Back to airfoils. I havent seen any mention of Bernouli Effect or Coanda effect in explaining how airfoils generate lift.
Peter

Oh no, Peter; don't start that one!!!![sm=what_smile.gif][sm=confused_smile.gif][sm=75_75.gif][sm=72_72.gif][sm=50_50.gif]

Last thread about that had about 200 posts.............

The jury is still out on this one. If you ever want to start an argument between two aerodynamic engineers, ask them which force produces lift.

Personally, I subscribe to the theory that the Coanda effect deflects air downward, and Newton's third law of motion (for every action, there is an equal and opposite reaction) takes over.

Bernoulli's Principle has little to do with it. But that's my opinion, others may differ.

Well, there is the possibility that they BOTH contribute to generating lift along with the plate effect of the lower surface of the wing.
Peter

Here we go again...................[sm=spinnyeyes.gif]

That's just it - there are so many contributing factors that it's hard to pinpoint just what's causing it.

Of course, the plate factor is a direct result of Newton's third law, so the evidence appears to point to that as having the most to do with it.

The truth is, it's that real thin string that is connected right at the centerline of the center of gravity that holds the thing up. I know this is true because I saw the real thin string on "Men in Black 2".

Remember, as it was said on "The Spirit of St. Louis" (the movie), suspenders. That's the ticket.

There ya go.. two more theories.

CGr.

Wow! (this really isn't in response to your post CG, it's in general to the thread). A pilot, early on,is the product of his/her environment, so.... (something for the IPs to think about)
Anyhow, theories aside, hold your hand flatpalm down outside your car window while driving about 35-50 mph (more speed means more "ouch"). Then lightly tilt it up, hmmmm. I think you'll find that all those tiny molecules of air do a bang up job of deflecting orpushing your hand upward. Not the engineers explanation, but a very simple way for someone with no knowledge of it to see it and feel it in action. As for dihedral, what about those airplanes with anhedral in the wings? I guess that's why the AV-8 has to do VTOL. Camber, you could call any wing that uses DLE's or leading edge slats and trailing edge flaps a "cambered" wing, look at the cross section of the airfoil with slats and flaps deployed (DC-9, B-727, B-737, NA-40, DA-20 to name a few)
Fly smart, flysafe!
hQQk

Looks like you guys scared off korps
I've read the arguments on lift go back and forth over the years but I found the manuscript of (sorry I can't quote exact references) One engineer arguing with NASA or terms and the inaccurate models that are still out there that mislead how lift occurs. The explanation given is that the aircraft/body etc itself has to be seen as the object that the force is being exerted on. The resultant force comes from the change in the momentum of the fluid or air (insert your various airfoils for desired effect) that results in creating a greater amount of accumulated perpendicular force on one side of the body than the other resulting in what is termed lift. The dynamics of what is happening in the fluid on the top side is secondary in regards to, changing air velocities, pressure, drag etc.

So to Korps the airfoil that creates lift, and look up Wikipedia definition in the link provided earlier as it is from Nasa's rewrite of the definition, is changing the momentum of air to exert a greater force on the body or airfoil on one side more than the other by how it changes the momentum of the fluid or air on one side over the other.
And oversimplifying... the top side of the fiol changes the momentum of the fluid to not act on the body perpendicularly as much but since the air on top and botttom have the same mass the air on top instead exerts it force in the way of drag which is more so a horizontal force which is overcome by the forward thrust of the aircraft. So the top side air doesn't get a chance to cancel the bottom side perpendicular force.

I'm in the middle of gluing a plane together but I couldn't resist throwing in a simplified explanation at the risk of being attacked for it. Oh well....

Jeez, but you guys have been busy yesterday. Damn!

I now get what airfoil is about and how lift works (well it seems that people have different ideas about it), but I have the basic knowledge now.

Newtons third law I know, but what on earth is this Coanda effect? Somewhere I have heard this term used in a discussion, but I was listening with half an ear so didn't really catch the whole debate. As I could gather from what was said that evening was that the Coanda effect is when a gas flows over a convex contour that it will follow this surface over which it is going - and if I have to implement this theory into a planes wing it will then result in a downward "push" which will cause lift. Is this correct? Sorry it's early - to lazy to do a google now

Very simply stated an airfoil when passing through the air creates lift. How this occurs is the wing, if it is semi or symetrical is curved at the top and bottomand it takes longer for the wind to pass over this curved surface. As a result based on a principle called bournoulis (forgive my spelling)principle, (same as a venturi cut in half) this causes a low pressure moment on the part of the wing that is pointed up. (An airplane flying level will always have a high angle of attack eitherinverted or right side up.As a result the wing wants to lift towards the low pressure area to fill the void, this is called lift.

A flat bottom wing is more stable and will want to right itself due to the nature of the wing being flat on the bottom and curved on the top.

A semi or full symetrical wing is more aerobatic in nature and will tend to stay where you point it.

Di-hedral is another aspect that helps flat bottom wings be more stable and self righting, the more dihedral the more stable the airplane, on a flat bottom wing.

hope this helps

Glenn Williams

Wassamatta minnflyer? Does your chunk of kansas lack swimming pools?

From what I have read and can understand,change in momentum (Newton) and pressure differential (Bernoulli etc.) are not necessarily at odds with eachother; rather different ways to look at it. But that comes from a book that I have as my primary source of enjoyment reading on aerodynamics etc. I must admit though, the bookseems to confuse me on as manyoccassions as it seems to clarify . I've made a mentalnote to go back and reference this tidbit...maybe I can pass it along.

Having said that though, there is one part of this that I had been studying relating to a post I started in the Aerodynamics forum on Spanwise Life and Stall Sequence.You guys did a great job helping my understanding of my primary question. But in studying it further I got twisted around on the concept of vortices generating the change in momentum (as if vortices were a good thing!). I need to formulate my question better and I have been meaningto add it to the other post but haven't got around to it yet. I'll do that soon. See you over there and thanks in advance for the help!

To thegentleman that referenced anhedral I think we are more likely to see this on swept wings like in jets and high speed applications. While thesweep is needed for high speed/super sonic stuff it also producesa dihedral effect that the anhedral serves to compensate for...There is alot written about it by people smarter than me but this is the basicprincipleof it.

On adifferent note, I have REALLYBIG plans to take my 10 year old flying today.The snow is gone, it's cool but drytoday, and the first flights of the year in upstate NY are always a reallybig deal!!

Keep up the good work guys, talk to you later!

Tom</p>

Korps, simple put, the Coanda effect says that when a fluid (remember that air is a fluid) flows over a concurved surface it will "stick" to that surface.

Think of putting the back of a spoon vertically into a thin stream of water. The water will follow the contour of the spoon instead of just dropping straight off.

Kavic Minnflyer did not say that you quoted the wrong person Sheesh!


OK I,am outta here to go fly my airplane:

The self righting nature of trainers has less to do with the airfoil type and more to do with the decalage and the placement of the CG further ahead of the center of lift than is required for positive stability. This increases the airplane's speed sensitivity.

The symmetrical airfoil has equal response to positive or negative angles of attack and zero pitching moment, while the flat bottom wing has a large negative pitching moment in response to creating lift.

Dihedral has nothing to do with type of airfoil.

High Plains, Dihedral definately plays a part in self righting characteristics. I don't see how you can deny this. I have a nexstar. The plane was very difficult to fly inverted with a dihedral wing. It was also a very forgiving plane. I wanted a more aerobatic plane, so I removed the dihedral. It now holds inverted flight much easier than it did. It is also less forgiving and more sensitive. I thought Minnflyer did a very good job of explaining this. From a physics point of view, it just makes sense. I also agree that a new pilot should be able to fly inverted figure eights with a trainer. It takes alot of concentration, increases skill, helps get a new pilot used to different orientations, and can be done. I don't think that minnflyer was saying it couldn't be done. It's just more difficult to do with dihedral.

It would be nice if you read the posts a little closer and considered what was being said. Quote me to point out where I said what you are saying, because it is not there.

Highplains, forgive me. I read your post above mine and interpreted it wrong. A question for you. Does Dihedral adds to the stability of a plane in level flight no matter what kind of airfoil is present?

Yes

Thanks.

While this is true of what is happening to the fluid, the argument was made that a vacuum doesn't apply any law to lift the plane. The fluid is not made static/electromagnetic enough so it does not draw the body/foil into the vacuum. Rather the vacuum which is looking at the state of the fluid, is a state where the momentum of the air in the vacuum is not directing a force on the body equal to the force excerted on the bottom of the body experiencing the greater force of momentum or pressure. So more accurately the pressure translated in to force is greater on the bottom of the body and thus is pushing it with greater force than the pressure on the toop of the body.
This is what the engineer was arguing that looking at the fluid is looking at the fluid but not lift. Lift is the result of what happended in the fluid to create a greater force on one side of the body than the other. Why this becomes important is when you are then combining various ways of changing the momentum like where a votex meets a fence or the canard on a SU-37 changing the stall point of the flow over the wing meeting the vortex or the sweep of a wing and the use of winglets etc. etc. etc.

The reason why this was argued was that models based on looking at the state of the fluid rather than its actual force excerted on the body lead to various inaccurate models like the vacuum sucking rather than the pressure pushing.

He really simplified it by saying I lift a box... that's lift. The fluid has little to no consideration. I take a air hose and blow on the box that is lift with the fluid. The air foil is just one of many diffferent type of air hoses nozels. Lift is the resulting force pushing the body up or down.
Thus engineers seek various ways to generate this force via vortex, lifting bodies and the use of vorticies over strakes, fences, canards, area rules etc. to generate lift in ways that go beyond the convention foil.

Yes Bernoulli and the many other calculation of what is happening to the fluid all apply but lift is the exploitation of the afore to direct the force from the moment of the air on the body to create lift.

let's simplify this. I will go one step further in simplicity.

Take a piece of flat cardboard. Go in front of a fan and place the cardboard where it is streamlined into the wind blast. There are no forces acting on it to produce either positive or negative lift. Now tilt the flat piece of cardboard up and now you have lifting force. Same as if you point the piece of cardboard down. What this simulates is angle of attack. Now take the cardboard and make a curve in the leading edge like a wing. Do the same tilting motion. It will be more smooth in it's transition to the up side. This is excersizing bernouilis (Spelling again) effect. The wind going on top of the curved surface takes longer to get over the wing than on the bottom In essence that my friend is "Lift". We can debate all day long.

Here are my qualifications if you are interested.

22 years as an A&amp;P and private pilot.
Background since childhood has been full size aircraft.
I have worked for Lear Jet, Bell Helicopter and a few others.

If you like you can pick up any pilot trainng manual and in essence everything I have written is the same.

You cannot argue with Physics. You can try but it just wont hold water. Speaking of which. Someone was talking about fluid a couple of posts back. Air and water can be considered a fluid. However you cannot fly an airplane under water, Last time I checked that is for submarines. Our fluid "Air" is less dense and does not act the same as water. It will be similar but not quite. Pass an airfoil in the water and place dye drops in front of the leading edge and you can see a similar comparison to our wings. However the trailing edge turbulence in water in completely different than air. That is another debate.

Glenn Williams

Willig10, yes, changing the angle of attack will undoubtedly creat lift.

What the OP wanted to know is, "How does an airfoil create lift?"

In other words, your flat piece of cardboard, while being held parallel to the airflow does not create lift, however, a flat-bottom wing being held parallel to the airflow will.

Most flat bottom airfoils will create lift until the angle of attack is somewhere between -2 and -4 degrees. Since on trainers they are often mounted with slightly positive incidence, these means that to fly inverted, you have to have more than 4 degrees nose up to create lift and significant speed.