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Aviation History
1928
1928 - 0515.PDF
JUNE 21, 1928 51 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT converting (12) to biplane characteristics for the above conditions we get :— from (7) kD = kv' -f A^'D where Akv = kL2 = 0-056 fcL2 in this particular example. From (10) we have x- = %' + 57-3 [0-056 + — < 0-93972 .. 0-89 ) kL = a' + 5 k\ dkLNow —^ for the mono = 0-0361 rfa and for the biplane we shall have d\ 0-0361 du = 1 + 5 X 0-0361 = 0-0306 Angle of no-lift for mono and biplane — — 5-3° ( i.e., — ). Therefore constant term for the biplane equation is 5-3 :•• 0-0306 = 0162. Hence. kL = 0-0306a + 0-162. In correcting kh max. there will be no full-scale correction necessary as the test on the aerofoil was done in the American high-pressure channel which, it is believed, gives results comparable to those likely to occur in actual full scale. Hence, from the curves ILmax, =0-684 x 0-925 X 1-041 x 1-0 = 0-6G where 0-925 is the chord correction 1-041 is the stagger correction and 1 -0 is the aspect ratio correction. Our next step will be the deduction of the upper and lower lift curves. From Fig. 6 we see that the mean ratio of the lifts at an angle of stagger of (20 + 5-3) = 25-3° (N.B. —This is the aerodynamic stagger measured from the no-lift attitude) is 1-24 and this is when T\ =0-33. .-. from (12) we get 2 v 0-33 — fru. = -ir-tr- =•" °-294 ; or = 0-892 kh and /Lu = 1-24 X 0-294 = 0-364 ; or = 1 • 106 ~kL The results are shown graphically in Fig. 7 , but can be expressed algebraically as i-LU = 1-106 X 0-0306a + 5-3 X 1-106 X 0 0306, i.e., itLU = 0-0338a + 0-1795 and Ar1L = 0-892 x 0-0306a + 5-3 x 0-892 x 0-0300 i.e., ku. = 0-0273a + 0-1448. We next need to find the moment curves for the individual wings. Glauert [3] states that the relationship between the moment and the lift coefficients of a wing should be indepen- dent of the multiplane system in which the wing is situated. That is to say, we can assume dkhdk m to remain constant. Thus, for this biplane system we are considering, the monoplane equation I-m = —0-229 h -0-04 becomes, with the applied corrections to convert it to biplane Im = - 0 • 229 X i kh - 0 • 04 by (11) orXm = -0-2 kL -0-04 This expression can thus be applied to the upper and lower wings and plotted, along with the other characteristics in diagram 8. Our last data are connected with drag, and here, as the effect on strength calculations is small, the writer suggests that for the biplane the total biplane drag coefficient should be used for the upper and lower wings alike. The errors so introduced should not give rise to any occasion for worry. In the diagram the separate drags are actually plotted and a warning must be added that it is assumed that for a given value of iL the value of the drag coefficient is assumed the same for upper, lower, or complete biplane wings. In other words. k\, is plotted on a kL basis. Diagram 8 thus gives in a graphical form all the data the stress calculator requires for proceeding to the determination of loads in such a wing structure as that indicated above. [U [] 13]W IB] Bibliography. R. & M. 867.—Interference of wind chaunel walls on the aerodynamic particulars of an aerofoil.—Ulauert.R. A M. 72:S—Aerofoil Theory.—Ulauert. K. * M. 9J1.—Theoretical relationship for a biplane— Olanert.R. * M. 9!I7.—Distribution of pressure over a biplane with wings oi unequal chord anil span.—Irving and ltatson.N.A.C'.A. Report :!3:i.—Seven whip Sections at Full Reynolds Number.— Munk and Miller.R. & M. 945.—Lift and drag of Junkers Monoplane. Comparison oi model and full scale.—Clark. Ac. TECHNICAL LITERATURE. SUMMARIES OF AERONAUTICAL RESEARCH COMMITTEE REPORTS. These Reports are published by His Majesty's Stationery Office, London, and may be purchased directly from H.M. Stationery Office at the following addresses : Adastral House, Kingsway, W.C. 2; 28, Abingdon Street, London, S.W.I ; York Street, Manchester; 1, St. Andrew's Crescent, Cardiff ; or 120, George Street, Edinburgh ; or through any book- seller. THE ONE-FOOT WIND TUNNEL AT THE NATIONAL PHYSICAL LABORATORY ; INCLUDING PARTICULARS OF CALIBRATION MADE WITH A PlTOT TUBE AND VANE ANEMOMETER AT LOW SPEEDS.—By L. F. G. SIMMONS, M.A.. A.R.O.Sc, and L. J. JONES. R,'& M. No..1103 (Ae. 280). (9 pages and 16 diagrams.) April. 1927. Price Qd. net. Mainly for testing anemometers and small measuring instruments, a windtunnel of 1 ft. square section has recently been constructed which is capable of providing a wide range of wind speeds, up to a maximum of 14(1 ft./sec.Apart from the inclusion of an expansion cone similar to that adopted in the R.A.E. 7-ft. No. 2 tunnel,* the new tunnel is of the customary N.l'.I,. design. The low speeds are obtained by the introduction of a diaphragm platedrilled with small holes between the working section and the fan. Two plates are provided ; one to cover a range 0 to 3 ft. sec. the other from 2 to14 ft. sec. Measurement? of wind speed were made at a numlier of points in theworking section with a Pitot tube, over the range 20 to HO ft./sec. l''or speeds below 20 ft.'see other methods had to be employed ; tlie»e aredescribed at length in the report. Although no distributor was fitted, it was fuund that the airflow, as regardsdistribution and steadiness, compares favourably with that of oilier tunnels. At low speeds the difference of pressure between the two sides of thediaphragm plate is used to indicate the air speed. In addition to establish- ing the relation between this pressure difference and the speed, it was shownthat the Pitot factor does not vary seriously from OS over the ranae covered by the experiments. Scale effects were shown to exist at low s|>eeds for otherpressure measurements made during the course of the investigation. Observations of the rate of flow of smoke introduced into the tunnel,showed the presence of a critical speed in the neighbourhood of 0-7 ft.'sec. ; this figure agrees with calculations based on data derived from the flow ofwater in a small rectangular channel. * R. & M. 574.—Report on tests of a model of the proposed No. 'I 7 ft. wind tunnel at the R.A.E.—Sandison and Alfovd. FX-RTHEB EXPERIMENTS ON A MODEL OF THE " BANTAM " AEROPLANE WITH SPECIAL REFERENCE TO THE " FLAT " SPIN.—By H. B. Irving, B.Sc, and A. S. Batson, B.Sc. R. & M.'No. 1107 (Ae. 284). (26 pages and 12 diagrams.) June. 1927. Price Is. 3d. net. The present experiments bear chiefly on the maiKruvre known as the " flat " spin, and are a continuation of experiments on " Hantam," described in R. tf M. «76.» The incidence range of previous experiments has been extended fromabout 40" to nearly '.Ml0, and measurements made of the three moments due to rolling about the wind axis through the centre of gravity of the aeroplane.The contribution of the tail organs to these moments has l>een investigated in some detail. The effect of rolling on drag has been measured for thecomplete model and for body with tail. • R A M. 970. Some experiments on a model of a fi.A.T. " Bantam "Aeroplane with special reference to spinning accidents. Paris 1 and II.— Irving and Batson, Townend and Kirknp. 464g
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