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Aviation History
1926
1926 - 0052.PDF
SUPPLEMENT TOFLIGHT JANUARY 28, 1926 THE AIRCRAFT ENGINEER For a complete biplane Fig. 4 shows Vector diagrams of rolling moments against yawing moments tested under four conditions :— (1) With no front slot, flap angle 0°, ailerons - 20° and + 20°. (2) With front slot open, flap angle 10°. ailerons — 5|° and + 26°. (3) With front slot open, flap angle + 10°, ailerons — 20° and + 20°, with a portion of the front slot equal to the span of the aileron closed on the side with the ailerons — 20°. (4) With front slot closed and flap angle 0°, ailerons — 20° and + 20°, with a portion of the front slot open on the side with the aileron at + 20°. In comparing these different cases, a point of particular interest is the improvement in control of the slotted machine over the standard type when both are fitted with slot and aileron working in conjunction with one another. The result of the use of this section for the design of an aircraft can readily be seen. Unslotted, the section has a lift coefficient of 0-51 at 12|° ; slotted, the maximum lift coefficient is 1 at an angle of 17|°. For the same landing speed, therefore, a slotted wing machine with this section could have double the loading of the unslotted type. Alter- natively, with the same loading the landing speed would be reduced approximately 70 per cent. Most important of all Hz SCALE MODEL BIPLANE, WITH FRONT SLOT & SLOTTED FLAP. AIRSPEED 44FT.SEC. TUNNEL 4X4' X Front slor open', Flap angle +10° Port-Aileron -20° Porf control slot" closest, Stt>d. Aileron +20° Srbd control slot- open ^ .. .. » , » - +10", - -Sk' • • - open, - « +26* •• CS « ' closed, • O*, 20* - • - closed . © o*, -20° + 2O + 20' closed YAWING MOMENT COEFFICIENT = KN = —012 —010 —008 —006 —004 --002 0 —02 -04-1 —06 -08 -10 „ —-— -— _——* _——— •002 *1 N 4-PV2S2C •004- ife" •006 008 -010 -012 > / -—— G a L. ' /iff l£ « sa?— a.* Fig. 4. Rolling moments and yawing moments are given in coeffi- cient form and are in relation to body axis. The tests are directly comparative and can be taken as a true indication of the advantages to be gained from ''slotted control." Reviewing these tests, Case No. 1 represents an unslotted biplane with slotted ailerons at ^ 20°. The results in Fig. 4 show that the rolling moment increases from 4° up to 12C, then diminishes, and the yawing moment attains maximum at 18°. Thereafter there is a diminution in yawing moment accompanied by a slight diminution in rolling moment. This is a distinct improvement on the ordinary type of air- craft without slotted ailerons. This curve is plotted with the points at the different angles marked in the centre of a circle. Case No. 2 is shown on the curves with the points enclosed within triangles. Here again the rolling moment even at 24° is considerable, showing the improvement obtained by using slotted ailerons, the front slot in this case being open the whole way along the span. Case No. 3 is that of a slotted machine in which the slotted ailerons are used in conjunction with the forward aerofoil. The results are shown on the curve in which the points are marked by crosses. It will be observed that the yawing moment even at small angles is less than that in the other cases, and that from 16° it becomes rapidly negative, assisting the machine in the direction of the turn. With increasing angle also the rolling moment is increased, the rolling moment at 22° being nearly 0#08 against a rolling moment of approxi- mately 0-045 at 0°. Case No. 4 shows a similar result with front slot closed, the results being somewhat similar to Case 3. The points are indicated on the curves in squares. It will be seen that the rolling moment remains practically stationary, although the yaw at 4° has vanished. is the great increase in lateral control at the stalling speed. Attention is particularly drawn to Case No. 3, plotted on Fig. 4. in which a very big yawing moment helping the turn is obtained by the use of the slot and aileron control. Tests on the full scale with this section will shortly be carried out. Tests both for lift coefficient and rolling moments on a completely slotted machine with a loading of l>etween 12 and 13 lbs. sq. ft. with a slightly different section have given confirmatory results on the values of the lift as well as rolling and yawing moments. The mechanical details present no difficulties in construction. The forward aerofoil is made out of a single Duralumin plate carried on links from the front spar. Closed, the aerofoil rests against the leading edge and the section is a standard unslotted one. It is hoped that photographs and details of this may be published in a later article. USE OF METAL FOR AEROPLANE CONSTRUCTION. By F. M. GREEN, M.Inst.C.E., F.R.Ae.S. In the early days of flying the problems of aerodynamics so occupied the experimenter that he paid little attention to the finer points of construction. Materials that were easy to obtain and quick to work up were used, and as a consequence practically all the first aeroplanes were made of wood with a minimum of metal fittings. It was soon discovered that silver spruce could be obtained at a low price as there was very little other use for it, and that this kind of timber had the maximum advantages for aeroplane construction. Its specific strength was high, it could be obtained in long pieces, and it, is very straight-grained. Other forms of timber were used, and some of the early machines were made of bamboo. While this wood possesses the advantage of being hollow, it is difficult to join, and from the nature of the wood it would be impossible to make aeroplanes to drawing without using 4Sd
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