Boeing XB-15

Source: Wikipedia, the free encyclopedia.
XB-15
XB-15 on a test flight
Role Heavy bomber
Manufacturer Boeing
First flight 15 October 1937
Status Canceled
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 (USAAC) to see if it would be possible to build a heavy bomber with a 5,000 mi (8,000 km) range. For a year beginning in mid-1935 it was designated the XBLR-1. When it first flew in 1937, it was the most massive and voluminous airplane ever built in the US. It set a number of load-to-altitude records for land-based aircraft, 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 flight engineers to enter the wing through a crawlway and make 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.

Design and development

The XB-15's .50 in (12.7 mm) front gun turret

The specification that produced the XB-15 began in mid-1933 as "Project A", USAAC discussions regarding the possibility of flying a very large bomber with a range of 5,000 mi (8,000 km).[2] In April 1934, the USAAC contracted with Boeing and Martin to design a bomber capable of carrying 2,000 lb (910 kg) at 200 mph (320 km/h) over a distance of 5,000 miles.[3] Boeing gave the project the internal name of Model 294, while the USAAC called it the XB-15. Martin's design, the XB-16, was judged inferior by the USAAC before a prototype was built, and was canceled.[2]

The Boeing design team, headed by Jack Kylstra, initially intended the aircraft to use 2,600 

kW) Allison V-3420 liquid-cooled W engines; since these were not ready, 850 hp (630 kW) Pratt & Whitney R-1830 Twin Wasp air-cooled radial engines were used instead.[2]

Starting in August 1934, Boeing began designing the Model 299 in answer to a proposal by the USAAC to replace the Martin B-10 bomber. The Model 299 design team incorporated elements of the Boeing 247[4] and the Model 294, especially its use of four engines.[5] The Model 299 design team worked alongside Klystra's team, but difficulties in fabricating such a large aircraft slowed progress on the 294.[3] The Model 299 flew first, on 28 July 1935.[6]

In mid-1935, the USAAC combined Project A with Project D; a proposal asking for "the maximum feasible range into the future." The combined program was designated BLR for "Bomber, Long Range". The XB-15 was renamed the XBLR-1; it was joined under the BLR program by two other projects: one from Douglas Aircraft, the XBLR-2 which later became the XB-19; and one from Sikorsky Aircraft called the XBLR-3, later canceled. The next year, the XBLR designation was dropped and the Boeing prototype was once again the XB-15.[2]

Unusual features that the XB-15 pioneered included an

Wright Field in Ohio to be accepted by the USAAC for testing.[7]

With the Twin Wasp radial engines installed — the same number and type of engines fitted to the later Consolidated B-24 Liberator, with individual turbochargers added on the Liberators' Twin Wasp powerplants — the specified speed of 200 mph (320 km/h) for the Twin Wasp-powered XB-15 was not quite reached even when the aircraft was empty; the best speed attained in level flight was 197 mph (317 km/h).[7] Loaded with the specified 2,000 pounds (910 kg), the maximum speed was a disappointing 145 mph (233 km/h).[3] This was considered too slow for a combat aircraft, and the project was abandoned.[8] However, Boeing engineers projected that the prototype would be capable of carrying the heaviest air cargo to date: a load of 8,000 lb (3,600 kg).[3]

The design challenges stemming from the great size of the XB-15 were difficult to master, but the lessons learned by Boeing were later applied to the

tricycle gear. The Model 316 was not built. The progression of design work starting with the XB-15 finally bore fruit with the Model 345 presented to the USAAC in May 1940, the very heavy bomber which resulted in the USAAF's Boeing B-29 Superfortress.[7]

Operational history

A Red Cross agent and Major Caleb V. Haynes supervise the loading of emergency medical supplies on the XB-15 in early 1939

The single prototype was assigned to the

MacKay Trophy.[9]

Haynes piloted the XB-15 again on 10 June 1939 to return home the body of Mexican flier

National Aeronautics Association (NAA) for an international record for "the greatest payload carried to an altitude of 2,000 metres".[12] The XB-15 was not fast for a bomber but it was the fastest aircraft that could carry so much weight, and for such distances. In July 1939, Haynes received certificates from the NAA for an international 5,000 km (3,100 mi) speed record with a 2,000 kg (4,400 lb) payload. The latter performance also established a national closed circuit distance record of 3,129.241 miles (5,036.025 km).[12]

Flying from Langley, the XB-15 arrived at Albrook Field in Panama on 10 April 1940 and immediately began classified bombing tests of canal lock protections, commanded by Haynes and including Captain Curtis LeMay as navigator and Lieutenant John B. Montgomery as bombardier.[13] Of 150 bombs dropped, only three hit the target: a specially made bunker simulating a reinforced machine room. The few hits nevertheless led to improvements in bunker design.[10] In early May, Haynes and LeMay made a survey flight from Panama over the Galapagos islands, the inspection including Baltra Island.[8] Haynes piloted the XB-15 back to the United States, leaving Panama on 11 May 1940.[13]

In late 1940, the XB-15's defensive guns were removed at

Lend Lease aircraft ferry crews could be returned after delivery.[13]

XC-105 "Grandpappy" in Panama
The XC-105 parked on Baltra Island in the Galápagos. Flying above are two Consolidated B-24 Liberators.
The flight crew in front of "Grandpappy" in Panama in 1943. Note the absence of the nose gun.

Cargo aircraft

On 6 May 1943, the Army Air Forces converted the only prototype into a

20th Troop Carrier Squadron airmen.[14] It displayed nose art depicting an elephant carrying a large crate on its back labeled "supplies".[13] During World War II, the XC-105 carried freight and personnel to and from Florida, and throughout the Caribbean, based out of Albrook Field beginning in June 1943. Hundreds of young women were flown in "Grandpappy" from Miami to the Canal Zone to engage in US government work; these trips were dubbed the "Georgia Peach Run".[13] "Grandpappy" traveled to the Galapagos, landing on Baltra Island at the same airfield built following the XB-15 aerial survey of May 1940.[13]

"Grandpappy"′s flight crew, reduced to six men, described the aircraft as difficult to fly and service. Two fires and a complete failure of the electrical system occurred in the air.[7][13] The aircraft was retired on 18 December 1944, assigned to Panama Air Depot.[13] In June 1945, it was ordered to be scrapped at Albrook Field in Panama,[7] its engines and internal parts removed along with its vertical stabilizer and rudder. The remaining airframe was deposited at Diablo dump, a swampy landfill southwest of the runway, where it slowly sank from sight.[10][13][14] Squatters built shacks on stilts in the swamp, covering the remains. The former dump is now an industrial area, with "Grandpappy" underneath.[14]

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.[13]

The XB-15 parked on an airstrip.

Operators

 United States
2d Bombardment Group
20th Troop Carrier Squadron

Specifications (XB-15)

Data from Boeing Aircraft since 1916.[15]

General characteristics

  • Crew: 10
  • Length: 87 ft 7 in (26.70 m)
  • Wingspan: 149 ft 0 in (45.43 m)
  • Height: 25 ft 10 in (7.87 m)
  • Wing area: 2,780 sq ft (258.4 m2)
  • Airfoil: root: NACA 0018; tip: NACA 0010[16]
  • Empty weight: 37,709 lb (17,141 kg)
  • Max takeoff weight: 70,706 lb (32,139 kg)
  • Powerplant: 4 × 14-cylinder Pratt & Whitney R-1830-11 radial engines, 1,000 hp (634 kW) each

Performance

  • Maximum speed: 197 mph (317 km/h, 171 kn) at 5,000 ft (1,500 m)[7]
  • Cruise speed: 152 mph (245 km/h, 132 kn) at 6,000 ft (1,800 m)
  • Range: 5,130 mi (8,260 km, 4,460 nmi)
  • Combat range: 3,400 mi (5,474 km, 2,957 nmi) [17]
  • Service ceiling: 18,900 ft (5,760 m)

Armament

See also

Related development

Aircraft of comparable role, configuration, and era

Related lists

References

Notes

  1. ^ Bowers says the record flight had a payload of 71,000+ lb (32,000+ kg) but the FAI record book shows 14,000+ kg (31,000+ lb)
  2. ^ a b c d e Yenne 2005, p. 43.
  3. ^ a b c d Moy 2001, pp. 70–72.
  4. ^ Swanborough and Bowers 1963, p. 74.
  5. ^ Moy 2001, p. 73.
  6. ^ "History: The Boeing Logbook: 1933–1938". Boeing. Archived from the original on 2006-12-08. Retrieved 2012-05-26.
  7. ^ a b c d e f g Kohn 2002 pp. 43–44.
  8. ^ a b Boniface 1999, pp. 64–67.
  9. ^ a b Haulman, Daniel L.One Hundred Years of Flight: USAF Chronology of Significant Air and Space Events 1903–2002. Maxwell AFB, Alabama: Air Force History and Museums Program, Air University Press, 2003.
  10. ^ a b c Liang, Susan Hall. "Grandpappy's dead and buried, but he's not forgotten." The Panama Canal Spillway, 19 October 1979, p. 3. Retrieved: 26 May 2012. Hosted by the University of Florida Digital Collections, George A. Smathers Libraries.
  11. ^ Maurer 1987, pp. 304–307, 355–360, 405–406.
  12. ^ a b "USAF Biography: Major General Caleb V. Haynes". Archived from the original on 2009-06-13. Retrieved 2014-06-25.
  13. ^ a b c d e f g h i j Bouché, Georges G. " 'Grandpappy'-The XB-15." Aerospace Historian, Air Force Historical Foundation, Volume 26, Number 3, September 1979, pp. 171–181.
  14. ^ a b c Millam, Ed S. Jr."Grandpappy". AAHS Journal (American Aviation Historical Society), Volume 50, 2005, pp. 46–54.
  15. ^ Bowers 1989, p. 230.
  16. ^ Lednicer, David. "The Incomplete Guide to Airfoil Usage". m-selig.ae.illinois.edu. Retrieved 2024-01-30.
  17. ^ "Fact Sheets: Boeing XB-15". National Museum of the United States Air Force. Archived from the original on 2007-11-21. Retrieved 2009-08-07.

Bibliography

External links

Wikimedia Commons has media related to Boeing XB-15.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Boeing_XB-15&oldid=1213734282"