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Aviation History
1937
1937 - 2146.PDF
SUPPLEMENT TO FLIGHT 132/ THE AIRCRAFT ENGINEER JULY 29, ig37 increased drag, while in landing increased drag is, within limits, as useful as increased lift. Hence the slotted flap and its extension—the Fowler—should be of particular use for take-off. The utility of flaps for take-off depends essentially on the thrust/weight ratio from rest to the take-off speed. If this lies between 0.2 and 0.3 only a slotted flap can be used with advantage, if it is greater than 0.8 almost any form of flap is likely to effect some saving. The increased load which can be taken off in a given distance by the use of flaps depends very greatly on the available thrust. The problem of landing a load of 20 lb./sq. ft. and upward in a given distance admits, broadly speaking, of two solutions. If a split flap of large size is fitted, giving high drag and comparatively small lift, the glide will be steep and fast and the landing speed high. If, on the other hand, a large size Fowler is used, giving comparatively small drag and high lift, the gbde will be flatter and slower, and the landing speed will be lower. The Fowler flap is only slightly superior to a slotted flap as a saver of distance either in take off or in landing. But it extends the range of maximum lift coefficient well beyond that obtainable with other forms of flap, and the consequent reduction of maximum speed on the ground and of rate of descent are practical advantages which may make its use essential for getting loads of over 20 lb./scj. ft. off and onto the ground. TESTS ON TWO STREAMLINE BODIES IN THE COMPRESSED AIR TUNNEL. By R. Jones, D.Sc, D. H. Williams, B.Sc, and A. F. Brown, B.Sc, of the Aerodynamics Department, N.P.L. R. & M. No. 1710. (6 pages and a diagrams.) April 29, 1936. Price is. net. Models of two airship forms have been tested in the compressed air tunnel up to a Reynolds number of 49 X 10s, the standard length being the length of the model. The forms were the original hull of R.101 and R.102, a shape having the same fineness ratio as R.101 but with a 10 per cent, greater block coefficient. The results are given on a surface area basis. There is a wide transition band from laminar to turbulent flow, but the curves are well defined above R = 107, where they lie above the turbulent skin friction curve. It is proposed to undertake drag tests on other models of different fineness ratios, and also to investigate the effect of surface roughness. FULL SCALE AND MODEL PORPOISING TESTS OF THE SINGAPORE lie. By W. G. A. Perring, R.N.C., and J. L. Hutchinson, B.A. Com municated by the Director of Scientific Research, Air Ministry. R. & M. No. 1712. (26 pages and 11 diagrams.) November 23 1935. Price 3s. 6d net. , The technique of testing dynamic models in a tank was developed at the Royal Aircraft Establishment about three years ago, and during the time that has elapsed since then a large number of dynamic models have been tested. Although it was believed that the model results corresponded closely with the full scale, no oppor tunity of a direct comparison between the model and full scale results occurred. Accordingly, model and full scale tests have been carried out on a typical seaplane. Tests in iie.i2.A_ii, tank were made on a 1/12 scale dynamic model and the full scale tests were undertaken at "Felixstowe ; an account of both the model and full scale tests is contained in the present report. The tests have demonstrated the usefulness of the model method of investigating the behaviour of seaplanes on the water in the planing condition. Tests on the dynamic Singapore lie model, showed that with the centre of gravity in the normal position, the model was extremely stable, and the angular range cf stability should enable the full scale seaplane to take-off and land without experiencing any por poising tendencies. The model tests showed that porpoising should only be possible full scale at small angles of incidence when the centre of gravity is moved forward of the normal position, and at large angles when the centre of gravity is moved aft. The vertical movement of the centre of gravity, overload conditions and increased pitching moment of inertia, were all found to have a negligible effect on the stability limits. The full scale tests agreed with the model in showing the great stability of the Singapore lie under all normal operating conditions. Full scale instability occurred at extreme attitudes and loadings, at small angles with centre of gravity forward and large angles with centre of gravity back, in close agreement with the model results. A comparison of the model and full scale results showed that the porpoising periods, model and full scale, were in very good agreement. A NEW FORM OF BIPLANE. By H. B Irving, B.Sc., and A. S. Batson, B.Sc. APPENDIX I. WHIRLING ARM EXPERIMENTS. By A. S. Halliday, B.Sc., Ph.D., D.I.C. APPENDIX II. FREE SPINNING TUNNEL EXPERIMENTS. By R. H. Francis, M.Sc. APPENDIX HI. THEORY OF A SPINNING MODEL TEST. R. & M. No. 1715. (44 pages and 30 diagrams.) Price 7s. net. The report deals with experiments on a new form of biplane whose special property is stability in roll up to angles of incidence of over 40'-' without any appreciable loss in performance in normal flight or extra weight entailed by additional mechanism or parts. Maximum lift is slightly increased and there are minor advantages as regards gliding angle for coming in to land, aileron control and possibly spinning. In this biplane the wings converge towards the tips owing to the lower wing being given an unusually large dihedral angle (12|°). The lower wing is also swept forward 10° and is of constant chord, while the upper wing is highly tapered. Half-wing experiments which gave promising results were followed by experi ments on a biplane cellule. The half-wing experiments included measurements of aileron and wing tip control. All the earlier experiments were made with R.A.F.15 section, but check experi ments were made later with R.A.F.38 section,first with a half-wing model, then on the rolling properties of a biplane cellule. Free spinning tunnel experiments were made at the R.A.E. with a complete model having wings of R.A.F.34 section. The most important result is that stability in roll on the model scale to over 40° incidence' has been obtained without any appreciable loss in performance in normal flight or when climbing. Maximum lift is slightly increased and the stall is a gradual process, beginning with a premature stalling of the upper (tapered) wing tips, which spreads inwards as the incidence increases. After the upper wing is completely stalled the lower wing begins to stall at the centre, but the stalling of the lower wing does not reach the tips until about 40° incidence. The early stalling of the upper tips leads to an early and more gradual retrograde movement of the centre of pressure than is usual, as well as a steeper gliding angle near the stall. Aileron control is normal at ordinary flying angles, but falls off less than is usual at angles near the usual stall; adverse yawing moment in this region is also less than usual. The whirling arm results show unusually large values of rolling moment due to a rate of yaw at high angles of incidence. The biplane will behave similarly in a prolonged spin to an equivalent orthodox biplane of high stagger, but no conclusion can be drawn as to liability to accidental spins. FULL SCALE TESTS OF SLOTS AND FLAPS ON A HEINKEL He.64 WITH SPECIAL REFERENCE TO LANDING. By J. E. Serby, B.A., and H. B Squire, B.A. Communicated by the Director of Scientific Research Air Ministry. R. & M. No. 1713. (15 pages and 10 diagrams.) November 5, 1935. Price 2S. 6d. net. > The Heinkel He.64 is a low wing monoplane equipped with lift slots, tip slots and plain flaps, which together give it a high speed range and enable it to do freak landings and take-offs. It was originally intended to use it to examine the technique of the " crash " landing but in spite of a special long-travel undercarriage it proved unsuitable for this, and the experiments were limited to measuring the ordinary aerodynamic characteristics and some landings. For the latter a photographic method was developed. Handling trials were done at low speeds. Lift and drag, trimming curves and landings were measured with the aircraft- in two eonditions, («) lift slots shut and flaps neutral, (*) lift slots locked open and flaps locked down. The tip slots were free in all the tests. The slots and flaps raise Clmalt. from 1.44 (at a = 20 deg.) to 2.2 (at a = 30 deg) and increase the profile drag of the wings by about 0.032, the minimum glidin« angles in conditions (a) and (6) being 5| deg. and 7 deg. As a landing device they are poor, since, due to the slots, the max. CL in con dition (b) is reached at too high an incidence for a normal landing, and consequently much of the reduction in stalling speed has to be sacrificed, a CLmax, of 1.6(1 liein'u the highest usable. The increase in gliding angle is small. By comparison a 0.15 c split flap covering the same span would raise'CLmax from 1.40 to 1.90 and increase •y to 8 deg. or 9 deg. for flap angles of 60 deg. or 90 deg. The aircraft cannot easily.be stalled in condition (b) as a very aft C.G. is required to do this. When stalled, however, it is very unstable laterally. Stalled in con dition (a) the tip slots make it nearly stable. The rudder control is worse at the lower stalling speed condition (&) but no effect of the flaps on the elevator was noticed. The landing distance from 50 ft. to rest is decreased from 1,700 ft. to 1,300 ft.— a saving of 24 per cent, (no wheel brakes being used). TESTS OF AEROFOILS R.A.F. 69 and R.A.F. 89, WITH AND WITHOUT SPLIT FLAPS, IN THE COMPRESSED AIR TUNNEL. By D. H. Williams, B.Sc., A. F. Brown, B.Sc., and E. Smyth, B.Sc., of the Aerodyna mics Department, N.P.L. R. & M. No. 1717. (24 pages and 6 dia grams.) May 25, 1936. Price 3s. 6d. net. The use of thick sections for wing profiles has become common with the develop ment of internally braced cantilever monoplanes, and with the use of tapered wings. The thickest sections hitherto tested in the Compressed Air Tunnel have been of the order of 15 per cent., and little information is available regarding the behaviour of thick sections at high Reynolds numbers. The minimum drag of such sections is found to increase rapidly with thickness whereas the maximum lift decreases as the thickness is increased except at low values of Reynolds number. The addition of flaps, however, increases the maximum lift to the same value as that for a thin section with flaps. Two sections, R.A.F. 69 and R.A.F. 89, of thickness 20.7 per cent, and 25 per cent, respectively, were tested up to a Reynolds number of 6 x 10* at positive and negative incidences, with 15 per cent, split flaps placed 15 per cent, forward of the trailing edge. PRELIMINARY CALIBRATION OF THE 24-FOOT WIND TUNNEL, R.A.E., WITH A SHORT DESCRIPTION OF THE TUNNFL. By W. G. Jennings, B.Sc., A. Terry, B.Eng., and P. J. Pearsall. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1720. (8 pages and 11 diagrams.) July, 1935. Price 2s. 6d. net, A preliminary exploration of the airflow in the R.A.E. 24-ft. tunnel, including a calibration of the air speed at certain sections of the working jet, has been made. These measurements were not intended to cover a complete investigation of the conditions of flow in the tunnel, but to provide sufficient data for the tunnel to be used for the first series of full-scale tests on the tunnel programme. A short descrip tion of the main features of the tunnel is included in an appendix to the report. The working of the tunnel in its present form is satisfactory ; within the centre 20 ft. of the jet the distribution of the velocity at any one section was within 1J per cent, of the mean. As originally designed severe pulsations occurred in the airflow at high speeds; by introducing fifteen tabs 0 in. square into the jet at the nozzle the periodic fluctuations of the airstream were eliminated ; the addition of these tabs did not affect the energy ratio of the tunnel appreciably, but the static pressure gradient down the axis of the jet was adversely affected. THE INFLUENCE OF DIFFERENTIAL AILERON CONTROL ON WING FLUTTER. By R. A. Frazer, B.A., B.Sc., of the Aerodynamics Depart ment, N.P.L. R. & M. No 1723. (20 pages and 7 diagrams.) Sep tember 10, 1934. Price JS. net The influence of differential aileron control on wing flutter recently came under consideration in connection with an investigation of the flutter characteristics 01 a model Puss Moth wing. The present report gives an account of the underlying theory. The principal conclusions are as follows :— (1) The basic dynamical equations involve 7 degrees of freedom and have non linear characteristics. • vWwl (2) If only small motions about a general equilibrium position.are consiaereo, the effective aileron stiffnesses and moments of inertia are acutely dependent upo the lateral control setting and the airspeed. The motion can only be reproduced in the wind tunnel by means of a complete model. • .^ (3) In the special case where the control column is central in equilibrium, motion is resoluble into a symmetrical ternary constituent and an anti-syniiiietr quaternary constituent. Both of these motions can be reproduced by means 0 half-model of the aeroplane. : " " . nt (4) The lowest critical speed obtainable by means of a half-model is uu necessarily the lowest possible for the actual aeroplane. , a]| (5) In the ideal case where the cables are inextensible the equations 01 s - motions-about a general equilibrium position are resoluble into a binary COI"^^j (pure flexure-torsion of the wings) and an " anti-symmetrical " motion or sp>»-» (6) Rough calculations indicate that when the control column is set well0 the reductions of the upward aileron angles at high airspeeds are very mar
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