Airport tarmacs of the 1970s and '80s were home to a menagerie of airliners, from humpbacked 747s and needle-nosed Concordes to T-tailed MD-80s. Today, much of that variety has vanished. Almost all medium and large jetliners fit into the same pattern: two engines, straight-tube fuselage, and a conventional tail. Where has all the imagination gone?

It's not that aeronautical engineers have run out of ideas. Instead, the demands for efficiency have driven designs to this narrow range of similarity. In the hyper-competitive world of airplane manufacturing, there's simply no room for inefficient flourishes. After all, a performance deficit of just a few percentage points could mean the difference between a successful airframe and a permanent scrapyard resident.

In some ways, it's not unlike the mechanics of nature. Just as convergent evolution caused ichthyosaurs and dolphins to look alike, the demands of the aviation industry have nudged aeronautical engineers toward maximum efficiency with little variation. These are some of the once-prominent features that have gone extinct, and why:

Pointed Noses

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Modern airliners, traveling at three-quarters the speed of sound, easily push air out of the way with their rounded noses. But at supersonic speeds, molecules of air don't have time to get out of the way, so jets like the Concorde (and other future supersonic concepts ) fly through the air like a nail drives through wood.

In the late '70s, Concorde was a technological marvel able to fly from New York to London in 3 1/2 hours. But its biggest problem was all that speed required lots of expensive fuel. Even during the plane's final year of service in 2003, transatlantic seats still cost $12,000 per round trip. Simply put, not enough passengers could afford to fly supersonic.

Physics also didn't help things since every time a supersonic jet reaches top speed, it creates an ear-shattering sonic boom. This means commercial planes like the Concorde could only safely fly over the ocean, eliminating immensely lucrative transcontinental routes. So goodbye, pointy noses.

The Hump

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The 747's iconic upper half-deck creates an unmistakable profile. The reason Boeing engineers included the feature when they drew up the blueprints in the 1960s was that it allowed them to incorporate a front-loading cargo bay with a hatch that hinged upward.

It's an innovation that never caught on. In the end, the plane turned out to be more popular for transporting passengers than cargo. With Boeing winding down production on the 747, the hump will gradually vanish from airport tarmacs.

Triple Engines

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During the '70s and '80s, three-engine planes like the wide-body DC-10 and L-1011 (pictured) were commonplace. Triple engines provided plenty of thrust and an increased safety margin in case one engine should fail. In the decades since, however, engine technology—like everything else—only got better. Today's turbofan engines provide significantly more thrust and are far more reliable, too.

ETOPS ("Extended Operations") certification means a plane with only two engines can safely fly for several hours away from land if one of its engines fails, meaning they can handle most of the long transoceanic routes that three- and four-engine planes once had to themselves. As you'd expect, operating fewer engines is also more efficient and therefore more economical. Today's longest regularly serviced route, from Doha, Qatar, to Auckland, New Zealand, is flown by a twin-engine 777.

T-Tails

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The McDonnell Douglas MD-80 was a popular narrow body airliner of the '80s and '90s, with more than a thousand built. On its backend it sported a T-tail, with the horizontal stabilizer and elevator mounted on the top of the vertical stabilizer rather than the base like a conventional tail. The advantage of this design was freeing up space next to the fuselage to mount engines on the tail.

Ultimately, though, aeronautical engineers concluded that a more practical solution is to mount the engines under the wings, where they're closer to the center of gravity and to the fuel in the wing tanks. Where you still see T-tails today is on smaller aircraft, like the Bombardier CRJ 100, because they don't have enough ground clearance to carry engines under the wings.

Although today's airliners are mired in design monotony, it doesn't mean it will be that way forever. Even now, aeronautics companies are trying to resurrect the supersonic jet , making it both economical and silent, and NASA even has plans for creating an all electric aircraft— with a crazy 14-engine design . Although these concepts won't be taxiing up to your gate anytime soon, the future of aviation design is far from over.

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