Subject: Bomber Series--Boeing XB-15

From: [email-masked]
Date: 5 Jul 94 16:25:40 GMT

>From [email-masked]

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 crew of ten has soundproofed, heated, and ventilated quarters with 
rest bunks, a kitchen, and a lavatory.  For the first time in an 
airplane, small auxiliary engines were fitted which powered a 110-volt 
electrical system.  The wing was so thick at the root that it was 
possible for a crew member to service the engine accessory sections in 
flight from a passageway extending behind the nacelles.  Such a system 
later appeared on the Boeing Model 314 flying boat.  The main 
undercarriage retracted into the rear of the inner engine nacelle.  
The aircraft was sufficiently heavy that it was necessary to fit two 
wheels on each main undercarriage truck.  

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.  

Although it was an older design than the Model 299 which eventually 
emerged as the B-17 and carried an earlier military designation, the 
XB-15 made its first flight two years later.  The XB-15 (serial number 
35-277) made its first flight on October 15, 1937 with Eddie Allen at 
the controls.  At the time of its appearance, it was the largest and 
heaviest aircraft yet to be built in the United States.  

The XB-15 proved to be seriously underpowered with the R-1830 radials.  
Because of its low performance as compared to later models, the XB-15 
was never ordered into production, and the prototype was the only 
example to be built.  Following the completion of the tests, the XB-15 
was turned over to the 2nd Bomb Group in August of 1938.  In spite of 
the fact that the aircraft was seriously underpowered for its size, it 
did manage to set several world records for weight carrying, including 
a 71,167-pound payload to 8200 feet on July 30, 1939 and a payload of 
4409 pounds carried over a distance of 3107 miles at 166 mph.  

In 1943, the sole XB-15 was converted into a cargo carrier by adding 
cargo doors and a hoist.  The aircraft was redesignated XC-105.  The 
gross weight increased to 92,000 pounds.  The XC-105 was scrapped at 
Kelly Field, Texas shortly before the end of the war.  

Two service test models of the XB-15 were ordered under the 
designation Y1B-20.  In an attempt to provide more power, these planes 
were to have been powered by 1400 hp Pratt & Whitney R-2180 radials.  
However, they were cancelled before anything could be built.  

Specification of XB-15: 

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.  

Sources:

  Boeing Aircraft Since 1916, Peter M.  Bowers, Naval Institute Press, 
  1989.  

  United States Military Aircraft Since 1909, Gordon Swanborough and
  Peter M. Bowers, Smithsonian, 1989.

  American Combat Planes, Ray Wagner, Third Edition, Doubleday, 1982.

  U.S. Army Aircraft, 1908-1946, James C. Fahey

Joe Baugher				AT&T Bell Laboratories
1000 E. Warrenville Road		Naperville, Illinois 60566-7013