Tag Archives: Pratt & Whitney Twin Wasp S1B3-G

6 April 1940

Jackie Cochran with her Seversky AP-7A, NX1384, prior to her speed record flight, 6 April 1940. )San Diego Air and Space Museum Archive)
Jackie Cochran with her Seversky AP-7A, NX1384, prior to her speed record attempt. (San Diego Air and Space Museum Archive)

6 April 1940: Flying her Seversky AP-7A, NX1384, Jackie Cochran set a Fédération Aéronautique Internationale and National Aeronautic Association speed record over a 2,000 kilometer (1,242.742 miles) course from Mount Wilson, California (northeast of Los Angeles) to Mesa Giganta, New Mexico (west of Albuquerque) with an average speed of 533.845 kilometers per hour (331.716 miles per hour).¹

National Aeronautic Asscoication Certificate of Record in the San Diego Air and Space Museum Archive, (Bryan R. Swopes)
National Aeronautic Association Certificate of Record in the San Diego Air and Space Museum Archive. (Bryan R. Swopes)

The Seversky AP-7 was an improved civil version of the Seversky P-35 fighter, which was the first U.S. Army Air Corps single engine airplane to feature all-metal construction, an enclosed cockpit and retractable landing gear. It was designed by Major Alexander Nikolaievich Prokofiev de Seversky, a World War I Russian fighter ace.

Jackie Cochran paints her race number, 13, of the fuselage of her Seversky AP-7. (Unattributed)
Jackie Cochran paints her race number, 13, of the fuselage of her Seversky AP-7. (San Diego Air and Space Museum Archives)

Cochran’s AP-7A was a specially-built racer, modified from the original AP-7 with a new, thinner, wing and different landing gear arrangement. It was powered by a 1,829.39-cubic-inch-displacement (29.97 liter) air-cooled, supercharged Pratt & Whitney Twin Wasp S1B3-G (R-1830-11) two-row 14-cylinder radial engine, with a Takeoff Power rating of 1,000 horsepower at 2,600 r.p.m., and Normal Power rating of 850 horsepower at 2,450 r.p.m and 5,000 feet (1,524 meters). It turned a three-bladed Hamilton-Standard controllable-pitch propeller through a 3:2 gear reduction. The engine had a dry weight of 1,320 pounds (595 kilograms)

This is the same airplane in which Jackie Cochran won the 1938 Bendix Trophy Race.

Jackie Cochran's Seversky AP-7, NX1384, at the Union Air Terminal, Burbank, California, September 1938.
Jackie Cochran’s Seversky AP-7A, NX1384, at the Union Air Terminal, Burbank, California, 1940. (Bill Larkins/Wikipedia)

¹ FAI Record File Number 12025.

© 2017, Bryan R. Swopes

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15 October 1937

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

15 October 1937: Free-lance test pilot Edmund Turney (“Eddie”) Allen made the first flight of the prototype Boeing XB-15, 35-277, at Boeing Field, Seattle, Washington.

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 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.

A large scale model of the Boeing XB-15 in the NACA Full Scale Tunnel, 6 May 1936. (NASA)

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

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21 September 1937

Jackie Cochran sits in the cockpit of the Seversky SEV-S1, NR18Y. Note how the landing gear retracts straight to the rear in this early version. It would be modified to retract inward to the airplane’s centerline, and more effectively streamlined in the future.

21 September 1937: Jackie Cochran flew a Seversky Aircraft Corporation SEV-S1, civil registration NR18Y, over a 3 kilometer course at Detroit Wayne County Airport, Romulus, Michigan, averaging 470.40 kilometers per hour (292.29 miles per hour). This was a new Fédération Aéronautique Internationale (FAI) speed record.¹

The Seversky SEV-S1 Executive was an improved version of the P-35 fighter, which was the first U.S. Army Air Corps single engine airplane to feature all-metal construction, an enclosed cockpit and retractable landing gear. It was designed by Major Alexander P. de Seversky. The airplane had been built as the SEV-2XP, a two-place monoplane with fixed landing gear, powered by an air-cooled, supercharged 1,666.860-cubic-inch-displacement (27.315 liter) Wright Aeronautical Division GR1670 two-row, 14-cylinder radial engine. The GR1670A1 had a compression ratio of 6.75:1 and was rated at 775 horsepower at 2,400 r.p.m., and 830 horsepower at 2,400 r.p.m. for takeoff. The GR1670B2C had a compression ratio of 7.0:1 and was rated at 750 horsepower at 2,500 r.p.m., and 850 horsepower at 2,600 r.p.m., for takeoff. These were developmental engines. Both variants had a propeller gear reduction ratio of 16:11. The SEV-2XP was to be a second entry, along with the SEV-1XP, to enter a fly-off at Wright Field. When it was damaged, though, it was rebuilt as a single place airplane with retractable landing gear and a 1,000-horsepower Wright Cyclone GR-1820G4 nine-cylinder engine, and designated SEV-1XP.

 The Seversky's passenger compartment was accessed through a hatch on the right side of the fuselage. (San Diego Air and Space Museum Archives) Jackie Cochran in the cockpit of the Seversky SEV-2S Executive, NR18Y. Note the passenger windows below and behind the cockpit. (San Diego Air and Space Museum Archives)
The Seversky’s passenger compartment was accessed through a hatch on the right side of the fuselage. (San Diego Air and Space Museum Archives)

After the Air Corps demonstrations, which resulted in an order for 100 P-35s, NX18Y was again repowered, this time with an 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 engine with a compression ratio of 6.7:1. The R-1830-11 was 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, burning 87-octane gasoline. The engine turned a three-bladed Hamilton-Standard controllable-pitch propeller 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).

With the R-1830, NR18Y was again redesignated SEV-S1. It was flown by Seversky’s chief test pilot, Frank Sinclair, at the 1937 National Air Races and the Bendix Trophy Race.

Major Alexander P. de Seversky and Jackie Cochran with a Seversky monoplane, circa 1937.
Major Alexander P. de Seversky and Jackie Cochran with a Seversky monoplane, circa 1937.

¹ FAI Record File Number 12026

© 2017, Bryan R. Swopes

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15 September 1939

Jackie Cochran with her record-setting Seversky AP-7A, NX1384. (FAI)

15 September 1939: Jackie Cochran set a Fédération Aéronautique Internationale (FAI) World Speed Record flying a Seversky AP-7A, civil registration NX1384, over a 1,000 kilometer course, from Burbank to San Francisco and back to Burbank. Her average speed was 492.34 kilometers per hour (305.93 miles per hour).¹

Jackie Cochran with the Seversky AP-7A, NX1384. Her racing number, 13, has not yet been painted on the fuselage. (San Diego Air and Space Museum Archive)
Jackie Cochran with the Seversky AP-7A, NX1384. Her racing number, 13, has not yet been painted on the fuselage. (San Diego Air and Space Museum Archive)

The Seversky AP-7 was an improved civil version of the Seversky P-35 fighter, which was the first U.S. Army Air Corps single engine airplane to feature all-metal construction, an enclosed cockpit and retractable landing gear. It was designed by Major Alexander Nikolaievich Prokofiev de Seversky, a World War I Russian fighter ace.

Cochran’s AP-7A was a specially-built racer, modified from the original AP-7 with a new-thinner wing and different landing gear arrangement. It was powered by a an 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 engine 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 engine turned a three-bladed Hamilton-Standard controllable-pitch propeller 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).

This is the same airplane in which she won the 1938 Bendix Trophy.

Jackie Cochran's Seversky AP-7, NX1384, at the Union Air Terminal, Burbank, California, September 1938.
Jackie Cochran’s Seversky AP-7A, NX1384. (Unattributed)

¹ FAI Record File Number 12027

© 2017, Bryan R. Swopes

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1 September 1938

Seversky AP-7 NX1384, c/n 145. (San Diego Air and Space Museum Archives)
Seversky AP-7 NX1384, c/n 145. (San Diego Air and Space Museum Archives)

1 September 1938: Jackie Cochran departed the Lockheed Air Terminal, Burbank California, at 3:00 a.m., flying her Seversky AP-7, NX1384, c/n 145. Her destination was Cleveland, Ohio, the finish line for the Bendix Trophy Race,  2,042 miles (3,286 kilometers) away.

Jackie Cochran steps out of her Seversky AP-7 at Cleveland, Ohio, after winning the 1938 Bendix Trophy Race.

NX1384 was built especially for Jackie Cochran, and had been flown from the factory to Burbank by Major de Seversky just two days earlier. His flight set an East-to-West Transcontinental Speed Record of 10 hours, 2 minutes, 55.7 seconds.

The specially built AP-7 racer was an improved version of Major Alexander Nikolaievich Prokofiev de Seversky’s P-35A fighter, which was the U.S. Army Air Corps’ first all-metal single-engine airplane with an enclosed cockpit and retractable landing gear. Cochran’s AP-7 was powered by an 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 engine 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 engine turned a three-bladed Hamilton-Standard controllable-pitch propeller 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).

Jackie Cochran paints her race number, 13, of the fuselage of her Seversky AP-7. (Unattributed)
Jackie Cochran paints her race number, 13, of the fuselage of her Seversky AP-7 at Burbank, California. (Unattributed)

“Finally the P-35 arrived. I decided that I didn’t want to take it into the air for a test even if I could. The racing officials impounded it because it was a prototype and there was some kind of rule about untested planes. I would test it en route. . . Finally, I got to sit in the cockpit. I began to study all the instruments by the hour. I can almost see them still.

 “There are about a hundred or more buttons, levers, and other gadgets to push, pull or twirl. . .  I close my eyes and reach for everything in the dark. And I keep at this until I can get to them blindfolded and with no false moves. . . 

“I finally see Cleveland. . . (a)nd am going so fast that I pass the airport and come in from the wrong side. . . Have I won? The crowds are cheering. It’s a standing ovation. . . I have won the Bendix.”

Vincent Bendix congratulates Jackie Cochran on winning the 1938 Bendix Trophy Race.
Vincent Bendix congratulates Jackie Cochran on winning the 1938 Bendix Trophy Race.

— Jackie Cochran: An Autobiography, by Jacqueline Cochran and Maryann Bucknum Brinley, Bantam books, New York 1987, Pages 160–165.

Jackie Cochran was the third pilot to leave Burbank, but the first to arrive at Cleveland. Her elapsed time for the flight from California to Ohio was 8 hours, 10 minutes, 31.4 seconds, for an average speed of 249.774 miles per hour (401.895 kilometers per hour).

After being congratulated on her win by Vincent Bendix and other race officials, Cochran had her Seversky monoplane refueled. She then got back in to its cockpit and took off for Bendix, New Jersey. She landed there 10 hours, 7 minutes, 1 second after leaving Burbank at 3:00 a.m. This was a new West-to East Transcontinental Speed Record.

Sversky AP-7 NX1384, seen from below. In this configuration, the landing gear folds rearward.
Sversky AP-7 NX1384, seen from below. In this configuration, the landing gear retracts rearward.

© 2016, Bryan R. Swopes

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