Boeing 307 Stratoliner

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.

C-75 conversion

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 being demonstrated to representatives
of KLM. After takeoff the aircraft climbed to an altitude of 11,000 feet. At
this altitude, longitudinal stability tests were made. The next tests, as
outlined by the flight plan, were side-slip tests. The aircraft went into an
inadvertent spin subsequent to a stall at an altitude of approximately 11,000
feet. It made two to three turns in the spin, during which the engines were used
to aid recovery. In recovering from the dive subsequent to the spin, the wings
and horizontal tail surfaces failed upward apparently due to air loads in excess
of those for which the aircraft was designed. The ten people aboard, including
the KLM technical director, a representative of the Dutch Air Ministry, a Boeing
test pilot, the Boeing Chief Aerodynamicist, the Boeing Chief Engineer, 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
91 hours 14 minutes set from 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.

Deliveries to Pan Am started in March 1940, with TWA receiving its first 307 in
April. TWA's Stratoliners flew three-stop flights between Los Angeles and New
York while Pan Am's flew from Miami to Latin America. Ten 307s were built, three
being delivered to Pan-Am (Clipper Flying Cloud, Clipper Comet, and Clipper
Rainbow) and five to TWA (Comanche, Cherokee, Zuni, Navajo, and Apache) with one
aircraft going to Hughes.

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

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.

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)
Powerplant: 4 × Wright GR-1820-G102A radial engines, 1,100 hp (820 kW) each

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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