Boeing B-9 bomber Model 215
The Boeing B-9 was the Air Corps' first all-metal low-wing monoplane bomber, and the last Army bomber to have open cockpits. By the early 1930s, aircraft design and construction technology throughout the world had advanced to the point where it was possible to mass-produce all-metal airplanes. There had been an all-metal plane as early as World War I, but it was an exception. Most airplanes of the war period and the 1920s had been primarily of wood and fabric construction, although many later ones had tubular steel fuselage frameworks.
Dubbed the “Death Angel” because she was capable of attaining highest speed of any bomber and can carry a ton of explosives, four machine guns fore and aft and a crew of five men, the giant Boeing bombing plane was predicted to become one of the nation’s most fearful weapons.
In 1930, Boeing had created the revolutionary Monomail, a civilian aircraft which made traditional biplane construction designa a thing of the past. The Monomail wing was set lower, was smooth, made entirely of metal and had no struts (cantilevered construction). The Model 200 Monomail was the first American plane to use a circular-section fuselage of metal monocoque construction, a neatly cowled radial engine offering good power and reliability with low fuel consumption, a cantilever low-set wing of metal stressed-skin construction, and retractable landing gear.
The Monomail was a revelation, for its full use of stressed-skin metal was both practical and beautiful. The retractable landing gear, the streamlined fuselage and the engine covered by an antidrag cowling added up to an advanced, extremely aerodynamic design. The Monomail Model 200 was a mail plane, and the Model 221 was a six-passenger transport. Both were later revised for transcontinental passenger service as Model 221As.
The major drawback of the Monomail was that its design was too advanced for the engines and propellers of the time. The airplane required a low-pitch propeller for takeoff and climb and a high-pitch propeller to cruise. By the time the variable-pitch propeller and more powerful engines were available, the Monomail was being replaced by newer, multiengine planes it had inspired.
The B-9A had a number of features borrowed from the experience of designing the Monomail high-speed passenger aircraft. These include retractable in-flight chassis, annular cowl for cylinder heads of air-cooled engines, smooth metal lining. But the Monomail was a rather smaller single-engine aircraft.
By design, the B-9 in many ways strongly resembled the Soviet TB-1, which was demonstrated in 1929 in the United States. In terms of speed, the B-9 bomber was superior to teh somewhat larger TB-1, but it was still inferior to new-generation passenger aircraft. On one of the ANT-4bis aircraft, called the "Country of Soviets", in 1929 a big flight was made on the route Moscow-New York. This flight of 21,242 km continued from August 23 to November 2, was carried out by the crew of SA Shestakov (first pilot), FE Bolotov, BV Sterligov and DB Fufaev and took 142 flight hours. During this flight 8000 km were passed over the sea, while the aircraft was placed on the floats. After this flight, the advanced aircraft construction company of the USA "Boeing" and then other aircraft manufacturers around the world began to build twin-engine aircraft according to the ANT-4bis scheme. This scheme, as is known, still remains the most common in aviation.
The Boeing B-9 bomber was the earliest plane based on the Monomail design. In 1932, Boeing launched a twin-engine B-9 bomber. The Boeing B-9 aircraft was the first twin-engine U.S. Army bomber to have a low-wing cantilever (internal bracing only) design. The YB-9 was originally owned, developed and tested by Boeing as the XB-901 (NX10633). The plane was based on the Model 200 commercial transport but was enlarged and adapted to the bomber role. The YB-9 was powered by two Pratt & Whitney R-1830-13 radial engines which gave it a top speed of 163 mph. Later in its service life, the YB-9 was fitted with the same engines powering the Y1B-9A service test aircraft bringing its top speed to 188 mph; as fast as the U.S. Army pursuit planes of the time.
It was an all-metal monoplane with a wing of a thick profile. To provide the crew accommodation, the fuselage was extended well forward of the wing. A bomb-aimer/gunner was accommodated in the nose and immediately behind him, within the fuselage, was a radio operator's position. Aft of the radio operator were two cockpits in tandem, for pilot and co-pilot, with a fourth open cockpit, just aft of the wing trailing edge, for the rear gunner. A bombload totalling 1025kg could be divided between an internal bomb bay and underwing racks.
The rudder of the B-9 bomber had an additional small hinged surface called a "tab" attached to its trailing edge. The rudder pedals were attached to it by cables, allowing a relatively small movement to produce a larger deflection of the rudder by using the advantage of leverage. The B-9 bomber was the first U.S. aircraft to incorporate the control.
The design took advantage of new research at the National Advisory Committee on Aeronautics (NACA), which gave it a tremendous advantage in performance when compared to the old lumbering Keystone biplanes. During testing at the 20 foot NACA wind tunnel at Langley Virginia built in 1927, engineers experimenting with a Sperry Messenger and discovered that drag could be decreased by 40% by installing retractable landing gear. Another experiment with a Curtiss Hawk in 1927 demonstrated the advantages of streamlining radial engines with a new NACA engine cowling. The NACA cowling increased airspeed from 118 to 137 mph (200 to 220 km/h). With the release of new data, aircraft manufacturers rushed to install NACA engine cowlings and began designing aircraft with retractable landing gear.
The B-9 had a maximum speed of 26 km / than that close in size and power of the power plant B-247. As the calculation shows, the drag coefficient of the bomber - 0.034 - was 1.5 times higher than the passenger Boeing (0.021). Sources of large additional resistance from the military machine were a thick wing, machine-gun turrets suspended under the fuselage of a bomb. But the greatest damage was created by open cabins of pilots and shooters, characteristic for military aviation. The cutouts for the cabins and the peaks in front of them to protect them from the air flow were sources of strong turbulence that violated the smoothness of the airflow around the aircraft.
The Y1B-9A was an improved version of the basic YB-9 airframe with a redesigned vertical stabilizer and more powerful engines. The plane was actually faster than the pursuit aircraft in service at the time. The Y1B-9A carried a crew of four, all seated in separate open cockpits along the length of the fuselage. Speeds attained by bomber aircraft like the B-9 made open cockpits impractical and except for the initial Martin B-10 prototype, the B-9 was the last U.S. Army bomber flown with the crew exposed to the elements.
The Y1B-9 was the second prototype (S/N 32-302) B-9 modified for Curtiss V-1570-29 Conqueror liquid-cooled engines. These powerplants each produced 25 more horsepower than the R-1860s of the YB-9. The increased power combined with more streamlined engine nacelles gave the Y1B-9 a top speed of 173 mph -- 10 mph faster than the first prototype.
After further evaluation, the Model 214 was later converted to Hornet engines. The liquid-cooled inline engine was tested on various U.S. Army bombers until the advent of jet bombers, but was never used on a production aircraft (with the exception of the Curtiss B-2). Air-cooled radial engines were lighter and considered to be more reliable than liquid-cooled engines. Also, air-cooled radials are generally less vulnerable to damage from enemy air attacks. Liquid-cooled engines were prone to losing coolant, resulting in overheating.
The Model 246 (Y1B-9A) was an improved version over the YB-9 which featured more powerful 600 hp (447 kW) Hornet engines and a redesigned vertical stabilizer. The new engines increased the Y1B-9A's airspeed to 186 mph (300 km/h). It now equaled the speed of all existing American fighter aircraft. To protect the flight crews from the increased speed, enclosed canopies were built, but were never installed. Other B-9 bomber design changes were made to the rudder shape and trim tab, using metal instead of cloth covered control surfaces, and using three-bladed instead of two-bladed propellers to produce additional torque.
The maximum speed of flight B-9 was lower than desired - less than 300 km/h. Without an internal bomb bay, bombers lose any speed advantage they may have until they drop their loads. This made them more susceptible to airborne attack. Produced during 1932-1933, the B-9 was outclassed by its contemporary all-metal Martin B-10 and only seven were purchased: the prototype YB-9, a liquid-cooled engine Y1B-9, and five service test Y1B-9As. 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 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 accident being fatal, with the remaining aircraft gradually phased out over the follwoing two years, with the last being withdrawn on 26 April 1935.
The aircraft never entered full-scale production mainly because there were even better aircraft being designed which would change the course of U.S. bomber development. This came as a great disappointment to Boeingy, which had produced this first revolutionary bomber with performance superior to most contemporary fighter aircraft. Boeing built the YB-9 prototype bombers at company expense to show their design potential to the military. However, this small B-9 family marked the very beginning of the company's specialization in bomber design. This high-speed aircraft inspired other airplane manufacturers to launch a new generation of bombers, such as the Martin B-10.
Because fighters were expected to be faster than bombers, the B-9 also led to the first monoplane fighters. The Air Corps' first all-metal monoplane fighter was the Consolidated P-25 of 1933. Although only two were procured, the P-25 design was modified into the P-30, later redesignated the PB-2, of which 54 were purchased in 1935. The first all-metal fighter ordered in quantity was the Boeing P-26; 139 were purchased from 1932-1936.
the B-9, the immediate predecessor of the first truly modern airliner, the Model 247, in 1932. The Model 247 was a remarkable airplane, and perhaps deserved to enjoy greater commercial success than it did. Charles N. "Monty" Montieth, Boeing's first nationally recognized chief engineer. designed the Monomail, the B-9, and other early pioneerign aircraft. Montieth was forced to retire from Boeing in 1938 because of failing eyesight. Despondent, according to his wife, at the prospect of going blind, the consequence of the strain of writing his textbook on aeronautics, Montieth shot himself on March 17, 1940. He was forty-eight.
|
NEWSLETTER
|
| Join the GlobalSecurity.org mailing list |
|
|
|
