Several models of the basic idea of the B-17 were developed between 1935 and 1942, as improvements were needed. The most notable feature of this design is that the overall design of the B-17 remained the same over each new development. The initial design was meant to be one that could be changed slightly, but produced in large quantities, therefore, an easy template to follow.
The Model 299
The first B-17 was the model 299. Only one of these planes was produced, and it was the plane used in the ill fated test flight of July 28, 1935. The test pilot crashed the plane because he failed to unlock the elevators. What this means is that the plane was fitted with a special device that would lock the elevators in position in strong winds while the plane was on the ground. These locks were intended to be released in a pre flight check.
The Model Y1B-17
The Boeing Aircraft Co. was dropped from the bomber production competition after the test flight of the Model 299, but once it had been determined that the crash was due to pilot error, the Army Air Corps ordered 13 test aircraft in 1936. The main design difference was that the Pratt & Whitney engines were replaced with 850 hp Wright 1820s and the undercarriage was modified. Of the 13 planes ordered, the 13th was the only unit to undergo exhaustive flight testing. The Y1B-17 was put to the test during a demonstration flight where they were to intercept the Rex, an Italian liner, while it was 610 miles away from United States soil, at sea. Testing continued for three years, after which time (October, 1940), they were officially transferred to the 19 Bombardment Group at March Field.
This model was developed from the Boeing Model 299F, which was only intended to be a static test bed, not an aircraft capable of flight. It was eventually converted to be capable of flight, in order to test supercharged engines. Only one prototype was ever developed, and it underwent various engine tests, ending up with a bottom mounted turbo supercharger, the eventual standard on the B-17B. The turbo supercharger engines allowed this aircraft to fly much faster and higher than the YB-17. After adequate testing and experimentation with engines, this model became the B-17A.
This plane was a much improved version of the B-17A. The more notable changes included a redesigned nose, a much larger rudder and a bigger set of flaps. In redesigning the nose, the metal had been replaced with plexiglass, allowing the gunner a better view and making it shorter than the 17A by a full seven inches. 39 of these planes were ordered by the USAAC between 1938 and 1939.
The noted improvements to the Model B-17C were a change from a 1,000 hp engine to the 1,200 hp Wright R-1820-65 radial. The waist gun blisters formerly located on the sides of the plane were replaced with sliding panels that could be closed or opened, affording better safety for the crew of the plane. A bathtub turret replaced the ventral gun blister.
Some improvements over the B-17C included cowl flaps, a much better electrical system, armor plating and self sealing fuel tanks. One of the more notable B-17Ds is “The Swoose” currently on display at the National Museum of the US Air Force.
This modified and improved model had a completely redesigned tail with a vertical stabilizer and fairing. The tail gunner area was added because of the vulnerability of the earlier models to an attack from the rear. The waist gunner windows were enlarged from the basic teardrop shape to a larger rectangle design, allowing for better sighting. The bathtub turret was also replaced with a Bendix remote controlled belly turret. Eventually, the Bendix turret was replaced by a Sperry ball turret after 112 planes had been produced. A further Bendix turret was added just behind the cockpit on the top fuselage. In total, 512 of the B-17E were produced between 1941 and 1942. Most of the improvements were aimed at keeping the crews of these planes safe and alive during combat.
The B-17F could carry just about double the bomb load of any previous versions of the B-17 at 8,000 pounds. The result was that the cruise speed dropped by about 70 miles per hour due to the large weight increase. 3,400 of the B-17F were produced by the combined efforts of three manufacturers – Boeing, Lockheed-Vega and Douglas. The most famous of this production run was the Memphis Belle.
More than 8,500 of this model were produced and it was considered the final result of continual improvement of its predecessor models. The Bendix chin turret was introduced in this model. After their use in World War II, many of these planes were converted for other uses, including VIP transport, special duty training, drones, engine test beds, early warning aircraft and air-sea rescue units.