Aeroplane -- Lift Force Generation

[Harmonica]

OK, so to make it easier, let's cut out an airfoil (or aerofoil) section -- say what? ... . an airfoil section is a crossection of the wing. Kind of looks like a banana.

How then is the upward Lift (force) generated when an aeroplane moves forward?

The name of the gentleman whose equation comes in handy here?

Have fun!

Regards

[Khun Jean]

This is just google stuff. Too easy!

But i now from my computer background that the guys name is Bernoulli (sp).

[Darknight]

OK, so to make it easier, let's cut out an airfoil (or aerofoil) section -- say what?  ... .  an airfoil section is a crossection of the wing.  Kind of looks like a banana.

How then is the upward Lift (force) generated when an aeroplane moves forward?

The name of the gentleman whose equation comes in handy here?

Have fun!

Regards

<{POST_SNAPBACK}>

the airfoil is lifted due to the unequal pressure between the top and the bottom. This difference in pressure is caused because the air going over the curved top surface creates a lower pressure.

The wing is actually sucked up instead of pushed up.

So a question back at ya .

What does a wing and the pistol on the end of a gasoline filling station pump have in common ?

[buadhai]

I thought the Bernoulli effect has been shown to be an incorrect explanation for how airplanes fly. If airplanes are able to fly because of the Bernoulli effect, then how can they fly upside down?

[lampard10]

It's not just two forces operating it's four. They are coupled together and strange as it may seem called couples. Lift & drag,thrust & weight.

Try explaining a helecopter though. In principle a helecopter cannot fly.

[Harmonica]

OK, so to make it easier, let's cut out an airfoil (or aerofoil) section -- say what?  ... .  an airfoil section is a crossection of the wing.  Kind of looks like a banana.

How then is the upward Lift (force) generated when an aeroplane moves forward?

The name of the gentleman whose equation comes in handy here?

Have fun!

Regards

the airfoil is lifted due to the unequal pressure between the top and the bottom. This difference in pressure is caused because the air going over the curved top surface creates a lower pressure.

The wing is actually sucked up instead of pushed up.

So a question back at ya .

What does a wing and the pistol on the end of a gasoline filling station pump have in common ?

>>>>>>>> the airfoil is lifted due to the unequal pressure between the top and the bottom. This difference in pressure is caused because the air going over the curved top surface creates a lower pressure. <<<<<<<<<

and why , amy I ask, does "the air going over the curved top surface create a lower pressure?"

[Harmonica]

It's not just two forces operating it's four. They are coupled together and strange as it may seem called couples. Lift & drag,thrust & weight.

Try explaining a helecopter though. In principle a helecopter cannot fly.

Yeah, that's correct.

The 2 pairs of forces you mentioned are perpendicular to each other -- there are no absolutes, but I would venture to say that one could, for discussiion sake neglect one while estimating or gauging the other, to a reasonable limit anyway?

Jet Propulsion and Aerodynamics (Fluid Mechanics for Mechanical Engineers) go hand in hand, but there is plenty of room for design aerodynamically before one even gets to the engine department.

Thanks

[Harmonica]

This is just google stuff. Too easy!

But i now from my computer background that the guys name is Bernoulli (sp).

Yes, googling does simplify things -- but, couldn't you try working it out without ..... ?

Point well taken, though.

Either way, I shall try to come up with stuff that is not googleable.

Try Level 10 -- its posted in another thread. I'd be mighty surprised if google could come up with even the question!

[Harmonica]

It's not just two forces operating it's four. They are coupled together and strange as it may seem called couples. Lift & drag,thrust & weight.

Try explaining a helecopter though. In principle a helecopter cannot fly.

Yeah, that's correct.

The 2 pairs of forces you mentioned are perpendicular to each other -- there are no absolutes, but I would venture to say that one could, for discussiion sake neglect one while estimating or gauging the other, to a reasonable limit anyway?

Jet Propulsion and Aerodynamics (Fluid Mechanics for Mechanical Engineers) go hand in hand, but there is plenty of room for design aerodynamically before one even gets to the engine department.

Thanks

Perhaps I should add that the original question was meant to be "simple" -- Bernouli's equation in its early stages of application, neglects Friction altogether to come up with a simplistic basis for study. Of course we know that in real life we cannot neglect such an important parameter.

So Lamp, your statements about Lift and Drag are right on; and obviously to design a wing, one must consider thrust/power requirements because velocity is a variable in the equation.

There are other variables, like the angle for example.

But the original question is just an opener -- meant to be kept very simple and in line with "pure" Aerodynamics -- if such a thing is even possible.

Sorry for the lack of proper explanation in the opener.

[lampard10]

It's not just two forces operating it's four. They are coupled together and strange as it may seem called couples. Lift & drag,thrust & weight.

Try explaining a helecopter though. In principle a helecopter cannot fly.

<{POST_SNAPBACK}>

Yeah, that's correct.

The 2 pairs of forces you mentioned are perpendicular to each other -- there are no absolutes, but I would venture to say that one could, for discussiion sake neglect one while estimating or gauging the other, to a reasonable limit anyway?

Jet Propulsion and Aerodynamics (Fluid Mechanics for Mechanical Engineers) go hand in hand, but there is plenty of room for design aerodynamically before one even gets to the engine department.

Thanks

<{POST_SNAPBACK}>

No,the couples must work in direct proportion to one another,apart from the case of a glider where thrust & weight do not really exist.

[Maka]

Same princeple as a Sail on a boat. (Same shape as a wing)

The boat/ sail is pulled rather than pushed.

This is visibly apparent when you look at the "tell tails" on the sail, that help the sailors determine proper sail trim. Tey stick out forward or away from the sail on the leeward (down wind) side of the sail.

This force on the sail/wing is increased with velocity. The faster the air moves the greater the force. Wind on a sail boat, forward motion on a plane wing. This is why planes land and take off into the wind. The planes reletive ground speed/to lift is reduced proportiontly by the wind speed.

[Khun Jean]

Still doesn't tell you why.

Because of the shape of the wing the air has to travel a longer distance on the top than at the bottom of the wing. This will give a lower pressure on the top. Because of this difference that gets bigger when you move faster the wing is pulled up.

[Kalavo]

Bernoulli is a great way of giving a simple explination to people to stop them asking how a wing works, you can blow over the top of a bit of paper, watch the paper rise, think that makes sense and you're happy. Bernoulli does play a part, but only a very small one - approx 10% for your average Cessna (this changes depending on reynolds numbers)

Most people think of a simple venturi...

http://astron.berkeley.edu/~jrg/ay202/img381.gif

..and if you take the top half of the venturi away assume the same thing will happen (correct but not as efficient), now if you take the two walls away where the air is low velocity but high pressure, you're left with the shape of the wing (again this is all good for a basic explination to stop people asking).

That second 'wall' where the air is moving from high velocity back to low velocity is actually very important for Bernoulli's theorem to work, it helps increase the static pressure and decrease the velocity. Take it away and you're left with high velocity, low pressure air that follows the curve of the wing and is accelerated downards (F=m*a) accelerate enough air downards (generating lift) to overcome the weight of the aircraft and you're cooking with gas. Of course we pay a price for disturbing the air, which is what we call drag, so we need to add enough energy to the system to overcome this in the form of thrust.

There's a reason it's called an airplane, and that's the best way to think of it - a plane flowing through the air, the more angle you give it relative to the airflow (referred to as angle of attack) the more it deflects the air downards creating lift (and the more it disturbs the air creating drag) for a given velocity.