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Aviation History
1910
1910 - 0656.PDF
[/ycHf] AUGUST 13, 1910. would be proportionate to D2. Any change in a factor that is not common to both expressions, however, will destroy the relationship, thus, for instance, if the chord of the blade can be effectively increased, then the thrust of one blade will be proportionately greater, and the thrust of a two-bladed propeller might in that case be equal to the theoretical value derived by the alternative method. Whether this is or is not a reliable method of estimating the permissible number of blades we do not pretend to say, but it is at least worth considering. It may be remarked that the chord of the blade is practically the only factor that affects one expression without affecting the other. It has been commonly supposed that the chord of an aeroplane defines the sweep of the stratum of air deflected; and since it may be presumed that the sweep is one of the factors that determine the range of the disturbance created by each blade, it might be argued that the chord should certainly be considered in « ® ® ® LONG-DISTANCE FLYING BY FRENCH OFFICERS. estimating the permissible number of blades, as it undoubtedly is by the method adopted above. It is important to bear in mind when dealing with Froude's ratios that the four-bladed propeller is taken as unity, and in utilising data of this description, it is by no means justifiable to assume that they are equally accurate when used in the reverse sense as has been done in estimating the thrusts for the three and four-bladed pro pellers above. In other words, the mere application of those ratios in that way is no sort of proof that it should be possible to obtain a thrust of 140 lbs. from a iour-bladed propeller of which a single blade has a calculated thrust of 45 lbs. according to the formula previously established. If, however, we assume that Froude's ratios are accurate within limits that are otherwise ordained, we are pro vided with a very useful method of deciding on the permissible number of blades, provided that we can define the above-mentioned limit. EXTRAORDINARY success attended some experiments carried out by the French military authorities on Sunday afternoon. Five military officers were given instructions to go by air to Nancy from Chalons, and this task was satisfactorily carried out. Lieuts. Cammerman and Viullerme were the first to leave, at a quarter past four, and with the former officer in the pilot's seat the Farman machine made a wide detour over Verdun and Toul, observations being taken en route, and eventually a landing safely made at Nancy at 8.45 p.m. Lieut. Fequant, with Capt. Marie as the observer, left Chalons at a quarter past five, and taking the route over Pagny and the Hove Forest landed at Nancy at 7.20. Soon after Lieut. Fequant started he was followed by Lieut. Caumont on a Sommer biplane, and he reached Nancy at 7.47. He flew mostly at a height of 900 metres, and kept Lieut. Fequant in sight for some time. On Monday Lieut. Caumont flew over to the camp at Luneville, and after delivering despatches there returned to Nancy. The same day Lieut. Crosnier started to fly from Vincennes to Chalons, accompanied by Lieut. Jost. He had risen to a height of 20 metres when, for some unexplained reason, the biplane pitched to the ground. Lieut. Jost escaped uninjured, but his companion sustained, a broken leg, and was taken to the military hospital at Vincennes. CORRESPONDENCE. *#* The name ana address of the writer (not necessarily for publication) MUST in all cases accompany letters intended for insertion, or containing qtieries. Correspondents asking' questions relating to articles which they have read in FLIGHT, would much facilitate our work of reference by giving the number of the letter. NOTE.—Owing to the great mass of valuable and interesting corre spondence which we receive, immediate publication is impossible, but each letter will appear practically in sequence and at the earliest possible moment. MR. J. T. C. MOORE^BRABAZON AND AVIATION MEETINGS. [676] There seems to be an impression that I have definitely given up aviation, owing to its dangers or what I do not know, so that if you will grant me a few lines of your paper for an explanation as to my apparent cessation of experiments, you would do me a favour. First of all, re the danger of aeroplaning. This, to my mind, is diminishing every day—granted, owing to there being many more aviators, there are, consequently, more accidents ; but nothing will persuade me that aviation is not getting safer every day, engines are more reliable, machines more stable, engineers more conversant than formerly with the construction of machines. It seems, therefore, to me hardly fair, either to Mr. Cockburn or myself, to assume that we are giving up aviation because it is, or has become, dangerous. If it is dangerous now, it was more dangerous a year or more ago, before most of the present-day cracks had learnt to handle a machine. What has happened is that Mr. Cockburn, as also myself, have realised the small chance and impossible position the real amateur has at public meetings. He has to compete, not against men of similar means with machines of their own, but against firms with a great deal of capital at their back, and with the idea of advertisement before them accruing from winning certain prize-;, a situation entirely similar to what occurred in early motor-racing days. An engine misfires ! No one thinks of putting it right. Another engine is slipped on to the machine. A wheel buckles. Another machine is brought out, while half-a-dozen mechanics from the "maison " repair the disarranged parts. Were I a millionaire, I possibly could compete against such organisation, but unfortunately I am not, and therefore I believe it best to let it alone as far as appearing in public is concerned. In the very early days, private men with time and money were wanted, and I think, perhaps, did a lot to help the movement on, but now the private man is the unfortunate individual the cracks wish to sell machines to. Do not let it be supposed I think ill of the professional with a firm at his back. On the contrary, I think he is doing a lot of good, more than the private man now could ; but do not let us confuse the two individuals, the private individual and the firm's professional. The day of the private investigator is over, and I for one very much regret it, but it is for the good of the movement that it is so, and consequently we must welcome it. Flying in public, or at meetings, I certainly have given up, under present conditions, but that in no way is the same as abandoning flying altogether. To abandon aviation at the present time would be similar to abandoning motoring after the Paris-Bordeaux race, when the automobile movement was in its infancy. When I took up aviation nearly four years ago, I looked upon it as a scientific investigation with a vast future before it. In that future I still believe, but whether the best interests of aviation are being studied by turning a highly complex mechanical problem into a travelling form of entertainment, I very much question. That Mr. Rolls' death was directly due to this form of gymkhana I emphatically believe, and, on this account alone, you will forgive me if the tone of this letter is somewhat bitter against aviation meetings of any kind. J. T. C. MOORE-BRABAZON. THE ANGLE OF DEFLECTION. [677] I have carefully read your article "Can we fly faster for less power ? " in issue of July 9th, and think I see many possible pitfalls therein for the average reader. For instance, what would be the " curve " if there be no angle of deflection ? From an excessive and really dangerous camber—particularly in some of the mono planes—I am of the opinion your article will tend towards accelerating the other extreme, too little camber. I do not remember having read in your journal a clear description of why the camber is necessary. Penge. A. EDMUND PARNACOTT. [A plane having no angle of deflection would, of course, be flat, that is to say, it would have no curvature at all. On the other hand we consider that a flat plane flying with a positive angle of incidence has a virtual angle of deflection in excess of the angle of incidence, owing to the upward trend of the wind caused by the cyclic current. We believe that the neglect of this upward trend is the reason why ordinary calculations for the inclined flat plane inadequately account for the lift that they are known to produce. An inclined flat plane flying in a horizontal path gives rise to a cyclic disturbance round the leading edge which causes the relative wind in which it is flying to have an upward trend in the immediate vicinity of the leading edge, and in order to receive this relative wind tangentially without shock the leading edge itself must be dipped downwards so as to lie tangential to the relative stream. A plane thus constructed would have a sharp angle where the leading portion joins the trailing portion, and in order to avoid such an obvious source of inefficiency the plane is made with a gradual curved surface from one edge to the otter, thus retaining the dipping 654
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