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Aviation History
1923
1923 - 0474.PDF
THE D.H.50 : View of the cabin. Note the absence of wire bracingon the starboard side. is a well-known fact that it is not possible to land the majorityof machines at their absolute minimum speed, owing to the controls becomiflg " sloppy " at low speeds. In other words,lack of controllability prevents full use being made of the speed range of which the machine is capable. In the D.H.50it appears that a very marked improvement in this respect has been effected, and that this type will come much nearerto the ideal than even its designers had expected. The natural question that will be asked, as the generalappearance of the machine does not at once indicate the Teasons for this all-round improvement, is : Which are thecauses that have contributed towards making the D.H.50 not merely a good machine, but something considerablymore than that ? The answer must be that no one feature of the design is responsible, but that the improvement is due tothe cumulative effect of a number of things. For instance, as regards the reduction of 100 lbs. in weight which has beeneffected, this is the result of the most painstaking care in detail Structural design. Thus, by way of an example, it may bementioned that the fuselage has " bulges " on the sides to give " elbow room." By making the fuselage itself narrowerby the extent of the " bulges " something like 4 ins. in the width has been saved, with consequent reduction in fuselageweight. This is only one item ; a number of others could be mentioned but this will serve as an example of the attentionwhich has been given to detail, and which has resulted in such a considerable saving in structure weight. As regards the aerodynamic reasons for the improved performance, and the vastly improved controllability., it is AUGUST 9, 1923 more difficult to get at the facts. To beginwith, the fuselage, with its small nose radiator and enclosed cabin top, is much " cleaner "than that of the D.H.9, giving the air, one may assume, a more undisturbed flow. Thenthere is no cut-out in the trailing edge of the top plane, nor any cables running alongthe leading edge, nor any wing flap cranks projecting upwards on the upper surface, sothat here again the air flow is probably greatly improved, with resultant improve-ment in the aerodynamic efficiency of the machine. The improvement in controllability is due,in the first place, to the de Havilland patented type of differential ailerons, inwhich system the upward-moving flap travels through a greater angle than that movedthrough by the corresponding downward- moving flap on the opposite side. Thissystem of aileron control is not, however, in itself sufficient to account entirely for thebetter controllability, which must be partly due to other causes, connected, probably,with the generally cleaner air^flow over the wings. The degree of differential movement,and the area and shape of the ailerons, play an important part, and perhaps the best onecan do is to say that here is one of those cases where a machine has come out" right " from the first. Any designer knows that this occasionally happens, and that onecan never be quite certain beforehand whether it will or will not happen. In this case there is not the slightest doubtthat the machine is exactly "right," and one can but congratulate the designers on their achievement. Considered as a commercial machine, the D.H.50 is intendedfor use on " feeder " lines, where the employment of a larger machine is not justified by the volume of traffic, or as a" taxi-plane " in place of the D.H.9's, which have hitherto been employed for this purpose with such remarkable success. THE D.H.50 : Tail and tail skid. THE D.H.50 : Three-quarter rear view. 474
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