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Aviation History
1927
1927 - 0211.PDF
MABCH 31, 1927 25 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT IN THE DRAWING OFFICE. WIRING LUG DESIGN. By C. CHAPLEO. The design of a wiring lug is a problem presented to the aeronautical draughtsman probably more frequently than any other. Therefore, from the point of view of the drawing office, much may be said in favour of a quick and simple method of obtaining the dimensions of a lug to comply with any given conditions. The following is suggested as such a method. (See page 24.) Referring to the chart, it will be seen that there are five scales. Taken in order, the first (the left), is a " thickness " scale, the second a " load " scale, the third a scale of "-widths," the fourth gives the dimension from the edge of the hole to the end of the lug, and the fifth gives the pin diameter for bearing in the plate. For simplicitv, these will be referred to as the " t" " load," " w " " 6," and " d " scales respectively. A straight line connecting points on the " t " " load ," and " iv " scales gives the width required for a given thickness and load. From the point of intersection of this line with the " w " scale, a line drawn at right angles to the scales, through the "fo" and "d" scales, gives the values of "6" and "d" for this particular lug. As an example, the design of a lug for an H in. B.S.F. fork end is shown. The load in this case is 7,150 lb., the thickness adopted being 0-22-in. (i.e., one 10 G plate, and one 12 G, minimum thicknesses, 0-122 in. and 0-098 in.) From the chart, w — fc in., b = H in., and d = ^i in. For an offset lug the radius is ^V in. + - , in. = If in., and the offset is -^-J in. — -£? in. = ^ in. For a con- centric lug the radius is t'i in. -f- i\ in. = £-j in. When the pin diameter has been checked for shear, the lug is com- pletely designed. In this example, the pin diameter as given by the chart, happens to coincide with the diameter of the pin in the fork end. When this is not the case, i.e., when the pin in the fork end is larger than is necessary for bearing, the value of " d " used in arriving at the offset or radius for the lug is the diameter of the pin in the fork end, the " d " scale just being used as a check. Alternative lugs for a given load may be quickly seen by pivoting a straightedge about the required point of the load scale. With regard to the construction of the diagram, the theory of alignment charts may be found in almost any practical mathematical text book, so it will be sufficient to deal with this application only. The five scales are traced from a 10 in. slide rule, the " D " scale of the rule being used for the " <•," " w," " 6," and " d " scales of the chart, and the " A " for the " load " scale. The " t " and " w " scales are drawn first, then the " load " scale, placed midway between them, its relative position vertically being obtained by calculating one value of the load for a given thickness and width, and plotting from that point. The dimension " h " is obtained from the expression, load = 2 x b X t X shear stress. Also, load = w X t X /( = d x t x /;„ where ff and /,, represent tensile and bearing stresses respectively. If /„ = shear stress, = r—r = -x — = '722 and — = w. 2.j« 2 X 18 w f, 26 ',-= j. = 0-591. The "6" and "d" scales are placed, relative to the " w " scale, to give these ratios, i.e., 0-722 on the " b " scale, and 0-591 on the " d " scale, are placed level with 1 on the " w " scale. The short article printed above, and the full-page chart on the previous page, is an excellent example of the type of article suitable for inclusion in THE AIRCRAFT ENGINEER under the section headed " In the Drawing Office." There must be, in our various drawing offices in the British aircraft industry, many draughtsmen and junior designers who are making daily use of such labour-saving devices as Mr. Chapled's wiring lug chart. The Editor will always be pleased to consider for publication articles of this nature. In the case of contributors not personally known to the Editor it will be necessary to give an undertaking that the material submitted is wholly, or at any rate mainly, the contributor s own work, and that if he is employed by any aircraft firm, his firm raises no objection to the material being published. TECHNICAL LITERATURE. SUMMARIES OF AERONAUTICAL RESEARCH COMMITTEE REPORTS. THE EFFECTS OF BODY INTERFERENCE ON AIRSCREW PERFORMANCE. By WT. G. JENNINGS, B.SC. of the Aeroplane and Armament Experimental Establishment (Home). Presented by the Director of Scientific Research. R. & M. No. 1046 (Ae. 232) (10 pages and 3 diagrams). July, 1926. Price M. net. Reasons for Enquiry.—A considerable amount of experi- mental work, covering a number of years, has been carried out in wind tunnels on the mutual interference of airscrews and bodies. It was thought desirable to investigate to what extent the more recent tests supported the results of the earlier work, and how far the present state of knowledge of the interference effect on models could be usefully applied to full-scale experiments. The results of the wind tunnel tests* have been examined and their application to full-scale performance work discussed in the present report. It appears that the increase of body resistance due to slip stream can be expressed in the form Jl _ bT This equation is well supported by all model tests, but in view of the fact that recent results have shown a considerably increased value of the constant b, due possibly to a pressure gradient effect, it seems desirable that an investigation should he made into the pressure distribution over a fuselage in the slip stream. It is shown that for bodies of good shape, b is in the form b = a.2 L -a-«'r>i where aa and a$ are constants. The method of determining the net efficiency of a combina - tion of airscrew and body by reference to airscrew and aircraft characteristics in free air, may lead to appreciable errors in the prediction of performance. Further work requires to be done before it is established that the overall efficiency obtained from the analysis of full- scale tests is sufficiently independent of aircraft characteristics to enable airscrew performances to be compared. It is considered that a reliable thrust meter fitted to the airscrew shaft would greatly assist the examination of inter- ference effects in full-scale work, since it would provide a means of establishing the parasitic drag of the aircraft. * K. & M. No. 985. The reduction of aircraft performance tests.* K. & M. No. 830. Experiments with a family of airscrews, including effect of tractor and pusher bodies. Part II. * K. & M. No. 1030. Experiments with a family of airscrews, includingeffect of tractor and pusher bodies. Part IV. On the effect of placing an airscrew in various positions within the nose of a streamline body.* Jt. &• M. No. 344. An investigation of the mutual interference of an airscrew and body of the " tractor " type of aeroplane. MODEL TESTS OF A COMBINED SLOT AND AILERON CONTROL ON A WING OF R.A.F. 15 SECTION. PUSH FORWARD TYPE OF AUXILIARY. By F. B. BRADFIELD, Maths, and Nat. Sci., Trip., and A. S. HARTSHORN. Presented by the Director of Scientific Research. R. &M. No. 1047 (Ae. 233) (10 pages, 9 diagrams.) May, 1926. Price M. net. The slot-and-aileron control, as described in a number of previous publications, has been fitted to the R.A.F. 15 section, and the tests are described in R. & M. 1008*. Since the publication of this paper, it has been decided to fit a slot control to a wing of R.A.F. 15 section, such that the section should be identically R.A.F. 15 when the auxiliary was in its closed position, and the Handley Page thin-plate type of auxiliary was chosen for this purpose. Rolling and yawing moments, and the force, on the * E, & M. 1008. Wind channel tests of slot-and-aileron control on a wing of R.A.F. 15 section.—F. B. Bradfield, A. S. Hartshorn and L. Caygill. 188e
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