facing seats would give better results. If, however, the seats do not come away from the floor, and there is no damage to the fuselage, the fate of passengers facing forward would seem to depend largely on whether or not they are strapped in. Now passenger harness does not include shoulder straps, and what we need before deciding on the way seats should face is evidence to show what sort of injuries are suffered by people who are thrown forward when held only by lap straps. My guess is that there is a strong argument here for backward-facing seats without waiting to see what happens in the next crash where such seats are being used. In the case of an undamaged fuselage where the passengers are not strapped in, forward-facing seats provide no safeguard at all. Prima facie, backward-facing seats would seem here to give some protection. Structural damage to the fuselage in the conditions postulated usually involves complete destruction of the whole width for a varying distance along the length; splitting of the fuselage along its length like a pea-pod; or damage to one side only. In the latter two cases one cannot forecast what the results are likely to be and there is, therefore, no argument for or against either side. However, in all three cases the argument with regard to harness is still valid; and there seems again to be a strong prima facie argument for backward-facing seats since any of them out of the actual zone of destruction will provide protection to the occupant. If destruction is complete the position of the seats is irrelevant. What we really want, it seems, is seats which will not move re- lative to the floor in any conditions short of complete destruction. It is only when this has been achieved that it becomes important to decide firmly which way seats are to face. Even so, there is still a snag; B.E.A. have recently said that they are considering economic and engineering evidence on rear-facing seats. If the engineering problem is as simple as I think it is (perhaps wrongly ?) the economic problem seems to have several important aspects. First there is the question whether immovable seats must be permanent or not in the way that fins and wing stubs are perman- ent; this is clearly of importance where aircraft are required to be interchangeable in the passenger and freight roles or of variable seating-arrangement. Secondly, any operator who installs rear- facing seats is clearly assuming that his aircraft may crash. We all know that some will, but no operator wishes it to be assumed by the unthinking public that he is the only one who needs to take this particular precaution. Advocacy of forward- or rear- facing seats on the basis of vaguely generalized humanitarian feelings, and in the absence of evidential facts and figures, is over simplifying a complex situation and is in any case slightly prema- ture. I suggest that one of the Corporations should fit rear-facing "immovable" seats (since we know what happens with forward- facing seats) and see what happens. The effect of sales may be disastrous, though I think not; in any case it would seem to be a legitimate function of H nationalized concern (whose criterion is not solely the commercial one) to take the risk. The more im- portant question of trie value of such seats in a crash will no doubt be demonstrated in due course whether we like it or not, although I should have thought that theoretical considerations alone would have justified their use from the point of view of safety, if not of economics. Oxford. B. J. L. HAIMES. Test-flight Evidence SINCE the war ended in 1945, British test-pilots have beensacrificing their lives at the rate of five each year. Until such time that the widespread testing of aircraft is by remote control, it is inevitable that lives will continue to be spent in the quest for aeronautical knowledge. No effort should be spared, therefore, in making sound-record- ings of the test-pilot's voice throughout a flight, and in filming both the instrument panels within the machine, and (from a distant part of the structure) the aircraft itself. ' Tightly packed as the modern research aircraft is, such re- cording gear should always be included in the basic equipment; no aerodynamicist will begrudge a small blister housing a camera within a wing or fin when information gained therefrom can enable aviation to be made safer. On occasion, lives must be spent. Let us not allow them to be wasted. Reading, Berks. DAVID R. MACFARLANE. [We believe that voice-recording equipment was installed in at least one prototype lost during the past year, but that it was not in use at the crucial moment.—ED.].
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