Exo Cruiser: The Dornier Do. X

Dornier Do. X at the Bodensee (Lake Constance), at the left Dornier-Werke GmbH factory buildings at Altenrhein Switzerland near Austria-Germany-Switzerland border crossing

THE DORNIER DO. X

First Authentic Data and Particulars /1/

"RARELY in the history of flying has a machine so captured the imagination as has the large Dornier flying ship, the "Do. X". The size is beyond anything previously accomplished; the lines of the machine are unusual; and the power plant arrangement is novel. Ground enough surely, for being intrigued, and for wishing "to know all about it." FLIGHT has published illustrations of the Do. X on more than one occasion. and has commented editorially on its main features. Hitherto, however, the necessary authentic data have not been forthcoming, in the absence of which it has been a little difficult to form a true picture of what the Do. X is, and what it really means.

Do. X close to the water, LW and MW aerial visible.

We have now received from Dornier Metailbauten of Friedrichshafen on Lake Constance, a small booklet in which is set forth an account of the underlying ideas of the Dornier engineers in producing this machine, details given of the construction, and accurate data supplied concerning such items as dimensions and areas, weight. performance. etc. Thus we feel that we are better equipped to deal with what is the most interesting design of modern times, and that FLIGHT readers will not mind - in fact, will wish us to - if we return once more to the subject of the Do. X.

Dr. Claudius Dornier

Dr. Claudius Dornier, like Dr. Rohrbach, began his aeronautical career with the Zeppelin company, and during the early days, when Rohrbach and Baumann were designing the large four-engined Zeppelin Staaken monoplane which, as a result of gross stupidity, was later destroyed because of certain clauses in the Treaty of Versailles (1919), Dr. Dornier began to occupy himself with the subject of seaplanes and flying-boats.

Zeppelin-Staaken E-4/20 maybe the first 4-engined all-metal heavier-than-air aircraft ever built.

[At a time when most aircraft were small single-engined biplanes made of wood and canvas, the E-4 was a large - 102-foot wingspan all-metal four-engined stress-skinned, semi-monocoque, cantilevered-wing monoplane with enclosed cockpit, accommodation for up to 18 passengers plus crew, including 2 pilots, radio operator, engineer and steward as well as full radio-telegraph communications, toilet, galley and separate baggage and mail storage.] /3/

Prof. Alexander Baumann, Chief Designer of Zeppelin Staaken factory during WW I.

[At the start of World War I, Ferdinand von Zeppelin brought Baumann into the Versuchsbau Gotha-Ost (VGO) consortium to design, develop, manufacture and test Riesenflugzeug ("giant aircraft"), a type to be larger than the Gotha G bombers. The first Riesenflugzeug built was the VGO.I in April 1915. Baumann, an expert in light-weight construction techniques, placed the four engines in nacelles mounted between the upper and lower wing decks to distribute the loads to save weight in the wing spars.

The follow-on VGO.III prototype, a 3-engine open cockpit bomber, produced greater power and validated the soundness of the basic design. Baumann designed and developed three successors, including the Zeppelin-Staaken R.VI, which became the largest bomber produced in quantity by the Germans in World War I.

The Wilhelm Cross with Swords and Crown was awarded 108 times, the Wilhelm Cross with Swords 5,329 times and the Wilhelm Crosses without swords just 1,943 times. A very good example of a relatively rare award.

For his achievements, Baumann was awarded the Royal-Württemberg Wilhelm Cross without Swords (Königlich-Württembergisches Wilhelmkreuz ohne Schwerter) in 1917.] /3/

Dornier Machines until 1920

Dornier produced, first as chief designer at the Zeppelin Lindau works and later as head of his own company, a series of flying-boats, the earlier types of which those sufficiently interested may find described in FLIGHT of December 16 and 23, 1920.

[1914 wurde für den Zeppelin-Mitarbeiter Claude Dornier, der 1910 in die Firma eingetreten war, die Abteilung DO in der Luftschiffbau Zeppelin GmbH gebildet, um im Auftrag von Graf Zeppelin große Ganzmetall-Flugboote zu bauen. 1916 wurde diese Abteilung in die Zeppelin GmbH Lindau eingebracht, die später in Dornier Metallbauten GmbH umfirmierte und 1932 aus dem Zeppelin-Konzern ausschied.]

Dornier-Werke manager Paul Berner (with the hat), workers and visitors standing on the Do. X stump wing.

Quite early in his career Dr. Dornier adopted short wing stumps springing from the sides of the boat hull for obtaining lateral stability on the water. In one early example, the Do. Rs. II, these stumps were braced by struts from below, and they must have caused the machine to be very "dirty" on the water.

Zeppelin (Dornier) Rs II

In those early days, too, the tail surfaces were carried either on boom outriggers or on a fuselage placed high above the hull.

Dornier Gs I (1919)

In the Gs. I, produced in 1919, Herr Dornier for the first time carried his tail surfaces on the main hull, which was extended right aft instead of the rather short sort of " Bat boat " hull which he had previously favored.

Dr. Adolf Rohrbach died suddenly at the age of 51 similar to Ernst Udet, Hans Jeschonnek and Erwin Rommel in a bit mysterious circumstances in Germany under Nazi influence.

[Flight Magazine, GB, July 1939

Obituary

AVIATION circles the world over learned with deep regret of the death in Berlin last week of Dr. Adolph Rohrbach, the famous German aircraft designer, at the early age of 51. Dr. Rohrbach's aeronautical career dates back to the early days of flying. For a period both he and Dr. Claude Dornier were in the employ of the Zeppelin company, and while Dornier specialised, at quite an early date, in the design of flying boats, Rohrbach concentrated on landplanes, of which he designed a considerable number of types. He was always rather ahead of his time, and it should be placed to his credit, now that he is no longer among us, that as early as 1917 he designed the big four-engine Zeppelin-Staaken cantilever monoplane, which was possibly too far advanced for the time, but which would not look out-of-date at the present time.]

In the Do. Gs. I the wing stumps had become pure cantilever members; and, furthermore, the main wing lift struts were anchored to the tips of the stumps. The power plant consisted of two water-cooled engines in tandem, placed above the monoplane wing. From this machine developed as a logical outcome the Dornier Gs. II, the Wal, and the Superwal, gradually increasing in size and power, but retaining all the fundamental features of the Gs. I.

Dornier Wal

From that machine, therefore, may be said to date Dr. Dornier's real programme of flying-boat development, and the Gs. I is the ancestor of the long series of boats which has now culminated in the production of the Do. X. No other flying-boat designer in the world has had the opportunities of Dornier, who, already during the war, was not expected to turn out military aircraft which must be immediately successful, but who was given more or less a free hand to prepare for the future by evolving commercial flying-boats.

Dornier-Werke GmbH under construction 1926 at Altenrhein, Switzerland (near Lindau), the home of the Do. X flying boat.

We have dealt with this phase of Dr. Dornier's work at some length, because only if one knows something of his earlier history can one obtain the correct perspective for judging his latest work. We believe we are correct in stating that altogether Dr. Dornier has produced no less than 28 types (not all flying-boats).

Dornier Do. X engine test setup at Altenrhein Dornier Works

Before the actual work of designing the Do. X could be started, a large number of theoretical and scientific investigations had to be made because, although it was not desired to introduce any unknown features where it could be avoided, the very size of the projected machine called for much work in determining the most economical type of structural members, and so forth. This preliminary work was begun in 1924. In December, 1927, actual construction was commenced in the new works at Altenrhein. The first test flight was made on July 12, 1929.

Dornier-Werke GmbH, Altenrhein Switzerlan, 1928

The Dornier Do. X with 12 Siemens-Jupiter 525 h.p. Engines

Weights:
Tare Weight (stripped) - 28.2 tons ( 62,100 lbs.)
Tare Weight (equipped) - 30.0 tons ( 66,000 lbs.).
Gross Weight (normal) - 46.0 tons (101,200 lbs.).
Gross Weight (maximum) - 52.0 tons (114,400 lbs.).

Dimensions:
Length o.a. - 40.05 m. (131 ft. 4 in.).
Wing Span - 48.0 m. (157 ft. 5 in.)
Height - 10.25 m. ( 33 ft. 7 in.).
Wing Chord - 9.5 m. ( 31 ft. 2 in.).
Total Wing Area - 486.2 sq. m. (5,225 sq. ft.).
Max Beam of Hull - 4.8 m. ( l5 ft. 9 in.).
Beam over Stumps - l0.0 m. ( 32 ft. 10 in.).
Total length of Cabins - 23.5 m. ( 77 ft.).
Mean Width of Cabins - 3.2 m. ( 10 ft. 6 in.).

Fuel Capacity
In Hull, 4 tanks at 3,000 l - 12,000 l. (2,640 gals.).
In hull and leading edge 4 - 4,000 l. ( 880 gals.).
Normal Capacity - 16,000 l. (3,520 gals.).
Further tanks can be added of - 8,600 l. (1,890 gals.).
Max. Petrol Capacity - 24,600 l. (5,412 gals.).

Oil Capacity
6 tanks at 100 l. in nacelles - 600 l. (132 gals.).
1 tank in hull - 1,300 l. (286 gals.).
Total Oil Capacity - 1,900 l. (418 gals.).

Performance
Max. Speed (according to engines fitted) - 210-230 km./h. (130-143 m.p.h.).
Cruising Speed - 170 km./h. (105 m.p.h.).
Duration (normal capacity) - 12 hrs. at cruising speed.

Dornier Do. X was about half the size of Spruce Goose and modern jumbo jets

Aerodynamic Design

The Do. X is a semi-cantilever monoplane flying-boat, with the engines placed above the main wing, in six tandem pairs, and a small auxiliary wing joining them. A good deal of speculation concerning this wing has occupied those interested in the Do. X, and it has even been claimed that by fitting it Herr Donier has obtained a "sort of slot effect" and greater lift. We could never, personally, see any reason for this supposition, and the booklet sent us by the Dormer company makes it quite clear that the auxiliary wing is a structural member first and foremost, serving to steady the engine mountings laterally (this small wing was later removed from the Do. X #1 when new Curtiss engines were installed and the wing was replaced by tubes only).

Do. X three-view general arrangement drawings

The boat hull is of fairly normal Dornier design as regards its external shape. Minor differences are formed on the one hand by the control cabin, which projects above the main deck and may be expected slightly to increase the drag. and on the other hand by a rounding of the stumps into the hull, which may slightly reduce the drag. The control surfaces are fairly normal and are all balanced by secondary surfaces.

The flying boats Do. X #1 and #2 in construction 1929 (Altenrhein Switzerland). Between the two flying boat hulls a wing skeleton and in front of that the skeleton for the rear wing edge.

As regards the aerodynamic efficiency of the Do. X the aspect ratio (if one may be so old-fashioned as to use this expression) is low (about 5) and the span loading is very high. This is, of course, merely another way of saying that the induced drag is high. To that the designers of the Do. X would probably reply that this is not of serious consequence, as the machine has a small speed range and a high take-off speed.

Do. X #1 engine change 1930. Mounting the engine nacelles with new Curtiss Conqueror engines on the main wings. The small wing and engine supports have been replaced by tubes.

Curtiss V-1570 Conqueror

[The Curtiss V-1570 Conqueror was a 12-cylinder vee liquid-cooled aircraft engine. Representing a more powerful version of the Curtiss D-12, the engine entered production in 1926 and flew in numerous aircraft.]

If one now turns to the - in this particular instance, perhaps, more important - question of minimum drag coefficient, it is of considerable interest to find that this is rather surprisingly low for a multi-engined machine. For example, at the normal gross weight of 46 metric tons (101.200 1hs.) the wing loading is 193 lbs./sq. ft. Assuming the engines to develop a normal output of 500 h.p. each, the total power is 6,000 b.h.p. and the power loading is 16.88 1bs./h.p. The "wing power" in that case is 12.33 h.p./sq. in. (1.15 h.p./sq. ft.). For a top speed of 130 m.p.h. this corresponds to a "high-speed figure" [n/(2*Ap)] of 13, which would appear to be as high as that attained by many smaller machines, even single-engined types. Doubtless the tandem engine arrangement has resulted in the drag being quite considerably lower than it would have been had the engines been spread out.

Ferdinand von Zeppelin, who employed many aircraft engineers in Germany.

[After his resignation from the army in 1891 at age 52, Zeppelin devoted his full attention to airships. He hired the engineer Theodor Gross to make tests of possible materials and to assess available engines for both fuel efficiency and power-to-weight ratio. He also had air propellers tested and strove to obtain higher purity hydrogen gas from suppliers. Zeppelin was so confident of his concept that in June 1891 he wrote to the King of Württemberg's secretary, announcing he was to start building, and shortly after requested a review from the Prussian Army's Chief of General Staff. The next day Zeppelin almost gave up as he realised he had underestimated air resistance, but resumed work on hearing that Rudolf Hans Bartsch von Sigsfeld made light but powerful engines, information soon shown to be overoptimistic. Whereupon Zeppelin urged his supporter Max von Duttenhofer to press Daimler-Motoren-Gesellschaft for more efficient engines so as not to fall behind the French.] /3/

Constructional Features

The boat hull of the Do. X is, in its outward shape, very similar to that of previous Dornier machines. The main step is placed rather farther aft than in British flying boat hulls, and is formed with fore-and-aft shallow steps which gradually merge into the forward vee of the bottom. The rear step does not, as in British practice, extend laterally out to the chines but is of narrower beam than the main bottom, and is fairly deep. The Germans term this form of step a "displacement step" (Verdrängungssporn), presumably because it acts by displacement rather than by dynamic pressure. From the main step to the stern post the chine members are straight and swept up at a fairly pronounced angle so as to get the tail well clear of the water. Forward of the step the main bottom becomes, as already indicated, of pronounced V-form, to terminate finally in a straight raked stem.

The total length of the boat hull is 40.05 m. (131 ft. 6 in.). The beam, over the stumps, is 10 m. (32 ft. 10 in.), and the maximum beam of the hull itself is 3.5 m. (11 ft. 6 in.). The greatest depth of hull is 6.4 m. (21 ft.), and the draught empty is 0.8 m. (2 ft. 8 in.). At a gross weight of 50 metric tons the draught is 1.05 m. (3 ft. 5 in.), and the meta centric height 4.58 m. (15 ft.). Inclusive of the stumps, the hull has a volume of 400 Cu. m. (141,200 cu.ft.), and in this connection it is interesting to record that the bull weight has been reduced in the Do. X to 21 kg/cu. m. (1.3 lb./cu. ft.). whereas in the "Wal" it was 26.2 kg./cu. m. (1.62 lb./cu. ft.) and in the little "Libelle" it was as high as 29.9 kg./cu. m. (1.85 lb./cu. ft.). The maximum cross-sectional area of the hull, exclusive of the stumps. is 17.2 sq.m. (185 sq. ft.).

Do. X #2. Skeleton frames jacked up on a metal rail and is held laterally by a metal band. Claude Dornier in front of the support structure.

There are in the hull 58 main frames, spaced 0.7 m. (2 ft. 4 in.) apart. An innovation in construction as far as Dr. Dornier is concerned is the introduction of a deep keel girder which runs from the bows to the rear step and has a length of 23.3 m. (76 ft.5 in.) and a greatest depth of 2.12 m: (6 ft. 11 in.). This fore-and-aft girder stiffens the hull very considerably. Parallel with the keel girder, and spaced from it 0.9 m. and 1.58 m. (2 ft. 11 in. and 5 ft. 2 in.), are two keelsons on each side. These, with the transverse frames and keel girder, form a very strong structure and reduce the panels (themselves of heavy gauge) of the botttom to squares of about 0.63 sq. m. (6.8 sq. ft.).

Sectional side elevations and transverse sections of the Do. X. Note the longitudinal steps and tumble home sides. The rear step is narrow, and carries a water rudder (not shown).

The large dimensions of the Do. X have allowed of an internal arrangement unlike those of previous flying boats, and more resembling the lay-out on board a surface vessel. The main deck is located some 4 ft. above the load water line, and forms the floor of the main accommodation for passengers. Below this deck, the hull is divided by eight watertight bulkheads into nine compartments. The side stumps themselves (of a total volume of 43.5 cu. m. (l,550 cu. ft.) are divided each into four watertight compartments, so that altogether the hull would have to sustain very considerable damage before the machine is likely to sink, providing the bulkheads do not give way.

Do X #2, fuel supply, look in the direction of flight from the B-deck into the open C-deck. On the port side (left) bearing shells fitted with tanks. The starboard side (right) with empty cups.

Below the main deck, in the watertight compartments, the main petrol tanks are mounted, their number depending upon the length of route over which the machine is to be operated. The passengers quarters are totally above the water line. and the construction is such that the subdivision of them is reduced to a minimum, the watertight compartments finishing at the main deck. Above the passengers' quarters are the crew's quarters. and the various service compartments, such as pilots' cabin, chief engineer's control station, wireless room and so forth. The forward portion of this upper deck has windows along the sides and rounded front, and is in fact, a sort of enclosed "bridge" for the pilots and navigators. The other service compartments, engineer's control station, wireless room, auxiliary engine room, etc., are, however, inside the center of the wing, and have consequently no windows on the sides. They extend aft as far as the trailing edge of the wing.

Do. X #2 outdoors on the rail carrier turnaround. The large visible components wing and fuselage before returning back to the hangar for finishing. Dornier-Werke GmbH, Altenrhein Switzerland, about 1929.

The wing, which has a span of 157 ft. 6 in., and a chord of 31 ft. 2 in., differs in construction from previous Dornier types in that three main spars are employed, of which the middle is situated at approximately the greatest depth of the wing section. The front and rear spars are placed 9 ft. 2 in. from the middle spar. The spars are built up of angle sections and laminated flange strips, the number of laminations in the flanges being proportional to the stresses from point to point. Box ribs are placed at distances of from 2.8 to 3.6 m. (9 ft. 2 in. to I I ft. 10 in.), and the metal panels of the wing covering are riveted to them and to the spar flanges. This metal covering extends outward to the outer engine nacelles only, the wings from there to the tips being covered with fabric. The maximum depth of wing section is 1.28 m. (4 ft. 2½ in.), and the result is that almost every part of the internal wing structure can be reached for inspection by a man crawling about inside. Attachment of the wing to the hull is by a number of large bolts, situated inside the covering and offering no extra drag.

The Do. X engine control room is placed on the upper deck and communicates with the wing and, through it, the engine nacelles. (Flight engineer's station).

The small auxiliary wing serves to brace and steady the engine mountings, and it is worth noting that it is so designed as to take no part of the wing stresses. In fact, in order to avoid the possibility of throwing unexpected stresses on the main wing, the auxiliary wing is arranged with flexible joints between the outer engine nacelle and the next. so that should the main wing deflect under load. the auxiliary wing can "give" to any extra loads.

The control surfaces are of fairly normal design, and are all provided with separate surfaces acting as balances. The tail is of "sesquiplane" type in that there is a small tail plane resting direct on the stern portion of the hull, and a main tail plane higher up. braced to the lower and to the hull by struts. The rudder balances take the form of vertical surfaces placed between the top and bottom tail planes, as distinct from the horn balance or servo rudder used on large British flying-boats. The operation of the control surfaces is by steel rods, or tubes, suspended on pendulum cranks. Ball bearings are used throughout. Trimming of elevators and rudder is achieved by a setting of the separate balance surfaces, the angle of which in relation to the main surface which they balance being adjustable from the cockpit. This setting is reported to be very easy. i.e., to require but very small forces, and the machine is stated to be as easy on the controls as are smaller aircraft.

Do. X #1 with original Siemens-Jupiter engines, small wing and motor mounts.

The power plant consists of 12 Siemens-Jupiter engines. arranged in six tandem pairs . The large number of engines required forced, it is stated, this arrangement on the designers, and it is an arrangement the advantages and disadvantages of which are familiar to the Dornier designers from more than 10 years' experience.

The Bristol-Jupiter engine was license produced by Siemens-Halske in Germany and was widely used in airplanes in 1920's and 1930's.

[The Bristol Jupiter was a British nine-cylinder single-row piston radial engine built by the Bristol Aeroplane Company. Originally designed late in World War I and known as the Cosmos Jupiter, a lengthy series of upgrades and developments turned it into one of the finest engines of its era.

The Jupiter was widely used on many aircraft designs during the 1920s and 1930s. Thousands of Jupiters of all versions were produced, both by Bristol and abroad under licence. A turbo-supercharged version of the Jupiter known as the Orion suffered development problems and only a small number were produced.]

The Dornier engineers argue that the use of tandem engines almost reduces the number of separate units to one-half, in that each tandem unit of two 9-cylinder engines is very little more complicated than one 18-cylinder engine, and is much more reliable in service. The drag of a tandem installation is, it is claimed, no greater than that of one larger engine, and the propeller diameter, for same efficiency, is smaller. The Siemens-Jupiter engines of the Do. X are of the geared type, with 2:1 reduction gears.

Access to the engines was possible in flight, Siemens-Jupiter and Fiat engine models. The Curtiss engine version had tubes instead of the motor mounts and small wing.

Great importance has been attached to accessibility of the engines, and by mounting the nacelles on streamline supports, all the engine nacelles can be reached from the interior of the wing. Inspection doors in the covering of the streamline supports give access to the interior of the nacelles when the machine is at rest.

The Do. X: View of the pilots' control cabin.

As already mentioned, the quantity of petrol carried will depend upon the route operated. Normally. there are four main tanks of 3,000 liters (660 gallons) capacity each, resting on the floor of the hull, and a further two tanks of 1,700 liters (374 gallons) each also resting on the floor. but slightly farther forward (see sectional side elevation).

Do. X #2 fuel supply. Starboard nose tank in the wing. Hull at the right and partly below. View from the front to the wing inside.

There are, furthermore, two small tanks of 300 liters (66 gallons) each housed in the leading edge of the wings, a total petrol capacity (normal) of 16,000 liters (3,520 gallons). The main tanks and leading edge tanks are connected to a collector (Sammeltopf), and the fuel is pumped from the main tanks to the leading edge tanks. In order to avoid any possible break- down in the petrol system, no less than three separate pump systems are provided: a windmill-driven pump, an electric pump, and a hand pump. From the leading edge tanks, the petrol is pumped by A.M. pumps to the carburetors, surplus petrol draining back into the collector. Oil tanks of 100 liters (22 gallons) capacity are housed in the engine nacelles, and there is a main oil tank of 1,000 liters (220 gallons) in "bilge."

Flying boat Do. X #1 in flight. Accordion player Schüttenhelm on the 2nd pilot seat in the cockpit, pilot not identified.

The engine controls of a multi-engined flying-boat like the Do. X presented something of a problem. Obviously, the pilot cannot himself attend to all the engines, their Controls, etc. On the other hand, it is essential that the pilot should have full control of all the available power. With the arrangement selected, there is a main engine control room, reigned over by the chief engineer, and in this are concentrated the individual engine controls, engine instruments, etc. To avoid confusion, all the controls and instruments appertaining to the port engines are collected on the port side of the engine control room, and all those of the starboard engines on the starboard side. From this engine control room, two sets of engine controls are taken to the cockpit, or rather pilots' control room.

Do. X #1 instruments fom the Pioneer Instrument Company in Brooklyn, New York: speed and altimeter, steering indicator, inclinometer and ascent meter, compass. Also Firma Askania AG Berlin and others were used to supply instruments.

[The Pioneer Instrument Company was started by Morris Maxey Titterington and Brice Herbert Goldsborough in Brooklyn, New York in 1919. Charles Herbert Colvin was the president. They specialized in aeronautical instruments including a bubble sextant and the Earth Inductor Compass. The company later acquired control of Brandis & Sons, Inc., in 1922, and Pioneer was later acquired by the Bendix Aviation Corporation in 1928. As the United States was entering World War II, the company became the Pioneer Instrument Division of Bendix Aviation, and moved to New Jersey. By 1943 it had become the Eclipse-Pioneer Division of Bendix Aviation.]

Dornier Do. X #1 cockpit.

[Die Askania Werke AG mit Standorten in Berlin und im Berliner Umland wurden zum bedeutendsten deutschen Unternehmen für Luftfahrt- und Navigationsinstrumente. Die Nachtfluginstrumente, Bord- und Pilotenuhren halfen Pionieren der Luftfahrt, beispielsweise Ehrenfried Günther Freiherr von Hünefeld bei seiner Atlantik-Erstüberquerung oder Elly Beinhorn bei ihren Langstreckenflugrekorden. Es wurden auch Filmkameras gebaut, die unter anderem bei den Dreharbeiten zum Film Der Blaue Engel mit Marlene Dietrich zum Einsatz kamen. Zu den hergestellten optischen Geräten zählten auch Kino-Filmprojektoren und Stereoskopie-Kameras.]

Thus the pilot has but two engine controls, one of which operates the 6 port engines, and the other the 6 starboard. He also has two revolution indicators, of which one shows the mean revolutions of the six port engines, the other the mean revolutions of the six starboard engines. If one of the engines is disconnected from the pilot's engine controls, a red lamp lights up, on port or starboard side, to let the pilot know that he has not available the full power of all six engines on that side. Starting of the engines is by means of compressed air worked by an auxiliary engine in the main engine control room. The average time for starting all 12 engines is 4-5 mins. They have been started in 3 wins. It is reported that the engine installation is remarkably free from vibration.

Do. X passenger room (cabin) simple version. By taking 169 passengers Dornier Do. X made a record flight which kept for 20 years.

The arrangement of the passengers' accommodation will depend upon the length of route and number of passengers carried . Normally, comfortable accommodation cannot be provided for more than 100 passengers, and it is pointed out that when the machine is used for routes so short that the pay load exceeds 10,000 kgs. (a passenger is taken to weigh, with luggage, 100 kgs., i.e., 220 lbs.), the difference between the weight of the 100 passengers and the lift available for pay load will have to be made up of mails and/or freight. The various cabins, etc., available for passengers, measure, altogether, some 24 m. (78 ft. 9 in.) in length, and have an average width of about 3 m. (10 ft.).

Range and pay load of the Do.X. The chart is self-explanatory, but it might be pointed out that comfortable accommodation can be provided for 100 passengers only, so that when the range is short, and the pay load exceeds 22,000 lb., the balance must be made up with mails and/or freight.

A chart has been prepared which indicates the distances that can be traversed by the Do. X without refuelling. and the number of passengers, or the weight of mails and goods which can be transported over these distances. A few representative distances have been drawn in to give a better picture of what the various distances mean in practice. The chart has been based upon a take-off gross weight of 45 tons (100,000 lbs.), and in estimating the pay load available for the various distances, ideal weather conditions have been assumed, i.e., still air. B' carrying the usual 30 per cent. reserve of fuel, the take-off weight would be increased. Thus, is stated that with a 30 per cent. petrol reserve for a distance of 1,800 kms. (1,120 miles), the take-off gross weight would be increased to 49.5 tons (109,000 lbs.)."

Dornier Do X Historic Notes and Construction Details /4/

"The Dornier Do X flying boat, which first flew in 1929, was one of the most remarkable aircraft, either landplane or flying boat, ever built. This unique flying boat was the largest aircraft ever constructed up to that time and had a gross weight variously listed as 105 820 or 123 459 pounds. The lower value was probably the design gross weight: the higher, likely an allowable overweight condition for special long-range flights.

Air Routes 1930's

A great effort was then being made in a number of countries to develop aircraft suitable for airline use across the oceans, particularly the North Atlantic. The aircraft were of two main types: rigid airships of the Zeppelin type and large flying boats like Dornier’s. The wing of the DO-X projected from the top of an ample hull with a span of 157 feet and a chord of 30 feet. Lateral stability on the water was obtained by the use of sponsons, or short and stubby winglike structures that projected from the bottom of the hull on each side.

Dornier Metailbauten GmbH, Altenrhein Switzerland, Lake Constance (Bodensee)

[Dornier Company had many names: Dornier Flugzeugwerke, originally Dornier Metallbau or Dornier Metallbauten and also Dornier-Werke GmbH was used.]

Constructed in the late 1920s at Altenrein, Switzerland, on Lake Constance (German Bodensee) and near Friederichshafen, Germany, the DO-X could accommodate sixty-six passengers comfortably over a range of 700 to 900 miles, but could not lift any kind of payload over transatlantic distances, the minimum such distance being roughly 2,000 miles. (During a test flight Do X #1 utilized Azores so it only needed about 1000 miles.)

Dornier logo

On one flight from adjoining Lake Constance, though, 169 [or 170, by other accounts] people were crowded into the airplane (nine were stowaways by one account), making quite a record at that time.

Douglas XB-19

In the United States, no aircraft exceeded the gross weight of the Do X until the one-of-a-kind experimental Douglas XB-19, at a gross weight of about 140,000 pounds, flew in 1941, and the Boeing B-29 bomber of on World War II fame was the first production aircraft to have a higher gross weight. Incredibly, the Do X was powered by 12 engines. They were positioned in six nacelles, tractor-pusher style, strut-mounted on top of the wing. Tests were made with several different engines in the three Do X aircraft that were built. British-made Jupiters were rated at 550 horsepower each, providing a total of 6600 horsepower. The 12-cylinder Curtiss V-1570 water-cooled engines of 640 horsepower each provided a total of 7680 horsepower. Perhaps fortunately, no other aircraft has ever been equipped with so many engines. One can only guess at the difficulties encountered in keeping all of them operating simultaneously in an efficient manner.

Do. X #1, installation of the wing in the hangar. Looking through the cross bar of the wing tip on the port side.

The monoplane wing was mounted flush with the top of the hull-fuselage, and the six engine nacelles were located on struts above the wing. Instead of lateral stabilizing floats, short stub wings (wing stumps), called sponsons, projecting from the sides of the hull near the waterline provided lateral stability in the water. Each wing was braced by three struts extending upward and outward from near the tip of the sponsons. In turn, the sponsons were braced by three additional struts extending downward and outward from near the top of the hull to about the mid-point of the sponsons.

Dornier Do. X #1 tail.

Two sets of horizontal tail surfaces of different size were configured in a sesquiplane arrangement, and directional stability and control were provided by a single fin and rudder. To reduce pilot control forces needed to maneuver so large an aircraft, small surfaces connected to the main control surface, called park-bench balances, were mounted above and ahead of the elevator and aileron hinge lines.

Navigation room just behind the cockpit.

The all-metal hull had a modified vee bottom with a single transverse step and an afterbody that tapered to a sharp vertical stern post. To assist in maneuvering on the water, a small rudder was mounted at the stern post. Accommodations in the hull were divided among three decks. On the top deck were the pilots' compartment, navigation room, captain's cabin, and flight-engineers' compartment. Instruments and controls for operating the battery of 12 engines were located at the engineers' station.

Do. X #1 cabin interior, toilet, hand wash basin with special faucet and soap dispenser.

The passengers were carried on the second deck, which had several cabins with seats and sleeping accommodations as well as a bar and smoking and writing rooms. Cabins were spacious, and appointments included wood paneling, rugs, and other features of contemporary luxury liners of that day. Perhaps some of the weight of this equipment was more appropriate to a surface ship than an aircraft where lightness is an essential ingredient of efficient flight. But the 66 passengers for which the aircraft was configured no doubt traveled in a regal style unknown today. (On one occasion, 150 passengers, 10 crew, and 9 stowaways were carried on one short record flight.) Fuel and stores were carried on the lower deck.

Do. X #1. On the ground the wing skeleton with the 3 bars. In the foreground on the wing end segment the framework for the skin fields is already inserted.

The wing and tail surfaces consisted of a metal framework covered mostly with fabric. Having an area of 4844 square feet and a span of 157.5 feet, the large wing was sufficiently thick to incorporate walkways on which a person could pass through the inside of the wing. Access to the engines for maintenance was provided by hatches above the walkways at each engine nacelle position.

Flying boat Dornier Do X #1. Cabin interior, front lounge. Passage through the central lounge, through the smoking section until to the board bar with locked manhole.

With a maximum speed of 134 miles per hour and an estimated cruising speed of 122 miles per hour at 75 percent power, the performance of the Do X appears, at first glance, to be very creditable (ref. /6/, table IV). The zero-lift drag coefficient of 0.0472 was also as low or lower than most contemporary flying boats. Because of the low wing aspect ratio of 5.12, however, the maximum lift-drag ratio was a low 7.7, a full 22 percent lower than that of the Consolidated Commodore. In addition, the useful load fraction (ratio of payload weight plus fuel weight to gross weight) was only 27 percent for the 105 820-pound gross weight condition. By comparison, the useful load fraction for the Commodore was 35 percent and for the World War I vintage NC-4, 42 percent. (Meaning that Do. X was rather heavy construction.)

Consolidated Commodore

[The Consolidated Commodore was a flying boat built by Consolidated Aircraft and used for passenger travel in the 1930s, mostly in the Caribbean, operated by companies like Pan American Airways. In response to losing a Navy contract, Consolidated offered a passenger-carrying version of their XPY-1, which became known as the Commodore. The monoplane all-metal hull could accommodate 32 passengers and a crew of three. The full complement of passengers, located in three cabins, could be carried only on relatively short route segments. For a 1000-mile flight, the boat probably could accommodate no more than 14 people including the crew. Wing and tail construction consisted of a metal frame structure covered with fabric, except for metal-covered leading edges. With a first flight in 1929, a total of 14 Commodore boats were built.]

The useful load fraction of modern jet transport varies between 45 and 55 percent. The combination of low maximum lift-drag ratio and small useful load fraction doomed the Do X as a commercial airplane capable of carrying an economically attractive payload on transoceanic routes. For example, estimates suggest that at a gross takeoff weight of 105,820 pounds, including 66 passengers and a crew of 6, the maximum achievable range was between 600 and 650 miles at a cruising speed of 108 miles per hour at sea level.

Dornier Do X #1 in New York

In 1930, the Dornier Do X (#1) went on a world trip which took it to New York via South America. Ground effect is a phenomenon that has been noticed for some time. Early aviators noticed the increased lift on landing when their aircraft approached the ground. A number of early aircraft used the additional lift from ground effect to increase their efficiency. The increased lift to drag ratio due to ground effect gave the Dornier additional range to complete its mission and could be used to save fuel.

Dornier Do X #1 Transatlantic Test Flight around the Atlantic Ocean 1930-1932.

A total of three Do X aircraft, including two for the Italian government, were constructed. The Dornier Do X suffered from a number of mechanical problems and minor disasters during its service. On a trip from Amsterdam via Lisbon, Rio de Janeiro and Miami to New York, the Do X was dogged by troubles and took from 2 November, 1930 until 27 August, 1931 to complete the trip. (The aircraft returned to Germany 1932. It must be remembered that the Great Depression started 1929 and Hitler became dictator in Germany during that period. So the market for any aircraft vanished.)

[The Great Depression was a severe worldwide economic depression in the decade preceding World War II. The timing of the Great Depression varied across nations, but in most countries it started in 1930 and lasted until the late 1930s or middle 1940s. It was the longest, deepest, and most widespread depression of the 20th century.

Cities all around the world were hit hard, especially those dependent on heavy industry. Construction was virtually halted in many countries. Some economies started to recover by the mid-1930s. In many countries, the negative effects of the Great Depression lasted until after the end of World War II.

The Great Depression in Germany provided a political opportunity for Hitler. In 1932, Hitler ran against Hindenburg in the presidential elections. The viability of his candidacy was underscored by a 27 January 1932 speech to the Industry Club in Düsseldorf, which won him support from many of Germany's most powerful industrialists.]

Dornier Do X was the central exhibit of the former German aviation collection. The destroyed metal residues were melted down after the war. This bulkhead illustrates the size of that structure.

The aircraft is considered as an engineering achievement of considerable magnitude for the time; it showed that very large and heavy aircraft could fly and be built and indicated some of the problems of such aircraft. Preserved for many years in a Berlin museum, the original Do X was destroyed in Allied bombing raids during World War II."

Bomb damage at the Berlin Museum during WW II

[During World War II, the Berlin Museum was bombed seven times in Allied bombing raids, destroying the larger wall murals which had been cemented into place and could not be moved; 28 of the finest paintings were totally destroyed. Smaller pieces were hidden in bunkers and coal mines at the outbreak of war and survived the bombings.

When the Russians arrived in 1945 they looted at least 10 crates of treasures that they discovered in a bunker under the Berlin Zoo which have not been seen since.

WW 2 was the most widespread war in history, and directly involved more than 100 million people from over 30 countries. In a state of "total war", the major participants threw their entire economic, industrial and scientific capabilities behind the war effort, erasing the distinction between civilian and military resources.]

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