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Boeing 307 Stratoliner

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Boeing 307 / C-75
A restored (ex-Pam Am) Boeing 307 on display at the Steven F. Udvar-Hazy Center
Role Airliner
Manufacturer Boeing
First flight 31 December 1938
Introduction 8 July 1940
Retired 1975
Primary users TWA
Pan Am
United States Army Air Forces
Number built 10
Developed from Boeing B-17 Flying Fortress

The Boeing Model 307 Stratoliner was the first commercial transport aircraft with a pressurized cabin. This feature allowed the aircraft to cruise at an altitude of 20,000 ft (6,000 m), well above weather disturbances. The pressure differential was 2.5 psi (17 kPa), so at 14,700 ft (4,480 m) the cabin altitude was 8,000 ft (2,440 m). The Model 307 had capacity for a crew of five and 33 passengers. The cabin was nearly 12 ft (3.6 m) across. It was the first land-based aircraft to include a flight engineer as a crew member (several flying boats had included a flight engineer position earlier).[1]

Development and design

In 1935 Boeing designed a four-engined airliner based on its B-17 heavy bomber (Boeing Model 299), then in production, calling it the Model 307. It combined the wings, tail, rudder, landing gear, and engines from their production B-17C with a new, circular cross-section fuselage of 138 in (351 cm) diameter,[2] designed to allow pressurization.[3]

The first order, for two 307s (named Stratoliners), was placed in 1937 by Pan American Airways; it was followed shortly by an increase to six by Pan Am, and a second order for five from Transcontinental & Western Air (TWA), prompting Boeing to begin production on an initial batch of the airliner.[3][4]

C-75 conversion

At the time the U. S. entered World War II in December 1941, flying across oceans was a rare luxury. The war required government and military officials to do so and most four-engined long-range commercial aircraft, including Pan Am's 14 flying boats and TWA's five Boeing 307s, were pressed into service. Additional fuel tanks were added to give them the extra range required; once converted they were designated C-75 for military use. Before World War II ended their production, 10 commercial 307s had been built. TWA flew domestic routes between New York and Los Angeles for 18 months until the Army purchased their Stratoliners for wartime use as long-range, transatlantic transport for various VIPs or critical cargo. TWA converted their 307s to military service in January 1942,[5][page needed] and its Intercontinental Division (ICD) then operated these C-75s under contract to the Army's Air Transport Command (ATC) until July 1944.[2] These were the only U. S. built commercial aircraft able to cross the Atlantic with a payload until the arrival of the Douglas C-54 Skymaster in November 1942.

Conversion to the C-75 included removal of the pressurization equipment to save weight, removal of the forward four (or five) of nine reclining seats along the port side, and alteration of the two forward Pullman-like compartments (of four) starboard of the left-of-centerline aisle. Space was thus provided for crew requirements on extremely long flights and for the addition of five 212.5 U.S. gal (804 L; 177 imp gal) fuel tanks. The landing gear was strengthened, the maximum take-off weight was increased from 45,000 to 56,000 lb (20,400 to 25,400 kg)), and the exterior painted military olive drab.[2]

Operational history

The maiden flight of the first Boeing 307 Stratoliner (not a prototype, as it was planned to be delivered to Pan Am following testing and certification), registration NX 19901 took place from Boeing Field, Seattle on December 31, 1938.[6] It crashed, however, on March 18, 1939, while being demonstrated to representatives of KLM. At the time, the 307's performance with two engines inoperative on one wing was being demonstrated. When the engines were shut down, the pilot moved the rudder to maximum deflection to counter the resulting yaw. The Stratoliner then experienced "rudder lock," the hinges preventing the rudder from being re-centered. As a result, the 307 went into a spin and crashed. The 10 people aboard, including KLM test pilot Albert von Baumhauer, Boeing test pilot Julius Barr, Boeing Chief Aerodynamcist Ralph Cram, Boeing Chief Engineer Earl Ferguson, and a TWA representative were killed. Subsequent wind tunnel testing showed that the addition of a extended dorsal fin ahead of and attached to the vertical tail prevented "rudder lock" from happening. This was incorporated into the 307's rudder redesign, while also being incorporated in Boeing's rear fuselage redesign for their models "E" through "G" B-17 long-range bomber. [7]

The first delivery to a customer was to multi-millionaire Howard Hughes, who purchased one 307 to carry out a round-the-world flight, hoping to break his own record of 91 hours 14 minutes set between July 10–14, 1938, in a Lockheed 14. Hughes' Boeing Stratoliner was fitted with extra fuel tanks and was ready to set out on the first leg of the round-the-world attempt when Nazi Germany invaded Poland on September 1, 1939, causing the attempt to be abandoned. This 307 later had the extra fuel tanks removed, was fitted with much more powerful Wright R-2600 engines, and was transformed into a luxurious "flying penthouse" for Hughes, although it was little used, eventually being sold to oil tycoon Glenn McCarthy in 1949.[8][9]

Deliveries to Pan-Am started in March 1940, with TWA receiving its first 307 in April. TWA's Stratoliners were used on services between Los Angeles and New York, while Pan-Am's flew routes down to Latin America. In all, only 10 307s were built, with four being delivered to Pan-Am and five to TWA, together with the one aircraft for Howard Hughes.[10]

On the entry of the United States into World War II following the Attack on Pearl Harbor, Pan-Am continued operating its Stratoliners on routes to Central and South America, but under direction of the Army Air Force,[11] while TWA's 307s were sold to the U. S. government, being designated Boeing C-75 and operated by the United States Army Air Forces (although normally still flown by TWA crews).[12]

The U. S. Army returned the five C-75s to TWA in 1944, and they were sent to Boeing for extensive overhauls and rebuilding. Boeing replaced the wings and horizontal tail with those from the improved B-17G model, while more powerful engines were fitted and the electrical system was completely replaced by one based on Boeing's B-29 Superfortress. Passenger capacity was increased from 33 to 38.[13] The rebuild cost TWA a total of $2 million for the five aircraft, which then re-entered passenger service on April 1, 1945. Although TWA was now committed to the larger and faster Lockheed Constellation, the Stratoliners remained in use, being transferred to regional services, until withdrawn and sold in April 1951.[14]

TWA's Stratoliners were purchased by the French airline Aigle Azur, who used them for scheduled flights from France to North and Central Africa, and later to French Indo-China. These 307s were later transferred to Aigle Azur's Vietnamese subsidiary, and were used by a number of airlines in South East Asia, with at least one aircraft remaining in commercial use until 1974.[15] Pan-Am disposed of its unmodified Stratoliners earlier than TWA, with them being sold to a number of small operators. One aircraft was purchased by the Haitian Air Force, being fitted out as a Presidential transport for Papa Doc Duvalier. This aircraft was later returned to the United States and was purchased by the Smithsonian Museum.[16]

C-75

Two main routes were flown: Washington, D.C., to Cairo across the South Atlantic, and New York to Scotland across the North Atlantic.[17] They often flew non-stop the 2,125 statute miles (3,415 km) between Gander, Newfoundland and Prestwick, Scotland in the north, and the 2,550 statute miles (4,100 km) between Natal, Brazil and Accra, Ghana in the south. These were very long flights for the time. After July 1942, a refueling stop at Ascension Island was an option in the south.[18] In the north, stops at Iceland or Greenland were often necessary, especially flying westbound against the prevailing winds. As C-54s took over the Gander to Prestwick route, the C-75s operated a Marrakech to Prestwick service out over the Atlantic.[17]

In April 1945, the five C-75s were returned to TWA, having been restored by Boeing and recertified by the CAA as SA-307B-1 civilian transports with their old registration numbers. The restoration included new B-17G Flying Fortress wings and engines, horizontal stabilizer moved three feet (0.9 m) aft, and improved B-29-type electronics. TWA then restyled the interior cabin in two sections, 10 seats forward and 28 aft.[2]

Variants

Passengers aboard Pan Am Boeing 307
307
equipped with Wright Cyclone GR-1820-G102 engines with single speed supercharger; 5 crew.
307B
equipped with Wright Cyclone GR-1820-G105A engines with two speed supercharger for improved high altitude performance; 7 crew.
C-75
Five Trans World 307Bs were pressed into service with the USAAF as military transports; the cabin pressurization was removed to save weight.
307B-1
Following military service, the C-75s were overhauled and updated with B-17G wings and tailplane, four Wright Cyclone GR-1820-G606 engines, and B-29-type electronics.

Operators

Civilian operators

 France
  • Aigle Azur bought in 1951 ex-TWA aircraft with new engines and wings replaced with B-17G ones
 Laos
 United States

Military operators

 Haiti
 United States
  • United States Army Air Forces, the five TWA 307Bs were impressed into service and designated as C-75s. The three Pan Am 307s were also operated for the USAAF during the World War II but retained civil registrations and were not re-designated.

Survivors

Boeing 307 (NC 19903) in Elliott Bay, Seattle, March 28, 2002

The only surviving Boeing 307 Stratoliner (NC19903) is preserved in flying condition at the Smithsonian Museum's Steven F. Udvar-Hazy Center. On March 28, 2002, this particular aircraft was subject to a dramatic crash in which it ditched into Elliott Bay in Seattle, Washington, on what was to be its last flight before heading to the Smithsonian.[19] Despite the incident, it was again restored, flew to the Smithsonian, and is now on display.[20]

The fuselage of Howard Hughes' personal 307 also survives, although it has been converted into a house boat.[21]

Specifications (Boeing 307)

Data from Jane's AWA 1942 (apart from wing area and loading)

General characteristics

  • Crew: 5, including two pilots and flight engineer
  • Capacity: 38 passengers in daytime, 25 by night

Performance

See also

Related development

Aircraft of comparable role, configuration, and era

Related lists

References

Notes
  1. ^ Cite error: The named reference aviation-history.com was invoked but never defined (see the help page).
  2. ^ a b c d Betts, Ed. "The Boeing Stratoliners and TWA." American Aviation Historical Society Journal, Volume 38, Issue 3, 1993}}.
  3. ^ a b Hardy, Air International January 1994, p. 21.
  4. ^ a b Bowers 1989, p. 231.
  5. ^ Jane's Fighting Aircraft of World War II. London: Random House, 1989. ISBN 1-85170-199-0.
  6. ^ Ford 2004, p. 55.
  7. ^ Abzug, Malcolm J. and , E. Eugene Larrabee. Airplane Stability and Control: A History of the Technologies that Made Aviation Possible. Cambridge, UK: Cambridge University Press, 2005. ISBN 978-0521021289.
  8. ^ Hardy, Air International, January 1994, pp. 22–23.
  9. ^ "Houston's Aviation History Timeline at ." The 1940 Air Terminal Museum . Retrieved: January 28, 2012.
  10. ^ Taylor 1979, pp. 58–59.
  11. ^ Taylor 1979, p.59.
  12. ^ Hardy, Air International February 1994, p. 69.
  13. ^ Bowers 1989, pp. 234–235.
  14. ^ Hardy, Air International February 1994, p. 70.
  15. ^ Hardy, Air International February 1994, pp. 70–72.
  16. ^ Hardy, Air International February 1994, p. 71.
  17. ^ a b Berry, Peter. "Transatlantic Flight 1938-1945 (Part I 1938-1943)." AAHS Journal, Volume 40, Issue 2, 1995.
  18. ^ Berry, Peter. "Transatlantic Flight 1938-1945 (Part II 1943-1945)." AAHS Journal, Volume 40, Issue 3, 1995.
  19. ^ "4 escape injury as historic Stratoliner ditches in Elliott Bay." Seattle Post-Intelligencer.[dead link]
  20. ^ Whitford, Ellen. Once More withe feeling." Boeing Frontiers Online, September 2003. Retrieved: January 28, 2012.
  21. ^ "Green Design Will save the World: The Cosmic Muffin: A Boat Recycled From Howard Hughes’ Plane." Inhabitat. Retrieved: January 28, 2012.
Bibliography
  • Bowers, Peter M. Boeing Aircraft since 1916. London: Putnam, Third edition, 1989. ISBN 0-85177-804-6.
  • Bridgman, L. Jane's All the World's Aircraft 1942. London: Sampson Low, Marston & Co., 1942.
  • Ford, Daniel. "First and Last 'Strat': Boeing's Model 307 and its Survivors". Air Enthusiast, No. 110, March/April 2004, pp. 54–60. Stamford, UK: Key Publishing. ISSN 0143-5450.
  • Hardy, Mike. "The Stratoliner Story (Part 1)." Air International, Vol. 46, No 1, January 2004, pp. 21–24. Stamford, UK: Key Publishing. ISSN 0306-5634.
  • Hardy, Mike. "The Stratoliner Story (Part 2)." Air International, Vol. 46, No 2, February 2004, pp. 69–72. Stamford, UK: Key Publishing. ISSN 0306-5634.
  • Taylor, H.A. "Ten Big Boeings ... The Stratoliner Story". Air Enthusiast, Ten, July–September 1979, pp. 58–67. Bromley, UK: Fine Scroll.
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