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Aviation History
1938
1938 - 1030.PDF
FLIGHT. APRIL 14, 1938. The striking general arrangement of the Do. 17 as fitted with Gnome Rhone 14N0. engines for Yugoslavia. The wir4g, it will be noted, is of fairly low aspect ratio. tained at Manzell, but this I was not shown. By the water's edge is a '; •• ' / ' •-•- great hangar wherein the flying boats are assembled and lifted out by a travelling gantry on to the bosom (not always so gentle) of Constance. From across the lake came the mumbling of twin Diesels in a Do. 18 of the type which I was able to examine in de- tail within the hangar. The Do. 18 is generally regarded as a civil machine, and was, in fact, originally pro- duced as a long-range mail carrier for Luft Hansa's South Atlantic service—in which sphere one example has recently distinguished itself by a 5,220-mile record. But the machines I saw belonged to a large order for the Luftwaffe (German Air Force), which has standardised on the type for long-range reconnaissance and bombing. Gun rings are fitted in the bow and aft of the wings, but turrets are not demanded by the comparatively low performance, the top speed with two 560 h.p. Jumo 205 Diesels being rather less than 160 ;n.p.h. Where the Do. 18 does score, however, is on range ; with the small wing panels, as fitted to the boats I saw, the figure is about 3,200 miles; larger wings, permitting an all-up weight of 24,200 lb., allow tankage for 400 miles more. For military service the boats will not normally have the assistance of a catapult, as do the Luft Hansa machines, but take-off is aided by three-bladed V.D.M. variable-pitch airscrews. The general nature of the Do. 18 is already known to readers, but there are several points worth emphasising. Spaced a surprising distance apart and mounted back to back, the two slab-sided Jumos have their thrust lines set at different angles. The front unit is horizontal, but its companion is tilted downward quite sharply at the rear, so that its propeller, driven through a long shaft mounted in a tunnel, is at an angle to the hull. This arrangement gives a good sweeping nacelle line, and, of course, directs the Below are details of the wing construction of the Do. 17 showing the use of extruded sections. On the right is a fairly representative piece of fuselage construction. slipstream efficiently on to the tail surfaces. The Diesels seem to start quite easily (as, indeed, they should, after such long de- velopment), albeit with a great grinding noise, for the two six-throw crank- shafts are connected by a train of gears down the front of the crankcase. Like Junkers, the Dornier company is a confirmed user of the '' double wing,'' the inner sections of which are lift flaps, while the outer, or aileron portions, are differenti- ally operated. This feature is common to all modern Dornier multi-engined types. As there are no outboard engines, the Do. 18 needs two water rudders at the end of the second step. There is a fore-and-aft step on each side of the keel. The trailing edges of the sponsons finish astonishingly sharply, though the leading edges and tips are well faired. I was disappointed in not seeing a complete Do.24 boat as now being supplied to the Dutch Government, for this machine has exceeded all expectations—which expecta- tions, as I learned in Holland some time back, were very high. Unlike the Do.18, in which the wing is supported on a faired superstructure, housing, among other things, the radiators, the three-engined Do.24 has strut bracing be- neath the central nacelle, though the structure of the wings and sponsons is generally similar. The hull, too, follows modern Dornier practice, but noticeable differences are the twin fins and rudders, tail gun position and cupolas (exter- nally reminiscent of that on the Blenheim, though more angular) for each of the three gunners. Wright Cyclone G radials (850/1,000 h.p.) are specified for the Dutch boats, but I heard of a special version for the German Navy with' different power plants. In addition to the slotted flaps (which also serve as ailerons) on the outboard wing panels there is a split flap on the centre section. A top speed of over 200 m.p.h. is attainable; other data are: all-up weight, 29,760 lb. ; wing area, 1,162 sq. ft.; and range over 2,100 miles.
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