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Aviation History
1938
1938 - 1034.PDF
FLIGHT. APRIL 14, 1938. Close-ups of (left) the Retractableundercarriage and a section of the "double wing" of the D0.17 and(below) the somewhat unusualtail. unsymmetrical section with a projecting flange, the gauge of the metal being thinned at will throughout the length of each spar. There is thus a certain affinity between the Do. 17 wing and that of the Do.X. The girder-type spar bracing is by lightened dural members of broad channel section; the ends of these are flanged inward and are anchored on substantial plates. Main ribs are built up of duralumin channel sections; intermediate ribs have tubu- lar bracing. Fuel tanks are carried between the spars on the inboard sections. Fabric covering extends between the spars on the lower surface of the wing, the remainder of the wing having smooth metal covering with flush riveting. The trailing edge is of special formation to give a slotted effect to the flaps, which extend between the ailerons and fuselage; they have set-back hinges, and are operated mechanically. The slotted ailerons are of high-aspect ratio and incorporate trimming tabs. •-.'• •••'•.:. Fuselage Construction In section the slim fuselage starts off more or less oval, but quickly changes to a flat-bottomed structure which must be about twice as wide at the top as at the bottom, returning once more to elliptical and circular section as it nears the tail. Built-up frames and intermediate stiffeners are em- ployed in the fuselage construction, being notched to receive the channel-section stringers, the lips of which are flattened where required, at the intersection with a frame. The frames are most substantial, of course, in the vicinity of the wing. At the forward end of the fuselage the covering is applied in large formed panels. Trimming tabs and mass balances are incorporated in all the moyable tail surfaces .and the tailplane is (strangely enough, in such a fast machine) adjustable. This latter feature is probably necessitated by the marked change in fore-and-aft trim occasioned by the slotted flaps. -The twin fins (like the tailplane, metal-skinned) and aerodynamically balanced rudders are faired in at the extremities of the tailplane, which has holes to receive the mass-balance weights of the elevators. Power Plants -.- Do. 17s of the first series delivered to the Luftwaffe wet* fitted with two unsupercharged B.M.W. VI Prestone- cooled vee-twelves giving a maximum output of 750 h.p. apiece. The arrangement of the reduction gearing on these units results in an unfortunate cowling shape, the thrust line being well below the cylinder banks. With the Daimler-Benz (Mercedes) D.B.600 950 h.p. liquid-cooled inverted vees, as specified for later machines, performance and appearance are much improved. The radiator is mounted below the front portion of the crankcase. Three- bladed V.D.M. variable-pitch airscrews (as made in Eng- land by Constant Speed Airscrews, Ltd.) are fitted. As already explained, the Yugoslav machines ate powered with two-row Gnome-Rhone radials. These are fitted with N.A-C.A. cowlings of unusually long chord; " dishpan " crankcase cowlings and trailing-edge cooling flaps are features of this installation. Whatever the power plant, the undercarriage of the Do. 17 is always the same, each half retracting with a rearward motion into a nacelle and leaving a section of the wheel exposed. Retraction is effected hydraulically in the manner indicated in the accompanying drawings. The " clam shell " doors close and the tail wheel retracts during the final stage of the operation. For normal bombing duties a crew of three is carried^ being grouped in the forward part of the fuselage so that intercommunication is easy. In the extreme nose are transparent panels which give light for bomb sighting (Concluded on p. 368.) - The Do.i7 as powered with two Daimler-Benz D.B.600 inverted vee-twelves. This version is very fast indeed.
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