The Boeing 377 Stratocruiser was a large long-range airliner developed from the C-97 Stratofreighter military transport, itself a derivative of the B-29 Superfortress. The Stratocruiser's first flight was on 8 July 1947. Design features included passenger decks and a pressurized cabin. It could carry up to 100 passengers on the main deck plus 14 in the lower deck lounge; typical seating was for 63 or 84 passengers or 28 berthed and five seated passengers.
The Stratocruiser was larger than the Douglas DC-6 and Lockheed Constellation and cost more to buy and operate. Its reliability was poor, mainly due to problems with the four 28-cylinder Pratt & Whitney R-4360 Wasp Major radial engines and structural and control problems with their propellers. Only 55 Stratocruisers were built for airlines, along with the single prototype. One was converted into the Aero Spacelines Pregnant Guppy by John M. Conroy for NASA's Gemini space program.
Design and development
The Boeing 377 Stratocruiser was a civil derivative of the Boeing Model 367, the Boeing C-97 Stratofreighter, which first flew in late 1944. William Allen, who had become president of the Boeing Company in September 1945, sought to introduce a new civilian aircraft to replace reduced military production after World War II.Redding and Yenne 1997, p. 68. Boeing saw in their large-bodied, fast, and long-ranged military transport potential for a passenger aircraft suited for premium service on long transoceanic routes, expanding on the precedent set by their Boeing 314 Clipper with Pan American World Airways. Despite a recession in late 1945, Allen ordered 50 Stratocruisers, spending capital on the project without an order from an airline customer.Redding and Yenne 1997, p. 69.
On 29 November 1945, Pan American World Airways (Pan Am) became the launch customer with the largest commercial aircraft order in history, a $24.5 million order for 20 Stratocruisers. Earlier in 1945, a Boeing C-97 had flown from Seattle to Washington, D.C. nonstop in six hours and four minutes; with this knowledge, and with Pan Am President Juan Trippe's high regard for Boeing after their success with the Boeing 314 Clipper, Pan Am was confident about ordering the expensive plane.
The 377 shared the distinctive design of the C-97, with a "double-bubble" fuselage cross-section, resembling a figure-8, with the smaller loop on the bottom, and of interior space shared between two passenger decks. Outside diameter of the upper lobe was , compared to for the DC-6 and other Douglas types (and for today's 737). The lower deck served as a lounge, seating 14, earning it the nickname of "Stratoboozer." The 377 had innovations such as higher cabin pressure and air conditioning; the superchargers on the four Pratt & Whitney R-4360 engines increased power at altitude and allowed constant cabin pressure.Redding and Yenne 1997, p. 71.
The wing was the Boeing 117 airfoil. In all, 4 million man-hours went into the engineering of the 377.Redding and Yenne 1997, p. 70. It was one of only a few double-deck aircraft ever built for commercial use, another being its French contemporary, the Breguet Deux-Ponts, as well as later models, the 747 and the Airbus A380.
The first flight of the 377 was on 8 July 1947, two years after the first commercial order. The flight test fleet of three 377s underwent of flying to test its limits before certification.
Other carriers who adopted the Stratocruiser were British Overseas Airways Corporation, American Overseas Airlines (merged with Pan Am in 1950) and United Airlines. The last 377 was delivered to BOAC in May 1950. On this delivery flight, Boeing engineer Wellwood Beall accompanied the final 377 to England, and returned with news of the de Havilland Comet, the first jet airliner, and its appeal. The tenure of the Stratocruiser with United ended in 1954, when United had the opportunity to sell them to BOAC after finding them unprofitable without the extra mail subsidies enjoyed by Pan Am and Northwest.
Only 56 were built, one prototype (later reconditioned) and 55 production aircraft. As a result of low production volume, Boeing lost $7 million on the aircraft.
Operational history
As the launch customer, Pan Am was the first to begin scheduled flights, from San Francisco to Honolulu in April 1949. At the end of 1949, Pan Am, BOAC and American Overseas Airlines (AOA) were flying 377s transatlantic, while Northwest Orient Airlines was flying in the United States; in January 1950, United began flights from San Francisco to Honolulu. Stratocruisers were pressed into emergency military service after the onset of the Korean War. In late 1950, Northwest Stratocruisers were serving New York City, Chicago, Detroit, Minneapolis/St. Paul, Milwaukee, Spokane, Seattle, and Honolulu.http://www.timetableimages.com, 24 September 1950 Northwest Orient timetable
By late 1952, Northwest Stratocruisers replaced DC-4s to Tokyo via Anchorage, Alaska; Northwest replaced the Stratocruiser on the Honolulu run in 1953 and to Tokyo in 1955. For a short time, Pan Am 377s flew to Beirut, Lebanon, but after 1954, no 377 was scheduled east of Europe or west of Singapore. In 1954, United Stratocruisers flew Los Angeles to Honolulu and between Seattle and San Francisco;http://www.timetableimages.com, 1 August 1954 United timetable United's B377 flights to Honolulu were all first class. In 1955, BOAC 377s had 50 First Class seats (fare $400 one way New York to London) or 81 Tourist seats (fare $290).Flight 28 October 1955 p671 In 1956, Pan Am 377s flew from Los Angeles and San Francisco to Sydney with stops at Honolulu, Canton Island and Suva (via Nadi Airport in Fiji).http://www.timetableimages.com, 1 July 1956 Pan American timetable
By 1958, Pan Am was operating the Stratocruiser between Seattle, Washington and Fairbanks, Juneau and Ketchikan, Alaska and between Seattle and Whitehorse, Yukon.http://www.timetableimages.com, 1 January 1958 Pan American timetable Within six years of first delivery, the Stratocruiser had carried 3,199,219 passengers; it had completed 3,597 transcontinental flights, and 27,678 transatlantic crossings, and went between the United States and South America 822 times. In these first six years, the Stratocruiser fleet had flown 169,859,579 miles (273,362,494 km).
The 377 was one of the most advanced and capable propeller-driven transports, and among the most luxurious, but it was troubled by reliability issues and maintenance costs. Problems included catastrophic failures of propellers, failures of propeller pitch control leading to overspeed incidents, issues related to the poor thermal design of the engine and resultant aerodynamic problems. Its service record was marred by a high incidence of in-flight emergencies and hull-loss accidents related to those issues. The propellers were the subject of Airworthiness Directives in 1955, 1957, and 1958.
In 1953, United's Chief Executive Ray Ireland described the aircraft as "unbeatable in luxury attraction but... uneconomical." Ireland said PAA's Stratocruiser competition to Hawaii induced United to buy the plane originally."Aviation Week 31 August 1953, p.57. The article discusses CAB rulings, and Ireland was perhaps speaking at a hearing. In 1950, United's seven 377s averaged $2.46 "direct operating cost" per plane-mile, and "Indirect costs are generally considered to be equal or greater than the direct costs."American Aviation 23 July 1951 p37 Most operators used Stratocruisers on long-range routes where higher prices could be charged, off-setting the higher operating costs."Classic Airliners: Boeing Stratocruiser", p.64-67
The exception was Northwest Airlines, which managed to keep the aircraft competitive on shorter U.S. domestic routes where the aircraft's higher payload capacity benefited from lower fuel weights. United however could not integrate their six-plane fleet of 377s. By 1954, the lack of spares and the inability to cross-train their Douglas crews with the type relegated their Stratocruisers primarily to their Hawaii route, where they faced stiff competition from Pan American and Northwest. By the end of that year, the six United 377s were all sold to BOAC in a deal orchestrated by Douglas Aircraft. BOAC, which was short of aircraft following the grounding of the Comet 1, paid between US$895,000 and US$995,000 per unit and spares for what were essentially five-year-old aircraft. In 1954, an equivalent brand new Douglas DC-7 cost US$775,000 (~$ in )."Airliner Tech Series, Vol. 9: Boeing 377Stratocruiser, p.60-61
Boeing set the never-exceed speed at IAS but in testing, the 377 reached IAS (about TAS) in a 15–20 degree dive at ;American Aviation 8 January 1951, p.23. another reportThe Aeroplane 15 October 1948 said it reached true airspeed while diving from altitude to in 50 seconds using "full rated power". Typical airline cruise was less than ; in August 1953, Pan Am and United 377s (and United DC-6s) were scheduled between Honolulu and San Francisco () in 9 h 45 min each way.
The longest (by distance) 377 nonstop flights were made by Pan Am from Tokyo to Honolulu during four winter seasons beginning in 1952–1953. In January 1953, two nonstops a week were scheduled with a flight time of 11 hr 1 min due to tailwinds; the following August all flights took 19 hours, with a stop at Wake Island Airfield. In winter 1953-54, one Tokyo-Honolulu flight took 9 hr 35 min for .Aviation Week 15 February 1954 p100
By 1960, Stratocruisers were being superseded by jets: the de Havilland Comet, Boeing 707, and Douglas DC-8. The last flight of the 377 with United was in 1954, the last with BOAC was in 1959, and the last with Northwest was in September 1960. In November 1960, only a weekly Pan Am Honolulu to Singapore flight remained, and the 377 was retired by Pan Am in 1961. High operating costs (notably the fuel consumption and maintenance of the Wasp Major engines) led to rapid abandonment of the 377 with the onset of the jet era. Its contemporaries such as the Douglas DC-6 and the Lockheed Constellation continued longer, on secondary routes or rebuilt as freighters. A few 377s were sold to smaller airlines, used as freighters, or converted by Aero Spacelines into heavily modified enlarged freighters called Guppies.Wilson 1998, p. 16.
During 1959 and 1960, Transocean Air Lines (TAL) assembled a fleet of fourteen at bargain prices. In 1960, TAL went bankrupt and only four were in operable condition. The hulks were stored at Oakland International Airport through the 1960s and cannibalized for parts, contributing some to the Aero Spacelines Guppies. Five remaining 377s were modified by Bedek Aviation to resemble former U.S. Air Force Model 367 Stratofreighters and pressed into service with the Israel Defense Forces. Two were shot down during the course of their service and the three remaining 377Ms were retired in 1978 and later scrapped. None of the 56 377s built were preserved for display in original condition, although one airframe remains today as the Mini Guppy; the IAF Museum in Israel has a C-97 (4X-FPM) on display painted to resemble their most famous 377M, Masada.
Variants 377-1 Proposed variant to be powered by Wright R-3350 Duplex-Cyclone engines. It was to be fitted with the flaps and deicing boots from the B-29.Veronico, p.17 377-6 Proposed variant to be powered by supercharged Allison V-3420 engines. 377-10-19 Prototype Stratocruiser; one built. Later brought up to 377-10-26 standard and sold to Pan American World Airways in 1950. 377-10-26 Variant built for Pan American World Airways with round windows.Veronico, p.30 20 new aircraft built, plus one converted from the 377-10-19 prototype.Bowers, p.367 377-10-26S Super Stratocruiser 10 refitted with more powerful engines and a larger fuel capacity for Pan American transatlantic flights. 377-10-27 Variant intended for Transcontinental & Western Air, but not built. 377-10-28