The Boeing YB-9 was the first all-metal

monoplane A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple wings. A monoplane has inherently the highest efficiency and lowest drag of any wing con ...

bomber A bomber is a military combat aircraft that utilizes air-to-ground weaponry to drop bombs, launch aerial torpedo, torpedoes, or deploy air-launched cruise missiles. There are two major classifications of bomber: strategic and tactical. Strateg ...

aircraft designed for the

United States Army Air Corps The United States Army Air Corps (USAAC) was the aerial warfare service component of the United States Army between 1926 and 1941. After World War I, as early aviation became an increasingly important part of modern warfare, a philosophical ri ...

. The YB-9 was a much enlarged twin-engine development of Boeing's single-engine Model 200 Monomail commercial transport.

Design and development

In May 1930,

Boeing The Boeing Company, or simply Boeing (), is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, and missiles worldwide. The company also provides leasing and product support s ...

had flown its Model 200 Monomail single-engined mailplane. The Monomail was of radical design for the time, being a semi-

monocoque Monocoque ( ), also called structural skin, is a structural system in which loads are supported by an object's external skin, in a manner similar to an egg shell. The word ''monocoque'' is a French term for "single shell". First used for boats, ...

stressed skin In mechanical engineering, stressed skin is a rigid construction in which the skin or covering takes a portion of the structural load, intermediate between monocoque, in which the skin assumes all or most of the load, and a rigid frame, which has ...

cantilever A cantilever is a rigid structural element that extends horizontally and is unsupported at one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cantilev ...

with a retractable undercarriage. Air Corps bomber squadrons of the day were largely equipped with slow strut-braced

biplane A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While ...

s built from steel-tube frames covered in doped fabric, such as the Keystone B-6, and Boeing decided to design and build a twin-engined bomber using the same techniques used in the Monomail to re-equip the Air Corps.Pelletier 2002, p. 44.Swanborough and Bowers 1963, p. 72. Boeing built two prototypes of a new bomber as a private venture, which differed in the engines used, with the Model 214 powered by two liquid-cooled Curtiss V-1570-29 Conqueror engines while the Model 215 had two Pratt & Whitney R-1860 Hornet B

radial engine The radial engine is a reciprocating engine, reciprocating type internal combustion engine, internal combustion engine configuration in which the cylinder (engine), cylinders "radiate" outward from a central crankcase like the spokes of a wheel. ...

s.Bowers 1989, p. 200. Both aircraft were low winged cantilever monoplanes with a slim, oval cross-section fuselage accommodating a crew of five. The pilot and co-pilot sat in separate open cockpits, with the co-pilot, who doubled as the bombardier sitting forward of the pilot. Two gunners, each armed with a single machine gun sat in nose and dorsal positions, while a radio operator sat inside the fuselage. Like the Monomail, a retractable tailwheel undercarriage was used.Pelletier 2002, pp. 44–45.Bowers 1989, pp. 200–201. The first of the two prototypes to fly was the radial powered Model 215 which, carrying civil markings and the

aircraft registration An aircraft registration is a code unique to a single aircraft, required by international convention to be marked on the exterior of every civil aircraft. The registration indicates the aircraft's country of registration, and functions much li ...

''X-10633'', made its first flight on 13 April 1931.Bowers 1989, pp. 202–203.Pelletier 2002, p. 47. It was leased to the Air Corps for testing under the designation XB-901, demonstrating a speed of . Testing was successful, and both the XB-901 and the as-yet incomplete Model 214 were purchased as the YB-9 and Y1B-9 respectively on 13 August 1931, with an order for a further five for service testing following.Pelletier 2002, pp. 46–47. The Y1B-9 (''Y1'' indicating funding outside normal fiscal year procurement), powered by two liquid-cooled Curtiss V-1570-29 'Conqueror' engines, first flew on 5 November 1931. The increased power from these engines, combined with improved streamlining of the engine

nacelle A nacelle ( ) is a streamlined container for aircraft parts such as Aircraft engine, engines, fuel or equipment. When attached entirely outside the airframe, it is sometimes called a pod, in which case it is attached with a Hardpoint#Pylon, pylo ...

s, increased its top speed to . The YB-9, meanwhile, had been re-engined with more powerful Hornet Bs, demonstrating slightly better performance than the Y1B-9, which was therefore also re-engined with Hornet Bs. The five Y1B-9A service test aircraft (Boeing Model 246) had the Pratt & Whitney R-1860-11 Hornet B engines which powered the re-engined YB-9 and Y1B-9 and a redesigned

vertical stabilizer A vertical stabilizer or tail fin is the static part of the vertical tail of an aircraft. The term is commonly applied to the assembly of both this fixed surface and one or more movable rudders hinged to it. Their role is to provide control, sta ...

modeled on the 247D transport. While enclosed canopies were considered and designed, the B-9 was never fitted with them. Although it equaled the speed of existing American

fighter aircraft Fighter aircraft (early on also ''pursuit aircraft'') are military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air supremacy, air superiority of the battlespace. Domina ...

,"YB-9 factsheet."
''National Museum of the United States Air Force''. Retrieved 7 July 2010. no further aircraft were built, as the

Glenn L. Martin Company The Glenn L. Martin Company, also known as The Martin Company from 1917 to 1961, was an American aircraft and aerospace industry, aerospace manufacturing company founded by aviation pioneer Glenn L. Martin. The Martin Company produced many impo ...

had flown a prototype of a more advanced bomber, the XB-907, which was ordered into production as the Martin B-10.

Operational history

The first of the five Y1B-9As entered service with the 20th and 49th Bombardment Squadrons, 2nd Bomb Group on 14 September 1932, with all examples built being in service by the end of March 1933. The new bomber proved impossible to intercept during air exercises in May 1932, strengthening calls for improved air defense warning systems. Two B-9s were destroyed during crashes in 1933, one of the accidents being fatal, while the remaining aircraft were gradually phased out over the next two years, with the last being withdrawn on 26 April 1935.Pelletier 2002, pp. 48–49.

Variants

*YB-9 (one produced). Pratt & Whitney R-1860-13 Hornet B (). Reengined with supercharged Pratt & Whitney R-1860-11 Hornet B () and was fitted with three-bladed propellers. Trim tab ran the full height of the rudder ::Boeing model B-215 ::contract number: XB-901 * Y1B-9 (one produced). Curtiss GIV-1570 Conqueror ( Curtis V-1570-29 Conqueror) (600 hp). Reengined with supercharged Pratt & Whitney R-1860-11 Hornet B (600 hp) and was fitted with three-bladed propellers. Short trim tab on rudder. ::Boeing model B-214 * Y1B-9A (five produced). Pratt & Whitney R-1860-11 Hornet B (Y1G1SR-1860B) (600 hp). Metal instead of fabric covering on the control surfaces. There were also many internal structural and equipment changes ::Boeing model B-246 * B-9B (not built). Proposed development of Y1B-9A with minor changes. ::Boeing model B-276

Operators

; *

Specifications (Y1B-9A)

References

Citations

Bibliography

* * * * * * {{Wright Field project numbers B-09, Boeing Boeing B-09 Low-wing aircraft Aircraft first flown in 1931 Twin piston-engined tractor aircraft Aircraft with retractable conventional landing gear