Forward Swept Wing

Technology Surprise, 1945-Style

Spy flights over Germany during World War 2 had revealed some of the nation's military secrets, but what was discovered in the months after V-E Day was still mindboggling. Retreating in the East and Italy, its cities bombed daily and nightly, Nazi Germany had continued investing in advanced technology that would not provide any military benefit until the late 1940s, even if it worked. Allied scientists were awed and envious at the sight of research establishments at Volkenrode and Gottingen, with wind tunnels that outperformed anything else in the world.

Those wind tunnels were a big reason why Germany had pulled well into the lead in the design of aircraft that could take full advantage of jet propulsion by reaching high subsonic Mach numbers. By the end of the war, German engineers had designed almost every transonic configuration used to this day, built some of them, and flown one: the extraordinary Junkers Ju287.

The creation of Dr Hans Wocke, the Ju287 V1 was the first aircraft with a forward-swept wing (25 deg.) designed for transonic speeds. The V1 prototype itself could not do this: it was a lash-up with a He177 bomber fuselage and a fixed landing gear made from salvaged parts. Adding to its freakish appearance, two of the four jet engines were installed either side of the nose.

The FSW had been chosen for several reasons. Wind tunnel tests had shown that aft-swept wings, although efficient at 600 mph and more, were susceptible to tip-stall. This was due to aft-and-spanwise airflow, which caused pitch-up and an unstable, divergent stall at low speeds, with loss of aileron control. Wocke reasoned, and wind-tunnel tests confirmed, that the FSW would stall more benignly as long as slats were fitted to the root, to delay the sall there. Still, nobody actually believed it - hence the lash-up testbed, which flew in August 1944 before any aft-swept aircraft took to the air.

Another feature of the FSW was packaging. A besetting problem in bomber design was that the weapons bay and the wing spars all wanted to be in the same place. The FSW placed the bay in front of the wing.

Wocke's contemporaries also designed aft-swept-wing aircraft - including Brunolf Baade's EF150, which inspired the Boeing B-47 and is the ancestor of every contemporary airliner - delta wings, crescent wings, variable-sweep wings and even the asymmetric slewed wing.

There was one thing that Aviation Week did not know about the Ju287 - and nobody much in the West knew about it either until the end of the Cold War. Junkers had been building a high-speed, retractable-gear prototype, the Ju287 V3, and it had been removed to the Soviet Union. it was tested briefly in 1947, with a cluster of three engines under each wing, and was followed by the refined EF 140 with Klimov VK-1 engines, reverse-engineered from the Rolls-Royce Nene.

That was the end of the FSW for some time. But Wocke was still a believer, and designed the HFB 320 Hansa Jet, a Lear jet competitor, for the Hamburger Flugzeugbau (now part of Airbus) in the early 1960s. Like the Ju287's weapon bay, the Hansa Jet's cabin was ahead of the wing, so the jet could have a mid-mounted wing and a small frontal area. 47 Hansa Jets were built - the only FSW jet to enter production.