Mike SVOR

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Not sure if this is going to ruffle some feathers, but I'm about tired of hearing people say that all the lift is generated from the top side of the wing.

skeeter_ca

Are saying this is not true or not complete?

skeeter

Mike SVOR

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Well its not really true.

The curved top wing is designed to eliminate stall upon high angles of attack and slower than efficient speed over the wing.

There is some downward redirection of airflow going on here but at say 5 degrees of downward flow, this doesnt make the plane fly.

It's not the low pressure on top of the wing that makes a plane fly, it's the high pressure on the bottom of the wing that makes it fly.

mboland

Or are you just tired?

What exactly were you trying to get going with this topic?

'Why do people say the top of the wing causes the plane to fly?' umm .... maybe cause it does, ever tried one without a top?

but then you could argue that it is the movement of the wing through the air, and so on, and so on.

I think the subject is called Aerodynamics

Mike SVOR

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so you are saying that a plane with perfectly flat wings or perfectly symetrical wings wont fly?
remember now, if it's a symetrical airfoil, the bottom would cancel out the top of the wing if this theory was true about vacuum causing lift.


and yes, I have tried flying without the top of a wing before.
Great Planes Trainer 40. I removed the entire top monocote and flew it with just the bottom monocote in place.

mboland

Yes, that's exactly what we are both saying.
Unless you give it an angle of attack, thereby providing a pressure differential.
Some say it's the drop in pressure over the wing (Burnourley - how is that spelt?) or rise in pressure under the wing (Newton -much easier to spell his name)
There is apparently an excellent book around called 'Model Aircraft Aerodynamics' which I hope to locate one of these days myself.

crasherboy

I have always thought that the idea that the wing top shape is what keeps the plane in the air is something along the same lines as the argument that if a tree falls in the forest and no one is around to hear it ,there is no noise. Oh really? If vacume on top of the wing is all there is to it,then a bumblebee could not fly! He is to heavy for the limited amount of vacume that is available. Or you could say the to skip a flat stone on the water the vacume on top of the stone is what keeps from sinking into the water. What say you to that?!

ArCeeFlyer

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That's a nice little book. It was first published in 1978. I bought the second edition in 1992 pictured below. They still sell it and it's up to the fourth edition now. Here's a link to it on Amazon.

[link=http://www.amazon.com/Model-Aircraft-Aerodynamics-Martin-Simons/dp/1854861905]http://www.amazon.com/Model-Aircraft-Aerodynamics-Martin-Simons/dp/1854861905[/link]

OffroadBEAR

My Feedback: (2)

The two books below are good books regarding aerodynamic theory and application. Fundamentals of Aerodynamics is heavy on theory, but it can better explain "where lift comes from," and Introduction to Flight is a great book regarding applied aerodynamics and aircraft performance.

[link=http://www.amazon.com/Introduction-Flight-John-D-Anderson/dp/0071263187/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1221785734&sr=8-1]Introduction to Flight[/link]

[link=http://www.amazon.com/Fundamentals-Aerodynamics-John-D-Anderson/dp/0071254080/ref=pd_bbs_2?ie=UTF8&s=books&qid=1221785734&sr=8-2]Fundamentals of Aerodynamics[/link]

Lift force is generated by pressure differential between the top surface and the bottom surface of the wing. It is not one or the other.

I have the fourth edition of "Model Aircraft Aerodynamics," and a very nice, cut and dried explanation of how an airfoil generates lift is given in the beginning of the book.

BMatthews

You folks may want to do some searches on "lift bernoulli newton" and spend an evening reading the results. There's been some really long and interesting threads on this over the past couple of years.

Bottom line is that I don't see much in the posts in this thread so far that are correct at all so far other than the advice to buy Martin Simons' book.

banktoturn

Mike,

It is the pressure difference between the top and bottom surfaces that produces lift. It's specifically incorrect to say that it's the high pressure on the bottom of the wing that makes a plane fly. It is entirely possible, and not uncommon, for the pressure on the bottom of a wing to be lower than the ambient pressure of the air away from the wing. It is completely nonsensical in this case to say it is the high pressure on the bottom that is causing lift. Moreover, when airfoils are designed, it is common for the shape to be modified to give a specific pressure profile on the top surface. The pressure profile on the bottom surface is not generally considered.

It is more legitimate to characterize the top surface as the object of wing designers' scrutiny. In casual conversation, I would be inclined to say the top surface is the critical one, and the bottom surface is just along for the ride.

banktoturn

Mike SVOR

My Feedback: (1)

[respectfully]
I really don't agree with any of that, except for the designers taking careful consideration of the top wing because that would compliment the aircraft's projected speed envelope.

The top of the wing is designed to maximize airflow and NOT cause a vacuum. If it were only trying to create a vacuum, then there would be no upper wing area after the curve, creating a huge vacuum'd surface.

Take a formula 1 car's rear wing. Do you think the car's downforce is caused from the front facing (upward turned) section of high pressure or because of the back side of the wing causing low pressure and it being sucked to the ground?
Mike

banktoturn

It's not clear to me what you disagree with. Airplane wings can generate lift even when the pressure on both surfaces is lower than the ambient pressure. Do you disagree with this? To me, this pretty much says that it's not "high pressure on the bottom" that makes an airplane fly.

I don't know what you mean by "maximizing airflow", but the shape of the wing is definitely designed to produce lower pressure on the top surface. You have already said you disagree with this. Perhaps you could explain why.

The lower surface of a Formula 1 wing definitely generates lower pressure than the ambient air, and lower pressure than exists on the top surface. Because those wings tend to operate at high angles of attack, it's possible that the pressure on the top surface is higher than ambient, but this condition is not necessary for a wing to generate lift. To answer your question, I know that the Formula 1 wing generates downforce by creating lower pressure on the bottom surface than on the top surface. If you prefer, it creates higher pressure on the top surface than on the bottom surface. It is completely invalid to consider the pressure on either surface alone; only the pressure difference is significant.

It's not valid to assume that either the bottom surface pushes the wing up or the top surface sucks the wing up. As intuitive as this may seem, it is not a valid explanation of the way a wing generates lift.

banktoturn

rmh

Ok sport
how about this:
lift occurs ANYTIME there is a pressure difference- between bottom surface and upper surface .
the shape means NADA
The lift is simply a result of mother nature trying to equalize pressure.
Or my third rule of aerodynamics which states : lift is drag and drag is lift .
You can't have one without the other .

anytime lift occurs , thre is an unbalance in air pressure - and drag. If you could get lift without drag - you would zip off to the moon.

banktoturn

Dick,

I'll assume that I get to be 'sport' today.

I can agree with much of that. Lift indeed occurs when there is a pressure difference between the top and bottom. I don't agree that "shape means NADA", because the shape is what we use to cause said pressure difference. Nature will indeed try to equalize pressure, but I personally wouldn't say that lift is the result of the equalization; it's the result of the inequality. To say that "lift is drag and drag is lift" is incorrect and unhelpful, as the two quantities are unambiguously defined and unambiguously different. I would say instead: "there can be no lift without drag".

banktoturn

onewasp

To say that "lift is drag and drag is lift" is incorrect and unhelpful, as the two quantities are unambiguously defined and unambiguously different. I would say instead: "there can be no lift without drag".
A difference in semantics only.

I'll take Dick's view all the way as it causes thought rather than "Oh, THAT's the definition."

If you think through what is (what has been said here) said including your quote you end up in the same place ____ all be it by different conveyances.

I had a grad school Prof who would state things at their harshest to promote the same type of thought.
It works! It is an excellent teaching device.

OffroadBEAR

My Feedback: (2)

Drag is aerodynamic force that is parallel to the flow velocity, which has the same direction as the flow velocity.

Lift is the (positive-upward) aerodynamic force that is normal to the flow velocity (perpendicular to the flow velocity). Lift is not drag and drag is not lift.

In the case of a non-rotating cylinder or a fully symmetric airfoil at zero angle of attack (with respect to flow velocity), there is drag without lift. The pressures at the top and bottom surfaces are the same, resulting in no net force. However a body cannot generate lift without generating drag.

ArCeeFlyer

My Feedback: (1)

[sm=thumbs_up.gif]

Top_Gunn

My Feedback: (6)

I think we all agree that there's lift only when the pressure on the bottom of the surface is greater than that on the top. Since this is so, it is wrong to attribute lift to the bottom only (or, for that matter, to the top only). That would be like arguing about which blade of the scissors does the cutting. The "sucking" one gets from a vacuum (complete or partial) and the "pressure" that causes something to move toward a vacuum are the same phenomenon, described differently, not two separate things. When you drink a milkshake through a straw, it's air pressure that pushes the shake up the straw when you reduce the pressure inside the straw. Most people would say you've sucked the shake up the straw; nothing wrong with that.

To those who seem to think the shape of the top irrelevant: consider slats. They increase lift (by increasing the speed of the air over the top of the wing) without in any way changing the shape of the bottom of the wing.

BMatthews

There HAS to be a pressure difference or there's no lift. However if you did the search I suggested you'll also have found that along with the pressure difference there's a redirection of the airflow mass that also HAS to be there. These two are linked and interdependent and are an integral part of any surface be it flat or curved or a spinning cylinder (magnus effect) that is generating lift.

So why do we fret over airfoil shapes so much? Because an optimized shape can generate the pressure differneces and airflow re-direction that goes with the pressure difference with the least amount of drag. And when we can do that with less drag the model flies better...... at least it does when it's a glider or sailplane. SOME models such as 3D stunters WANT the huge amounts of drag that come with sudden and extreme angle of attack changes.

banktoturn

onewasp,

The word "semantics" means "meaning". I suspect that you may have wanted the word "syntax". As it happens, your statement is correct; Dick's statement and mine do indeed differ in meaning. His statement is not correct, while mine is. Even so, you seem to prefer Dick's statement, finding it more thought provoking.

I don't share your view; a correct, factual statement can also be thought provoking. Give it a try, and see what kind of thoughts you get from the true statement. It's better for you, and you deserve it.

banktoturn

rmh

OK try THIS one :
when there is lift there is drag and when there is lift or drag there is a pressure differential. You may not think what I said is true but you would be hard pressed to proove your point in an open debate . all three are irrevocably linked

Efficiency is what you go to airy plane theory school to learn. This is where you get lost in seeing the obvious.
You say lift and drag are always in concert .
I say they are simply parts of an orchestra.
perhaps we should coin a word which suggests they are one. - -
how about - drift?
Sorry that one has been taken
-I'll work on it.

Jezmo

Soda and popcorn anyone. I smell a troll and I know his screen name. I've got better things to waste time on.

Mike SVOR

My Feedback: (1)

I seriously hope you're not refering to me.

I've been on this board for years.

OffroadBEAR

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Just out of curiosity Dick, did you go to airy plane theory skool (this is in no way meant to be an attack, just an honest question)?