How Wings Create Lift (Bernoulli's principle stands corrected.)

StoneH

Friend of Leo's
Gold Supporter
Joined
Sep 20, 2021
Posts
2,016
Age
66
Location
Florida Gulf Coast
Heck yes. They learned about this from examining the shape of birds' wings. Otto Lilienthal and Orville and Wilbur Wright used the same approach many years later. The Wrights were the first to build a wind tunnel to test their airfoil shapes in a laboratory environment. Yeah, it was the back room of their bicycle shop, but who's counting Erlenmeyer flasks? ⚗️
I received my Aerospace Engineering Degree from the Air Force Institute of Technology. The Air Force Aviation Museum was just down the hill. The Wright Bros 1916 wind tunnel was/is displayed there. It's a work of art.

I specialized in advanced propulsion. The concept is summarized as follows:

SUCK - SQUEEZE - BANG - BLOW

1642306868312.png
 

Recce

Poster Extraordinaire
Gold Supporter
Joined
May 3, 2016
Posts
5,267
Location
Northern Alabama
It's like the argument about when geese fly in a V formation and one side is always longer than the other side: you need a PhD and $250K in student debt to figure this stuff out.

geese-V-formation.jpg


Cheers,

PhDgoo
I think I need a cookie. Maybe in the shape of a wing because that’s how they bake.
 

bcorig

Friend of Leo's
Gold Supporter
Joined
Mar 11, 2018
Posts
4,099
Location
Lost in the 909 trying to find my way home
I received my Aerospace Engineering Degree from the Air Force Institute of Technology. The Air Force Aviation Museum was just down the hill. The Wright Bros 1916 wind tunnel was/is displayed there. It's a work of art.

I specialized in advanced propulsion. The concept is summarized as follows:

SUCK - SQUEEZE - BANG - BLOW

View attachment 940620
You dated her too?
 

StoneH

Friend of Leo's
Gold Supporter
Joined
Sep 20, 2021
Posts
2,016
Age
66
Location
Florida Gulf Coast
One more:

In the days before PowerPoint, we had slide decks we presented on overhead projectors. There was a slide that occasionally showed up during briefings . . . it was a naked girl under the heading "No Nozzle Model".

If that happened today, you would be standing in front of the General.
 

jimd

Friend of Leo's
Joined
Nov 3, 2006
Posts
3,580
Location
Cleveland, Ohio
There is a pressure difference across the airfoil. But what causes that difference is usually explained incorrectly. If you are willing to invest some time, Prof. Babinsky’s explanation is excellent and doesn’t involve too much math. He is a professor at Cambridge in the UK and is a great engineer and teacher. Babinsky’s explanation of lift.
 

dogmeat

Friend of Leo's
Joined
Oct 12, 2017
Posts
3,563
Age
71
Location
Alaska
I think he mixed concepts between DRAG (induced) and LIFT.

IMO That diagram hardly applies to a wing foil.

If that Cessna is yours... You are a lucky Man!
Yes... the hi/low pressure mix at the trailing edge (and wingtips) he is talking about is drag or at least wasted energy... but not lift. whether drag it is induced or parasitic depends on where and how its measured. in theory, induced drag carries a lift component. if you measure where there is no reaction point, I don't see how you can call this lift. its wasted energy, more like wing (and tip) vortices.

the diagram applies. consider the old adage... with enough horsepower, you can fly a barn door. ever hold your hand out the window of a moving car?

part of my BST in Aviation Sciences was a project where I studied the relationship between airfoil Clmax and Alpha angle. it was a 15 week project where I built a 24" section wind tunnel and tested multiple airfoils trying to prove a relationship that wasn't there. (Clmax could predict the maximum Alpha angle on a given airfoil)(it can't)(far as I know)(that was over 30 years ago, maybe computers can do that now)(I still think there is a relationship but it is more complicated than I anticipated).

as for the plane... yes, mine. Piper PA18, 160hp on Edo 2000 floats
 

DugT

Tele-Afflicted
Joined
Sep 22, 2017
Posts
1,302
Location
Truckee, CA
I sheepishly admit to being the OP. After reading four pages of lift theory info at NASA.gov, I realized that lift cannot be explained simply and they admitted that on page five. The video on page one was refreshingly simple but post #3 convincingly refuted #1. Many comments below the #1 YouTube video also found fault with it.

The video on post #27 was convincing to me and simple enough but I wouldn't be surprised if someone here proved that Babinsky is the UK's Pillow Guy.

Maybe I thought lift should be easy to explain because it is so easy to make things that fly. Paper airplanes, Frisbees and Aerobies are a good examples.
 
Last edited:

MarkieMark

Friend of Leo's
Joined
May 7, 2016
Posts
3,915
Location
Eastern USA
No reason to feel "sheepish" IMO.
The video was just another common attempt at a convincing argument that "we had it wrong all this time" when in reality it didnt really bring anything new to the table, again IMO.
Current times provide us with ample examples of this kind of presentation. One needs a healthy dose of doubt and skepticism... About everything we are "fed"
But I appreciate that it provoked stimulating conversation none the less.
 

Bob Womack

Friend of Leo's
Joined
May 28, 2016
Posts
2,319
Location
Between Clever and Stupid
One more:

In the days before PowerPoint, we had slide decks we presented on overhead projectors. There was a slide that occasionally showed up during briefings . . . it was a naked girl under the heading "No Nozzle Model".

If that happened today, you would be standing in front of the General.
That was a common attention retainer in the Air Force. I encountered it in briefings at Blytheville SAC base and Eglin AFB.

Bob
 

DugT

Tele-Afflicted
Joined
Sep 22, 2017
Posts
1,302
Location
Truckee, CA
In my 8th grade catholic school class in 1964, a student brought to class several close up photos of missile launch structures that his dad provided. Some of them had several bare breasted women hanging out over railings. They were small but to scale and you had to look for them but it was worth it. As soon as a girl complained to our nun teacher the show was over. That was one of the most exciting days at that school.

Maybe a close second was the day a chubby student accidentally farted loudly during "Silent reading". At first it was a high pitched squeal as he was fighting to hold in but when he realized that wasn't working he let it go. It was loud and his face was a red as I have ever seen. I hope he wasn't permanently traumatized by his embarrassment. The nun did a good job of explaining that **** happens and we were all very understanding.
 

jimd

Friend of Leo's
Joined
Nov 3, 2006
Posts
3,580
Location
Cleveland, Ohio
I sheepishly admit to being the OP. After reading four pages of lift theory info at NASA.gov, I realized that lift cannot be explained simply and they admitted that on page five. The video on page one was refreshingly simple but post #3 convincingly refuted #1. Many comments below the #1 YouTube video also found fault with it.

The video on post #27 was convincing to me and simple enough but I wouldn't be surprised if someone here proved that Babinsky is the UK's Pillow Guy.

Maybe I thought lift should be easy to explain because it is so easy to make things that fly. Paper airplanes, Frisbees and Aerobies are a good examples.
You are absolutely right that lift cannot be explained simply. When people try they ultimately oversimplify and start violating physics. The funny thing is that a complete understanding of lift isn’t really necessary to build a plane. If you ask most aero engineers they will give you some version of one of the flawed descriptions. But they can still design a wing because we know what works.

The video I posted by Babinsky is the best I’ve seen. But even there I have two very minor issues. But they don’t contradict what he says (one is on a side comment about why putting your finger over the end of a hose creates faster flow - another simple but flawed explanation). Full disclosure: I work at NASA and know the guy who wrote the NASA webpages on lift (he’s now retired). I also know Prof. Babinsky and can definitely say that he is not the UK’s pillow guy. He is well respected and a darn good teacher and presenter.
 

Peegoo

Doctor of Teleocity
Joined
Oct 11, 2019
Posts
12,888
Location
Beast of Bourbon
That was a common attention retainer in the Air Force. I encountered it in briefings at Blytheville SAC base and Eglin AFB.

Bob

I remember that from my AF days.

Another one was at a Gubmint Agency where I worked, the central photo lab (remember wet film processing?) would often include as the last picture a really cheesecakey bikini girlie with her bee-hind prominently facing the camera and the words THE END across the bottom. It was a goofy joke at the time, but now? NoFreekinWay.

Times is certainly differnt!
 

trev333

Telefied
Ad Free Member
Joined
Dec 3, 2009
Posts
30,266
Location
Coolum Beach,Australia
I watched the Babinski lecture...

some thoughts..... air compresses, fluids don't.... using fluid dynamics to describe the action of air over a wing might not quite be the same as with water... or flowing over a cylinder...

his early description of a sail with air passing over inside/outside the same speed is wrong in practice...

the air hits the front edge flows over the outside, but it causes eddy currents along with the low pressure along the inside, he shows that toward the end....

if you've trimmed a sail you'll notice a few clear windows in a sail with small bits of wool either side "telltails" that show you the different flows of air outside and inside.... a good setting for max lift has the outer wool flat with the wind and the inside one weightless drifting up.....

pressure is a term we know well for drive,.... a lift/knock is when the wind alters direction slightly one way or another... within a steady breeze.

a sail foil is a totally different angle than a plane wing to the wind...and is capable of moving/reshaping..

he should have left yacht sails and fluid out of his descriptions about wing lift in air...
 

StoneH

Friend of Leo's
Gold Supporter
Joined
Sep 20, 2021
Posts
2,016
Age
66
Location
Florida Gulf Coast
I watched the Babinski lecture...

some thoughts..... air compresses, fluids don't.... using fluid dynamics to describe the action of air over a wing might not quite be the same as with water... or flowing over a cylinder...

his early description of a sail with air passing over inside/outside the same speed is wrong in practice...

the air hits the front edge flows over the outside, but it causes eddy currents along with the low pressure along the inside, he shows that toward the end....

if you've trimmed a sail you'll notice a few clear windows in a sail with small bits of wool either side "telltails" that show you the different flows of air outside and inside.... a good setting for max lift has the outer wool flat with the wind and the inside one weightless drifting up.....

pressure is a term we know well for drive,.... a lift/knock is when the wind alters direction slightly one way or another... within a steady breeze.

a sail foil is a totally different angle than a plane wing to the wind...and is capable of moving/reshaping..

he should have left yacht sails and fluid out of his descriptions about wing lift in air...

One of the few things I remember from my hypersonic days: "Newtonian physics works, then it doesn't, then it does"

I think wing and sail analogies are a case in point.

1642423894619.png
 

Sparky2

Poster Extraordinaire
Joined
Apr 15, 2017
Posts
5,064
Age
62
Location
Harvest, Alabama
When I went thru flight school in the Army many decades ago, we learned a lot of information about how the rotor blades on the helicopter produced lift. Most of it was either incorrect, or overly-simplistic.

When I became a flight instructor a few years later, I was required to teach that same incorrect, overly-simplistic nonsense to my students.
(For a few years anyway.)

After awhile, it all became clear to me when I flew with a pragmatic evaluator.

He said, "Okay John. I don't want the book solution to lift, and airfoils, and the aerodynamics of autorotation, okay?"
We were 700 feet above a training runway at the time, doing 90 knots.

The man continued, "I don't want you to draw anything out on a piece of paper, and I don't want you to give me a class or anything."

He then chopped the throttle to idle, and said, "I just want you to autorotate the helicopter, and land on the numbers at the approach end of that runway down there."

And then we flew a few more patterns, talking about how and why I landed a bit long or short, and what I needed to do in order to teach pilots how to make subtle corrections in order to land the helicopter onto a given spot on the ground.

Best lesson there ever was.

;)
 
Last edited:




Top