Acustic Properties of Horns

[Jay481985]

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On 1/18/2005 12:25:59 AM William F. Gil McDermott wrote:

When this started, I thought it was a foolish question. Now I think it is a rather profound question. Additional profound questions have come up.

I do think the notion that an airplane wing works because the air travels a farther distance over the top than the bottom is a great old wives tale . . . and should be challenged.

Look at a sail boat sail or a hang glider wing. The "wing" is just a thin piece of curved cloth. There is no difference in path length to speak of. Yet each produced an overall force perpendicular to the relative air flow. So when there is no path difference, there is still lift.

The same can be said of our little balsa wing toy gliders. There is the same sort of curve and the balsa wing is very thin. No path length difference.

In a typical airplane wing the top camber is indeed longer. Yet there are diagrams of the measured air pressure at each point along the surfaces. They are very messy. At some points on the top there is relative positive pressure. It all just averages out to a lift.

Of course we should be suspicious at any explanation that assumes the little air molecules have two synapses to rub together. It is as if the guys on the top surface "know" they have to go faster to catch up with their brothers at the bottom surface. How do they know there is a bottom surface in any case?

Smile,

Gil

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Sailboats do not have lift due to the weight and simple fact that the wind pushes perpendicular to the object.

Hang gliders actually only go down until they hit thermals. Until they hit a thermal they keep a slow decent down.

Paper airplanes even have the same bernoulli principle of air traveling faster over the top as the way you fold it the top actually has a curve.

Try this experiment, get a normal piece of paper, place the edge near your lips, and blow sort of hard over just the top of the paper, if done right the paper should raise up. It is like a wing of sort where you just forced high pressure over the top.

Little toy basla gliders probably due have a slight curve on top but it is probably very slight do to the scale size of an object.

It should be noted that race cars actually in non aero modified stock will actually produce lift do to the shape of cars in general. Though they relieve this mostly with spoilers that have reverse wings where the air rushes faster over the bottom. Some race cars abtain 1000 pounds of downforce at 200 mph.

With the theory on air molecules in general rubbing each other, actually small molecules do have friction, even light is supposed to have a miniscule level of friction as it moves through objects. (wonder why a diamond is so sparkly and brilliant? the light reflects off the diamonds facades and slows down enough to make it seem to sparkle) Also there are theories about different reasons why things have friction. two rough objects have high friction, though one very smooth object and one smooth object is better then both very smooth objects. (case in point, try to move two mirrors parrallel to each other) this goes into atomic theory where actually they believe the molecule's electrons are "grabbing" each other.

With the question on why the two air molecules need to try to get to the other side of the wing as equally as possible? that is do to equallibrium, just as if you would left a hot cup of coffee in a 70 degree room, the coffee a hour later with become 70 degrees. The universe is mostly about equallibrium, just like why we are here in the first place. Not bringing in religion and using the scientific way to explain life, the universe started out with the big bang. So technically there was a fight and explosion between all the matter in the universe and all the antimatter (antimatter does exist, it just means the electron has positive charge and the proton has negative charge. Actually CERN particle accelerator labs produces tiny bits and nasa routinely captures antimatter in space.) When anti matter and matter collide, they explode with a burst of light. But what sceintist theorize was there was equal amounts of matter and anti matter. But one problem, we are alive and living. Now I probably confused alot of people. Sorry

[sunnysal]

one last note, the correct term for the force created over a wing (or a sail) is "lift" it does not matter the orientation of the object. so a sail does create lift, even though it ends up pulling in a horizontal direction. BTW some sailboats (some racing catamarans for example) actually use wings, just like airplane wings, almost the same section, mounted on deck instead of the traidtional soft sail. they are mounted on turntables and rotated to the correct angle of attack to the wind to create maximum "lift" and hence forward movement. regards, tony

[artto]

Physics 101 for a lot people. Oh well. I didn't learn all this stuff in a few short years either (even after having taken Physics).

Bottom line: I wouldn't worry about painting the inside of the 811's. There are much more influential things that are of far greater importance to good sound reproduction.

[D-MAN]

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On 1/18/2005 12:25:59 AM William F. Gil McDermott wrote:

So when there is no path difference, there is still lift.

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Wow, this one went WAY off topic, but it is an interesting subject... I'll throw in my two cents, too, with regards to something that Gil said.

I think that there has to be a difference in air flow path sufficient to cause lower air pressure in order to achieve any sort of directional variance.

Any wing or sail device requires at least one curved surface that provides an unequal path for the air in a particular direction of air flow. Efficiency generally requires a curved surface to keep air friction to a minimum.

The action of lift is better described as "suction" in that the lower air pressure caused by the passage of air over the longer path of the wing/sail/curved panel is rapidly filled by surrounding air, with the exception that the wing itself is acting somewhat as a baffle as long as it is moving or the air is moving past it as in a wind tunnel, so the surrounding (higher pressure in relation to the lower pressure variance) air and the wing acting as a baffle, somewhat "sealing" it from instant equalization, is moved toward the area of lower pressure by the force of suction.

That is, the tendency for air to fill even a slight partial vacuum.

It is the suction that allows for sailing vessals to exceed the speed of the wind.

DM

[pauln]

There is no suction, only positive pressure - for that matter, there are no negative values of ANY physical perameter, but that's a different story.

The longer path over the wing top IS the reason for the lift. The faster air speed results in LOWER pressure relative to the slower straight path under the wing. Lift is the difference between the higher pressure under the wing and lower pressure above.

Faster air results in lower pressure because the individual molecules of H2, O2, N2, etc. have less time and likelyhood to bump agaist a particular region of the wing surface. Roughly, molecular bumps against the surface per unit surface area is the pressure.

[D-MAN]

That is a big bunch of wrong.

The effect of a partial vacuum caused by lower air pressure is SUCTION on the more positive pressure around it, the lesser pressure being the natural result of EXPANSION.

Positive air pressure is the result of COMPRESSION, the results of higher molecular density for a given area.

Planes do not fly because they COMPRESS the air under their wings. They fly because of the lower pressure created on top of their wings. They stop flying when the air density around them is not capable of sustaining a pressure differential on the wings adequate to support the weight of the plane.

Nature abhors a vacuum.

DM

[Olorin]

You guys are both right, but you're arguing over the wording. The assertion that there is no such thing as "suction" is correct if you're going to speak absolutely strictly. There are only lesser and greater pressures. It's analogous to saying there is no such thing as cold -- there are only lesser and greater amounts of heat.

In any event, you're both right that the air moving over the top of the wing at a higher rate than it is moving under the wing creates a zone of lower pressure over the wing. You can think of the lower pressure as sucking the plane up if you want to, and it works conceptually. Strictly speaking, however, it is more correct to say that the difference in pressures between the top and bottom of the wing causes the bottom of the wing to be pushed up, taking the rest of a properly designed airplane with it.

Peace.