The Dornier DO-X: What Might Have Been

The Dornier Flugboot "DO- X"

The Dornier Flugboot "DO- X"

Dornier is one of the most distinguished and long lived names in aviation history, gracing a whole series of companies and aircraft from 1912 through 2002. In those eighty years, dozens of brilliant Dornier designs emerged, including the record setting flying boats, Luftwaffe warplanes and more recently swift turbo-prop and jet airliners. Yet Dr. Claudius Dornier is still most readily associated with the Do X. a huge flying boat that was the largest aircraft in the world at the time it was flown. Unfortunately, the Do X was technically a total failure in spite of the nine years of effort and the immense, highly nationalistic promotional effort that surrounded it.

Ironically, the twelve-engine Do X could have been Dornier’s greatest success, had he been as willing to try new propulsion combinations in the same way that he was willing to gamble on the sheer size of the aircraft. Instead, he insisted from the first that “all experimentation is to be avoided,” apparently to avoid compromising the potential success of a mammoth aircraft with unproven modern techniques. Unfortunately, this short-sighted approach doomed his Do X to technical, if not promotional, failure.

Born in Kempten, Germany on May 14, 1884, Dornier was perceived over his life time not only as a great designer and entrepreneur, but as an academician. Less obvious, but equally important, he was an astute politician who managed to not only to survive but prosper despite the hardships of Germany’s defeat in the First World War, the restrictions of the Versailles Treaty, the predatory mismanagement of the Nazi era and the second German defeat in 1945.

Dornier graduated with distinction from the Technische Hochschule inMunich in 1910 and was snapped up by the Zeppelin company, where his experience with metal structures was invaluable in airship construction. Impressed by the young man, and wishing to build giant aircraft as well as airships, Count von Zeppelin authorized a special facility for Dornier’s use at Seemoos, on Lake Constance  (theBodensee). There, in 1915, only twelve years after the Wright’s first flight, Dornier built the Zeppelin-Lindau Rs 1, a metal-structured 142 foot wingspan tri-motor flying boat weighing 23,000 pounds. Unfortunately, it was damaged before it could fly. Dornier completed three more giant flying boats before the end of the war. None were important combat aircraft, but each brought him closer to his classic formula of an all metal aircraft with a wide, streamlined, two-step hull, “Dornier-Stummel” sponson stabilizers, huge monoplane wing and tandem engines mounted on a pylon.

Dornier also built some advanced fighter and observation aircraft during World War I. These were the first to use all-metal, stressed skin duraluminum construction that became a Dornier hallmark. Engineers trained by Dornier in his very advanced all-metal construction methods included Dr. Alfred Rohrbach, who would design the revolutionary four-engine all-metal Staaken E.4/20.

With Germanybanned by the Versailles Treaty from building large aircraft, Dornier transferred his operations in 1919 to Manzell, Switzerland. There he designed the famous Do J Wal (Whale) which flew for the first time on November 12, 1922. Treaty restrictions forced Dornier to establish a company, the Societe di Costruzionia Meccaniche di Pisa to produce the airplane in Italy. The Wal was so successful that it was also built inJapan, theNetherlands,Spain andSwitzerland, before production finally began at Friedrichschafen in 1933. The twin-engine Wals set many records and were used by explorers of several countries. They were followed in production by the Super Wal of 1926, which could be equipped with two or four engines, establishing a  Dornier flying boat franchise that would flourish for decades.

Dornier’s landplane transports, including the Komet and Merkur series had done well, but none were as successful as the Wal of which 320 were built.  Together, however, they assured Dornier’s commercial success, and he decided to push the envelope with his gigantic Do X, starting design work in 1924. Because of treaty restrictions, the aircraft was built on the opposite side ofLakeConstance, inAltenrhein,Switzerland. More than 240,000 man-hours were expended over the next five years and perhaps the first full-size one-to-one wooden mock-up was constructed.

Somewhere in the process Dr. Dornier lost control of the project in terms of weight and drag. Although schooled in Zeppelin’s art of light structures, and using his famous combination of steel and duraluminum, Dornier seemed smitten by a nautical Art Deco complex. He saw the Do X not so much as a flying-boat but as a flying ocean liner. It became structurally complex as well as excessively ornate. Sadly, as weight and drag grew, the anticipated available engine power diminished.

As completed, the Do X had three levels. The uppermost was divded into five compartments for the aircrew—pilots, captain and navigator, navigators, radio man and engineers. The second deck was lavishly fitted for passengers, their luggage, and (somewhat optimistically) for freight. Reminiscent of advertisements for the current Airbus Industrie A-380, the Do X featured sleeping quarters, smoking room, a bar, writing rooms, bathrooms, a kitchen and a long, elegant dining room salon. The third deck was used for storing fuel, oil, and equipment.

With a wingspan of 157 feet and a wing area of just under 5,000 square-feet, Dornier had achieved his goal of building the biggest aircraft in the world. Unfortunately, at about 72,000 pounds empty, it was also the heaviest. Dornier had hoped to acquire twelve 640 horsepower Curtiss Conqueror liquid cooled engines for it, but these were initially unavailable. He had to settle instead for twelve 525 horsepower Siemens-Halske radial engines, license built versions of the Bristol Jupiter. So from the start, he had only a total of 6,300 horsepower available instead of the (still inadequate) 7,680 horsepower that he had planned.

Richard Wagner was pilot on the first of the aircraft’s 239 flights, taking off fromLakeConstance on July 12, 1929. As all test pilots tend to do, he described the flight in glowing terms, although later there was some comment on the adverse effect that operating fromLakeConstance had on performance. The lake’s 1,300 feet altitude sapped the Do-X’s engines of a another 240 horsepower. The Do X displaced two percent more fresh water than it salt water, increasing drag during takeoff.

If Dornier’s weight control capabilities had flagged, his promotional ability had not, and the aircraft was given a full-court press in the press. On September 4, 1929, an exhibition flight was made by the Do X to celebrate the return of its airship rival, the Graf Zeppelin, from its famous round-the world flight.  Three American naval officers who had been aboard the Graf Zeppeliln  were invited for a flight in the Do-X, along with fifty seven others. All were impressed with the luxurious fittings and comfortable seats aboard the aircraft.  Lieutenant Commander James M. Shoemaker (later to command the USS Franklin during World War II) said that the airplane “fairly jumped on the step” and was enthusiastic about the apparent ease of handling.

Shoemaker noted that no servo or other mechanical means were used to move the huge control surfaces. Instead, the typical Dornier system of adjustable balances were fitted to each of the control surfaces. These were effective, but caused a great deal of induced drag.  He observed that the Do X pilot had only two throttles, one for the engines on each side of the plane. Control rods from these throttles were routed back through the navigation compartment to the engine room, where the individual engines were controlled by the engineer.

The complex engine installation—six tractor and six pusher engines, mounted on a wing-like pylon system with sets two, four and six being staggered just slightly to the rear—required four engineers. Two were in the “engine room” and with one for each bank of six engines. The depth of the Do X wing made it possible to have passageways through which the engineers could walk out to hatches which allowed them to access the engines in flight.

On October 21, 1929, the Do X made a record flight with 169 people on board, including nine stow-a-ways.  By this time, almost thirty-five hours of test flying revealed that the Siemens engines were hopelessly unsuitable, and a fortunate change inU.S.policy permitted the Curtiss company to loan Dornier its proven Conqueror engines.

The new engines improved performance, but only marginally. The Do X, which Dornier claimed to have a 137 mph top speed, cruised at about 105 mph, but had a service ceiling of about 1,650 feet, far less than the planned 5,000 foot ceiling. Part of the problem was Dornier’s insistence on using large wooden fixed pitch propellers, which the good Doctor felt had the advantage of acting as a fly-wheel to smooth engine operation.

Despite the less than smoldering performance, the Do X was launched on an international sales tour, departing on November 5, 1930 for what would become a long, trouble-ridden, but none-the-less well received flight toAmericaand (eventual) return.

Dornier selected a formidable World War I ace  to command the Do X on the flight,  Kapitanleutnant Frederick Christiansen, the famous “Fighter of Zeebrugge.”  Christiansen, flying Brandenburg twin-float seaplanes, scored thirteen official and eight unconfirmed victories to win the Blue Max, a decoration he wore proudly as a Generalleutnant, commanding the German Werhrmacht inHolland during World War II. He died in 1972 at the age of 93.

Christiansen had under his command two excellent pilots. The first was on loan from Lufthansa, Captain Horst Merz. The second was Clarence H. “Dutch” Schildhauer, a captain in the Navy reserve who set an endurance record in a Naval Aircraft Factory PN-9 flying boat.

The Do X flew from Lake Constance to Lisbon on a trans-Atlantic proving flight, carefully following waterways as it passed through Europe, Africa, South America, the Caribbean and the Eastern Coast of the United States before crossing the north Atlantic on its return to Berlin.  (See sidebar for the itinerary), The nineteen month long trip was an adventure in adversity as one damn thing after another extended the flight.

The first in a series of incidents  occurred inLisbonwhen a canvas cover ignited, setting the wing fabric on fire. The damage was severe, and more than a month was needed for repairs. Given the relatively light duraluminum  and steel structure of the Do X, it is amazing that the fire did not render it un-airworthy.

When finally repaired, the Do X flew toLas Palmasin the Canary Islands where an attempted take offs atLas Palmascaused severe damage, requiring another ninety-days of repair.  During this time, a weight reduction program was carried out to improve the Do X’s take-off capabilities, with all the heavy furniture being thrown out, and the crew getting rid of their personal possessions, right down to their razors.  In addition, Dornier sent a veteran Wal pilot, Captain Cramer von Clausbruch to replace Schilhhauer. Clausbruch knew how to extend range by flying in ground effect, a condition for which the huge wing of the Do X was ideally suited.

The Do X was airborne again on May 3, 1930, making its way south to an island, Bubaque, off the coast of what was then the Portugese colony ofGuineainWest Africa. After another agonizing four weeks spent waiting for adequate weather, the Do X flew the shortest way across tha Atlantic, 1440miles,  heading forNatal,Brazil. Von Clausbruch earned his pay by wrestling the heavy Do-X into the air by rocking the aircraft from side to side it on the step and flying at an altitude of thirty feet to take advantage of ground effect.

After the all hardships, the Do X and its crew luxuriated in a rousing South American welcome that took it up and down the coast of Brazil. Forty-seven days were spent in Rio De Janiero. Christiansen protested at the long delay and was relieved as commander by Captain Fritz Hammer, who then headed the famed Condor Syndikat,Germany’s thin edge of the wedge into South American aviation.

The Do-X hoped up the northern coast of South America, halting atBelemfor ten days to have an engine replaced. It then departed for theUnited Stateson August 18, stopping at coastal cities all the way, arriving inNew Yorkto a thunderous reception on August 27, 1931—nine long  months after its departure.

Other than the general joy of arrival inNew York, and the usual warm American welcome to trans-Atlantic flyers, with Mayor Jimmy Walker pinning medals on the crew, the news was terrible. Curtiss wanted payment for the twelve engines, but the Dornier company had been hard hit by the depression, and was unable to come up with the required $60,000. Attempts were made to sell the aircraft to American interests, but to no avail, and the Do-X was buttoned up for a long, perhaps permanent stay inNew York.

Eventually, Dornier received a loan from the faltering German government, and purchased the refurbished Curtiss engines. The return flight began on May 19, 1932 carrying among others the second woman to cross theAtlantic, Antonie Strasser. A pilot and actress, she served as an assistant purser.

The Do X flew by way ofNewfoundlandand the Azores, finally landing in belated triumph on the Müggelsee atBerlinon May 24, 1932, In the next month, 200,000 people would come to see it. The trans-Atlantic venture completed, control of  the Do X now passed to the German government.

Mussolini had made Fascist Italy aviation minded, and Dornier sold them two examples of the Do X. These were the Do X1 and Do X2, named Umberto Maddalena and the Alessandro Guidoni respectively for two Italian aviation luminaries. They were powered by 550 horsepower Fiat A-22-R engines in neatly cowled pairs. The first, the Umberto Maddalena, was delivered to the Italian government on August 28, 1931, flying at an impressive 12,000 feet to cross theAlps.  The second was delivered on May 13, 1932, just a few days before the prototype arrived back inBerlin. The Italians investigated both themilitary and civilian potential of the huge flying boats without success, and both were subsequently scrapped.

In a desire to recoup some of the money expended on testing the Do X, the German government sent the Do X on a tour of German cities.The flight lasted from June 23 to November 14, 1932, and was another publicity triumph for the giant seaplane. A similar tour was planned for 1933, with the Do X to fly along the Danube and down toIstanbul. Unfortunately, a misjudged landing by Captain Merz damaged the airplane. It was repaired, a few more flights were made, and then the plug was pulled. The aircraft was taken out of service and given to theGermanAirMuseuminBerlinin June, 1936. There it remained in good company with such aircraft as a Fokker Dr 1 triplane in von Richthofen’s markings until it was destroyed by an air raid in November, 1943.

What Might Have Been: the Do Xtra.   

It is possible that the Do X paid for its construction with the political benefits that accrued from its acclaimed if attenuated flight back and forth across theAtlantic. But for an engineer such as Claude (as he preferred to be called) Dornier, technical success was the goal. As well versed as Dornier was in the fundamentals of weight, lift, thrust and drag, he must have known of the Do X performance deficiencies before it ever flew. The first trial flights confirmed that it was underpowered and far too heavy. While economics might have prevented him altering the first Do X, he might well have been able to revise one of the Do X’s then under construction.

His first act should have been to conduct a ruthless weight control program. All of the heavy, ocean-liner style furnishings, the smoking room, the showers, everything extraneous to flight should have been eliminated. Next he could have analyzed the entire structure, reducing the size and weight of fittings wherever possible. The control system could have been simplified, and the number of the crew reduced. Taken together, these actions surely would have reduced empty weight by at least ten thousand pounds. A reduction from sixty-six to forty passengers would have saved another four thousand pounds. This fourteen thousand pound reduction in gross weight would have other benefits, including requiring less fuel.

Next, he should have removed the awkward engine installation, junking the pylons and the stub wing structure. The engines could have been submerged into the wing, or he might have borrowed a note from his colleague Rohrbach, who had faired engines into the wings in his 1919 Staaken. (Dornier himself later estimated that placing the engines in the wings would have increased cruise speed by 36-mph, or, alternatively, range by 26 percent.)

From 1929 to 1931, there were at least eleven aircraft engines either in production or under development with a horsepower rating in the 1,000 horsepower range.  Among these were the Beardmore Simoon, Sunbeam Sikh, Packard X-2775, Daimler-Benz F-2, Fiat A-25, Isotta- Fraschini Asso-1000, and others.

These engines had not been built in quantity, nor were most in general use, but the Do X was in crisis, and it would have been worth the gamble to choose one model, install it properly, and see what the difference was. The Fiat A-25 had been used in production aircraft from about 1926 on, and would have been the safest bet.  Dornier could have elected to run it at power settings which generated only 900 horsepower, and thus had 10,800 horses at his command. If he wished, he could have reduced the number of engines to ten or even to eight, trading power for reductions in weight and drag.

Whatever he chose to do, he could have harnessed the available horsepower far more efficiently by turning to a new development, the Hele-Shaw automatic variable pitch propeller, then being built in cooperation with Gloster inGreat Britain. Variable pitch propellers had a long history, and were about to burst upon the aviation scene every where, but the Hele-Shaw would have been a good choice for Dornier. The same unit developed into the Rotol variable speed propeller which was used extensively during World War II. Using a variable pitch propeller would have vastly improved take-off performance while still permitting a good cruise speed.

There is no doubt that Dorneir was daring—the very size of the Do X proves this. It is just a shame that he had not been equally daring in making decisions about revising the aircraft. If he had, the result might well have been an aircraft capable of trans-South Atlantic performance by 1932. The improved Do X would have servedItalywell in theMediterranean, and lifted flying boat performance a decade into the future. The risks would have been great, and the probability of technical success of using new engines and a new propeller would perhaps have been low. Yet given that the Do X was a technical failure from the time of its roll-out, the risks of making it a success with new engines, new engine placement and new propellers were well worth taking.


13 responses to “The Dornier DO-X: What Might Have Been

  1. What a great article on the might Dornier DO-X. In many respects it was a decade ahead of its time. I agree with your comments about weight reduction. However, I wonder if it would have better to re-engine the giant with the Wright J-1 whirlwind. Versions were available as early as 1921 but called the Lawrence J-1.

    Embedding the engines into the wings would have been a bold move. Of course Sikorsky did it in 1934 with his remarkable S-42 flying boat, but only after engine reliability was well established. His contemporary flying boats, the twin engine S-38 and the later S-40, had engines suspended between the two wings.

    There is a good discussion in Sikorsky’s book, “Winged “S”. As I understand the engineer’s concerns were the lost wing lift behind a wind-milling prop. Since propeller brakes did not work well and feathered props were still something only in the engineers dreams.

    Jamie Dodson
    Author of the award winning Nick Grant Adventures series,
    Flying Boat & Spies, China Clipper, and coming soon – Mission: Shanghai

  2. Thank you Jamie, for a great comment. You are an authority in the field, of course! Flying the big boats was a challenge as you had to be both a pilot and on the water, a master sailor. There were no doubt money and national pride reasons for their failure to adopt more modern American engines. But a great effort, anyway!



    • Thank you Jamie, for a great comment. You are an authority in the field, of course! Flying the big boats was a challenge as you had to be both a pilot and on the water, a master sailor. There were no doubt money and national pride reasons for their failure to adopt more modern American engines. But a great effort, anyway!



  3. I remember seeing the Do-X land at North Beach, New York City then known as Idlewild now LaGuardia. The colorful Italian captain smoked a cigar and lit it at every port where he landed…I am trying to recall his name. ..perhaps because I was only 11 years old then in 1929 or -30. Can you supply that name for me?

    • It may just be possible that your recollectioins are of the flight of the Savoia Marchetti flying boats, under the leadeship of Italo Balboa. I doubt if the captain of the DO-X, Christiansen (a WW I ace, and an important figure in WW ) could have been mistaken for an Italian. Balboa was an important figure in Italian aviation, but was shot down by Italian flak–some say on purpose because Mussolini feared him–and died. I could look it up but I believe that mass formation flight from Italy to Chicago took place in 1933.

  4. Thank you for your information about the DO-X. My grandfather was Capt. Clarence “Dutch” Schildhauer. I grew up with the DO-X as being part of my family’s history- along with the list of his other friends- Lindbergh, Earhart, Rickenbacker, etc- My grandfather was an amazing man-wonderful aviator, and a truly a man whose heart was in the clouds. My grandparent’s house was even called Happy Landings.

  5. I am very happy on that great resurch you did, cause like Mrs Vogel abov my father father Alfred Schmid worked for Dornier as an pilot and engineer He worked also in Istanbul, where then he met my turkisharmenian garndmother. The whole family came back to Switzerland in 1936, where my grandfather died after a airplain crash due to his not recoverd health still working for Dornier. My father was a very smart man, also very talented technical person. The only thing he always was about to tak was Dornier and his father working for that Company… So also to me it’ very special evenmore sinxe my father died in 2000 and in 2012 my sister’s 2nd boy is born on augst 27!!!! a day befor me…

    • Thanks so much for your comments, it is wonderful to have someone with a direct contact write. I appreciate it!


    • Dr. W.C. Hofmann

      Sehr geehrte Frau Carmen Schmid,
      ich hätte sehr gerne mit Ihnen ein paar Gedanken zum Thema DOX und Ihrem am 22.09.1902 geborenen Großvater Alfred F. Schmid, der schon am 05.05.1950 verstarb, ausgetauscht.
      Wenn ich richtig informiert bin, dann wurde Ihr Vater am 20.11.1930 in Istanbul geboren und war bis zum Jahr 2000 als Ingenieur für eine Züricher Gruppe tätig. Auch hier hätte ich für eine Recherche noch einige Fragen.
      Ich würde mich sehr freuen, wenn Sie mich via email unter kontaktieren würden. Ich wohne in Deutschland und würde Sie direkt anrufen, wenn Sie mir Ihre Telefonnummer schicken würden.
      Freundliche Grüsse

  6. Paul Lindemeyer

    The Italian defense ministry has the records of the Do Xs in service with their air force from 1931-’35. A finding aid is available online, along with a summary of the planes’ activities. They were used as flying classrooms for officers, did flyovers at air shows and important public events, and at least twice went out on joint air/naval exercises.

    One of the planes had two major accidents in two years, and by 1935 they seem to have been taken off the roster. One, and probably the other, went to the scrap yard in 1937.
    (pages are in Italian)

    • Thanks, Paul, this is very interesting and I appreciate your sending it. Not a bad record for such huge aircraft with all the possible maintenance problems inherent in a twelve engine design!

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