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Air Force Museum error?

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Air Force Museum error?

Old 10-26-2013, 03:39 PM
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bokuda
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Default Air Force Museum error?

On a visit to the Air Force Museum last summer I saw a placard in the aerodynamics section that said the curvature of a wing's airfoil causes lower pressure on the upper surface of a wing than the lower and the wing is "literally sucked upwards." I had quite a discussion with one of the docents who could not understand why I saw this as an error.

What do you think of this?

I was concerned because the Air Force should obviously be knowledgeable about aerodynamics and this sign is read every day by the public.
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Old 10-26-2013, 05:46 PM
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They're just using simplistic terms that won't give the general public a massive headache caused by confusion. Most people wouldn't understand Bernoulli's Principle and how it relates to aerodynamics.

Last edited by jkpape; 10-26-2013 at 05:51 PM.
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Old 10-26-2013, 05:48 PM
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Originally Posted by bokuda View Post
On a visit to the Air Force Museum last summer I saw a placard in the aerodynamics section that said the curvature of a wing's airfoil causes lower pressure on the upper surface of a wing than the lower and the wing is "literally sucked upwards." I had quite a discussion with one of the docents who could not understand why I saw this as an error.

What do you think of this?

I was concerned because the Air Force should obviously be knowledgeable about aerodynamics and this sign is read every day by the public.
I agree with the statement on the placard ............and with the docents maybe ............. and it would be interesting to learn what makes you perceive it as and error.
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Old 10-26-2013, 06:02 PM
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Originally Posted by Lnewqban View Post
I agree with the statement on the placard ............and with the docents maybe ............. and it would be interesting to learn what makes you perceive it as and error.
It is incorrect because air cannot "suck." The wing is being pushed up by the higher pressure on the lower surface. It's basic physics.

I don't think this is too difficult for the average person to understand.
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Old 10-26-2013, 06:16 PM
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Most people, if they can't touch it, feel it, or see it, have a hard time comprehending it. Especially when it comes to theory.
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Old 10-26-2013, 07:16 PM
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When you suck you are lowering the pressure and the higher pressure is forcing whatever you are sucking.
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Old 10-27-2013, 05:32 AM
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I do not see it as an "error" at all. It is merely another way of stating it. It is stated in a way that the greatest number of people will understand it.
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Old 10-27-2013, 05:43 AM
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All that you would ever want to know on why airplanes fly
http://www.allstar.fiu.edu/aero/airflylvl3.htm
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Old 10-27-2013, 05:44 AM
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Originally Posted by bokuda View Post
It is incorrect because air cannot "suck." The wing is being pushed up by the higher pressure on the lower surface. It's basic physics.

I don't think this is too difficult for the average person to understand.
Actually, many things can suck and do all the time. When you lower the pressure on one side of an object or place, the "normal" pressure on the other side of the object or place, combined with the lower pressure opposite causes a force that moves the object, or moves the air within the area of divergent pressures.

You're absolutely right that it's basic, but it appears you're simply not happy with the way the museum phrased it.

Modelers talk all the time about our motors sucking air into the carbs. It's the same thing. The model motors aren't pulling the air in, they're creating internal pressures that are lower than the atmospheric pressure outside, and the atmosphere pressures air into those engines. People often make up terms like "suck" that mean more than one words worth of definition.

BTW, I used the word "motor". Same deal.

Last edited by da Rock; 10-27-2013 at 05:48 AM.
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Old 10-27-2013, 05:54 AM
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That is the description that has been given for decades. I saw something not long ago stating that's not really what is happening. Unfortunately, I don't remember what the person claimed was actually happening. But I decided it didn't really matter. I'm pretty for sure that wings work.
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Old 10-27-2013, 06:31 AM
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air cannot "suck." The wing is being pushed up by the higher pressure on the lower surface. It's basic physics.
I don't see any problem with the AF explanation either. It's a cumulative result of pressure differential, air deflection (action/reaction), and has been taught that way for decades.
I could cut & paste a couple chapters from my old "Aerodynamics for Naval Aviators", but that would further confuse the issue.
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Old 10-27-2013, 07:31 AM
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You can say the lower pressure on the top is pulling the wing up and/or the higher pressure on the wing on the bottom is pushing it up. To seay it sucks the wing up is wrong because there is no fan or pump pulling air off the wing, as with a vacuum cleaner holding a piece of paper at the nozzle. That is not what is happening at all.
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Old 10-27-2013, 08:06 AM
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To seay it sucks the wing up is wrong
No, that's exactly what's happening. Pressure differential is how a Shop Vac works, after all.
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Old 10-27-2013, 08:36 AM
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To seay is not correct either, you mean to say!!!!
To suck, on a straw for example you decrease the pressure in your mouth! Get it. Higher pressure outside pushes the soda into your mouth!
It is the USAF, the higher authority in flying things in this country, believe me they KNOW aerodynamics.
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Old 10-27-2013, 08:53 AM
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They are talking about the "Bernoulli Effect." The effect is real, but here's the thing: How does a symmetrical wing get "sucked upward," or a flat piece of Depron foam on an electric foamy? It doesn't. Lift is created because air pressure is higher under the wing. Your hand is not shaped like a Clark Y airfoil, yet you can create lift with it by sticking it out the window of a moving car and tilting it slightly so its angle of attack to the oncoming relative wing creates lift, or pressure under your hand that causes it to fly up.

Higher pressure is created under a wing by increasing its angle of attack to the relative wind. It's as simple as that. I suppose you could say that having higher pressure on one side of something causes it to be "sucked" to the other side, but why confuse the issue?
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Old 10-27-2013, 10:21 AM
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Does a jet engine push against anything to make it move, or does it suck it's way along?
On that note, how about a balloon? Does it push or does the low pressure inside as the nozzle is released "suck" it forward...
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Old 10-27-2013, 10:53 AM
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To be semantically correct there's no such thing as suction. The universal constant is primarily a total vacuum. Everything else is a variety of higher localized pressures that try to move from a location with higher pressure to one with lower pressure in an attempt to equalize the difference and attain a homogenous balance.

Our planet earth happens to use gravity to trap and constrain some air at what happens to be 14.7 lbs/sq in.... give or take a little. And things we do can shift this in a highly localized manner one way or the other as well. At all times though we still retain some amount of pressure that is greater than a universal vacuum. So no, there's no such thing as suction.

But it's sure a lot easier to say and it seems to be pretty universally understood. Even you guys know what it means even if some of you take exception to the use of the term.

This is supposed to a forum for aerodynamics and not about semantics. Unless there's a shift in focus towards some form of aerodynamics content I'm going to lock this thread later today.
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Old 10-27-2013, 11:22 AM
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Originally Posted by bokuda View Post
It is incorrect because air cannot "suck." The wing is being pushed up by the higher pressure on the lower surface. It's basic physics.

I don't think this is too difficult for the average person to understand.
A quick response before BMatthews locks this thread:

The reason for which I believe that they are explaining what really happens in the most understandable way for a lay-person is more aerodynamic than semantic.

The fact is that any airfoil at certain angle of attack induces higher air velocities over the upper surface than under the lower surface.
In each case, the absolute value of the measured pressure on the top (below atmospheric value) is higher than the absolute value of the measured pressure on the top (above atmospheric value).

What really does the work of lifting is the difference of the average of both values times the area of the wing.

Total P differential = Top mean P + Bottom mean P

We invented the concept of pressure, which in nature is nothing but the number of molecules of air times their kinetic energy.

The airfoil going through a mass of air does the magic of creating two different "zones of disturbance" for those peaceful molecules.

What happens in the upper zone is so influential that it determines where the center of pressure (CP) is located along the chord.

More can be read here:
http://www.grc.nasa.gov/WWW/k-12/airplane/cp.html



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Old 10-27-2013, 11:27 AM
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I also agree with the Air Force statement. It may be simplistic but they DO know what they are talking about. It Bernoilli's effect.


Vacuum lifting a wing is more accurate rather than pressure pushing up a wing. The top of the wing forms an area of lower pressure either by its shape or angle of attack (in the case of a symmetrical wing). The faster the wing moves the greater the lower pressure or vacuum. The point on the wing with the lowest pressure is known as the "center of lift".


If the wing was lifted from high pressure underneath as some here are saying then why would a wing ever stall?


A wing stalls because the boundary layer of air has separated from the wings upper surface causing a loss of lift, vacuum, being sucked up or whatever you want to call it.
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Old 10-27-2013, 12:13 PM
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Aerodynamics for Naval Aviators...a great resource.

https://www.sportys.com/PilotShop/product/13307
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Old 10-27-2013, 01:07 PM
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Why lock the thread? Just some good discussion going on.

Is is education bad?
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Old 10-27-2013, 01:12 PM
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Originally Posted by jkpape View Post
All that you would ever want to know on why airplanes fly
http://www.allstar.fiu.edu/aero/airflylvl3.htm
Retired Airline Transport Pilot here and do you really think that I even care anymore ? LOL
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Old 10-27-2013, 01:21 PM
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Originally Posted by Quikturn View Post
................If the wing was lifted from high pressure underneath as some here are saying then why would a wing ever stall?...........
That is a very good point, Quickturn !!!





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Old 10-27-2013, 02:57 PM
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Why is it called "lift" and not "push".

I've worked on jet aircraft for 40 years, military for 24 and now civilian. They all suck.
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Old 10-27-2013, 03:29 PM
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Originally Posted by bokuda View Post
It is incorrect because air cannot "suck." The wing is being pushed up by the higher pressure on the lower surface. It's basic physics.

I don't think this is too difficult for the average person to understand.
That's just perception, being sucked or pushed. To an astronaut being "sucked" out of a pressurized spacecraft that had a hull breach, I doubt he'd describe it as being "pushed" out versus "sucked" out despite being right or wrong. It's like cold, there is no such thing as cold really, just lack of heat but people still think the refrigerator and A/C make things "cold" versus conduct and transfer the heat away...

Jack
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