| Boeing XB-15 | |
|---|---|
| XB-15 on a test flight | |
| Role | Heavy bomber |
| Manufacturer | Boeing |
| First flight | 15 October 1937 |
| Introduction | n/a |
| Status | Cancelled |
| Primary user | United States Army Air Corps |
| Number built | 1 prototype |
| Developed into | Boeing Y1B-20 |
The Boeing XB-15 (Boeing 294) was a United States bomber aircraft designed in 1934 as a test for the United States Army Air Corps to see if it would be possible to build a heavy bomber with a 5,000 mi (8,000 km) range. It was originally designated the XBLR-1 (experimental bomber, long range). When it first flew, it was the most massive and most voluminous aircraft ever built in the United States. It set a number of load-to-altitude records for landplanes, including carrying a 31,205 lb (14,154 kg) payload to 8,200 ft (2,500 m) on 30 July 1939.[1]
The aircraft's immense size allowed for passages within the wing, allowing minor repairs in flight. A 5,000 mi (8,000 km) flight took 33 hours at its 152 mph (245 km/h) cruising speed; the crew was made up of several shifts, and bunks allowed them to sleep when off duty.
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The XB-15 was designed to use 2,600 hp (1,900 kW) Allison V-3420 liquid-cooled inline engines; since these were not ready, 850 hp (630 kW) Pratt & Whitney R-1830 air-cooled radial engines were used instead. With these engines, its top speed of 200 mph (320 km/h)—145 mph (233 km/h) when loaded with bombs—was far too slow for a combat aircraft, and the project was abandoned.[2]
The single prototype was assigned to the 2nd Bombardment Group at Langley Field, Virginia. Commanded by Major Caleb V. Haynes, it flew an earthquake relief mission, carrying medical supplies to Chile in February 1939, earning its crew the MacKay Trophy. In 1940, the XB-15 was based in the Panama Canal Zone, taking part in classified bombing tests of canal lock protections. In May, a survey flight was made from Panama over the Galapagos islands, with then-Captain Curtis LeMay as navigator, the inspection including Baltra Island.[2]
In late 1940, the XB-15's defensive guns were removed at Duncan Field in Florida. Seats were attached so that Lend Lease aircraft ferry crews could be returned after delivery.[3]
In May 1943, the Army Air Forces converted the only prototype into a transport, the aircraft being redesignated XC-105. A cargo hoist was mounted, and cargo doors fitted. Its maximum gross weight was increased to 92,000 lb (42,000 kg).[4] By this time, the aircraft was nicknamed "Grandpappy" by 20th Troop Carrier Squadron airmen.[5] It displayed nose art depicting an elephant carrying on its back a large crate labeled "supplies".[3] During World War II, the XC-105 carried freight and personnel to and from Florida, and throughout the Caribbean, based out of Allbrook Field in Panama beginning in June 1943. "Grandpappy" traveled to the Galapagos, landing on Baltra Island at the same airfield built following the XB-15 aerial survey of May 1940.[3]
"Grandpappy"′s flight crew, reduced to six men, described the aircraft as difficult to fly and service. Two fires occurred during flight.[4] The aircraft was retired in December 1944. In June 1945, it was ordered to be scrapped at Allbrook Field in Panama,[4] its engines and internal parts removed along with its vertical stabilizer and rudder. The remaining airframe was pushed by bulldozer into the swamp adjoining the airfield.[3][5]
During its 18 months of transport service, the XC-105 carried more than 5,200 passengers, 440,000 lb (200,000 kg) of cargo and 94,000 lb (43,000 kg) of mail. It flew 70 cargo trips and 60 missions including anti-submarine patrol. Unusually, the aircraft was consistently referred to as "he" by its crew.[3]
Despite its cancellation, the XB-15 did feature a number of significant innovations:
Data from Boeing Aircraft since 1916 [6]
General characteristics
Performance
Armament
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