Editing Boeing B-17 Flying Fortress (section)

== Design and variants ==
{{Main|List of Boeing B-17 Flying Fortress variants}}

[[File:Boeing XB-17 blister turret.jpg|thumb|Waist position gun blister of Model 299, not adopted for production]]
{| class="wikitable floatright" style="text-align:center; width:25em"
|+ Production numbers
! Variant
! Produced
! First flight
|-
| Model 299 || style="text-align:right;| 1 || 28 July 1935<ref name="first flight" />
|- style="background:#f5faff;"
| YB-17 || style="text-align:right;| 13 || 2 December 1936<ref name="Bowers Boeing p292" />
|-
| YB-17A || style="text-align:right;| 1 || 29 April 1938<ref name="Donald" />
|- style="background:#f5faff;"
| B-17B || style="text-align:right;| 39 || 27 June 1939<ref name="Bowers boeing p294" />
|-
| B-17C || style="text-align:right;| 38 || 21 July 1940<ref name="Bowers Boeing p295" />
|- style="background:#f5faff;"
| B-17D || style="text-align:right;| 42 || 3 February 1941<ref name="Swan Mil p76" />
|-
| B-17E || style="text-align:right;| 512 || 5 September 1941<ref name="Bowers Boeing p297" />
|- style="background:#f5faff;"
| B-17F (total) || style="text-align:right;| '''3,405''' || 30 May 1942<ref name="Bowers Boeing p299" /><ref name="Swan Mil p78" />
|-
| B-17F-BO || style="text-align:right;| 2,300 || <ref name="Bowers Boeing p299" />
|- style="background:#f5faff;"
| B-17F-DL || style="text-align:right;| 605 || <ref name="Bowers Boeing p299" />
|-
| B-17F-VE || style="text-align:right;| 500 || <ref name="Bowers Boeing p299" />
|- style="background:#f5faff;"
| B-17G (total) || style="text-align:right;| '''8,680''' || 16 August 1943 <!--- what is this?---<Osborne, Story, page 98/>---->
|-
| B-17G-BO || style="text-align:right;| 4,035 ||
|- style="background:#f5faff;"||
| B-17G-DL || style="text-align:right;| 2,395 ||
|-
| B-17G-VE || style="text-align:right;| 2,250 ||
|- style="background:#f5faff;"
| Total || style="text-align:right;| '''12,731''' ||
|-
| colspan="3" style="text-align:left;" font-size: 70%| B-17s were built at Boeing Plant 2, Seattle, Washington (BO), Lockheed-Vega, Burbank, California (VE) and Douglas Aircraft, Long Beach, California (DL)<ref>Yenne, Bill, ''B-17 at War'': p. 16; Zenith Press; 2006: {{ISBN|978-0760325223}}</ref>
|}

The aircraft went through several alterations in each of its design stages and variants. Of the 13 YB-17s ordered for service testing, 12 were used by the 2nd Bomb Group at Langley Field, Virginia, to develop heavy bombing techniques, and the 13th was used for flight testing at the Material Division at Wright Field, Ohio.<ref name="Y1B-17" /> Experiments on this aircraft led to the use of 4 General Electric turbo-superchargers, which later became standard on the B-17 line. A 14th aircraft, the YB-17A, originally destined for ground testing only and upgraded with the turbochargers,<ref name="flightinter" /> was redesignated B-17A after testing had finished.<ref name="Bowers Boeing p293-4" /><ref name="Wixley p23" />

As the production line developed, Boeing engineers continued to improve upon the basic design. To enhance performance at slower speeds, the B-17B was altered to include larger [[rudder]]s and [[Flap (aircraft)|flaps]].<ref name="Bowers boeing p294" /> The B-17C changed from three bulged, oval-shaped gun blisters to two flush, oval-shaped gun window openings, and on the lower fuselage, a single "bathtub" gun [[Gondola (airplane)|gondola]] housing,<ref name="Bowers Boeing p295" /> which resembled the similarly configured and located ''Bodenlafette''/"Bola" ventral defensive emplacement on the German [[Heinkel He 111]]P-series medium bomber.

While models A through D of the B-17 were designed defensively, the large-tailed B-17E was the first model primarily focused on offensive warfare.<ref name="flightinter" /> The B-17E was an extensive revision of the Model 299 design: The fuselage was extended by {{convert|10|ft|m|abbr=on}}; a much larger rear fuselage, vertical tailfin, rudder, and horizontal stabilizer were added; [[Tail gunner|a gunner's position was added in the new tail]];{{NoteTag| During the crash investigation of [[Boeing 307 Stratoliner#Operational history|Boeing 307 Stratoliner NX19901]], it was found that two B-17s had already spun from lack of directional stability. British combat experience with the B-17 was also showing the need for a tail gunner. Boeing was not willing to add a turret because they did not want to disrupt the clean aerodynamics. The inadequate directional stability exposed by two spin incidents and a crash, brought about a redesigned vertical stabilizer and dorsal fin. A compromise for the tail turret resulted in handheld tail guns. The combination created a successful design. Not only were defensive needs solved, but the improved lateral stability made precision high altitude bombing possible.<ref>{{cite web |url=https://www.thisdayinaviation.com/tag/boeing-model-307-stratoliner/ |title=Boeing Model 307 Stratoliner |website=Archives – This Day in Aviation |access-date=2021-06-19}}</ref><ref>{{cite web |url=http://www.b17queenofthesky.com/variants/prototype.php?id=10&tle=B-17E |website=B-17 Queen of the Sky |title=B-17E page |access-date=2021-06-19 |archive-date=21 June 2021 |archive-url=https://web.archive.org/web/20210621212650/http://b17queenofthesky.com/variants/prototype.php?id=10&tle=B-17E |url-status=dead }}</ref>}} the nose (especially the bombardier's framed, 10-panel nose glazing) remained relatively the same as the earlier B through D versions had; a [[Sperry Corporation|Sperry]] electrically powered manned dorsal [[Aircraft gun turret|gun turret]] just behind the cockpit was added; a similarly powered (also built by Sperry) manned ventral [[ball turret]] just aft of the bomb bay – replaced the relatively hard-to-use, Sperry model 645705-D<ref>B-17 Erection and Maintenance Manual 01-20EE-2</ref> remotely operated ventral turret on the earliest examples of the E variant. These modifications resulted in a 20% increase in aircraft weight.<ref name="flightinter" /> The B-17's [[turbocharged]] [[Wright R-1820]] Cyclone 9 engines were upgraded to increasingly more powerful versions of the same powerplants throughout its production, and similarly, the number of machine gun emplacement locations was increased.<ref name="WoF p56-7" />

[[File:An Army sentry guards new B-17 F (Flying Fortress) bombers at the airfield of Boeing's Seattle plant. The ship will... - NARA - 196372.jpg|thumb|left|Boeing-built B-17Fs, with the clear-view two-piece Plexiglas bombardier's nose.]]
The B-17F variant was the primary version used by the Eighth Air Force to face the Germans in 1943, and standardized the manned Sperry ball turret for ventral defense, also replacing the earlier, 10-panel framed bombardier's nose glazing from the B subtype with an enlarged, nearly frameless Plexiglas bombardier's nose enclosure for improved forward vision.

Two experimental versions of the B-17 were flown under different designations, the [[XB-38 Flying Fortress|XB-38 'Flying Fortress']] and the [[YB-40 Flying Fortress|YB-40 'Flying Fortress]].' The XB-38 was an engine testbed for [[Allison V-1710]] liquid-cooled engines, should the Wright engines normally used on the B-17 become unavailable. The only prototype XB-38 to fly crashed on its ninth flight, and the concept was abandoned. The Allison V-1710 was reallocated to fighter aircraft.<ref name="Francillon Lock p213-5" /><ref name="WoF p66" />

The [[Boeing YB-40 Flying Fortress|YB-40]] was a heavily armed modification of the standard B-17 used before the [[North American P-51 Mustang]], an effective long-range fighter, became available to act as escort. Additional armament included an additional dorsal turret in the radio room, a remotely operated and fired Bendix-built "chin turret" directly below the bombardier's accommodation, and twin 50 caliber (12.7&nbsp;mm) guns in each of the waist positions. The ammunition load was over 11,000 rounds. All of these modifications made the YB-40 well over {{convert|10000|lb|abbr=on}} heavier than a fully loaded B-17F. The YB-40s with their greater weight, had trouble keeping up with the lighter bombers once they had dropped their bombs, so the project was abandoned and finally phased out in July 1943.<ref name="WoF 62-3,5" /><ref name="Francillon Lock p212" /><ref name="Bowers Boeing p307-8" /> The final production blocks of the B-17F from Douglas' plants did, however, adopt the YB-40's "chin turret", giving them a much-improved forward defense capability.<ref>{{cite web |url=http://www.b17queenofthesky.com/variants/prototype.php?id=12&tle=B-17F |title=B17 – Queen of the Sky – The B-17F |last=Lyman |first=Troy |date=12 May 2003 |website=Troy Lyman's B-17 Flying Fortress Site |access-date=24 June 2014 |archive-date=9 August 2014 |archive-url=https://web.archive.org/web/20140809192902/http://b17queenofthesky.com/variants/prototype.php?id=12&tle=B-17F |url-status=dead }}</ref>

By the time the definitive B-17G appeared, the number of guns had been increased from seven to 13, the designs of the gun stations were finalized, and other adjustments were completed. The B-17G was the final version of the Flying Fortress, incorporating all changes made to its predecessor, the B-17F,<ref name="flightinter" /> and in total, 8,680 were built,<ref name="WoF p63-4" /> the last (by Lockheed) on {{Nowrap|28 July}} 1945.<ref name="Francillon Lock p211" /> Many B-17Gs were converted for other missions such as cargo hauling, engine testing, and [[Reconnaissance aircraft|reconnaissance]].<ref name="Bowers Boeing p286-7" /> Initially designated SB-17G, a number of B-17Gs were also converted for search-and-rescue duties, later to be redesignated B-17H.<ref name="Bowers Boeing p303-4" />

Late in World War&nbsp;II, at least 25 B-17s were fitted with radio controls and television cameras, loaded with {{convert|20000|lb|abbr=on}} of high explosives and designated BQ-7 "Aphrodite missiles" for [[Operation Aphrodite]] against bombing-resistant German bunkers. The operation, which involved remotely flying the Aphrodite drones onto their targets by accompanying CQ-17 "mothership" control aircraft, was approved on {{nowrap|26 June}} 1944, and assigned to the [[388th Bombardment Group]] stationed at [[RAF Fersfield]], a satellite of [[RAF Knettishall]].<ref name="Ramsey" />

The first four drones were sent to [[Fortress of Mimoyecques|Mimoyecques]] (V-3 site), the [[Siracourt V-1 bunker]], and the V-2 [[Blockhaus d'Éperlecques]] at Watten, and [[La Coupole]] at Wizernes on 4 August, causing little damage and two pilots were killed. On August 12, a [[Consolidated B-24 Liberator]], part of the [[United States Navy]]'s contribution ("Project Anvil"), en route for [[Heligoland]] piloted by Lieutenant [[Joseph P. Kennedy Jr.]] (future U.S. president [[John F. Kennedy]]'s elder brother) exploded over the [[River Blyth, Suffolk|Blyth estuary]]. Blast damage was caused over a radius of {{convert|5|mi}}. Naval flights stopped but a few more missions were flown by the USAAF. The Aphrodite project was effectively scrapped in early 1945.<ref name="Ramsey">Ramsey, Winston G. "The V-Weapons". London: ''After the Battle'', Number 6, 1974, pp. 20–21.</ref>