Huff-Daland B-1 As early as April of 1926, the Army had decided that single-engined bombers were unsatisfactory, concluding that the more conventional twin-engined configuration was safer and had the additional advantage of allowing for a gunner and/or bomb-aiming position to be mounted in the nose. The B-1 had two gunners, one seated in the rear of each engine nacelle. Twin Lewis guns were provided for each of these gunners, with a third pair provided for a gunner's position in the nose. The Huff-Daland B-1B was powered by two 600 hp Curtiss V-1570-5 Conqueror liquid-cooled engines. Maximum speed 117 mph at sea level, service ceiling 15,000 feet, range 700 miles. Weights: 9462 pounds empty, 16,500 pounds gross, 17,039 pounds maximum. Wingspan 85 feet, length 62 feet, height 19 feet 3 inches, wing area 1604 square feet. Armed with six Lewis machine guns, paired in engine nacelle and nose positions and 2500 pound bombload
Curtiss B-2 Condor First flight of the XB-2 took place in September 1927. The Conqueror engines were housed inside nacelles mounted on top of the lower wing. A defensive gunner position was in the rear of each engine nacelle. An additional gunner position was provided in the nose. In June, 1928 Curtiss was given a contract for two B-2s with a further ten examples were ordered in 1929. The type was withdrawn from service by 1936. The Curtiss B-2 Condor was powered by two 633 hp Curtiss V-1570-7 Conqueror liquid-cooled engines. Maximum speed 132 mph at sea level, 128 mph at 5000 feet. Cruising speed 114 mph, landing speed 53 mph. Service ceiling 17,100 feet, absolute ceiling 16,400 feet. Initial climb rate 850 feet per minute. An altitude of 5000 feet could be attained in 6.8 minutes. Range was 780 miles. Empty weight 9039 pounds, gross weight 16,516 pounds. Wingspan 90 feet, length 47 feet 6 inches, height 16 feet 3 inches, wing area 1499 square feet. Armed with two Lewis machine guns in each of the gunner positions at the rear of the engine nacelles, plus an additional pair of Lewis guns in the nose position. Bombload was normally 2508 pounds, but could be increased to 4000 pounds on short flights.
Keystone B-3 The 17th production Keystone LB-6 on the 1929 contract had been completed as the LB-10. The LB-10 differed from the LB-6 in being powered by a pair of experimental 525 hp Wright R-1750-1 Cyclone radial engines, plus it had a single rudder in place of the twin rudders which Keystone had standardized on the LB-5A. However, before the first LB-10A could be delivered, the USAAC had dropped the LB designation and was listing all of its bombers under the B series. The LB-10A was redesignated B-3A. A total of 63 B-3 bombers were built. The B-3 was powered by two 525 hp Pratt & Whitney R-1690-3 Hornet air-cooled radial engines. Maximum speed 114 mph at sea level, 109.5 mph at 5000 feet. Cruising speed 98 mph. Landing speed 56 mph. Service ceiling 12,700 feet. Initial climb rate 650 feet per minute. An altitude of 5000 feet could be attained in 9.4 minutes. Range was 860 miles. Weight: 7705 pounds empty, 12,952 pounds gross. Wingspan 74 feet 8 inches, length 48 feet 10 inches, height 15 feet 9 inches, wing area 1145 square feet. Armed with three Browning machine guns, one in each of nose, dorsal, and ventral positions. A bomb load of 2500 pounds could be carried.
Keystone B-4 In 1930, seven Keystone biplane bombers were ordered under the designation LB-13. They were to be equipped with single vertical tails and were to be powered by a pair of 525 hp Pratt & Whitney GR-1690 radials. Five were completed as Y1B-4s with 575 hp R-1860-7 engines (30-344/348). On April 28, 1931, the Army ordered 25 examples of the B-4A, which was an improved production version of the Y1B-4. The B-4A was externally almost identical to the B-3A which preceded it (as well as to the B-5 and B-6 which followed it). These Keystone bombers usually differed from each other only in the type of engine which powered them, and it was often only possible to distinguish one from the other by an examination of their serial numbers. Their performance was identical.
Keystone B-5 In 1930, three Keystone biplane bombers were ordered under the designation LB-14. They were to be equipped with single vertical tails and were to be powered by a pair of 525 hp Pratt & Whitney GR-1860 radials. The LB-14s that were ordered were completed under the designation Y1B-5s with 525 hp Wright R-1750-3 engines. However, it is uncertain if these were ever actually delivered. 27 production versions of the Y1B-5 were obtained by converting existing B-3As. These conversions were assigned the designation B-5A. They were powered by a pair of Wright R-1750-3 Cyclone air-cooled radial engines.
Keystone B-6 Two LB-13s were completed as Y1B-6 with 575 hp Wright R-1820-1 Cyclone engines (30-349/350). Three more Wright-powered Y1B-6s (30-351/353) were produced by conversion from production Pratt & Whitney-powered B-3As On April 28, 1931, the Army ordered 39 B-6A bombers. The B-6A was an improved production version of the Y1B-6.
Douglas B-7 In early 1930, the Douglas aircraft company submitted a proposal to the Army for a twin-engined observation plane. On March 26, 1930, the Army ordered two example of the Douglas proposal. One was designated XO-35 and the other XO-36, the primary difference being that the XO-35 had two geared 600 hp Curtiss V-1570-29 Conquerors driving three-bladed propellers and the XO-36 had two direct-drive 600 hp Curtiss V-1570-23 Conquerors driving two-bladed propellers. The performance of the XO-35/36 promised to greatly exceed that of the lumbering Keystone biplanes that were at that time the standard USAAC light bombers. Consequently, the Army decided to have the XO-36 completed as a light bomber rather than as an observation plane. It was assigned the designation XB-7, and was to have been equipped with racks for 1200 pounds of bombs underneath the fuselage. On August 22, 1931, the USAAC ordered seven Y1B-7 bombers and five Y1O-35s, these being delivered between August and November of 1932. The Y1B-7 was powered by two 640 hp Curtiss V-1570-33 or 675 hp V-1570-52 Conqueror twelve-cylinder liquid-cooled Vee engines. Maximum speed: 182 mph at sea level, 177 mph at 5000 feet. Cruising speed: 155 mph. Landing speed 78 mph. Climb to 5000 feet in 3.7 minutes. Climb to 10,000 feet in 8.7 minutes. Service ceiling 20,400 feet, absolute ceiling 21,800 feet. Normal range 411 miles, maximum range 632 miles. Weights: 5519 pounds empty, 9953 pounds loaded, 11,177 pounds maximum Dimensions: wingspan 65 feet, length 45 feet 11 inches, height 11 feet 7 inches, wing area 621.2 square feet. Armed with two 0.30-inch machine guns, one in a flexible nose position and the other in a flexible dorsal position. 1200 pounds of bombs could be carried on racks underneath the fuselage.
Fokker XB-8 In 1929, the Fokker design department developed an observation aircraft that could replace the Douglas O-25. This was a true cantilever monoplane with no struts or rigging wires. The plywood-covered high-mounted wing was made of wooden box spars with plywood spars and ribs, covered with a plywood veneer. The fuselage was made of steel tubing and was covered with fabric. The aircraft was powered by a pair of Curtiss V-1570-9 Conqueror twelve-cylinder liquid-cooled engines mounted in the leading edge of the wing. The landing gear was retractable, the first such to be fitted to an Army Air Corps observation or bombardment aircraft. Three crew members (1 pilot plus two gunners) could be carried in open cockpits. Armament was to consist of two flexible 0.30-inch machine guns, one operated by a gunner in a nose position and the other by a gunner in a dorsal position. In 1929 the Army decided to have the second prototype of both designs completed as a light bomber rather than as an observation plane. The designation XB-8 was assigned to the Fokker design. On April 11, 1931, the company received a contract for six service test B-8s. This was subsequently reduced to a single aircraft, the type proving inferior to the B-7.
Boeing B-9 The Boeing B-9 was the first cantilever monoplane bomber to be produced for the US Army. 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 Army ordered five new planes under the designation Y1B-9A. 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 that 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.
Douglas B-11 The Douglas B-11 was a 1932 project for an amphibian bomber that would fly over water along with formations of conventional land-based bombers to act as navigation leaders and as rescue aircraft in case one of the bombers went down. The idea was abandoned.
Boeing XB-15 In April 14, 1934, the Army Air Corps issued a request for a long-range bomber. A 5000 mile range with a 2000-pound bombload was envisaged.
The Boeing Airplane Company submitted its Model 294 in response to this requirement. The Army expressed sufficient interest in the Model 294 that it issued a contract on June 28, 1934 for design data, wind-tunnel tests, and the construction of a mockup under the designation XBLR-1, the letters standing for "Experimental Bomber, Long Range". On June 29, 1935, a contract was approved for one example of the XBLR-1. The BLR category was later eliminated, and the aircraft was redesignated XB-15 in July 1936.
The XB-15 was a large, four-engined mid-wing cantilever monoplane with all-metal semi-monocoque construction. The structure was generally similar to that of earlier Boeing monoplanes that had been based on the Monomail design, with the exception that the wing from the main spar aft was covered with fabric instead of metal. The XB-15 was originally to have been powered by four Allison V-1710 liquid cooled V-12 engines. However, before the aircraft was built, the powerplants were changed to four 1000 hp Pratt & Whitney R-1830 twin-row air-cooled radials. The defensive armament was the heaviest yet to be fitted to a bomber. It carried six machine guns. One of these guns was mounted in a nose turret and another one was carried in a forward-facing belly turret mounted below the pilot's cabin. A 0.50-inch gun was mounted in a top turret which could rotate through 360 degrees. One gun was carried in each of two waist blisters attached to the fuselage behind the wings. A sixth gun was housed inside a rearward-facing belly turret. The XB-15 proved to be seriously underpowered with the R-1830 radials. Because of its low performance as compared to later aircraft, the XB-15 was never ordered into production, and the prototype was the only example to be built
The XB-15 was powered by four Pratt & Whitney R-1830-11 Twin Wasp air cooled radials, rated at 850 hp at 2450 rpm at 5000 feet, and 1000 hp for takeoff. Maximum speed: 200 mph at 5000 feet, 197 mph at 6000 feet, cruising speed 152 mph at 60 percent power at 6000 feet. Service ceiling 18,900 feet, absolute ceiling 20,900 feet. Climb to 5000 feet in 7.1 minutes, climb to 10,0000 feet in 14.9 minutes. Range 3400 miles with 2511 pounds of bombs, maximum range 5130 miles. Weights: 37,309 pounds empty, 65,068 pounds gross, 70,706 pounds maximum. Dimensions: wingspan 149 feet, length 87 feet 7 inches, height 18 feet 1 inches, wing area 2780 square feet. Armed with two 0.50-inch and four 0.30-inch machine guns. A bomb load of four 2000 pound bombs could be carried. Maximum bombload was 12,000 pounds.
Martin XB-16 In April 14, 1934, the Army Air Corps issued a request for a long-range bomber. A 5000 mile range with a 2000-pound bombload was envisaged. The Glenn L. Martin Company of Baltimore, Maryland submitted its Model 145, a large cantilever monoplane powered by four Allison V-1710 liquid-cooled V-12 engines. This was later enlarged to a 173-foot wingspan aircraft powered by six Allison V-1710-2 engines, four of them operating as tractors and two as pushers. Twin rudders were to have been mounted behind two tail booms. A tricycle landing gear was to be used. The maximum weight was to have been 105,000 pounds. The Martin XB-16 was considered as being too large and expensive, and the project was cancelled before anything could be built.