A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Is it possible to loop or roll a 747 jet?

October 27, 1978

Dear Cecil:

Is it possible to roll or loop a 747 or DC-10 loaded or empty? I have a bet with my roommate and he says the wings would shear off. I say it could because otherwise they wouldn't allow it to fly people.

Cecil replies:

No one has ever tried to get fancy with one of the Big Birds, but there once was a Boeing test pilot who, in a moment of frivolity, took it into his head to execute a barrel roll in a 707. He made it, but he didn't exactly endear himself to his superiors. The consensus at Boeing seems to be that a 747 would probably survive a barrel roll, but to try it would be, and I quote, "an extremely foolish action."

The problem is not so much with the strength of the wings, which are designed to stand much greater pressures, as with the skill of the pilot. Enough forward speed must be maintained during the roll to compensate for the loss of lift that occurs when, in effect, the wings cease to function. That happens when the wings are perfectly perpendicular to the ground--in the vertical position, they can no longer hold the plane up. In a small plane, the problem is minimal: the wings spin out of the vertical position in a split second. But in a larger plane that takes longer to roll, the margin for error is increased, and the fatal moment could be stretched out enough to pull the plane down.

Looping a 747 or a DC-10 would be trickier still. (Bear in mind that a "roll" means you flip to the right or left; a "loop" is roughly analogous to a backwards somersault.) You'd have the problem of lift again, at the moment when the tail is down, but it would be harder to overcome, since the plane must be climbing, not merely maintaining its altitude, at the same time. One way to get a plane to climb is to make it go faster (increasing the speed increases the air pressure under the wings, which is what holds the plane up in the first place). But there's some doubt as to whether a 747 or a DC-10 could achieve enough forward speed to deliver the extra shot of lift that a loop would require. Boeing suspects its planes could make it, but since no one has ever been silly enough to try, there's no way of knowing for sure. So it looks like your bet is a draw.

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