How Shit Works - A Wing and a Principle

I still can't write about politics.

At least not now.

The Republicans are still bitching and moaning about pork even after the Democrats mollified them with a tax cut pacifier. I think I'll wait until the Obama Administration gets around to dealing with the rule of law. According to this post that Blue Gal put up a few days ago, I could be waiting a long time.

While I wait, I thought I'd introduce a new and irregular blog feature that helps me evacuate some of the useless information that clogs my brain.

I call it How Shit Works.

Click off now if you're not into techie stuff. While I consider this post very safe for work, I don't want to kill you with boredom.

Today's topic of conversation is flight. Specifically, what makes fixed-wing* aircraft fly.

* - Wings that are not supposed to move.

First, to answer the smart-asses reading this post, the not-so-subtle secret of flight is in the wings.

Well, duh.

While the first powered-flight did not take place until the Wright brothers did it in 1903 at Kitty Hawk, North Carolina, the principle upon which came fixed-wing flight is based goes back to the year 1725. That's when Daniel Bernoulli, a young-stud, Dutch mathematician, with way too much time on his hands found that as the speed of a fluid increases, the pressure within the fluid decreases.



Break out your calculators and do the math yourself. Here's the equation:


Where is total pressure, is dynamic pressure, and is static pressure. Makes sense, right?

Okay, it will. Follow me on this. Will ya?



There are several ways in which to demonstrate this effect. One way is to move the fluid through an object with a constriction as illustrated on the left. It does not matter if the fluid is in a liquid state or a gaseous one. The effect is still the same.





What's more is that the same principle applies if an object is moved through the fluid, as in a wing through air. The curve on the upper half of a wing forces the air mass passing over it to move faster than the air beneath it, creating a pressure differential that literally sucks up the wing and all objects attached to it.

It should be noted that Bernoulli showed no interest in building a flying machine. The first practical application of his idea was used in measuring blood pressure in humans.

In the intervening years between the time Bernoulli published his principle and the Wright Brothers famous flight, countless people attempted to build flying machines, most of which were based on the way birds fly.

That's not to say that there were no important advances in flight in those prevailing years. Beginning in 1809, Sir George Cayley of Brompton, England, a wealthy landowner and inventor published three detailed papers explaining how it was folly for humans to try and fly like birds. He opined that in order for a heavier-than-air craft to achieve flight, the thrust and lift mechanisms need to be separate, and that the wings on the aircraft need to be in a fixed position.

This was a huge leap forward, but the idea never really took off until a German engineer named Otto Lilienthal developed a table of lift by curved wings in 1891. He borrowed heavily from Sir Cayley's ideas while experimenting with hand gliders. Sadly, Otto died in a hand-glider accident in 1896.

It was Lilienthal's work that influenced George and Orville Wright's success. What made their flight so special was they were the first to incorporate control surfaces that stabilized their airplane along three axis of movement, known as pitch, roll and yaw. As the illustration below demonstrates, the control surfaces on the horizontal stabilizer (elevators/pitch), the wings (ailerons/roll), and vertical stabilizer (rudder/yaw) help an airplane maintain level flight and allow it to directionally maneuver in flight.

It is the Wrights' discovery that spawned modern aviation.

Captain Chesley Sullenberger knows all about this principle. When his airplane lost thrust shortly after taking off from LaGuardia Airport in New York City, and realized it would not make it to another nearby airport, he turned Flight 1549 South with its ailerons and rudder to align it with the Hudson River. Then, using his elevators, he tilted the nose of the plane downward to increase speed, allowing the wings to do their work. At the last moment, he pitched the nose of the airplane up -- again, with the elevators -- so he can safely splash down onto the river and hydroplane to a stop.



Okay class. That's all for this installment of How Shit Works. Until next time, this is Professor Useless Information signing off.