Tag Archives: Wright Aeronautical Division Cyclone C666A

8 July 1941

Fortress Mark I, AN521 ‘WP-K’, of No. 90 Squadron RAF based at West Raynham, Norfolk, preparing for take off at Hatfield, Hertfordshire, during an inspection of newly-arrived American aircraft by the Chief of the Air Staff and the US Air Attache. (Photograph by Flight Lieutenant Bertrand John Henry Daventry, Royal Air Force/CH 2873, Imperial War Museum)
Boeing Fortress Mark I AN521, ‘WP-K’, (U.S.A.A.F. serial number 40-2052) of No. 90 Squadron R.A.F., based at West Raynham, Norfolk, preparing for take off at Hatfield, Hertfordshire, during an inspection of newly-arrived American aircraft by the Chief of the Air Staff and the U.S. Air Attache. Photograph by Flight Lieutenant Bertrand John Henry Daventry, Royal Air Force. © IWM (CH 2873)

00DD3437_5056_A318_A85F9DA3980B669B8 July 1941: Three Royal Air Force Boeing Fortress Mk.I heavy bombers departed from their base at RAF Watton to attack Wilhelmshaven, Germany. This was a daylight bombing mission, with the airplanes flying at 30,000 feet (9,144 meters). One bomber diverted to a secondary target because of engine trouble, while the remaining two Fortresses continued to the primary target.

At the very high altitudes flown, the defensive heavy machine guns that gave the airplane its name froze due to the low temperatures and could not be fired. (In standard atmospheric conditions, the temperature at 30,000 feet would be -45 °C., or -49 °F.)

"Vertical aerial reconnaissance of Wilhelmshaven." © IWM (HU 91201)
“Vertical aerial reconnaissance of Wilhelmshaven.” © IWM (HU 91201)

All three aircraft returned safely to their base. The mission was completely ineffective, however.

This was the very first use of the Boeing B-17 Flying Fortress in combat.

Fortress B.I WP-F
Fortress B.I AN530, WP-F (U.S.A.A.F. B-17C 40-2066) (Royal Air Force)

The Boeing Model 299H, designated B-17C, was the second production variant ordered by the U.S. Army Air Corps. 38 were built by Boeing for the U.S. Army Air Corps, but 20 were transferred to Great Britain’s Royal Air Force, designated Fortress Mk.I. (Boeing Model 299T.) They were initially assigned to No. 90 Squadron, Bomber Command. (A 1941 book, War Wings: Fighting Airplanes of the American and British Air Forces, by David C. Cooke, Robert M. McBride & Company, New York, refers to the B-17C in British service as the “Seattle,” which is in keeping with the R.A.F.’s system of naming bombers after cities.)

Of the 20 Fortress Mk.I bombers, 8 were lost in combat or in accidents.

Boeing Fortress Mk.I AN529 at Heathfield, Scotland, after arrival from United States, May 1941. © Imperial War Museum E(MOS) 276

The Boeing B-17C/Fortress Mk.I was 67 feet, 10-9/16 inches (20.690 meters long with a wingspan of 103 feet, 9 inches (31.633 meters) and the overall height was 15 feet, 4½ inches (4.686 meters). The B-17C had an empty weight of 30,900 pounds (14,016 kilograms). The maximum design gross weight was 47,500 pounds (21,546 kilograms).

The B-17C was powered by four air-cooled, supercharged, 1,823.129-cubic-inch-displacement (29.876 liters) Wright Cyclone G666A (R-1820-65)¹ nine-cylinder radial engines with a compression ratio of 6.70:1. The engines were equipped with remote General Electric turbochargers capable of 24,000 r.p.m. The R-1820-65 was rated at 1,000 horsepower at 2,300 r.p.m. at Sea Level, and 1,200 horsepower at 2,500 r.p.m. for takeoff. The engine could produce 1,380 horsepower at War Emergency Power. 100-octane aviation gasoline was required. The Cyclones turned three-bladed, constant-speed, Hamilton-Standard Hydromatic propellers with a diameter of 11 feet, 7 inches (3.835 meters) though a 0.5625:1 gear reduction. The R-1820-65 engine is 3 feet, 11.59 inches (1.209 meters) long and 4 feet, 7.12 inches (1.400 meters) in diameter. It weighs 1,315 pounds (596 kilograms).

Crew members of a No. 90 "RAF Fortress crew at RAF Polebrook July 19, 1941." (IWM CH 3090)
“RAF Fortress crew at RAF Polebrook July 19, 1941.” © IWM (CH 3090)

The B-17C had a maximum speed of 323 miles per hour (520 kilometers per hour) at 25,000 feet (7,620 meters). Its service ceiling was 37,000 feet (11,278 meters) and the maximum range was 3,400 miles (5,472 kilometers).

The Fortress Mk.I could carry 4,800 pounds (2,177 kilograms) of bombs in an internal bomb bay. Defensive armament consisted of one Browning AN-M2 .30-caliber air-cooled machine gun at the nose and four Browning AN-M2 .50-caliber heavy machine guns in dorsal, ventral and waist positions.

Fortress I AN528 (Getty Images/Three Lions)
Royal Air Force Fortress Mk.I AN528 (B-17C 40-2064) prior to being camouflaged. (Getty Images/Three Lions)

© 2018, Bryan R. Swopes

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