The Boeing B-9 was the first cantilever monoplane bomber to be produced for the US Army. The B-9 began life as the Boeing Models 214 and 215. These were company-funded new bomber designs that were based on the concepts developed by the Model 200 Monomail commercial mail carrier.
Both the Model 214 and the Model 215 were low-winged, all-metal cantilever monoplanes. The fuselage was of semi-monocoque construction, which permitted the use of a more nearly circular cross section. The main landing gear retraced rearward into the engine nacelles, but the lower halves of the wheels remained exposed.
Five crew members were carried--pilot, copilot, nose gunner/bombardier, rear gunner, and a radio operator. Four of the crew members sat in separate open cockpits, widely separated from each other. The bombardier/nose-gunner sat in a cockpit in the nose, which was equipped with a bomb sight and aiming window in the bottom and had a mount for a single flexible 0.30-inch machine gun around the top. Because the fuselage was so narrow, the pilot and copilot sat in separate tandem cockpits immediately behind the nose gunner. A fourth cockpit for a rear gunner was located on top of the fuselage behind the wing. He operated a single flexible 0.30-inch machine gun. The radio operator was located inside the fuselage just ahead of and below the pilot, and had a window on each side of the nose. Because of their wide separation, crew members had difficulty in communicating with each other in flight. The pilot had limited visibility because of the radial engines on each side and the long forward fuselage immediately ahead.
The Models 214 and 215 had rudder servo tabs to assist the pilots in moving the controls, which was the first such installation on an American-designed aircraft. There was no internal bomb bay--there were four hardpoints loctated underwing between the fuselage and engine nacelles.
The Models 214 and 215 were virtually identical to each other, differing primarily in the choice of engines. The Model 214 was to be powered by pair of 600 hp Curtiss V-1570 Conqueror Prestone-cooled V-12 engines, whereas the Model 215 was to be powered by a pair of 600 hp Pratt & Whitney Hornet air-cooled radial engines with NACA cowlings fitted around the cylinder heads for aerodynamic drag reduction. On the 214, the servo tab on the rudder was a small auxiliary surface, whereas on the 215 the tab ran the full height of the rudder.
The radial-powered Model 215 was the first to be completed. It took to the air for the first time on April 12, 1931. Since it was a Boeing-owned airplane, it was painted in civilian colors and carried a civilian registration number (NX10633). It was initially powered by a pair of 575 hp Pratt & Whitney R-1830-13 commercial engines. It was tested by the Army on a bailment contract under the designation XB-901. It achieved a maximum speed of 163 mph at sea level.
Favorable testing of the XB-901 resulted in the Army deciding on August 14, 1931 to purchase both the Model 215 and the Model 214. The Model 215 was assigned the designation YB-9 and was given the serial number 32-301. Now owned by the Army, the plane was repainted in military colors and the civil registration number was cancelled. The Model 214 (which had not yet flown) was designated Y1B-9 and was assigned the serial number 32-302. At the same time, the Army ordered five new planes under the designation Y1B-9A. Serials were 32-303/307
Following the Army order, the YB-9 was re-engined with Pratt & Whitney R-1830-11 Hornets supercharged to yield 600 hp at 6000 feet and was fitted with three-bladed propellers. With these new engines, the YB-9 attained a maximum speed of 188 mph at 6000 feet, an impressive performance for 1931. The era of the biplane bomber was clearly nearing its end.
The Y1B-9 (Model 214) flew for the first time on November 5, 1931. The increased power of the Curtiss Conqueror liquid-cooled engines plus the more streamlined engine nacelles gave the Y1B-9 a top speed of 173 mph--10 mph faster than the YB-9. However, after testing with the liquid-cooled Curtiss Conqueror engines at the Boeing plant in Seattle and at Wright Field in Ohio, these engines were later replaced by Hornet radials, duplicating the YB-9. The radial engine was favored by the Army at the time, because it was simpler and more reliable than liquid cooled engines which were more vulnerable in battle if the cooling system was hit.
The Model 246 was the company designation for a small batch of five Y1B-9A evaluation aircraft that had been ordered by the Army at the same time that the two prototypes were purchased. The Y1B-9A was powered by a pair of Pratt & Whitney Y1G1SR-1860B Hornet radials, rated at 600 hp at 6000 feet. Externally, the Y1B-9A was virtually identical to the YB-9. However, the Y1B-9A had the rudder tabs of the Y1B-9 and it had metal instead of fabric covering on the control surfaces. Three-bladed propellers were fitted. There were also many internal structural and equipment changes. Later, the shape of the rudder was changed to more closely resemble that of the Boeing Model 247 commercial transport. Maximum speed was up to 186 mph with the altitude-rated engines. The Y1B-9A carried a crew of four, all seated in separate open cockpits along the length of the fuselage. The defensive armament consisted of two 0.30-inch machine guns, and the bomb load included four 600-lb bombs carried externally.
The first Y1B-9A flew on July 14, 1932 and was delivered to the Army on July 21. The last Y1B-9A on the contract was delivered on March 20, 1933. The five Y1B-9As served with the 20th Bomb Group based at Langley Field, Virginia. The high speed of the Y1B-9A indicated that open cockpits were now impractical, and that enclosed cockpits for the crew would be needed in the future. Although a greenhouse cockpit canopy was designed for the Y1B-9A, it was never actually fitted.
The B-9 was a truly revolutionary design, and had a speed fully 60 percent greater than that of the Keystone biplane bombers that were still the backbone of the American bomber force in 1932. In war games held in May of 1933, the Y1B-9A could not be intercepted by six Boeing P-12 fighters, giving the USAAAC a bomber with a performance superior to that of its pursuit aircraft. In view of its superior performance, Boeing fully anticipated an Army order for substantial numbers of the new design. However, The Glenn L. Martin company in Baltimore, Maryland had in the meantime brought out a competing design of its own, the XB-907. The XB-907 was even more revolutionary than the XB-901. It was slightly larger than the XB-901 and had a substantially better performance. The Army decided to order the Martin design into production under the designation B-10 and B-12, and no production examples of the B-9 were ordered.
The service of the Y1B-9A was relative short, with all surviving examples being removed from service and surveyed in 1934. So far as I am aware, no examples of the B-9 survive today.
32-301 Boeing YB-9 (XB-901) 32-302 Boeing Y1B-9 32-303/307 Boeing Y1B-9A
Specification of the YB-9:
Two 600 hp Pratt & Whitney R-1830-13 air-cooled radial engines. Maximum speed 188 mph at 6000 feet, cruising speed 165 mph, landing speed 63 mph, initial climb rate 1060 feet per minute, service ceiling 22,600 feet, absolute ceiling 14,400 feet. An altitude of 5000 feet could be attained in 6 minutes. Range was 495 miles with 1997 pounds of bombs. Dimensions: wingspan 76 feet 9 inches, length 51 feet 6 inches, height 12 feet 8 inches, wing area 954 square feet. Weights: 8362 pounds empty, 13,351 pounds gross. Two 1100-pound bombs could be carried. Defensive armament consisted of two 0.30-inch machine guns in nose and dorsal flexible positions.
Specification of the Y1B-9:
Two 600 hp Curtiss GIV-1570 (V-1570-29) Conqueror liquid-cooled twelve-cylinder Vee engines. Maximum speed 173.5 mph at sea level, 171.5 mph at 5000 feet, cruising speed 147.5 mph, landing speed 62 mph, initial climb rate 1160 feet per minute, service ceiling 19,200 feet, absolute ceiling 21,000 feet. Range was 1250 miles. Dimensions: wingspan 76 feet 9 inches, length 51 feet 6 inches, height 12 feet 8 inches, wing area 954 square feet. Weights: 8618 pounds empty, 13,591 pounds gross. Two 1100-pound bombs could be carried. Defensive armament consisted of two 0.30-inch machine guns in nose and dorsal flexible positions.
Specification of the Y1B-9A:
Two 600 hp Pratt & Whitney Y1G1SR-1860B Hornet supercharged air-cooled radials, rated at 600 hp at 6000 feet. Maximum speed 188 mph at 6000 feet, cruising speed 165 mph, initial climb rate 900 feet per minute, service ceiling 20,750 feet, absolute ceiling 22,500 feet. An altitude of 5000 feet could be attained in 7.1 minutes. Range was 540 miles with a 2260 pound bombload, maximum range was 990 miles. Dimensions: wingspan 76 feet 10 inches, length 52 feet, wing area 954 square feet. Weights: 8941 pounds empty, 13,932 pounds gross, 14,320 pounds maximum. A load of 2260 pounds of bombs could be carried. Defensive armament consisted of two 0.30-inch machine guns in nose and dorsal flexible positions.