Cubdriver

I just heard Ira Flato, the big science guy who does NPR's Science Friday series claim that aircraft wings do nothing on the bottom side as far as lift is concerned and it all comes fom the top side. Brilliant! I can't believe it, next week he will say the earth is flat. And this is coming from NPR of all places. He said that engines and armaments like rockets are mounted on the underside of wings because nothing much goes on under aerodynamically, and it's a great place to put stuff. I think someone should offer to put him under there and go flying. No wonder the public is so dense about aviation.

KiloAlpha

You only need the top portion of the "wing" in order to create lift. No need for a bottom, although I wouldn't say that is has no effect of lift.

Cubdriver

Suction on the top is not even half of the lift force being generated. Most of it is from the air hitting the bottom of the wing and deflecting downward. Air has mass, so if you throw it downward then by Newton's second law (F=ma) there has to be a reaction upward by the wing. As a thought experiment, imagine trying to hold a piece of plywood in the air as you go fast. It will lift like nobody's business. At about 40 mph or so you won't be able to hold it down. There will be some lift from the topside due to air trying to get over the top and meet up at the back, but most of it is from air hitting the bottom side and being thrown down. Downwash is the same thing, air that made it around the wing at an accelerated speed due to venturi effect, getting thrown downward behind the wing. Both forces contribute to lift (Newton and Bernoulli) although it is inaccurate to say they simply add up. It's also way off to say the topside of the wing is the only place where lift is created. Circulation is the total picture, lift is created from air circulation around the wing. Here's a pretty good link explaining circulation.

daytonaflyer

There's a book called Stop Abusing Bernoulli that claims the popular way lift is taught in text books is incorrect and the wind deflection theory is the correct one.
However, I don't agree with your plywood example since that is more of an example of how drag works than lift. The reason it's hard to hold onto the piece of plywood is due to increased form drag as you accelerate, not increased lift. Remember, drag is a byproduct of forward motion (thrust), which is why it becomes harder to hold onto as you speed up. Impact air does supply some lift, but I don't think imagining a piece of plywood is a good way to explain it.
For example: no matter what speed you're driving before you let go, once you do, the plywood would not continue to climb higher into the air due to excess lift. It would simply fall to the ground.
Using your example, the plywood should continue to develop enough lift to gain some altitude, however, in reality, it would not.

Cubdriver

Ok use a kite as an example then. As long as you hold the rope and there is some wind, up she goes. I would be willing to accept that even a kite is not a very good thought experiment though, because all lift is a mix of Newton and bernoulli and you cannot separate them out so easily. This may be why so few people understand lift. You really need to work with a variety of airfoils under a variety of conditions to understand. For example, smoke tunnels show air flow, airfoil codes show pressure distribution, and in both you need to change angle of attack, airspeed, and airfoil shape to get an understanding of what goes on. This plus a ton of theory helps. There is a basic discussion in Pilots Handbook of Aeronautical Knowledge (PHAK) on lift. Somebody needs to send it to NPR.

rickair7777

That's all wrong...the only exception might be certain extreme aerobatic aircraft while doing extreme manuevers.

Bernoulli (on top) provides the vast majority of the lift...we could not fly without it. Newton (equal-and-opposite reaction on the bottom) provides some lift, but the amount is far smaller than bernoulli in normal ops and varies with flight conditions and wing design.

For a typical subsonic aircraft the lift breakdown is like this...

Bernoulli: 70-90%
Newton 10-30%

It should be obvious that high angles of attack produce more Newton. But in order to achieve Newton lift you need a large deflecting surface...large surfaces in the slipstream create large amounts of drag. Because drag is product of Newton in this case, we prefer to use as much Bernoulli as possible (it has it's own drag, but far less than Newton). Airplanes are designed for max Bernoulli lift in cruise flight to reduce fuel burn and extend range.

HSLD

This text is a good review of Aerodynamics:
http://www.amazon.com/Aerodynamics-N.../dp/156027140X

subicpilot

This has to be about the dumbest "thing" I have ever heard come out of a pilot's mouth...

On second thought, maybe you should take this idea and run with it...think of the weight savings! You'll be rich!

Then again, I think your avatar has a better understanding of lift than you do...

aero550

Now, throw in a treadmill and we've got us a party.

FlyerJosh

Man, I was just thinking that! Great minds think alike... so do ours!)