Coming Soon:

The following books by Robert Paul Wolff are available on Amazon.com as e-books: KANT'S THEORY OF MENTAL ACTIVITY, THE AUTONOMY OF REASON, UNDERSTANDING MARX, UNDERSTANDING RAWLS, THE POVERTY OF LIBERALISM, A LIFE IN THE ACADEMY, MONEYBAGS MUST BE SO LUCKY, AN INTRODUCTION TO THE USE OF FORMAL METHODS IN POLITICAL PHILOSOPHY.
Now Available: Volumes I, II, III, and IV of the Collected Published and Unpublished Papers.

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Saturday, April 3, 2010

A PUZZLEMENT

Here is another one of those things I think about as I take my morning walk. How can an airplane fly upside down? Having studied Physics sixty years ago, I am a little rusty, but we all remember Bernoulli's Principle [same guy -- Daniel Bernoulli -- who solved the St. Petersburg Paradox and gave rise to modern utility theory. There were giants in the earth in those days. Genesis 6:4] You know, flow of air over a wing whose upper side is curved, producing differential pressure below and above the wing, known as the "lift." The faster the plane goes, the more the lift. Hence planes always take off and land into the wind, increasing the airspeed [which is all that matters] over the ground speed. So, when you roll a plane over, as we have all seen done in the movies, if not in real life, how does the plane fly? Why don't the same forces drive it into the ground?

Well, I googled the question, and found what looks like a very plausible answer. I also checked Wikipedia, and found a monstrously complicated discussion of the general subject that makes it clear that it is not at all obvious exactly why airplanes fly. The simple answer is that although flying upside down does indeed put downward pressure on the airplane, one can, by tilting the plane up [which is accomplished, upside down, by pushing the joystick down, of course], create an angle between the wing and the air that results in the onrushing air pushing the airplane up. If you balance things just right -- which the author of this answer, an Air Force pilot, says one can do -- the result is that you can fly upside down horizontally.

I am glad I thought to look this up after getting home from Europe! I do not want to have to count on US Airways to understand these things.

3 comments:

NotHobbes said...

(This may be the single most stupid thing I have ever said but....)
Tilting the nose of the plane up to combat downforce then it`s not perfectly horizontal is it?

Brenda said...

I've seen it done many times, both real and model planes. My sons and grandsons probably could give you a clear explanation but since I tune them out about such things I can't answer the question. Model plane and helicopter building and flying has been epidemic in this household since our older son could manage a glue tube. He did a demo on Zoom in the early '70's on the kitchen table and nearby grass. My contribution has been to say UhHuh at intervals.

Robert Paul Wolff said...

It is horizontal because the upward tilt is balanced by the downward thrust on the wings. The resolution of forces is such that the plane flies horizontally, even though it is not oriented horizontally.

Brenda, in my forties, I spent a good deal of time building model airplanes from kits of balsa wood and tissue paper, wielding an exacto knife. I am afraid they did not really fly [somehow I always managed to mke them nose heavy], but they looked pretty good.