The Blohm und Voss Bv 138 was a three-engined long-range reconnaissance flying boat that was the most numerous of their own aircraft produced by Blohm und Voss.
The Blohm und Voss ship building firm founded an aircraft subsidiary, the Hamburger Flugzeugbau, on 4 July 1933, under the control of Walter Blohm. Its first aircraft, the Ha 135, was designed by Reinhold Mewes, but he was soon replaced by Dr Ing Richard Vogt, who was responsible for most Blohm and Voss designs (many of which was for quite unusual aircraft).
From 1933 until 1937 Blohm und Voss aircraft carried the Ha designation, but from that year they changed to Bv. This change came during the development of the Bv 138, so the prototypes were known as the Ha 138 while production aircraft became the Bv 138.
The Bv 138 was the first flying-boat to be produced by Blohm und Voss. A series of possible designs had been examined, before project P.12 was selected as the basis for a long-range reconnaissance aircraft. The original design had a short hull and a high mounted wing, with twin engines and booms, and floats attached to the wings.
A mock-up was built early in 1935, and Blohm und Voss were rewarded with a contract to produce three prototypes, each to be powered by a different type of 1,000hp engine. All three of the intended engines then ran into design problems, forcing Vogt to redesign the aircraft to use three 650hp Junkers Jumo 205C diesel engines, with the third engine mounted above the centre of the wing. These three engines produced almost the same amount of power as two 1,000hp engines (1,950 compared to 2,000), but the third engine introduced extra weight and drag.
The first prototype, Ha 138V1, made its maiden flight on 15 July 1937, and the V2 was completed in August of the same year. Tests began in November 1937.
These first two prototypes had short hulls, smaller tail surfaces and narrow booms. Tests revealed that they were unstable both in the air and in the water. Attempts to modify the existing prototypes failed, and a complete re-design began in 1938.
The new design shared the same basic layout as the first two prototypes, but with a longer hull, larger tail surfaces and stronger booms. The first of the new aircraft was designated as the Bv 138A-01, and was followed by five more pre-production aircraft, Bv 138A-02 to 06. These aircraft were armed with one 20mm cannon in a nose turret and two flexibly mounted rear firing 7.9mm MG 15s, one just behind the central engine and one at the back of the hull, with a field of fire somewhat restricted by the twin booms and horizontal section of the tail.
The five A-0 pre-production aircraft were followed by twenty five A-1 production aircraft, with the first making its maiden flight in April 1940. The first two production aircraft took part in the invasion of Norway, but the type didn't really enter service until October-November 1940.
The Bv 138 was used by long range reconnaissance units of the Luftwaffe, operating mainly off the coasts of France and Norway, from where they helped support the U-boat campaign. The initial A-1 was not a great success in service, and neither was the strengthened B-1, but the even stronger C-1 solved this problem, and accounted for 227 of the entire production run of 279 aircraft.
Five pre-production aircraft, with the revised hull, larger tail and stronger booms and powered by three 650hp Junkers Jumo 205C diesel engines. The A-0 was armed with one 20mm cannon in a nose turret and two 7.9mm MG 15s, one at the rear of the central engine and one at the back of the hull.
The first twenty-five production aircraft, similar to the A-0.
The first attempt to strengthen the aircraft, the B-1 was powered by three 880hp Junkers Jumo 205D engines. The B-1 was armed with two 20mm cannon in powered turrets, one in the nose and one in the rear of the hull. The B-1 could carry 330lb (150kg) of bombs below the root of the starboard wing or four times that payload at maximum overload weight. Nineteen were produced
The C-1 was the main version of the aircraft, with 227 produced. It had a stronger structure, and retained the same 880hp engines as the B-1, but with different propellers - the central engine had a four-blade propeller, while the outer engines used three-blade propellers with wider blades than on the B-1. This eliminated a vibration problem present on older aircraft. The C-1 carried the same two 20mm guns as the B-1 as well as a 13mm MG 131 machine gun in the position behind the central engine. The standard C-1 could carry the same three 50kg bombs as the B-1, while the C-1/U-1 could carry six 50kg bombs or four 150kg (331lb) depth charges. Some C-1s were able to be catapult launched.
The Bv 138MS was a mine-sweeper produced by modifying B-0 aircraft. All guns were removed and a circular dural hoop was installed surrounding the fuselage. This was used to detonate magnetic mines (a very similar technique was used in Britain with Wellington bombers).
Engine: Three Junkers Jumo 205D Diesel Engines
Power: 880hp each
Crew: Six plus up to ten passengers
Wing span: 88ft 7in
Length: 65ft 3.5in
Height: 21ft 8in
Empty Weight: 17,860lb
Normal Loaded Weight: 32,413lb
Max Speed: 171mph at sea level
Cruising Speed: 146mph
Service Ceiling: 16,400ft
Range: 3,105 miles
Armament: Two 20mm cannon, one 13mm MG 131 machine gun
Bomb-load: Three 50kg/ 110lb bombs under starboard wing root as standard