Strings explain the bernoulli theory

[fly_tornado]

A lot of people find it difficult to understand how the low pressure above a wing creates lift.

 

these tufts of string show whats happening

 

 

 

[facthunter]

I don't like to get involved with Bernoulli, but the tufts sure show when the wing stops working. Note how far the flow reverses, and the separation point. Nev

 

 

[metalman]

This should be sent to NASA, I think they have problems with Bernoulli s theory!

 

 

[Ultralights]

is it a demonstration of Bernoulli's theory or a demonstration of flow separation over the wing commonly called a stalled situation, and how the air moves over the wing in a spin manoeuvre?

 

The best example of Bernoulli's theory in an aircraft would be the carby venturi or a airflow Vacuum venturi system seen on older aircraft.

 

and let me get some popcorn..

 

 

[Old Koreelah]

...enough to send you into a spin...

 

 

[Gnarly Gnu]

This should be sent to NASA, I think they have problems with Bernoulli s theory!

Deniers!

 

 

[farri]

I`m not going to argue with those who say Bernoulli`s principal is a myth. I know I taught it and none of my students fell out of the sky ( so to speak ) I never have either,for that matter!

 

There`s a hell of a lot of pilots who were taught that the camber of the wing determines the speed of the airflow over the top surface of the wing, thereby, decreasing static pressure and creating lift! As far as the pilot is concerned, does it realy matter whether Bernoulli`s principal is a myth or not? what the pilot realy needs to know most is how to fly the aircraft.

 

Frank.

 

 

[facthunter]

Won't stop people flying Farri, but I prefer more realistic explanations that apply everywhere. Like if air goes in a curved path there has to be higher pressure on the outside and lower on the inside, but if you say "static pressure plus dynamic pressure is a constant' the interview person will give you a tick... Nev

 

 

[fly_tornado]

I don't know why people use the venturi to explain how low pressure works, where is the low pressure in a venturi?

 

 

[facthunter]

Near the narrowest part. It is used in carburetters. Nev

 

 

[fly_tornado]

but where is the giant piston in the sky creating the vacuum?

 

 

[facthunter]

Well I feel you have got me there, because I have no idea what you are talking about. Nev

 

 

[fly_tornado]

carburettors and low pressure.

 

Wonder how flying schools will explain it once carburettors are only found in museums.

 

 

[farri]

Won't stop people flying Nev

So what is being taught at the moment?

 

Frank.

 

 

[facthunter]

Probably Bernoulli. That would only be a guess on my part, Farri How does one tell unless we do a survey. It is a long time since everyone taught from one reference, like AP 1732A and there are a lot of books put out by flying instructors, that have their own way of explaining things. Most would have one or two points of contention... Nev

 

 

[Mark11]

Coanda effect is more accurate than Bernoulli theory - and is just newtons balance of forces

 

The shape of the wing makes air deflect downwards. Air has weight and this change in direction creates a force in the opposite direction = lift

 

 

[fly_tornado]

maybe instead of calling it lift it should be called push?

 

 

[facthunter]

Call it an aerodynamic reaction. PUSH doesn't do it for me, LIFT has been around for a while and it is a simple and explanatory word of how the WEIGHT (mass x "G" force) is opposed. and the aircraft LIFTed into the air. Nev

 

 

[metalman]

Newton seemed to have a neat and tidy explanation , although his laws don't explain why the top of a wing needs the shape it has,

 

I prefer to call it magic , and leave at that

 

Matty

 

 

[kaz3g]

Newton seemed to have a neat and tidy explanation , although his laws don't explain why the top of a wing needs the shape it has,I prefer to call it magic , and leave at that

Matty

I seem to remember my balsa wood gliders flew pretty well with just a thin flat sheet for a wing. The spitfire wing is a very thin section and worked a treat, too. .

 

Kaz

 

 

[fly_tornado]

have you seen the wings on a 787? hard to believe they can carry 250 ppl

 

 

[Ultralights]

There's almost no curve at all to the top of the wing on a F18, or similar fighter aircraft.

 

 

[metalman]

There's almost no curve at all to the top of the wing on a F18, or similar fighter aircraft.

so how does bernoulli relate to that airfoil?

As for it not being important ,it depends on the person, I like to have an understanding of what's happening, some mightn't care and thats fine , but I always thought what was taught in ground school (bernoulli)just didn't add up,,,,,

 

matty

 

 

[kaz3g]

I venture to suggest the correct answer is "all of the above".

 

Bernoulli works best at lower air speeds hence the wings of slow moving aircraft generally have wings with a significantly thicker leading edge. As the aircraft's Cruising speed increases more effect is gained from COANDA because the force on the underside of the wing increases with it as does the equal and opposite reaction (lift).

 

Hence your favourite big kero burner has slats on the leading edge and flaps the size of your hangar door to give it the Bernoulli result at takeoff speed then retracts them as it accelerates and COANDA takes over.

 

That's my theory, anyway.

 

Kaz

 

 

[M61A1]

According to one of the NASA articles, lift is a complex thing involving both Bernoulli and Newton's laws. I think the example of a symmetrical wing as proof that Bernoulli has nothing to do with lift, is not accurate. Regardless of which way up a symmetrical wing is flying, the AoA necessary makes the distance over the top longer than that underneath.