Tag Archives: Edmund Turney Allen

31 December 1938

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Boeing Model 307 Stratoliner with all engines running, Boeing Field, Seattle, Washington, circa 1939. (San Diego Air & Space Museum Archives)

31 December 1938: Boeing Model 307 Stratoliner NX19901 made its first flight at Boeing Field, Seattle, Washington. The test pilot was Eddie Allen, with co-pilot Julius A. Barr.

The Model 307 was a four-engine commercial airliner that used the wings, tail surfaces, engines and landing gear of the production B-17B Flying Fortress heavy bomber. The fuselage was circular in cross section to allow for pressurization. It was the first pressurized airliner and because of its complexity, it was also the first airplane to include a flight engineer as a crew member.

Boeing 307 Stratoliner NX19901 with both propellers on right wing feathered. (Boeing)
Boeing 307 Stratoliner NX19901 with both propellers on right wing feathered. (Boeing)

The Associated Press news agency reported:

Test Of Big Craft Begins

     SEATTLE, Dec. 31—(AP)—The world’s first plane, designed for flying in the sub-stratosphere, the new Boeing “Stratoliner”, performed “admirably” in a 42-minute first test flight in the rain today.

     The big ship, with a wingspread of 107 feet, three inches, climbed to 4,000 feet, the ceiling, and cruised between here, Tacoma and Everett. Speed was held down to 175 miles an hour.

     “The control and stability and the way it handled were very nice,” Edmund T. Allen, pilot, said. “She performed admirably.”

     The 33-passenger ship was built to fly at altitudes of 20,000 feet.

     No more tests are planned until next week. The supercharging equipment for high altitude flights will be installed later.

—Arizona Republic, Vol. IL, No. 228, Sunday, 1 January 1939, Page 2, Column 4

Boeing Model 307 Stratoliner NX19901 taking of at Boeing Field, Seattle, Washington. (San Diego Air & Space Museum Archives)

Giant ‘Stratoliner” Wheeled From Factory, On First Flight

SEATTLE, Dec. 31—(AP)—The newest thing in aviation—a giant, 33-passenger stratoliner named and built by Boeing Aircraft Company—met enthusiastic approval of its test pilot today after preliminary test runs.

     Scarcely 24 hours after it left the factory, the newest Boeing plane tested its wings yesterday. Test Pilot Edmund T. Allen taxied the plane along the ground, gunned it a bit and flew it in the air a short time at an altitude from 15 to 30 feet.

     Allen did not class the short hop as the ship’s maiden flight, which he said formally remained to be made, probably within a week.

     He said the big ship, minus general airplane characteristics, would not require any super-airports as the demonstration showed it would be able to take off and land at any ordinary-sized field.

     The stratoliner has four 1,100-horsepower motors which will enable it to cruise at an altitude of four miles at a speed of more than four miles a minute.

     Most unusual feature of the silver colored plane is the shape of the cabin, which bears a distinct resemblance to a metal dirigible. The cabin is circular throughout its length of 74 feet, four inches.

     The shape was adopted because of the necessity of sealing the cabin so passengers can enjoy low-level atmospheric conditions while soaring at high altitudes. The door, instead of opening outwards, is opened from the inside, so that the higher air pressure in the cabin will keep it sealed.

     The stratoliner’s wings compare in design with the Boeing flying fortresses but because of the larger cabin, the wing span is 107 feet, three inches, greater than that of the bombers, the new plane’s height is 17 feet, three inches.

     “Outside of scientific and engineering circles the substratosphere has been generally regarded as something far away and mystical, but now it is being brought ‘down to earth,’ C. L. Engtvedt, president of Boeing said.

     “The stratoliner will fly below the true stratosphere, but above the heavy air belt that brews surface weather conditions. Here we get most of the benefits of the stratosphere without getting into complex problems of flight in the extremely rare atmosphere and low temperature of the true stratosphere,” he said.

     Engtvedt predicted stratosphere type planes would lend a tremendous stimulus to the growth of air transportation.

     The first three stratoliners are being built for pan-American airways. Six more are in the course of construction for buyers whose identity has not been announced.

—Eugene Register-Guard, Vol. 95, No. 1, January 1, 1939 at Page 3,  Columns 5 and 6

On March 18, 1939, during its 19th test flight, the Stratoliner went into a spin, then a dive. It suffered structural failure of the wings and horizontal stabilizer when the flight crew attempted to recover. NX19901 was destroyed and all ten persons aboard were killed.¹

Boeing 307 Stratoline NX19901. (Boeing)
Boeing Model 307 Stratoliner NX19901. (San Diego Air & Space Museum Archives)
Boeing 307 Stratoliner NX19901, right rear quarter. (San Diego Air & Space Museum Archives, Catalog #:01_00091289)
Boeing Model 307 Stratoliner NX19901. (San Diego Air and Space Museum Archive, Catalog # 01 00091288)
Boeing Model 307 Stratoliner NX19901. The engine cowlings have been removed. The inboard right engine is running. The arrangement of passenger windows differs on the right and left side of the fuselage. (San Diego Air & Space Museum Archives)

The Boeing Model 307 was operated by a crew of five and could carry 33 passengers. It was 74 feet, 4 inches (22.657 meters) long with a wingspan of 107 feet, 3 inches (32.690 meters) and overall height of 20 feet, 9½ inches (6.337 meters). The wings had 4½° dihedral and 3½° angle of incidence. The empty weight was 29,900 pounds (13,562.4 kilograms) and loaded weight was 45,000 pounds (20,411.7 kilograms).

The cockpit of a Boeing 307 Stratoliner, photographed 12 March 1940. (Boeing)
Cutaway illustration of a Boeing Model 307 Stratoliner. (NASM SI-89-4024)

The airliner was powered by four air-cooled, geared and supercharged, 1,823.129-cubic-inch-displacement (29.875 liter) Wright Cyclone 9 GR-1820-G102 9-cylinder radial engines with a compression ratio of 6.7:1, rated at 900 horsepower at 2,200 r.p.m., and 1,100 horsepower at 2,200 r.p.m. for takeoff. These drove three-bladed Hamilton-Standard Hydromatic propellers through a 0.6875:1 gear reduction in order to match the engine’s effective power range with the propellers. The GR-1820-G102 was 4 feet, 0.12 inches (1.222 meters) long, 4 feet, 7.10 inches (1.400 meters) in diameter, and weighed 1,275 pounds (578 kilograms).

Boeing Model 307 Stratoliners under construction. (SDASM Archives Catalog #: 00061653)

The maximum speed of the Model 307 was 241 miles per hour (388 kilometers per hour) at 6,000 feet (1,828.8 meters). Cruise speed was 215 miles per hour (346 kilometers per hour) at 10,000 feet (3,048 meters). The service ceiling was 23,300 feet (7,101.8 meters).

Boeing Model 307 Stratoliner NX19901 with all engines running. (San Diego Air and Space Museum Archive, Catalog # 01 00091291)
Boeing Model 307 Stratoliner NX19901 with all engines running. (San Diego Air & Space Museum Archives, Catalog #: 01_00091291)
A Transcontinental and Western Airlines (TWA) Boeing 307 Stratoliner with cabin attendants. (TWA)
A Transcontinental and Western Airlines (TWA) Boeing 307 Stratoliner with cabin attendants. (Trans World Airlines)

As a result of the crash of NX19901, production Stratoliners were fitted with a vertical fin similar to that of the B-17E Flying Fortress.

Pan American Airways’ Boeing 307 Stratoliner NC19903, photographed 18 March 1940. Note the new vertical fin. (Boeing via Goleta Air and Space Museum)

During World War II, TWA sold its Stratoliners to the United States government which designated them C-75 and placed them in transatlantic passenger service.

Boeing C-75 Stratoliner. (San Diego Air and Space Museum Archive, Catalog # 01 00091316)
Boeing C-75 Stratoliner “Comanche,” U.S. Army Air Corps serial number 42-88624, formerly TWA’s NC19905. (San Diego Air & Space Museum Archives, Catalog # 01_00091316)
Two TWA stewardesses with a Boeing 307 Stratoliner, circa 1950. (San Diego Air & Space Museum)

In 1944, the 307s were returned to TWA and they were sent back to Boeing for modification and overhaul. The wings, engines and tail surfaces were replaced with those from the more advanced B-17G Flying Fortress. The last one in service was retired in 1951.

Of the ten Stratoliners built for Pan Am and TWA, only one remains. Fully restored by Boeing, NC19903 is at the Stephen F. Udvar-Hazy Center of the Smithsonian Institution.

The only existing Boeing Model 307 Stratoliner, NC19903, Clipper Flying Cloud, at the Smithsonian Institution National Air and Space Museum, Steven F. Udvar-Hazy Center. (Photo by Dane Penland, National Air and Space Museum, Smithsonian Institution)
The only existing Boeing Model 307 Stratoliner, NC19903, Clipper Flying Cloud, at the Smithsonian Institution National Air and Space Museum, Steven F. Udvar-Hazy Center. (Photo by Dane Penland, National Air and Space Museum, Smithsonian Institution)

¹ Please see This Day in Aviation for 18 March 1939 at: https://www.thisdayinaviation.com/18-march-1939/

© 2019, Bryan R. Swopes

3–4 November 1945

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Boeing 314, California Clipper, NC18602, over Oakland, California, 1937. Photographed for Pan Am by Clyde Herwood Sunderland, Jr. (1900–1989).(Clyde Sunderland Photograph Collection, Library, University of California Berkeley)

3–4 November 1945: On the evening of Saturday, 3 November 1945, the Boeing 314 Honolulu Clipper, NC18601, departed Honolulu, Oahu, Territory of Hawaii, enroute to San Francisco, California. The flying boat was under the command of Captain Sanis E. (“Robby”) Robbins, Pan American Airways, with First Officer Wally Reed, Second Officer Dunbar Carpenter, Radio Officer Jack B. Crawford, First Engineer Dan W. Broadwater, Second Engineer Robert J. Dernberger. There were 13 passengers and 10 crew members on board. The flight to San Francisco was expected to take 11 hours.

Approximately 5 hours into the flight, the number 3 engine (starboard wing, inboard) began to backfire. It was shut down and the propeller feathered. Captain Robbins decided to return to Hawaii. A short while later, the number 4 engine (starboard wing, outboard) also started to malfunction. It continued to run but eventually it was also shut down.

With two engines inoperative, the airplane was unable to maintain altitude. At 11:07 p.m. local, Captain Robbins, in total darkness, brought the flying boat to a “masterful”  landing on the relatively calm surface of the Pacific Ocean. There were no injuries. The airplane suffered minor damage to the port sea wing, and started taking on water.

California Clipper, NC18602, another Boeing 314, also enroute to San Francisco, orbited Honolulu Clipper‘s position to guide rescue ships to scene. The following message was broadcast from Pearl Harbor:

PAN AMERICAN CLIPPER DOWN AT SEA AT 040935Z POSITION 2749N 14802W. PLANE IN GOOD CONDITION. IS ABLE TO COMMUNICATE ON [frequency deleted] KCS VOICECALL C18601 ON [frequency deleted] KCS. INVESTIGATE SIGHTINGS REPORT PERTINENT INFO TO ORIGINATOR.

The United States Army transport ship, U.S.A.T. John Henry Payne sighted flares fired from the flying boat and quickly arrived on scene. The ship took all of the passengers on board. Ten crew stayed aboard flying boat.

USS Manila Bay (CVE 61), a Casablanca-class escort aircraft carrier under the command of Captain Leon Johnson, was approximately 60 miles (97 kilometers) away, and had been ordered to take charge of efforts to salvage the airplane.

On arrival, a whale boat was sent to remove the remaining crew members from the flying boat. Wind and waves had increased and it was feared that the boat might damage the hull of the flying boat, so a rubber life raft was used to transfer the Clipper‘s crew to the whale boat. Aircraft mechanics were sent from Manila Bay to attempt to repair the airplane, but were not successful.

A whale boat from USS Manila Bay approaches Honolulu Clipper, 4 November 1945. (U.S. Navy)

Plans were made to rig the airplane for towing. 200 fathoms (1,200 feet/366 meters) of 6-inch (15.2 centimeter) diameter hawser was rigged from the aircraft carrier to the nose of the flying boat. Stabilizing lines were tied to the propeller hubs of the outboard engines. Manila Bay began towing the Honolulu Clipper and was gradually able to increase speed to 6 knots (7 miles per hour/11 kilometers per hour). About an hour after sunset, at about 7:30 p.m., the tow line parted.

Darkness and rising seas made it impossible to rig a new tow. Manila Bay stood by awaiting arrival of USS San Pablo (AVP-30) (Commander Charles Robert Eisenbach), a Barnegat-class seaplane tender, on Tuesday, 6 January, then departed for Pearl Harbor.

Seaplane tender USS San Pablo (AVP-30) standing by Honolulu Clipper. (U.S. Navy)
USS San Pablo approaches the undamaged Honolulu Clipper. (U.S. Navy)

During the several days that Honolulu Clipper was afloat in the open ocean, weather increased to the point that it was considered too hazardous to approach it in a small boat, so the aviation tender closed on the airplane directly to try to take it on tow. Unfortunately, San Pablo hit the clipper and caused significant damage.

Hawaii Clipper from the bridge of USS San Pablo. The starboard wing is damaged and the Number 4 engine is missing. (U.S. Navy)

With salvage impossible, the derelict Honolulu Clipper was now considered a hazard to navigation. It was sunk by 20 mm gun fire from San Pablo.

Honolulu Clipper was the prototype for the Boeing Model 314 series flying boat. It had been designed to carry a maximum of 76 passengers and a crew of 10 a distance of 5,200 miles at 184 miles per hour. The design used the wings and engine nacelles of Boeing’s experimental Model 294 (XB-15) very long-range heavy bomber.

The Boeing Model 314 was a large four-engine, high-wing monoplane flying boat designed and built by the Boeing Airplane Company to take off and land on water. It was 106 feet (32.309 meters) long with a wingspan of 152 feet (46.330 meters). It had a maximum take off weight of 82,500 pounds (37,421 kilograms).

Boeing 314 prototype NX18601 in original configuration. (Boeing Airplane Company)

The airplane was built at Boeing’s Plant 1, then transported by barge to Elliot Bay. It carried experimental registration NX18601. Test pilot Edmund Turney (“Eddie”) Allen made the first flight of the prototype on 7 June 1938. He reported that the flying boat had insufficient rudder control and that he had to vary engine power to turn it. The prototype was modified to a twin-tail configuration.

Boeing Model 314 NX18601 flying over Elliot Bay. Note the twin-tail configuration. (Boeing Airplane Company)

With two vertical fins and rudders, control was improved, but was still insufficient. A third, center, fin was added and this became the production configuration.

Prototype Boeing 314 NX18601 in triple-tail configuration, 24 November 1938. (U.S. Air Force/San Diego Air and Space Museum)

The Boeing 314 was powered by four air-cooled, supercharged, 2,603.737-cubic-inch-displacement (42.668 liter) Wright Aeronautical Division Cyclone 14 GR2600A2, two-row, 14-cylinder radial engines with a compression ratio of 7.1:1. They were rated at 1,200 horsepower at 2,100 r.p.m., and 1,550 horsepower at 2,400 r.p.m. for takeoff, burning 91/96 octane gasoline. These engines (also commonly called “Twin Cyclone”) drove three-bladed Hamilton Standard Hydromatic full-feathering constant-speed propellers with a diameter of 14 feet (4.267 meters) through a 16:9 gear reduction. The GR2600A2 was 5 feet, 2.06 inches (1.576 meters) long and 4 feet, 7 inches (1.387 meters) in diameter. It weighed 1,935 pounds (878 kilograms). The engines could be serviced in flight, with access through the wings.

The Boeing 314 had a maximum speed of 199 miles per hour (320 kilometers per hour), with a range of 3,685 miles (5,930 kilometers) at its normal cruising speed of 183 miles per hour (295 kilometers per hour). Its service ceiling was 13,400 feet (4,084 meters). The fuel capacity was 4,246 gallons (16,073 liters).

Boeing built six Model 314 and another six 314A flying boats for Pan American Airways and British Overseas Airways Corporation. Pan Am paid $549,846.55 for each 314, about $9,545,726.07 in 2017 dollars, and Boeing lost money on every one sold.

Honolulu Clipper was leased to the United States Navy by Pan American Airways, 17 December 1942, and assigned Bureau of Aeronautics serial number (“Bu. No.”) 48227. The airplane continued to be operated by Pan Am crews.

A Pan American Airways Boeing 314 at Hawaii. (San Diego Air and Space Museum)

Sanis E. (“Robby”) Robbins was born at Matthews, Indiana, 17 September 1898. He was the sixth of seven children of William S. Robbins, a real estate agent, and Sarah Ellen Brokaw Robbins.

Robbins enlisted as a Private, United States Army, at Camp Dodge, Iowa, 26 June 1916. He was promoted to Private First Class on 1 August 1916, and to Corporal, 18 December 1916. Corporal Robbins was hospitalized at Brownsville, Texas, 4–23 January 1917. He was released from military service at Fort Des Moines, Iowa, 20 February 1917, shortly before the United States entered World War I. A 1920 Air Service Information Circular listed Second Lieutenant Sanis E. Robbins as a pursuit pilot, residing at Cassia, Florida.

Robby Robbins married Miss Virginia J. Bing. They would have three children.

Robbins was commissioned as a Lieutenant Commander, United States Naval Reserve, 15 September 1940. He held this rank until at least 1955.

Captain Sanis E. Robbins died at Palo Alto, California, 8 August 1961, at the age of 62 years. He was buried at the Golden Gate National Cemetery, San Bruno, California.

Pan American Airways Boeing 314 NC18604, Atlantic Clipper, taking off. (NASM)

© 2017, Bryan R. Swopes

15 October 1937

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The Boeing XB-15 takes off on its first flight, Boeing Field, 15 October 1937. (U.S. Air Force)

15 October 1937: Test pilot Edmund Turney (“Eddie”) Allen, a consulting engineer to Boeing, and Major John D. Korkille, Air Corps, United States Army, made the first flight of the prototype Boeing XB-15, 35-277, at Boeing Field, Seattle, Washington. Major Corkille reported that the airplane “handled easily and maneuvered readily.”

The flight deck of the Boeing XB-15. The radio operator’s station is on the left, and the navigator’s on the right. (The Boeing Company)

The Boeing Model 294, designated XB-15 by the Air Corps, was an experimental airplane designed to determine if a bomber with a 5,000 mile (8,047 kilometers) range was possible. It was designed at the same time as the Model 299 (XB-17), which had the advantage of lessons learned by the XB-15 design team. The XB-15 was larger and more complex than the XB-17 and took longer to complete. It first flew more than two years after the prototype B-17.

The Boeing Model 294 (XB-15) at Boeing Field, Seattle, Washington. The prototype bomber was rolled out for engine tests, 27 September 1937. (The Boeing Company)

Designers had planned to use an experimental 3,421.19-cubic-inch-displacement (56.063 liter) liquid-cooled, supercharged and turbosupercharged Allison V-3420 twenty-four cylinder, four-bank “double V” engine which produced a maximum of  2,885 horsepower at 3,000 r.p.m. The engine was not available in time, however, and four air-cooled Pratt & Whitney R-1830 (Twin Wasp) engines were used instead. With one-third the horsepower, this substitution left the experimental bomber hopelessly underpowered as a combat aircraft.

Boeing XB-15 35-277. (U.S. Air Force)
Boeing XB-15 35-277. (U.S. Air Force)
Boeing XB-15 35-277. (U.S. Air Force)

The XB-15 was a very large four-engine mid-wing monoplane with retractable landing gear. It was of aluminum monocoque construction with fabric-covered flight control surfaces. The XB-15 had a ten-man crew which worked in shifts on long duration flights.

Boeing XB-15 35-277

The prototype bomber was 87 feet, 7 inches (26.695 meters) long with a wingspan of 149 feet (45.415 meters) and overall height of 18 feet, 1 inch (5.512 meters). The airplane had an empty weight of 37,709 pounds (17,105 kilograms) and maximum takeoff weight of 70,706 pounds (32,072 kilograms)—later increased to 92,000 pounds (41,730 kilograms).

As built, the XB-15 was powered by four air-cooled, supercharged, 1,829.39-cubic-inch-displacement (29.978 liter) Pratt & Whitney Twin Wasp S1B3-G (R-1830-11) two-row 14-cylinder radial engines, rated at 850 horsepower at 2,450 r.p.m. at 5,000 feet (1,524 meters), and 1,000 horsepower at 2,600 r.p.m. for take off. The engines turned three-bladed controllable-pitch propellers through a 3:2 gear reduction. The R-1830-11 was 4 feet, 8.66 inches (1.439 meters) long with a diameter of 4 feet, 0.00 inches (1.219 meters), and weighed 1,320 pounds (599 kilograms).

These gave the experimental airplane a maximum speed of 197 miles per hour (317 kilometers per hour) at 5,000 feet (1,524 meters) and a cruise speed of 152 miles per hour (245 kilometers per hour) at 6,000 feet (1,829 meters). The service ceiling was 18,900 feet (5,761 meters) and maximum range was 5,130 miles (8,256 kilometers).

The Boeing XB-15 experimental long-range heavy bomber flies in formation with a Boeing YP-29 pursuit. (U.S. Air Force)

The bomber could carry a maximum of 12,000 pounds (5,443 kilograms) of bombs in its internal bomb bay, and was armed with three .30-caliber and three .50-caliber machine guns for defense.

Only one XB-15 was built. During World War II it was converted to a transport and redesignated XC-105. In 1945 it was stripped and abandoned at Albrook Field, Territory of the Canal Zone, Panama.

The XB-15 set several Fédération Aéronautique Internationale (FAI) world records:  On 30 July 1939, the XB-15 carried 14,135 kilograms (31,162 pounds) to an altitude of 2,000 meters (6,562 feet) over Fairfield, Ohio.¹ The same flight set a second record by carrying 10,000 kilograms (22,046 pounds) to an altitude of 8,228 feet (2,508 meters).² On 2 August 1939, the XB-15 set a World Record for Speed Over a Closed Circuit of 5000 Kilometers With 2000 Kilogram Payload, at an average speed of 267.67 kilometers per hour (166.32 miles per hour).³

Boeing XB-15 35-277. (LIFE Magazine)

¹ FAI Record File Number 8739

² FAI Record File Number 8740

³ FAI Record File Number 10865

© 2017, Bryan R. Swopes

21 September 1942

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A Boeing XB-29 takes off from Boeing Field, Seattle, Washington. (SDASM)
Edmund T. ("Eddie") Allen
Edmund T. (“Eddie”) Allen

21 September 1942: At Boeing Field, Seattle, Washington, the Boeing Model 345, the first of three XB-29 prototypes, Air Corps serial number 41-002, took off on its first flight.

Edmund T. “Eddie” Allen, Director of Aerodynamics and Flight Research, was in command, with Al Reed, Chief of Flight Test and Chief Test Pilot, as co-pilot. They climbed to 6,000 feet (1,829 meters) and began testing the XB-29’s stability and control, control power and response, and stall characteristics.

The flight was uneventful. Landing after 1 hour, 15 minutes, Allen is supposed to have said, “She flew!”

Eddie Allen lean’s out of a cockpit window following the first taxi test of the XB-29. (Boeing)

The XB-29 was 98 feet, 2 inches (29.921 meters) long with a wing span of 141 feet, 3 inches (43.053 meters), and 27 feet, 9 inches (8.458 meters) high to the top of its vertical fin. The prototype bomber had a gross weight of 105,000 pounds (47,627 kilograms).

Boeing XB-29-BO, 41-002, the first XB-29 built. (U.S. Air Force)
Boeing XB-29-BO, 41-002, the first of three prototypes. (U.S. Air Force)

The prototype bomber was powered by four air-cooled, supercharged and fuel-injected 3,347.662-cubic-inch-displacement (54.858 liter) Wright Aeronautical Division Duplex-Cyclone 670C18H1 (R-3350-13) twin-row 18-cylinder radial engines with a compression ratio of 6.85:1. The R-3350-13 was rated at 2,000 horsepower at 2,400 r.p.m., and 2,200 horsepower at 2,800 r.p.m. for takeoff, burning 100-octane gasoline. These engines drove 17-foot-diameter (5.182 meters) three-bladed Hamilton Standard constant-speed propellers through a gear reduction of 0.35:1. The R-3350-13 was 76.26 inches (1.937 meters) long, 55.78 inches (1.417 meters) in diameter, and weighed 2,668 pounds (1,210 kilograms). Wright built 50 of these engines.

Boeing XB-29 41-002. (SDASM)

The XB-29 had a maximum speed of 368 miles per hour (592 kilometers per hour) and cruised at 255 miles per hour (410 kilometers per hour). Its service ceiling was 32,100 feet (9,784 meters).

The airplane was designed to carry 20,000 pounds (9,072 kilograms) of bombs. Though the prototypes were unarmed, the production B-29s were defended by 10 Browning AN-M2 .50-caliber machine guns in four remotely-operated power turrets, with 2 more .50-caliber machine guns and a single AN-M2 20mm autocannon in the tail.

Boeing XB-29 41-002. (SDASM)

The B-29 Superfortress was the most technologically advanced—and complex—aircraft of the War. It required the manufacturing capabilities of the entire nation to produce. Over 1,400,000 engineering man-hours had been required to design the prototypes.

The B-29 was manufactured by Boeing at Seattle and Renton, Washington, and at Wichita, Kansas; by the Glenn L. Martin Company at Omaha, Nebraska; and by Bell Aircraft Corporation, Marietta, Georgia. There were three XB-29 prototypes, 14 YB-29 pre-production test aircraft, 2,513 B-29, 1,119 B-29A, and 311 B-29B Superfortress aircraft. The bomber served during World War II and the Korean War and continued in active U.S. service until 1960.

The first prototype, 41-002, was scrapped in 1948.

Boeing B-29A-30-BN Superfortress 42-94106, circa 1945. (U.S. Air Force)
Boeing B-29A-30-BN Superfortress 42-94106, circa 1945. (U.S. Air Force)

© 2018, Bryan R. Swopes

26 March 1940

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Curtiss-Wright CW-20T, NX19436, s/n 101.

26 March 1940: At Lambert–St. Louis Municipal Airport, just to the west of the Mississippi River in the state of Missouri, test pilots Edmund Turney Allen and Dean Cullen Smith took the prototype Curtiss-Wright CW-20T, NX19436, for its first flight.

BIMOTORED GIANT READY FOR TESTS

Curtiss-Wright Substratosphere Plane Works Smoothly in Takeoff

By DEVON FRANCIS

Associated Press Aviation Editor.

     ST. LOUIS, March 27.—The world’s first bi-motored transport plane designed and powered to eliminate the hazard attending the failure of one engine on takeoff was made ready for two months or more of flight-testing today before being offered to commercial airlines.

     The 19-ton, 36-passenger Curtiss-Wright substratosphere transport was engineered to permit one engine to go dead at any point on the take-off as a pilot climbs for altitude and still maintain safe flight.

     Each of its engines produces 1700 horsepower. The largest engines ever to be fitted to a transport plane heretofore have been of 1500 horsepower. Either one of the new transport’s engines will carry it to an altitude of 13,000 feet.

     Fastened to the 108-foot wing with rubber cushions to produce what Curtiss-Wright engineers described as “dynamic balance,” the engines transmit only about 50 per cent of the normal vibration to the cabin of the plane.

     C, s/n 101. W. France, vice president and general manager of the St. Louis airplane division of the company, yesterday witnessed the maiden take-off of the transport from the ground. Then he climbed to the control tower of the St. Louis municipal airport for an innovation in airplane testing.

     France called the test pilot, Eddie Allen of Seattle, on the tower radiophone.

     Dean Smith, co-pilot, answered.

     “Dean,” he said, “that looked grand. Congratulations.”

     “O. K.,” replied Smith, “I’ll tell Eddie.”

     A little later Allen brought the huge plane into a smooth landing. He remarked that the plane had flown 190 miles an hour on only 30 per cent of its power. Transports usually cruise at 50 to 55 per cent.

     The additional testing will be for an approved type certificate from the government.

—Buffalo Evening News, Vol. CXIX, No. 142, Wednesday, 27 March 1940, Page 18, Column 3

Curtiss-Wright CW-20T NX19436, s/n 101.

The Curtiss-Wright CW-20T, NX19436, (manufacturer’s serial number 101) was a prototype twin-engine commercial airliner designed by George Augustus Page, Jr. Originally built with a twin-tail configuration, flight testing resulted in a change to a single, large vertical fin and rudder. Designed to be pressurized, the fuselage had a Figure 8 cross section, with the cabin floor at the narrowest point for increased strength. In this prototype, the fuselage was faired over to provide a smooth, more cylindrical shape. Considerable wind tunnel testing had been performed by CalTech in Pasadena, California, resulting in a very sleek nose section.

Curtiss-Wright CW-20T NX19436, after modification to a single tail configuration, photographed at Midway Airport, Chicago, 19 May 1941. (Midway Airport)

On 20 June 1941, the United States Army Air Forces ¹ purchased the CW-20T and designated it as the Curtiss C-55, serial number 41-21041. It would become the prototype of the C-46 Commando military transport. The Army Air Forces returned the C-55 to Curtiss-Wright for modifications.

The CW-20T was 76 feet, 4 inches (23.266 meters) long with a wingspan of 108 feet, 0 inches (32.918 meters). It was powered by two air-cooled, supercharged, 2,603.7-cubic-inch-displacement (42.688 liters) Wright Aeronautical Corporation Cyclone 14 GR2600A5B-5 (R-2600-17A) two-row, 14-cylinder radial  engines, driving three-bladed Curtiss Electric C-533-D controllable-pitch propellers through a 16:9 gear reduction. This engine had a compression ration of 6.9:1 and required 100/130 aviation gasoline. It was rated at 1,500 horsepower at 2,400 r.p.m., and 1,700 horsepower at 2,500 r.p.m. It was 5 feet, 3.1 inches (1.603 meters) long, 4 feet, 6.26 inches (1.378 meters) in diameter and weighed 1,980 pounds (898 kilograms). Only four of these engines were built.

Curtiss-Wright CW-20T NX19346, at right, with a CW-21B prototype, NX19441.

NX14936 was sold to the British Overseas Airways Corporation (BOAC) in September 1941 and registered in the United Kingdom as G-AGDI. The airline named it St. Louis. It was converted to a 24-passenger configuration with long-range fuel tanks. It frequently flew between Lisbon, Gibraltar and Malta. The airplane was scrapped 29 October 1943.

British Overseas Airways Corporation Curtiss-Wright CW-20T, G-AGDI, “St. Louis,” at Gibraltar, circa 1942. (Imperial War Museum)

After the necessary redesign, which included a large cargo door and strengthened floor, and the substitution of 2,000 horsepower Pratt & Whitney R-2800-51 engines for the Wright Cyclone 14s of the C-55, the Army Air Forces ordered the airplane into production as the C-46A-CU Commando. An order was placed for 200 aircraft. The U.S. Navy placed 160 in service as the R5C-1. Curtiss-Wright built the C-46 at St. Louis and Buffalo, New York. The first, 41-5159, was delivered 13 July 1942. More than 3,000 C-46s were built in nearly 30 variants. Two C-46A-1-HI Commandos were built by Higgins Aircraft at Michoud, Louisiana.

Like the CW-20T, the C-46A/R5C-1 was also 76 feet, 4 inches (23.266 meters) long with a wingspan of 108 feet, 0 inches (32.918 meters) and overall height of 21 feet, 8 inches (6.604 meters). The wing area was 1,360 square feet (126.35 square meters). It had an empty weight of 30,241 pounds (13,717 kilograms) and maximum take off weight of 52,000 pounds (23,586 kilograms). The maximum payload was 10,000 pounds (4,536 kilograms). The maximum package size was 7 feet, 6 inches × 5 feet × 6 feet, 8 inches (2.286 × 1.524 × 2.032 meters).

The C-46A was powered by two air-cooled, supercharged, 2,804.4-cubic-inch-displacement (45.956 liter), Pratt & Whitney R-2800-51 two-row, 18-cylinder radial engines with a compression ratio of 6.65:1. They drove three-bladed propellers through a 2:1 gear reduction. These engines had a Normal Power rating of 1,600 horsepower at 2,400 r.p.m. at 5,700 feet (1,737 meters), or 1,400 horsepower at 13,000 feet (3,962 meters). The Military Power rating was 2,000 horsepower at 2,700 r.p.m. at 1,500 feet (457 meters), or 1,600 horsepower at 13,500 feet (4,115 meters). Takeoff power was 2,000 horsepower at 2,700 r.p.m. The R-2600-51 was 6 feet, 3.72 inches (1.923  meters) long, 4 feet, 4.50 inches (1.335 meters) in diameter, and weighed 2,300 pounds (1,043 kilograms). All R-2600-51s were built by the Ford Motor Company.

The C-46A had a maximum speed of 233 knots (268 miles per hour/432 kilometers per hour) at 16,100 feet (4,907 meters). Its service ceiling was 20,600 feet (6,279 meters). With a fuel capacity of 3,000 gallons (11,356 liters), the maximum range was 1,960 nautical miles (2,256 statute miles/3,630 kilometers) at 121 knots (139 miles per hour/224 kilometers per hour).

During World War II, the C-46 famously flew “The Hump,” from bases in Burma, over the Himalaya Mountains, and into China.

The first Curtiss-Wright C-46A-CU Commando, 41-5159, circa 1942. (U.S. Air Force)

¹ The United States Army Air Corps (USAAC) became the United Army Air Forces (USAAF) on 20 June 1941.

© 2023, Bryan R. Swopes