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Who is right on lift the FAA or NASA?

rumpletumbler

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Jul 3, 2002
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I loathe aerodynamics. Everytime I think I'm getting a grasp I read something else that says, "nope it's not like that it's like this." All from credible sources. I have an FAA examiner telling me that Jeppensen textbooks are wrong. I guess before my checkride I should call the DE and say, "How do you think lift is produced? and are you an adverse yaw junkie?" so I'll get it the way he wants it then. Seems like something like aerodynamics would be a "STANDARD" it is mathematical isn't it? Are there any two folks who agree on it?

Check this out:

http://www.grc.nasa.gov/www/k-12/airplane/wrong1.html

Edit: they actually show two more so called incorrect theories, here:

http://www.grc.nasa.gov/www/k-12/airplane/short.html

RT
 
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flydog

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Its not that its "Wrong" its that the actual lift theory is way more complicated. For pilots and the average person this theory needs to be explained in layman's terms that can be understood without a mathematical or engineering degree. Suffice to say that the Aviation textbook explanation is close enough to do the job

If you want a thorough understanding of how lift is created pick up "Theory of Wing Sections". Its over 500 pages of theory. Lift actually comes from many different sources including relative wind (equal and opposite reaction), thrust vector, unequal flow around the airfoil, and ground effect (when close to the ground)

To explain the actual theory to a flight student is unnecessary and would take a very long time. They would also need a strong background in mathematics including differential equations and boundary value problems. I took a full year of Aerodynamics in College and still didnt know everything about lift.
 

Timebuilder

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First, it seems to me that Tom is agreeing that the lift is indeed caused by a difference in pressure "above" and "below" the wing. His simulator shows that the molucules of air don't have to "meet" at the trailing edge.

From what I can see, most of the change in velocity is caused by the apparent retarding of the upper flow near the leading edge, which then accelerates to equalize with the low pressure area, which extends to the trailing edge.

On a side note, I found it interesting that the maximum positive angle of attack yielded a lift value of 911 pounds.

Thanks for sharing an interesting page.
 

GeorgeTG

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who is right?!

When talkin to the FAA make sure to recite the party line about lift...

Yessir, yesmam!

for your own sake and understanding repeat after me:

Newtown makes the airplane fly...

It's not that Bernoulli is wrong.
It's just that his theories for noncompressible liquids have been misappropriated.
No argument, there is lower pressure above the wing and higher pressure below the wing, but:

Effect is not Cause!

How do you explain ground effect with "suction"?
How does an F15 fly?
could the wing be shaped like a wedge with the top parallel to the relative wind? would that shape create lift?
how does the pressure on the top of the wing know when the nosewheel comes off the ground so it can start generating wingtip vortices?

Next up: what controls altitude?!

Flame away
PM me for a less heated rational discussion if you wish...

Cheers
George
 

generaltso

Marcy Projects
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Jan 12, 2002
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The wing accelerates air downward. The acceleration is due to the low pressure area on top of the wing. Bernoulli said that low pressure = high velocity. So because there is a low pressure area on the top of the wing, the air is accelerated.

Also, the air is turned. If you look at the downwash coming off a wing, it is not the same as the upwash (or the wing would not be producing lift).

With the air turning, and accelerating, you have a force

Newton says an object at rest will stay at rest, and an object in motion will stay in a straight line unless acting upon by an outside force. This means there is a force because the air is turned and accelerated.

The force is related to another one of newtons Laws, F=ma. The more acceleration you make (the lower the pressure on the top of the wing), the greater the force (lift is the force we are taking about).

Finally, Newton also says that anytime you have a action you have an equal and opposite reaction. Accelerating and turning the air creates that force on the wing which is lift.

Just my take on it, it has been debated, and will continue to be debated, for quite a while. It's like "which came first, the chicken or the egg"? Bernoulli and Newton - you can't have one without the other.
 

surplus1

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Jan 21, 2002
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You mean H doesn't really = p + q? Woe is me. So that's why Bumblebees can't fly but do.

Good luck.

PS. Does E=mc2 ? (I don't know how to make the 2 smaller and higher. Its supposed to mean "square").
 

Purple Haze

Out there and lovin' it
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Nov 25, 2001
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Keep it simple

I agree with George TG: the evaluator is always right (at least until the paperwork is in your pocket!).

I am a simple man. Your complicated "theories" frighten me. But I do know this: a kite is a wing -- and it flies.

The simplest explanation I know of is in "Stick and Rudder: An Explanation of the Art of Flying" by Langewiesche. You can get it from amazon.com or your local library..........Simple.


Question: Are you an engineer or a pilot (or a test pilot -- both)? The engineer must understand the science. The pilot is the artist who must master the instrument and make it sing.
 
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