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Aviation History
1925
1925 - 0355.PDF
JUNE 11, 1925 In aerodynamic design of biplanes this country has, we think, nothing to learn from Germany. Cantilever biplanes were entirely unrepresented in the Round-Germany flight and the braced biplanes were of quite orthodox design ; indeed, one might even say old-fashioned, since plain stranded cables seem still to be used exclusively for the'wing bracing, and one did not observe a single instance in which streamline wires had been employed. In the Heinkel machines an attempt had certainly been made at reducing the biplane bracing to a minimum by giving the wings a stagger and using but a single set of bracing cables, but, otherwise, the majority of biplanes were of the orthodox single-bay type, with front and rear lift and anti-lift wires. In the matter of wing sections only a few monoplanes showed extremely great thickness, such as the Focke-Wulf and Junkers machines. A number of monoplanes were of medium-section cantilever type, but more often strut-braced, and in the biplanes one saw a few thin sections, no very thick sections, and, generally speaking, sections of medium thickness. A few of the wing sections were of the " Schouk- owsky " or " tadpole " type, which has been so thoroughly tested out at Gottingen, but these were seen on a relatively small number of machines, and the tendency seems to be more towards the flat-bottomed section of medium depth, something after the style of our Airscrew 4 or T.64 sections. stunt " flying, while in the case of commercial low-wingmonoplanes it was held that they would not in any case be " stunted " and that, therefore, this difficulty did not arise.While it is of course perfectly true that " stunting " is not one of the functions of a commercial aeroplane, there may easilybe cases where a machine accidently goes into a spin, such as when flying in fog or clouds, and in that case, of course, thesame disability would be present, although a large machine would presumably spin at a less violent rate. Whether therereally is anything in this contention or whether it is merely that control surfaces already on the small side are renderedless effective by the position of the main wing is difficult to say, and we merely raise the point here as one which is thecause of some concern in Germany at the present time. On the subject of wing flaps, fairly normal proportienswere, generally speaking, observed in the case of " normal " machines, but a not inconsiderable number made use ofmodern ideas on the subject of lateral control. This was particularly the case in the Heinkel machines, in which slottedailerons of the Handley Page type were employed, apparently with excellent effect. It might be mentioned that on theHeinkels the flaps did not run the whole length of the wing, but formed about the average proportion of the span. Inthe new Junkers low-wing monoplane (the type T.29) ailerons of very unusual type were employed. It was denied that this TWO OLD-TIMERS : On the left, the L.F.G., V.39, and on the right the Albatros L.30. Both machinesare fitted with 100 h.p. Mercedes engines and both are of 1914 design. On the vexed question of tails, one received the impression that the majority of German tails are still considerably on the small side. We are aware, that, generally speaking, the tails of British machines appear excessively large to foreign design- ers, but we think we shall not be accused of boasting if we claim that more work on the controllability near or above the stalling angle has been carried out in this country than any- where else, and it seems to us that German theory has failed to take this side of the question into account. In normal flying the German tails seemed adequate enough, but one seriously doubts their effectiveness at very large angles. It must be admitted that during our stay in Berlin we had no opportunity of seeing any slow flying, as the practice of the majority of pilots seemed to be to land their machines well above the stall, but on more than one occasion we did see machines " chasing their tail "on the ground which seemed to indicate that the rudder control, at any rate, was scarcely all that it might be. We gathered the impression that there is in Germany, apart from the distrust of the monoplane on structural grounds, a volume of opinion which considers that the low- wing monoplane is inclined to be dangerous on account of certain difficulties which have been found in getting machines of this type out of a spin. It was gathered that this was more particularly so with small machines that might be used for represented an attempt to obtain " slot effect," and probably this is strictly true since the effect obtained would seem to be more in the nature of tandem aerofoil effect, such as that obtained when two wing sections are placed close together with but a small opening separating them. Experiments carried out at the N.P.L. indicate that although extra lift is obtainable in this manner the increase is not of such a high order as that obtainable by the use of " slotted-wings " of the Handley Page type. One of our photographs shows a Junkers aileron and its mounting, and it will be observed that when a flap is pulled down its leading edge approaches the trail- ing edge of the main aerofoil. It should also be noted that on the aileron fittings a series of holes are provided by means of which the size of opening with flap full down is altered so that an easy means is provided for ascertaining the best slot size. On the small Mercedes-Daimler machines a combination of trailing edge flap and wing tip flap were linked together under the wing by cranks and pull-and-push rods in such a manner that the two flaps worked together, the trailing edge flap being directly operated from the controls while the wing tip flap was indirectly operated via the trailing edge flap. One of our photographs shows this aileron combination, which, apparently, has for its object the increase of the effectiveness of the trailing edge flap. As the Mercedes- 355
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