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Aviation History
1909
1909 - 0820.PDF
DECEMBER IS, 1999. 1. The effect of pqnents of wing supplies a righting 2. The effect of a CORRESPONDENCE. *#* The name and address of the writer not necessarily for publication) MUST in all cases accompany letters intended for insertion, or containing queries. NOTICE.—Correspondents asking questions relating toarticles which they have read in FLIGHT, would much facilitate our work of reference by kindly indicating thevolume and page in their letters. THE DIHEDRAL ANGLE. To the Editor of FLIGHT. SIR,—This subject has been discussed at such length in your columns that one hesitates to add anything further on it. The letter of Mr. Flight, however, in your issue of November 27th, does not seem to the writer to leave the question in a satisfactory position. The stability has been explained by correspondents in two different ways, viz. :— a tilt is to render the vertical com- pressure unequal, which inequality force. tilt is to bring into action a lorce which urges the aeroplane sideways and downwards (whilst still travel- ling forward), causing an increased pressure on one wing which rights the machine. Now these two explanations are distinctly different. (1) requires no deviation of the e.g. from a straight path, whilst (2) does require such a deviation. It appears to rhe writer that (i) is quite inadmissible. This ex- planation might be correct, were an aeroplane acted on by a pressure which is always vertical, like a ship j on water. With a dihedral angle, however, / the resultant pressure on the two planes acts /' a'ong a l'ne bisecting the angle, and always W / passes through the centre of gravity, whatever the tilt—provided the e.g. continues in a straight line—thence, in this case the tilt (as already pointed out by Mr. Kemp, in your issue of October 30: h), produces no righting couple. This argument, be it noted, assumes 10 particular relative positions of e.g. and c.p. Mr. Olley's diagram in your issue of October 30th, given also by Mr. Edgcumbe on November 20th, surely gives the true explanation No. 2 above). Referring to Mr. Edgcumbe's letter, it will be ieen that whatever the tiit, the resultant pressure, P, acts in a line sassing through the e.g., and therefore has no righting moment. But the aeroplane immediately commences to move along, O, F, i.e., t deviates from its course. This at once gives an extra pressure on he right hand wing, and rights the machine. Although, doubtless, we can consider an aeroplane as supported jy the pressure due to constant " fall," this is not in itself sufficient to iccount for stability. It is the real downward motion produced by he vertical component of the force, O, F, which assists in righting he machine. Yours, &c., Letchworth. R. C. CLEUKER. [The principle of the dihedral angle is a subject which can stand [uite a lot of discussion, not so much because of the rights and vrongs of the case as because it is so essentially one of those techni- :alities which present themselves to different people from different >oints of view. In technology there are many instances of alternative ' treatments " and it is a well known fact that students of all degrees re commonly only able to see the truth of one ; which one, depends m the style of logic that appeals to their individual minds. We ancy that the dihedral angle is a case in point among the problems n aerodynamics, and consequently we welcome the views of readers s the most satisfactory way of presenting the subject in every ,spect. We have reproduced the diagrams which originally accompanied he letters of former correspondents and are referred to above.—ED.] power. Could you advise me as to this ? The motor would be a j. Bonn and Co.'s double-geared elastic motor of 36 ins. length and 8 ozs. weight, or else the clockwork one made by Messrs. A. W. Gamage, weight 28 ozs. The wing area is 525 sq. ins. Is this sufficient for the weight »f motor (clockwork) ? Could you furnish me with these particulars ? Wishing your paper every success. Yours truly, Canterbury. ERIC A. LATTBR. [The great difference in the weight of the two motors suggests that it would be advisable to try the lighter one first. It is always diffi- cult to estimate the carrying capacity of the model, and more thaa disappointing to find that it has been overlooked. If the elastic motor is successful, it would be real progress to try and make the machine carry a clockwork motor, as not only would there be the additional weight, but much would be learnt about the respective balance as the result of concentrating the weight in another part of the machine. It is along these lines that model experiments have such an educational value.—ED.] ELASTIC V. CLOCKWORK. To the Editor of FLIGHT. SIR.—I am building a model Antoinette monoplane of ij ins. to ft., and am doubtful whether to use clockwork or elastic as motive ASH V. SPRUCE. To the Editor of FLIGHT. SIR,—Referring to the reply of your correspondent, Lilian E. Bland, in your issue of last week, may I submit some addi- tional particulars to the subject, ash v. spruce, as follows, that while ash is much tougher, and will bear a greater tensile strain than spruce, it is not nearly so stiff as spruce or yellow deal, and while spruce is not nearly so durable as yellow deal, it has the disadvantage of containing many small round " dead" knots, which besides shrinking considerably, and easily falling out, also cause a serious local weakness, and knowing well the characteristics of both the ash and spruce and yellow deal, I should most certainly use the latter, wherever possible, especially as most of the knots found in yellow deal are an element of strength rather than weakness, as they are mostly " live" knots, and do not as a rule shrink, loosen, or fall out, although, of course, I should choose spars cut out of boards as nearly as possible entirely free from knots of any kind whatsoever. The best yellow deal spars are those cut out of boards " between " the heartwood and the sap woo 1, thus in cutting up a I in. board, say, into strips or spars of i£ ins. wide, I should choose a board, not exactly out of the "centre" of the tree, but slightly, though entirely, outside the real "pith centre" as one or two boards immediately central are very liable to " sun shake," and may split up after working and exposure, so, taking a board of 1 in. thick by 11 ins. wide, I should leave 1 in. each side of this centre, and mark off towards outer edge cf this board 2 or 3 spars each side, and that is all, for, by getting too near the outside edge, one cuts into the " sapwood " which has no " life," is porous, and very soon becomes weak on exposure, and will break "short" in any sudden and undue strain, either tensile, compressive, or torsive. Further, I should find the " root " end of the board and mark this carefully, and in building the body of a flying machine or aeroplane, put this root end of each spar always in front if possible and the " heart side " upper- most, these being in my opinion the best positions for equalising the various members in bracing up, and where uprights or posts are used, always put the " root" end at the bottom. May 1 say I have had a rather wide experience, covering many years of my life, in working up these and many other woods, and practically am well acquainted with their behaviour in uses under many and various conditions. I fear this letter is too long for insertion in your splendid work FLIGHT, the numbers of which I possess from the first one, but having derived much pleasure and information fro-n their pages, I beg to offer the above remarks for any use to which you may think them worthy of application. Yours faithfully, Newport Pagnell. HENRY BATH. BOX GIRDER CONSTRUCTION. To the Edit»r of FLIGHT. SIR,—I see that one of your correspondents is in trouble about the construction ot the bamboo box girder ; he does not see how to get the steel wire inside the pole. Possibly you might find space for the following explanation, and help him out of his difficulty. The holes to allow the wire to pass through the noses of the bamboo pole, were obtained by the simple experiment of heating a ^V*in- bar of round iron red hot at one end, and pushing it through the pole. Nice clear holes are in this way obtained, and the bar itself can be used as a needle for pulling through the wire. I would warn your correspondent that the process described has the diiad- 822
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