Boeing XB-15

The XB-15 parked on an airstrip.

The Boeing XB-15 (Boeing Model 294) bomber aircraft was first designed in 1934 as a test for the United States Army Air Corps to see if it was possible to build a heavy bomber with a 5,000-mile range. It was originally designated the XBLR-1 (experimental bomber, long range, model 1). When it first flew, it was the most massive and most voluminous aeroplane ever built in the United States. It set a number of load-to altitude records, including a 31,205-pound flight to 8,200 feet (1939 July 30). One notable product of this size was that the crew could use passages in the wing to make minor repairs while the plane was flying. Due to limits on the technology it used, a 5,000 mile flight took several days. Thus, the crew had bunks to sleep on between shifts. It was meant to use liquid-cooled 1,000 hp (750 kW) engines. Unfortunately, these were not available, so 850 hp (637 kW) engines were used instead. These engines significantly underpowered the plane; its top speed of 200 mph (322 km/h) was far too slow for an acceptable bomber, and the project was eventually scrapped. No B-15s were put into service; the USAAC converted the only XB-15 to a cargo carrier, designated the XC-105.

XB-15 on a test flight.

Despite its failure, the XB-15 did have a number of significant features:

Automatic pilot
De-icers
Auxiliary power units independent of the main engines to power the electrical system
Engines serviseable in flight using an access tunnel inside the wing
Crew compartment with rest bunks, galley and lavatory
Double wheel main landing gear.

Specifications (XB-15)

General Characteristics

Crew: 10
Length: 87 ft 7 in (32.6 m)
Wingspan: 149 ft 0 in (45.5 m)
Height: 18 ft 0 in (5.5 m)
Wing area: ft² ( m²)
Empty: 65,000 lb (30,001 kg)
Loaded: 69,000 lb (31,000 kg)
Maximum takeoff: 77,000 lb (37,000 kg)
Powerplant: 4× Pratt & Whitney R-1830-11 of 850 hp (640 kW) each

Performance

Maximum speed: 200 mph (346 km/h)
Cruising speed: 152 mph (294 km/h)
Combat Range: 3,400 miles (2,200 km)
Ferry Range: 5,130 miles (8,250 km)
Service ceiling: 18,900 ft (7,380 m)
Wing loading: lb/ft² ( kg/m²)
Power/Mass: 0.0490 hp/lb (0.0813 kW/kg)

Armament

3× .30-calibre (7.26 mm) machine guns, 3× .60-calibre (14.5 mm) machine guns
12,000 lb (5,400 kg) bombs

Boeing XB-15

Specifications (XB-15)

General Characteristics

Performance

Armament

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