Aerodymamics...

just to clarify is the bound vortex creating a lower pressure on the top of the wing? I did pull from you explination that the principale is correct to a point (mach 0.7) but for me I'm still thinking about high and low pressures and that they have to be created some how for the speeds below that. I guess the question is for planes that have the same chamber on the top as well as bottom whats stopping the bound vortex from being created on the bottom of the plane? graviety?

[edit on 22/08/06 by Canada_EH]

Originally posted by Canada_EH
just to clarify is the bound vortex creating a lower pressure on the top of the wing?

The bound vortex results in a higher speed on the top of the wing.

Using Bernoulli (wholly applicable below Mach 0.3 and partially appliciable to around Mach 0.7), the pressure is then lower.

Originally posted by Canada_EH
I did pull from you explination that the principale is correct to a point (mach 0.7) but for me I'm still thinking about high and low pressures and that they have to be created some how for the speeds below that.

See above. The bound vortex always exists (after creation of the starting vortex) until the flow is supersonic.

Originally posted by Canada_EH
I guess the question is for planes that have the same chamber on the top as well as bottom whats stopping the bound vortex from being created on the bottom of the plane?

A symmetric aerofoil at zero angle of attack (say NACA 0012) produces no lift or downforce. If the aerofoil is inclined at a positive angle of attack, then there is a positive camber between leading edge stagnation point and trailing edge stagnation point - thus lift is generated (through the vortex mechanism).

Tilt the aerofoil down and downforce will be generated.

Ok this is what I think I've understood so far.

-The Bernoulli explanation exists and correctly explains that differences in air-speeds are directly proportional to differences in air-pressure. The Bernoulli explanation works for all fluids and gases.

-Restrictions are that it only works with incompressible fluids (low speeds).

-You don't assume changes in heat.

-This explanation applies to all physics not just aerodynamics.

-The longer path explanation states that the Bernoulli phenomena is a result of "air particles starting at the front of the wing (at the same time) have to meet eachother exactly same time at the back of the wing."

-There is no science to this. No law in physics demand that the two particles have to meet eachother the same time at the back of the wing. This makes the "longer path" explanation faulty.

-Therefore the conclusion is that the Bernoulli phenomena exists, it just isn't a result of the longer path explanation.



Tip Vortex

I assume that tip vortex is created by the higher air-pressure (under the wing) that can escape around the tip above the wing where the pressure is lower. Thus creating in a sort of a spin. This is also the reason for turbulence.

In your NASA picture there was two tip vortexes. How come? The air can't escape around the wing at the end that is close to the fuselage?

Bound Vortex

It's the bound vortex that actually lifts the plane. Above the wing the bound vortex "goes with the flow", thus creating higher air-speed and lower pressure (Bernoulli explanation).

Under the wing it doesn't go "with the flow" but against it, thus slowing the airflow and creating higher pressure. This leads to creation of lift with the F=p*A formula.

Now if this is correct, I still don't understand why bound vortex slows the airspeed down under the wing but increases it above the wing??


[edit on 7-6-2007 by Figher Master FIN]

kilco im just reading this book, only glossing over so far, but its making it sound as if the bound vortex system, is an hypothetical representation of the wing.

its saying, use of an evquivaltent vortex system to model the wing.

just wondering, because u do seem to know a bit, if you can explain
actually where pressure difference does come from, and why.

Originally posted by Figher Master FIN
Tip Vortex

I assume that tip vortex is created by the higher air-pressure (under the wing) that can escape around the tip above the wing where the pressure is lower. Thus creating in a sort of a spin. This is also the reason for turbulence.

(everything above this was ok)


Yeap, tip vortex is from high pressure air leaking around to low pressure side. This is a form of turbulence.

Originally posted by Figher Master FIN
In your NASA picture there was two tip vortexes. How come? The air can't escape around the wing at the end that is close to the fuselage?

It was a wing without a fuselage

Originally posted by Figher Master FIN
Bound Vortex

Now if this is correct, I still don't understand why bound vortex slows the airspeed down under the wing but increases it above the wing??

Uhh, imagine the velocity direction of the bound vortex if there was no ambient airspeed.

Above the wing, it would add to any airspeed, below the wing, it would reduce it.

Originally posted by tiddly54
kilco im just reading this book, only glossing over so far, but its making it sound as if the bound vortex system, is an hypothetical representation of the wing.

The bound vortex in itself is not a hypothetical representation of the wing, but all 4 vortices (the system) can be.

Originally posted by tiddly54
just wondering, because u do seem to know a bit, if you can explain
actually where pressure difference does come from, and why.

Uhh, its all above.

Basically:

Bound vortex creates velocity differential between top and bottom.

From bernoulli, this velocity differential creates pressure differential.

This pressure differential creates lift.

Ok then, I think I understand this. Thanks alot Kilcoo
It's the shape of the wing that results in bound vortex. Now comes the obvious question.

How can aircraft fly upside down?

If lift is created by higher air-pressure under the wing than above it, wouldn't it be more logical to see the plane simply stall or even be forced down when we "turn around the plane, and therefore the whole concept". I doubt that the plane can move forward only do to thurst created by the engines, lift is required.

I remember reading something about the angles of attack being big enough. This would result in creation of lift somehow. Care to explain? thank you.



[edit on 7-6-2007 by Figher Master FIN]

Originally posted by kilcoo316
A symmetric aerofoil at zero angle of attack (say NACA 0012) produces no lift or downforce. If the aerofoil is inclined at a positive angle of attack, then there is a positive camber between leading edge stagnation point and trailing edge stagnation point - thus lift is generated (through the vortex mechanism).

Tilt the aerofoil down and downforce will be generated.

It think this would be a part of having a wing fly upside down. Alot of those wing designs are created for prolonged inverted flight. As long as there is a positive incline to the wing it will continue to keep the plane in the air. with some of the wings that are symectical as long as there is a slight incline it will produce lift.

The wing camberline (as seen by the airflow) is from the leading edge stagnation point to the trailing edge stagnation point. (NOT the same as geometric leading edge and geometric trailing edge - which are the traditional points used for the geometric camberline).


So, if you wanna fly upside down, you need to have sufficient... uhhm, negative (from the pilots point of view in control movement) angle of attack to get this camberline sorted so upward lift can be produced.

Basically if the pilot became inverted but was perfectly level he would lose lift and begin to lose alt. hence the need to have the angle of attack basically the opposite of what it would be in normal rightside up flight. Is that right Kilco?

Yeap, spot on.


The pilot would need to have a slightly higher (inverted) angle of attack compared to normal flight, as they wouldn't have the natural geometric camber of the wing working "for" them.

Hmm, let's see.

If the aerofoil is inclined at a positive angle of attack, then there is a positive camber between leading edge stagnation point and trailing edge stagnation point - thus lift is generated (through the vortex mechanism).

How can lift be created through bound vortex "just" because the plane has a positive angle of attack (from the pilots point of view)? Or should I say simply because there is a positive chamber?

*EDIT*

Is it because a positive chamber results in higher pressure under the wing and lower above it (again from the piltos point of view)?

[edit on 8-6-2007 by Figher Master FIN]

I should really gte my book from flight school and scan some of the images for you FIN because they go a long way to explaining airflow and camber. just give me until later tonight and I'll do it for you. Its a great book called "From The Ground Up" (FTGU) that is used in north america or at least canada as the flight training manual of sorts. You ever read throught the FTGU Kilcoo?

I would think that agility would be improved with the downward wings due to bernoulli's principal, downward facing wings would better trap air, this would increase lift, and therefore mobility.

"downward" ??? what do you mean a downward facing wing? as in the camber, attached to the belly? I don't understand. Can you use a plane as an example or a type of wing camber?

If you could do that I'd be greatful Canada

I think he talks about anhedral wings.

Which is a completely different subject then lift in the sence that we have been talking about with compression and vortex.

Indeed, I think he read the first page only wich was about anhedral/dihedral wings, posted and didn't notice that the discussion wasn't about that anymore

I'm assuming he's talking about a high mounted wing, like the C-5/17/141 as opposed to a low mounted wing like the 747/57/67 etc.

Allright, I made a quick illustration. Try to imagine that my picture represents a plane that flies upside down.



-When a plane flies upside down there has to exist a positiv chamber between the leading edge stagnation point and the trailing end stagnation point. In other words the chamber is positive when the plane has an angle of attack larger than 0 degrees (horisontal flight).

-The positive chamber results in an inverted phenomena. The vortex velocity component now acts with the airflow above the wing, but against it under. Notice that above and under are actually opposite in normal level flight.

-And as you said Canada, the moment the plane loses its' positive chamber no lift will be produced and the plane will stall.

Correct?


[edit on 10-6-2007 by Figher Master FIN]