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RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 4:20:09 AM   
ptulmer



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From: Brunswick, GA, USA
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quote:

ORIGINAL: dick Hanson

Well shoot - Ulmer - I had not heard those explanations before.
But you are right
misinformation is rampant!


Well shoot - Hanson - Thanks, I think. Unless you mean I'm completely misinformed!

I think you guys have reconfirmed what I had previously thought. Of course, alot of what I know can be contributed to Ben,Bruce,Paul, etc. You guys normally put me on the straight and narrow.
One more thing. I haven't seen anybody address the movement of the air. These pictures I see show the air moving straight across the airfoil. But that's not true is it? The air actually rolls across the wing in a manner that can be seen in a flag waving in the wind. These columns of air play major factors in everthing that's been discussed and alot of stuff that hasn't been. (flutter comes to mind)

Now, Bryan, do you mean you'd rather have an entertaining, but completely wrong article to read? That's truly ridiculous.

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(in reply to dick Hanson)
       Post #: 51

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 4:43:41 AM   
Tall Paul



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Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		The flapping flag doesn't illustrate what the wind does to a smooth solid surface.. that's another kettle of fish.
Look at the photo of the left side of the vertical on the Tristar in the 'Non-aircraft aerdynamic Question" thread.
The air flow is smooth and regular.
The flap flaps because it isn't stiff, and moves with the air, probably as a function of its length and the speed of the wind.
Large flaps have a different flapping period than smaller flags in the same wind, and because there's no stiffness in the cloth there's a "natural frequency" of flapping dependent on the material and the wind.
The "wave length" is shorter than the flag is long, so it develops those curliques along its length.
A solid plate on the same pole as a flag, the same size as a flag would pretty much indicate a steady wind direction.

< Message edited by Tall Paul -- 2/16/2005 4:44:12 AM >

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(in reply to ptulmer)
       Post #: 52

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 5:14:53 AM   
leszek_k


 

Posts: 30
Joined: 7/25/2003
From: Dubai, UNITED ARAB EMIRATES
Status: offline 		RIGHT - and Einstein was wrong bubbling something about relativity, energy being an equivalent of mass ???!!!. What did he know after all.

I thing you all missed one thing in a little article I have pointed to :

Dept. of Aeronautics and Astronautics
University of Washington
Seattle WA 91895-2400
scott@aa.washington.edu

In my view they are a teachers and we are a students, they wouldn't be teaching if they were so far off.

(in reply to Tall Paul)
       Post #: 53

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 7:42:55 AM   
Siefring



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Joined: 10/22/2003
From: Owings, MD, USA
Status: offline
quote:


I thing you all missed one thing in a little article I have pointed to :

Dept. of Aeronautics and Astronautics
University of Washington
Seattle WA 91895-2400
scott@aa.washington.edu

In my view they are a teachers and we are a students, they wouldn't be teaching if they were so far off.


The general wise-crack is: Those Who Can Do, Those Who Can't Teach

A more appropriate comment is, don't be so impressed by people's credentials. You can not be an engineer or scientist and accept statements just because someone has a PhD or is more senior. You will not be in a job long if you can't critically examine an argument. Professor's, PhD's, senior engineers, they all make mistakes. Even Einstien -- he seemed to be smart enough to figure out his mistakes and admit them.

< Message edited by Siefring -- 2/16/2005 7:46:37 AM >

(in reply to leszek_k)
       Post #: 54

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 8:24:59 AM   
leszek_k


 

Posts: 30
Joined: 7/25/2003
From: Dubai, UNITED ARAB EMIRATES
Status: offline 		It is not easy to impress me - but - that is what they teach their students - and do not tell me that an amateur like me and probably most of the other guys on this forum, have any SCIENTIFIC arguments to argue it.

I believe in what I can see, touch etc.

2 x 2 is always 4 (sorry it is around 4 if you use an old fashioned slider).

And if somebody proves to me matematically and then in a wind tunnel that Mr Bernoulli is not enough to make a plane fly - I have nothing to say.

Unless I have a better arguments - but words and believes are not an arguments.

So far nobody managed to prove Mr Einstein wrong. And lots of peaple tried very hard to do so.

Just found something a bit more comprehensive :

http://www.lerc.nasa.gov/WWW/K-12/airplane/short.html

OK, some may say - what do they know, after all some of their space shuttles wend down in smoke.

< Message edited by leszek_k -- 2/16/2005 11:05:11 AM >

(in reply to Siefring)
       Post #: 55

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 12:51:15 PM   
Johng



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From: Deland, FL, USA
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Arrrrhg. I gotta get some stuff off my chect, then I'm unsubscribing.

First:
quote:

A more appropriate comment is, don't be so impressed by people's credentials. You can not be an engineer or scientist and accept statements just because someone has a PhD or is more senior. You will not be in a job long if you can't critically examine an argument. Professor's, PhD's, senior engineers, they all make mistakes. Even Einstien -- he seemed to be smart enough to figure out his mistakes and admit them.


In these forums, especially, I couldn't agree more. Either you make a good argument or you don't. Whether you have a degree doesn't matter. Otherwise we all pull out our diplomas and there's nothing to discuss.

As for downwash, it is a by-product of lift, not a cause of lift. That is what Ben was saying when talking about the pressure pulling the air down.

As for the "infininte wing" argument, it is absolutely a valid prrof that lift is not caused by deflecting air, notwithstanding Lou's attempt to discount it. This can be demonsrated in a wind tunnel of any size, where there is not an "infinite mass" of air to work on. Yet still, there is lift (pressure change) where no downwash occurs.

LouW also states that :
quote:

For a lifting wing this net deflection is downward (the hand). It always happens and is always proportional to the lift being generated


Which is true, but read carefully. Proportional means just that. It does not mean that there is a fixed relationship between lift and downwash among different wings. In order to turn a proportional relationship into an equation, you need a "K" multiplication factor. And in aerodynamics that is a measure of how efficient the wing is. It is a measure of how much lift a particular wing can make, per unit of downwash. This is why we make long glider wings for efficiency. They make more lift with less downwash. If downwash was a "cause" of lift, this wouldn't be possilble at all. It concerns me that some might read LouW's words and say - airplane A lifts more than airplane B, so it must deflect more air. And that just isn't true.

Now here is a lttle tweak for people that can only think about wings as air deflectors. After 100 years of flight, billions of flights, airplanes now continuously in the air all around the world; If they are all deflecting air downwards, wouldn't the atmosphere be about 2 feet thick by now?

The fact is, the air only deflects downwards if the streamline pictures you consider are clipped off prematurely, like the ones Siefring posted. In the short term, it deflects downwards. Then it rebounds to normal height. So where is the "negative lift" being applied to get the air back to normal height?

(Not that I want an answer, I'm unsubscrbing. PM me if you want a serious discussion)

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(in reply to leszek_k)
       Post #: 56

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 1:54:29 PM   
BRYAN01601



Posts: 560
Joined: 11/6/2002
From: berlin, CT, USA
Status: offline 		OK had a chance to re-read the article and this is my conclution.

First off the title of Jeffs Monthly column is : Primary Training
not Aerodynamics for the univesity professor and engineering experts

Secondly: I think the point of the article was to illistrate to a beginer (not the expert engineer or aeronautic physisist) that when you increase your angle of attact you will increase the lift of the plane and cause it to go up to a point and then it will stall and loose all lift (this is a loose interpretation) to show the beginer that ikf your not carfull you will stall and crash. It also teaches the "beginner" how the elevator causes the plane to move in different directions

Third: Jeff states in his article that he is going to loosly interprest things and not get into all of the physics involved as to keep it simple and that the subject matter is far more complicated than his simplistic view of things. After all this is a beginers article not for all of you engineering experts. hence the name of the column (primary training)

Fourth: I would say to a beginer or a layman this artlicle is helpfull and gets his point across about AOA and stalling to "help a Beginer" Understand things. It may not be the correct method of doing such for the university professor or NASA but for the begining pilot he gets his point across without boring the reader with all the engineering jargon.

IT's a good and usefull article for the beginner.

< Message edited by BRYAN01601 -- 2/16/2005 1:58:00 PM >

(in reply to Johng)
       Post #: 57

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 2:34:44 PM   
LouW



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From: Moreland, GA, USA
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quote:

As for the "infininte wing" argument, it is absolutely a valid prrof that lift is not caused by deflecting air, notwithstanding Lou's attempt to discount it. This can be demonsrated in a wind tunnel of any size, where there is not an "infinite mass" of air to work on. Yet still, there is lift (pressure change) where no downwash occurs.


The wind tunnel doesn’t prove any such thing. Since the walls of the wind tunnel are solid and the air cannot move through them, downward deflection is stopped just as if it encountered an infinite mass, thus giving results as if the span were infinite.

quote:

This is why we make long glider wings for efficiency. They make more lift with less downwash. If downwash was a "cause" of lift, this wouldn't be possilble at all. It concerns me that some might read LouW's words and say - airplane A lifts more than airplane B, so it must deflect more air. And that just isn't true.


A wider span affects a larger mass of air so that it doesn’t require as much deflection to generate the same lift as a lesser span. The less deflection is more efficient because the resultant force is not tilted as much aft. The various tip treatments used to increase efficiency simply cause a wing of a given physical span to affect a little more mass of air.

In fact, a heavier airplane (A) does deflect more air than a lighter airplane (B). If you have ever flown into the downwash from a heavier airplane, this would be obvious. You are apparently using the terms “downwash” and “deflection” to refer to the angle through which the air is deflected (a common engineering definition), whereas I am using the terms to mean the total mass of air affected and its change in momentum. The same pressure field that lifts the wing deflects a mass of air downward. Neither effect can exist without the other. They are both necessary parts of the same phenomenon.

quote:

Now here is a lttle tweak for people that can only think about wings as air deflectors. After 100 years of flight, billions of flights, airplanes now continuously in the air all around the world; If they are all deflecting air downwards, wouldn't the atmosphere be about 2 feet thick by now?


In reaction to this little piece of silliness, I might ask “After 100 years of flight, billions of flights, airplanes now continuously in the air all around the world; If they are all creating an area of reduced pressure above the wing, wouldn’t the atmosphere be a hard vacuum by now?”

Obviously, just as pressure differences equalize after a wings passage, the motion imparted by its passage also dissipates.

Guys, we’re arguing over a non-issue. Both points of view are valid. The pressure field is real, and so is the change of momentum.

(in reply to Johng)
       Post #: 58

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 4:02:49 PM   
flyswatter



Posts: 499
Joined: 2/21/2004
From: St. Simons Island, GA, USA
Status: offline 		I know better than to post anything to this thread. I have been in this argument before. Between the emotion and in some cases - bad science, no one is going to convince anyone of anything! But come on guys, down wash from an airfoil never lifted any object. Thrust and lift has. Down wash occurs but it is a secondary effect - at most. Using down wash to explain lift is less realistic than trying to calculate the speed of an unknown vehicle by studying its skid marks!

Finally, for Jeff Raskin, I promise not to tell him how to design computers if he promises not to try to rewrite the aerodynamics I learned in school.


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wat
Vertical and tracking...

(in reply to LouW)
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RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 4:03:50 PM   
bdavison


 

Posts: 3333
Joined: 8/23/2004
From: Warner Robins, GA, USA
Status: offline 		Guys,

You can beat around the bush as much as you want saying "he was just writing an article for beginners" "he was just giving a basic description"...simple fact of the matter is IT WAS WRONG.

Wings do NOT fly as a result of deflecting wind, air, whatever downward. Not in a test tunnel, not in "real" air, not anywhere. While most wings do deflect wind downward, this is not was makes if fly. The downwash is just a by-product of the wings angle of attack, incidence, and other various factors. While the downwash certainly produces an effect, as shown in helicopters for example. And while it certainly contributes to the over all performance of the wing. It is still not what causes lift on the wing or rotor blade.

Pressure causes lift.
If you were to hold a weight by a string. It hangs there by pressure you are exerting on the string. You can blow at the weight so that it deflects air downward till your blue in the face, but it still doesnt change the fact that the pressure your exerting on the string is whats holding it up.

Anyone who honestly buys into the garbage written in that magazine, is going against every mathematical, physics,and aerodynamics theory that has been proven time and time again.

leszek_k
You've probably never seen a million dollars, but I'll bet you believe it exists. You've probably never seen a nuclear explosion, but I'll bet you believe it exists. We put our trust in things everyday that we cant see. You trust the guy at McDonalds not to spit in your Spicy McChicken, but you cant actually see to make sure thats not what happens.

If there's one thing I learned during all the physics classes, and mathematical classes, its that there are plenty of things that are not able to be seen with the naked eye, but can still be proven correct. And the other thing I learned. Philosophy has no place in science, it just screws up the works.
I=T+X....well how do you know I=T+X, truth is according to the general concensus...No, truth is cause Im a mathematician and know how to use a calculator you silly philosopher.
You get the idea.

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(in reply to LouW)
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RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 7:05:05 PM   
leszek_k


 

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Joined: 7/25/2003
From: Dubai, UNITED ARAB EMIRATES
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quote:

ORIGINAL: bdavison

Wings do NOT fly as a result of deflecting wind, air, whatever downward. Not in a test tunnel, not in "real" air, not anywhere. While most wings do deflect wind downward, this is not was makes if fly. The downwash is just a by-product of the wings angle of attack, incidence, and other various factors. While the downwash certainly produces an effect, as shown in helicopters for example. And while it certainly contributes to the over all performance of the wing. It is still not what causes lift on the wing or rotor blade.

Pressure causes lift.


I am not a professional so I do not argue that. I am just pointing to a sites/articles, written by a professionals, and they say something different.

Never have seen a 1M$ - but it is not a matter of trust to know it does exist, it can be proven.
Never seen an A-bomb in action - good for me, I am still here - again - it has been proven it works (Mr. Einstein again).

You are very right - proof is as good as a real thing - but that is what I said before.

As a mathematician you should know better than to search for a truths - scientist are looking for facts - you see, there is a room for a philosophy in science. And some more of a philosophy - if there is something I am not sure of - I turn to professionals for answers.

(in reply to bdavison)
       Post #: 61

RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 7:13:53 PM   
Ben Lanterman



Posts: 1284
Joined: 10/27/2002
From: St. Charles, MO, USA
Status: offline 		"When two solid objects interact in a mechanical process, forces are transmitted, or applied, at the point of contact. But when a solid object interacts with a fluid, things are more difficult to describe because the fluid can change its shape. For a solid body immersed in a fluid, the "point of contact" is every point on the surface of the body. The fluid can flow around the body and maintain physical contact at all points. The transmission, or application, of mechanical forces between a solid body and a fluid occurs at every point on the surface of the body. And the transmission occurs through the fluid pressure.
Since the fluid is in motion, we can define a flow direction along the motion. The component of the net force perpendicular (or normal) to the flow direction is called the lift; the component of the net force along the flow direction is called the drag. These are definitions. In reality, there is a single, net, integrated force caused by the pressure variations along a body. This aerodynamic force acts through the average location of the pressure variation which is called the center of pressure. "

Then after doing such a great job of describing lift they go on to say -

"There are many explanations for the generation of lift found in encyclopedias, in basic physics textbooks, and on Web sites. Unfortunately, many of the explanations are misleading and incorrect. Theories on the generation of lift have become a source of great controversy and a topic for heated arguments. To help you understand lift and its origins, a series of pages will describe the various theories and how some of the popular theories fail.
Lift occurs when a moving flow of gas is turned by a solid object. The flow is turned in one direction, and the lift is generated in the opposite direction, according to Newton's Third Law of action and reaction. Because air is a gas and the molecules are free to move about, any solid surface can deflect a flow. For an aircraft wing, both the upper and lower surfaces contribute to the flow turning. Neglecting the upper surface's part in turning the flow leads to an incorrect theory of lift."

Out of one mouth they say, "The component of the net force perpendicular (or normal) to the flow direction is called the lift."

The other mouth says, "Lift occurs when a moving flow of gas is turned by a solid object."

When a moving flow of gas is turned by a solid object - - we call that deflection. Not lift. Apparently two different people wrote the two sections.

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< Message edited by Ben Lanterman -- 2/16/2005 7:38:38 PM >


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Ben Lanterman

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RE: Jef Raskin article on aerodynamics in Fly RC Magazine - 2/16/2005 7:39:41 PM   
Ben Lanterman



Posts: 1284
Joined: 10/27/2002
From: St. Charles, MO, USA
Status: offline 		Ben's Sketch of how it works showing everything except the airplane.

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< Message edited by Ben Lanterman -- 2/16/2005 7:41:58 PM >


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