W.Green, G.Swanborough The Complete Book of Fighters

ZEPPELIN-LINDAU D I Germany

   The D I single-seat fighter biplane created by the Abteilung ‘‘Dornier” in 1918 at the Lindau-Reutin plant was of all-metal construction with stressed fuselage skinning and cantilever wings of torsion-box construction, and carried a jettisonable fuel tank beneath the fuselage - features well ahead of the contemporary state of the art. Powered by a 160 hp Mercedes D IIIa engine, the first prototype flew on 4 June 1918, but shed the upper wing during flight testing in the following month, apparently justifying the caution with which the innovatory Dornier fighter was viewed by the Inspektion der Fliegertruppen (Idflieg). Nevertheless, two further prototypes powered by the 185 hp BMW IIIa engine were completed, with strengthened wing bracing and attachments. One of these participated in the third D-Type contest, but displayed a disappointing performance. The D I carried twin synchronised 7,92-mm machine guns. Although no production was ordered, three additional examples were completed (two with the Mercedes and one with the BMW engine), two of these being taken to the USA for evaluation after the Armistice. The data relate to the BMW IIIa-engined model.

Max speed, 124 mph (200 km/h) at sea level.
Time to 3,280 ft (1000 m), 2.6 min.
Range, 168 mis (270 km).
Empty weight, 1,598 lb (725 kg).
Loaded weight, 1,947 lb (883 kg).
Span, 25 ft 7 in (7.80 m).
Length, 20 ft 11 9/10 in (6,40 m).
Height, 8 ft 6 1/3 in (2,60 m).
Wing area, 200.86 sq ft (18,66 m2).

M.Schmeelke Zeppelin-Lindau Aircraft of WW1 (A Centennial Perspective on Great War Airplanes 42)

Zeppelin-Lindau D.I

  On February 11th, 1918, Claude Dornier submitted an offer to IdFlieg for an all-metal fighter. This aircraft, a D-type (= single-seat biplane armed with two MGs), would be put into service at high altitudes since it would be able to fly at 8,000 meters.
  After thorough deliberation within IdFlieg, ZWL received a preliminary agreement on February 28th, "for the delivery of six test aircraft."
  The written confirmation arrived on March 11th, 1918. The order included the delivery of six ZWL all-metal D cantilever aircraft. Apparently, IdFlieg was not completely comfortable with Dornier's modern wing structure, without fabric coverings and purely made of metal. Included in the order was a set of wings with fabric covering. The D.I was to be powered with Daimler IIIa and Benz Bz IIIb engines.
  The six aircraft received the military designations D.1750-D.1755/18. At the same time of the order, Daimler and Benz were instructed to each send an appropriate engine to Reutin. Benz also delivered a cooling system for its Bz.IIIa as well while IdFlieg prepared a cooler for the ED IIIa engine. The armament and the instruments and accessories including the instrument panel, seatbelts, and high-altitude oxygen system came from IdFlieg supplies.
  Engineer Albert Presser led the development of the D.I, and Eugen Jager was a member of his staff. In the following weeks the first all-metal cantilever single-seat fighter came into being in Reutin, where the monocoque construction technique of the fuselage was also transferred to the wings. The supporting structure was made of continuous upper and lower wings. The design as a cantilever biplane enabled the wings to sit on the fuselage, connected only by four cabane struts. Struts and tension cables were unnecessary. The lower wing was connected to the fuselage at three places. All of the ribs were of equal length on the three-spar, rectangular wings. This led to a simple and economical construction style, which Dornier kept for many of the designs in the following 20 years. In addition to the duraluminum-planked wings, another set covered in fabric was also constructed, as per IdFlieg’s request. Later there was a compromise: half of the D.I's wing was covered in duraluminum, and half in fabric. For the parts covered in fabric, the workers in Reutin used the army's five-color camouflage (D.1752/18) and the three-color navy camouflage (D.1751/18) and 1753-1755/18), which was in ample supply because of the flying boats.
  The pilot's seat could be adjusted up and down, as in the V1. The undercarriage consisted of two teardrop-shaped hollow bodies made of duraluminum that would serve as the legs, connected by a steel axle. The aircraft was armed with two LMG 08/15.
  The streamlined main fuel tank, which could hold 80 liters (of which 20 liters were for reserves) hung under the fuselage so that it could be jettisoned to minimize the danger of fire. Similarly, the auxiliary tank, which was located under the pilot's seat, could also be thrown overboard in case of fire. The oil tank, which held 10 liters, was placed lower so that the oil was fed to the oil pump by the downward slope of gravity. Engineers built adjustable side flaps into the cooling system to regulate the temperature of the cold engine and the discharge of air during flight.
  The D.I type's (D.1752/18) maiden flight took place on June 4th, 1918 in Zech; the pilot was Sergeant Ruppert. After a few taxi tests and short flights, he took the aircraft on a 20-minute flight at 1,500 meters where the aircraft showed good climbing and flying capabilities. After the flight, pilot Ruppert determined:
  “[...] flies wonderfully, climbs excellently. Almost no vibration, elevator and rudder control are fine and impeccable engine (Mercedes). ”
  While landing, Ruppert overlooked a ditch on the former military training ground and damaged the left landing gear.
  “[...] Unfortunately, it was not all sheer joy. Our pilot had a small accident during the landing. While taxiing he rolled into a small ditch and the shock forced the left landing gear to buckle. The airfield was actually not an airfield, but rather a military exercise area and therefore scarred with trenches and dugouts. The aircraft was disassembled and transported back to the workshop in Reutin for repairs.”
  In the workshop, a new engine, a 185 HP BMW IIIa, was installed in the repaired fuselage. The engine that had been planned for the aircraft, the Benz Bz IIIb, was eliminated from consideration due to the unsatisfactory results of that engine type in the Cs.I.
  A new cooling unit from the Suddeutsche Kuhlerfabrik (Southern German Cooler Factory) was mounted for the more powerful BMW engine.
  On June 15th, the first measurement flights were conducted with the second D.I, the 1751/18, which had been completed in the meantime. The measured take-off roll and landing roll were both less than 100 meters and the top speed was 195 km/h. This aircraft with the 160 HP D IIIa engine was immediately sent to Adlershof to take part in comparison flights for fighters. Time was of the essence because the competition had already begun on May 27th. Experienced combat pilots judged the various new designs the German aviation industry had to offer, and IdFlieg’s future orders would be heavily influenced by their verdicts.
  Following the order and delivery requirements set out by IdFlieg, every participating aircraft must have already passed resistance testing. IdFlieg skipped these structural tests due to time constraints, with what turned out to be fatal results.
  On July 3rd, First Lieutenant Hermann Goring climbed into the D.I at the airfield in Adlershof, flew a few circuits and landed without incident. Following his flight, Captain Kurt Schwarzenberger and Lieutenant Konstantin Krefft flew the aircraft. Then Captain Wilhelm Reinhardt, Commander of the Richthofen 'Flying Circus' (JG I) took his turn to fly the D.I.
  Reinhardt climbed to 1,000 meters and then the airplane dropped into a steep nosedive. The strain was too much for the spars of the upper wing, which broke off. Captain Reinhardt died in the crash.
  Ironically, a set of reinforced spars had already arrived in Adlershof, ready and prepared to be mounted to the aircraft. After the aircraft had been shipped from Reutin to the comparison flight program, the designers had also had some quiet doubts. Recalculations supported these doubts and reinforced spars were immediately constructed and sent to Adlershof. In addition, ZWL had requested the D.I be taken out of the comparison testing program until the modifications had been completed. It is unclear why those responsible at IdFlieg did not grant this request.
  Employees of the company had been banned from approaching the aircraft after the comparison testing had begun. Despite this tragic accident, IdFlieg was still very interested in the D.I. The combat pilots, including a member of the Austro-Hungarian air corps, gave the aircraft a positive rating.
  Between September 23rd and October 11th, 1918, structural tests were conducted on D.I 1750/18 in Adlershof. The only modifications that were requested were that the cabane struts were to be attached to the horizontal beam and a few insignificant improvements on the fuselage.
  At the next comparison testing event that took place in Adlershof between October 15th and 31st 1918, two Zeppelin-Lindau aircraft were present: D.I 1751/18 E (for "Ersatz" - replacement) and 1752/18 with a BMW IIIa engine. The competition was being conducted to choose the combat aircraft for a planned spring offensive in 1919. Dornier's D.I achieved excellent results, including climbing 1,000 meters in 2.6 minutes, fully loaded with fuel, armed and outfitted with an oxygen system. The targeted ceiling of 8,400 meters was reached after 45 minutes. The range was 270 kilometers, and top speed was 200 km/h.
  The only complaint was the pilot's limited visibility directly upward and downward. Cutouts in the upper wing at the height of the pilot's seat and at the roots of the lower wings remedied this. Combat pilots' lives rested on good visibility, especially in dogfights, and therefore this was an important assessment criterion in all new aircraft.
  The ceasefire on November 11th, 1918 did not mean production within ZWL immediately ceased. Work in Lindau continued until the end of the year with a smaller staff. The company was still in possession of the D.I aircraft completed during this time, the 1753/18, in December 1918. In 1921 it was sold to the U.S. Navy for $9,000. The D.I 1754/18, after it was stored at the Riechs military airfield in Schliessheim from 1919, was also purchased by the U.S. Air Service, via arrangement through a Swiss company.
  Members of the construction crew were able to hide the final specimen, D.I 1755/18, from the interallied military control commission. Later, it was a big attraction at the Dornier Museum in Manzell and in the Salzstadel in Friedrichshafen. During the Second World War, the museum was badly damaged by an allied bombing campaign, and the D.I was scrapped for its metal.
  Although it is not likely that many ZWL (Do) D.I would have been used in the German air corps, this type of aircraft, along with the Siemens-Schuckert D.VI, were considered equal to the enemy French high-altitude fighter such as the Nieuport 29 (peak altitude 8,300 meters).
  Dornier used the rich data from the D.I to move on to his new fighter airplane project at the end of 1921, the Dornier H Falke (Falcon).



Specifications of Zeppelin-Lindau Aircraft

Type Length, m Span, m Height, m Chord, m Propeller Manufact. Armament
(guns) Weight, kg Motor Crew
D.I 6.40 7.80 2.60 Heine 2.75 2 fixed 883 Daimler D IIIa/BMW IIIa 1



Military Numbers of Dornier-ZWL Aircraft
Military Designation Manufact. Type Class Engine Notes
1750/18 ZWL (Do) D.I
1751/18 ZWL (Do) D.I DIIIa
1751/18 E ZWL (Do) D.I BMW IIIa Replacement for the D.I crashed 7/3/18
1752/18 ZWL (Do) D.I D IIIa Mothballed in Adlershof
1753/18 ZWL (Do) D.I DHIa Sold to the USA in 1922
1754/18 ZWL (Do) D.I BMW IIIa Mothballed in Schleissheim 1919/1920
1755/18 ZWL (Do) D.I BMW IIIa Possibly Dornier Museum Friedrich.

M.Dusing German Aviation Industry in WWI. Volume 2 (A Centennial Perspective on Great War Airplanes 85)

Zeppelin-Werke Lindau GmbH (ZWL), (Do)

Aircraft Development:

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  It was only a logical development of the experience gained with the use of sheet metal that in the spring of 1918 the first completely tension-free aircraft with a pure sheet metal construction was launched. In this Do D.I type, the sheet metal skin of the wings was the strength bond of a large hollow beam. With a completely smooth and robust outer surface, a high level of structural safety was achieved, as detailed load tests proved.
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