Airframe: The B-17 Flying Fortress

  • Published
  • By Bennie J. Davis III
  • Airman Magazine

The B-17 Flying Fortress is a success story born from disaster. In fact, it could be argued no other aircraft has had a more horrible first impression, especially for a machine that would eventually revolutionize American aviation history in more ways than one.

In 1934, during the golden age of flight and with a dire need for a long-range bomber capability, the Army Air Corps issued a multi-million dollar competition to the aircraft manufacturers Boeing, Martin and Douglas. They were to produce an airframe to defend U.S. coastlines and strike targets deep into enemy territory in lieu of another world war.

Boeing developed the Model 299, the prototype to the B-17, which was an impressive sight. The aircraft was larger and more powerful than its competitors and it carried five times the number of bombs while boasting four engines under its wings. The standard configuration of the era was two engines, giving the model 299 twice the flying range.

The first flight of the Model 299 was July 28, 1935, during a series of “fly-off” evaluations against the Martin Model 146 and the Douglas DB-1. Richard Williams, at the time a reporter for The Seattle Times, described the Model 299 as a “15-ton flying fortress” due to the number of machine guns mounted on the aircraft.

Boeing quickly adopted and trademarked the name “Flying Fortress,” while claiming in early press releases that Model 299 was the first combat aircraft that could continue its mission if one of its engines failed.

On August 20, 1935, the prototype flew from Seattle to Wright Field, Ohio, in 9 hours and 3 minutes with an average cruising speed of 252 miles per hour, besting all competition.

The U.S. Army Air Corps and Maj. Gen. Frank Andrews were so impressed with the prototype they suggested an order of 65 Boeing aircraft before the competition ended. They believed the Boeing model was best suited to implement the new strategic daylight bombing doctrine.

Unfortunately, on October 30, 1935, during the second flight of the air trials, disaster struck. As the Flying Fortress lifted off the runway at Wright Field, Ohio, it began a steep climb before stalling and crashing to the ground, killing both pilots and injuring the rest of the aircrew. The pilots had forgotten to disengage the gust, or elevator locks, which made the aircraft unresponsive to pitch control.

The Model 299 was disqualified. Army Chief of Staff Gen. Malin Craig cancelled the order for the 65 prototype B-17s and instead ordered 133 twin-engine Douglas B-18 Bolos.

The loss was devastating to Boeing, but a think-tank session in response to the crash determined the advancements in aircraft technology used on the Flying Fortress were making flying controls too complex for pilots to memorize.

From this failure, pre-flight checklists were born and quickly adopted across the Army Air Corps.

The USAAC, still impressed with Boeing’s advances in technology, eventually ordered 13 Model 299s for service testing. Using a legal loophole for purchase, the Army Air Corps called them YB-17s. The YB-17 included a number of substantial changes from the Model 299, including more powerful Wright R-1820-39 Cyclone engines.

The implementation of pre-flight checklists allowed YB-17s to fly 1.8 million hours without incident. This proved to the Army Air Corps they were safe and eventually 12,731 were built.

The B-17 would go on to drop more bombs than any other aircraft in the U.S. arsenal during World War II.

Gen. Carl Spaatz, the American air commander in Europe, said, “Without the B-17 we may have lost the war.”



In total, 8,680 Flying Fortress bombers were built and the aircraft went through several variations and alterations before the final B-17G version of the aircraft. While models A-D were created for defensive purposes, the E-G models focused on offensive warfare.

By the time the B-17G entered World War II, the aircraft had been outfitted with additional manned gun turrets in the upper fuselage, belly and tail. Each turret contained a pair of 0.50 caliber machine guns. The number of guns had increased from seven to 12. The increased firepower made the B-17 a threat to enemy fighters, especially when flying in tightly stacked defensive “box” formations for protection. The engines were upgraded with Wright R-1820 Cyclone 9 turbochargers.

The B-17, a high altitude strategic bomber, achieved its accuracy from the secretly developed Norden bombsight. The Norden consisted of a gyroscopically stabilized telescopic sight paired with an electromechanical computer where flight conditions were inputted. During a bomb run, the bombardiers would take over flight controls and the Norden sight would set the aircraft into autopilot and guide the aircraft to the precise release point. With a skilled bombardier at the helm, the Norden was remarkably accurate.

Another innovation of World War II was the creation of staggered combat “box” flying formations for heavy bombers, which used nine or 12 squadron aircraft in defensive patterns, which massed the firepower of the bomber’s machine guns.

Three squadron box formations staggered vertically and horizontally across formed a group. Three groups formed a combat wing, which was a formation comprised of 54 aircraft. Bombing formations dropped their loads on the lead bombardier’s command leading to dispersed bomb patterns. A 4,000-pound bomb load was typical for long missions, but the B-17 could carry 8,000 pounds for shorter distances and at lower altitudes, which proved successful in the carpet-bombing raids on German oil and aircraft industries before the Normandy Invasion.

A crew of 10 including the pilot, copilot, navigator-radioman, bombardier and gunners operated the B-17G.



 The Flying Fortress was used extensively during World War II in the Pacific, European and combined theaters. B-17s equipped 32 overseas combat groups with inventory, peaking in 1944 at 4,574 U.S. Army Air Forces aircraft worldwide. The B-17 dropped 640,036 short tons of bombs on European targets during the war.

Following the end of World War II, the B-17 was quickly phased out of use as a bomber and the Army Air Forces retired most of its B-17 fleet after the development of the B-29 Super Fortress. The majority of the bombers were ferried back across the Atlantic to the United States where the majority were sold for scrap metal and melted down.

The durability and survivability of the B-17 after taking damage made it a legend and the preferred bomber to fly by the pilots of World War II.





  • Primary function: Heavy Bomber

  • Builder: Boeing

  • Power plant: Four Wright R-1820-97 “Cyclone” turbo supercharged radial engines, 1,200 horsepower (895 kW) each

  • Wingspan: 103 feet, 9 inches (31.62 meters)

  • Length: 74 feet, 4 inches (22.66 meters)

  • Height: 19 feet, 1 inch (5.82 meters)

  • Speed: 287 mph

  • Range: 2,000 miles

  • Ceiling: 35,600 feet (10,850 meters)

  • Maximum takeoff weight: 65,000 pounds (29,700 kilograms)

  • Armament: Guns: 13 × .50 in (12.7 mm) M2 Browning machine guns in nine positions (two in the Bendix chin turret, two on nose cheeks, two staggered waist guns, two in upper Sperry turret, two in Sperry ball turret in belly, two in the tail and one firing upwards from radio compartment behind bomb bay) Bombs: Short range missions (<400 miles): 8,000 pounds (3,600 kilograms); Long range missions (≈800 miles): 4,500 pounds (2,000 kilograms); Overload: 17,600 pounds (7,800 kilograms)

  • Crew: 10 (pilot, copilot, navigator, bombardier/nose gunner, flight engineer/top turret gunner, radio operator, waist gunners (two), ball turret gunner, tail gunner)

  • Initial operating capability:  1938

  • Unit cost:  $238, 329 (1945) $2,581,000 million (2016)

  • Inventory: 12,731

  • Retired: 1959 by U.S. Air Force, 1968 by the Brazilian Air Force