#b-17e

[lonestarflight]

B-17 Evolution

Taken from Popular Science magazine August 1945 pages 92-93.

source

[redarmyscreaming]

The B-17E was the first version of the Fortress to be produced in large numbers. It was originally designed to correct some of the deficiencies in the earlier Fortresses that had been brought to light as a result of combat reports coming in from Europe. The modifications which resulted in the B-17E were destined to turn an airplane which had been a relative failure into an outstanding success. A Bendix electrically-powered turret containing two 0.50-inch machine guns was installed on the upper fuselage immediately behind the flight deck. This turret was usually operated by the flight engineer. A power-operated belly turret replaced the ventral "bathtub" housing of the B-17D. This turret was remotely-controlled by a system of mirror periscopic sights from a Plexiglas bubble below the waist hatches. In order to achieve better stability during the bomb run, the span of the horizontal tailplane was increased, the vertical tail was greatly increased in area, and a long dorsal fin was fitted in front of the tail. The first B-17E flew on September 5, 1941. It immediately superseded the B-17D on the production line, and as fast as they could leave the production line, they were issued to operational units.

[bmachine-blog1]

B-17E, equipped with a non-standard lower Bendix turret, similar to that installed on the early Mitchells.

[lonestarflight]

Evolution of the B-17

[lonestarflight]

[lonestarflight]

Boeing XB-38 Flying Fortress

"Essentially an Allison-powered B-17E, the XB-38 was a project developed by engineers at Lockheed-Vega. The ninth production B-17E (SN 41-2401) had been delivered to Lockheed-Vega to help in setting up a Flying Fortress production line at their Burbank, California facility. This was the aircraft modified as the prototype for the XB-38 design.

The standard 1,200 hp Wright Cyclone R-1820-65 nine cylinder radial engines were replaced with Allison V-1710-89 in-lines. Both types of engines were turbocharged to improve performance at altitude. The Allisons each developed 1,425 hp, an increase of 225 hp per engine over the Cyclones.

Work on the project began in the Summer of 1942, but it was not until May 19, 1943 that the XB-38 first took to the air.

The aircraft handled well during testing, but the project was delayed while problems with exhaust manifold leaks were corrected.

Boeing lacked an indoor paint shop at their Seattle facility which might explain the natural metal finish on 41-2401 when it was delivered to Lockheed-Vega.

Four weeks into the testing program while on its ninth flight, the XB-38 developed a fire in the right inboard engine nacelle. Efforts to extinguish the fire were unsuccessful and the aircrew bailed out. The co-pilot was killed when his parachute failed to open.

While the Allison powered Fortress was slightly faster than the Cyclone powered version, it was also heavier and had a projected lower maximum ceiling. In addition, the Allison engine was in demand for several USAAF Pursuit aircraft, including the P-38, P-39, and P-40 among others. With no clear advantage to changing the design, the decision was made to continue Flying Fortress production with Cyclone engines. Here is the XB-38 sharing the apron with a B-17F.

Markings were standard for the time, and included the 'U.S. ARMY' lettering on the underside. Noteworthy is the lack of defensive armament with only the dorsal turret having guns mounted. The ventral ball turret is a dummy. Interestingly, the sighting blister and scanning windows associated with the Sperry remote turret are still in place.

A beautiful profile view which shows off the contours of the Allison engine nacelles well. Certainly an attractive aircraft!

From the front the aerodynamic streamlining of the engine nacelles is apparent. Inline engines are generally heavier and require more maintenance than radials, but have a smaller frontal area which helps the designer reduce drag."

Photos and text from Inch High Guy: link

[lonestarflight]

Boeing B-17E Flying Fortress (SN 41-9112) "Dreamboat"

"While the Boeing B-17 Flying Fortress was arguably one of the most important aircraft designs of the Second World War, even the best designs can be improved. Combat experience against the Luftwaffe over Europe identified the need for several potential modifications suggested by the crews. The job of evaluating those changes was given to Major Robert J. Reed. Reed was sent to Wright Field in Dayton, Ohio and given B-17E 41-9112 to experiment on.

Reed replaced much of the B-17E defensive armament with components already in production for the Consolidated B-24 Liberator. The most obvious changes were mounting powered turrets in the nose and tail positions. Jagdwaffe pilots had identified the hand-held nose armament as a weak point in the Fortresses defenses, and the tail position had a very restricted field of fire. The Liberator turrets remedied both these problems at a stroke.

With the nose position now occupied by a turret the bombardier was moved to a gondola under the nose, similar to the original design of the Boeing Model 299. From this position the bombardier could also function as navigator which freed up a crew position. Like many Fortresses, the Dreamboat featured her own artwork.

The radio operator was moved to the nose compartment and a powered twin .50 caliber mount was installed in the old radio compartment. This eliminated both single waist gun positions while increasing the 'broadside' firepower which could be brought to bear defending against a beam attack. Shifting the crew and equipment weight forward also helped correct a balance problem in the Fortress – the center of gravity was aft of the center of lift, resulting in the Fortress being tail heavy and fatiguing to fly.

Reed completely redesigned the bomb bay doors. Instead of two large doors which opened into the slipstream when opened, the new bomb bay doors folded back against the fuselage sides. This not only reduced drag but was also less noticeable to intercepting Luftwaffe pilots who knew the big bombers were restricted in their ability to maneuver while on their bomb runs.

The hybrid bomber was named the 'Dreamboat'. One of the more important changes was not apparent when looking at the aircraft from the outside. The B-17 crew’s oxygen system was adequate, but hypoxia was potentially fatal if the system suffered damage. Reed installed a dual-feed system on the Dreamboat which increased capacity and provided redundancy, a potentially life-saving modification.

The Dreamboat never saw combat, but was returned to England. Combat crews were enthusiastic about the improvements – defensive firepower and fields of fire had been improved, crew requirements were reduced from ten to eight, the CG problem had been solved, and the oxygen system and bomb bay doors were improved.

In the end, the modifications demonstrated on the Dreamboat were not adopted for factory production. A premium was placed on quantity production above all else, it was felt that the changes suggested by Major Reed would prove to be too much of a disruption to the production lines, and the modifications were too extensive to be performed at the depot level. The Dreamboat would remain a dream."

Photos and text from Inch High Guy, link

[bmachine-blog1]

Tests refueling in air bomber B-17E from a tanker at the base of the B-24D in the summer of 1943 in Eglin, Florida. Successful tests increased the range of the B-17 (with three tons of bombs) from 1,000 to 1,500 miles. This method of refueling was demonstrated to army in January 1944, but did not develop.