Misconceptions of lift

[stevem1928]

I found an interesting web site which describes the misconceptions of lifting force taught in text books. I have seen this topic discussed here on Ezone. I thought some people would like to see this concise description.

http://travel.howstuffworks.com/framed.htm?parent=airplane.htm&url=http://www.eskimo.com/~billb/wing/airfoil.html

The "How Stuff Works" web site has a lot of plain English explaninations of flight. Neat site.

[Andy W]

Without getting into the theory, which is over my head, I'm more inclined to believe the 'displaced air' theories. As an exercise, we fly through the wake of the tow plane in full-scale sailplanes - that wake is considerably lower than the airplane at only 200' back.
..a

[Ollie]

http://www.av8n.con/how/

Plain English!

[Andy W]

Bad link..

[slipstick]

Try .com

S

[vintage1]

Without getting into the theory, which is over my head, I'm more inclined to believe the 'displaced air' theories. As an exercise, we fly through the wake of the tow plane in full-scale sailplanes - that wake is considerably lower than the airplane at only 200' back.
..a

If you think about it, the moment of air downwards is what 'creates' the low pressure area above the wing.

If its the old Bernoulli versus Newton thing again, they are different ways of saying the same thing, and produce the same answers.

[Andy W]

It's all greek to me.. works rather well, though, doesn't it.
..a

[globemaster3c17]

http://www.av8n.com/ Try that. Glad to see someone else knows of Denker's site. I went over parts of his site in my advanced aerodynamics class.
Airplanes don't fly only because of Newtonian physics, nor do they fly only because of Bernulli's principle. They fly because of both. There is a difference in pressure between the top and bottom of the wing. That is part of the lift vector. Air is deflected downward, that is another part of the lift vector.

[banktoturn]

I found an interesting web site which describes the misconceptions of lifting force taught in text books. I have seen this topic discussed here on Ezone. I thought some people would like to see this concise description.

http://travel.howstuffworks.com/framed.htm?parent=airplane.htm&url=http://www.eskimo.com/~billb/wing/airfoil.html

The "How Stuff Works" web site has a lot of plain English explaninations of flight. Neat site.

I personally find that the objections & explanations on this site are of little value. Many individuals who take issue with various "theories" are mistaking theory with models or design tools. In my opinion, the most practical explanation of lift for the layman is that the flow of air around the wing creates lower pressure on the top than on the bottom. This is true, and engineers can do a pretty good job of predicting the pressures, as well as finding ways to change the shape to get the kind of pressure they want everywhere on the wing. Any dogmatic preference for the "deflection" theory, or any of the others that keep coming up, is really not very useful. The pressure on the top is lower than the pressure on the bottom, and if you want to understand it more thoroughly than that, it will probably take more effort than most people are interested in investing.

banktoturn

[marcusdrake]

It's like a boat. A boat must displace a mass of water equal to or greater than itself in order to float. Likewise, a plane must displace a mass of air. A plane in level flight has achieved neutral bouyancy whereas a plane that is climbing is displacing a greater mass. Part of that mass is displaced by the wings and fuse and part is displaced by the engine thrust.

[banktoturn]

It's like a boat. A boat must displace a mass of water equal to or greater than itself in order to float. Likewise, a plane must displace a mass of air. A plane in level flight has achieved neutral bouyancy whereas a plane that is climbing is displacing a greater mass. Part of that mass is displaced by the wings and fuse and part is displaced by the engine thrust.

I don't find the analogy of bouyancy to be very helpful in understanding how lift is generated by a wing. The underlying physical phenomena are not really very similar.

banktoturn

[banktoturn]

http://www.av8n.con/how/

Plain English!

Yes, this site gives the best explanation of lift production that I have seen outside of an Aerodynamics classroom.

banktoturn

[globemaster3c17]

A plane in level flight has achieved neutral bouyancy whereas a plane that is climbing is displacing a greater mass. Part of that mass is displaced by the wings and fuse and part is displaced by the engine thrust.
I was agreeing with you right up until you basically said a plane is generating more lift than required for level flight in order to climb. No offense, but *buzzer sound* wrong. Airplanes climb because of excess power, not lift. Full-scale pilots often have that misconception about what makes a plane climb too. If you climb at full throttle, your plane will probably climb like a homesick angel. Then pull the throttle back to half and try to climb at the same airspeed as the first climb. Your plane may or may not be able to climb, that depends on the design and engine size. The difference between the two climbs is simply how much power the engine is producing.

[KillerWatt]

Whatever the reasons, give any wing enough positive angle of attack with enough air-speed and it WILL supply enough lift to fly.....For a dramatic, radical example, the stock, highly undercambered, high lift and dihederalled Slow Stick wing will fly inverted, gain altitude and be controlably banked and turned if given enough angle of attack and motor thrust despite going against most "old school" physics explainations of wing lift theories....... kw

[mwraight]

marcusdrake: It's like a boat. A boat must displace a mass of water equal to or greater than itself in order to float. Likewise, a plane must displace a mass of air. A plane in level flight has achieved neutral bouyancy whereas a plane that is climbing is displacing a greater mass. Part of that mass is displaced by the wings and fuse and part is displaced by the engine thrust.

While an airplane flying straight and level is in a neutral state - but it's not neutral buoyancy. Airplanes don't float. If they did, by that analogy, a boat would sink if it stopped moving forward - which doesn't happen. Now someone being pulled on skis behind a boat will sink if they stop forward motion -- because the skis are being kept up by Newton's 3rd Law (every action has an equal and opposite reaction) -- not buoyancy. It is 25% of Newton's 3rd Law that keeps and airplane up - basically displacing the air downward. The remaining 75% is supplied by the high pressure on the bottom of the wing, lift as we know it.

An airplane only needs to develop enough lift to support it's own weight to fly straight and level (neutral). The above theory of displacement and buoyancy falls apart because to float or be positively buoyant an object only need to displace a little more than it's own weight. A boat doesn't weigh more than the water it displaces. A jet weighing 200,000 pounds sitting on the runway is obviously negatively buoyant - it sank to the bottom of the liquid/gas it's in. But even at 500 mph that plane weighs 200,000 pounds -- and is still negatively buoyant in reference to the air. Speed does not increase the buoyancy of the aircraft. At any speed that aircraft is negatively buoyant and will always sink to the bottom of the medium it's in. So lift from the wings, and air hitting the bottom of the wing and pushing the wing up (Newton) is the explanation.

Your theory of buoyancy will only work for a hot air balloon, but it was an interesting thought!

[ChrisP]

Of course buoyancy is only a prerequisite for boats when floating or moving slowly. A proprider speedboat generates aerodynamic lift to compensate for its lack of buoyancy when only the prop is in the water.

[mwraight]

A fast moving boat isn't generating aerodynamic lift unless it has some sort of airfoil section/hydrofoil on it. I'm not sure what a proprider speedboat is, but it would have to be a hydrofoil design to generate any sort of lift. You could design a fast boat that sunk if you ever stopped moving - but the force keeping that boat up while it moves is explained by Newton's 3rd Law - just like skipping a stone across the water.

[Tim Green]

A helicopter rotor is a wing, with an airfoil.
It's interesting, because the wing stays over the same bit of ground, if the chopper's hovering.
It's more interesting if you stand under one, because it's thrusting massive amounts of air down.
It's wings are deflecting air down.
Now - what's keeping that chopper up?

[DesignGeek]

Whatever the reasons, give any wing enough positive angle of attack with enough air-speed and it WILL supply enough lift to fly.....

Another dramatic example: All those mattresses that fly off the the tops of cars on the highway....

[RANSWrench]

A helicopter achieves flight by beating the air into submission.

[mwraight]

[QUOTE]A helicopter rotor is a wing, with an airfoil.
It's interesting, because the wing stays over the same bit of ground, if the chopper's hovering.
It's more interesting if you stand under one, because it's thrusting massive amounts of air down.
It's wings are deflecting air down.
Now - what's keeping that chopper up?[/QUOTE}

You're right that a helicopter rotor is a wing. But even though that helicopter is hovering over the same bit of ground - that wing is being moved through the air by the engine. So the wing is constantly moving - just in a different way than a conventional airplane.

A rotor is also like a propeller in that it develops lift - in an airplane that lift acts to create what we call thrust. It's the same in a helicopter except that thrust is pushing the helicopter up in the air. In it's simplest terms its a giant screw that screws up in to the air. Vary the angle of attack of the rotor and you can change how much thrust you have. All that air you feel rushing down is the effect of that screwing action - just like the prop wash from the propeller.

An airplane with enough thrust can hover just like a helicopter - but you have to have a lot of thrust (and a skilled pilot!!!).

[Tim Green]

In an airplane, the wing develops thrust too, just like the helicopter rotor. It thrusts air down, and the plane stays up.

[mwraight]

Whatever the reasons, give any wing enough positive angle of attack with enough air-speed and it WILL supply enough lift to fly.....


Another dramatic example: All those mattresses that fly off the the tops of cars on the highway....

I had a professor that used to say "you can get a barn door to fly if you have enough horsepower." That mattress is blowing off the car because of that impact air - the equal and opposite reaction. The wind is blowing very hard on that mattress and if you get going fast enough the wind is pushing harder on the mattress than the mattress weighs! (I just drove with a mattress on my roof a few months ago...thankfully no flying!). But that mattress...and any other object like this isn't developing like we think of it in an airplane.

You can argue it one of two ways. 1. You can blame it on Newton and say that the force of the air is more powerful than the mattress (or any other non airfoil thing) and it simply "flies". 2. You can say that the air hitting the bottom of the mattress is impacting and compressing, thereby creating a high pressure on the bottom - and developing lift.

I've seen slope gliders with nothing but flat wings built out of foam board fly, and fly decently...but it's different than what a true wing is designed to do. It's more like that stone skipping across the water than a wing developing lift.

Generally a lot of the stuff you see about lift is written for the layman - and it just gives the old story of low pressure on top/high pressure on bottom...but that's only 75% of the story. The rest of that lift is from the same thing that makes that mattress fly off your roof (and into the windshield of a $100,000 BMW) - Newton's 3rd Law.

[mwraight]

In an airplane, the wing develops thrust too, just like the helicopter rotor. It thrusts air down, and the plane stays up.

That downwash you're talking about, or "thrust" as you're calling it, isn't developed by the wing - it's a by product of that impact air hitting the wing and being deflected downward. It's 25% of the story...

[TJTucson]

A helicopter achieves flight by beating the air into submission.

ROFL :D This is more my speed :D

Interesting thread :rolleyes:

[vintage1]

All I have to say is that it is apparent from this thread that aeroplanes fly despite none of the builders and pilots having any more than vague superstitions about how they actually do it.

"Will you please stop standing on my foot because it hurts?"

Newton: "That is because the attraction of the earth to his body causes a force to be applied to his foot that you experience as pain"

Swami Chas: "If you let go of your attachments, you wouldn't feel the pain, and indeed might leviatet upwards"

Einstein: "Its a matter of local space time curvature being intense at the the point where three bodies of apprecaible amass distort it"

Marx: "Its all due to opression of the working classes by Capitalism"

Darwin: "You are a failure, as you should have evolved better reflexes an removed your foot first"

Shoe salesman: "Just be glad he wasn't weaing Doc Martens".

Carpet Salesmen: "If you had been standing on Supaflor (TM) you wouldn't have felt a thing"

My Mate from Oz: "Jeez mate, kick the pommie bastard in the nuts and make sure he understands why".

Bernoulli: "There is no flow, so its nothing to do with me. Another pint please".

Descartes: "I think I am going to punch you on the nose, therefore I will"

T E Lawrence: "The secret is to not mind it hurting"

Joyce: "Afetr a morning gazing lustfully at Fiona McLaggans shapely thighs, George considered the question of whether to make some overt protest, but discarding it on the grounds that the effort involved and the temporary loss of social dignity would not be outweighed by the slight improvement in his material condition, sighed deeply, farted loudly, and proceeed to drain his glass of stout in a measured, and prolonged, swallow".

[Tim Green]

vintage1 from UK - thanks so much for sharing (especially that bit provided by your girlfriend Joyce). A couple of points though ...

My superstitions aren't vague.

Airplane is not spelled aeroplane.

Where on earth is UK? It's not on my map. (is it in Texas?)

"pommie"? I probably shouldn't even ask.

[RANSWrench]

This is all rubbish...I didn't see one post that mentioned fairy dust or happy thoughts and we all know this is what really makes things fly.

Idea... I know how we can settle this: "Celebrity Deathmatch" Bernoulli vs Newton

[Sparky Paul]

Tim, Joyce's first name is James...

[Tim Green]

James Joyce? Yeah sure - and I suppose that my first name is Ulysses?

And what kind of a first name is James for a girlfriend anyway? I'll bet there's tatoos involved.

[Sparky Paul]

Tatoo unfortunately left the program, seeking a better job. There weren't any.

[mwraight]

Here's the main MISCONCEPTION OF LIFT: that people think anything other than Newton and Bernouli have anything to do with it. Why is everyone seeking some Holy Grail that doesn't exist? We know full damn well what makes a airplane (aeroplane) fly. There are no misconceptions.

Those misconceptions are all started by people who know nothing about aerodynamics or think they know everything in the universe. I don't know why anyone even bothers trying to post the truth at RCGroups...because there are always a handful of trolls or fools in the wings waiting to destroy true knowledge with b.s. Somewhere, at this very moment, there is a child giving a report at school...telling his classmates that airplanes fly because they are positively buoyant...

You can either chose to believe my explanation about lift and aerodynamics or not. My explanation is based on science and has proof behind it. I'm also of the opinion that I might be qualified to explain lift and how airplanes fly -- having received an Associates and Bachelors of Science in Aviation, been a Commercial pilot since 1997, a Flight Instructor since 1997, logged over a thousand hours and taught nearly 100 students. But what the hell could I possibly know about what makes an airplane fly???? Listen to people just built a model in their garage a flew for the first time last week. They know everything.

[mwraight]

Update on Tatoo: He went to meet his dimunitive maker on Sept 4, 1993. Guess he offed himself.

[Tim Green]

I've always enjoyed both Sparky's and Vintage1's posts. I've learned much from both of them. Attempting levity on the web's always problematic. Doesn't hurt to try though. Usually.

And discussions of lift, which are always interesting (I always bite), are also typically emotional. That's ok with me though - goes with the territory. I still jump in. Can't help it.

I'd be upset though, if people got so po'd they stopped contributing.

[Tim Green]

Tatoo - ink that gets under your skin.

[vintage1]

I'll just say thanks for takiing up with the humour, (replies had me in stitches as well) and yes mwraight, of all the posts, in a serious mode, I tend to agree with yours.

But I got a little tired of the rest, hence trying to make a serious point about the difference between what actually happens and hypothetical models.

The truth is that science has no absolute answers, It merely has models that give good predictions. Bernoulli and newton give the same result ultimately, because they are actually saying the same thing. Bouyancy has nothing to do with it.

The fact that most people get confused is not an issue to crow about. Its actually bloody hard to get to grips with, and what I was really trying to say apart from 'lighten up guys' was that the same thing can be seen and discussed and interpreted in many different ways, and none of them are exactly wrong, but none are the whole picture either.

Its not Bernouli OR Newton, its BOTH, and you use whichever one is easiest on the maths. The earth doesn't go round the sun any more than the sun goes round the earth, Its just easier to do the maths if you stick the sun in the middle.

You cannot create a pressure differential without moving some air. Bernoilli goes straight to the pressure differential, but Newtonian analysis shows that the down wash creates a force. Its no suprise hat its the same force as the Bernouili one.

What is tricky is tracing the 'streamlines' in Bernoulli analysis: Flat plate wings work because (in the Bernoulli model) the path lengths are not the same top and bottom if the wing is at an angle of attack.

Bernolii is fine and dandy for carbirettors. Wihout Bernoulli carburettors don't work. Newtonian anslaysis is vile. I mean of course the DO work and fuel IS sucked out of the jets in the fastest flowing part of the device, but Newtonian anlaysis is very hard to do: Bernoulii is relatively easy.

Wings? No easy answers whichever way you look at it. take your pick. Both models are linear flow models and take no account of turbulence in the simple cases. All wings show turbulent flow..bernoulli cannot accomdate turbluence, Newton can, but its an utter pig to model it - you need a super computer to be anywhere near right.

[mwraight]

and yes mwraight, of all the posts, in a serious mode, I tend to agree with yours.

Thank you Vintage1, that does mean a lot to me. It wasn't at you that I meant to voice my frustrations - I just lost my cool in general - and I put you in the crossfire. So I would like to apologize to you for that. I have also removed that part of my post, as I don't think it very mature or appropriate to attack anyone personally here. I actually found your post funny, it was the others that got my ire up. So again, I am sorry for that. I think you are a very intellegent person and your posts contain a lot of useful information.

I have to agree with you on a number of your points above - we can't say with 100% certainty why anything happens. We only have the best educated guesses science can come up with and a lot of models that seem to agree with those educated guesses. Science is something we have to take on faith. I prefer to go with the generally accepted answers out there...but those who are attempting to come up with their own theories of lift are really off base. It's definitely not buoyancy! While we can't prove with exact certainty how a wing develops lift - two theories are the primary suspects and have the most science behind them.

As for the others, everyone here is free to voice there own opinions and ideas - but I caution you in doing so - even if you're trying to be funny, there might be someone out there that takes what you say as Gospel. The internet is becoming a major source of research for students young and old - and lots of other people. It's already so full of trash and misinformation it makes me ill. Wouldn't it be nice if RCGroups continues to be a place where people can go to get correct information and not have to sort through tripe to find the good!? I'd hate to see this become the next AskJeeves.

[HELModels]

You can have some fun on this forum if your not looking for your every word to be validated, completely correct, sole authority. Plus, lots of people on this thang have real stick time in various amounts and forms. Keep plugging away Vintage and others.

[globemaster3c17]

mwraight, I know what you mean in the 3rd paragraph of post #32. I was just in a pretty good discusion about how planes fly on spadworld.net. The guy wouldn't believe me that there is no difference in flying upwind or downwind except for one thing: groundspeed. Letting him know that I'm a 220 hour instrument rated commercial pilot didn't seem to convince him one bit that I was telling him the correct thing. I've seen similar discussions a few times before. I guess there will always be two basic groups of people on the forums: those who have spent a lot of time learning about how planes fly and what's really going on with them, and the guys who come up with their own ideas and stick to them no matter what you try to teach them. It's frustraiting to know the facts, yet not being able to get the guys with misconceptions to listen to the facts.

[robert harik]

globemaster, I have to laugh, the dreaded down wind stall rears its ugly head once more. That old myth will never die!( or my bad spelling)

[mwraight]

mwraight, I know what you mean in the 3rd paragraph of post #32. I was just in a pretty good discusion about how planes fly on spadworld.net. The guy wouldn't believe me that there is no difference in flying upwind or downwind except for one thing: groundspeed. Letting him know that I'm a 220 hour instrument rated commercial pilot didn't seem to convince him one bit that I was telling him the correct thing. I've seen similar discussions a few times before. I guess there will always be two basic groups of people on the forums: those who have spent a lot of time learning about how planes fly and what's really going on with them, and the guys who come up with their own ideas and stick to them no matter what you try to teach them. It's frustraiting to know the facts, yet not being able to get the guys with misconceptions to listen to the facts.

Yeah, it seems that some people just have their minds made up regardless of what the voice of experience wants to tell them. These are the same people who probably go to court and represent themselves, perform their own medical procedures (hey, all you need for liposuction is a knife and a shop-vac, right?), fix their own cars, and know how to convert lead into gold. I guess the difference between us and them is that we understand we don't know everything - and aren't afraid to seek someone with knowledge on a subject when we have a question. I had the hardest time believing that when an airplane was straight and level at a constant speed that thrust equalled drag. After all, how could the plane keep going forward if lift and drag were equal? So I went and talked with a Professor of Physics...and he explained it all in plain english.

But there are people who will never listen to those with knowledge on the subject.

It's sad that there are people who also don't comprehend the upwind/downwind debate. I think if you put them in a real plane and let them fly a turn about a point or S-turns they might finally get the concept...but standing on the ground looking at that model is a different story. It sure LOOKS like it's going to stall and fall out of the sky. But airspeed is airspeed and the plane flies irregardless of ground reference.

I guess the best we can do is try and give the correct information in an understandable way - and hope that it helps someone - but those others won't ever be persuaded. I think some of it can be attributed to trolls trying to get under our skin...but not all of it!

Good luck with the flying Globemaster -- both scale and full size!

[HELModels]

The guy wouldn't believe me that there is no difference in flying upwind or downwind except for one thing: groundspeed.

Maybe, he didnt care and knew it bothered the "intelligencia."
Maybe, he felt your only point was to make him submit - it is human nature to resist that.

I think Yogi Berra said, If it aint free, it aint free.
If youre looking for absolute clarity in a free speech forum you will not find it.
You wont find it in life either. You got to see through the crap.

Since this whole thing was about flight theory:

My hunk of junk, built on the kitchen table, in the cellar, out in the garage, flight tested in the yard "last week", has a right turn tendency under power. What might the intelligencia stink causes that?

[vintage1]

On flying downwind:

If the wind is utterly steady, the only way you will ever tell from inside the plane is by looking at the ground. This is encapuslated in Newtons laws of relative motion.

The wind is not utterly steady tho, and its a bit of a theory of mine that gusts happen faster than lulls, so when flying downwind, a sudden DECREASE of airspeed is more likely than a sudden increase. This, plus the apparent much higher speed of the model, is enough to perpetuate the myth that flying downwind it's easier to stall than upwind AT THE SAME AIRSPEED.

The reality is that it IS much easier to stall going downwind when flying a model. The explanation though, is not what many people say it is.


As far as why you get a right turn under power, turning tendencies are complex things.

Suggested effects are:-

Angle of prop disk to direction of flight causing greater pitch speed on one blade than the other - i.e. down or upthrust will also provide a turning moment. On our models with anti-clockwise prop direction (viewed from front) downthrust will e.g. theoretically provide a slight right turning tendency, as each blade has a bit more airspeed on the left hand side of the plane.

Prop torque which tends to roll the model to the left, at all times, under power.

The gyroscopic precession that makes the model yaw left or right when up or down elevator is applied. This was certainly a feature of WWI aircraft with massive rotating engines, and is claimed to be the cause of ground wander on tail draggers like the Hawker Typhoon as the tail was lifted on takeoff.

Spiralling propwash that - if it e.g. hits a fin are that is substantially above the thrust line, will cause a left yawing moment.

There is no doubt that ALL of these effects exist, and may make a detectable difference. Which one predominates is down to details of design.

But the most likely reason for a turn under power is a warped airframe :D

[mwraight]

My hunk of junk, built on the kitchen table, in the cellar, out in the garage, flight tested in the yard "last week", has a right turn tendency under power. What might the intelligencia stink causes that?

Could be a number of things...but if it's happening under power, the first culprit would be engine/motor position. Likely that you've got it canted to the right a bit too much. There could be a hundred explanations if that isn't the source.

I think Yogi Berra said, If it aint free, it aint free. Not even freedom's free - it's paid for by sacrifice.


But what is liberty without wisdom, and without virtue? It is the greatest of all possible evils; for it is folly, vice, and madness, without tuition or restraint.
Edmund Burke

Education is a better safeguard of liberty than a standing army.
Edward Everett

A great deal of laziness of mind is called liberty of opinion.
Unknown


But I don't think anyone here is trying to limit anybody's speech or freedom - just to try and correctly inform others. I would rather help people expand their minds than continue to believe in incorrect and ridiculous information - because it is knowledge and intellegence that keeps us free and empowers us.

As for the phrase "intelligencia" - is there a problem with intellegent people or someone being intelligent? Anyone can learn, any one can be smart - all it takes is a little effort on that person's part and the right method of learning. Nobody is born stupid and nobody is born smart. Many factors can influence how a person turns out - but that does not limit their potential. Learning is not something that just happens - you have to work at it - and sometimes you have to work extremely hard at it. I had a D+ to C- minus GPA all through high school. I was told I would never make it to college. Luckily I got into a university and I graduated in the top 10% of my class. It had nothing to do with intellegence - it had to do with hard work. Your mind is your number 1 asset. Our brains evolved to what they are because we used them - but anyone wanting to de-evolve back to Cro-Magnon is more than welcome to it. If you're not willing to invest in your number one asset what reason do you have for doing anything?

[Ollie]

Most only had flat Earth. The first to be told to the theory.

[Sparky Paul]

Vint, any sloper KNOWS the airplane sees and responds to the air mass, sometimes faster than the flier can!
One wing in a gust, the other in air moving a different direction, and over she goes..
Same with your decrease in airspeed due to a change in the "tailwind".. an "uncontrolled descent into terrain" is not uncommon due to this, no matter how much up elevator is pulled.. :)

[HELModels]

No problem. Dont tread on me either.

As for warped airframe? If it was really the airframe Vint was referring to, I'd say right on, brother.

[globemaster3c17]

mwraight,
I agree with you, but easy on the guys who work on their own cars, I'm one of em. :) Working on them is a good way to learn about them.
There are a lot of things about flying that are not intuitive to people. So I kind of understand when someone sees something and says it is due to the wrong thing. It's hard to go from ground-based thinking to thinking like a pilot. But when someone establishes that they do know what they are talking about, I'll listen and listen well to them. I hope my debating with guys that don't listen will shed some light on the subject for others that read the post and want to learn.
Thanks for the good luck, good luck to you too. Tomorrow I take my first CFI flight lesson, it's about time, I haven't been in a plane since my instrument checkride May 9th. :)

[mwraight]

I agree with you, but easy on the guys who work on their own cars, I'm one of em. Working on them is a good way to learn about them. Don't think I was coming down on the shadetree mechanic - for I too am one. But only with the more simple stuff. I wouldn't ever presume to know enough to rebuild my automatic transmission or my V-6 engine -- which is why I go to a mechanic -- a person who has the knowledge rather than trying it myself!

Have fun with the CFI - it's a real challenge - much more mental than it is flying the plane. The amount of knowledge you have to have seems very intimidating, but you'll easy get there. After awhile it'll all be second nature. If you haven't flown right seat much that will be interesting to get used to. The checkride is different too - since you don't even do 1/2 of the flying! I went to the FAA for my ride, very tough, but very satisfying to pass. Good luck with all the training!

[banktoturn]

While an airplane flying straight and level is in a neutral state - but it's not neutral buoyancy. Airplanes don't float. If they did, by that analogy, a boat would sink if it stopped moving forward - which doesn't happen. Now someone being pulled on skis behind a boat will sink if they stop forward motion -- because the skis are being kept up by Newton's 3rd Law (every action has an equal and opposite reaction) -- not buoyancy. It is 25% of Newton's 3rd Law that keeps and airplane up - basically displacing the air downward. The remaining 75% is supplied by the high pressure on the bottom of the wing, lift as we know it.

An airplane only needs to develop enough lift to support it's own weight to fly straight and level (neutral). The above theory of displacement and buoyancy falls apart because to float or be positively buoyant an object only need to displace a little more than it's own weight. A boat doesn't weigh more than the water it displaces. A jet weighing 200,000 pounds sitting on the runway is obviously negatively buoyant - it sank to the bottom of the liquid/gas it's in. But even at 500 mph that plane weighs 200,000 pounds -- and is still negatively buoyant in reference to the air. Speed does not increase the buoyancy of the aircraft. At any speed that aircraft is negatively buoyant and will always sink to the bottom of the medium it's in. So lift from the wings, and air hitting the bottom of the wing and pushing the wing up (Newton) is the explanation.

Your theory of buoyancy will only work for a hot air balloon, but it was an interesting thought!

mwraight,

I agree with your later post about some of the nonsensical explanations of lift which are espoused here. Having said that, your claim of "25% Newton's third law and 75% high pressure on the bottom of the wing" is also not valid. It makes no sense to distinguish between the fact that there is a pressure differential between the upper and lower surfaces and the fact that air is 'deflected'. These are not two independent phenomena, and the 75/25 split is just not there. The pressure on the bottom of the wing is higher than the pressure on the top of the wing, but is often lower than the freestream pressure. Wings generate lift because the airflow around them causes the pressure on the bottom to be higher than the pressure on the top. Beyond that, I seldom see an explanation that is valid or adds clarity. There is more analysis to be done, but it is not all that useful to the layman, or quite as intuitively obvious as we would like it to be.

banktoturn

[martimer]

It always seems to me that the problems involved in discussing aerodynamic forces revolve around the fact that not everybody has the same mathematical background and some of the math requires an above average education and understanding level.

It seems to me (based on my undergraduate degree in aeronautical engineering) that there are three ways to calculate it: Pressure (P upper - P lower), momentum (downwash speed * mass of air so moved) and vector (total of all velocity vectors). Pick your poison.

My favorite way of explaining lift (that I have used with children) is to consider two air molecules sitting side by side when a wing flies through them. Being friends, the two molecules remain together when the wing is gone. If you think about a lot of those pairs, you can imagine that the space between the molecules on top of the wing is greater (because the upper surface is longer) and therefore it is more crowded on the lower surface. A crowd will always spill into a sparsely populated area, so the wing gets pushed upwards - lifted. Not the way we were taught in school, but it leaves out all the 'messy' math (hey, no diffy q's! got to be good!).

[Tim Green]

Stand under the "wings" of a helicopter - and then tell us what you feel.

[mwraight]

Stand under the "wings" of a helicopter - and then tell us what you feel. You'll fell wind blowing down on you Tim...I think we've established that...and maybe if you're lucky enough it will blow your pants off.

your claim of "25% Newton's third law and 75% high pressure on the bottom of the wing" is also not valid. Please don't tell my father this after he spent $100,000 on my education. Also please don't tell the FAA or they'll have to rewrite everything - as will many, many authors of scholarly aviation books. You could kill so many people with this information - it's deadly.

That 25% Newton's 3rd is the impact air hitting the bottom of the wing when it's at a positive angle of attack in regards to the relative wind - and has nothing to do with those two "friendly" molecules (a very good description btw martimer) staying together. As I stated earlier with the mattress analogy - you can either say that that impact air compresses and causes a high pressure on the lower surface of the wing or you can say that the equal and opposite reaction of the air slamming into the bottom of the wing pushes it up. Tom-ah-to / Tu-mae-to.

These are not two independent phenomena, and the 75/25 split is just not there. But they are. Not all those air molecules in front of the wing have the glory of hitting it and splitting over the top and bottom surfaces - some of them slam into the bottom of the wing (poor buggers, they have no friends!) - hence the impact air - hence Newton's 3rd, but not Beethoven's 9th.

[kristianb]

Martimer,
You should not tell lies to children! The chance that two moleculefriends which are separated will ever meet again must be as close to zero that it´s possible to get!

Lift, my personal view
a wing passing through air needs an angle of attack to accelerate air downwards, which gives a reaction more or less upwards which is lift. Moving molecule friends around gives pressure differences which is the mechanism that transfer the force from the air to the wing.
A laboratory person has the wind tunnel view, 100% of the lift comes from pressure differencies.
A person on the ground standing below a helicopter (or a model pilot?) have the spectator view, 100% of the lift comes from accelerating air downwards.
A pilot in a plane sits in between, so it´s roughly 50/50%?
What I wanted to say is that I believe we all say the same thing, but in different ways.
Of course there is a physical explanation why airplanes flies, it´s neither magic or faith or something else. But to calculate lift from an airplane exact needs that the path of every molecule is calculated which is a tremendous work even for the best of computers. But then the answer is given, what is the pressure in every point, how big mass of air is accelerated downwards with which speed in each point.

Tim, I really like your chopper example
This also gives a good understanding of the dangerous downwind turn. A helicopter that hovers steadily over the ground against the wind have some extra lift from fresh air coming into the rotor (some of the work to pull air downwards comes from speed relative the air).
If the pilot turns the chopper 180 degrees and leave everything as before, the helicopter will start to move with the air. It will after a while reach the air speed and loose lift. This is the danger of downwind turns with airplanes, after a sharp turn at low speed it will take some time before the plane picks up the previous air speed and risk of stalling is big.
less problem in a full size plane where You have instruments to show air speed and normally makes more comfortable slow turns compensating with some throttle but for a model pilot, especially flying a heavy model there is a risk!
KristianB

[martimer]

Uhm, we all lie to children in some way. Think Santa Claus, Easter Bunny, "It will all be fine in the morning", any Disney movie, myths, fables, Dr. Suess. I am not bad for using that explanation.

I readily and completely agree that the two air molecules will probably never meet again. But as I tried to explain (poorly, apparently) this is an explanation for people without a lot of scientific/engineering background. I have had exactly ONE person come back to me after hearing that story and calling me on it (after taking some classes). My response was to mention the difference in education level before and after and then to discuss the momentum theory of lift (which that listener understood by that point) and we agreed that lift was caused by a synergy of both conditions (pressure and momentum - we went to good schools). It is a slightly different take on things, and is just as valid as 'ignoring friction' in a high school or college introductory physics class. It allows discussion of some principles without getting too complicated.

The funny thing is that if you just look at the EFFECTS of the pressure theory, you see a downwash after the wing - which validates the momentum theory. If you just look at the EFFECTS of the momentum theory you do see a pressure difference between the upper and lower surfaces - which validates the pressure theory. As with everything in the wonderful and imperfect compressible fluid we call air, nothing is simple and everything is linked to everything else.

Kind of cool, even if it does make the math hard. Just think for a moment what would happen if Lift really equalled one half the lift coefficient times the density times the area over the surface times the square of velocity (where Cl was just a constant). Life would be simpler, but then EVERYBODY would be an engineer and all the coolness of pocket protectors and slide rules would be diminished!

[banktoturn]

You'll fell wind blowing down on you Tim...I think we've established that...and maybe if you're lucky enough it will blow your pants off.

Please don't tell my father this after he spent $100,000 on my education. Also please don't tell the FAA or they'll have to rewrite everything - as will many, many authors of scholarly aviation books. You could kill so many people with this information - it's deadly.

That 25% Newton's 3rd is the impact air hitting the bottom of the wing when it's at a positive angle of attack in regards to the relative wind - and has nothing to do with those two "friendly" molecules (a very good description btw martimer) staying together. As I stated earlier with the mattress analogy - you can either say that that impact air compresses and causes a high pressure on the lower surface of the wing or you can say that the equal and opposite reaction of the air slamming into the bottom of the wing pushes it up. Tom-ah-to / Tu-mae-to.

But they are. Not all those air molecules in front of the wing have the glory of hitting it and splitting over the top and bottom surfaces - some of them slam into the bottom of the wing (poor buggers, they have no friends!) - hence the impact air - hence Newton's 3rd, but not Beethoven's 9th.

mwraight,

The FAA isn't in the aerodynamics business, because pilots don't really need to understand aerodynamics, any more than the driver of a car needs to understand the physics underlying the functioning of his car. Both the pilot and the driver need to understand what their vehicles will do in different circumstances, but both of them tend to misunderstand why. You'd better call the FAA and get them started rewriting.

banktoturn

[Tim Green]

About the impact of air against the bottom of the wing ...
The air a pilot is interested in (the air which gets energy added to it and is diverted down) pretty much comes off of the top surface of the wing. That air's been both accelerated and diverted down (Coanda effect). And it's the energy added to that air, and it's redirection downward, which makes flying fun.

Air doesn't have to impact bottom of wing ...
Since flying's possible without air impacting the bottom of the wing (0 AOA of the bottom surface), I'm not sure how much part it plays when the AOA is increased to the point where air meeting the bottom surface of the wing comes into effect. (A0A is Angle Of Attack for you newbies)

What's the air doing with that airfoil?
Note that although flying's possible without air impacting the bottom of the wing it's not possible if the top isn't also curved in a typical airfoil shape. It's this shape, which effectively creates a positive AOA if the bottom's at 0 AOA. And it's this shape which diverts air down, while also accelerating it.

How does it get accelerated?

Glad you asked.

Not because it has a longer distance to go than the bottom air, and has to meet up with it. It never meets up with it - and it actually beats the bottom air to the trailing edge

Because of the vacuum formed behind the hump in the airfoil.

(Remember - the scenario we're looking at here is with 0 AOA on the wing's bottom surface)

Bernoulli's part in all this?

Thus, Bernoulli can be used to calculate lift, because the pressure differential is an indication of the amount of air which will be accelerated down. But falls short as being the direct cause of lift. As the direct cause is the air diverted down which ultimately keeps pilots happy.

The vacuum is a way to measure lift - yes. But an explanation of lift - only indirectly.

Note - two ways to measure lift
1. the vacuum above the wing
2. the amount and velocity of air being diverted down

Note - One way to explain lift
1. the amoung and velocity of air being diverted down

[martimer]

Ooh, so close to being a perfect post, Tim. I am not trying to be a smartass, I mean it. Good post.

You left out two interesting facts not supported by your post: Flat 'airfoils' can generate lift, just not at 0 AoA. Incidentally, even a 'curved' airfoil has an AoA at which no lift is generated.

In the first case (at some positive AoA), it is either the 'deflected' air or the pressure differential (depends on where you went to school or what books you read) that generates the forces - probably a combination of the two, but I am probably barking at a wall with that point. In the second case (usually at some negative AoA), it is likely that the pressure differential is 'downward' enough to counteract (or balance against) the forces generated by the downwash.

I loved your last note (despite the typo - again, not intended as a put down). Yeah, lift is pretty much the (force generated by the) air being diverted downwards from the airfoil. Where we all seem to start haggling (and it is not just this happy dysfunctional family) is WHY that air goes the way it goes.

[robert harik]

Turning a full scale or model airplane down wind does not make it easier to stall for any aerodynamic reason.

In the case of a full scale aircraft, when you are flying along at a given throttle and trim setting , your reference is your airspeed indicator and your airpeed does not change whether you are flying upwind, downwind, or turning from one to the other.

The reason for this is, that when an aircraft is flying on a windy day it is
moving with the air mass(even in gusty conditions), and the airplane does not know up wind from down wind. The only thing that changes is your ground speed.

A model is easier to stall when turning downwind, but not for any aerodynamic reason , but because the pilot is useing ground speed as his reference. When he turns down wind the high ground speed (plane speed plus wind speed) gives the plane the look of flying well above its stall speed.

At a throttle setting that will keep the model in the air, a downwind turn is no problem. There is a problem if you are turning downwind in your landing pattern and the throttle is closed, the apparent high speed of flying down wind will cause many people to slow the model up to much, causing a stall and crash.

[mwraight]

The FAA isn't in the aerodynamics business, because pilots don't really need to understand aerodynamics, any more than the driver of a car needs to understand the physics underlying the functioning of his car. Both the pilot and the driver need to understand what their vehicles will do in different circumstances, but both of them tend to misunderstand why. You'd better call the FAA and get them started rewriting. Once again you're WRONG WRONG WRONG.

Where do you think most of the accepted answers for the pilot knowledge tests come from? The FAA. Where do the acceptable anwers for the practical test come from? The FAA. Try taking a Flight Instructor checkride and blowing out some b.s. about lift and see what kind of pink slip the examiner hands you (courtesy of the FAA). If you ever go for that check ride you better know lift inside and out and from the middle both ways.

Furthermore full scale pilots BETTER know about lift - or they have no business flying. I believe about every pilot exam in the past 50 years has asked the applicant to describe lift. If you think a pilot should only know as much about his plane and the dynamics of flight as someone driving a car - then do me a favor and never fly full scale! I know the fuel systems and electrical systems of every plane I've ever flown - as well as the hydraulic system and pitot static system. I know the weights, limits and airspeeds. I would think this constitutes a hell of a lot more than I know about my vehicle. Pilots need to know everything about their plane and about the physics of flight or they have absolutely no business up in the air - and have the highest likelihood of becoming flaming holes in the ground.

[mwraight]

Since flying's possible without air impacting the bottom of the wing (0 AOA of the bottom surface), I'm not sure how much part it plays when the AOA is increased to the point where air meeting the bottom surface of the wing comes into effect. (A0A is Angle Of Attack for you newbies)

And how many planes do you know of that fly well with a 0 AOA??

[mwraight]

As for me, I can't tolerate Idiot Fest 2004 anymore. I've tried to contribute in a meaningful way to people's understanding - in as simplified way as possible to make it meaningful. It's apparent that there are a multitude of people out there that want to continue to sow ignorance, lies, myths, misconceptions and conjecture about lift. So have at. Knock yourselves out. Nobody here wants to learn anything anyway.

[Tim Green]

I differentiated 0 AOA for the bottom of the wing from the AOA of the whole wing. Please take that into account in your responses.


Thus, I never said a flat airfoil wouldn't fly - I only said that if the bottom of the wing's flat and at 0 AOA, then the top better not be flat - or it won't generate lift.

[Sparky Paul]

And how many planes do you know of that fly well with a 0 AOA??
.
Just about all the planes with any camber. Zere LIFT and Zero AOA are two way different quantities.

[vintage1]

Where we all seem to start haggling (and it is not just this happy dysfunctional family) is WHY that air goes the way it goes.

Because nature abhors a vacume, and air has mass, viscosity and therefore density.

The wing forces the air molecules to accelerate. If we ignore turbulence, the fact that air doesn't have a vacuume left in after the wing is gone, means that the amount the air is moved creates Bernouilli's pressure diference, or if you want to look at the mass of air displaced downards, (which creates the pressure difference that can be calculated by Bernouilli equation) you have the Newton analysis. Guess what? Same answer, Bernoulli is just a short cut for laminar airflow that's all. If you don't have a Cray, just a slide rule, Bernoulli gets you to an answer quicker, that's all.

Flat plate airfoils are just as amenable to Bernoulii, BUT you have to examine the way the airflow moves over the plate - it doesn't - and can't be considered to - 'hug' the surface anymore. Its intertia causes the streamlines to follow a path that is not what simple theory expects. So at this point you might as well use Newton and the Cray.

Once into fully turbulent flow the concepts of laminar flow are so broken all you can use is Newton and even then it gets very hairy.

Which is why weather forecastng is rubbish by and large. Too complex.

This is as Mwaright said, getting to be an idiot fest.

I suppose no one who is still arguing has actually ever done teh mathematics of a tranfsorm?

Take a Fourier transform. A sine wave is descrbed by the function [ A sin(w)]

It is also described by teh function [Aw] where w is the frequency of the sine wave.

Which is correct? Neither or both. They are TRANSFORMS of each other...if you are considering single frequencies, its a bit easier to use the transformed version. If you are dealing with pulsed waveforms, sometimes its easier to look at them in the time domain rather than the frequency domain.

Bernoulli is derivable from Newton - in a sense it's a transfom of it - but the derivation depends on the assumption of laminar flow. IF laminar flow exists or nearly so (good airfoil design) you can calculate lift very accurately using little more than a ruler and a slide rule using Bernoulli. It takes a supercomputer to do it Newton's way though.

[Tim Green]

Calculations used to predict lift are useless as explanations for why wings generate lift.

For instance, you've got plenty of formulas for predicting the effects of gravity. Please explain though, why bodies attract each other. You can't. And no one on this earth, today, can.

That takes care of "the formula is the explanation" myth.

But flight's different from gravity - there are effects that wings in air produce which can be seen, and felt. There are physical similar phenomena we can use to try to model the airflow in our minds, in an effort to understand lift. Even simple experiments that can be done in one's own house.

So, unlike gravity, lift can be seen and understood - but in neither case will formulas used to predict behavior promote this understanding - not for gravity, and not for lift.

[vintage1]

Tjher is no difference. Gravity - its effects - can be seen and felt just as much as lift can be felt through a kites string.

Any explanation of anything is in terms of something more basic.

We explain stones falling by hypothesising a force of gravity. We explain the way things move by hypothesing the laws of motion - mass, time ,acceleration force - Newton tied them all in to a set of laws that have yet to be broken, except by relativity, which only modifies them.

All science is painting imaginary entities behind the picture of the world. Its no different for flight, or stones falling.

You see a screen in front of you with words on it. You hypothesise me sitting here typing them. Its seems reasonable. It may even be true. You can never prove it is though.

All of this is just imagination - imagining the world has things called forces and laws that tie it all together mathematically. None of it can ever be proved true. At best it is both conceivable that it be proved false, and one can say it hasn't been proved false yet.

Perhaps that is at the root of the problem here. Confusing models and suppositions about the world with the world itself. The map is not the territory. The only map that is 100% accurate is the territory itself.

Its a real shame that science gets taught the way it seems to be. I wasn't taught that way. The course I did in physics, reproduced all the experiments from Galileo up to pretty much quantum physics, and our teacher never ever claimed that what he said was true. He taught it as theories that fitted in with the way those experiments were done, and the history of the emergence of a complex, but seemingly accurate picture of how the physical world seems to work.

Subsequent exposure to philosophers of science has shown me the quandary he was in, and how carefully he stepped round it. Science is not truth, its just the best explanation we have for how some things seem to work, or at least it gives predictable results. The fact that it employs numinous concepts like force, time, energy, space, pressure, viscosity and the like rather than angels and demons, and the whims of the Gods, makes it no different from any other load of superstitious nonsense apart from one important fact.

It works. I CAN key in a bunch of stuff for a plane in Motocalc, and whilst it may not be 100% accurate, in general the plane flies more or less the way the science says.

If you want absolute certain explanations, try a church. They specialise in them. Of course you have to leave your need for proof at the door, and use Faith instead. :D

Science never really answers the question of how things work: At best it decribes their presumed workings sufficiently accurately to be able to design reliable technology, and it never even addresses the real issue, of why things are the way they are (or seem to be, anyrate).

But of course, if you ask why things are the way they are, you imply in the language some form of choice - that things could be different, as if some mind had decided one thing rather than another. Asking this very human question of the very unhuman universe, is where people end up theorising God, because if there was a primary choice, someone had to make it. Sloppy thinking and a catch question.

The only answer to why the universe is the way it is , is because that is the way it is.

Science and philosophy between them have answers for all the questions, Trouble is not many people want to understand the answers, or accept them. Its much easier to live in a world of cosy comforting explanations where you can be right all the time, than in the real scary enormous universe, which we really don't understand at all - or put our trust in something supernatural, when the world is littered with natures mistakes, and for all we know, we are the next one.

Real scientists are people who grew up and stopped believing what they were told, and went out and diccovred things that didn't fit, and thereby made new things for people to believe in. Instead of Santa Claus, you come to realise that your parents seem compelled to spend money they haven't got on stuff you don't really want. Try making sense of THAT! :D

If you examine Berboilli, you find that his thery says that if a liquid or gas has to speed up to get past an obstacle, then there must be a pressure gradient to cause it to speed up. Bits of air that go the 'long way round' a wing must therefore find themselves at lower pressure than bits of air that take the short cut. Is all perfectly consistent with newton, it just uses pressure rather than force as its primary equation.

And if you think about it, anything that forces air downwards must create an area of low pressure above it. Its the same ruddy thing, just analysed in two different ways, thats all.

I think I have had enough at 3:30 am with no coffee.

[mwraight]

I have to agree with Vintage1 100%. And there are no absolute certainties in this world...and nothing can have total proof.

As for Mr. Green being able to see and feel lift - WOW! I'm not sure where that super human power comes from, but it must be an amazing thing to have! You can't see lift and you can't feel it. You can feel the effects of it lifting your plane up in the air, but you ain't feeling the lift itself!

Also Mr. Green...Calculations used to predict lift are useless as explanations for why wings generate lift. Unfortunately for you math is what makes the world go 'round. I don't know one thing in the entire world that isn't subject to mathematics in some form. Math is pretty much a universal language as well. If you can't use math to explain lift, then you really can't use science, and then you can't explain lift. They are all interdepedent.

There are a hundred thousand ways to arrive at the same conclusions...and you can split the proverbial hair all you want...but you have nothing to say that hasn't already been said and you bring nothing worthwhile to the table. You're just trying your hand at "obfuscation".

Sparky Paul: Just about all the planes with any camber. Zere LIFT and Zero AOA are two way different quantities.
Zero angle of attack on almost any wing develops so little lift as to be useless. While a symmetrical airfoil will develop lift at zero AOA - it isn't enough to do much with. While Zero AOA and Zero Lift may be too different quantities...they aren't two WAY DIFFERENT quantities...you'll find there is a direct correlation between angle of attack and lift - up to the stalling point.

[Sparky Paul]

T


Zero angle of attack on almost any wing develops so little lift as to be useless. While a symmetrical airfoil will develop lift at zero AOA - it isn't enough to do much with. While Zero AOA and Zero Lift may be too different quantities...they aren't two WAY DIFFERENT quantities...you'll find there is a direct correlation between angle of attack and lift - up to the stalling point.
.
No doubt.
Wrong, certainly forcefully put, with a certain amount of the "straw man" red herring smell.
Taking a simple common airfoil's characteristics from NACA 824, the NACA 2412, which is common all over the field of aerodynamics, at 0 AOA, the lift coefficient is .22.
Doing a simple calculation using a model of 5 sq. ft. of wing area at various speeds, the lift the 2412 develops is shown...
If the Cl of .22 is not changed, the lift from the 5 feet of area grows to 23 times the weight of the airplane.
Adjusting the AOA and therefore the Cl to produce only the lift needed for level flight, the Cl drops to .0094, which isn't much of a number, but it flies the airplane.
The AOA MOF will be negative for this conditions...
"idiot fest" indeed... :(

[raptor22]

You can either chose to believe my explanation about lift and aerodynamics or not. My explanation is based on science and has proof behind it. I'm also of the opinion that I might be qualified to explain lift and how airplanes fly -- having received an Associates and Bachelors of Science in Aviation, been a Commercial pilot since 1997, a Flight Instructor since 1997, logged over a thousand hours and taught nearly 100 students. But what the hell could I possibly know about what makes an airplane fly???? Listen to people just built a model in their garage a flew for the first time last week. They know everything.

This is kinda a while back int he thread, but I just read it and feel compelled to comment.

My ground school instructor has logged 10,000 hours over a course of 40 years. He firmly beleives in the "air flows farther over the top" theory. Flight experience means nothing!

My current flight instructor grasuated w/ the same degree you have from embry riddle (the best school of its kind), and know just enough to tell me that an "aviation" degree really is not nearly enough to understand any of the real complexities of lift.

I hate to say it, but we are speaking of the theoretical and your practical experience is nearly worthless (found in concrete evidence of your comments "downwash is caused by air hitting the bottom"). The model flier with alot of independent research may know more than you.

Most of the downwash is caused by flow OVER the wing. I am not supporting any theory (I have to agree completely vintage1), but most of the downwash is not like "a stone skipping over water". This is seen that airfoils at low lift angles of attack actually have suction on the bottom of the wing which, as we have see argued by vintage1, goes completely in hand with downwash or upwash.

--Alex

[Tim Green]

I agree with Vintage1 too :cool: - at least when he said that you can use either newton or Bernoulli to predict an airfoil's lift. I'm not sure he said anything else specific enough to comment on though. :p

BTW - for the normal formulas to work, it's got to be a standard airfoil. Come up with anything too radical, and you're back in the windtunnel, making observations and measurements, trying to come up with new ways to apply the old formulas.

Meaning if you really understood what was going on, you wouldn't need wind tunnels at all.

For me - I'm still looking for the perfect explanation of lift. ;)

[vintage1]

Pearls before swine really isn't it? :D

I give you the complete answer as to what scence can and can't do, and even indicate why most people feel happier with fairy stories, and ........."I'm not sure he said anything else specific enough to comment on though."

:D :D

[mwraight]

Here we go with the fallacies again. So you have one ground instructor that's an idiot and therefor all ground instructors must be idiots.

My current flight instructor grasuated w/ the same degree you have from embry riddle (the best school of its kind), and know just enough to tell me that an "aviation" degree really is not nearly enough to understand any of the real complexities of lift.
Someone went to Embry Riddle and received a substandard education, therefore all aviation students must recieve a substandard education.

I wonder if you feel the same about lawyers, doctors, engineers, teachers, etc. There are stupid lawyers, doctors, engineers and teachers - but not all of them are. Does that make all of them that way? Did you stop to consider, for even a moment, that not all aviation degrees and programs are structured the same way?

You know nothing about my educational history, my course of study or anything of that nature. Not enough to make any judgements about me. I went above and beyond the call of duty. Just because there is one or two idiots in aviation doesn't mean I'm one. Don't presume to know anything about my knowledge base - what I've spent my life doing. I guarantee that in a head to head challenge over knowledge of flight or anything in regards to aviation you would lose to me.

I hate to say it, but we are speaking of the theoretical and your practical experience is nearly worthless (found in concrete evidence of your comments "downwash is caused by air hitting the bottom"). The model flier with alot of independent research may know more than you.

Quite honestly Raptor22, you can kiss my rear. What have you brought to this thread? Nothing. I know enough about the theoretical and the practical to run circles around you. You could take your knowledge of flight and put it on the head of a pin.

Someone stated that they hoped no one ever got so mad as to not post here again -- well, too bad - because I have. No one here wants to have a serious discussion. They want you to post something so they can sit there and screw with you all day long. Then they want to attack your educational background. RCGroups is about the most worthless place for information I've ever come upon.


As for Sparky, I wrote something without double checking it. I am human and do make mistakes. Notice however that your 5 pound airplane has to be going over 200 mph to develop that much lift. My model planes don't generally go that fast. Also notice that at 34 mph your plane doesn't have enough lift yet? I don't know how fast you expect to fly that plane - but it obviously isn't very efficient at 0 AOA, now is it? Now crank that AOA up and watch that wing really develop some lift. Obviously at 10,000 mph hour you would be talking serious lift at 0 AOA, but we don't hit that speed very often with models or full scale planes -- and we don't often fly 5 pound full scale planes. So your analysis is worthless. For our purposes - 0 AOA and little lift are pretty closely related.

[vintage1]

Chill buddy, chill...:D

[banktoturn]

Here we go with the fallacies again. So you have one ground instructor that's an idiot and therefor all ground instructors must be idiots.


Someone went to Embry Riddle and received a substandard education, therefore all aviation students must recieve a substandard education.

I wonder if you feel the same about lawyers, doctors, engineers, teachers, etc. There are stupid lawyers, doctors, engineers and teachers - but not all of them are. Does that make all of them that way? Did you stop to consider, for even a moment, that not all aviation degrees and programs are structured the same way?

You know nothing about my educational history, my course of study or anything of that nature. Not enough to make any judgements about me. I went above and beyond the call of duty. Just because there is one or two idiots in aviation doesn't mean I'm one. Don't presume to know anything about my knowledge base - what I've spent my life doing. I guarantee that in a head to head challenge over knowledge of flight or anything in regards to aviation you would lose to me.



Quite honestly Raptor22, you can kiss my rear. What have you brought to this thread? Nothing. I know enough about the theoretical and the practical to run circles around you. You could take your knowledge of flight and put it on the head of a pin.

Someone stated that they hoped no one ever got so mad as to not post here again -- well, too bad - because I have. No one here wants to have a serious discussion. They want you to post something so they can sit there and screw with you all day long. Then they want to attack your educational background. RCGroups is about the most worthless place for information I've ever come upon.


As for Sparky, I wrote something without double checking it. I am human and do make mistakes. Notice however that your 5 pound airplane has to be going over 200 mph to develop that much lift. My model planes don't generally go that fast. Also notice that at 34 mph your plane doesn't have enough lift yet? I don't know how fast you expect to fly that plane - but it obviously isn't very efficient at 0 AOA, now is it? Now crank that AOA up and watch that wing really develop some lift. Obviously at 10,000 mph hour you would be talking serious lift at 0 AOA, but we don't hit that speed very often with models or full scale planes -- and we don't often fly 5 pound full scale planes. So your analysis is worthless. For our purposes - 0 AOA and little lift are pretty closely related.

mwraight,

Don't take it so personally. Pilots aren't aerodynamicists, medical doctors aren't scientists, drivers aren't automotive engineers, and so on. It's just fine for pilots to misunderstand, or simply not understand, all the details of aerodynamics. If they needed a better understanding, they'd be required to get engineering degrees, or something similar. Pilots need to know what their planes will do in different situations, and they get a great education in that regard.

I'd love to have a serious discussion, as opposed to a dogmatic, hot-headed one. You seem to have a problem with anyone who doesn't accept what you say at face value. You are correct on one point: there is definitely at least one person on this thread who does not want to learn anything.

banktoturn

[raptor22]

Here we go with the fallacies again. So you have one ground instructor that's an idiot and therefore all ground instructors must be idiots.

I didn't say that. I was only stating that if he can log 10,000 hours without ever learning the truth (and I can attest that he has quite a good reputation and is a very smart person), than you can go 1000 hours without it making much difference int he theoretical field. I'm not saying that your 1000+ hours is not ahuge accomplishment, and I don't doubt youa re a far better pilot than my student self, but that does not neccessarily make you any more qualified than someone else to siscuss the theoretical aspects of flight.


Someone went to Embry Riddle and received a substandard education, therefore all aviation students must recieve a substandard education.

Once again, I did not say that. Embry Riddle is widely regarded as the best school of its kind (for flight training and engineering) in the US, if not the world. If you call that a substandard education then you do not know what you are talking about in any way. He had enough for advancement as a pilot, and more. I was just saying that if the top-school for this subject has only passed basic aerodynamics than I'm sure your own BS has not gone much further. So, that also is not a huge weapon for your own credibility.


As for Sparky, I wrote something without double checking it. I am human and do make mistakes. Notice however that your 5 pound airplane has to be going over 200 mph to develop that much lift. My model planes don't generally go that fast. Also notice that at 34 mph your plane doesn't have enough lift yet? I don't know how fast you expect to fly that plane - but it obviously isn't very efficient at 0 AOA, now is it? Now crank that AOA up and watch that wing really develop some lift. Obviously at 10,000 mph hour you would be talking serious lift at 0 AOA, but we don't hit that speed very often with models or full scale planes -- and we don't often fly 5 pound full scale planes. So your analysis is worthless. For our purposes - 0 AOA and little lift are pretty closely related.

Two words: Vector, F5D.


Quite honestly Raptor22, you can kiss my rear. What have you brought to this thread? Nothing. I know enough about the theoretical and the practical to run circles around you. You could take your knowledge of flight and put it on the head of a pin.

Someone stated that they hoped no one ever got so mad as to not post here again -- well, too bad - because I have. No one here wants to have a serious discussion. They want you to post something so they can sit there and screw with you all day long. Then they want to attack your educational background. RCGroups is about the most worthless place for information I've ever come upon.


SERIOUSLY, CALM DOWN! I wasn't being insulting, only pointing out that you shouldn't say others are "ignorant" because they do not agree with you and do not happen to have what I consider completely irrelevant credentials. Try to listen a bit; there's alot here you could learn. You were bringing up something completely pointless and insulting othes because they are not like you with their credentials that have little to do with the topic.

As for my own input, I just noticed this thread and thereforce had nothing new to input since Vintage said it anyway. As far as me to you, you know far less about me than I know about you from this thread (plus others) and I would like to tell you and your insulting comments to go to hell. You have demonstrated little real knowledge about aerodynamics. That's not a problem if you have a desirte to learn. As things stand, listen or shut up. You are overly emotional about others comments and obviously cannot recognize a meaningful discussion.


--Alex

BTW, I do not have a history of ranting about other members (this is my frist), but your emothional idiocy has royally pissed me off. And I am not insulting rcgroups and threatening to leave, either.

[martimer]

I think the only thing I have ever seen posted here on RCGroups that really made me angry was when a moderator scolded me for posting in the wrong forum in spite of the fact that several people appreciated my post and applauded my posting of it. Who was wrong - the moderator for enforcing his own brand of rules or the poster (me) for not following the rules.

It seems safe to post that there are a variety of opinions about what makes an airplane fly.

Ask an aerodynamicist and the response will probably be: "The lift generated by the lifting surfaces."

Ask an engine mechanic and the response will probably be: "The power put out by the prop."

Ask a jet mechanic and the response will probably be: "The thrust produced by the turbine."

Ask an aeronautical engineer and the response will probably be: "A good design balancing the weight of the payload with the mission requirements for operating envelope."

Ask a structural engineer and the response will probably be: "That is not my problem. As long as it does not break when landing I have done my job."

Ask an aicraft company CEO and the response will probably be: "A good team of engineers and a lot of money."

Ask a physicist and the response will probably be: "The proper application of the principles mathematics."

Ask a methematician and the response will probably be: "The equations prove that it has been done, what else do you need to know."

Ask an pilot and the response will probably be: "I do."

All valid answers yet none of them truly explain what is actually happening. There have been pretty forceful disagreements made here, yet nobody can prove anything. This has been the most hotly and angrily discussed topic that I have been a part of. Perhaps we (collectively) should just take a deep breath, let go of the domains we are holding on to (seems to be a running problem in academia) and try to actually listen to ALL of what someone is posting.

Rigorous debate teaches us to pounce on any mistake in a statement to disprove the entire statement. When did it teach us to disparage the maker of the mistake? Many times the essential point is valid, even with what may be perceived as a mistake. I have read some pretty good ideas here - some of which I have agreed with and some not so much. It seems to me that this is a pretty learned bunch, perhaps we should meet over pizza and beer rather than the playground.

[stevem1928]

I think Martimer summed it up well.

[martimer]

Careful, Steven. Agreeing with me or complimenting me in any form seems to be a sign of being deranged at the worst and grounds for expulsion at the least. Most people just ignore me. It is the price I pay for being right in a world full of left. ;-)

[KillerWatt]

You've all got me ticked now........i'm just gonna rubberband my SS's wing upside-down and go fly......!!!!!

[HELModels]

Good Luck with your SS experiment, I've seen that very suggestion posted somewhere before. Maybe someone can make a video.

As for the "5 lb." plane, I believe that was just a wing, built by hand, by a craftsman, to fly in a windtunnel to provide useful data to people who knew how to use it, then and in the future. If it were not for the hard work of NACA, a lot of cool designs might not be so cool.

[martimer]

Way back when I was in college, The Theory of Wing Sections was a required purchase. Great book, if you are interested in that sort of thing...

[Tim Green]

Was it required reading too? :D

[gouch]

RCGroups is about the most worthless place for information I've ever come upon

What's your problem? By your rantings, you KNOW everything there is to know already, with that 100K education daddy bought you ;)

Cheers
and SEE YA.....NOT :p
Paul

P.S I was actually enjoying reading your stuff in here until you turned into a goose.

[martimer]

There were several times when reading ToWS was required. Usually when doing senior projects and some 'big homework'. I used to have the specs for several airfoils memorized, but that was a few years/brain cells ago. ;-)

Somewhere in my files I have the logic and code for a program that took a NACA looking number and spat out the shape of the airfoil (as data points for plotting). It was orginally intended that the program would be modified to spit out some theoretical lift and drag data for different configurations, but that instructor left the school before we got that far. That would have been GREAT for RC since we remain in the incompressible region and the math is actually pretty easy and accurate. I keep promising to revisit the whole thing, but after a few moves all my files are buried. That and it is easier to just buy a kit someone else has done all the grunt work on...

[Sparky Paul]

A five pound plane flying 200 mph.. but not with an NACA 2412... might be commonly seen at any decent slope, DS'ing on the back side... :)

[Chas]

Prop torque which tends to roll the model to the left, at all times, under power

Spiralling propwash that - if it e.g. hits a fin are that is substantially above the thrust line, will cause a left yawing moment.




Vintage, I hope you are utterly, thoroughly ashamed of yourself. But I know you won't be for your pedantic trolling.

mwraight and martimer

Don't get sucked in to these semantic p****** matches; Vintage argued with me, stultifyingly, that a RIGHT rolling/yawing moment occured from torque and propwash, in another thread. He is just a sad case (8,000 + posts, using terms like "pearls before swine", which should indicate to you where he's coming from).

I know this is off topic with regard to lift, but it is on topic in a way - because yet another reasonable contributor (you!) has been diverted from an entertaining and hopefully enlightening discourse as a result of the professional Jodrells on RC Groups. The net result is that the field will be left to the Jodrells, and RC Groups will suffer fatally; which is a great pity.

Chas

[martimer]

I am not sure 'trolls' are capable of feeling remorse or shame because of the nature of why they post.

[Chas]

I think he's a schoolboy! Keeps wiffling on about his physics teacher, refers often to "books", has a zillion hours a day to post. The grammar, spelling and syntax would also support this conjecture.

Therefore, he's not likely to feel guilty, as I said, because being "naughty" is exactly the thrill he's after.

"Nah nah" etc.

Chas

[vintage1]

Nice day isn't it?

[Chas]

I did frame and post an answer to this but frankly I'm past arguing with someone who posts a copy of their degree, even if it is a Bachelor of Arts - in Engineering.

Why not wait until I answered the question, before posting "I thought not." ? You assumed the answer was "No, I don't know what a anticyclonic tensor is". I rest my case.

I have encountered a great many people like you in life Vintage and am surprised at myself that I have been sucked in thus far with all the argol/bargol. Certainly, I'm done with RC Groups (the next ten thousand posts will probably applaud that!), as it just isn't worth the candle.

I am amazed that you criticise anyone for their arrogance or rudeness, when you suggest that they are a danger to young children. You had better be careful, my old son.

Bye

Chas


PS
For the information of anyone who wonders what this is all about (including the moderators), Vintage has deleted his entire previous post, wherein he insultingly rubbished pretty much everything I said. Which is fair; I was pretty disparaging towards him, too.

Such is not surprising, though, as he claimed that I was a danger around young children.


He has lacked the "courage of his convictions" (UK speak), or "cajones" (North America straight talk) to let his post stand - just to set the record straight.

Chas

[martimer]

I am not going to post a copy of my degree here. I hope no one is offended.

[Chas]

Any fool can understand that, but not you it seems.

How about you? Do you even know what tensor calculus is?


:D :D

[Ollie]

Too long.

"Rules:

1. This is a family friendly site. Users shall refrain from cursing, posting lewd or offensive pictures, text, or other media, or in any other way conducting themselves in a manner that would be uncomfortable for children or the parents of children who browse here.

2. We strive to be a place for courteous discussion. Users shall treat each other with respect at all times. There shall be no name-calling. Users shall not provoke one another. Please pause for a moment before sending your post and consider how you would view it if you were reading it as addressed towards you personally."

[robert harik]

I enjoy reading both your posts, but you guys are taking the fun out of it now.
Both of you keep posting , maybee just not to each other.
Rob

[vintage1]

Certainly, I'm done with RC Groups (the next ten thousand posts will probably applaud that!), as it just isn't worth the candle.


Bye

Chas
and then...two minutes later..another post..again.
Chas. If you want to leave, just leave.

[Chas]

Could storm later.

[Steve McBride]

Ok - without reading back to where it started (I have a good idea), I find that I need to remond everyone of the rules that Ollie posted above. Please try and be considerate to one another and if someone posts something that gets on your nerves (some poster just like to get on peoples nerves) take a few hours before posting a reply.

Steve

[mwraight]

I have to agree with our able moderator. Especially after getting mindlessly bashed in this thread by trolls with hammers! This is such a flame war!

I had hoped that this thread would just die out and no one would ever notice it again. Who's the one responsible for bringing it back to life?

[raptor22]

I have to agree with our able moderator. Especially after getting mindlessly bashed in this thread by trolls with hammers! This is such a flame war!

I had hoped that this thread would just die out and no one would ever notice it again. Who's the one responsible for bringing it back to life?

I thought you said we would have the pleasure of you stop posting on rcgroups?

If its really a "worthless place for information" theyn you should ignore the new interest in this thread and leave like you promised.

--Alex