O.Thetford, P.Gray German Aircraft of the First World War (Putnam)

Albatros D XI

   The D XI was the first of the Albatros D type lineage to use a rotary engine, and was fitted with the powerful geared Siemens-Halske Sh III of 160 h.p. This engine was installed in a horse-shoe cowling with pointed "elephant-ear" extensions to the rear. These acted as venturi and assisted cooling by sucking air through the cowling, which action also reduced drag.
   Two prototypes were built, the first with a four-blade airscrew and balanced ailerons of parallel chord, and the second machine with unbalanced ailerons of inverse taper and a two-blade propeller. Hollow wooden I struts braced the wings. Flying and landing loads were taken by two hollow diagonal struts, which dispensed with need for wire bracing. Both aircraft featured plywood box-type fuselage with built-in fin, the remainder of the aircraft being fabric covered.
   Initially flown in February 1918, the D XIs participated in the second D type competition. Remarkable climb performances were established, but no production order was given. Span, 8.0 m. (26 ft. 3 in.). Length, 5.58 m. (18 ft. 3 3/4 in.). Height, 2.86 m. (9 ft. 4 5/8 in.). Area, 18.5 sq.m. (199.8 sq.ft.). Weights: Empty, 494 kg. (1,087 lb.). Loaded, 689 kg. (1,516 lb). Speed, 190 km.hr. (118.75 m.p.h.). Climb (D Comp. at loaded weight of 723 kg.), 15,000 m. (16,400 ft.) in 151 min. Duration, 1.5 hr. Armament, twin Spandau machine-guns.

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

ALBATROS D XI Germany

   Flown for the first time in February 1918, the DXI departed from the traditional Albatros formula in certain respects. Like its predecessors, it was of wooden construction with fabric-covered wings and plywood-covered fuselage, but the unequal-span staggered wings had inclined aerofoil-section I-struts braced from their bases by pairs of diagonal struts which eliminated the need for wire bracing. For the first time in an Albatros fighter a rotary engine was employed, this being a 160 hp Siemens-Halske Sh III, and the unusually large propeller necessitated an exceptionally tall undercarriage. Armament comprised the usual twin 7,92-mm machine guns, and two prototypes were built, the first having a four-blade propeller and balanced parallel-chord ailerons, and the second having a two-blade propeller and unbalanced ailerons of inverse taper.

Max speed, 118 mph (190 km/h).
Time to 6,560 ft (2 000 m), 4.65 min.
Endurance, 1.5 hrs.
Empty weight, 1,089 lb (494 kg).
Loaded weight. 1,519 - 1,594 lb (689 - 723 kg).
Span, 26ft 3in (8,00m).
Length, 18ft 3 1/2 in (5,58m).
Wing area, 199.13 sqft (18,5 m2).

Jane's All The World Aircraft 1919

The single streamlined and outwards inclined strut idea has been carried out with the clear object of minimising the interplane connection head resistance, and in conjunction the inclined struts from the interplane strut bottom joint to the upper fuselage longitudinals doing althogether away with wiring. The Albatros strut form was first seen in the fashion of the 1916-17 L.F.G. Roland Whale effort, while the two inwards inclined struts appear to be of usual streamline shape.
   The body nose and the fairly forward position of the Albatros gives the impression of a rotary engine installation.
   One fails to see immediately the object of advancing the fin and balanced rudder on the Albatros.
   The tail fin and undivided balanced elevator is similar to the one of the biplane scout of the same firm.

J.Herris Albatros Aircraft of WWI. Vol.4: Fighters (A Centennial Perspective on Great War Airplanes 27)

Albatros D.XI

   Idflieg ordered two Albatros D.XI prototypes, 2208/18 and 2209/18 (work number 5045), and the first prototype was completed in March 1918, this being 2209/18. However, the Siemens-Halske Sh.III rotary was in limited supply and an engine could not be delivered until May, when the first flights were made.
   The D.XI was entered in the Second Fighter Competition but was flipped over on landing by the Albatros pilot after a mediocre climb performance had been demonstrated. Idflieg eliminated the D.XI from the competition after deciding it had a "decided penchant for flipping over," due to the tall landing gear and short fuselage. Moreover, the SSW D.III and Pfalz D.VIII that used the same engine were already in production and had priority for the engine.
   Despite this setback, Albatros continued development of the D.XI. In particular, the second prototype, 2208/18 featured aerodynamically-balanced ailerons to improve roll rate and a four-bladed propeller was fitted, enabling the landing gear to be shortened, thus making it easier to land.
   The Third Fighter Competition in October 1918 was officially limited to fighters powered by the 185 hp BMW.IIIa. Regardless, a number of rotary-powered fighter prototypes were included for comparision as 'interesting types' and the Albatros D.XI was one of them. Flying characteristics were generally good but aileron response (roll rate) was still too slow, a serious handicap in a fighter. Superior fighters were available and development of the Albatros D.XI was abandoned.


Albatros Fighter Specifications
D.XI D.XII/1 D.XII/2 D.XIII D.XIV
Engine 205 hp Sh.III 170 hp Mercedes D.IIIa 185 hp BMW.IIIa 170 hp Mercedes D.IIIa 185 hp BMW.IIIa
Span (Upper) 8.00 m 8.20 m 8.85 m 9.50 m 8.80 m
Span (Lower) 6.60 m 7.46 m 7.42 m - -
Chord (Upper) 1.5 m 1.4 m 1.4 m 1.65 m 1.7m
Chord (Lower) 1.0 m 1.4 m 1.4 m 1.10m 1.10 m
Gap 1.43 m 1.45 m 1.45 m 1.32 m 1.37 m
Stagger 0.43 m 0.28 m 0.28 m 0.75 m 0.70 m
Wing Area 18.5 m2 19.84 m2 20.01 m2 20.6 m2 20.64 m2
Length 5.58 m 6.62 m - 5.85 m 6.20 m
Height 2.87 m 2.68 m - 2.75 m 2.82 m
Empty Weight 494 kg 619 kg 621 kg 639 kg 640 kg
Useful Load 195 kg 180 kg 180 kg 181 kg 180 kg
Loaded Weight 689 kg 799 kg 801 kg 820 kg 820 kg
Wing Loading 37.2 kg/m2 40.3 kg/m2 40.0 kg/m2 39.8 kg/m2 39.7 kg/m2
Power Loading 3.36 kg/hp 4.70 kg/hp 4.33 kg/hp 4.82 kg/hp 4.43 kg/hp
Max. Speed 180 km/h 180 km/h 180 km/h 185 km/h 185 km/h
Climb, 1,000 m 1.8 minutes - 1.9 minutes 2 minutes 2 minutes
Climb, 2,000 m 4.3 minutes - 4.1 minutes - -
Climb, 3,000 m 6.3 minutes - 6.8 minutes - -
Climb, 4,000 m 9.3 minutes - 10.4 minutes - -
Climb, 5,000 m 12.8 minutes - 16.7 minutes 23 minutes 23 minutes
Climb, 6,000 m 17.8 minutes - - - -
Notes: All were armed with two machine guns. D.XIII track 1.75 m; D.XIV track 1.76 m.