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Aviation History
1911
1911 - 0080.PDF
fSGHTj Let us hope to see this plan adopted in the rules of this year's Michehn Cup and any other prizes offered on the lines of the de t orest prize. Bedford Park. j RuRT [The Royal Aero Club have already passed a regulation whereby •Ul annual competitions for the future must terminate not later than October 31st in any year.—ED.]. Speed-Alarm Competition. [1040] In reproducing the design I submitted, I notice vou have mentioned the width of the apertures in the whistle barrel at J in. This should be ^ in., as stated in the specifi- cation sent you, and I shall be glad if you will kindly make the necessary correction. I am aware, of course, that the width of these slots would depend upon the scale of the complete apparatus and this I purpose y did not state. At the same time, judging from the size of the sectioned strut, the whistle barrel would be J in to I in. diameter and Jt in. slots would be in order Mosele>r" G. BOOCOCK. Propellers. [1041] Can any readers of your valuable journal give me the reason why the entering edge of a Chauvitre trlctor is the thinner and that of the Normale the thicker ? It appears Ci-IAUVIER^E rJ^ NORM^LE DEVOLVING .STATIONARY ENTERING EDGE '^ENTERING EDGE to me that when a Chauviere is revolving the attacking surface takes the same form as that of a stationary Normale as illustrated in accompanying sketch. W. WEEBT. Relative Winds. [1042] I would be much obliged if you could tell me if the following supposition is correct: Suppose that there is an aeroplane moving forward with a speed which would be 30 m.p.h. in still air. Suppose there is also a wind blowing at right angles to this apparent direction of flight of 20 m ph. Is it correct in order to find the resultant direction and speed of the aeroplane to complete the parallelogram of velocity, and draw the diagonal and measure it as is done in a good many mechanical problems ? Cr°ydon- S. A. HALL. [It is only correct to use the diagram of the parallelogram of velocities for the purpose of finding the relative velocity and direction of the apparent wind, provided that the aeroplane does not drift but is headed into the wind sufficiently to preserve its course as a whole. If, however, the line of thrust is maintained, say, north and south, so that the machine drifts with the side wind then the side wind ha* no other effect. It is necessary to bear in mind in this connection that in practice the machine must be actually headed into the wind in order to counteract drift, consequently there is, one might almost say, no such thing as a side wind unless drift takes place, for it is essen tial to assume that the aeroplane will offer resistance to the side wind if it feels its effect. There is a hypothetical case in which it might be supposed that a side wind is counteracted by an independent thrust. Under these circumstances there is an actual relative wind blowing diagonally across the planes of a velocity and direction represented by the diagonal of the parallelogram of forces as suggested in the above letter. The effective value of this resultant relative wind cannot, however, be estimated with any degree of accuracy because the planes are not designed to fly in this attitude. Thus, for example, if we resolve the resultant into its two original components and consider each separately it is quite obvious that the effect of 20 miles an hour flying broadside on will be infinitely superior to the effect of flying 20 miles an hour end-on. In the one case the apparatus represents a proper cambered plane and in the other case it corre sponds to a flat plane operating under very inefficient conditions. Unquestionably the end-on flight would result in some supporting effect, but it would not be of corresponding magnitude, and the effect of the resultant would certainly be less than the effect produced under corresponding conditions with the aeroplane heading into the wind and si ill travelling with its initial velocity on its true north and south course.—ED.]. JANUARY 28, 1911 MODELS. Model Monoplane. [IO43] I enclose drawings of a model monoplane which I have constructed. The following particulars are :—Span of main planes, 3 ft. ; chord, 6 ins. ; length of machine, 2 ft. $ ins. It is driven by a Chauviere type propel'er and 22 strands of T\ in. strip elastic. The length of the power plant is 2 ft. 10 ins. Weight of machine in working order, 15 ozs. The model rises off the ground, and flies about 30 yards. I hope to get a longer flight than this after a little tuning up. Lewisham. ARTHUR F. CHINNERY. Farman Model. [1044] The enclosed photo is an exact scale model H. Farman 1 in. to the foot. It is complete with propeller, dummy engine petrol tank, &c, and.is covered with aero fabric. It is only a show model, and was strung up for the purpose of photographing. Manchester. C. H. ASHLEY. A Model and its Construction. [1045] I am going to build a model for long-distance flight, and should esteem it a favour if you would furnish me with a few details necessary for its construction. 82
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