Straight wings are easy. Wings that jut out from the fuselage at 90 degrees are simple to build. They’re also good: when the wings are perpendicular to on-coming air they get the most bite in air and generate the most lift. And yet, no jet-powered aircraft has straight wings.
Why? The Sound Barrier. (Technically, compressibility.) We always knew that to fly faster, you’d have to put in more power. And there’s even an equation that your tenth-grade algebra teacher used as an example of a polynomial equation, because he was really stretching for examples of polynomial equations. But near the speed of sound, going faster gets harder than your calculator would predict. Air stops being an ideal fluid and is just a bunch of molecules that can’t get out of the way fast enough.
What do you do when the math breaks down and going fast takes more power than expected? Aeronautics found an answer sure to warm your eleventh-grade trigonometry teacher’s heart: More Math! You “sweep” the wings, by turning them backwards. The plane and the wing face in different directions. Air now hits the wing off-angle, which means that when the plane is going at the speed of sound, the wing sees air hitting it at the speed of sound times the cosine of the sweep angle. Or in people-speak: less than the speed of sound!
450 mph is a dividing line. If a plane wants to fly faster, it needs swept wings. Below that sweeping the wings is a waste (it makes the wing heavier for no benefit). Jetliners have a V-shape for a different reason than flocks of geese have a V-shape (unless someone’s been dumping cocaine at your local park).
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