Click on Picture to enlarge Model 299 Prototype

 After the loss of the Model 299, the Boeing Aircraft Company was dropped from the Army Air Corps competition for a new bomber. However, the cause of the Model 299 crash was determined to be pilot error--the pilot took off with the elevator lock still engaged. The Army leadership was convinced the aircraft had the potential to fill the long-range bomber requirement and ordered 13 service test aircraft (Boeing Model 299B) as Y1B-17 in 1936. The Y1 (instead of Y) indicates a funding source outside of the normal fiscal year procurement. The designation changed to YB-17 on 20 November 1936 before the first aircraft flew.

The Second Bomb Group based at Langley Field, Virginia took delivery of the first YB-17 on 1 March 1937. General Andrews (Commander of the Army's General Head Quarters Air Force) wanted heavy bomber techniques developed as quickly as possible so all but one of the 13 YB-17s ordered were assigned to the 2nd BG. The thirteenth YB-17 was the only aircraft actually used for extensive flight testing. It was assigned to the Material Division at Wright Field, Ohio.

TYPE Y1B-17

Number Built/Converted 13

Remarks Service test aircraft

• Serial Numbers: 36-149 to 36-161

SPECIFICATIONS
Span: 103 ft. 9 in.
Length: 68 ft. 9 in.
Height: 15 ft. 0 in.
Weight: 34,873 lbs. gross
Armament: Five .30-cal. (or .50-cal.) machine guns and 8,000 lbs. of bombs
Engines: Four Wright R-1820-39 Cyclone radials of 930 hp. each

PERFORMANCE
Maximum speed: 256 mph at 14,000 ft.
Cruising speed: 175 mph
Service ceiling: 30,600 ft.
Range: 3,320 miles

PHOTOGRAPHS AND TEXT COURTESY OF THE AIR FORCE MUSEUM

 

 

Boeing Y1B-17

 

Click on Picture to enlarge

Click on Picture to enlarge

In December 1936, the Air Corps changed the designation YB-17 to the odd designation "Y1B-17" to indicate that these aircraft were specially funded. In practice, the aircraft were still referred to as YB-17s in most documentation.

The first Y1B-17 was delivered to the Air Corps in January 1937, with the last of the 13 delivered that August. The Y1B-17 looked very much like the Model 299 prototype, but there were significant differences. The Model 299's main wheels had been mounted on a two-sided strut assembly, which made them difficult to swap out. The Y1B-17 featured a one-sided strut that allowed the tires to be changed more easily. Rubber de-icer boots were installed on the leading edge of the wing of the Y1B-17. The landing flaps had been covered with aluminum on the Model 299, but were fabric-covered on the Y1B-17.

The most important change was a switch from Pratt & Whitney Hornet engines to Wright R-1820 Cyclone engines. The Cyclone was, like the Hornet, a nine-cylinder single-row radial engine, but had more growth potential. The R-1820-39 Cyclone provided 710 kW (950 HP) for take-off, about 25% more than the Hornet.

The Air Corps was engaged in an internal struggle for operational independence within the Army. Many senior Army officers believed that the only role of air power was to support ground forces, and there were those in government and particularly in the Navy who supported that concept. The Navy had traditionally been America's means of projecting military power overseas, and the admirals did not want Army aircraft to intrude into their domain. Many Air Corps officers, in contrast, felt that air power could play an important strategic role in its own right, and the Flying Fortress figured prominently in their thinking. Twelve of the new bombers were sent to a special bombing unit, the 2nd Bombardment Group at Langley Field, Virginia, under the direct control of General Headquarters Air Force.

These Fortresses were sent out on a number of publicity exercises. One Y1B-17 flew coast to coast and back again in early 1938, breaking transcontinental speed records. In February 1938, six Fortresses made a goodwill trip to Buenos Aires, Argentina, stopping in Lima, Peru, on the way down and in Panama on the way back. A few days later, seven of the bombers made a similar trip to Rio de Janiero, Brazil. Formations of Fortresses overflew major American cities, including overflights of New York City in May 1937 and early 1938.

One of these publicity stunts led to trouble with the Navy. In May 1938, three Fortresses flew 1,125 kilometers (700 miles) out into the Atlantic to find the Italian ocean liner REX, where one dropped a message on its deck. The primary navigator on this mission was a young Air Corps lieutenant named Curtis LeMay, who would be an influential player in the growth of American strategic air power. The interception of the REX infuriated the Navy. An order quickly came down from the Army high command restricting Army operations to within 160 kilometers (100 miles) of the US coast. The incident also led to increased political pressure in Washington to suppress the strategic bombing concept, though this would subside after the Munich crisis in September 1938.

Despite the frictions, the USAAC had been refining their strategic bombing ideas anyway. While the fourteenth Y1B-17 was only built for static test, it was upgraded to flight status and its engines were fitted with exhaust-driven turbochargers. This aircraft was designated the "Y1B-17A".

The turbochargers proved troublesome, and though the Y1B-17A was scheduled to fly in late 1937, it did not actually take to the air until April 1938. Flight tests proved troublesome as well. The turbochargers were mounted above the engine nacelles, and their exhaust disrupted the airflow over the wing, leading to vibration. Quick fixes didn't work, and Boeing engineers decided to relocate the turbochargers to the bottom of the nacelles. This rework was done at a company expense of almost $100,000 USD, since the penny-pinching Air Corps would not cover the cost. Performing this modification and getting it to work right took until spring 1939, but the results were impressive. The service ceiling increased from 9,450 meters (31,000 feet) to 11,580 meters (38,000 feet) and the maximum speed increased from 412 KPH (256 MPH) to 500 KPH (311 MPH).

By this time, new Fortresses were already rolling down the production line. The Air Corps had signed a contract with Boeing in late 1937 for ten improved Fortresses with turbochargers, to be designated "B-17B", and orders for 29 more B-17Bs followed.

Greg Goebel / Public Domain

 

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