Most fighters carry the engine in the nose and the propeller out front. The Swedish Saab 21 did the opposite: it put the engine behind the pilot and the propeller at the very back, spinning between two slender tail booms. It was an elegant answer to an old problem — a clear nose for a heavy battery of guns and a superb forward view — but it created a lethal new one. How does a pilot bail out without being cut to pieces by the propeller turning directly behind him?

Saab’s solution was an ejection seat, making the J21 one of the first operational aircraft in the world to carry one. And then, in a feat almost no other design ever managed, the entire aircraft was rebuilt as a jet.

Engine at the back, guns at the front

The pusher layout was deliberate. With a licence-built Daimler-Benz DB 605B and its propeller mounted at the rear of the fuselage nacelle, the nose was free to carry a dense concentration of cannon and machine guns, and the pilot enjoyed an unobstructed view forward. The Saab 21 first flew on 30 July 1943 and entered service in December 1945. The catch was obvious to everyone who looked at it: the propeller arc sat exactly where a pilot would tumble if he tried to jump.

One of the first ejection seats in the world

Saab’s engineers studied several escape methods, including blowing off the propeller or the whole engine with explosive charges before the pilot bailed out. In the end they adopted an ejection seat developed by the defence firm Bofors, fired by a cartridge to throw the pilot up and clear of the blades. It made the J21 one of the first operational aircraft anywhere to be fitted with an ejection seat — a technology that would go on to save thousands of lives.

From propeller to jet

In 1947 Saab did something almost no one else achieved: it turned its piston fighter into a jet. The DB 605 and its propeller were removed and a British de Havilland Goblin turbojet installed in their place, breathing through an intake beneath the nose and exhausting between the booms. More than half of the airframe had to be changed. The first 21R flew on 10 March 1947 in the hands of test pilot Åke Sundén, and it became Saab’s first jet aircraft.

Only one other fighter in history made the same leap successfully — the Soviet Yakovlev Yak-15. The Saab 21 is, almost uniquely, an aircraft that carried its country into the jet age using the body it had already flown as a propeller fighter. Put the propeller where nobody else would, solve the resulting danger with one of the world’s first ejection seats, then keep the airframe and change the engine for a jet: pragmatic, contrarian, and unmistakably Swedish engineering.

Sources: Wikipedia; Plane-Encyclopedia.