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Aviation History
1927
1927 - 0117.PDF
FEBRUARY 24, 1927 17 THE AIRCRAFT ENGINEER STJPPLEMEKT TO FLIGHT - terhaps not least, undercarriages that are for service at an Ititude as well as on the ground. It is well to remember Jiat " fineness " is synonymous with " economy," and that '••• is a point open to much debate whether the un-economical fcsign pays back the disadvantage in other ways, such as improved cabin accommodation, or slightly improved view, t.tc,, and with regard to such doubtful advantages as a high op speed regardless of efficiency, it is worth while to note that the Fokker F. VII-3m. is now fitted with three " Lynx " engines of 180 h.p. each, in place of the three Wright " Whirl- z ZuJ zz DO > Fig. 4. wind'' engines of 200 h.p. each, the result being a total reduction of 60 h.p., a loss of 10 miles per hour at sea-level, an improved L/D, viz., 4-52, an increase in radius, and a reduction in the cost per ton-mile. The approximate relationship between this ton-mile con- sumption and the L/D is given by the curves shown in Fig. 4, that have been derived from the formulas (1) Water-cooled engines (9-50 lbs. per h.p.-hr.) 1120 HPPetrol consumption in lbs. per ton-mile ... = (2) Air-cooled engines (0-45 lbs. per h.p.-hr.) Petrol consumption in lbs. per ton-mile... = 1009 HP— r ^— It may be as well to draw attention to the variability of consumption with different engines, and to mention that the figures given above represent the average for six engines in each class. TECHNICAL LITERATURE. SUMMARIES OF AERONAUTICAL RESEARCH COMMITTEE REPORTS. ACCIDENTS TO AEROPLANES INVOLVING FLUTTER OF THE WINGS. REPORT OF THE ACCIDENTS INVESTIGATION SUB-COMMITTEE. B. & M. No. 1041 (A.3) (19 pages and 15 diagrams). December, 1925. Price Is. U. net. The problem of flutter in aeroplane parts is likely to become of increasing importance as the speed of aeroplanes is increased, and some of the occurrences affecting flutter of the )vings were referred to the Accidents Sub-Committee for investigation. The whole problem of flutter and vibration in aeroplanes s^ proved to be a much more complex problem than was urst realised, and a general investigation has been started uch will take more than a year to complete. 3ome definite conclusions were reached at an early stage the investigation, and these have been put together in the sent Report. The aeroplanes in question (which are not •v used in the Royal Air Force) developed an unusual aunt of oscillating movement of the wing tips of consider- '•' '', magnitude accompanied by excessive vibration of the '^e Machine. The apparent movement of the wing tips ,'^ u°out an inch at rates which have been estimated between '' TO 1,000 per minute. It would appear that there are various means of overcoming the vibration difficulty or of postponing its occurrence to a higher speed, as, for example, (1) by the movement of the point at which aileron is con- trolled ; (2) by arranging that the C.G. of the aileron should be on the hinge ; (3) by an attachment designed either to limit the motion of the spar or to increase its stiffness. Some theoretical work on the subject, and some of the conditions as reproduced experimentally at the Royal Aircraft Establishment are reported in appendices. ON THE EQUIVALENCE BETWEEN THE DYNAMICAL SYSTEM OF A MULTI-CRANK FLYWHEEL SYSTEM AND A CERTAIN ELECTRICAL CIRCUIT, WITH SOME SUGGESTIONS FOR MEASURING CRITICAL SPEEDS AND SHAFT STRESSES BY ANALOGY. By E. B. MOTTLLIN, M.A. R. & M. No. 1045 (E. 21) (9 pages and 5 diagrams). April, 1926. Price 9d. net. Breakages of the crankshaft of large aeroplane engines have occurred, and on account of their complication and relative lightness compared with other heavier engines, existing methods of analysis have to be modified to find and avoid critical speeds, and for the calculation of stresses. Another attack on the problem can be directed experimentally, as is suggested in the present paper. It is known that if the equivalent inertia of the rotating masses and the equivalent stiffness of the portions of the shaft can be stated, then the critical frequency can be calcu- lated. A simple method of avoiding the calculation is to devise an electrical circuit equivalent to the dynamical system, and the author has shown how this can be done. An extension has been proposed to include the case of variable inertia, and also the case of a couple acting on each crank. Some suggestions are added for suitable sizes of the moments of inertia of the system. SLOT AND AILERON CONTROL ON A WING OF R.A.F. 31 SECTION WITH VARIOUS TYPES OF AILERONS. By F. B. BRADFIELD, Maths, and Nat. Sci. Trip., and A. S. HARTSHORN, B.SC. Presented by the Director of Scientific Research. R. & M. No. 1048 (Ae. 234). (16 pages, 10 diagrams). May, 1926. Price Is. net. The slot and-aileron control has been previously fitted to an Avro with standard and balanced ailerons (R. & M. 916)* and also tested on the R.A.F. 15 section (R. & M. Nos. lOOSf and 1047).^ Model experiments on the same control are described in the present report as fitted to a wing of R.A.F. 31 section intended for use on a Bristol Fighter aeroplane ; for performance measurements on this wing section reference should be made to R. & M. 990. § Rolling and yawing moments were measured from 0C= 0° to 30° incidence, on R.A.F. 31 with slot control, with symme- trical balanced, Frise balanced, and slotted ailerons. Aileron hinge moments were measured for the symmetrical balanced, Frise balanced and slotted ailerons. Hinge moments of the auxiliary aerofoil forming the slot control were also measured. The additional drag due to the slot was determined. Rolling and yawing moments were measured on a 6-6-in. chord model, hinge moments on a 13 -2-inch model, both at V = 60 ft./sec. R.A.F. 31 section is not adapted to this type of auxiliary aerofoil; the increase of drag is too great. But Frise balanced or slotted ailerons without slot control give good results on the model if used to large angles. The scale effect on R.A.F. 31 near stalling is very large, and no deductions can be made as to full scale stalling conditions. * R. & M. 916.—Slot control on an Avro, with standard and balanced ailerons.—i". B. Bradtield. t R- & M. 1008.—Wind channel tests of slot-and-aileron control on a wingof R.A.F. 15 section.—F. B. Bradfield, A. S. Hartshorn and L. E. Caygill. % It. & M. 1047.—Model tests of a combined slot-and-aileron control on awing of R.A.F. 15 section. Push forward type of auxiliary.—F. B. Bradlield and A. S. Hartshorn. Presented by the Director of Scientific Research. § R. A; M. 990.—Full scale and model measurements of lift and drag of ristol Fighter with R.A.F. 31 wings.—B. D. Clark, B.Sc., and R. G. HarrisBristo D.Sc. 100*
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