Designed from the outset for use on U-boat "cruisers", like the Type XI B, the Ar 231 was a light parasol-wing aircraft. The aircraft was powered by a 119 kW (160 hp) Hirth HM 501 inline engine, weighed around 1,000 kg , and had a 10 m  wingspan. The design led to a simple and compact aircraft that could be fitted into a storage cylinder only 2 m  in diameter. For ease of storage, the Ar 231's wings featured detachable sections that two operators could remove in less than six minutes. One unusual feature was an offset wing design, with the right wing root attaching to the wing's tilted center section (elevated above the fuselage, as on all parasol-wing designs) and lower than the left wing root, to allow the wings to be quickly folded up.
Testing soon revealed the Ar 231s to be fragile, underpowered, and difficult to fly even during calm weather, and as a result, development ended in favour of the Focke Achgelis Fa 330 gyroglider. Some of the testing was done on the auxiliary cruiser Stier, two of the six prototypes being taken on one voyage.
Type Single seat reconnaissanse seaplane for use on submarines
Engine 1 Hirth HM 501
Dimensions Length 7,81 m, height 3,83 m, span 10,18 m, wing area 15,2 m2
Weights Empty weight 833 kg, flying weight 1050 kg, fuel 103 l
Performance Max. speed 170 km/h, cruising speed 140 km/h, range 420 km, service ceiling 3000 m, endurance 3,5 h, climb to 1000 m 6,0 min.
Type Werk.Nr Registration History
V1 231 0001 KK+BP First flight 25 July 1940. Scrapped March 1943
V2 231 0002 KK+BQ Scrapped March 1943
V3 231 0003 KK+BR Used on the "Stier" 1942. The ship was sunk on 27th of September 1942
V4 231 0004 KK+BS Used on the "Stier" 1942. The ship was sunk on 27th of September 1942