Boeing 377 Stratocruiser 377-10-19

The Boeing 377 Stratocruiser was the civil derivative of the Boeing Model 367, the C-97 Stratofreighter, which had first flown in late 1944; both stemmed from the B-29 Superfortress bomber, and the airliner used the wings and engines of the improved B-50 Superfortress. William Allen, Boeing's president from September 1945, was looking for a civil aircraft to offset the drop in military production after the Second World War, and despite the recession of late 1945 he ordered fifty Stratocruisers built before a single airline order was in hand. On 29 November 1945 Pan American World Airways became the launch customer with an order for twenty aircraft worth $24.5 million, then considered the largest commercial order in aviation history. In all, 4,000,000 man-hours went into the engineering of the 377.

As an immediate forerunner, the sole military YC-97B (45-59596) had previewed the commercial version Boeing had in mind, with round windows, an 80-seat upper deck and the spiral staircase leading to the lower deck. That aircraft belongs to the C-97 family and should not be confused with the civil 377-10-19 prototype covered on this page.

The 377-10-19 was the Stratocruiser prototype and only one was built, carrying the experimental registration NX90700 and construction number 15922. It was rolled out of Boeing's Plant 2 at 11:30 a.m. on 2 July 1947. Six days later, on 8 July 1947, Project Test Pilot John Bernard Fornasero Jr. took it on its first flight from Boeing Field, Seattle, Washington. Fornasero had been co-pilot on the first flight of the XC-97 Stratofreighter nearly three years earlier.

The aircraft took off at 2:40 p.m. Pacific time and was airborne in only about 427 m. Fornasero climbed to 3,353 m and, during the 1 hour 24 minute flight, held the airspeed to just 418 km/h, well below the estimated maximum speed of 547 km/h. It landed at 4:04 p.m., and the reversible-pitch propellers brought it to a stop in 366 m. Fornasero told reporters: "The flight was uneventful and highly satisfactory."

The 377-10-19 was powered by four air-cooled, supercharged Pratt & Whitney Wasp Major B5 four-row, 28-cylinder radial engines of 71.49 litres displacement. They had a compression ratio of 6.375:1, required 100/130 aviation gasoline and were rated at 2,650 hp normal and maximum continuous power at 2,550 rpm, and 3,250 hp for take-off at 2,700 rpm with water/alcohol injection. Each engine weighed 1,583 kg. The production Stratocruisers that followed used the Wasp Major B6 instead, rated at 3,500 hp for take-off at 2,700 rpm with water/alcohol injection: the powerplant is one of the documented differences between the prototype and the production aircraft.

The prototype led a flight test fleet of three Boeing 377s that flew 402,000 km exploring the aircraft's limits before certification, a process that took longer than the development of the Model 377 itself. The first airline to begin scheduled services was Pan Am, between San Francisco and Honolulu, in April 1949.

Once the flight test programme was over, NX90700 was not kept as a test aircraft: it was reconditioned to the 377-10-26 production standard, that of the Pan American aircraft with round windows and a rear galley, and sold to Pan American World Airways in 1950. It entered service on 24 October 1950, named Clipper Nightingale and registered N1022V. The twenty 377-10-26s built new for Pan Am were thus joined by this converted prototype. It remained in the Pan Am fleet until 1960, when it was sold back to Boeing.

Boeing then sold it to Rutas Aéreas Nacionales, S.A. (RANSA), which converted it into a freighter, named it "Carlos" and re-registered it YV-C-ERI. The former prototype was finally retired in 1969 and scrapped.

A total of 56 Stratocruisers were built: the prototype, later reconditioned, and 55 production aircraft for the airlines. Because of that low production volume, Boeing lost $7 million on the programme. The 377-10-19 was therefore the first of a short run, and its career mirrors that of the type: from test bed to Pan Am airliner and, finally, to second-hand freighter.