Monday, April 20, 2015

Boeing B 17 Flying Fortress

Although it is sometimes introduced as the most famous of all US World War II aircraft, there are many who will argue that Boeing's B-17 Flying Fortress ranks equally with several other superb machines which became available to the US Army at just the right moment. The North American P-51 Mustang has its ardent advocates for pride of place in the USAAF's wartime armoury, but it was a child of war, conceived to live, fight and endure in the battle-torn skies of Europe. The origin of the Fortress was very different, its gestation long and troubled.

In the first few years after World War I the US Army Air Corps' Brigadier General William ('Billy') Mitchell began his campaign in favour of strategic bombing, demonstrating (perhaps inconclusively) the ascendancy of bomber over battleship in July 1921 and September 1923 by the destruction of captured or obsolete warships anchored at sea. His burning belief in air power led to a bitter campaign, against the US Navy initially, but later involving also the US Army. In the last month of 1925 'Billy' Mitchell was court-martialled and suspended from the service. He resigned very soon after this verdict, so that he could continue his campaign for the creation of the air force which he believed was needed by the USA. World War II was to prove him right in his ideas for in 1946, 10 years after his death, he was elevated to the rank of the nation's heroes by the posthumous award of the Congressional Medal of Honour.

Although Mitchell had been discredited in 1925, there were many of his former colleagues who were less outspoken but nevertheless believed in the concept of air power. With Mitchell no longer there to provide support and encouragement, the efforts of this small steering nucleus were necessarily slow. More far sighted, in some ways, were the nation's aircraft manufacturers. Boeing, for example, began work in 1930 on its Models 214 and 215, twin-engined developments of its revolutionary Model 200 Monomail civil airliner. Built as a private venture these were ordered in small numbers as Y1B-9 and YB-9, but the first significant order for monoplane bombers went to the Glenn L. Martin Company for 48 twin-engined B-10 bombers.

Deliveries of production B-10s began in June 1934, and in a changed climate of opinion the US Army had issued a month earlier its specification for an even more advanced multi-engined bomber, able to haul a bomb load of 2,000 lbs (907 kg) over a range of between 1,020 miles (1640 km) and, optimistically, 2,200 miles (3540 km), at speeds of between 200 - 250 mph (322 - 402 km/h). So far as the US Army was concerned, 'multi' meant more than one engine but Boeing, invited to submit its proposal for this requirement, elected to use four engines to power its Model 299, on which design work was initiated in mid-June 1934.

For Boeing the Model 299, built as a private venture, was a make or break gamble. Hitherto the company had built aircraft in only 'penny packet' numbers. The failure of the B-9 to win a worthwhile order had forced economies af near desperation upon Boeing, with its work force split in half and working two weeks on and two weeks off. Unless the Model 299 entered production in significant numbers the company faced, at the least, a very bleak prospect. Not surprisingly, every effort was devoted to the success of the project; every employee knew that he or she had an important contribution to make if the company was to survive.

The US Army specification had stipulated that the prototype should be available for test in August 1935, and however impossible this target had seemed in mid-1934, it became reality on 16 July 1935 when the Model 299 was rolled out of its hangar at Boeing Field, Seattle, for its first introduction to the press. Headlines on the following day announced the new'15-ton Flying Fortress', and seizing upon the name the company had it registered as the official name of its Model 299. Contrary to popular belief, this was not because of its defensive armament, but because it was procured as an aircraft which would be operated as a mobile flying fortress to protect America's coastline, a concept which needs some explanation.

USAAC protagonists of air power were still compelled to step warily, despite procurement of the B-10 bomber, for the US Navy had the most prestigious support in the corridors of power and was determined to keep the upstart US Army in its place. Even if strategic bombers were required, efforts must be made to prevent the US Army acquiring such machines. The USAAC was, however, quite astute when needs be and so, with tongue in cheek, succeeded in procuring 13 YB-17s, the original service designation of the Fortress, for coastal defence. However, this explanation anticipates the story.

On 28 July 1935 the Model 299 flew for the first time: just over three weeks later it was flown non-stop to Wright Field, Ohio, to be handed over for official test and evaluation. The 2,100-mile (3 380-km) flight had been made at an average speed of 252 mph (406 km/h), a most impressive performance which augured well for the future. The elation of the Boeing company was understandable, especially with confirmation that initial trials were progressing well. On 30 October 1935 hopes were dashed with the news that the prototype had crashed on take-off. Subsequent investigation was to prove that the attempt to take-off had been made with the controls locked, and in view of the satisfactory testing prior to this accident, the USAAC decided on the procurement of 13 YB-17s (later Y1B-17s), plus one example for static testing.

The prototype (X13372) which had crashed at Wright Field was powered by four 750 hp (559 kW) Pratt & Whitney R-1690-E Hornet radial engines. The cantilever monoplane wings were in a low-wing configuration, the wing section at the root so thick that it was equal to half the diameter of the circular-section fuselage; and wide-span trailing-edge flaps were provided to help reduce take-off and landing speeds. Landing gear was of the electrically retractable tailwheel type. Armament comprised five machine-guns, and a maximum bomb load of 4,800 lbs (2177 kg) could be carried in the fuselage bomb bay.

The initial Y1B-17 (36-149) flew for the first time on 2 December 1936, and differed from the prototype by having 930-hp (694-kW) Wright GR-1820-39 Cyclone radials, accommodation for a crew of nine, and minor changes in detail. Twelve were delivered between January and August 1937, equipping the USAAC's 2nd Bombardment Group at Langley Field, Virginia. The thirteenth aircraft went to Wright Field for further tests and after one of the Y1B-17s survived without damage the turbulence of a violent storm, it was decided that the static test example would, instead, be completed as an operational aircraft. Designated Y1B-17A, this aircraft (37-369) was provided with 1,000 hp (746 kW) GR-1820-51 engines each fitted with a Moss/ General Electric turbocharger (supercharger powered by a turbine driven by exhaust gases). It flew for the first time on 29 April 1938, and subsequent testing by the USAAC gave convincing proof of the superiority of the turbocharged engine over those which were normally aspirated, and such engines were to become standard on all future versions of the Fortress.

The utilisation of the Y1B-17s, designated B-17 in service with the 2nd Bombardment Group, did little to improve relations between the US Army and US Navy. When three of the force were used to stage an 'interception' of the Italian liner Rex some 750 miles (1207 km) out in the Atlantic, to demonstrate that the USAAC was more than capable of defending the nation's coastline, it sparked a row which dispersed the air power disciples from General Headquarters Air Force (GHQAF) to other commands, where they were remote from each other and potential influential supporters. Orders for additional B-17s had to be reduced after it had been underlined by Major General Stanley D. Embrick that . . . "the military superiority of a B-17 over the two or three smaller aircraft which could be procured with the same funds has yet to be established." This helps explain why, despite the growing war clouds in Europe, the USAAC had less than 30 B-17s when Hitler's forces invaded Poland on 1 September 1939.

The order for Y1B-17s was followed by a contract for 39 B-17Bs, more or less identical to the Y1B-17A prototype with turbocharged engines. The first of these flew on 27 June 1939, and all had been delivered by March 1940. In 1939 the B-17C was ordered, the first of the 38 on contract making its first flight on 21 July 1940. They differed by having 1,200 hp (895 kW) R-1820-65 engines, and by an increase from five to seven machine guns.

The B-17C was the first version of this bomber to be supplied to the RAF in Great Britain, which designated the 20 examples received in early 1941 as Fortress I. Equipping No. 90 Squadron, they were used operationally for the first time on 8 July 1941 when aircraft launched a high-altitude (30,000 ft / 9145 m) attack on Wilhelmshaven. In the 26 attacks made on German targets during the next two months the Fortress Is proved unsatisfactory, although there was American criticism of the way in which they had been deployed. Nonetheless, their use in daylight over German territory had proved that their operating altitude was an inadequate defence in itself, and so they needed more formidable defensive armament, for Messerschmitt Bf 109E and 109F fighters had little difficulty in intercepting them at heights of up to 32,000 ft (9750 m). Until improvements in the Fortress were made, or means found of deploying them more effectively, they were withdrawn from operations over Europe.

With the end of 1941 drawing near, the USA was soon to become involved in World War 11, initially in the Pacific theatre, but following the containment of the initial explosion of Japanese expansion it was decided that the Allies would first concentrate their efforts on bringing about a speedy conclusion of the war in Europe. Thus, large numbers of B-17s which otherwise would have found employment in the Far East were instead to equip the USAAF's 5th Air Force in Britain. Those allocated to serve with the Anglo-American Northwest African Air Forces were later to become part of the US 15th Air Force.

In 1940 Boeing received an order for 42 B-17Ds. These differed little from the B-17C, but as a result of early reports of combat conditions in Europe were provided with self-sealing tanks and additional armour for protection of the crew, and these were delivered during 1941. The B-17E which followed was the first version to benefit from the RAF's operational experience with its Fortress Is. A major redesign provided a much larger tail unit to improve stability at high altitude, and to overcome the criticism of inadequate defence 13 machine-guns were mounted in one manual and two power-operated turrets, radio compartment, waist stations and in the nose. Of the 512 of this version built under two contracts, the first flew on 5 September 1941. B-17Es were the first to serve with the 8th Air Force in Europe, with deliveries beginning in July 1942. They were used operationally for the first time by the 97th Bombardment Group, 12 aircraft being detailed for a daylight attack on Rouen on 17 August, with fighter escort provided by RAF Supermarine Spitfires.

The B-17F, of which the first flew on 30 May 1942, was the first version to be built in large numbers. Boeing produced 2,300 at Seattle, and further construction of 1,105 came from Douglas (605) and Lockheed Vega (500). Major changes included a redesigned nose, and strengthened landing gear to cater for a higher gross weight. Other changes included increased fuel capacity, the introduction of additional armour, provision of external bomb racks beneath the inner wings and, on late production aircraft, the introduction of R-1820-97 engines.

The B-17Es and B-17Fs became used extensively by the 8th Air Force in Europe, but in two major operations against German strategic targets, on 17 August and 14 October 1943, a total of 120 aircraft were lost. Clearly the Fortresses could not mount an adequate defence, no matter how cleverly devised was the box formation in which they flew. The hard truth was that without adequate long-range fighter escort they were very vulnerable to attack during mass daylight operations. Many of the losses were attributed to head-on attack, and the final major production version was planned to offset this shortcoming.

Thus the B-17Gs had a 'chin' turret housing two 12.7 mm (0.50 in) machine guns mounted beneath the fuselage nose, which meant that this version carried a total of thirteen 12.7 mm (0.50 in) guns. To increase the aircraft's operational ceiling, later production examples had an improved turbocharger for their R-1820-97 engines. B-17G production totalled 8,680, built by Boeing (4,035), Douglas (2,395), and Lockheed Vega (2,250).

Although used most extensively in Europe and the Middle East, B-17s were operational in every area where US forces were fighting. In the Pacific theatre they offered invaluable service for maritime patrol, reconnaissance, and conventional and close-support bombing. A number of variants were also produced or converted for special purposes and operations, and details of these follow. Although almost 13,000 B-17s were built, only a few hundred B-17Gs were retained in USAAF service after the end of the war, and these were soon made redundant

Nicknames: Fort;
Specifications (B-17G):
Engines: Four 1,200-hp Wright R-1820-97 Cyclone turbocharged radial piston engines
Weight: Empty 36,135 lbs., Max Takeoff 65,500 lbs.
Wing Span: 103ft. 9in.
Length: 74ft. 4in.
Height: 19ft. 1in.
Maximum Speed at 25,000 ft: 287 mph
Cruising Speed: 182 mph
Ceiling: 35,800 ft.
Range: 2,000 miles with 6,000 lb. bomb load
13 12.7-mm (0.5-inch) machine guns
Up to 17,600 pounds of bombs
Number Built: ~12, 800+

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