page_title: List of Boeing B-17 Flying Fortress variants
section_title: B-17F
hierarchical_section_title: List of Boeing B-17 Flying Fortress variants / B-17F
caption_attribution_description: English: Boeing B-17F-85-BO (S/N 42-30043) of the 384th Bomb Group, 547th Bomb Squadron. (U.S. Air Force photo)
context_page_description: The following is an extensive catalogue of the variants and specific unique elements of each variant and/or design stage of the Boeing B-17 Flying Fortress heavy bomber.
context_section_description: The B-17F was an upgrade of the B-17E, although outwardly the types were distinguished only by exchanging the bombardier's ten panel, well-framed nose glazing that had originated with the B-17B, for a molded one-piece or two-piece plexiglas cone, the two-piece version having a nearly-transparent diagonal seam. Fully-feathering paddle-bladed propellers were also provided. Numerous internal changes were made to improve the effectiveness, range, and load capacity of the B-17. However, once placed in combat service, the "F" series was found to be tail-heavy. The weight of gunners and ammunition when combat-loaded moved the center of gravity rearward from its original design point and forced the constant use of the elevator trim tab, stressing this component. In combat the B-17F proved almost immediately to have inadequate defensive protection when attacked directly from the front. Various armament configurations of two to four flexible guns in the "cheek" windows (with the starboard emplacement further forward) and bombardier's nose glazing were utilized in the field. Late production "F" series aircraft received substantially-enlarged mounts for the "cheek" guns on each side of the nose, replacing the previous window-mounted guns. These mounts allowed the guns to fire more directly ahead.
  The problem of head-on defense was not truly adequately addressed until the introduction of a powered, Bendix-designed remotely operated "chin" turret in the final production blocks of the F-series Fortresses — starting with the last 86 B-17Fs built by Douglas of the 605 B-17F-DL bombers built, from the B-17F-75-DL production block — directly derived from its debut on the YB-40 experimental "gunship" version.
  By using a stronger undercarriage, the maximum bomb capacity was increased from 4,200 lb (1,900 kg) to 8,000 lb (3,600 kg). Though this modification reduced cruise speed by 70 mph (110 km/h), the increase in bomb capacity was a decided advantage. A number of other modifications were made, including re-integrating external bomb racks, but because of its negative impact on both rate-of-climb and high-altitude flight the configuration was rarely used and the racks were removed.
  Range and combat radius were extended with the installation in mid-production of additional fuel cells in the wings. Called "Tokyo tanks", nine self-sealing rubber-composition tanks were mounted inside each wing on each side of the joint between the inner and outer wing sections. With an extra 1,080 US gal (4,100 l) to the 1,700 US gal (6,400 l) available on the first B-17Fs, the Tokyo tanks added approximately 900 mi (1,400 km) to the bomber's range.
  3,405 were built: 2,300 by Boeing, 605 by Douglas, and 500 by Lockheed (Vega). These included the famous Memphis Belle. 19 were transferred to the RAF, where they served with RAF Coastal Command as the Fortress II.  Three examples of the B-17F remain in existence in the 21st century, including the now-restored Memphis Belle.
caption: Boeing B-17F-85-BO (S/N 42-30043) of the 384th Bomb Group, 547th Bomb Squadron
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