completeaerogeek

Some extra reading on lift...Ok. here is a pretty simple way of putting it...;)

 

The reason that the air sticks to the top of the wing is found in the boundary layer. This is a layer of air, on the surface, less than an inch (2.5 cm) thick. Because the air is slightly sticky (it has viscosity) the part in contact with the wing actually clings to the surface, and doesn't move. You will notice this when your car gathers dust on a dirt road. You come to the tar and put your foot down, hoping to blow it off, but not one grain moves. This is because the air at the surface of your car is completely still, despite the fact that you might be travelling at over 100 km/hr.

 

So a thin sliver of air right next to the wing is stationary. The next layer up moves very slowly, the layer above that moves a bit faster and so on, until at about one inch from the surface the air moves at the normal speed.

 

Imagine a little gnome, only one inch tall, standing on the wing in the boundary layer. He is facing towards the tail of the aircraft. There is no wind blowing on his heels, a strongish wind blowing on his butt and a gale on his head and shoulders. His feet stay put but the rest of him pitches face-down on the surface of the wing.

 

This is exactly what the airflow does — it's pulled down on to the surface of the wing.

 

So now we have this layer of air that clings to the upper surface and is bent downwards. This drags more air down with it. In fact it drags a huge mattress of air down.

 

For those who like figures, a Cherokee or C172 at cruise speed, displaces a 3 metre thick layer of air downwards at a vertical speed of about 9 knots. To supply the 1000 kgs of lift needed for level flight, the wing deflects over 2.5 tonnes of air every second!

 

If you start moving huge volumes of air downwards,

 

you leave a void where it came from. In other words this downward movement of air creates a low-pressure area above the wing.

 

Let's take stock for a moment. We know that the wing gets lift by deflecting air down. But we also know that it gets lift from low pressure above, and high pressure below the wing.

 

Strangely, both these statements are correct. The pressure difference, and the deflected air are both part of the same system.

 

Because many folk battle to come to grips with this, I have developed three different ways of explaining it, in the hope that one makes sense to you.

 

Example 1. The air over the top of the wing is pulled in two different directions. Newton’s first law decrees that it should carry on in a

 

straight line, while Coanda insists on curving it downwards. This conflict causes the air to be lifted slightly above the wing, forming a partial vacuum.

 

Example 2. Imagine speeding your car over a humpback bridge. As it follows the downward curve of the bridge you feel yourself lifting out of your seat. The air curving down over the top of the wing behaves in the same way it tends to lift away from the surface, causing a partial vacuum.

 

Example 3. This example is to clarify the relationship between the partial vacuum and the down force.

 

Imagine your aircraft being picked up by a crane. But instead of ropes round the wings we attach the aircraft to the crane with a whole lot of suction cups.

 

The aircraft's weight pushes down on the ground through the crane's wheels. But it's being supported by suction on the top of the wings. Exactly the same happens in flight — the aircraft's weight pushes down on the air, and it's being supported by suction above the wings. Make sense?

 

For the purist, it's not just a matter of low pressure, or suction, above the wing. Lift comes from the difference in pressure between the partial vacuum above the wing and the increased pressure below it.

 

Finally, some people want to apportion the lift. They think that part of it comes from deflecting air down, and part from suction.

 

You can't do this — they are both components of the same system, which accounts for 100% of the lift. Apportioning the lift is like saying that a car is partly supported by the air pressure in its tyres, and partly by the road. Each is a component of a system that supports the entire weight of the car.

 

So that's it.

 

• Lift comes from deflecting air downwards.

 

• The suction above a wing is caused by the air leaving a void as it's bent downwards by Coanda Effect.

 

Some extra reading on lift...Ok. here is a pretty simple way of putting it...;)

 

The reason that the air sticks to the top of the wing is found in the boundary layer. This is a layer of air, on the surface, less than an inch (2.5 cm) thick. Because the air is slightly sticky (it has viscosity) the part in contact with the wing actually clings to the surface, and doesn't move. You will notice this when your car gathers dust on a dirt road. You come to the tar and put your foot down, hoping to blow it off, but not one grain moves. This is because the air at the surface of your car is completely still, despite the fact that you might be travelling at over 100 km/hr.

 

So a thin sliver of air right next to the wing is stationary. The next layer up moves very slowly, the layer above that moves a bit faster and so on, until at about one inch from the surface the air moves at the normal speed.

 

Imagine a little gnome, only one inch tall, standing on the wing in the boundary layer. He is facing towards the tail of the aircraft. There is no wind blowing on his heels, a strongish wind blowing on his butt and a gale on his head and shoulders. His feet stay put but the rest of him pitches face-down on the surface of the wing.

 

This is exactly what the airflow does — it's pulled down on to the surface of the wing.

 

So now we have this layer of air that clings to the upper surface and is bent downwards. This drags more air down with it. In fact it drags a huge mattress of air down.

 

For those who like figures, a Cherokee or C172 at cruise speed, displaces a 3 metre thick layer of air downwards at a vertical speed of about 9 knots. To supply the 1000 kgs of lift needed for level flight, the wing deflects over 2.5 tonnes of air every second!

 

If you start moving huge volumes of air downwards,

 

you leave a void where it came from. In other words this downward movement of air creates a low-pressure area above the wing.

 

Let's take stock for a moment. We know that the wing gets lift by deflecting air down. But we also know that it gets lift from low pressure above, and high pressure below the wing.

 

Strangely, both these statements are correct. The pressure difference, and the deflected air are both part of the same system.

 

Because many folk battle to come to grips with this, I have developed three different ways of explaining it, in the hope that one makes sense to you.

 

Example 1. The air over the top of the wing is pulled in two different directions. Newton’s first law decrees that it should carry on in a

 

straight line, while Coanda insists on curving it downwards. This conflict causes the air to be lifted slightly above the wing, forming a partial vacuum.

 

Example 2. Imagine speeding your car over a humpback bridge. As it follows the downward curve of the bridge you feel yourself lifting out of your seat. The air curving down over the top of the wing behaves in the same way it tends to lift away from the surface, causing a partial vacuum.

 

Example 3. This example is to clarify the relationship between the partial vacuum and the down force.

 

Imagine your aircraft being picked up by a crane. But instead of ropes round the wings we attach the aircraft to the crane with a whole lot of suction cups.

 

The aircraft's weight pushes down on the ground through the crane's wheels. But it's being supported by suction on the top of the wings. Exactly the same happens in flight — the aircraft's weight pushes down on the air, and it's being supported by suction above the wings. Make sense?

 

For the purist, it's not just a matter of low pressure, or suction, above the wing. Lift comes from the difference in pressure between the partial vacuum above the wing and the increased pressure below it.

 

Finally, some people want to apportion the lift. They think that part of it comes from deflecting air down, and part from suction.

 

You can't do this — they are both components of the same system, which accounts for 100% of the lift. Apportioning the lift is like saying that a car is partly supported by the air pressure in its tyres, and partly by the road. Each is a component of a system that supports the entire weight of the car.

 

So that's it.

 

• Lift comes from deflecting air downwards.

 

• The suction above a wing is caused by the air leaving a void as it's bent downwards by Coanda Effect.

 

A wing doesn't 'suck at all' In fact suction is a very misunderstood and somewhat mythical concept. When a piston moves down in a cylinder atmospheric pressure pushes the air into the increasing space . The 'suction' idea is why so many pilots have problems understanding why a MAP gauge goes up and pressure increases when they open the throttle. isn't it 'sucking harder' shouldn't the pressure go down as 'suction increases?

A wing (the simplest kind is a flat plate) moves trough the air and as it does so at an effective AOA, the lower surface pushes the 'lower air' air forwards and downwards. Lift Component 1. The Pressure bubble (bow wave_ caused by this disturbance pushes the remaining air up and over the wing where it is held against the upper surface by normal atmospheric pressure. Imagine the wing under water. The physics is identical. Now try to use your explanation. if it doesn't work it is wrong. Simple.

The air that us pushed up and over the wing follows the upper surface because it has nearly 15lb/sq in making it do so. As it changes direction a force results (as it must Newton's 2nd and 3rd laws.) This resultant force is Lift Component #2.

Lift is caused by the mechanical intervention of a wing bending the air away from its resting position. Pressure variations are a result of lift production not the cause. Flat wing- no AOA no lift. Flat wing, AOA + movement = lift. QED.

Some extra reading on lift...Ok. here is a pretty simple way of putting it...;)

 

The reason that the air sticks to the top of the wing is found in the boundary layer. This is a layer of air, on the surface, less than an inch (2.5 cm) thick. Because the air is slightly sticky (it has viscosity) the part in contact with the wing actually clings to the surface, and doesn't move. You will notice this when your car gathers dust on a dirt road. You come to the tar and put your foot down, hoping to blow it off, but not one grain moves. This is because the air at the surface of your car is completely still, despite the fact that you might be travelling at over 100 km/hr.

 

So a thin sliver of air right next to the wing is stationary. The next layer up moves very slowly, the layer above that moves a bit faster and so on, until at about one inch from the surface the air moves at the normal speed.

 

Imagine a little gnome, only one inch tall, standing on the wing in the boundary layer. He is facing towards the tail of the aircraft. There is no wind blowing on his heels, a strongish wind blowing on his butt and a gale on his head and shoulders. His feet stay put but the rest of him pitches face-down on the surface of the wing.

 

This is exactly what the airflow does — it's pulled down on to the surface of the wing.

 

So now we have this layer of air that clings to the upper surface and is bent downwards. This drags more air down with it. In fact it drags a huge mattress of air down.

 

For those who like figures, a Cherokee or C172 at cruise speed, displaces a 3 metre thick layer of air downwards at a vertical speed of about 9 knots. To supply the 1000 kgs of lift needed for level flight, the wing deflects over 2.5 tonnes of air every second!

 

If you start moving huge volumes of air downwards,

 

you leave a void where it came from. In other words this downward movement of air creates a low-pressure area above the wing.

 

Let's take stock for a moment. We know that the wing gets lift by deflecting air down. But we also know that it gets lift from low pressure above, and high pressure below the wing.

 

Strangely, both these statements are correct. The pressure difference, and the deflected air are both part of the same system.

 

Because many folk battle to come to grips with this, I have developed three different ways of explaining it, in the hope that one makes sense to you.

 

Example 1. The air over the top of the wing is pulled in two different directions. Newton’s first law decrees that it should carry on in a

 

straight line, while Coanda insists on curving it downwards. This conflict causes the air to be lifted slightly above the wing, forming a partial vacuum.

 

Example 2. Imagine speeding your car over a humpback bridge. As it follows the downward curve of the bridge you feel yourself lifting out of your seat. The air curving down over the top of the wing behaves in the same way it tends to lift away from the surface, causing a partial vacuum.

 

Example 3. This example is to clarify the relationship between the partial vacuum and the down force.

 

Imagine your aircraft being picked up by a crane. But instead of ropes round the wings we attach the aircraft to the crane with a whole lot of suction cups.

 

The aircraft's weight pushes down on the ground through the crane's wheels. But it's being supported by suction on the top of the wings. Exactly the same happens in flight — the aircraft's weight pushes down on the air, and it's being supported by suction above the wings. Make sense?

 

For the purist, it's not just a matter of low pressure, or suction, above the wing. Lift comes from the difference in pressure between the partial vacuum above the wing and the increased pressure below it.

 

Finally, some people want to apportion the lift. They think that part of it comes from deflecting air down, and part from suction.

 

You can't do this — they are both components of the same system, which accounts for 100% of the lift. Apportioning the lift is like saying that a car is partly supported by the air pressure in its tyres, and partly by the road. Each is a component of a system that supports the entire weight of the car.

 

So that's it.

 

• Lift comes from deflecting air downwards.

 

• The suction above a wing is caused by the air leaving a void as it's bent downwards by Coanda Effect.

 

Hey all,Was reading an article in this months Australian Pilot magazine entitled 8 common aviation myths.

 

The first myth basically said that Bernouli's principle was irrelevant to flight. While it does in fact exist he goes on to give a lengthy argument on why it doesn't really matter for flight.

 

He says that while it doesn have an effect on a wing, it is only a minor effect.

 

The wings are cambered, according to Austin Collins in order to acheive a greater range of AOA's and still maintain flight.

 

Arguments are:

 

1- Aircraft can fly upside down

 

2- Some aircraft have camber on top and bottom of wing

 

3- Ultralights and gliders with single surface wings (ie. no top or bottom)

 

4- No law of physics that says two air molecules that are seperated must meet again

 

5- Actual "suction" on the wing due to the principle is quite small

 

6- Even a flat peice of board with an appropriate angle of attack will fly.

 

Just wondering what everyones thoughts on this were? I grew up in aircadets and the first principle of flight we learnt was bernouli's principle. Hard to let go that it is irrelevant to flying...

OK my partners grandson is dead sure that an aircraft is sucked off the ground rather than lifted. If he keeps tweaking his theory he'll have me convinced. his main argument is 'that an area of high pressure( underside of wing) moves to an area of low pressure. as the high pressure can't get to the area of low pressure because the wing is in the way then the difference between high and low pressure has to cause more 'suck' than lift. i advised him to keep this to himself otherwise he'll end up like Galileo fella. If the two air molecules are seperated at the leading edge and the lower molecule is 10 inches past the T/E when the upper molecule is at the T/E., Is this then the real measurement of the co efficient of lift? maybe they had to come up with that fancy formula as you can't see a molecule of air to work it out. ;)

ozzie

No I have started at the start and my point was that although the material may or may not be correct, the way that it has been put forward has been in my opinion, dismal. If you were trying to prove that people get their back up because of confirmation bias, you have not, what you have proven is that people get their back up when called stupid, or told bluntly that what they believe (because that's what they were taught) is nonsense. No one asked the question, you essentially just marched on in and told everybody that if they didn't believe you that they were stupid.I would personally rethink your satisfaction scores, many students I have been on courses with, just tell the instructor what they want to hear, because they don't want to be pinned down and grilled by someone who is just going to tell them how stupid they are. No it's not how course critiques are supposed to work, but frequently it's what happens.

On that note, you appear to have some confirmation bias of your own, inasmuch as you believe that it's your student's fault that they don't believe you, not your own instructional technique or condescending attitude.

 

A good instructor will find a way to help all of the students understand, not beat them into submission.

 

No captive audiences? Yes they are, their boss decides that in order to comply with their legally required SMS, that they should receive regular lectures about such stuff, he picks out something he thinks will comply, and there you are talking to a bunch of people who would rather just be out doing their job. Been there many times, enjoyed it once ( a well spoken funny doctor about DAMP).

Mr M61-

If you were trying to prove that people get their back up because of confirmation bias, you have not, what you have proven is that people get their back up when called stupid, or told bluntly that what they believe (because that's what they were taught) is nonsense. No one asked the question, you essentially just marched on in and told everybody that if they didn't believe you that they were stupid.

A lot of emotion in your statement there M61.

Firstly, I started the post to offer correct information. That I did and there is no doubt that it is correct. It is not my information. it is from unimpeachable sources.. No-one was obliged to comment. So why di you suppose I was abused or belittled on the basis of offering information?

At no time did I say that if they didn't accept the information they were stupid. Why would you feel the need to make such a statement?

I did not respond impolitely to anyone who behaved in the same way. The escalating response was only to those who initiated hostility.

So one may well ask, why the hostility to correct information? if people are not mature enough to re-evaluate what they believe in the light of new evidence I wonder if they should be behind the controls of an aircraft.

On that note, you appear to have some confirmation bias of your own, inasmuch as you believe that it's your student's fault that they don't believe you, not your own instructional technique or condescending attitude. A good instructor will find a way to help all of the students understand, not beat them into submission.

Confirmation bias is subconsciously selecting only that information that fits your perception and then altering your behaviour comply with it.

A good facilitator offers information to people and leaves it up to them to evaluate. If they disagree then the conversation is expanded looking for perceptual flaws that can be identified so that they can then understand the information. If it involves a conceptual debate then that is a good thing to increase understanding.

You cannot force listeners to participate but interestingly all the insults that have been initiated have come from people telling me I was 'full of crap' or more specifically 'horseshit' instead of questioning the validity of the various concepts I was explaining or asking for clarification. Perhaps you should review some of the commenters here and ask them why they attacked me so rudely?

No captive audiences? Yes they are, their boss decides that in order to comply with their legally required SMS

Ahhh no. No I am talking about corporate audiences at conferences and workshops. People who pay to come voluntarily. You won't last long in business if you suck and I have been doing this successfully for over a decade so..

I would personally rethink your satisfaction scores, many students I have been on courses with, just tell the instructor what they want to hear, because they don't want to be pinned down and grilled by someone who is just going to tell them how stupid they are.

I don't think you understand how tertiary scores are evaluated. They are anonymous and I can assure you that students have no problem eviscerating an lecturer they do not like.

And again, if that is how you run a lecture, your students don't turn up. My classes were always exceptionally well attended.

Perhaps students understand that they are there to learn and have open minds... Something in that for all of us I think...

Well Complete, your statement that " the plane is moving and the air is not".. is at best irrelevant and at worst means you have an incorrect understanding of the physics of motion. I could continue like this but have a better idea...How about this to settle the argument about my Jabiru...we can be real scientists and run an experiment.

I will run a tube from the rear of my fuselage to the door and put in a sensitive pressure meter or a flow-meter. ( I can make use of a variometer which is a very sensitive flow-meter and is already in my panel).

 

If the pressure is MORE at the door or the flow is AWAY from the door then I will donate $100 on your behalf to the site. But if, as I say from my understanding of Bernoulli, the pressure is LESS at the door or the flow is TOWARDS the door then you will make the donation for me.

 

Be aware that the fuselage at the doors is over 100cm in diameter, and the fuselage near the tail is about 25cm in diameter. Slipstream from the propeller adds to the speed of the airflow over both points. You can see a bit of the actual fuselage in my photo.

 

Lots of details to work out, like how to agree on a trusted observer, and who will hold the money, but are you game?...I am.

Well put M6. I was a trained secondary teacher and some of them did indulge in ridicule and put downs . I hope I avoided that. Students do not respond well to that technique. Input should be encouraged from all, and this won't happen if there is likely public embarrassment involved. Nev

I don't mind it as long as the overall information and discussion of benefit.If your ego isn't in the way you can learn many new concepts. I have no problem being wrong. it is how we all learn. But if you care going to criticise me then you need to support it with facts and objective assessment. Otherwisse it is just your ego talking.

So my question to you is this: Is your statement and that of M61 an objective one?

Read my first post with all of the valid information and then see the hostile response it got from some. No-one was coerced into responding or commenting.

Their egos led them to lash out and insult me despite the fact that what I was saying was 100% correct.

This has been happening from time immemorial when anyone dismantled cultural myths. it is called shooting the messenger and it comes from insecurity and lack of intellectual courage.

If one person on this site now better understand basic aerodynamics then I have succeeded in my intent.

This guy works for CASA.

I'm reading all these very interesting posts but having trouble with some of the technical descriptions. My main problem is that I keep confusing `completeaerogeek' with `completelyarrogant'. Could somebody please explain the difference?rgmwa

Would you please specify why giving information that some clearly do not understand was arrogant?

I've been following this thread for a bit now...... is this some sort of "Human Factors" exercise on your (geek) part, so that you can write some sort of thesis?If it's not, I'm quite sure that I wouldn't like to be one of your students. I was going to ask if you really taught in the defence force, but then I remembered most defence instructors (tech) that I ever had, most were ex-tradies, and often the worst. Usually people that hated what they did, so to get off the floor, did a Cert whatever, and became instructors.

If you really teach Human Factors, (amongst other things) I would expect a better grasp on how to interact and put the subject matter forward in a manner that people are more receptive to. You may well be 100% correct(or not) in what you say, but I am finding the way in which the material is presented somewhat inconsistent. I doubt that you intend to come across like Sheldon Cooper on hallucinogens, bit it's what I'm getting out of it.

Ahhh M61. I see you have twigged. Thanks for your comments.

The first part of my purpose was to explain clearly that what may people think is correct is in fact nonsense and hopefully be of help. The second part was to see what sort of response I got.

The vociferous arguments based on fallacies are exactly what we in the industry need to fix. An authority figure (instructor or captain) using the cockpit or classroom power gradient consciously or unconsciously can teach new pilots or F/Os all kinds of bad habits or suppress their correct views and the junior pilot will often accept this just to 'get along'.

This is the 'Authority from Eminence' logical fallacy I mentioned earlier. (I am currently writing a book on this)

One of the posters said just this thing "it's just a hoop you have to jump through to get to the next stage". That is dangerous unprofessional thinking.

(As for being one of my students, I had the highest Student Satisfaction scores ever recorded in the department. Students still call me for advice and mentoring because they know I genuinely care about them knowing the right information and how to use it in the real world, not just the lecture room.

As for inconsistent- can you point it out please? The only thing I would ask is that you view the comments in context and start by reading my first post on Page 1.

It was concise, referenced and provided resources. If you are jumping in the middle no doubt it would look fragmented but you have to look at the whole subject in context.

Providing information with references that are unimpeachable and then watching people make emotional and inflammatory comments without having read them is quite interesting.

It is the kind of mentality that says 'I have always operated this way and I haven't had any problems in 30 years and you are not going to convince me otherwise' and then next thing you read about them in an ATSB report.

See Mr Turboplanner' comments. He is comprehensively wrong but will not see it. This is called 'Confirmation Bias' where someone only accepts information that fits with their pre-existing view. This has been a significant causal factor is quite a number of airline accidents.

The unwillingness to revise opinions or practices on the basis of new information is extremely dangerous and one of the contributing factors for the number of GA/RA accidents.

And no. Most of my facilitation has been in the corporate world-Airline and business and a corporate speaker here and overseas in Aviation where if you are crap, they don't ask you back.

No captive audiences there.

I hope that has made some sense to you.

Cheers.

Quote: "When you crack the window of your car does the air go out or in?It goes in because it has been displaced by the solid form of the car just like a boat displaces water.

If the 'faster air' outside, moving past your window was at a lower pressure as you suggest, the air would go out not in would it not?"

 

With all due respect: Horse s***t. What you describe would happen if you were trying to float a car upside down in water - i.e. it's a hydrostatics answer. Not relevant to the issue in question.

 

Bruce Tuncks has correctly described what happens in an unpressurised streamlined fuselage that has openings around the maximum cross-section and at the tail, such that flow can occur between the tail opening and the cabin. Whether flow goes into or out of such an opening (in the absence of anything that acts as a deflector or a scoop) depends on the difference between the static pressure on the outside of the fuselage and the static pressure in the cabin. The static pressure in the cabin depends on the aggregate effect of all the leakage points, but it will generally be somewhere between the free stream static pressure and the local pressure at the point of maximum local velocity; so it usually comes in at the tail and goes out at the cabin window or door leakage point - and this is well known as a source of carbon monoxide contamination of cockpits.

 

You may be surprised to learn that open cockpit aircraft are notorious for CO contamination of the cockpit air; but if you think about what I have said above, the reason will be obvious.

No that would be a buoyancy problem.

Wow you guys really need to read what I am saying and think before you post...Could you please explain why if the relative air speed outside the aircraft was higher than inside (which of course it is) that by his explanation of Bernoulli the air would not go out? Air goes from high to low pressure.

Daffyd, in what way is air different to water? (apart from density) I am always happy to learn new things.

And I am sorry but you are incorrect. Again...The principle I was describing was a hydrodynamics one not a hydrostatic one.. Might be time for some reading.

If an aircraft is a solid form immersed in air it behaves exactly the same as a solid object immersed in water. That’s why aerodynamics is also called fluid dynamics. Air is considered incompressible below M1.0.

Also it is perfectly reasonable that an open cockpit aircraft is subject to fumes for the same reason. There is a pressure wave built up at the front of the aircraft. Combine this with slipstream (if the aircraft is accelerating, and you have a higher dynamic pressure forward of the cockpit. If the dynamic air pressure is higher than that in the cockpit- Fumes. Not difficult really.

In your last point you missed the dynamic pressure rise where the air is impinging on the vertical and horizontal stabilisers at the root. This is a higher pressure point as at the leading edge of a wing so if the air is ingressing there of course it will be higher than in the cabin and push fumes in.

Of course initially it "goes in" momentarily due to both wanting to seek a lower pressure area and simple inertia, but the moment it finds pressure balance and then continues to come in raising pressure, it then tries to go back out again. I have done tufting tests on race cars to prove to the owners that their cooling system problem's are due to airflow actually going forward against the direction of travel much to their disbelief's. They also are somewhat distrusting when I greatly reduce the size of the cooling openings.You will not duplicate this result with water.

 

When you strut around treating others to be of inferior intellect, it's no surprise to end up with a few insults.

Well Complete, your statement that " the plane is moving and the air is not".. is at best irrelevant and at worst means you have an incorrect understanding of the physics of motion

Bruce, I am afraid you have a shovel and you keep digging yourself a bigger hole.

I have used this example in a conceptual (not mathematical) context every time I have mentioned it. Conceptually it is important as people ascribe all kinds of properties to the air that it does not have. Still air does not have momentum or kinetic energy. It has inertia and potential energy. Is that irrelevant?

Your statements are a perfect reason why this perspective is important. You seem to be unable to visualise flow.

To understand the concept of lift or flow it is important to visualise it in the way that it occurs not the way you think it does.

Now to your statement:

Of course initially it "goes in" momentarily due to both wanting to seek a lower pressure area and simple inertia, but the moment it finds pressure balance and then continues to come in raising pressure, it then tries to go back out again. I have done tufting tests on race cars to prove to the owners that their cooling system problem's are due to airflow actually going forward against the direction of travel much to their disbelief's

Now on to some other glaring conceptual errors:

First I think you mean momentum not inertia. Inertia is resistance to change or motion. (Newton’s 1st Law)

Secondly, what you are describing is ram effect. Ram effect occurs when the volumetric capacity of an intake is reached and the pressure in the intake equals or exceeds static.

Our Nene Vampires had this problem with the elephant ear intakes. The usual solution to this is spill doors. (I don't think it is me with the problem with the physics of motion...)

Also your racing car analogy is not valid here because you have not mentioned a key aspect-heat.

You can reduce the size of the intake while enlarging the exit and actually increase the velocity of the air because as the air is heated by the engine it expands. This principle was applied to the Spitfire and Mustang in their radiators by having a variable exit. It actually gave a thrust boost. This is called the Meredith effect after the RAE engineer who discovered it

Now on to your challenge. I would think carefully if I were you. I am happy to take your money and donate it.

Let me use an analogy:You see I have a nice Porsche and when I crack the window driving down the freeway it gives me a nice breeze for as long as the window is open...

It doesn't fill up and magically reverse flow.

Again what you are describing is ram effect not parallel flow.

The pressure at the point where the windscreen rises from the bonnet is higher than static. It creates a bow wave (pressure wave) that forces air up and over and round the side of the pillar.

At that point the air comes in if I choose. Your plane is no different. Aircraft are solid objects immersed in a viscous gaseous fluid. They behave in exactly the same way.

Aircraft are subject to the laws of displacement just like a submarine.

Now if your door apertures are parallel to the airflow and the air comes in it entirely defeats your Bernoulli explanation because if the streamline flow along the fuselage (which is obviously at a higher relative speed to the air inside the cabin) causes a pressure reduction the air would go out not in.

Physics is simple you can't have it both ways. Simply put, if outside pressure is higher than inside, air comes in. F=Ma is not negotiable.

As for your fume problem: Your tailplane probably has a localised flow impinging somewhere that creates a pressure wave higher than static and it is this that is causing a pressure rise, pushing the fumes back into your cabin. Pressure rises like this occur where the vertical or horizontal stabs join the aircraft.

Now to your insult: I don't think there is evidence of me strutting or treating people as inferior. If giving correct information is strutting then the problem doesn't lie with me.

In fact your statement about me not knowing about the physics of motion when you are clearly incorrect in your assertions rather points to you doesn’t it?

Bruce, air is a fluid. Water and air act in the same way. Air is considered incompressible below M1.0.

That is why the study of aerodynamics comes under fluid dynamics. Air and water behave in exactly the a same way unless you have come across a law of physics I have not heard of.

In post #163 Guernsey made an attempt at humour using an aviation termIn post #164 Eightyknots joined in with another one

In post #165 I joined in with another one

 

I just want to reassure you that were were feeding off each other's jokes rather than baiting you to keep up your dialogue.

 

Having done some checking, I already knew from the 'repetitive' tag that it was going to be continuing regardless of what I said, probably until the last man standing was disposed of.

 

I'm happy to summarise my comments by recommending people buy the book "Aerodynamics for Naval Aviators" NAVWEPS 00-80T-80, Naval Air Systems Command, United States Navy - available now on www.amazon.com for $20.67

You may take it or leave it. Entirely up to you.

I suggest you look at the Royal Aero Society data (now ESDU data) on the subject of the downwash field caused by the wing vortex system. Call it a flow vector if you will; I'm not going to get into an argument with you over semantics. I'm not aware that the Biot-Savart "law" has been repealed. I'm not talking about the disturbed air in the wing wake - though that can have significant effects on longitudinal stability. However the positioning of the horizontal tail is a more critical design consideration than is commonly recognised.

I have looked up and read several references on this. Biot-Savart is associated with Prandtl's lifting line theory and to do with circulation theory and unbound vortices.

A couple of problems I can see:

The Kutta condition ceases with vortex breakaway at relatively low speeds.

Winglets and swept tips significantly reduce the strength of wing tip vortices and unbound vortices have no influence on the wing.

Downwash velocity of wingtip vortices is does not appear to be relevant.

In any case this is far too complex for a pilot. Again this can be left to aerodynamicists to argue over.

The basic Newtonian explanation is clear and correct in terms of lift due to turning flow which was my original point.

I hope that clears up my question.

Hi Complete, all motion is relative. If the wind was blowing at 60 knots and the Jabiru was flying at 60 knots into the wind then there would not be the slightest difference in what I described, even though some silly people might think that because the Jabiru was now stationary with respect to the ground there was a big difference.And Bernoulli does indeed apply to two different points along a streamline, and a streamline which passes the Jabiru doors and then passes the tail fits this perfectly. I don't know what you mean by "displacement disturbance" and how you relate this to pressure differences, please explain with some calculations.

 

On the subject of university degrees, I know only too well how dumbing down has taken over in some places, having fought a rearguard action for years from within. And yet there are high standards still out there in some places as you say. I reckon we need a national public examination authority to set and mark university exams. I personally knew lecturers who passed students (who they should have failed) because they saw that this was in their best career interests.

 

And, Complete, I am wondering if you deserve a pass grade after your comments about relative motion and Bernoulli and displacement disturbances.

My apologies about the Uni bit I have sticky key problems. That was meant for Turbo and his nasty little insults.

I agree with you about the National Assessment idea but the variation in lecturers is a problem world wide. I lived and worked in the US for 9 years a lot of that for a major carrier and I was often astounded at the lack of knowledge of college graduates I dealt with.

Still the level of education here is far better than many places. OECD shows us 13th in the world where the US/UK are around 35th.

Hi Complete, all motion is relative. If the wind was blowing at 60 knots and the Jabiru was flying at 60 knots into the wind then there would not be the slightest difference in what I described, even though some silly people might think that because the Jabiru was now stationary with respect to the ground there was a big difference.And Bernoulli does indeed apply to two different points along a streamline, and a streamline which passes the Jabiru doors and then passes the tail fits this perfectly. I don't know what you mean by "displacement disturbance" and how you relate this to pressure differences, please explain with some calculations.

 

On the subject of university degrees, I know only too well how dumbing down has taken over in some places, having fought a rearguard action for years from within. And yet there are high standards still out there in some places as you say. I reckon we need a national public examination authority to set and mark university exams. I personally knew lecturers who passed students (who they should have failed) because they saw that this was in their best career interests.

 

And, Complete, I am wondering if you deserve a pass grade after your comments about relative motion and Bernoulli and displacement disturbances.

Please read my statement again and let let me know specifically where it is incorrect. I am happy to learn.

Bernoulli does apply along two different places of a streamline. That particular streamline, not somewhere else in the flow field.

Bernoulli is explaining F=Ma.

So what I would like to know is:

To what force is the static air in the hidden part of your tail section subject?

By conventional Bernoulli explanations the higher relative speed of the flow past the empennage would mean a lower pressure.

Would not the static air inside the aircraft push the fumes out not in?

When you crack the window of your car does the air go out or in?

It goes in because it has been displaced by the solid form of the car just like a boat displaces water.

If the 'faster air' outside, moving past your window was at a lower pressure as you suggest, the air would go out not in would it not?

Let me know about that passing grade.

In mathematics, as I have said earlier the perspective does not matter but conceptually it does vert much. Relative velocity as a concept is skewed by imagining the air moving as it implies that the air has kinetic energy at rest which it does not.

Pilots only need a conceptual understanding of lift and Newton does that without any complications.

Can you supply a wind tunnel photo of a Jab and we will see here the streamlines go. Again, imaging the aircraft immersed in water and see what you think the cause is.

This is what I said: "Supercritical wings were introduced originally to help break the sound barrier and are irrelevant to RA and GA flying and irrelevant to supersonic flying, and seem to have been used just as distraction by the geek."This was the Wikipedia paragraph I quoted from:

 

"Research aircraft of the 1950s and '60s found it difficult to break the sound barrier, or even reach Mach 0.9, with conventional airfoils. Supersonic airflow over the upper surface of the traditional airfoil induced excessive wave drag and a form of stability loss called Mach tuck. Due to the airfoil shape used, supercritical wings experience these problems less severely and at much higher speeds, thus allowing the wing to maintain high performance at speeds closer to Mach 1."

 

Since despite, explanations you've been unable to comprehend that this comment was solely used due to your assertion that a supercritical wing has a flat top and a curved bottom, I'll leave you to work through this one yourself.

 

I don't now how you do it! You have misread this again! It did not say that supercritical wings provided the solution to supersonic flight. They were not invented until years later.. They are two separate statements. it says that SC aerofoils do not suffer this as much it did not say they were the cure to M1.0. Tha's what you get for using Wiki... educated people do not. We use the references and actually read them.

 

Don't be sad, I only quoted a passage verbatim from the book and recommended people buy it. How that translates into understanding/not understanding I don't know.

 

Yes, I'm sorry Tomahawk

 

Let's not get off the subject, you were talking about supercritical aerofoil sections, so you can bite your tongue on this one.

 

You were corrected on this one by another poster but appear to have overlooked it.

 

I didn't say you did although you certainly didn't emphasis that in the NASA material you supply to cadets NASA says it is right. What you did say is that Bernoulli is irrelevant and that's BS.

 

Did I say that Bernoulli is irrelevant? If you choose to see that as irrelevant so be it.

 

The fact is that you don't need it at all to understand how wings work unless you are an aerodynamicist and then only for very specific uses. Newtonian explanations are much clearer and not open to misinterpretation.

 

No that's not my assertion - you said "A SC wing (that most pilots will spend most of their careers sitting on top of)"

 

I pointed out you were talking to the wrong audience on this site where most of the people fly for recreation and only three or four are involved in airline flying. I also gave you a link to a site where professional pilots, instructors and students wo will go on to fly for airlines hang out.

 

And I showed you that a Tomahawk uses an aerofoil with SC characteristics.

 

It is amusing that virtually all your triumphant winning bullet points appear to have flaws; what's not so amusing is that this two dimensional garbage could be coming out the end of one of our Universities.

Your understanding of how things work is so poor that you say that 'sometimes a Sprint car wing acts like a flat plate and sometimes like an aerofoil.'

A flat plate inclined to airflow IS and aerofoil.

Hi Daffyd, no intent to argue here just to make sure I understand you. Lots of people refer to' downwash' as a reason for lift but one the air has transited the wing it has no further effect.

I am very aware of the positioning of the tailplane as a a design factor hence my reference to Deep Stall.

I will look into the issues you have mentioned. I am always keen to learn something new. Thanks for your feedback.

Quote"... "If any body ever tells you anything about an aeroplane which is so bloody complicated you carn't understand it , take it from me - its all balls ". - R J Mitchell .Mike

Lift is conceptually simple. Anyone who has stuck their hand out of a car window has experienced it. It can be explained simply to a six year old who has never heard of Bernoulli but apparently not to some amateur pilots who have...

Wouldn't start a victory dance just yet, he may have just grown tired of trying to educate the flat earth society

Many years ago, on my aircrew course I was taught that challenge and response checklists must be given correctly. If one word of the response was correct it was repeated so that the understanding was clear. We cannot have aviation sitting 'thumb in bum - mind in neutral' and just accepting what they are told.

it just leads to tragedy.

He answered a question no one asked and then expects everyone to fall over themselves praising him at the foot of his plinth.Now excuse me, I'm late for a witch trial, anyone got a spare duck?

Who asked the question no-one was asking? Isn't understanding how your aircraft works a good thing?

So is the horizontal stabiliser using a downforce ( due to a negative angle of attack) or is it being sucked down, because having a movable surface at the trailing edge makes Newtons law more relevant

The condition for longitudinal stability means that the more forward "lifting" surface - the wing in a conventional layout, or the foreplane, in a canard - must always carry a greater upward load per unit of its planform area, than the more rear surface. It does not necessarily mean that the tailplane mustalways produce a downforce; tho with a highly-cambered wing, it generally work out that way, especially at forward CG, especially if the aircraft has conventional wing flaps. Use of negative flap in cruise reduces the tailplane loads and helps performance a bit for that reason. Some aircraft - for example, the Fokker F-27 - use an inverted airfoil section on their tailplane, because it predominantly works to generate a downforce.The mechanism whereby the tailplane develops either upward or downward force, is exactly the same as the mechanism by which a wing does it; and it will have its own system of vortices accordingly.

 

The fact that a tailplane operates inside the downwash field of the wing, simple alters its zero-lift angle, and the rate of change of the wing downwash as the wing angle of attack changes, means the tailplane has a reduced effective lift-curve slope - which means it has to be larger than if it were not affected by the wing downwash.

 

The presence of a separate elevator is simply a means of simultaneously altering the tailplane incidence as well as its camber.

What it a downwash field? I thought the whole downwash thing was dead and buried? If the resultant flow vector of the air at the trailing edge is downward (there is no 'washing, the air is exiting the trailing edge at a lower 'relative speed' than the wing due to form drag and induced drag) there is no way for the disturbed air to impinge on the stabiliser except at very high AOA.

(The is the reason for deep stall in T tailed aircraft)

Also most non canard aircraft that I am aware of have the 'inverted aerofoil' tail as a requirement of dynamic stability but the primary reason for it is that the CofG is forward of the C/L and the stab provides a balancing force to maintain longitudinal stability. It is trimmed to allow for drag minimisation as CofG and C/L changes due to fuel use, airspeed changes, flap changes and other changes in flight.

So is the horizontal stabiliser using a downforce ( due to a negative angle of attack) or is it being sucked down, because having a movable surface at the trailing edge makes Newtons law more relevant

It does not 'suck' anything. It creates a resultant force on the aircraft by bending the airflow upwards instead of downwards. The amount of force can be varied by moving the stab through a range that either increases or decreases the angular momentum change of the air, no different from pitching an aircraft up and down..

Simples...

Here's an example of where a knowledge of Bernoulli helped me.There was a whiff of exhaust smell one day when flying. Bernoulli says that the flow in the fuselage will go from a hole in the rear forwards to exit at the doors.

Why? Because the flow velocity is higher at the doors and therefore the pressure is less.

 

Sure enough, on removing the sub-fin, I found that the sealing tape blocking the cable-hole had come off. Exhaust gases were mixed in with the flow at the fuselage rear and were entering the sub-fin and then into the fuselage to be sucked forward and exit at the imperfectly-sealing doors.

 

There was another aircraft at Gawler where the builder had designed and put in an "exit vent" at the fuselage rear, and I couldn't make him believe that he had made an inlet vent.

 

Air flowing forward is counter-intuitive, even inside a fuselage.

 

But yes, Complete, if you must dumb down the physics and only tell part of the story, the reaction to pushing air down is a better description of lift than Bernoulli.

 

You would be in good company, the universities now give out masters degrees for what used to be school stuff.

 

Personally, I reckon the vortex stuff explains things like wake danger and it should be taught, even though I personally find it difficult.

G'day Bruce,

"Why? Because the flow velocity is higher at the doors and therefore the pressure is less."

See this is where not understating the specifics of Benoulli can lead you astray.

Please remember that the plane is moving, the air is not. What you are talking about is relative flow speed and that is not really an explanation using Bernoulli.

Bernoulli is simply expanding on Newton's 2nd law. F=Ma. Bernoulli applies in a single streamline not at two different unrelated locations.

What you are describing is a displacement disturbance. A lot of these misinterpretations would disappear if we imagine the aircraft submerged in water which behaves the same as air.

Imagine your aircraft immersed in water like in a shipping test tank and being moved along. Where would the water come in and why?

Areas exposed to direct flow will 'scoop' the water in and the water will continue moving until it finds an exit where the dynamic pressure is less.

As for your comments about Master's Degrees, I would respectfully suggest you either have never been to university or went to a very dodgy one. On my MSc course I had military and civilian test pilots, a professor from Cranfield University and former chief pilots from major airlines as my course supervisors.

It was by no means easy.

Your statement is unfair, inaccurate and silly.

Australia ranks very highly in the world in University education and in my years lecturing I was very tough on the knowledge level of would be pilots.

Please restrain yourself to statements supported by facts not opinions.