B-18 Bolo
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The Douglas B-18 Bolo was a United States Army Air Corps and Royal Canadian Air Force bomber of the late 1930s and early 1940s based on the Douglas DC-2.
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History
In 1934, the United States Army Air Corps put out a request for a bomber with double the bomb load and range of the Martin B-10, then the Army's standard bomber. In the evaluation at Wright Field the following year, Douglas showed its DB-1. It competed with the Boeing Model 299 (later the B-17 Flying Fortress) and Martin Model 146. While the Boeing design was clearly superior, the crash of the B-17 prototype (caused by taking off with the controls locked) removed it from consideration. The Douglas design was ordered into immediate production in January 1936 as the B-18.
The DB-1 design was essentially the same as the DC-2, with several modifications. The wingspan was 4.5 ft (1.4 m) greater. The fuselage was deeper, to better accommodate bombs and the six-member crew; the wings were fixed in the middle of the cross-section rather than to the bottom, but this was due to the deeper fuselage. Added armament included nose, dorsal, and ventral gun turrets. The bomber used two Wright R-1820-45 ‘Cyclone 9’s, of 930 hp (694 kW) each.
The initial contract called for 133 B-18s (including DB-1), using Wright radials. The last B-18 of the run, designated DB-2 by the company, had a power-operated nose turret. This design did not become standard. Additional contracts in 1937 (177 aircraft) and 1938 (40 aircraft) were for the B-18A, which had the bombardier’s position further forward over the nose-gunner's station. The B-18A also used more powerful Wright R-1820-53 engines of 1,000 hp (746 kW).
By 1940, most Army bomber squadrons were equipped with B-18s or B-18As. Many of those in the 5th Bomb Group and 11th Bomb Group in Hawaii were destroyed in the attack on Pearl Harbor.
B-17s supplanted B-18s in first-line service in 1942. Following this, 122 B-18As were modified for anti-submarine warfare. The bombardier was replaced by a search radar with a large radome. Magnetic anomaly detection (MAD) equipment was sometimes housed in a tail boom. These aircraft, designated B-18B, were used in the Caribbean on anti-submarine patrol. The Royal Canadian Air Force acquired 20 B-18As (designated the Douglas Digby Mark I), and used them for patrols also.
Variants and Design Stages
- DB-1—Prototype; first of B-18 production run. (×1)
- B-18 (http://www.wpafb.af.mil/museum/research/bombers/b2-23.htm)—Initial production version. (×131, or 133)
- B-18M—Bomb gear removed from B-18 to serve as trainer.
- DB-2—Powered nose turret prototype; last of B-18 production run. (×1)
- B-18A (http://www.wpafb.af.mil/museum/research/bombers/b2-24.htm)—B-18 with more powerful Wright R-1820-53 engines, bombardier’s station moved. (×217)
- B-18AM—Bomb gear removed from B-18A to serve as trainer.
- B-18B (http://www.wpafb.af.mil/museum/research/bombers/b2-25.htm)—Antisubmarine conversion. (×122)
- B-18C—Antisubmarine conversion. (×2)
- XB-22 (http://www.wpafb.af.mil/museum/research/bombers/b2-30.htm)—Improvement on B-18 using Wright R-2600-3 radial engines (1,600 hp, 1194 kW); never built, largely due to better light bombers such as the B-23 Dragon.
- C-58—Transport conversion.
- Digby Mark I—Royal Canadian Air Force modification of B-18A.
Specifications (B-18A)
General Characteristics
- Crew: 6
- Length: 57 ft 10 in (17.6 m)
- Wingspan: 89 ft 6 in (27.3 m)
- Height: 15 ft 2 in (4.6 m)
- Wing area: 959 ft² (89.1 m²)
- Empty: 16,321 lb (7,400 kg)
- Loaded: 22,123 lb (10,030 kg)
- Maximum takeoff: 27,500 lb (12,600 kg)
- Powerplant: 2× Wright R-1820-53, 1,000 hp (750 kW)
Performance
- Maximum speed: 215 mph (346 km/h)
- Combat Range: 1,150 miles (1,850 km)
- Ferry Range: 2,100 miles (3,400 km)
- Service ceiling: 23,900 ft (7,280 m)
- Rate of climb: 1,030 ft/min (310 m/min)
- Wing loading: 23.1 lb/ft² (113 kg/m²)
- Power/Mass: .090 hp/lb (.15 kW/kg)
Armament
- 3× .30-calibre machine guns
- 4,500 lb (2,200 kg) of bombs
References and External links
- USAF Museum description of B-18 (http://www.wpafb.af.mil/museum/research/bombers/b2-23.htm)
Related Content
Related development: Douglas DC-2
Designation sequence: XB-15 - XB-16 - B-17 - B-18 - XB-19 - Y1B-20 - XB-21 - XB-22 - B-23 - B-24 - B-25
Related Lists List of military aircraft of the United States - List of bomber aircraft
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