Basic Aerodynamics question

[Victor Squawk]

So, you are banging on the door of one of the most commonly misunderstood - and often not at all understood - assumptions in aviation.

Most pilots have little idea how a wing actually produces lift, nor how that lift is actually related to drag. But to blame them for their ignorance is likely akin to blaming a crack baby for being addicted to crack. It's not much their fault for misunderstanding a concept that was poorly explained to them.

Here's the thing. Fluid dynamics are a female dog. Even very clever physicists find the topic highly challenging.

While I very much appreciate your intuitive sense of WTF? and your curiosity to learn more, you will be hard pressed to find binocular vision in the kingdom of one eyed men.

At some point, we mere practitioners of aeronautical appliance operation must accept the abstract of the actual physics and take the practical outcome of those facts at some level of "faith". If pilots actually understood physics, most of them would be working for NASA or, more likely, working as quants on Wall Street.

Sadly, the physics of lift production by an airfoil is typically abstracted to an absurdity that the molecules of air impacting the leading edge of a wing split - with half of them moving above the wing and half of them moving below. It should already be obvious that we have already entered fairy tale land. But now it gets even better. The tale continues with a bunch of big words to explain how the top molecules are moving faster than the bottom molecules. Then it goes full crack-head and suggests that baby Jeebus demands that all those molecules MUST meet up at the trailing edge of the wing.

All of that is pure bunkum.

Three are several complicated factors that create lift. And yes, some of them have to do with the Bernoulli effect. But at the end of the day, just think of lift using a basic understanding of the 3rd law of Newtonian mechanics. The wing diverts the air molecules smashing into it into a net downward force. That net downward force creates an equal and opposite upward force that we chain smoking drunks refer to as "Lift".

Ahahahaha I bet you just can't stomach the implications of absolute space! Physics these days runs on spazzytime thanks to einsteinian relativity??

I'm just joking. There's no need to bash my idea bout why air gains velocity above the wing. I was just trying out an explanation and seeing if it helps me understand.

I hadn't thought of Newtonian mechanics. We were told they are also at play. That's my fault, since I was hyperfocusing on trying to understand Bornoulli's explanation. Thanks for the guidance; I'll try to think more flexibly about it.

 

[form810]

Ahahahaha I bet you just can't stomach the implications of absolute space! Physics these days runs on spazzytime thanks to einsteinian relativity??

I'm just joking. There's no need to bash my idea bout why air gains velocity above the wing. I was just trying out an explanation and seeing if it helps me understand.

I hadn't thought of Newtonian mechanics. We were told they are also at play. That's my fault, since I was hyperfocusing on trying to understand Bornoulli's explanation. Thanks for the guidance; I'll try to think more flexibly about it.

I wasn't bashing YOUR anything. I was bashing the commonly assumed, and oft passed-on tribal bunkum that infects our industry to this day.

Many in this industry are still teaching stuff that is just plain wrong and indefensible. Why would YOU, as a student, think what you were being taught (likely at the cost of many dollars) was wrong if you had no context in which to judge the truth of it?

 

[Victor Squawk]

I wasn't bashing YOUR anything. I was bashing the commonly assumed, and oft passed-on tribal bunkum that infects our industry to this day.

Yeah but that was the explanation I thought up in my attempt to explain. It might be a common misunderstanding, but I misunderstood it, m'self.

It's MY explanation lol

Anyway, this thread, altogether, has helped me in various ways, primarily with equipping my imagination, sharpening my thinking, and inspiring me for future, more sophisticated, understanding. I even wondered if I could ever work on a plane of my own, however I want, and it helps to see that I think I can find my way to being able to do so, with time, of course.

 

[form810]

Yeah but that was the explanation I thought up in my attempt to explain. It might be a common misunderstanding, but I misunderstood it, m'self.

It's MY explanation lol

Anyway, this thread, altogether, has helped me in various ways, primarily with equipping my imagination, sharpening my thinking, and inspiring me for future, more sophisticated, understanding. I even wondered if I could ever work on a plane of my own, however I want, and it helps to see that I think I can find my way to being able to do so, with time, of course.

Oh, sorry. I failed to grok that you reinvented Bernoulli. Here I was, like an idiot, thinking you were just referencing Bernoulli. My bad.

 

[inigo88]

So that does provide some logic for integrating more information to the function of lift (or, lift as a function). Yet it still takes for granted that lift and induced drag coincide (and thus produce the various consequences being discussed throughout this thread, even to include concerns for designing an experimental airplane).

Yes, they must indeed coincide and I cannot doubt that, since - planes fly and pilots use the assumption to fly them well. But defining lift as a function is more like "redefining" it to protect the assumption. It's just another way of "taking it on faith" (as our instructor in PPGS says from time to time, implying that we will gain the understanding later on).

The part that stands out to me is the emphasis on airflow as the input for the function. This ascribes to it causality. It begins with a pressure differential. Then stuff happens to the airfoil like developing lift? Do the air molecules gain velocity above the wing because the wing moves through the same absolute space at a constant speed, while the molecules are forced to cover a longer distance due to the shape of the wing?

Like, why do they gain velocity just because an airfoil is there, man. I guess I can intuit the pressure differential since the engine produces both suction and blast. But what about the velocity of air above the wing? I kinda think I got it, but then I think about it some more and I probably dont.

NASA Glenn has a dated but excellent website on aerodynamics and how wings generate lift.

What is Lift:

What is Lift?

Aerodynamic Forces:

Aerodynamic Forces

Lift from Flow Turning:

Lift from Flow Turning

Incorrect Theory #1 (Equal Transit):

Incorrect Lift Theory

Incorrect Theory 2 (Skipping Stone):

Incorrect Lift Theory

Incorrect Theory 3 (Venturi Nozzle):

Incorrect Lift Theory

Bernoulli vs Newton:

Bernoulli and Newton

The real details of how an object generates lift are very complex and do not lend themselves to simplification. For a gas, we have to simultaneously conserve the mass, momentum, andenergy in the flow. Newton's laws of motion are statements concerning the conservation of momentum. Bernoulli's equation is derived by considering conservation of energy. So both of these equations are satisfied in the generation of lift; both are correct. The conservation of mass introduces a lot of complexity into the analysis and understanding of aerodynamic problems. For example, from the conservation of mass, a change in the velocity of a gas in one direction results in a change in the velocity of the gas in a direction perpendicular to the original change. This is very different from the motion of solids, on which we base most of our experiences in physics. The simultaneous conservation of mass, momentum, and energy of a fluid (while neglecting the effects of air viscosity) is called the Euler Equations after Bernoulli's student, Leonard Euler. If we include the effects of viscosity, we have the Navier-Stokes Equations which are are named after two independent researchers in France and in England. To truly understand the details of the generation of lift, one has to have a good working knowledge of the Euler Equations.

Navier-Stokes Equations:

Navier-Stokes Equations

The equations are a set of coupled differential equations and could, in theory, be solved for a given flow problem by using methods from calculus. But, in practice, these equations are too difficult to solve analytically. In the past, engineers made further approximations and simplifications to the equation set until they had a group of equations that they could solve. Recently, high speed computers have been used to solve approximations to the equations using a variety of techniques like finite difference, finite volume, finite element, and spectral methods. This area of study is called Computational Fluid Dynamics or CFD.

 

[Victor Squawk]

Oh, sorry. I failed to grok that you reinvented Bernoulli. Here I was, like an idiot, thinking you were just referencing Bernoulli. My bad.

I'm about to re-invent Bernoulli
here i go ....

"Due to absolute space being true, instead of relativistic spacetime, the airfoil penetrates the field of air-fluid and separates the molecular plane according to its camber. The speed of the aircraft fails to move the various parts of the aircraft at varying speed; instead it moves the aircraft as a whole. The speed of the whole aircraft is in unison. Thus, all the parts of the wing move as if the wing is a singular object.

"Suddenly, the wing (as the exemplary airfoil) moves through absolute space at a constant speed, while the air-fluid, above and below the wing, is left behind to fend for itself. The camber of the wing forces the air-fluid above the wing to move a longer distance in absolute space. This effectively "stretches" the molecular plane of air above the wing. This stretching lessens the pressure of the air above the wing, while the pressure below the wing remains constant."

"Unfortunately, this also means that the faster the aircraft moves through space, the faster it lifts. Pilots will now have to adjust to this new reality and learn to fly accordingly. Thank you and good evening, y'all."

 

[inigo88]

 

[form810]

NASA Glenn has a dated but excellent website on aerodynamics and how wings generate lift.

What is Lift:

What is Lift?

Aerodynamic Forces:

Aerodynamic Forces

Lift from Flow Turning:

Lift from Flow Turning

Incorrect Theory #1 (Equal Transit):

Incorrect Lift Theory

Incorrect Theory 2 (Skipping Stone):

Incorrect Lift Theory

Incorrect Theory 3 (Venturi Nozzle):

Incorrect Lift Theory

Bernoulli vs Newton:

Bernoulli and Newton

Navier-Stokes Equations:

Navier-Stokes Equations

I don't think he really wants help. I think we are being trolled. Kinda thought that initially, but thought I'd try to help anyway. Oh well.

 

[Victor Squawk]

Incorrect Theory #1 (Equal Transit):

Incorrect Lift Theory

Awwww yeaaah, #1

 

[Victor Squawk]

I don't think he really wants help. I think we are being trolled. Kinda thought that initially, but thought I'd try to help anyway. Oh well.

Hey, come on. I was just joking. I thought that would be funny.

I didn't know Bornooli was sacred? Isn't it obvious by the end of my silly post that it's not serious?

"Unfortunately, this also means that the faster the aircraft moves through space, the faster it lifts. Pilots will now have to adjust to this new reality and learn to fly accordingly."

 

[Victor Squawk]

I've never flown a plane, guys. Don't take me too seriously. I'm going through PPGS because my college treats it as a prerequisite class for taking the dispatcher course. When I get to the point where I fly solo, courtesy of being able to pay for the privilege to do so, I won't be confused about whose life is on the line when I get into the plane. I've no stake in any scientific theory or another, as long as I am able to fly the plane. How could it matter?

edit
There be some sensitive ppl on here, man. It'd be nice if there was a list of things not to say, so everyone will like me and also not bitterly discredit me into a troll. That's like trying to amputate all my threads before I even make them. And for what? I made fun of air.

 

[Victor Squawk]

Awwww yeaaah, #1

Anyway so, if the lift develops due to longer distance on the upper camber of the wing

- planes wouldn't fly upside down
- symmetrical wings couldn't fly
- wings with a longer lower camber wouldn't fly

Yet they do all fly, so that explanation doesn't work.

I also add my reasoning that (since I based my explanation on speed) it would also mean that higher speed directly translates to lift in all standard cases. That was just me having a bit of fun at my own mis-take.

I found the list to be apt and brilliant and I plan to read about the other explanations when I'm less sleep deprived.

I read every word that was written here gratefully and I am thankful for the time and expertise which was offered here to me and others who found something valuable here. Thank you all once again for the knowledge, ideas and information resources.

I think it's fair to say that it's probably time for me to take another break away from jc. This place stresses me out. I'm never sure what I can ask or if I should answer and i somehow get it wrong no matter what i choose.

Peace until next time

 

[inigo88]

I read every word that was written here gratefully and I am thankful for the time and expertise which was offered here to me and others who found something valuable here. Thank you all once again for the knowledge, ideas and information resources.

Glad you enjoyed it! You had a lot of specific questions and that’s one of the most straight forward resources I knew on the subject. Unfortunately aerodynamics doesn’t have straightforward conceptual answers until you get to systems of partial differential equations being solved by computer models, so most people settle for Bernoulli and Newton being two halves of the same coin and move on. There are a lot of pilots out there whose CFIs taught them the equal transit theory (incorrect theory #1) who still understand aerodynamics well enough to fly safely - so at the end of the day you don’t need to have a scientist/engineer level understanding of the topic to work in aviation, unless you WANT to dig that deep.

 

[knot4u]

One of my A/P school teachers liked to say "A barn door will fly at the right angle of attack.". We were required to build a model and prepare a report. One of my classmates was a lazy smartass, his model was a barn door from some childrens farmyard play set and his report was basically "A barn door wil fly at the right angle of attack.". His model joined other examples of brilliant thinking that hung from the classroom ceiling.

 

[knot4u]

Cooling and parasite drag reduction was always paramount in my formative years as a mechanic. What many people never understood, and the evidence was tossed into the scrap pile years ago, was the importance of the exhaust system on the Rare Bear. It was an enormous pain in the ass and I hated it. Taking it apart wasn't that bad but putting it back together was always a nightmare. But it was built that way for a reason, it was "tuned", meaning each cylinders exhaust would help evacuate the next cylinder in the firing orders exhaust. It actually produced a small amount of thrust, but that's only part of why it was so important. If you look at the picture I posted of the Bearcat you might notice how small the gap between the spinner and the cowl was. This gap was not based on aesthetics, it was optimized. The cowl on the bearcat was originally built for a DC-7, obviously it was modified for use on the bearcat. It's a pressure cowl, meaning it's pretty tightly sealed and pressurized from the ram air when the airplane's flying. This is not always optimal, that previously mentioned gap needs to only let a certain amount of air in, it also needs to let the air spend enough time flowing through the cooling fins to absorb as much heat as possible, if it's too slow the engine overheats, if it's too fast the engine overheats. When I mentioned that we spent an inordinate amount of time working on cooling drag what I meant was we'd spend hours sealing all of the baffles that directed the air across the cooling fins to make sure they were "perfect". This brings me to the exhaust, the exits on both sides of the airplane worked as venturis, and because the exhaust was painstakingly built to optimize the scavenging of each cylinder it provided the motive flow for the cowl exits. After my time with the airplane the powers that be decided to scrap the exhaust and build a much more reliable system reminiscent of every other 3350 equipped racer. I think the special mojo was tossed out because it was too hard.

 

[Victor Squawk]

One of my A/P school teachers liked to say "A barn door will fly at the right angle of attack.". We were required to build a model and prepare a report. One of my classmates was a lazy smartass, his model was a barn door from some childrens farmyard play set and his report was basically "A barn door wil fly at the right angle of attack.". His model joined other examples of brilliant thinking that hung from the classroom ceiling.

"A barn door will fly at the right angle of attack." I was helping with marshaling out a plane at work the other day (on the ramp) and was being hit by strong gusts of wind a few different times while stepping and had an epiphany. Something suddenly clicked for me and I started to understand lift more tangibly.

It also helps me understand my PPGS instructor more since he teaches from a pilot's perspective so his reasoning is more practical-intuitive. I think I really get it now (at least to the point of being satisfied with how I understand so far).

 

[Victor Squawk]

Glad you enjoyed it! You had a lot of specific questions and that’s one of the most straight forward resources I knew on the subject. Unfortunately aerodynamics doesn’t have straightforward conceptual answers until you get to systems of partial differential equations being solved by computer models, so most people settle for Bernoulli and Newton being two halves of the same coin and move on. There are a lot of pilots out there whose CFIs taught them the equal transit theory (incorrect theory #1) who still understand aerodynamics well enough to fly safely - so at the end of the day you don’t need to have a scientist/engineer level understanding of the topic to work in aviation, unless you WANT to dig that deep.

I probably do want to dig that deep, but later. Right now I'm still taking on the firehose of information about aviation in general (PPGS level of detail) and my focus right now is to become a 121 dispatcher (due to life situation) before anything else so I've been noticing how that's pretty niche with what I need to know for work/career, despite my curiosity.

 

[form810]

I've never flown a plane, guys. Don't take me too seriously. I'm going through PPGS because my college treats it as a prerequisite class for taking the dispatcher course. When I get to the point where I fly solo, courtesy of being able to pay for the privilege to do so, I won't be confused about whose life is on the line when I get into the plane. I've no stake in any scientific theory or another, as long as I am able to fly the plane. How could it matter?

edit
There be some sensitive ppl on here, man. It'd be nice if there was a list of things not to say, so everyone will like me and also not bitterly discredit me into a troll. That's like trying to amputate all my threads before I even make them. And for what? I made fun of air.

Pray tell, what is PPGS?... Is that a cowwwege course? I can't wait!

 

[form810]

One of my A/P school teachers liked to say "A barn door will fly at the right angle of attack.". We were required to build a model and prepare a report. One of my classmates was a lazy smartass, his model was a barn door from some childrens farmyard play set and his report was basically "A barn door wil fly at the right angle of attack.". His model joined other examples of brilliant thinking that hung from the classroom ceiling.

Pretty sure it was Paul Richter (back in the 1920s) who said that. Except what he really said was, "give me enough power and I can make a brick fly". But, who's counting?

Whatever was said by whom, the notion is correct and the point stands.

 

[Victor Squawk]

Pray tell, what is PPGS?... Is that a cowwwege course? I can't wait!

It's Private Pilot Ground School. Yeah it's at college, since that's what I can afford. You can focus on me being pretty broke and working full time while studying if that helps you get past the bitterness that you couldn't write something more interesting on the thread and took it all too personally, focusing on attempting to discredit me on a site where I'm asking for help.