Debunking Lift Theories Still Taught

[completeaerogeek]

Hi all, it is amazing to me that there are still people out there teaching silly ideas about how lift works.

 

Even CASA is still pushing things that aero professionals laugh at despite being told so many times that what they say is fiction.

 

As a 33 year aviation professional and University lecturer with an MSc in this stuff, it drives me nuts!

 

Here are several references that may embarrass your flying instructor (and a lot of professional pilots)

 

A clue: One if from NASA the other from Cambridge University so we can be pretty confident in what they say.

 

In reality there is NO DEBATE or 'alternate theories' about how lift works amongst aerodynamics specialists.

 

At the fringes in tiny percentages there is some weird stuff but for 99% of what is relevant this is the story...

 

If your flying instructor or aero guru tries to argue-tell them to write to NASA and explain themselves. Should get a laugh from the team at the Glenn Research Centre!

 

http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html

 

 

http://www.219sqn.aafc.org.au/Flight/Simple%20Aerodynamics-How%20planes%20fly.pdf

 

Read/watch and enjoy.

 

In summary:

 

Lift IS NOT caused by two air particles racing eachother over the upper and lower surfaces. They never even get close. (watch the streamlines in the video)

 

A wing IS NOT A VENTURI. Once you take the top of a venturi is is not longer a closed system so that goes out the window.

 

Lift is caused by bending the air just like a ceiling fan. Both surfaces bend the air downwards causing a reaction force.

 

The pressure differentials ARE NOT caused by wing shape. They are caused because the wing is pushing and pulling the air in different directions.

 

If wing shape was the reason then how would a hang glider, kite,or sailboat work? They have single surface aerofoils with the same distance top and bottom.

 

They use exactly the same physics and formulas.

 

Also paper planes have flat wings, so to missiles and some aircraft like the F-104. Most military aircraft for a long time have had symmetrical wings (equal camber)

 

And here's the kicker:

 

Every airliner flying today has a supercritical wing that is curved on the bottom and flatter on top... How's them apples?

 

Please don't assume your flying instructor has any special knowledge that can refute the laws of physics.

 

A good pilot will always question things that sound dodgy. Oh and "You don't have to understand - it you just have to believe it" is nonsense.

 

This works fine for religions where there is no proof or evidence but not in physics...

 

Have fun!

 

The Completeaerogeek...

 

 

[johnm]

I'm with you - go get 'em Completeaerogeek

 

 

[ianboag]

A propellor is a rotating wing. Does it suck or blow ... ? I'll go with blow .....

 

 

[M61A1]

Every airliner flying today has a supercritical wing that is curved on the bottom and flatter on top... How's them apples?

The Completeaerogeek...

Show me some....I've not seen any.

[djpacro]

Even CASA is still pushing things that aero professionals laugh at despite being told so many times that what they say is fiction.

CASA's Day VFR Syllabus wasn't too bad itself (of course, many people did not know how to correctly apply that element of the syllabus) but with its replacement by the Part 61 Manual of Standards they have definitely gone down the wrong track.

 

As a 33 year aviation professional and University lecturer with an MSc in this stuff, it drives me nuts!

33 years ago is 1981 by my calculations - only a few years after people like Garabedian & Korn developed the tools to enable the design of stuff like this

which became the wing of the A320.

 

Every airliner flying today has a supercritical wing that is curved on the bottom and flatter on top... How's them apples?

I never compare apples with oranges. Lots of airliners without supercritical aerofoil sections. Some with semi-supercritical sections. Some just with classic sections from the book.

[completeaerogeek]

CASA's Day VFR Syllabus wasn't too bad itself (of course, many people did not know how to correctly apply that element of the syllabus) but with its replacement by the Part 61 Manual of Standards they have definitely gone down the wrong track.33 years ago is 1981 by my calculations - only a few years after people like Garabedian & Korn developed the tools to enable the design of stuff like this

 

[ATTACH]31879[/ATTACH]

 

which became the wing of the A320.

 

I never compare apples with oranges. Lots of airliners without supercritical aerofoil sections. Some with semi-supercritical sections. Some just with classic sections from the book.

 

 

[completeaerogeek]

Yes your calculations are correct. I joined the RAAF in 1981.

 

Now on to business- Not that this is the point - I was demonstrating that a conventionally cambered wing is a lot less common than people think)

 

Which modern airliners do not have supercritical wings? The entire Airbus family does (unless you can find otherwise) and most certainly The A380 does. IN fact it is an SC(2) -0606 Airfoil (see attached)

 

All modern airliners use SC wings or MCrit would be lower than it is.. SC reduces the standing shock wave as the upper surface air flow approaches M1.0.

 

The M.1.0 issue is related to the density drop and the air 'turns the corner of the upper surface. Lower density, lower speed of sound.

 

Attached Files:

 

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• 
  A380 NASA wing profile.JPG
   
   
  

 

 

 

 

[completeaerogeek]

Show me some....I've not seen any.

Been on an airline lately? Then you have sat on top of one.

 

How about the biggest - the A380. (see attached) How's them apples?

 

All modern airliners do. The entire Airbus family and all Boeings from the 767 on. Otherwise they would have to lower their cruising speed as MCrit would be too low. Standing shockwaves (which are visible by the way) would be too large and fuel consumption too high.

 

 

 

[completeaerogeek]

A propellor is a rotating wing. Does it suck or blow ... ? I'll go with blow .....

You are right. It blows. Both surfaces change the direction of the air from in line with the horizontal or rotational plane to a rearward vector. (just alike a desk fan!)

 

 

[ianboag]

And of course a helicopter rotor is another wing going round and round .... does it suck or does it blow? I'll go with "blow" on that one too.

 

Try flying an aircraft at zero angle of attack and see how well the "top wing suction" keeps you up there ....

 

 

[completeaerogeek]

You are essentially correct. However an aircraft with a conventional cambered upper surface will be creating lift at zero AOA.

 

Angle of incidence is usually 3 degrees which equates to three degrees of AOA.

 

Also the upper surface in a conventional cambered wing still bends the upper surface air downwards even if you are at zero AOA.

 

You have to lower the nose to about 3 degrees to reach zero lift pitching angle.

 

A helicopter usually has a symmetrical aerofoil so is producing no lift at zero AOA.

 

 

[Soleair]

I'm surprised nobody has mentioned inverted (aerobatic) flight yet. Many aerobatic wings are symmetrical, relying on incidence to create lift.

 

 

[completeaerogeek]

I'm surprised nobody has mentioned inverted (aerobatic) flight yet. Many aerobatic wings are symmetrical, relying on incidence to create lift.

You are correct. Not just aerobatic aircraft either. Military aircraft since the 1940 have been using symmetrical aerofoils. The Canberra is a good example of this.

 

In reality a flat plate is a very good wing with an exceptional L:D ratio. It just stalls earlier.

 

All teaching should start with a flat plate wing (such as a paper plane) I do and it is very effective in debunking silly ideas.

 

 

[fly_tornado]

Most pilots will learn Bernoulli without question purely and simply because its just a hoop to jump through to get the licence. Its just how the aviation industry is. you wanna get ahead: don't rock the boat.

 

 

[Derby]

Right on you just have to look at a mustang P51 wing its the same on top as the bottom.

 

Rory

 

 

[pmccarthy]

The upper aero foil section reduces turbulence and hence drag as I understand it. The airflow goes more or less where it would go anyway due to the angle of attack and the aero foil is shaped to meet that path and insert a more laminar boundary layer. Or is that more myth?

 

 

[SDQDI]

A propellor is a rotating wing. Does it suck or blow ... ? I'll go with blow .....

It sucks if it stops spinning:yikes:

 

 

[completeaerogeek]

The upper aero foil section reduces turbulence and hence drag as I understand it. The airflow goes more or less where it would go anyway due to the angle of attack and the aero foil is shaped to meet that path and insert a more laminar boundary layer. Or is that more myth?

Not really. it is pretty simple. See my first post above or look at the NASA reference which explains it all.

 

 

[completeaerogeek]

Most pilots will learn Bernoulli without question purely and simply because its just a hoop to jump through to get the licence. Its just how the aviation industry is. you wanna get ahead: don't rock the boat.

The problem with that philosophy is that it is dangerous and goes against basic Aviation Human factors philosophy which says to question things that look wrong.

 

This philosophy when employed works extremely well. When ignored is deadly. I could list many, many accidents caused by the junior pilot not challenging the captain or the pilots ingnoring a query from a flight attendant about 'strange noises'..

 

That CASA should still be teaching nonsense should not really be of any surprise to us...

 

It also leads to accepting other dangerous concepts taught in basic flying like Power + Attitude = Control.

 

This only works if you are flying a centreline thrust aircraft not on any aircraft with podded engines. . Just ask the guys on AF447. Oh you can't because they believed it.

 

This should have long ago been changed to ATTITUDE + POWER = CONTROL. With decaying airspeed or high AOA LOWER THE NOSE FIRST.

 

Applying thrust to correct low airspeed/high AOA in most airliners with underslung engines is a death sentence. You can ask the crew of Asiana 214 at least they survived.

 

We must continue to educate our young aviators as to the actual physical laws under which they operate. Anything else is at the least embarrassing and at worst deadly...

 

 

[Guernsey]

We all know that the prop is just a fan to keep the pilot cool.....just see how hot he gets if it stops.

 

Alan.

 

 

[flyerme]

Why is there 2 threads on this subject?

 

1 . Debunking lift theories is still taught

 

2. Bernouli's irrelevant

 

They need amalgamating!

 

Just saying!

 

 

[ianboag]

You are essentially correct. However an aircraft with a conventional cambered upper surface will be creating lift at zero AOA.Angle of incidence is usually 3 degrees which equates to three degrees of AOA.

 

Also the upper surface in a conventional cambered wing still bends the upper surface air downwards even if you are at zero AOA.

 

You have to lower the nose to about 3 degrees to reach zero lift pitching angle.

 

A helicopter usually has a symmetrical aerofoil so is producing no lift at zero AOA.

But the lower surface contributes zilch at zero AoA ..... probably makes it a bit harder to stay up there

 

 

[ayavner]

It also leads to accepting other dangerous concepts taught in basic flying like Power + Attitude = Control.

##########

 

This should have long ago been changed to ATTITUDE + POWER = CONTROL. With decaying airspeed or high AOA LOWER THE NOSE FIRST.

Hey this is a great post, and I am following because I am also one who wants to understand rather than just repeat if at all possible. Just wondered if you could clarify, but I am not seeing the difference between the 2 other than the order of attitude and power and the fact that they are in CAPS on the second sentence. I may just be dense, but can you help here? I am just looking at it as 1+2 = 2+1, but that's clearly not what you meant. cheers~!

 

 

[completeaerogeek]

We all know that the prop is just a fan to keep the pilot cool.....just see how hot he gets if it stops. Alan.

I don't know, glider pilots look pretty cool...

 

 

[completeaerogeek]

Hey this is a great post, and I am following because I am also one who wants to understand rather than just repeat if at all possible. Just wondered if you could clarify, but I am not seeing the difference between the 2 other than the order of attitude and power and the fact that they are in CAPS on the second sentence. I may just be dense, but can you help here? I am just looking at it as 1+2 = 2+1, but that's clearly not what you meant. cheers~!

You mean the concept? The order of power and attitude can mean the difference between life and death.

 

Apply power first in a low airspeed situation in an airliner with underslung engines and you will violently pitch up far beyond you elevator authority to correct. STALL-STALL-STALL-DEAD