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

Lohner 10.21

  In early 1914, Uzelac asked Lohner to submit specifications for a multi-seat battleplane powered by two 150 hp engines. The LA returned the drawings for additional study on 30 March 1914. One month later, Lohner received funds to design a twin-engined battleplane which featured steering vanes mounted between the outer wing struts to counteract the turning moment and maintain a straight flight in the event one engine failed. The schematic planview was published in Austrian Patent No. 79202 granted on 2 May 1914. The battleplane drawings were re-submitted to the LA on 27 May 1914, but further work was held in abeyance.
  The LA issued new battleplane specifications on 20 August 1914, calling for a speed of 125 km/h (78 mph) and a climb to 1000 meters (3281 ft) in 8 minutes carrying a crew of six. The contract to build one prototype, known as the Lohner Type U (AD 925) and later designated 10.21, was signed on 31 August 1914. The final drawings, dated 9 July 1915, had four crew members; two located in the forward turret, one pilot behind the wings, and one gunner in the rear cockpit. The Lohner 10.21, the first twin-engined aircraft built for the LFT, was reported ready for flight trials in January 1916, but test pilot Karl Kriger's log book reveals that final assembly and ground tests were not completed until 14 April 1916 when he piloted the 10.21 on the maiden flight. During the course of sporadic testing through June 1916, the wing steering vanes and braking wheel were removed. The opposite-rotating 150 hp Daimler engines were replaced by engines revolving in the same direction but performance remained unsatisfactory. The 10.21 was accepted in June 1916 and assigned to Flek 6 in Wiener-Neustadt for further evaluation. Showing little interest, the LFT placed the 10.21 in storage until it was written-off in October 1917. The serial number was reassigned to the single-engined Lohner Type F.

Lohner 10.21 Specifications
Engine: 2 x 150 hp Daimler
Wing: Span Upper 21.00 m (68.90 ft)
Span Lower 16.00 m (52.49 ft)
Chord Upper 2.54 m (8.33 ft)
Chord Lower 2.20 m (7.22 ft)
Total Wing Area 77 sq m (829 sq ft)
General: Length 13.00 m (42.65 ft)
Height 4.20 m (13.78 ft)
Empty Weight 1920 kg (4234 lb)
Loaded Weight 2700 kg (5954 lb)
Maximum Speed: 120 km/hr (74.5 mph)

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
10.21 Löhner DD Type U 2 x Dm 100