Why an Airplane Flies (Bernoulli's Principle vs. Newton's Third Law)

[studiot]

 

Your ideas are 15 years behind the times.

 

So are you suggesting that 15 years ago balloons rose for one physics reason, but today they rise for an entirely different one?

[Strange]

I can assure you that they are not bothered, as you put it, but they are more than happy to respond.

 

Perhaps you can ask them if airplanes fly due to buoyancy, as you claim.

[John Cuthber]

John, you say “perhaps you can stop bothering these people.”

I can assure you that they are not bothered, as you put it, but they are more than happy to respond.

 

Your ideas are 15 years behind the times.

I challenge you and, anyone else, to contact the physics departments of any university in the UK or America and, put your argument to the head of department.

Of course you won’t, because I have challenged you and you will be proved wrong—but others might.

 

These links will get you all the universities in the UK and USA.

http://en.wikipedia.org/wiki/List_of_universities_in_the_United_Kingdom#Universities_alphabetically

 

http://www.utexas.edu/world/univ/state/

 

I won't, not because I " will be proved wrong" but, because it would prove nothing.

Do you still not understand the problem with argument by authority?

 

I'm also puzzled about what you think has changed about aeronautics in the last 15 years.

[Talos]

Studiot,

So are you suggesting that 15 years ago balloons rose for one physics reason, but today they rise for an entirely different one?

NO. I'm suggesting that there's more to it than buoyancy.

Strange, "Perhaps you can ask them if airplanes fly due to buoyancy, as you claim."

I never claimed that. I'm claiming that the same physics apply to a balloon as they do to an airplane, and it isn't buoyancy. It's to do with equal and opposite reactions. Lift for an airplane or a balloon is an equal and opposite reaction to a downwash of air.

[studiot]

Let us suppose that the inflated balloon is resting on the ground, so it is as low as the lowest level of air.

 

Just where exactly will the alleged descending air descend to?

 

On your mechanism the balloon would never start to rise since at the outset there is no reason for any air to descend.

When the balloon starts to rise the only direction it can push the air out of the way is sideways. This does not change the elevation of that air and therefore cannot change the potential energy of that air.

 

You have a further problem to surmount if you wish to employ reaction forces in your model.

Reaction forces are contact forces and only do work if the contact bodies deform, since the point of application is not moved by those forces.

Edited December 6, 2014 by studiot

[Strange]

Lift for an airplane or a balloon is an equal and opposite reaction to a downwash of air.

 

Right. So when a balloon reaches the ceiling and stays there, it is held in place by a continuous downwash of air. Got it. Thanks. That makes so much sense.

[studiot]

A further problem with your model for you to overcome.

 

If a 1 cubic metre helium balloon rises 100 metres it will gain 100*0.175*9.8 = 173 Joules of potential energy.

 

How far will 1 cubic metre of air have to fall to release this much potential energy?

 

I make it 14 metres.

 

So if the helium balloon rises 1000 times this are you saying there will be a downwash of air 14 kilometres below the balloon?

[Talos]

Strange

Right. So when a balloon reaches the ceiling and stays there, it is held in place by a continuous downwash of air. Got it. Thanks. That makes so much sense.

It makes no sense at all. When the balloon reaches the ceiling and stays there, it doesn’t require any more lift. It only required lift by means of a downwash of air in order to get it there.

 

Studiot

So if the helium balloon rises 1000 times this are you saying there will be a downwash of air 14 kilometres below the balloon?

No. The downwash only occurs locally where the balloon is in space, and it continues locally around the balloon all the way up to your 1000 times 100 metres.

 

[studiot]

 

So if the helium balloon rises 1000 times this are you saying there will be a downwash of air 14 kilometres below the balloon?

No. The downwash only occurs locally where the balloon is in space, and it continues locally around the balloon all the way up to your 1000 times 100 metres.

 

 

Let us suppose that the inflated balloon is resting on the ground, so it is as low as the lowest level of air.

 

Just where exactly will the alleged descending air descend to?

 

On your mechanism the balloon would never start to rise since at the outset there is no reason for any air to descend.

When the balloon starts to rise the only direction it can push the air out of the way is sideways. This does not change the elevation of that air and therefore cannot change the potential energy of that air.

 

You have a further problem to surmount if you wish to employ reaction forces in your model.

Reaction forces are contact forces and only do work if the contact bodies deform, since the point of application is not moved by those forces.

 

 

 

Locally around the balloon?

 

Since you could not be bothered to answer my previous post (did you even read it????) your statement above means that you are stating categorically that the air descends below a balloon sitting on solid rock.

 

*!WOW!*

 

 

Let us suppose that the inflated balloon is resting on the ground, so it is as low as the lowest level of air.

 

Just where exactly will the alleged descending air descend to?

 

On your mechanism the balloon would never start to rise since at the outset there is no reason for any air to descend.

When the balloon starts to rise the only direction it can push the air out of the way is sideways. This does not change the elevation of that air and therefore cannot change the potential energy of that air.

 

You have a further problem to surmount if you wish to employ reaction forces in your model.

Reaction forces are contact forces and only do work if the contact bodies deform, since the point of application is not moved by those forces.

 

Further if you state that the downwash is only local to the balloon (is 100 kilometers above the balloon local?) you need to propose more detail for your energy generation mechanism since my calculation proves there is not enough energy in descending local air to power the balloon's rise.

Edited December 6, 2014 by studiot

[Strange]

Strange

Right. So when a balloon reaches the ceiling and stays there, it is held in place by a continuous downwash of air. Got it. Thanks. That makes so much sense.

It makes no sense at all. When the balloon reaches the ceiling and stays there, it doesn’t require any more lift. It only required lift by means of a downwash of air in order to get it there.

 

You are saying that one effect causes it to rise but a different force takes over and holds it against the ceiling.

[studiot]

 

it doesn’t require any more lift

 

Not a different force, Strange, he seems to be saying that the balloon does not press against the ceiling at all, unlike the rest of the air in the room.

 

Again this is so against observable reality that all I can say is

 

WoW!

[John Cuthber]

He isn't going to let a mere fact get in the way of his idea.

I predict the he will email a famous physicist and ask a pointless question.

[studiot]

As a pilot(!) Talos should be aware of the ICAN (International Commission for Air Navigation) standard formulae for atmospheric pressure.

 

From zero to 11km they offer a formula that is temperature compensated (derivations available)

 

P = P₀(1 - 0.0226z)^5.26

 

Where height, z in km, is above sea level where P = P₀

z is measured in km and other figures are in cgs units.

 

Above 11km temperature is assumed constant at 216.5 K and the formula becomes

 

P = 1.26P₀e^-0.158z

 

 

If we can take the simpler 'schoolboy' formula for pressure

 

[math]P = {P_0}{e^{ - \frac{{gz}}{k}}}[/math]

 

Where k is a constant.

A spherical balloon, radius r, Weight W, floats at neutral bouyancy at a height

 

given by
^{[math]{e^{\frac{{gz}}{k}}} = \frac{{4\pi {P_0}k}}{{gW}}\left( {r\cosh \frac{{gr}}{k} - \frac{k}{g}\sinh \frac{{gr}}{k}} \right)[/math]}

Edited December 6, 2014 by studiot

[Strange]

It only required lift by means of a downwash of air in order to get it there.

 

What causes this "downwash"? What causes it to stop? Why isn't there an upwash or seidewash?

[Talos]

Studiot, you say:

Let us suppose that the inflated balloon is resting on the ground, so it is as low as the lowest level of air.

Just where exactly will the alleged descending air descend to?

It gets under the balloon thereby pushing the balloon up which increases the balloons potential energy. The increase in the balloon’s potential energy comes from the air’s loss of potential energy as it descends.

 

Recall one of my earlier posts.

Answer from Andrew Hanson, CPhys
Outreach Manager
National Physical Laboratory
Hampton Rd | Teddington | Middlesex | UK | TW11 0LW

THE DISPLACED AIR COMING DOWN LOSES POTENTIAL ENERGY AND THE BALLOON GAINS IT.

 

How many times must I repeat this before you cotton on?

 

[Strange]

THE DISPLACED AIR COMING DOWN LOSES POTENTIAL ENERGY AND THE BALLOON GAINS IT.

 

Ahem.

 

What displaces the air? It wouldn't be the balloon, by any chance . . .

[studiot]

 

How many times must I repeat this before you cotton on?

 

As many times as necessary until you actually offer a mechanism that conforms to the known laws of Physics

 

Merely stating

"It gets under the balloon thereby pushing the balloon up which increases the balloons potential energy."

does not cut it.

 

How and why?

By what law of Physics does this happen?

 

Why would any air have any reason to move at all, before the balloon has started rising?

 

Or are you suggesting the Enron philosophy "buy before you have the money"

That was a new philosophy in the last 15 years and look where it got them.

 

In Physics for money read potential energy.

 

Final question, "what lifts the heavier than air container off the ground in both the cases of rigid and flexible containers?"

 

 

.

Edited December 6, 2014 by studiot

[Talos]

John,

He isn't going to let a mere fact get in the way of his idea.

I predict the he will email a famous physicist and ask a pointless question.

 

It’s not my idea. And famous physicists' don't answer pointless questions. I suspect it is you that has asked pointless questions and got no answers.

 

You, studiot and Strange win the prize for claptrap. And you are bringing this forum to the point of ridicule. Mark my words, you will all be proved wrong.

 

[Strange]

Mark my words, you will all be proved wrong.

 

That would require evidence, rather than unsupported assertions.

[John Cuthber]

John,

He isn't going to let a mere fact get in the way of his idea.

I predict the he will email a famous physicist and ask a pointless question.

 

It’s not my idea. And famous physicists' don't answer pointless questions. I suspect it is you that has asked pointless questions and got no answers.

 

You, studiot and Strange win the prize for claptrap. And you are bringing this forum to the point of ridicule. Mark my words, you will all be proved wrong.

 

OK You say this isn't your idea of how balloons float.

fair enough.

What is your idea of how balloons float?

Is it, by any chance, the stuff you have been talking about in this thread?

If so then it is your idea - whether you originated it or not.

And you seem to have fallen so deeply in love with it that you can not bear to see it questioned.

That would explain why you don't answer questions like "what drives the generator?"

 

It would also explain why you deceive yourself into thinking that other Great Names agree with it.

You haven't actually asked them the real question "do balloons fly for the same reason that planes do?" because you know you daren't.

It's plainly true that they don't but you are so infatuated with the idea that you can't see its faults.

 

Whether physicists answer pointless questions rather depends on the meaning of "pointless".

If I email a physicist and ask if a rock weighs less on the moon that it does on earth, the question is pointless- because I already know the answer. But it's easier for the physicist to send an email saying " yes" than to work out why I'm asking and what I already know.

 

 

You asked a question to which we all agree on the answer- as long as you don't explain the context.

So that question was pointless.

Not only that, but you did it to support a logical fallacy- one that you have already been called out on- so that also makes it pointless.

 

So, you are simply wrong; physicists do answer pointless questions.

Would you like to try to refute that by saying what the point of those questions actually was?

 

I, on the other hand, do accept that I ask pointless questions at least some of the time.

For example, there is no point in me asking, yet again, "where does the energy to run the generator come from?"

It's pointless because I know you won't answer.

You can't answer because it would break your "faith" in this idea of yours.

 

None of what Studiot, strange and I have said is "claptrap".

It has all been directed towards a simple goal, showing you why you are simply wrong.

But, as I have said, you refuse to accept that.

It's impossible for you to see the error in this idea you have adopted.

So your only viable way forward is to resort to this

http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

[studiot]

If anyone is actually interested in the mechanics of flight, the mechanics of balloon flight is special.

 

For rigid bodies, including hollow ones, the upwards bouyant lift force is applied to the underside of the body by the external air.

This applies whether the body is 'heavier-than-air' or 'lighter-than-air'.

Of course, for heavier-than-air bodies an additional (non bouyant) source of lift is also required for flight.

 

For inflatable (non rigid balloons) the upwards lift force is applied, not to the underside of the balloon or by the external air, but by the gas inside the balloon to the inside surface of the top of the balloon.

This has implications for the centre of bouyancy and the stabilty of the body in flight.

 

I can post a working through the mechanics of this if anyone is interested.

Edited December 7, 2014 by studiot

[Talos]

Studiot,

Buy yourself a helium balloon and some joss sticks.

In a closed room light your joss stick/s and allow the room to fill with smoke.

When the smoke laden air has become static, release your balloon from floor level and watch the smoke laden air descend around it due to gravity*, while simultaneously moving underneath the balloon and rising as it lifts the balloon up in an equal and opposite reaction.

* the helium has weight because it is in a gravitation filed, but its weight is less than the air. Hence gravity has a stronger pull on the air than it does on the helium.

 

John,

I’ve really got you hot under the collar haven’t I. This gives me great pleasure.

 

[John Cuthber]

 

John,

I’ve really got you hot under the collar haven’t I. This gives me great pleasure.

 

I'm calling "troll!" on that

[StringJunky]

Hence gravity has a stronger pull on the air than it does on the helium.

 

By your logic then: a brick and a feather free-falling in a vacuum would fall at different rates because the Earth is pulling more on the brick than the feather, which is not correct. The gases with a higher molecular weight than helium push the helium atoms out of the way and assume a lower position.

[arc]

Studiot,

Buy yourself a helium balloon and some joss sticks.

In a closed room light your joss stick/s and allow the room to fill with smoke.

When the smoke laden air has become static, release your balloon from floor level and watch the smoke laden air descend around it due to gravity*, while simultaneously moving underneath the balloon and rising as it lifts the balloon up in an equal and opposite reaction.

* the helium has weight because it is in a gravitation filed, but its weight is less than the air. Hence gravity has a stronger pull on the air than it does on the helium.

 

Talos, you never addressed my questions I posed to you in post #93 - http://www.scienceforums.net/topic/31491-why-an-airplane-flies-bernoullis-principle-vs-newtons-third-law/page-5#entry837138

 

I think that you still need to address that post because you are claiming a mechanism for lift that my example directly refutes.

 

You claim; "When the smoke laden air has become static, release your balloon from floor level and watch the smoke laden air descend around it due to gravity*, while simultaneously moving underneath the balloon and rising as it lifts the balloon up in an equal and opposite reaction."

 

"simultaneously moving underneath the balloon and rising as it lifts the balloon up"

 

In post #93 I said;

 

"If we had a clear plastic cylinder 50 meters high containing water, it would have approximately 5 bars of pressure at its base and half that at 25 meters, and thus can effectively graduate the hydrostatic pressures so forth for its entire height.

To start with, we will lower a weighted balloon into the empty cylinder, the balloon is ballasted to have a neutral buoyancy at approximately 2.5 bars at 25 meters in depth.

Next, we will slowly fill the cylinder from below with water from a measured source.

I believe the balloon will not lift off the cylinder’s bottom until the water reaches above 25 meters. Do you agree?

When the water reaches 26 meters the balloon will be one meter off the bottom. Do you agree?

Do you believe the water moves down to raise the balloon?

As water is added the balloon will rise in proportion, this is neutral buoyancy. If the cylinder was full to the top and the balloon was released from the bottom it would rise to the 25 meter level and stop.

To do so the water above it will have to move down past the balloon as it rises, I think this detail is over complicating your understanding of this process. For example, when something sinks the water moves past the object.

Is this water pushing the object down?"

Talos, you are confusing the displaced volume that must move down as the balloon goes up as being the mechanism of lift. Gravity acting on the surrounding volume is providing the lift through pressure, it is squeezing the balloon (the lighter gas inside) and moving it upwards to a constantly lower state of pressure. Displacement of the surrounding volume by the lighter gas inside the balloon initiates and determines the degree to which the force will be provided.

 

Lift of the balloon will not be provided without displacement by a lower density of equal or greater volume, but displacement is not the force that provides lift. Hydrostatic pressure of the surrounding volume through gravity is.

I could have two balloons of identical weight and volume. But one is made to have a smooth outside surface, the other's surface is made to be very rough and resistant to air flow.

 

Do you think they will rise at the same rate?

 

The pressure that is raising the balloons from below is being opposed by the resistance that the rougher surface has on the downward flow of the displaced air as it moves past the rougher surface, thus slowing the balloon's rise. But its lift capacity remains the same due to the pressure and the gravity that provides it. This shows that you are incorrect and the force that provides the lift is not the air that is moving down from above.

 

The air "simultaneously moving underneath the balloon and rising as it lifts the balloon up" is simply a secondary reaction to the force that is raising the balloon from below.

 

edit; terminology

Edited December 8, 2014 by arc