Flight, October 1921

THE DORNIER "DRAGON FLY" FLYING BOAT

   FROM time to time we have published descriptions and illustrations of the various products of the Zeppelin firm built to the designs of Herr Dornier: ("Some Dornier Milestones," December 16, 1920; the C.III monoplane, March 31, 1921; the Cs.II monoplane flying boat, April 21, May 21, and June 9, 1921). This week we are able to give some illustrations and a few particulars of Herr Dornier's latest design, a small, low-powered, three-seater monoplane flying boat.
   The "Dragon Fly," as this machine is called, was constructed at Rorschach, on the Swiss side of Lake Constance (where a new factory has been formed by the Dornier Metal Aircraft Mfg. Co.), and it is, we believe, being used, by the Swiss Society Ad Astra Aero at Zurich and Geneva. It will be seen from the accompanying illustrations that the "Dragon Fly" possesses a pleasing and at the same time practical appearance. Also, several distinctive features of characteristic Dornier stamp may be noticed. The most prominent of these are the aerofoil-floats projecting from the sides of the hull, which take the place of the wing tip floats, and have the advanatage of contributing to the lift, instead of adding to the resistance, of the machine.
   As in previous Dornier models, the "Dragon Fly" is almost entirely of metal construction, duralumin being employed not only for the hull, but for the wings and wing covering as well. The wings are of the semi-cantilever type, without dihedral or sweepback. They are, unlike the wings on the previous Dornier boats, built up in three sections and are made to fold back - a useful feature not often to be found in connection with flying boats. A short centre section, no wider than the hull, is mounted above the latter on a cabane of four struts; the outer sections are mounted to this centre section, being hinged at the rear spar roots.
   Built up with the centre section is a streamlined housing for the engine and fuel tanks. The outer wing sections are braced to the hull by a pair of streamline struts each side. When the wings are folded back, the front struts are disconnected at the attachment to the hull, and are secured to a lug on the lower extremities of the rear struts. The attachment to the hull of the rear struts is, of course, of the swiveling type. It will be seen, therefore, that the wings are supported by the struts when the wings are folded right back. The folding operation is easily accomplished in about one and a half minutes, and it takes about a minute longer to extend them ; both operations can be carried out whilst the boat is on the water, and, furthermore, it is claimed that once erected the wings do not require any trueing up. With the wings folded it is stated that the "Dragon Fly" manoeuvres on the water as easily as a motor boat.
   In order to make room for the inner rear corners of the wings, when folded, the rear portion of the centre section aft of the rear spar either folds down out of the way, or is removed entirely - on which point we have no definite information, but it is probable that this portion is covered in with fabric when the wings are extended which is detached when the wings are folded. The ailerons are not hinged to the rear spar, but to auxiliary members between the latter and the trailing edge.
   The tail plane is of narrow rectangular plan form, fabric covered, to the trailing edge of which is hinged a one-piece elevator. A balanced rudder hinged to a vertical fin, both fabric covered, are mounted above the tail plane.
   The metal hull is of rectangular section, with a single step located below the position of the rear wing spar. It tapers to a shallow vertical knife-edge at the stern, and has a pronounced V at the bows and a shallow V rearwards from the step. A roomy cockpit is provided for the three occupants immediately below the wings, two seats being located in front, side by side, with dual control, and the third seat behind.
   In the model illustrated a 50-60 h.p. 5-cylinder radial air-cooled Siemens-Halske engine is fitted, but in subsequent models a 7-cylinder 80 h.p. engine of the same make will be fitted. The engine, as previously mentioned, is mounted in a streamline housing on the centre section, in front of the leading edge, and drives an 8-ft. diameter tractor screw.
   The "Dragon Fly," it appears, has a good performance, and handles very nicely. With the 50-60 h.p. engine, three on board and fuel for one hour's flight, it comes "unstuck" in about 30 seconds. The principal characteristics are as follows :-
   Span 27 ft. 7 ins. (folded, 10 ft.)
   Chord 5 ft. 5 ins.
   O.A. length 23 ft. 6 ins.
   Height 7 ft. 5 ins.
   Area of wings 150.5 sq. ft.
   Weight (empty) 770 lb.
   Weight (full load) 1,320 lb.
   Weight/sq.ft. 8.8 1b.
   Weight/h.p. 22 lb.
   Speed 80 m.p.h.
   Factor of safety throughout 8.

Flight, August 1923

GOTHENBURG International Aero Exhibition 1923

   Dornier-Metallbauten G.M.B.H., Friedrichshafen a.B. - As one of the pioneers of German all-metal construction, Herr Dipl. Ing. Claudius Dornier occupies a somewhat unique position in German aeronautics. The Dornier-Metallbauten company is an offshoot of the Zeppelinwerk Lindau, and its origin is traced back to the days before the War, when the late Count Zeppelin founded the Seemoos factory in 1914. This factory was intended to be, and so remained, a huge experimental laboratory for the production of aircraft on novel lines. Even during the War Herr Dornier, who was in charge of the Seemoos factory, was allowed to continue his research work and was in the enviable position of not having to worry over much about commercial problems, the proprietors taking a long view and making up their minds that this particular factory should experiment with the future, rather than with the present, in view. Thus Herr Dornier has been able to develop methods of construction entirely his own, and some time after the War the name of the Zeppelin-Lindau works was changed to the present title of Dornier-Metallbauten G.M.B.H. The peculiar features of Dornier construction are that high-tensile steels are used for all heavily-stressed parts, while the rest is made of smooth Duralumin sheet. All joints are made either by riveting or by bolts. Welding and soldering is not used at all in any of the Dornier machines.
   At the present moment three different types of commercial machines are being produced in quantities at the Seemoos factory. These are: the "Komet," a tractor monoplane land machine, which is not unknown to habitues at Croydon; the "Delphin," commercial flying boat; and the "Libelle" sporting type of flying boat.
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   The two machines shown on the Dornier stand were the "Delphin" and the "Libelle," both monoplane flying boats of all-metal construction. Photographs of both these types, as well as of the twin-engined "Wal," were published in our issue of July 26, 1923.
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   The Dornier "Libelle" (Dragonfly) is a low-powered flying boat monoplane intended for sport and touring. It is fitted with a Siemens radial engine, which can be either of the five-cylinder 60 h.p. or the seven-cylinder 80 h.p, type. Seating accommodation is provided for three, of whom two sit side by side in front, and a third occupant immediately behind them. Dual control is provided, the two sets being placed side by side, so that the machine lends itself particularly to school work.
   In general construction the "Libelle" resembles the "Delphin;" i.e., all highly-stressed parts are of steel, and the rest of Duralumin. It should be noted that tubular members are entirely absent in all Dornier machines, with the exception of the wing struts, which are streamline steel tubes. The parts which are not plain sheet metal (such as the boat and wing covering) are rolled or drawn to shape from the flat sheet. The number of rivets used is prolific, and as riveting is one of the most expensive jobs in metal work of this kind it might have been thought that this form of construction would prove rather expensive. We understand, however, that the "Libelle" takes but a relatively small number of man-hours to build, probably owing to the long experience and good organisation of the Seemoos factory.
   In order to facilitate storage, the wings of the "Libelle" are made to fold. For this purpose the trailing edge of the centre-section is removed, and when the bolts in the front spars are removed, and the wing-struts cast off, the wings fold back and are locked in position by the simple fittings illustrated in our sketches. The lower ends of the wing struts are then secured on the rear strut fitting. The whole operation can be carried out in a few minutes.
   The characteristics of the Dornier "Libelle" are: Length o.a., 7.15 m. (23 ft. 5 ins.); width with wings folded, 3.2 m. (10 ft. 6 ins.); height, 2.4 m. (7 ft. 10 ins.). When fitted with the 60 h.p. engine the weight empty is 390 kg. (850 lbs.) and the useful load 250 kg. (550 lbs.); the maximum speed is then 130 km. (80 m.p.h.) and the cruising speed 100 km. (62 m.p.h.). With the 80 h.p. Siemens engine the weight empty is 450 kg. (1,000 lbs.) and the useful load 300 kg. (660 lbs.). The maximum speed is 155 km. (96 m.p.h.) and the cruising speed 120 km. (74 m.p.h.).

Flight, August 1924

A FLYING BOAT ON WHEELS
The "Dornier Sparrow"

   AMONG the lower-powered types produced by Dornier-Metallbauten G.M.B.H., of Friedrichshafen, the "Dragonfly" (Libelle) is already familiar to readers of FLIGHT. One of these machines was exhibited at Gothenburg last year, when it was fully described. The "Dragonfly" is, of course, a flying boat of low power, carrying two passengers in addition to the pilot. The Dornier Co. has now introduced a very similar type, known as the "Sparrow" (Spatz)), for use as a school machine. The "Sparrow" is, however, an aeroplane, and so far as can be ascertained is merely the "Dragonfly" with wheels substituted for the small wing roots which in the flying boat type give lateral stability on the water.
   As in the case of the "Dragonfly" the construction is entirely metallic, even to the covering. Highly-stressed parts are made of steel, while the rest of the structure is in the form of duralumin members of various sections. Owing to the resemblance to the "Dragonfly" no detailed description of the "Sparrow" appears necessary. Following are, however, the main characteristics: Length over-all, 6-9 m. (22 ft. 7 ins.; span, 9-8 m. (32 ft. 2 ins.); height, 2-8 m. (9 ft. 2 ins.); wing area, 14-2 sq. m. (153 sq. ft.). Weight empty, 445 kg. (980 lbs.); useful load, 275 kg. (605 lbs.); total loaded weight, 720 kg. (1,585 lbs). Power loading, 20 lbs./h.p.; wing loading, 10-35 lbs./sq. ft. Maximum speed at sea level, 141 km./hour (87 1/2 m.p.h.); cruising speed, 120 km./hour (74 1/2 m.p.h.). Petrol consumption, 18 kg. (39-6 lbs.) per hour. Ceiling, 3,500 m. (11,500 ft.).
   The engine is a Siemens seven-cylinder radial air-cooled of about 80 h.p., mounted above the wing and driving a tractor screw.