OVEMBER 2, I939 IP ©GOtf

The Dornier Do 215 as fitted with Daimler-Benz DB 601 engines. THE DORNIER Development and Characteristics of the Do 17 and Do 215 J.R By H. F. KING

NYONE who, like the writer, has browsed round the tarised /3:01, was a standard type until two Dornier "museum" at Friedrichshafen will agree or three years ago, after which it was relegated to training Ai that this old German company has a distinguished duties. historical background of metal-aircraft construc­ The Do 23 was a high-wing monoplane with a fixed under­ tion. For the past five years or so it has been building carriage and two B.M.W. VI upright vee-twelve engines. bombers and flying boats for the German Air Force; this The plan form of the wing was remarkable, as the leading article will review the former. edge had a marked curve while the trailing edge was Production and flying activities centre round Manzell, straight. At a flying weight of 19,3001b. the top speed Allmansweiller and Lowenthal on the outskirts of Fried- was about 160 m.p.h., which permitted manual operation nchshafen, though Dornier bombers have also been con­ of the gun mountings in the nose, on top of the fuselage structed in series by other German manufacturers, notably and below the fuselage, the upper mountings being unpro­ Henschel. tected. Dormer's first tangible contribution to German rearma By 1936 there were whispers of a very fast and efficient ment was the Do 23 which, together with the mili- bomber then being introduced. For a considerable time p @m NOVEMBER 2, IQ39

The spar booms are thick duralumin extrusions of unsymmetrical section with a projecting flange, the gauge of the metal being thinned at will throughout the length of each spar. Thus, there is a certain affinity between the wing of the Do 17 and that of the twelve-engined Do X flying boat. The girder-type spar bracing utilises lightened duralumin members of broad channel section, details oi this aircraft were completely secret, but when their ends being flanged inward and anchored on sub­ the first pictures appeared it was seen that, in side eleva­ stantial plates. The main ribs are built up of duralumin tion, the fuselage was extremely graceful. This charac­ channel sections, while intermediate ribs have tubular teristic, which caused the machine to be dubbed the bracing. Fuel tanks are slung between the spars on the "flying pencil," was accentuated by the long nose then inboard sections of the wing. fitted, though this feature as we shall see, was subsequently Fabric covering extends between the spars on the modified very considerably. lower surface, the remaining covering being smpoth, The various models of the Do 17 differ only in the design flush-riveted metal. of the nose, the installation of the military equipment The trailing edge is of special formation to provide a and the power plant, so that the following structural slot effect for the flaps, which extend between the description will apply in the main to all varieties. ailerons and the fuselage and have set-back hinges. The slimness of the fuselage is apparent only in side Flap operation is mechanical. The ailerons are likewise elevation; when seen in plan it appears quite normal, and, slotted and are of high aspect ratio. They incorporate in fact, in the centre portion unusually broad, due to the trimming tabs. sloping sides. The cantile'ver wing intersects the fuselage In section the fuselage starts in such a manner that the machine is best described as a off more or less oval, but quickly "shoulder wing" type, or what the Germans call a changes to a flat-bottomed struc­ schulterdecker. It is of two-spar design, the covering ture which is about twice as being part metal and part fabric. In plan form it is of wide at the top as at the characteristically low aspect ratio with a gentle taper and bottom, returning once more rounded tips. to elliptical and circular MOVESL^ft 2, 1939 0&@BR section as it nears the tail. wireless and D/F f-quipment. The top gun position corre­ Built-up frames and inter­ sponds roughly with the leading edge of the wing, and is mediate stiffeners are used adequatelv^^J ^At. The mounting itself is not power- in the fuselage construc­ operated tion, being notched to Nose 1 ^and several photographs have receive the channel-section appeared no front gun at all. The stringers, the lips of which Yugoslav ve fixed guns in the front are flattened where required cowling, but :andard German installa- at the intersection with a tion is a single starboard frame. The frames are most side of v the cc substantial, of course, in on can be clamped in a fixed poi pilot uses the vicinity of the wing. the ring and bead sights At the forward end the a free gun by the occupant of the s> erated as covering is applied in very " freedom " obtained must be very li: pugh the large formed panels. be made for a downward-firing gun to •• sion can On the extremities of the floor of the fuselage. ^k on the tailplane are the twin fins Bombs are carried horizontally in the b J and aerodynamically lage behind the plane of the front spar balanced rudders, the tail- opening the traps being in the fore part plane having holes to re­ where it is accessible to the pilot and bom ceive the mass - balance ternal racks may be attached to the sides of weights of the elevators. A typical bomb loading would be about 1,5001b. Each half of the under­ carriage retracts hydraulic- Nose Design ally with a rearward motion The first Do 17, as already stated, had a long, pointed into an engine nacelle, leav­ nose without transparent panelling. Next came two modi­ ing a section of the wheel fied designs, one hemispherical (this was adopted as, exposed, though "clam­ standard for aircraft of the ) and one longer and shell" doors fair off the more angular with transparent panelling in the lower bottom of the nacelle. The section. The latter was used on the first Do 17 prototype tail wheel retracts during to be fitted with Daimler-Benz engines and on the Yugoslav the final stage of the dis­ machines. appearance of the main Do 17s of the first series delivered to the Luftwaffe were gear. fitted with two unsupercharged B.M.W. VI prestone-cooled For normal bombing engines, giving a maximum output of 750 h.p. apiece. duties a crew of • three is These units did not lend themselves well to a good nacelle carried, being grouped in entry, the thrust line being well below the cylinder banks. the forward part of the fuse­ With the Daimler-Benz DB 600 inverted-vees as specified lage. The pilot's seat is off­ for later machines smoother lines were obtainable. In both set to port and should cases the radiator is mounted below the crankcase. The permit changing pilots in standard airscrew is a three- flight. Internal equipment bladed variable-pitch V.D.M. which one noted in a Ger­ With the unsupercharged man Air Force machine at B.M.W. engines performance Allmansweiller includes an was quite low, the top speed automatic pilot, two-way near the ground being only

Above is a Flight copyright study of the " business end" of a Daimler-Benz-powered Do 215. Below is the Do 17. This drawing is based on one executed by Max Millar at the Dornier works. November 2, 3Q

A Do 215 as powered »;«. radials which may be B M W 132 Dc's or Bramo Fafnirs

and undercarriage of thi machine are similar to those of the earlier model I Hit the accommodation of the has been revised. crew

Like the Do i7, the new machine can be fitted out as a short-range heavy bomber- a long-range machine with a smaller bomb load; for lone- distance reconnaissance; for ground attack work and even as a fighter, though it is not used in the latter guise in the German Air Force. It may be distinguished from the Do 17 by the '' swollen '' nose sec­ tion which accommodates the crew. The extreme nose portion is composed of "facets" of transparent material which not only light the bomb aimer's position but improve about 235 m.p.h. The introduction of the B.M.W. 132DC the pilot's view in a forward and downward direction. In and Bramo Fafnir radials gave a much improved perform­ this respect the machine bears a marked resemblance to ance as, of course, did the fitting of the Daimler-Benz the "short-nosed" version of our own DB 600s. Unlike the Blenheim, however, the Do 215 has its pilot's Although the Dornier concern has been fairly liberal in windscreen and cockpit enclosure external to the main lines releasing structural particulars, performance and weight of the fuselage. Actually, this cockpit enclosure is data are very scanty and, for that matter, on the optimistic extended aft to a point just above the leading edge of the side. The following figures might apply to the machine as wing and terminates there as the upper gun position. On fitted with two Daimler-Benz DB 601 engines. Standard the underside the nose portion extends aft to a point just service aircraft would not be so efficient: Disposable load, forward of the leading edge and there embodies with the 6,6oolb. ; service ceiling, 29,500ft.; maximum speed, 310 lower gun mounting. m.p.h. ; range, 1,550 miles. In all there are three machine guns, one protruding With the exception of length, the following dimensions through the starboard panel of the windscreen, the second are common to all Do 17 models: Span, 59ft.; length, on a manually operated pillar-type mounting in the upper 55ft. 6in. ; wing area, 592 sq. ft. position already mentioned, and the third (in a hemi­ spherical mounting) firing below the fuselage. Do 215 Bomb stowage arrangements are similar to those on the Shortly before the war the Dornier Company announced Do 17, the horizontally stowed bombs falling through two the development of an improved version of the Do 17, sets of trap-doors in the flat-bottomed fuselage. which, for some obscure reason, bore the works number In addition to the pilot there is the bomb-aimer, who can Do 215. The wing, fuselage, tail, power plant installation use the "windscreen" gun as a free weapon, and two other members of the crew who look after navigation and wireless and man the upper and lower rear gun positions. The upper gun is fired from the sitting position, but the lower one is operated from a kneeling attitude or with the gunner lying prone on the floor. Three types of engine are normally specified. Two oi these are radials—the B.M.W. 132 Dc and the Bramo NOVEMBER 2, 1939 fflP®R 351

The obliterated markings indicate that this Do 17 (B.M.W. VI's) was taking part in manoeuvres.

Fafnir and are installed in the usual long-chord cowlings and the range 1,860 miles. Despite the fact that the wing with controllable gills. The best performance is obtained loading is higher (about 32 lb. /sq. ft.) it is claimed that the with Daimler-Benz DB 601 inverted vee-twelve liquid- landing speed is the same as that of the Do 17 (68 m.p.h.); cooled units, but in view of the poorer streamlining of the this is particularly surprising as split flaps have been fitted aircraft in comparison with the Do 17, it is difficult to see in place of the original slotted flaps. The top speed figure why the speed, even with these power plants, should be is optimistically published as 500 km./m. (310 m.p.h.), but as high, or higher, than that of the Do 17, as claimed. this, like other data, must be presumed to have originated Figures issued just prior to the war indicate that the in the Dornier publicity office rather than the technical all-up weight is 18,960 lb., the disposable load 7,270 lb., department.

it is calculated that , which last year produced 130,000 Death of Lt.-Coi Muirhead • tons of aluminium, stored during that period some 680,000 tons E regret to have to record the death of Lieut.-Col. A. J. of ore. Much of this, which in any case cannot meet the W Muirhead, M.C., M.P., late Parliamentary Under- tremendously increased war demand, is used in German Secretary for Air. He was found dead in his bed on October warship construction and, of course, general armaments 29. Born in 1890, he was educated at Eton and Oxford. production. During the last war he served in France and Italy with the Oxfordshire Yeomanry, was mentioned in despatches three times, and won the Military Cross and Bar. In 1929 he R.Ae.S. and the War entered Parliament as Conservative Member for Wells. T the outbreak of war, the Council of the Royal Aero­ In 1931 he became Parliamentary Private Secretary to the A nautical Society had to make important decisions concern­ Minister of Agriculture, and afterwards served in the Ministry ing the general policy of the Society. The archives of tht, of Labour. In 1937 he succeeded the late Sir Philip Sassoon Society have been moved to a place of safety in the country, as Under-Secretary for Air, and last year introduced the Air but No. 4 Hamilton Place is kept open and Capt. Pritchard, Estimates. In May last year he was transferred to the same the Secretary, remains in charge. Some of the rooms, includ­ position in the India and Burma Office. On the outbreak of ing the library, are available for the use of members and it is war he took up his duties as Commanding Officer of the 100th hoped that they will make as much use as possible of No. 4 (Worcestershire and Oxfordshire Yeomanry) Army Field Hamilton Place. Brigade, R.A. He had gone to his home for the week-end, and died before rejoining his unit. Col. Muirhead was The lecture programme for the session has, of course, been unmarried. cancelled, but the Wilbur Wright lecture will be given in May of next year. In a letter to members of the Society, the President, Mr. Germany's Aluminium Supplies A H. R. Fedden, expresses the thanks of the Society for the T'HE seizure by the British Navy recently of 15,500 tons generosity of a large number of members of the aircraft and •*• of alumina as contraband bound for Germany focuses allied industries which has enabled the sum of ^106,204 to be attention on the extent to which the Reich is dependent on collected. A complete list of the subscriptions towards the foreign supplies of this metal, which is vital to her aircraft funds of the Society will be published in the November issue industry. of the Journal of the Society. Germany, the largest consumer of aluminium among world Powers in J93gr had to import almost all her supplies of bauxite, the ore from which the metal is.obtained. Compared Personal Insurance «th a total of nearly 1,200,000 tons imported last year, rather ROM Capt. A. G. Lamplugh we learn that the British less than 18,000 tons were home-produced in Germany. About F Aviation Insurance Co., Ltd., has received a number of 0 per cent, of these imports came from Tugo-Siavia and enquiries from holders of personal accident policies who have undertaken some form of Service flying obligations and who Important supplementary supplies of bauxite were imported are anxious to know their position in respect of insurance. ™" the Dutch East Indies (190,000 tons), France (90,000 He points out that although obviously normal aviation per­ tons), and GGreec e (83,000 tons). Italy last year exported sonal accident insurance cannot be extended to include the onl„y 9o,°00 tons to Germany. risks of death or injury in action, many pilots, particularly imnt6' air f?rce is' therefore, faced with a considerable among the older pilots with dependants, have undertaken of coTiate ret!uc*'on °f her resources of aluminium, which is, duties which do not involve actual combat risks. It has been speed • Umversally employed in the construction of high- decided in fairness to such pilots that, subject to particulars $gl 1: aircryft, and without which adequate replacement of of the type of flying involved being supplied, the normal scope P is serioush tons~ofD • / impeded. On the basis that four of the personal accident policy may be extended to cover uxite are required to produce one ton of aluminium, Service flying, probably at a small extra premium.