Dornier The Yugoslav Saga 1926 - 2007

Dornier The Yugoslav Saga 1926 - 2007

Claude Dornier’s contribution in the field of aviation started with the recognition by Count Zeppelin, who immediately following his employment at Luftshiffbau Zeppelin, discovered young engineer’s potential and provided him with a team and tools to succeed. (...)

 

Dornier Do D

Development

The story of Dornier Do D began on 6 February 1924 when Dornier Metallbauten GmbH signed a contract with Kawasaki Dockyard & Co. Ltd from Kobe for the development and construction of a total of eight airplanes. This included the development and construction of a single engine military torpedo and reconnaissance floatplane as well as single engine land airplanes. To speed up the development process, Dornier decided to base the new floatplane on the projects already under development, the Do B, which became the civilian airplane Komet III, and Do C, a light bomber and reconnaissance airplane. A sequential designation Do D was assigned, and the project development continued at a rapid pace. Due to its military role, the Do D project relied more on the Do C type. It borrowed its fuselage design and landing gear was replaced with floats which had to be placed at such an angle to allow for the weapons to be carried below the fuselage.
Construction of the first Do D for the Japanese licensee, under W.Nr. (Werke Nummer - Construction number) 57, began in March/April 1924. It was powered by a 375 hp (horsepower) 12 cylinder Rolls-Royce Eagle IX engine coupled with a four blade wooden propeller and radiator in the nose. The cockpit was located below the wing. According to the Dornier factory documents, this floatplane was 90% complete as of 27 September 1924 and was fully complete in the early October 1924 but the exact date of the first flight remains unknown. Following several test flights, the official hand off to the Japanese delagation took place on 29 October at Manzell. In 1925 it took part in the official Japanese Navy bid for torpedo bomber and was the only one to satisfy the strict reqirements. Despite this, Kawasaki was unable to secure a production order. It was registered with the (IAACC) Inter-Allied Aeronautical Commission of Control officially as a civilian airplane since Germany was prohibited from developing and constructing military airplanes and this registration was officially received on 10 November 1924.
In 1926 a new 600 hp 12-cylinder BMW model VI engine became available. As soon as the type approval was granted, series production began and many airplane manufacturers considered it for their designs. Accordingly, in 1926/1927 the Do D series development continued with BMW VI engine without reduction gear, now under the designation Do D bis. Different versions were tested, with enclosed and open float struts, cockpit forward below the wing or behind the wing, belly or side radiator, different tail designs and wing arrangements.

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In the early 1920, PV KSHS did not posses floatplanes which could be used as torpedo carriers or bombers which significantly limited its ability to protect the vast coastline along the Adriatic Sea. The domestic industry lacked the technical expertise as well as the machinery to produce a modern floatplane which satisfied the demands set forth. Several state commissions visited European aviation manufacturers to familiarize themselves with the floatplanes available and evaluate which supplier shall be awarded the contract. As a result, in June 1926 Dornier received a contract from KSHS for the purchase of 10 Do D bis through a Zürich based Aero Metall AG. Another factor which influenced this decision was the fact that these floatplanes were to be paid from the war reparations fund. They were assigned W.Nr. 131 to 140 and were produced at Manzell. They differed from the base Do D also in that they had different radiators which were now located on each side of the fuselage as well as a new square window also on the fuselage directly below the wing trailing edge. The first Do D was completed in November and the factory validated that all the requirements were met. The first three were delivered to PV KSHS in January 1927, the next three in March, three by the middle of the year with exception of W.Nr. 139, which was used to attain eight world records between 16 July and 10 August 1927. This floatplane was modified for the occasion by adding the transmission to the BMW VI engine and using a more efficient propeller. It was registered on 13 July in Swiss airplane register as CH 177 and on 15 September, after the record flights, it was duly removed. These flights were conducted by three Dornier pilots: Georg Zinsmaier, Richard Wagner and Egon Fath. Before the delivery to PV KSHS in mid September 1927, the engine was reverted to the original configuration. The following world records were secured:
16 July – Maximum altitude of 5,851 m with 1000 kg load
4 August – Maximum speed of 190.435 km/h over a distance of 100 km with a load of 2,000 kg
8 August – Distance covered of 1,600 km with a load of 1,000 kg
8 August – Maximum speed of 175.600 km/h over a distance of 1,000 km with a load of 1,000 kg
10 August – Distance covered of 2,100 km without load
10 August – Distance covered of 2,100 km with 500 kg load

10 August – Maximum speed of 172.000 km/h over a distance of 2,100 km with a load of 500 kg
10 August – Maximum speed of 172.000 km/h over a distance of 2,000 km without load.
One of the Do D intended for the delivery, W.Nr. 135, crashed into Bodensee during flight testing on 24 February 1927 with pilot von Mitterwallner at the controls. The pilot allegedly fainted due to exhaust gas poisoning and despite hitting the water hard he was rescued before the floatplane sank, while one of the assemblers who was inside the fuselage, Lehre, drowned.

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Do D was subsequently recovered on 5 March. As a replacement for W.Nr. 135, Dornier began work on W.Nr. 149 which was constructed with several modifications requested by PV KSHS. These included moving the cockpit further aft behind the wing, eliminating the machine gunner position, moving the internal storage space forward as well as running the rudder control cables on the outside of the fuselage. This Do D was delivered in mid 1927. Moving the cockpit further aft did not improve visibility and following a crash landing on 28 July 1928 these changes were reversed back to the original configuration with exception of the control cables.
Towards the end of 1927 KJ ordered another 14 floatplanes to be delivered in 1929, thus becoming the major user of this Dornier type. The delivery did not take place sooner because war reparation payments assigned to KJ for the year 1928 were already booked. As the work commenced, Dornier believed that the floatplanes could be delivered ahead of schedule. The first flight of the second series Do D took place on 15 September 1928. In the end these were delivered as contracted in 1929, with four in July, six in August and the last four in September. Pilots kbb Većeslav Dujšin and pk Danilo Hubmajer were assigned to receive the newly arrived Do Ds into PV KSHS inventory.
The second series incorporated several changes and improvements over the first series:
The fuselage and the float struts were strengthened
The fuselage underside was not recessed and as a result there were no provisions to carry torpedoes, only bombs on external racks
The underside fuselage contour was straight towards the tail instead of having a gentle curve
The rudder control cables ran on the outside of the fuselage
The ruder was covered with fabric instead of duraluminium sheets
Two of the first floatplanes, W.Nr. 193 and 194, included additional modifications to the float to fuselage support struts, which were made from two distinct parts instead of a single float carrier. This change led to improved handling while turning but at the cost of decreased speed.
Apart from the KJ, RVM (Reichsverkehrsministerium - German Ministry of Transport) from Berlin purchased three floatplanes which were used for coastal flights by Lufthansa as well as by DVS (Deutsche Verkehrsfliegerschule – German commercial pilot school).
With the total of 29 floatplanes produced, Do D was not a major export success for Dornier, however it did help PV KSHS fill the gap in offensive capability which gradually began to degrade and would not be resolved until Do 22 arrived in 1938.

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Introduction into Service

The first two Do D flew over to Kumbor with Dornier pilots at the controls while the remainder were delivered by rail and were assembled with the assistance of Dornier engineer Götz and technician Balluff who was sent by the factory to KJ to provide maintenance and training of PV mechanics. Following the formal introduction into service, Do D joined 20.HE (Hidro Eskadrila – Hydroescadrille). They represented the first modern and all metal floatplanes in PV service. Götz and Balluff also helped establish an overhaul facility at this location as well as at Divulje naval base.
In the spring and summer of 1927, Do D’s intended role was put to test when torpedo drop trials began with borrowed 530 mm ship torpedoes, at first at the controls of the German pilot while later PV pilots took over. Pbb Miroslav Gogala conducted one such test on 15 July 1927. Tests showed that a fully loaded Do D with a torpedo could not climb to an altitude greater than 60 m, while torpedoes were dropped from 20 m. This performance was not practical, the floatplane was underpowered to carry such large torpedo and as a result after repeated trials their use in this role was definitely abandoned.
 

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In addition to the torpedo trials, very early on during its use Do D showed other limitations. Pilots complained that despite its robustness, this floatplane was very heavy and its engine underpowered which limited its ability to carry offensive weapons and be maneuverable enough to escape modern fighters which it may have encountered during an eventual war. Additionally, it was very tricky to land, and a number of accidents occurred, which further strengthened its dislike amongst the pilots. By the time the order for the second series was placed, only seven floatplanes of the original 10 remained, while the rest were destroyed in various accidents.
On 29 May 1929 Do D 201 flew at an altitude of 2,500 m for a total of 11 h 57 min and 44 sec back and forth between Kumbor and Sušak, for which the 20.HE CO and pilot, pbb Miroslav Gogala, received an award from the Dornier factory. During this flight, he was accompanied by mechanic pf Rafael Perhauc, pilot nar Špiro Knešević and radio operator nar Jovan Bek.
The second series of 14 airplanes arrived to KJ in several batches in 1929 where they joined the newly formed 25. and 26.HE while two were sent to the training HE . All three HE were based at the time at Kumbor. Along with the second series, sizeable quantities of spare parts, including floats and wings, were ordered in order to keep all floatplanes in flying condition.

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 As of 1 May 1932, seven Do D were on strength from the first series and 13 Do Ds from the second series.
By 1934, seven Do Ds were struck off charge, leaving 17 in service. PVKJ retrospective review from 1937 lists a total of four Do D were struck off charge: 202, 208, 213 and 221 along with two BMW VI engines. In 1938, four Do D were struck off charge: 211, 216, 219 and 224 along with six BMW VI engines.
Do D periodically operated from the sole floatplane tender ship, Zmaj, which was ordered in 1929. Dorniers were unable to take off from the ship due to a lack of a catapult, hence they were lowered with the crane prior to and picked up the same way following flight.
According to the plan formed during the 4 February 1936 KM (Komanda Mornarice - Naval Command) meeting, by 1936 obsolete floatplanes which included Do D were supposed to be replaced. This task was accomplished with the purchase of Do 22 and their introduction in 1938. In 1936 there were a total of seven Do D within 2.HK 25.HE, another seven within 3.HK 26.HE and three within PVŠ (Pomorsko-vazduhoplovna škola – Naval Aviation School) at Divulje. Of the 17 Do D, seven were inoperable. 25.HE and 26.HE were tasked to with reconnaissance within 30 nm from the KJ territorial waters. It is known that as of July 1936, 201, 206 and 210 were serviceable and in flying condition, while 215 was serviceable in 1937.

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 These floatplanes served in PVKJ until 25 August 1939 when an official order No.17 issued by the Naval Commander prohibited their further use, since new Do 22s were available in numbers to fully replace them. Do D were however allowed to be only used in sea rescue roles while speeding across the water. They were intended for removal from service in accordance with the report submitted to MViM (Ministarstvo Vojske i Mornarice - Ministry of Army and Navy) on 10 May 1940.

Accidents
Year after year a number of accidents with Do D occurred as a result of frequent use resulting in constant attrition and decrease in available number of serviceable floatplanes. Until 1939, one to two Do Ds were lost each year, for a total of 17 floatplanes. The following reconstruction was made based on available documents and photographs.

April War

When the April war began, only three Do D remained. On paper Do D 212 was assigned to 1.HK (Hidro Komanda – Hydro Command) 15.HE, 203 to 3.HK 20.HE and 204 to 3.HK 21.HE.
203 was listed as unserviceable as of 31 January 1941 and was to remain out of service until 1 April but its engine was listed as serviceable, so the reason why it was grounded and remained listed as unserviceable as late as 5 April remains unknown. Until that time, the register shows that this floatplane flew a total of 1,224 times since 1927, underwent six overhauls and its engine S/N 16700 had 650 hours and 25 minutes working time and was overhauled eight times. It was captured by the Italians at Divulje and was shortly thereafter adorned with an Italian flag for propaganda purposes.
204 was listed as serviceable also as of 31 January 1941 but unserviceable as of 5 April. It had a total of 790 hours and 38 minutes flight time during a total of 735 flights and was overhauled a total of seven times. Its engine S/N 16139 was serviceable and had a total of 319 hours and 56 minutes working time and was overhauled six times.
212 during the April war remained at 2.HK workshop at Divulje since it was unserviceable and was intended to be struck off charge and scrapped. Due to their obsolescence, the Italians did not press these floatplanes into service and they were eventually scrapped.
Do D did not take part in combat operations as it lacked any combat value due to its obsolescence. It was only suitable for support roles and would have been struck off charge eventually and scrapped in the coming year.

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[…]

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Versions armed with a 37 mm gun