P.Grosz, G.Haddow, P.Shiemer Austro-Hungarian Army Aircraft of World War One

Knoller 30.05

  As their first aircraft, the Knoller 30.05 prototype embodied many of Knoller and Fiala's theoretical and structural ideas. The Knoller rib section, tested in his wind tunnel, had a highly-flexible trailing edge designed to flatten with increasing velocity to reduce drag. Weight and drag were minimized by a wireless wing cellule using a Warren-truss layout. Knoller's participation in the re-design of the Lohner B.I (Type B) and B.II (Type C) biplanes may have delayed the preparation of a proposal acceptable to the LA. On 11 January 1915, the LA signed a contract with Thone & Fiala to build one prototype (30.05) and five production aircraft designated Knoller B.I (Th) series 35.8.
  The 30.05 prototype, powered by a 100 hp Mercedes engine, arrived for flight testing at Aspern on 6 June 1915. Some 20 flights totalling 8 hours duration were performed under Knoller's supervision. Various modifications, including stronger struts and an auxiliary tailplane (a biplane tail was designed but not used), failed to ameliorate the dangerous flight characteristics. The 30.05 was grounded in September 1915 for being "hazardous to life." On 8 November 1915, Thone &. Fiala proposed fitting a strengthened center-section and other changes but the work was shelved to concentrate their effort on the Knoller B.I (Th) production machines.
  On 16 February 1916, the Flars acceptance group issued orders to write-off the 30.05, but the Flars command intervened and on 1 August 1916 irresponsibly lifted the flight ban. Fortunately, in view of its dangerous flight characteristics the 30.05 never was flown again. It was accepted in February 1917 and employed as an instructional airframe in a mechanics school.


Knoller B.I(Th) Series 35.8

  On 11 January 1915, the LA ordered five Knoller B.I(Th) biplanes, numbered 35.81 to 35.85 and powered by a 100 hp Mercedes engine. The first machine, 35.81, delivered on 8 October 1915, performed the maiden flight on 13 November 1915, and was flown three times by Feldwebel Franz Kuntner with an passenger aboard. "Peculiar" flight characteristics were reported, induced by excessive fuselage twisting and a noticeable deformation of the outer wing when the ailerons were actuated. New ailerons and tailplane and a reinforced center-section failed to reduce wing deformation or improve the flight traits during tests on 4 and 15 December 1915. Withdrawn for modification, the 35.81 was ready to continue trials on 8 January 1916, being joined by the new, modified 35.82 later that month. To eliminate the tail heaviness and "bizarre" control response, Knoller and Fiala had designed new ailerons, an improved rib section, an airfoil-shaped tailplane, and changed the stagger. To reduce deformation, the wings were now given wire bracing. Flight evaluation by experienced test pilots (Kuntner, Hans Mandl, Viktor Nowy, Max Perini, Johann Varga) between January and mid-April, 1916, produced a formidable list of structural deficiencies and control problems.
  Although continuing flight investigations had exposed severe shortcomings, Flars inexplicably purchased an additional batch of ten aircraft, numbered 35.86 to 35.95, on 12 February, 1916. The first five production aircraft (35.81 to 35.85), suitably modified, were delivered in March 1916. The additional weight of the airframe modifications had reduced the performance below the contractual specifications. Sporadic testing of the five aircraft continued through 24 July 1916, when the acceptance group stopped all flights, contending that the aircraft were unsuitable for frontline or training service. Nevertheless, production of the next ten aircraft (35.86 to 35.95) proceeded apace. The first two aircraft were delivered on 21 November 1916 and the last in June 1917. Records show only one of these aircraft had been flown before all were placed in storage. The 15 stored airframes were provisionally accepted in October 1917.
  The inadequacy of the Knoller-Fiala design had been amply demonstrated. Yet in the face of the aircraft's unacceptable characteristics, Knoller's lofty reputation kept the program alive and contrary to pilots' advice, the LFT stubbornly approved Knoller aircraft production at Aviatik, Lohner, Phonix and WKF beginning August 1916.


Knoller C.I(Ph) Series 25

  In spite of dangerous aerodynamic and structural problems encountered in the early Knoller biplanes, the LFT and Flats, with unwarranted optimism, awarded Phonix an order on 24 December 1915 for 48 Knoller C.I(Ph) biplanes for which 200 hp Hiero engines were specified. Production was already under way and deliveries were scheduled to end on 13 February 1916. In fact, the first production aircraft, 25.01 powered by a 160 hp Daimler engine, did not arrive at Aspern until 15 April 1916. During the flight evaluation, the 25.01 was returned to Phonix for repair at least five times, once because a fuselage frame broke while taxiing (2 August 1916). Being very lightly built, the Knoller C.I(Ph) reached a top speed of 167 km/h (104 mph) and 2000 meters (6562 ft) in 10 minutes, a very respectable performance for its day. The 25.01 was reported stable but tail-heavy and the control forces were far too heavy. Toward the end of May 1916, Uzelac flew the 25.01. His impulsive statement that “the crate is good" was unfortunately mis-interpreted as highest praise and sufficient cause to continue production. Flars rejected Knoller's plea to make further modifications on grounds that "a serviceable, high-performance aircraft should be placed into operational service as soon as possible."
  While the next two aircraft, 25.02 and 25.03, with lightened fuselages were being completed, 25.01 was reinforced, again flight tested and accepted on 25 October 1916. Faced with delays and preferring to await frontline evaluation results, Flars reduced the production order to 16 aircraft (25.01 to 25.16) - all that would be built. In November 1916, the 25.01 went to Flik 23 where it was flown by Hauptmann Heinrich Kostrba, an experienced pilot. His report was totally negative: “stability poor, nose-heavy, difficult to control in wind gusts, maximum speed only 130 km/h (81 mph), forward visibility deficient." Damaged during landing, 25.01 was returned to Phonix for repair.
  Considering that Phonix was already building the superior Brandenburg C.I, it is difficult to understand why an additional 24 Knoller
C.I(Ph) aircraft were ordered on 29 December 1916. Fortuitously, the contract was annulled. Pilots were advised to fly the type “only when absolutely necessary (ie: performing acceptance flights) and avoid sharp turns". When the reinforced C.I(Ph) 25.08 was finally load tested on 21 September 1917, the airframe failed at a load factor of 3.9, well below the proscribed factor of 5.0. In September 1917, Flars proposed using the Knoller C.I(Ph) as a trainer powered by a 160 hp Daimler engine, but the proposal was rejected. Inexplicably, rather than halting production the remaining aircraft were completed, the last being accepted in March 1918. Having served no useful purpose, 15 engineless airframes were placed in storage.

Knoller C.I(Ph) Series 25 Specifications
Engine: 160 hp Daimler
Wing: Span Upper 12.7 m (41.67 ft)
Chord Upper 2.25 m (7.38 ft)
Chord Lower 1.76 m |5.77 ft)
Sweepback Upper 10 deg
Gap 2.10 m (6.89 ft)
Stagger 0.57 m (1.87 ft)
Total Wing Area 36.0 sq m (387 sq ft)
General: Length 8.50 m (27.89 ft)
Height 3.30 m |10.83 ft)
Track 2.23 m (7.32 ft)
Empty Weight 780 kg (1720 lb)
Loaded Weight 1217 kg (2683 lb)
Maximum Speed: 158-167 km/hr (98-104 mph)
Climb: 1000m (3,281 ft) in 4 min 45 sec
2000m (6,562 ft) in 10 min 2 sec
3000m (9,843 ft) in 17 min 5 sec


KNOLLER C.II (Lo) Series 19 and 119

  In the absence of a suitable design, Lohner, like Aviatik and WKF, was forced to accept the license-production of 48 Knoller C.II biplanes, assembly of which began in July 1916. The contract, formally signed on 8 December 1916, stipulated delivery of 48 aircraft to begin on 13 October 1916 and end on 6 January 1917. Production was to have been split evenly between 160 hp and 185 hp Daimler-engined versions, but the 185 hp engine shortage limited planned production to 16 C.II (Lo) aircraft, numbered 19.01 to 19.16. The remaining 32 machines, powered by the 160 hp Daimler engine, were to be numbered 119.01 to 119.32. In practice, the numbering scheme was changed and some unexplained numbers (ie. 19.25) have appeared in LFT records.
  Performance of the first C.II (Lo) series 19 biplanes, flight tested in November-December 1916, fell far short of expectation. Acceptance flights of the 24 completed C.II (Lo) machines was stopped in December 1916 pending correction of faults found in the Aviatik-built Knoller machines. In January 1917, aircraft 19.25, fitted with a reinforced center-section, arrived at Aspern for flight testing; however, after the wing failure of the C.II (Av) 36.07 in February 1917, Lohner designed a "normal" upper front wing spar, stronger wing fixtures and other modifications that were applied to the Aviatik and WKF-built Knoller machines as well. By mid-1917, after endless structural modifications to strengthen the airframe, the Knoller C.II aircraft were deemed safe to fly and the first Lohner production machines were accepted in May 1917.
  Flars, the driving force behind the Knoller program, was insistent that the type be evaluated at the Front. Aircraft 19.04, 19.07-19.10, a few series 119 machines, and several Aviatik-built C.IIs, were dispatched to Flik 50 and the Flieger-Versuchsabteilung Stryj (aircraft test section, later designated Flik 70) for trials in November-December 1917. Limited operational sorties were flown. The Knoller C.II was unpopular with aircrews who reported it useless as an operational machine. Flik 50 criticized the poor flight characteristics, the fragile construction, and the sloppy workmanship of the Lohner-built Knollers. The type was withdrawn from the Front.
  Most of the 185 hp engines of the C.II (Lo) series 19 were removed and the airframes placed in storage, but series 119 continued flying as an advanced trainer with Fleks 1, 5, 6, and 8. As of August 1918, four series 19 and two series 119 were carried in the frontline inventory; presumably these were used to carry mail. At the war's end, nine series 119 machines based at Flek 5 in Szeged became Hungarian property and two served with the Hungarian 5th Air Squadron. Aircraft 119.15, under repair at the Al-Ma factory in Prague, became Czechoslovakian property. After many years on exhibit in Prague, it has recently been restored.

Knoller C.II(Lo) Series 19 Specifications
Engine: 185 hp Daimler
Wing: Span Upper 10.00 m (32.81 ft)
Span Lower 8.00 m (26.25 ft)
Chord Upper 2.08 m (6.84 ft)
Chord Lower 1.08 m (3.54 ft)
Sweepback Upper 5.5 deg
Stagger. 0.68 m (2.23 ft)
Total Wing Area 28.0 sq m (301 sq ft)
General: Length 8.50 m (27.89 ft)
Height 3.20 m (10.50 ft)
Track 2.064 m (6.77 ft)
Empty Weight 695 kg (1532 lb)
Loaded Weight 1057 kg (2331 lb)
Maximum Speed: 161 km/hr (100 mph)
Climb: 1000m (3,281 ft) in 4 min 3 sec

Knoller C.II(Lo) Series 119 Specifications
Engine: 160 hp Daimler
Wing: Span Upper 10.00 m (32.81 ft)
Span Lower 8.00 m (26.25 ft)
Chord Upper 2.08 m (6.84 ft)
Chord Lower 1.08 m (3.54 ft)
Sweepback Upper 5.5 deg
Stagger 0.68 m (2.23 ft)
Total Wing Area 28.0 sq m (301 sq ft)
General: Length 8.50 m (27.89 ft)
Height 3.20 m (10.50 ft)
Track 2.06 m (6.77 ft)
Empty Weight 751 kg (1656 lb)
Maximum Speed: 125 km/hr (78 mph)
Climb: 1000m (3,281 ft) in 5 min 16 sec
3000m (9,843 ft) in 24 min 10 sec


Aviatik 30.08

  The 30.08 prototype, a standard Knoller B.I(Av) 35.02 airframe fitted with a 85 hp Hiero engine for evaluation purposes, was under construction in May 1916. The 30.08 prototype was ready for acceptance on 21 November 1916. In early 1917, a 100 hp Mercedes engine was fitted, returning the prototype to the standard Knoller B.I(Av) configuration. Renumbered 35.02, the aircraft was provisionally accepted and stored at the Aspern aircraft depot.


Aviatik 30.09

  In April 1916, Professor Knoller proposed a single-seat fighter conversion of the Knoller B.I(Av) powered by a 145 hp Hiero engine and armed with a gun canister on the upper wing. The aircraft was assigned the prototype designation 30.09. The maiden flight was performed by Feldwebel Ferdinand Konschel on 8 July 1916, who reported poor flight characteristics. A Flars engineering inspection on 21 August 1916 listed numerous defects, including shoddy workmanship. The 30.09 prototype, ready for acceptance on 21 November 1916, was not accepted until March 1917. In 1918 the 30.09 served as an instructional airframe at the Aspern apprentice school.


Aviatik 30.10

  Assembly of the Aviatik 30.10 biplane, prototype for the Knoller C.II(Av), began in the early summer of 1916. Although chief engineer Berg had expressed serious misgivings regarding structural integrity, the prototype was built as specified. Completed on 11 September 1916, the 30.10 was immediately grounded by Flars engineers to reinforce a fuselage frame.
  During the maiden flight on 20 September, the 30.10, powered by a 160 hp Daimler engine (not a 185 hp Daimler as specified), achieved respectable performance, reaching a top speed of 169 km/h (105 mph) and an altitude of 1000 meters (3281 ft) in 5:11 minutes. However, wing flexing and severe slipstream buffeting left the trailing-edge fabric in tatters. On 3 October the repaired 30.10 was aloft for further tests when a fuselage frame broke due to excessive elevator force and several lower wing ribs came apart. The 30.10 was grounded and, as part of the Knoller C.II(Av) program, submitted to static load tests that it failed on 31 October 1916. Aviatik director Janisch argued that the test should have been performed using a new production airframe, but Flars correctly insisted on the choice of a random airframe to prevent the company from taking special measures to assure test compliance. Further information is lacking.


Aviatik 30.11

  Existing archival records regarding the Aviatik 30.11 prototype are in conflict. One citation identifies the 30.11 as a Knoller B.I(Av) biplane modified to carry one machine gun for armament. Another document states that the prototype was similar to the Knoller C.I(Ph) but fitted with an observer's machine gun tower (Turm). Since no record of construction has been found, it is possible the 30.11 remained on the drawing board.


KNOLLER B.I(Av) Series 35

  Flars approved production of the Knoller B.I(Av) biplane at a time when the Thone &. Fiala 30.05 prototype was grounded because of structural weakness. Despite Professor Knoller's reputation and optimism, the design simply was not ready for manufacture. But powerful political pressure was involved. On 31 December 1915, Aviatik signed a contract for 32 Knoller B.I(Av) biplanes, numbered 35.01 to 35.32. They were powered by a 100 hp Mercedes engine. Delivery, scheduled to end on 5 March 1916, was not completed until two years later during which time only cursory flight testing took place.
  The Knoller B.I(Av) 35.01 was completed on 24 December 1915. Initial test reports revealed that not only did the aircraft possess abysmal flight characteristics but also displayed a catalog of structural and aerodynamic deficiencies. Other Knoller aircraft fared no better. During the maiden flight of 35.02 on 8 March 1916 both elevator horns failed. The observer's seat of 35.07 broke through the fuselage on 24 July 1916. That day, worried by recurring failures, Oberleutnant Viktor Nowy and Hauptmanns Josef Cejnek and Karl Nikitsch issued a joint statement condemning the Knoller B.I because "its use would place life in jeopardy." Thus, contrary to standing orders, the supervising acceptance officer temporarily prohibited further flights. Production was halted in August to await Knoller's improvements, but in reality the basic design was unsound and little could be done. Following an in-flight rudder arm fracture (35.10) and repeated load test failures (35.13 and 35.14), the acceptance officer reported on 31 October 1916 that the customary gust loads expected in flight had not been taken into account. Critics felt that while Knoller's theoretical calculations may have promised exceptional performance, his lack of design skill had produced a weak aircraft riddled with dangerous flight characteristics.
  All Knoller B.I aircraft were grounded on 8 November 1916 to allow Flars once again to methodically check the load calculations. The 35.01 was written-off after passing the static load tests on 6 March 1917. Four aircraft (35.03, 07, 08 and 12) were assigned to various training or test units and the remaining completed aircraft were stored at Aspern awaiting disposition. While Aviatik assembled the last aircraft, Knoller and Flars, as late as June 1917, were busy designing stronger fittings for the Knoller B.I(Av)! In August 1917 Flars, finally admitting the total failure of the Knoller program, accepted 31 B.I(Av) aircraft at 80 percent of cost value. The airframes were stripped and scrapped.

Knoller B.I(Av) Series 35 Specifications
Engine: 100 hp Mercedes
Wing: Span Upper 10.90 m |35.76 ft)
Span Lower 8.16 m (26.77 ft)
Chord Upper 1.65 m (5.41 ft)
Chord Lower 1.65 m (5.41 ft)
Dihedral Lower 3 deg
Sweepback Upper 5.5 deg
Gap 1.80 m (5.91 ft)
Stagger 0.85 m (2.79 ft)
Total Wing Area 29.86 sq m (321 sq ft)
General: Length 7.67 m (25.16 ft)
Height 3.01m (9.88 ft)
Track 2.05 m (6.73 ft)
Empty Weight 628 kg (1385 lb)
Loaded Weight 937 kg (2066 lb)
Maximum Speed: 132 km/hr (82 mph)
Climb: 1000m (3,281 ft) in 8 min 10 sec


KNOLLER C.Il(Av) Series 36 and 136

  Following the crash of the Aviatik 30.06 prototype, Flars switched the proposed contract for 48 machines to the Knoller C.II biplane. That this type went into production when the Knoller program was in deep trouble and largely discredited supports Graf Adalbert Sternberg's (a member of parliament) accusation of political influence wielded by Knoller's supporters. Two contracts were signed by Aviatik; one on 4 August 1916 for 24 Knoller C.II(Av) series 36 aircraft powered by a 185 hp Daimler engine, and the other on 23 September for 24 C.II(Av) series 136 powered by a 160 hp Daimler engine. The aircraft were numbered 36.01 to 36.24 and 136.01 to 136.24 respectively.
  In June 1916, with assembly already under way, Aviatik reported delays because manufacturing drawings were incomplete because of the many changes required by Knoller. The first production aircraft, 36.01, performed its maiden flight on 10 September 1916. Both the 30.10 prototype and 36.01 were temporarily grounded on 13 September 1916 for modification. Responsibilities were so ill-defined that director Janisch refused to work on the 36.01, and conversely Knoller rejected improvements suggested by Aviatik. To rectify "extreme" tail-heaviness, not alleviated by relocating the observer and internal equipment, Knoller devised an S-shaped airfoil for the tailplane. Aviatik regarded the additional lift forces imposed on the tail and fuselage as dangerous. In a climb, the aircraft remained tail-heavy and in level flight nose-heaviness increased with speed. The glide characteristics were considered good but the landing speed was unacceptably high. Throughout the flight test program, Knoller's ultra-light construction resulted in a long list of structural failures, among them: weak tail skid and control surfaces (26 October), rudder failure (8 November), static load test failure (36.08 - 21 November and 28 December), wing rib fracture (36.02 - 14 December), undercarriage collapse (36.02 and 36.04 - reported 12 January 1917).
  While the C.II aircraft were grounded, a much-modified 36.13, fitted with strut joints machined from solid steel, finally passed the static load tests on 9 January 1917. Flars permitted flight testing to continue on 17 January "but only if absolutely necessary." Steep turns were to be avoided until new strut joints were installed throughout. Despite growing aversion to Knoller aircraft, test flights continued. Flying 36.07, two aircrew were killed on 10 February 1917 when a lower wing came off. Once again the C.II was grounded. The flight restriction was lifted on 4 April, but Aviatik, under pressure to produce its own designs, had lost interest in the C.II and stopped work. Out of a total of 18 or 19 completed, only 8 C.II(Av) series 36 aircraft were accepted. None of the series 136 aircraft were completed. Forty C.II airframes were in storage at Aviatik when the war ended.
  Although Uzelac vetoed the idea, a special unit, known as the Flieger-Versuchsabteilung (experimental flying section) later to become Flik 70, was established to evaluate the C.II under service conditions. Aircraft 36.08, 36.10, 36.11, 36.14, and 36.20 formed part of the Knoller C.II contingent that went to the Eastern Front in July 1917. The Knoller C.II had such a poor reputation that few pilots cared or dared to fly it. The 18 January 1918 report shows that the years of effort were hardly worthwhile:
  The C.II can be flown only by skilled pilots, especially while landing. It tosses and swings in gusty weather but reacts rapidly and positively to the controls. In turns, altitude loss is rapid if airspeed is not carefully maintained. The observer is buffetted by a frightening propeller wash, to such a degree that he must hold on and take care not to fall out while operating the machine gun. In cold weather, impossible for the observer. Pleasant to fly in calm conditions. Good view forward.
  In August 1918, only one C.II series 36 was listed in the frontline squadron inventory against four C.II series 19, two series 119, and five series 81. A few series 36 aircraft became advanced trainers at Flek 5 or found use as instructional airframes in mechanic training schools.

Knoller C.II(Av) Series 36 Specifications
Engine: 185 hp Daimler
Wing: Span Upper 10.37 m (34.02 ft)
Span Lower 8.14 m (26.71 ft)
Chord Upper 2.09 m (6.86 ft)
Chord Lower 1.68 m (5.51 ft)
Sweepback Upper 5.5 deg
Stagger 0.59 m (1.94 ft)
Total Wing Area 30 sq m (323 sq ft)
General: Length 8.54 m (28.02 ft)
Height 3.02 m (9.91 ft)
Track 2.06 m (6.76 ft)
Empty Weight 695 kg (1532 lb)
Loaded Weight 975 kg (2150 lb)
Maximum Speed: 160 km/hr (99 mph)
Climb: 1000m (3,281 ft) in 4 min 24 sec


Knoller C.II(WKF) Series 81

  Faced by the failure of the Lloyd C.IV and lacking an inhouse replacement, Flars filled the production gap by assigning WKF the Knoller C.II, a design of great but never-realized expectations. To the extent that drawings were available, WKF began parts manufacture for 24 Knoller C.II(WKF) biplanes, numbered 81.01 to 81.24, in July 1916. By the time the contract was officially signed on 22 December 1916, most of the assembly work was complete. Originally the 185 hp Daimler engine was specified, but owing to the engine shortage, all aircraft were delivered with reconditioned 160 hp Daimler engines. The contract called for delivery to begin on 15 November and end on 31 December 1916. The first three aircraft were ready for acceptance in December 1916, but the flight trials of the first aircraft, 81.02, demonstrated such serious structural faults, particularly the wing attachment fixtures, that further modification was required before the aircraft were deemed airworthy.
  After the Flars inspection and critique (commissioning) on 14 January 1917, aircraft 81.02 was returned to the factory to await new drawings for re-designed parts issued in April. After a suitably modified aircraft (81.05) was re-commissioned on 21 May 1917, additional modifications were specified for all aircraft. By now Lloyd C.V output had priority at the expense of Knoller production, so it was not until December 1917, after a year's delay, that the first three Knoller C.II(WKF) biplanes were accepted.
  In spite of their obsolescence, aircraft 81.01, 81.02, and 81.05 were dispatched to Flik 66/D and 81.03 and 81.04 to Flik 67/D in January 1918, but details regarding service use are lacking. Other Knoller C.II(WKF) biplanes were sporadically flown as advanced trainers by Fleks 1, 5, 8, and 18. Aircraft 81.11 and 81.23 had a special four-hour fuel tank installed for service with the airmail flight at Aspern.

E.Hauke, W.Schroeder, B.Totschinger Die Flugzeuge der k.u.k. Luftfahrtruppe und Seeflieger 1914-1918

10. Flugzeuge der Fabrik Jacob Löhner & Co. Wien, Floridsdorf
19.01 — 19.26 Knoller C.II (Lo)
119.01 — 119.20 Knoller C.II (Lo)

20. Flugzeuge der Phönix-Flugzeugwerke, vormals Österr. Albatros
25.01 — 25.16 Knoller C.I (Ph) Dm 160

30. Flugzeuge der Österreichischen Aviatik-Werke Wien, Stadlau
30.05 Knoller B.I (Bruchzellenversuch) Merc 100
30.08 Knoller DD H 145
30.09 Knoller DD H 145
30.10 Knoller DD Dm 160
30.11 Knoller C.II (Waffenversuch MG-Turm) Dm 160
35.01 Knoller B.I (Av) Merc 100
35.02 (ex 30.08) Knoller B.I (Av) Merc 100
35.03 — 35.32 Knoller B.I (Av) Merc 100
35.81 — 35.96 Knoller B.I (Th) Type KNF Merc 100
36.01 — 36.23 Knoller C.II (Av) Dm 185
136.01 Knoller C.II (Av) Projekt Dm 160

80. Flugzeuge der Wiener Karosserie-Fabrik (W.K.F.) Wien und Hennersdorf
81.01 — 81.24 Knoller C.II (W.K.F.) Dm 160