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The B-17B was the last development version of the Flying Fortress. It was the first model of the aircraft to feature the distinctive flat-panelled Plexiglas nose that was used in early production aircraft and the first version to be produced in any numbers that used a turbo-supercharger.
The turbo supercharger was designed to improve engine performance at high altitudes. The higher an aircraft flies, the lower the surrounding atmospheric air pressure will be. Non-supercharged engines rely on that air pressure to force air into the combustion chamber, so at higher altitude less air, and therefore less oxygen, is available. This reduces the amount of fuel than can be burnt in each engine cycle, and thus decreases the power produced by the engine. Superchargers are designed to push air into the engine, increasing the oxygen supply at altitude and therefore the performance of the engine, increasing both the speed at altitude and the maximum altitude than can be reached.
The B-17 used a turbo supercharger. This used the exhaust gases from the engine itself to drive a turbine that powered the supercharger. A General Electric turbo-supercharger had been used on the Y1B-17A prototype, and had significantly improved the performance of the aircraft.
The B-17B saw a redesign of the aircraft’s nose. Earlier prototypes had a rounded Perspex nose that could rotate around 360 degrees, with a machine gun bubble carrying a single gun. The bomb aiming window was placed in the floor of the fuselage behind the nose. On the B-17B these features were replaced by a multi-piece Plexiglas nose, with a number of ball and socket machine gun mounts. The bomb aiming window was moved to form the lower half of the nose. The bombardiers position was moved closer to the nose, and a navigator was added to the crew.
The B-17B carried mountings for five machine guns – one in the nose, two in gun blisters on the side, one in a gun blister below the fuselage and one in a final blister above the radio operator’s position. A commander’s viewing dome was added above the pilot’s cabin, in the same position as the gun turret used on later models.
A first order for 10 B-17Bs was placed on 3 August 1937 and was soon expanded to cover 39 aircraft. The first B-17B made its first flight on 27 June 1939, and was delivered to the Army on 20 October. All 39 aircraft had been delivered by March 1940. The B-17B did not see combat. Many of the 39 aircraft were used as test beds for later developments, and the last B-17B was not retired until 1 January 1946.
Boeing B-17 Flying Fortress, Frederick A. Johnsen. A well researched and illustrated history of the B-17, with a very strong section on its combat record, an interesting chapter on the efforts made to improve the aircraft (including a number of suggestions that didn't enter production) and a good selection of colour pictures of the aircraft. [see more]
