When Burt Rutan rolled his latest creation out at Oshkosh in 1996, the reaction from a crowd that worshipped him was more or less: what went wrong? The Boomerang looked broken. There was a small engine boom stuck to the left of the fuselage. The right wing was about five feet shorter than the left. The wings swept forward. The tail was lopsided. It looked like an aircraft assembled from two different aeroplanes in the dark.

It was, in fact, one of the cleverest light aircraft ever built. When Rutan was later asked why it looked like that, he gave a two-word answer: “Self preservation.”

Why twin-engine planes kill pilots

To understand the Boomerang you have to understand what makes an ordinary twin dangerous. On a conventional twin like a Beechcraft Baron, the two engines sit far apart, one on each wing. Lose one, and the other — still pushing hard, several feet off to the side — violently yaws the aircraft toward the dead engine. Below a certain speed, the “minimum control speed,” the rudder can no longer hold it straight, and the aircraft can flip onto its back in an instant.

Fighting it takes brute force. In a Baron with one engine feathered, a pilot may have to stand on the rudder pedal hard enough to make his leg shake, while cranking in aileron, just to fly straight. Engine failure in a light twin is one of the classic killers in aviation, and every multi-engine pilot trains for it.

Rutan’s fix: lean into the asymmetry

Most designers try to make a twin as symmetrical as possible. Rutan went the other way. He pulled the engines in close to the centreline — on the Boomerang the gap between the two propeller discs is less than a foot, where a Baron’s is nearly six — and arranged the whole airframe in a carefully calculated lopsided shape so that, with one engine out, there is almost nothing left to yaw. The strange offset boom, the unequal wings, the forward sweep: every odd angle is there to balance the forces when an engine quits.

The aircraft drew on two of his earlier designs, the push-pull Defiant and the record-setting Catbird. His target was radical: a minimum control speed below the stall, so the aeroplane stays controllable even as it stops flying. The wing is built to stall at the root first, giving the pilot every warning while the outer wing is still lifting.

What it is like to fly

Everything about the Boomerang is unconventional. The pilot sits in the right seat, so the boom is on the far side and out of his sightline. There is no door — you climb in through a big oval window that slides back on a rail. The controls are a feather-light side-stick, and the only rudder pedals in the whole aircraft are on the pilot’s side.

And the engine-out trick genuinely works. Where the Baron demanded a leg-trembling shove on the rudder, the Boomerang, with one engine pulled to idle, simply keeps flying straight and level. On one demonstration flight the current caretaker lifted both feet clear of the pedals to prove he was not correcting anything at all. Built of light composites, turbocharged for high altitude, it carries five people close to 1,900 miles at around 300 mph — faster and farther than the Baron it was benchmarked against, on less power.

Rutan’s favourite

Rutan flew the Boomerang as his personal aircraft for six years. After he retired from Scaled Composites in 2010, rather than send it to a museum he handed it to a young company engineer, Tres Clements, who restored it and keeps it flying to this day. Of the dozens of groundbreaking aircraft Rutan designed — including the round-the-world Voyager and the spaceship-launching White Knight — the lopsided little Boomerang is the general-aviation design he is proudest of.

The Boomerang is a reminder that in engineering, the thing that looks like a mistake is sometimes the answer. It flies crooked so that, on the worst day, it flies straight.

Sources: Steve Schapiro, “Burt Rutan’s Favorite Ride,” Smithsonian Air & Space; Wikipedia; Scaled Composites.