okay let the debate begin...newton or bernoulli

[nosehair]

Don't get upset merely because your daddy never removed the training wheels.

...mmm, avbug, didn't mean to rant on you like that. I saw a couple words in your post that set me off and...off I went.

You are right, of course. I'm actually trying to justify "simplicity".

I can see that you are a teacher, and that you are passionate about it. That's what it's all about to me.

I do belive that, sometimes, a "simplistic" explanation, although not technically correct, can sometimes turn on a light in some people's minds. This requires caution, care, and being certain that you "clean up" the detailed misunderstandings that you knew were there during the initial discussion that led to the conceptual understanding.

For instance, "Now, you know how I said the air on top moves faster so it can catch up to the air underneath? Well, that's not exactly accurate. That was so that you could picture in your mind the lower pressure. Actually, they..."

What I was trying to say, avbug, is that not all persons can keep up with the technically accurate descriptions. They might be able to memorize facts: "A moving fluid has less pressure than a motionless fluid". But that is rote. And I know you teach to a higher level. I can tell from your posts.

And so, sometimes I use a not-technically-accurate description, using that persons vocabulary and mind-set until a basic concept forms, then I reconfigure the concept with the more-technically-accurate details.

 

[avbug]

Actually, when I begin to teach aerodynamic theory, I ask if the person has ever stuck their hand out a car windown when it's going down the highway. Did they every fly their hand, feel it go up and down? Have they ever felt a car slow down going up hill, speed up going downhill? Ever lean on bicycle? Ever put a finger over the end of a garden hose? Ever fly a paper airplane?

I've never met a person who hasn't, of course. Except a few folks overseas in grass skirts, but I've never had any of them for training...just for dinner.

I tell folks that having had those experiences, they already know most of what they need to know about flying, and then we talk about why. They already know it, they just don't know they know it.

Teaching someone about aerodynamics is really about helping them realize it's a subject they already know. I'm no einstein. I can't balance a checkbook. Or keep track of a grocery list. (or apparently keep from losing my daily planner, again...). I don't expect that of a student. But most physics require very little math to understand...just visuals dealing with what we already know. Waveforms can be taught with a slinkey, pendular dynamics with a yo-yo. Ballistics by throwing a football or striking a pool cue. Thermodynamics by making ice cream. Aerodynamics by folding a paper airplane and riding in a car.

Truth is, I learned more about aerodynamics...not the theory but coming to really understand the subject...by skydiving. Becoming the air foil, feeling the forces in a really big vertical wind tunnel, turning my hands and feet into control surfaces, listening for the pressure changes and airspeed changes around my ears, feet, and torso.

I never teach an incorrect subject, but I do approach it at the student's level. Truth is, that many students are far above me in the ability and understanding level. I'm a dirt-under-the-fingernails kind of guy. I drive at the speed limit or less. Eating out is going to burger king. My idea of education is looking something up on the internet, or reading a good book. I've bought my share of XXX for dummies. Just bought Zen for dummies. Got a lot out of it.

I trained in martial arts for many years. A very strict traditional asian school in which no words were spoken...you learn by doing. I've been on my face in the dirt with a drill instructor screaming in my ear. I've been smacked around while an education was beaten into me. I've sat in class, listened to lectures. I've educated myself, taught myself many subjects with no outside help at all. I've even spent a lot of time in the still quiet meditating, being taught things slowly, a little like dew settling on grass, taking lessons from sparrows, deer, trees, and wind. All sorts of learning and teaching styles, and I've had occasion to use them all to teach as well, at differing times.

I do not now, nor will I ever consider myself a teacher. I aspire to be, but probably never will be. Perhaps just a student with a viewpoint or two. One thing I do know is that most teaching involves helping the student understand what the student already knows, often better than I do. Most every student I've ever trained in this subject or that turns out to be so much better than me...I can help for a little while, and then I'm left behind. I have no problem with that. All I can do is teach correct principles to the best of my understanding, and then let the student go. The student always does the rest.

 

[VNugget]

I do belive that, sometimes, a "simplistic" explanation, although not technically correct, can sometimes turn on a light in some people's minds. This requires caution, care, and being certain that you "clean up" the detailed misunderstandings that you knew were there during the initial discussion that led to the conceptual understanding.

For instance, "Now, you know how I said the air on top moves faster so it can catch up to the air underneath? Well, that's not exactly accurate. That was so that you could picture in your mind the lower pressure. Actually, they..."

What I was trying to say, avbug, is that not all persons can keep up with the technically accurate descriptions. They might be able to memorize facts: "A moving fluid has less pressure than a motionless fluid". But that is rote. And I know you teach to a higher level. I can tell from your posts.

And so, sometimes I use a not-technically-accurate description, using that persons vocabulary and mind-set until a basic concept forms, then I reconfigure the concept with the more-technically-accurate details.

Once again, there is a GULF between "simplistic" or "not-technically-accurate" and COMPLETELY WRONG! You say that teaching that to a student would simplify things for the student, but how can it possibly do so? If he decides to investigate things, he'd get confused more because the wrong premise would lead to further conflicting conclusions.

They might be able to memorize facts: "A moving fluid has less pressure than a motionless fluid". But that is rote. Huh? It's a fact, and a fundamental one to aerodynamics. You can't get around it. The "recombination" explanation (explanation -- for lack of a better term) only provides a reason for the difference in speed, and the student would still have to understand the speed/pressure relationship even if he accepts it.

""Now, you know how I said the air on top moves faster so it can catch up to the air underneath? Well, that's not exactly accurate. That was so that you could picture in your mind the lower pressure. Actually, they..."

"You know when I told you that avgas burns because it's refined from a fossil fuel, which came from dinosaurs that were wiped out by a really HOT asteroid, and increases the pressure in the cylinder thus pushing the piston down? Well, that wasn't exactly accurate; in fact..."

Do you see it now? It's not an "inaccuracy," it's complete BS that serves no purpose! If you think that the chemical process of hydrocarbon combustion is too complex a subject to explain, just make the student accept the premise that "fuel burns when in the presence of oxygen" and leave it at that, but don't try to explain it in an unsupportable way. Likewise, if you can't explain why the air on top is faster, then you can only settle for having the student accept that it is. Giving a wrong reason is not gonna help anybody "picture" anything.

 

[nosehair]

Do you see it now? It's not an "inaccuracy," it's complete BS that serves no purpose! If you think that the chemical process of hydrocarbon combustion is too complex a subject to explain, just make the student accept the premise that "fuel burns when in the presence of oxygen" and leave it at that, but don't try to explain it in an unsupportable way. Likewise, if you can't explain why the air on top is faster, then you can only settle for having the student accept that it is. Giving a wrong reason is not gonna help anybody "picture" anything.

...mmmm, well, I'm not explaining myself very well, here.

I am not in agreement with your statement, "just make the student accept...".
That's ok in the short term, ie, "My controls", or "Go-Around!", or things that require immediate attention without time for explanation,...but, aerodynamics, or chemical combustion, or conceptual ideas of theory,....mmmm, I don't think it is ok to say "Accept the premise" and leave it at that. You might have the student accept the premise based on the assumption that furthur explanations, understandings, etc, will cause understanding of the accepted premise, but somewhere, somehow, understanding must occur.
And however you can get that to happen is what teaching is about.

But you are also very right about not using complete BS to achieve that. My initial understanding of lift was with the simple combinations of Bernoulli's therory and Newtons Law. As I learned more, I saw that it was actually very complicated and, as we were breaking the sound barrier, new knowledge of lifting forces continued to grow. It still does today. We still don't know it all.
...and I have stuck with the simple explanation 'cause it works. And I'm not seeing where it is complete BS. Just simple.

 

[VNugget]

I am not in agreement with your statement, "just make the student accept...".
...
but somewhere, somehow, understanding must occur.

Okay. I wholeheartedly agree. But notice that I did not only say that you should just make the student accept it; I said that you should do that IF you cannot teach him the underlying reason.

...and I have stuck with the simple explanation 'cause it works. And I'm not seeing where it is complete BS.

Once again, 1. look at figures 2 and 3. The layers do not reattach at the same place! 2. Assuming we did not have that direct observation, can you tell me how or why there exists a necessity for the layers to traverse the airfoil in the same amount of time? Can you tell a student?

 

[A Squared]

Giving a student patently false information doesn't serve any useful purpose.

The equal transit time fallacy at best provides no insight to aerodynamics. At worst it sets the student up for confusion and incorrect answers to checkride questions. remember the law of primacy? those things learned first leave the stronges impression? If hte student first learns the equal transit time fallacy, then later you explain that it's not true (ignoring the absurdity of teaching things you later have to tell the student aren't true) which is most strongly learned? the fallacy, or your repudiation of the fallacy?

One of the louder and more persistent "bernoulii debunkers" bases his entire "debunking" on the equal transit time fallacy. He mathematically computes the velocity difference between the upper air and the lower air, based on measureing the length of the upper and lower surfaces of a real aircraft wing, the airspeed of the aircraft, and the equal transit time fallacy. he then plugs the airspeed difference into bernoulii's equation and "proves" that "bernoulli is wrong" using bernoulii's own equation. The thing he doesn't grasp is that the equal transit time fallacy, is indeed a fallacy, the air over the top reaches the trailing edge long before the air under the airfoil, so his "proof" is just so much meaninless mathematical masturbation.
My question is this, why would you set a student up to play into the hands of such an idiot? If you teach the equal transit time fallacy to a student, one of two things will result 1) he will have a flawed understanding (not incomplete, but incorrect) aerodynamics and will be subject to the varagacies of folks like the aforementioned "debunker" , or 2) he will discover on his own that the equal transit time fallacy is indeed meaningless bull$hit and he will wonder what else you taught him is equally fallacious. Neither seem desirable outcomes.

Perhaps it would be better to explain the concept with an example that is removed from you personally, so that you aren't put in the position of being defensive: I once had an exchange with another instructor on another forum (you might recall the exchange) who said that he teaches aircraft stability and center of gravity using the example of a skier, because he teaches in ski country and it's someting which his students can relate to. All well and good, but the thing is skis and airplanes behave completely differently, an airplane becomes more stable as the cg moves forward, and less stable as the cg moves aft, while a ski is most stable with the skier's weight centered ,and becomes less stable if weight is shifted aft *or* forward, never mind that aircraft stability and ski stability are the result of completely dissimilar physics. ..... so what exactly is the useful lesson? It may be someting which the student can grasp, but it imparts erronous information which interferes with understanding the desired concept rather than aiding it.

 

[johnpeace]

Wow man!

I'd love to see what would result from inciting the 'pitch or power for airspeed' debate.

You guys are great!

 

[100LL... Again!]

It's an interesting discussion, but I tend to think that the 'basics' are good enough. While I also do not teach the molecules must meet up theory, I think that a basic understanding is enough.

I always assign importance to a concept by how likely it is that incomplete understanding could be disastrous.

For example, a student who is a brilliant aerodynamic engineer but can't learn the correct response to a stall is obviously more dangerous than one who makes the correct reaction, albeit with no knowledge of the theory.

The ideal is to have both, of course.

But truthfully, even the incorrect explanation that has been taught for years has worked, right? (This does not imply that teaching flawed info is okay, just that in SOME cases there is not as much of a detriment as in other cases.)

 

[RideTheWind]

It's not that hard to understannd, the author of Stick and Rudder makes it easy, the downwash from above the wing pushes the wing up the same way water coming out a fire hose pushes a fireman backward.