Anything can “fly” if you push it through the air, or propel it, as you might have done with a balsa wood airplane as a child. Or, if you played with dolls instead of airplanes, threw your Barbie across the room because your mother refused to let you wear your party dress to school. But if you aimed the airplane or the Barbie, or the Barbie in the airplane, straight ahead of you it quickly would have been pulled down to the ground by the relentless force of gravity.
For an object to continue on its path upwards it needs a force other than the thrust of an energetic arm to oppose the pull of gravity. Physicists give this mysterious force the simple but poetic name “lift.”
Lift, in an airplane, is created by the difference in air pressure above and below the wing. Due to the shape of the wing, air flows smoothly below the wing, but is disrupted above the wing by the wing’s curvature. This disruption causes gaps in the atmosphere, lowering the pressure above the wing such that the higher pressure beneath “pushes” the wing upward toward the lower pressure.
That is why nerdy, snooty types take joy in saying that it isn’t really the airplane that is flying, but rather the wing. For the most part, wings “carry” the fuselage and its passengers upwards. Not incidentally, when a pilot wishes to “roll” an airplane, that is, to rock its wings so that one goes up and the other goes down, he or she merely changes the shape of its wings by raising and lowering ailerons (a section of wing that is capable of moving).
Now, if you think about it for a moment, in order for the difference in air pressure to be created by the wing at all, the wing needs to have an air mass to oppose it. A wing won’t fly in a vacuum—which is why spacecraft don’t need wings at all. (Without gravity, there is no need for lift, and “up” and “down” have entirely different meanings; essentially, there is only “here” and “there”.)
Now, lest you think all this silliness is just random aviation arcana, I would suggest that it is rather important prelude to understanding the notion of “angle of attack,” which is the topic of today’s lecture. Simply stated, if you were to imagine a line drawn from the front edge of a wing to the back, and call that line the wing’s cord, then the angle between the cord and the wind is called the “angle of attack.” It is a beautiful name, as so many things are in aviation, because, in essence, the wing attacks the wind, and the result of that altercation is not fight but flight.
If I haven’t lost you yet, you should begin to appreciate the richness of this metaphor. First, you simply can’t get anywhere–you can’t even get off the ground, without creating a difference. Combine that difference with energy in the form of thrust and you really can take off. It gives new depth, at least for me, to the old French saw “vive la difference!” There really is no vive without difference.
But, too much difference may get you in trouble and lead to a stall. You see, when a wing exceeds its critical angle of attack, the air above the wing will burble, and the pressure difference needed for the wing to fly disappears. The wing “stalls,” is overtaken by gravity, and tumbles toward the earth.
I had a mentor who once said that the only difference between creative people and crazy people was that creative people get paid. Sometimes, I suppose, that may be true, but sometimes crazy is just taking creative a bit too far. Difference may be essential for flight, but too much difference may be hazardous.
As good metaphors would have it, exceeding one’s angle of attack and stalling is also a danger of metaphors themselves. One risks the danger of creating meta-metaphors, and rapidly spiraling toward oblivion. So, in a desperate effort to maintain your attention and remain airborne, let me lower my wings and get literal. Perhaps it is just a simple, physical truth that in order to achieve flight we must make a difference. That could be as simple as trying a new brand of coffee bean, adopting a neglected dog, or if you’re so inclined, creating a new vaccine. But going too far ahead of the curve might land you out of a job or earn you a ticket to the few remaining loony bins. Just remember to aim high, but when you begin to feel the burble, lower those creative wings of yours.
There will be a quiz next week.