Little known or remembered today, the Boeing B-47 Stratojet paved the way for the modern jet airliner. You might consider its history the next time you take an airline flight.
As you look out the terminal window at jet-powered rides, note the elegant profile, swept wings, and sleek tail surfaces of the aircraft on the ramp. Settling into your seat, examine the tightly cowled engine pods, multiple ailerons and spoilers, and smooth upper surface of the wing.
Have you ever wondered when all these elegant design features made their debut? The answer is December 17, 1947. On the 47th anniversary of the Wright Brothers’ first powered flight—and the 15th anniversary of the Douglas DC-3’s initial jaunt—a radical prototype, the XB-47 Stratojet, took to the air for its first flight. Aviation has never been the same.
However, the story really kicks off in 1943. As it began deploying fleets of B-17 and B-24 bombers to bases all over England, the Army Air Corps looked in its crystal ball and saw that the U.S. was woefully behind in the development of jet airplanes. Soon, four legendary aircraft companies were awarded contracts to develop four- and six-engine medium jet bombers. Three of these designs retained a conventional straight wing with engines embedded in the wing.
However, after the war in Europe ended in 1945, Boeing engineer George Schairer traveled overseas to learn of the advanced aerodynamics research done by German engineers and scientists. He immediately called home to Seattle and told the Boeing design team to brace for some major changes.
The XB-47 Stratojet that emerged featured 35-degree swept wings mounted at shoulder height on the fuselage. The six General Electric J47 engines were mounted in pods slung below the wing to ease engine access and keep the wing surface clean. The inboards were mounted in pairs of two and the outboards singly. The tail surfaces were swept, and when combined with the ultra-smooth fuselage, the XB-47 looked like it came right out of a science fiction novel.
Because of the requirement for a large bomb bay, the landing gear consisted of twin tandem bicycle-gear trucks mounted fore and aft on the fuselage and two outriggers located in the inboard engine pods. The two pilots sat above the fuselage in a fighter-style bubble canopy, and the navigator/observer sat in the partially glazed nose. Defensive armament consisted of just two radar-aimed cannons, operated by the copilot and located in the tail.
Why only two guns in the tail? When the B-47 made its debut, it could fly higher and faster than any fighters of the day.
However, it was the first large swept-wing aircraft. Following the dictum that “experience is a hard teacher as it often gives the test before the lesson,” the B-47 was developed carefully. The prototype suffered from a serious case of Dutch roll, a motion caused by a yaw condition inherent in swept-wing aircraft. The incorporation of a yaw damper, now commonplace, solved the problem. The prototype also pitched up at high speed, triggered by the stalling of the outer wing section. This was solved by adding vortex generators, now ubiquitous on modern jet aircraft.
By early 1949, it was time to let the world know what the Boeing engineers had created. The XB-47 flew from Moses Lake, Washington, to Washington, D.C., at an average speed of 606 mph, covering 2,289 miles in 3 hours and 46 minutes. This flight spelled the end for the competing designs, and eventually more than 2,000 B-47 Stratojets were built in various configurations, a production number now considered unheard of for a jet bomber.
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But the B-47 was not without its problems. Pilots who had grown up on piston-powered World War II aircraft had to adapt to this new jet, which demanded to be flown exactly by the numbers. With a moment’s inattention, the sleek B-47 could easily accelerate beyond its maximum design speed with disastrous results. At 40,000 feet, the aircraft introduced its pilots to the concept of coffin corner, where the gap between stall speed and maximum Mach number is quite small. Slow down and enter a stall; speed up and risk Mach tuck as the nose may pitch down uncontrollably.
The B-47’s flexible wing, great for high-speed flight, introduced the concept of aileron reversal. At 450 knots at low altitude, the ailerons, located at the wing tips, acted like trim tabs and simply twisted the thin wing without turning the airplane. The only way to restore control was to slow down. Next time you look out at the wing of a modern airliner, note that ailerons are placed both at the tip for low-speed flight and at the wing root for high-speed flight.
You can thank the lessons learned from the B-47 for that innovation. However, they came at a high cost: Approximately 10 percent of the B-47 fleet—203 aircraft and, sadly, 464 flight crewmembers—were lost to accidents. All completely unacceptable today, but at the time, it was the price of progress into the jet age.
If the B-47 is the mother jet, who are its famous children? The legendary Boeing B-52, which may fly for nearly 100 years, was the first to benefit. But the real winner was the Boeing 367-80, or known simply as the “Dash 80.” Boeing bet the company on developing the world’s first successful jet airliner, and the Dash 80 begat the 707, which begat the 747, which begat the 787. They all sported the same 35-degree swept wings, pod-mounted engines, and swept tail feathers as the B-47. Oh, yes, and a yaw damper, vortex generators, and various other innovations learned from the Stratojet.
So, as you take your seat for the next airline trip, look around you. Note the basic configuration of your Boeing or Airbus. It is little changed from the original Boeing 707 and the Dash 80, and you can thank Schairer, the groundbreaking engineers and skilled aircrews, and the incredible Boeing B-47 Stratojet for that.
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Editor’s note: This story originally appeared in the Nov/Dec 2023 issue of Plane & Pilot magazine.
