https://en.wikipedia.org/wiki/Boeing_307_Stratoliner
The Boeing Model 307 Stratoliner was the first commercial transport aircraft to
enter service with a pressurized cabin. This feature allowed the aircraft to
cruise at an altitude of 20,000 ft (6,000 m), well above many weather
disturbances. The pressure differential was 2.5 psi (17 kPa), so at 14,700 ft
(4,480 m) the cabin air pressure was equivalent to an altitude of 8,000 ft
(2,440 m). The Model 307 had capacity for a crew of six 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). In addition to its civilian service it was
also flown as the Boeing C-75 Stratoliner by the United States Army Air Forces,
who used it as a long-range cargolift aircraft.
In 1935 Boeing designed a four-engine airliner based on its B-17 heavy bomber
(Boeing Model 299), then in development, 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,
designed to allow pressurization.
The first order, for two 307s (named Stratoliners), was placed in 1937 by Pan
American Airways; Pan Am soon increased this to six, and a second order for five
from Transcontinental & Western Air (TWA), prompting Boeing to begin production
on an initial batch of the airliner.
At the time the United States 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 American Airways' 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, ten 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 transports for various VIPs or critical cargo. TWA converted their
307s to military service in January 1942, and its Intercontinental Division
(ICD) then operated these C-75s under contract to the Army's Air Transport
Command (ATC) until July 1944. 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 takeoff weight was increased from 45,000 to 56,000 lb (20,400 to 25,400
kg)), and the exterior painted military olive drab.
Role
Airliner
Manufacturer
Boeing
First flight
December 31, 1938
Introduction
July 4, 1940 with Pan American Airways
Retired
1975
Status
Retired
Primary users
TWA
Pan American Airways
United States Army Air Forces
Number built
10
Unit cost
$315,000 (in 1937 when ordered)
Developed from
Boeing B-17 Flying Fortress
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. It crashed on March 18, 1939, while its performance with two engines
inoperative on one wing was being demonstrated to representatives of KLM. 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, where
the control loads prevented the rudder from being re-centered. As a result, the
307 went into a spin and crashed. The ten people aboard, including KLM test
pilot Albert von Baumhauer, Boeing test pilot Julius Barr, Boeing Chief
Aerodynamicist Ralph Cram, Boeing Chief Engineer Earl Ferguson, and a TWA
representative were killed. Subsequent wind tunnel testing showed that the
addition of an extended dorsal fin ahead of and attached to the vertical tail
prevented rudder lock. 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 bomber.
The first delivery to a customer was to multi-millionaire Howard Hughes, who
bought one 307 for a round-the-world flight, hoping to break his own record of
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.
The Army returned its five C-75s to TWA in 1944, who sent them back to Boeing
for rebuilding. Boeing replaced the wings and horizontal tail with those from
the B-17G, while more powerful engines were fitted and the electrical system was
replaced with one based on the B-29 Superfortress. Passenger capacity was
increased from 33 to 38. The total rebuilding cost to TWA was $2 million; the
five aircraft re-entered passenger service on April 1, 1945. Although TWA was
committed to the larger and faster Lockheed Constellation, it kept the
Stratoliners until April 1951.
TWA sold its Stratoliner fleet to the French airline Aigle Azur who used them on
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.
Pan Am flew its unmodified 33-passenger Stratoliners between Miami and Havana
until 1947, then sold them to small operators. One aircraft was purchased by the
Doc" Duvalier. This aircraft later returned to the U.S. and was purchased by the
Smithsonian Museum.
Specifications (Boeing 307)
General characteristics
Crew: five: two pilots, flight engineer, two cabin crew
Capacity: 38 passengers in daytime, 25 by night
Length: 74.3 ft (22.6 m)
Wingspan: 107 ft (33 m)
Height: 20.79 ft (6.34 m)
Wing area: 1,486 sq ft (138.1 m2)
Empty weight: 30,000 lb (13,608 kg)
Gross weight: 45,000 lb (20,412 kg)
Performance
Maximum speed: 241 mph (388 km/h; 209 kn)
Cruise speed: 215 mph (346 km/h; 187 kn)
Range: 1,750 mi (1,521 nmi; 2,816 km)
Service ceiling: 23,300 ft (7,100 m)
Wing loading: 28 lb/sq ft (140 kg/m2)
Power/mass: 0.098 hp/lb
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