Boeing B-17 Flying Fortress

Manufacturer: Boeing Aircraft Company

Country: USA

Classification: Heavy Bomber, Reconnaissance

Crew: Pilot and co-pilot side by side in the enclosed flightdeck, and bombardier, navigator, radio operator and five gunners carried in the fuselage.

Date: 1937 till 1960's.

B-17 Flying Fortress

B-17G Specs:


Development History: In the early summer of 1934, the USAAC stated the requirements for a multi-engine, medium bomber which would be capable of opperating off the US coast lines in a tactical defense role. These requirements called for the ability to carry 2,000 lb of weapons, have an opperational radius of no less than 1,000 miles (preferably 2,200 miles) and a top speed of no less than 200 mph (preferably 250 mph). Boeing, one of several aircraft manufacturers of the time decided to get as much of a lead over the competition as possible since a flying prototype was required by August 1935.

Boeing had already secured a limited production contract for their B-9 twin engine bomber, and the design left little enough to work with for modification to the desired result proposed by the USAAC. The power requirements were far too demanding for the current radial engines available. As a result, the design team translated the 'multi-engine' requirement to mean... 'more than one, but not necessarily two' engines.

The three engine concept, as in the Junkers Ju 52, was eliminated as this was impractical considering that the central nose position was ideal for the bomb sight and defensive armament. It was then decided that a 4 engine configuration would be used. This meant a more expensive airframe and twice the engine cost of the 2 engine design being employed by the other companies, but the added power, greater weight and drag limits was an attractive trade off. Also the 4 engine design would offer better speed and climb potential, a higher service ceiling and more reliability in the long range overwater role it was intended to be used for.

At the time, Boeing was hard at work with their Model 294 (XB-15) bomber which became the basis of the new Model 299, being more or less a hybrid of the 294 and the Model 247 Transport plane. The basic structural design came from the 247 airframe lines, and the weapons layout (both offensive and defensive), crew positions, as well as the possiton of the communication and navigation equipment were all derived from the 294. This was the birth of what would become one of the most important aircraft ever in the history of military aviation.

The original design was an all metal airframe consisting of a circular fuselage and low-set wing, bearing the 4 engines and fule tanks. The entire crew and bomb load were housed inside the enclosed fuselage. The retractable main landing gear were drawn up into the inboard engine housing with the wheel of each unit exposed, while the cantilever tail unit had a semi-retractable tail wheel design.

Since the design was intended for coastal defense (a remote 'Fort' if you will), Boing registered the name for the aircraft as the 'Flying Fortress'. The USSAF accepted the name and assumed it refered to the defensive capabilities of the aircraft, not for it's offensive potential which was Boeing's intent.

The first Model 299 prototype flew in July 1935. This experimental design used four Pratt & Whitney R-1690-S1E-G Hornet radial egines rated at 750 hp each, a crew of 8 (two pilots, bombardier, navigator/radio operator and four gunners), an ordnance load of 4,800 lb (consisting of 8x 600 lb bombs in the internal bay), and a defensive armament package of 5x 30cal Browning machine guns (1 in a small nose turret, 1 in a dorsal blister, 1 in a ventral blister and 1 each at the two beam positions.) It reached a maximum level speed of 236 mph, and a maximum range of 3,101 miles. Empty weight was 21,657 lb and maximum take-off was 38,053 lb.

The Model 299 prototype was flown from Seattle, Washington to Wright Field, Ohio recording an average speed of 232 mph which was faster than any of their rivals in the competition. Unfortunately the prototype was damaged beyond repair in October 1935, when a USAAC pilot took off with the controls locked. However, the design had shown such outstanding performance that the USAAC placed an order for 13 Model 299B pre-production aircraft to be submitted for trials under the designation of YB-17 which was later revised to Y1B-17.

These aircraft were completed between January and August 1937 and had the same airframe, but incorporated a number of internal changes. The most prominent of these was the replacement of the engines with four Wright R-1820-39 radial engines rated at 1,000 hp for take off and 850 hp at 5,000 feet. In addition, the crew was changed to 6, and the internal ordnance load was increased to 8,000 lb. The new engines provided maximum level speed of 256 mph, and still managed an operational range of 1,377 miles. One of the 13 aircraft was used for flight testing by Boeing while the other 12 were delivered to Langley Air Field for operational trials. When the trial period was over, the aircraft was ordered into production as the B-17.

During the trials at Langley, one of the Y1B-17's was caught in a violent storm and emerged unscathed. The USAAF then requested another test prototype to be submitted for 'static testing'. Boeing deliver the Y1B-17A test aircraft and used the design to test a turbocharger installation for future use. Originally, the turbo charger was installed in the upper part of the engine housing, but was later revised to be in the underside which became standard on subsequent designs. The turbocharger significantly improved the speed and altitude perforance, bringing the top speed up to 311 mph and boosting engine performance to 800 hp at 25,000 feet, and offering a service ceiling of over 30,000 feet.


B-17B Flying Fortress: This was the first opperational variant of the Flying Fortress, and oddly enough, it's success caused the subsequent designs to be delayed. Since the aircraft was design for the coastal defense role, the US Navy claimed it was a Naval aircraft. This dispute prevented the USAAC from securing adiquate funds for extensive production. This early version introduced more changes in the design, including a larger tail, larger trailing edge flaps, and a revised nose section which replaced the 'green-house' gun turret and bombardier window with a glazed section fitted with a flat bomb-aiming panel on the underside. Internally, other changes were made as well. The crew distribution was modified, the breaks changed from pneumatic to hydrolic controls and the engines uprated to the Wright R-1820-51 radials rated at 1,200 hp.

B-17B Specs:

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The first B-17B flew in June 1939. Only 39 aircraft (built in six batches due to funding limitations) were delivered to the USAAC between July 1939 and March 1940.


B-17CFlying Fortress: Though only 38 aircraft were produced, the reputation forged by the B-17 and the B-17B was such that all of these were from a single order. The first B-17C flew in July 1940, and the remainder were delivered by November 1940. Several improvements on the B-17's defensive capabilities were intruduced with this variant as well. Armor for the crew and self sealing fuel tanks were added. The gun positions were upscaled as 1x 30 cal. machine gun in the tail position, one 50 cal. machine gun in the 2 waist gunpositions, the single nose gun was replaced with 2 50 cal. 'cheek' guns, the ventral blister was replaced with a a metal 'bathtub' gun point with 2x 50 cal. machine guns, and the dorsal blister was given 2x 50 cal. machine guns. Finally, the ordnance load was increased to 10,500 lb.

B-17C Specs:

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As the B-17C became available, the UK was in need of offensive weapons since they were the last of the European Nations still able to offer resistance to the Germans. The USAAC released 20 of the new bombers for use in the RAF which all recieved the UK designation of 'Fortress Mk I'. The US viewed this as an opportunity to see the new bomber in combat. The No.90 Squadron took command of the aircraft, and began daylight bombing raids. However, as a result of flying the aircraft too high, the bombers only managed to attack 25 targets on their first 51 sorties.

The B-17 had several problems which conviced the British that the Fortress was inefective in the European arena. There were problems with the Norden Bomb Sight, the guns had a tendency to freeze at high altitudes, there were mechanical and technical failures with many parts of the plane, the tail defense was inadiquate and the self sealing fuel tanks did not prevent the plane from buring up after they were hit. After 4 aircraft were tried in the Middle East, the remainder of the planes were transfered to the No.206 and No.220 squadrons for use in the reconnaissance role of the RAF Coastal Command.


B-17D Flying Fortress: 42 of this improved version of the B-17C were produced with number of changes directed at offering better combat performance. Externally, the B-17D was indistinguishable from a B-17C except for the addition of cowling flaps, but inside, a number of changes were made. The electrical system was redesigned and accomodations for an additional crewman bringing the total crew up to 10. The first order was placed in 1940, and all of this variant were delivered before the end of 1941 after the first successful flight was completed in February of that year. The remaining 18 B-17C's were converted to the B-17D standard and given the same designation.

These 60 aircraft were the most advanced air weapons available to the US when the Japanese attacked Pearl Harbor, and many were lost in the first few hours of that battle. 18 of the 33 B-17's at Clark and Del Monte air fields in the Philippines were destroyed on the ground. Another 12 were damaged as they arrived at Hickam Field in Hawaii durring the attack while they were still unarmed in order to cary extra fule and spare parts. The 16 surviving B-17D's became the first US aircraft to fly offensive opperations agains the IJN when they began bombing attacks against the Japanese invasion forces at Java of the Netherlands East Indies.


B-17E Flying Fortress: The limited data from these few B-17's which saw service set the foundation for the next line of the Fortress series. This was the first variant to be produced in large numbers (over 500 total) and it featured a number of significant changes to the original design. One of the most obvious changes was the revised rear fuselage with it's new dorsal tail fin based on the model 307 Stratoliner commercial aircraft, which was actually a transport version of the B-17C and D. Additional armor protection and a number of internal modifications were incorporated too, along with a further augmented defensive armament package. The new Armament included a simplified waist gun in the beam positions, Sperry power-operated gun turrets were added in the ventral and dorsal gun points and a manually opperated tail gun with twin 50 cal. machine guns was added to better arm the vulnerable tail.

After the first B-17E flew on September 1941, the USAAC ordered the plane into production. The first 112 B-17E's were equipped with a remote controlled ventral gun turret with a periscopic sight in a plexiglass blister located several feet to the rear of it's original position. From the 113th plane onward, this was replaced with the standard Sperry Ball Turret to accomodate one gunner.

The first B-17E's off the line were assigned to the 7th Bombardment Group which joined the 19th Bombardment Group in the Pacific from December 1941. Later, the remainder of the 512 aircraft produced formed the core of the 8th Army Air Force based in the UK from May 1942. The first element of the 8th AAF to be armed with the B-17 was the 97th Bombardment Group which flew it's first opperational sortie over occpied Europe in August 1942. Other medium range missions, mostly into North-West Europe continued into early 1943. Most of these aircraft however, were assigned to a newly formed 'Strike' element of the 12th AAF starting in October 1942. These served to support the Anglo-American invasion of North-West Africa, and on to the final victory over the Axis forces in Africa in May 1943.

B-17E Specs:

Ordnance: Generally comprising:

Powerplant: Four Wright R-1820-65 radial piston engines each rated at 1,200 hp for take-off and 1,000 hp at 25,000 ft.

Size:

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45 of the B-17E's serving in the UK were transferred to the RAF from the fall of 1942 for use by Coastal Command and given the designation 'Fortress Mk IIA'. Oddly enough, the newer B-17F's (which had already been transfered to the RAF) had the designation of 'Fortress Mk II' dispite it being the newer aircraft. These B-17's served with four maritime reconnaissance and four meteorological reconnaissance squadrons.

The XB-38 was an experimental version of the B-17 with the engines replaced by Allison Vee engines rated at 1,425 hp each. The prototype made it's maiden flight in May 1943, but developemt was cancelled after the aircraft was lost due to an in-flight fire during June 1943.


B-17F Flying Fortress: Just as the B-17E had been developed based on combat experience from British nits in Europe, the B-17F was derived from combat experience of American units in the Pacific. The B-17F looked the same as the B-17E except for the nose which had a single piece blown plexiglass transparancy rather than the multi-window framed nose. In fact, the B-17F incorporated a variety of changes, (over 400 in all) which added up to a much more capable warplane.

These changes were added during the whole production cycle of the B-17F, and not all at once. Still more armor protection was added, external bomb racks under the wings, ball and socket machine gun points were added in the nose and radio compartment (increasing the total defensive armamanet by another 3x 50cal guns), an electroninc control between the autopilot and the Norden bomb sight, modified control settings and oxygen equipment, additional photographic equipment, better landing gear, a dual breaking system, self sealing oil tanks, extra generators for onboard electric power, dust covers over carburetor inlets, the introduction of auxiliary fuel 'Tokyo Tanks' in the wings, and paddle-blade props with revised mounts to allow full feathering of of the wide-chord blades.

The first of the B-17F versions flew in May 1942, just 2 days after the last B-17E was delivered. This was the first aircraft to use the 'block' designation to distinguish sub-variants with minor changes which were not significant enough to earn a new letter designation. Of the 3,405 aircraft produced, 2,300 came from boing in 28 blocks, 605 came from Douglas in 18 blocks, and 500 from Lockheed's 'Vega' division in 11 blocks.

The first B-17F's were assigned to the US 8th Army Air Force in Europe and flew the first American bomb attack in Germany in January 1943. From that point on, the B-17 formed the core of rapidly growing 8th AAF Daylight Bombing forces. Early success inspired greater use of the massive bomber in daylight raids, but the Luftwaffe quickly learned how to exploit the weaknesses of the B-17, and losses quickly reached unacceptable numbers. In August 1943, a force of 376 B-17F's attacked factories at Schweinfurt, Wiener Neustadt and Regensburg. Over 60 bombers were lost in the raid. Soon followed another attack with 291 aircraft which also lost over 60 bombers. In both cases, the German fighters would simply follow along at a distance and wait until the escort fighters (which were very limited in range) turned back leaving the bomber group to attack alone. Then they would race in, attacking from head on where the B-17's defensive armament was weakest. The results were devistating.

19 of these B-17F bombers were transfered to the RAF with the deignation 'Fortress Mk II'. These, along with the B-17E's which came later served as roconnaissance aircraft for meteorological and maritime recon units.

B-17F Specs:

Ordnance: Generally comprising:

Powerplant: Four Wright R-1820-97 radial piston engines each rated at 1,200 hp for take-off and 1,000 hp at 25,000 ft.

Size:

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B-17G Flying Fortress: The major change from the B-17F was the addition of a Bendix power-operated 'Chin' turret armed with twin 50 cal. machine guns which was mounted under the nose position and remote controlled from the glazed nose position. This was a deturent to the fighters which naw made the head on attack a common tactic agains the Fortress. The two cheek guns were removed which never actually managed to be very effective due to a poor field of fire and dificulty of use in the cramped forward compartment of the nose section.

Other changes included improvements on the navigator position, bomb controls and cockpit instruments. In addition, a new electricly controlled turbo-charger (replacing the older hydrolic versions) was introduced, emergency oil suplies for prop feathering was added, and a power assisted control column for aid in handling the heavy aircraft while in tight formation. Finally, the defensive armament was revised yet again by staggering the two waist gun positions so both gunners could move about freely without getting in each other's way. Also the tail gun was modified with the 'Cheyenne' turret which improved the field of fire considerably and replaced the antiquated ring and bead sight with a reflector gun sight. Later, the Navigator's gun was removed since it did not offer a reasonable field of fire or vision.

This was the most heavily produced of the Flying Fortress series with 8,680 aircraft produced for a total of 12,731 of all variants. The first B-17G was delivered in September 1943, and production continued till April 1945 when the B-17 project was put to rest. Boing delivered 4,035 in 23 blocks, Douglas with 2,395 in 23 blocks and Vega with 2,250 also in 23 blocks. Boing was quick to eliminate this impresive weapon from their production efforts, all to eager to replace the obsolete aircraft with their highly advanced B-29 Superfortress which was already laying waiste to Japan's industrial potential.

The height of the B-17 career had peaked in August 1944 when the US 8th AAF (in the UK) operated 1,829 aircraft, and the 15th AAF (in Italy) operated 366 aircraft. In addition, 2,311 were still in the US in storage and modification centers and with 28 replacement squadrons in training. By VE day, the 8th commnded 2,800 B-17's in 106 squadrons and the 15th commanded 500 B-17's in 24 squadrons.

In February 1944, 85 B-17's were transfered to the RAF and given the local designation of 'Fortress Mk III'. Some of these were used in coastal reconnaissance roles, but some were assigned to two bomber groups which used them in the form of 'electronic warefare' utilizing specialized jamming and deception equipent.

With the arrival of newer and better bombers, the generally obsolete B-17 was removed from active service rapidly. By war's end, only a handfull of B-17G's still operated in it's original capacity and these were quickly phased out. The remainder of B-17's were then dismantled or relegated to other duties.


CB-17 Flying Fortress: This was a transport version converted from surviving B-17G's.


DB-17 Flying Fortress: The result of another B-17G conversion, this variant was used as a drone-control aircraft for QB-17 aerial targets. As the demand for the Qb-17 declined, two of these aircraft were designated QB-17P Flying Fortress, and were themselves used as flying targets. The last of this variant was retired in 1960.


EB-17 Flying Fortress: Owned and operated by Curtiss-Wright, this variant (later designated the JB-17G), was used for engine testing of new aircraft powerplants. The Flightdeck was move back and the nose was revised. The first engine test was the Wright XT35 Typhoon turbo-prop rated at 5,500 hp. Later the GE built XT64 turbo-prop engine was also tested. Pratt & Whitney also used a similar aircraft for engine testing with their XT34 turbo-prop.


QB-17 Flying Fortress: This was a radio-controled version of the B-17 which was derived from the original QB-17G which was a retro-designation to a 1948 conversion called the BQ-7 Flying Fortress 'Aphrodite' in the guided bomb catagory. It was intended for use against high value, yet heavily fortified military targets such as coastal artillery, U-boat and E-boat pens, etc... Project 'Castor', conducted by the USAAF in 1944, called for 25 B-17E and B-17F Fortresses to be equiped as radio guided bombs for use by the 8th Air Force 3rd Air Division. The stripped down aircraft would be loaded up with 1,000 gallons of fuel (enough for a 350 mile flight) and packed with 20,000 lbs of Torpex explosive in the fuselage. A bare bones crew of 2 men would get the plane off the ground, then bail out, turning control over to a land based remote pilot in England who would then fly it via remote radio controls to smash the whole plane into it's target. 15 such BQ-7's were launched against targets in northern Europe between August 1944 and January 1945, but they yeilded little success mainly because of the primitive and unreliable radio control equipment.

The QB-17 designation was also used for radio-control aerial targets. The first was the QB-17L Flying Fortress converted from the B-17G with a TV camera to provide the remote pilot with a target perspective view of the missile attack. The other was the QB-17N which was also converted from the B-17G but without the TV camera and with modified radio-control equipment.


MQ-17 Flying Fortress: This was a later version of the BQ-7 but converted from a B-17G Flying Fortress.


SB-17 Flying Fortress: This was a search and rescue version of the B-17, convertd from the B-17G standard. Of the 130 originaly planned for conversion, only 12 were ever completed. The Weapons bay was revised to house 1 self-righting, self-bailing life boat which would be dropped with 3 parachutes. In 1948, the sub-variant recieved the official designation SB-17G, which before that time was un-officially the B-17H. Some of these aircrafy retained their defensive armament for use in violent areas, and still more were refitted with weapons for this purpose during the Korean War. Others had all weapons removed and had search radar and antenna in a radome installed at the chin turret's location. The last of these Fortresses was retired in 1956.


TB-17 Flying Fortress: This was the trainer version of the B-17G bomber.


VB-17 Flying Fortress: This was a B-17G conversion used as staff-transport aircraft.


B-40 Flying Fortress: This designation was reserved for a planned coversion of the B-17F which would be used as a heavy escort 'gun-ship'. The concept was formed around the need for the heavy bombers to have adiquate protection all the way to target and back which fighters of the time could not yet accomplish. The first XB-40 prototype was armed with the standard twin 50 cal. dorsal, ventral and tail turrets which was then suplimented with an addition of two more twin 50 cal. turrets added to the chin and radio compartment. Finally the single waist guns were replaced by twin 50 cal. guns as well for a total of 14x 50 cal. machine guns. The ammo load was a standard 11,135 rounds which could be increased to 17,265 rounds if the fuel load was reduced.

Initial testing of the XB-40 was promising and the USAAF ordered 20 YB-40 service test aircraft to be converted from the B-17F. Operational testing proved that the concept did have a problem. Though the YB-40's could stick with their bombers on the approach leg, on the return, they fell behind since the bombers were several thousand pounds lighter after the drop. The project was cancelled and the surviving YB-40 aircraft were relegated to other duties.


C-108 Flying Fortress: This was the designation given to a series of B-17 transport conversions. The first of these was a B-17E conversion used as a personel transport in 1943 for General Douglas MacArthur in the Pacific which recieved the designation of XC-108. All armament except for the nose and tail guns were removed while the fuselage was modified with windows for lighting, space for an office, seating and a galley. The single YC-108 was a B-17F conversion used as a VIP transport. A single XC-108A was converted from the B-17E standard which was used to test the practicality of converting obsolete aircraft for service as transports. All military equipment was removed and a cargo door was installed in the port side of the fuselage. The XC-108B was a similar conversion of the B-17F standard, in this case it was optimized as a fuel transport for use over 'The Hump', (eastern Himalayas from India to China) with fuel storage tanks installed in the fuselage.


F-9 Flying Fortress: This was the photo-reconnaissance version of the B-17. The first of these were B-17F conversions which had the weapons bay modified to hold cameras and other survailance equipment. A camera was installed in the nose and some of the defensive armament was retained. Later, these recieved the revised designation of FB-17F, and eventually RB-17F. Following this successful version came another B-17F conversion which incorporated more advanced camera and survailance equipment. This became the F-9A and the F-9B (which had a different camera installed) of which there were a final 25 conversions completed. Finally there was the B-17G conversion which in 1948 recieved the official designation of RB-17G.


PB Flying Fortress: Although the B-17 was originally designed for coastal defense, it was only used once in this capacity at the Battle of Midway. The complications of level bombing a moving ship soon convinced the USAAF that such use of the bomber was impractical, and the concept was abandoned. However,the US Navy was of the opinion that the B-17 was more formidable in the maritime recon role than the flying boats which were available at the time.

One B-17F and one B-17G were transfered to the Navy and were later given a revised designation of PB-1 Flying Fortress in July 1945. Another 17 B-17G's were transfered to the US Coast Guard (but under naval command) durring WWII and these recieved the designation of PB-1G. The surviving aircraft continued to serve mainly as search and rescue aircraft until 1959 after a conversion to the standard B-17H with an air-drop life boat, but with the chin turret replaced with a radome search radar.

The last of the Naval variants was the PB-1W. This was a B-17G conversion used in the 'early warning' role which was equipped with a large 'guppy' radome under the center fuselage and sufficient fuel tankage for an opperational range of 2,500 miles. It entered service in 1946 and served till it was replaced in 1954 by the Lockheed WV-2.