The Focke-Wulf Fw 191 was a medium bomber designed in response to the German Air Ministry's 'Bomber B' specification of 1939, but that was let down by the failure of the engines it was designed to use and that never entered production.
The 'Bomber-B' programme called for a twin-engined aircraft capable of reaching any part of the British Isles. It was to have a top speed of 600km/h (373mph) and a payload of 4000kg (8,820lb). The aircraft was to be useable as either a high-altitude or dive bomber, reflecting the same obsession with the dive bomber that would cause so many problems in the development of the Heinkel He 177. The aircraft was to have a pressurized crew compartment and remote-controlled armament. The biggest weakness with the programme was that it relied on two engines that were still under development - the Junkers Jumo 222 and the Daimler-Benz DB 604. Both of these engines were expected to produce around 2,500hp, giving the bomber around 5,000hp.
Four companies submitted designs in response to the 'Bomber B' specification - Arado with the Ar 340, Dornier with the Do 317, Junkers with the Ju 288 and Focke-Wulf with the Fw 191.
Of the four designs the Arado Ar 340 was rejected outright and the Dornier Do 317 was given a low priority development contract. Focke-Wulf and Junkers were both given full development contracts, but with conditions. Junkers were to build the Ju 288 with as many hydraulic systems as possible, while Focke-Wulf were to use electrically powered systems wherever they could, including on all of the control surfaces. As a result the Fw 191 earned the nick-name of 'Fliegendes Kraftwerk', or 'flying power station'.
The Fw 191 was designed by a team led by Dipl Eng E. Kösel. It was an all-metal twin-engined monoplane with shoulder-mounted wings. It was designed to use two Jumo 222 engines, with straight sided wings inboard of the engines, and straight-sided tapering wings outboard. Ailerons were carried near the wingtip while a special combination landing flap and dive brake was carried on the trailing edge of both wings. The main wheels retracted by turning through 90 degrees before folding back into the nacelles, while the tail wheel retracted forward. The aircraft had twin fins and rudders with an almost square shape, carried at the tip of the tailplane.
The four-man crew were carried in a compartment in the nose. In production aircraft this would have been pressurised, but this wasn't installed on the prototypes. The pilot and bomb-aimer/ navigator sat behind the spherical nose. The second crewman had multiple positions, lying down in the nose to aim bombs or fire the nose gun, while as navigator he had a Plexiglas canopy that give him a view. This same position was to be used by the radio operator when controlling the three upper gun barbettes. The flight engineer had a gondola below the fuselage, with a glazed rear step to allow him to control the ventral gun barbette.
Work on the V1 and V2 prototypes began late in 1940, and it was soon clear that the Jumo 222 engine would not be ready, so the prototypes were powered by two BMW 801A air-cooled radials of 1,600hp each, for a total of 3,200hp, a drop of 1,800hp from the power levels that the aircraft was designed for.
The first two prototypes were completed without the pressurized cabins or their guns, which were replaced with mock-ups. Even with this reduction in weight the aircraft performed disappointingly during trials. The prototypes also suffered from a series of failures of their electrical systems, especially in the large numbers of motors needed to control the flaps and rudders. The first prototype made its maiden flight early in 1942, and was followed soon afterwards by the second.
After some effort on their part Focke-Wulf were given permission to abandon work on the V3, V4 and V5 prototypes and complete the V6 prototype using hydraulic power instead of electrical. This version of the Fw 191 was more reliable, but its engines were still underpowered, so its performance was no better.
V6 made its maiden flight early in 1943, and underwent a series of flight trials, before on 26 July 1943 it was flown from Delmenhorst to the Wenzendorf experimental station, on what was probably its last flight. By this point the failure of the two engine designs meant that the entire 'Bomber B' programme had been scrapped anyway, and work on the Fw 191 officially came to an end.
Three production versions of the Fw 191 were proposed during the design process.
The Fw 191A was the original production version, and would have been based on the V6. It would have had the pressurized nose and carried guns in five positions - one 7.9mm MG 81 in a chin turret, one each in barbettes carried at the back of the engine nacelles, and dorsal and ventral rear-fuselage barbettes that would have carried either twin MG 81s or a single 20mm MG 151 cannon. The Fw 191A would have carried a 8,820lb payload inside the bomb bay and 4,410lb under the wings.
The Fw 191B was proposed late in 1941 when it became clear that the original engines were falling behind schedule. It would have used the DB 606 or DB 610 paired engines, of 2.700hp or 2,870hp respectively. These paired engines had a worse power-to-weight ratio than the original engines, and would have reduced the aircraft's armament and payload. Probably for these reasons the Fw 191B was rejected.
The Fw 191C was suggested after the Fw 191A was cancelled. It was a simplified version of the aircraft, with four less powerful engines in the Jume 211/ DB 601E or DB 605 class, and with an unpressurized cabin and manually operated guns. Although the Fw 191C would have been easy to put into production, it wouldn't have been of much use to the Luftwaffe by 1943, and never entered production. Focke-Wulf used the designations Fw 391 and Fw 491 for different versions of the Fw 191C, but these were never official designations and were not used by the German Air Ministry.