Debunking Lift Theories Still Taught

[completeaerogeek]

Flat on the top is an approximation. So is flat on the bottom for a conventional airfoil.There is more curvature on the bottom of the SC airfoil. If you measure the distance along the surface from LE to TE it is further on the bottom - which is a problem for the equal transit time theory. But I thought we had agreed that the equal transit time theory doesn't hold water?

ETT never was an explanation. See wind tunnel pic attached. In all of my statements (please correct me) I have said 'flatter' not flat. See the A380 profile attached. Distance has nothing to do with anything.

 

 

 

 

[completeaerogeek]

There are certainly instructors who teach the equal transit time theory, and CASA appears to require it. From the part 61 MOS:"Apply Bernoulli’s theorem of constant energy flow to describe how an aerofoil produces lift, limited to the variation of kinetic energy (dynamic pressure) and potential energy (static pressure) as air flows through a venturi or over a aerofoil"

Explaining how an aerofoil produces lisft using the variation of pressure as air flows through a venturi seems to require an incorrect application of Bernoulli, presumably equal transit time.

 

In fact, a venturi doesn't explain lift at all, because the air comes out the other end travelling in the same direction at the same speed, so it cannot possibly produce lift.

CASA is talking about the Venturi Myth not ETT. I am in conversation with CLARC at the moment about changing this to a more clear explanation using Turning Flow and deleting reference to a venturi. See the first post in this thread for references.

 

 

[completeaerogeek]

If equal transit time worked you would have no drag. You can't get something for nothing. There is no reason to believe particles which separate have any reason to get together later after passing through some processing independently. It would be a baseless assumption. For air to move through a curved path there must always be more pressure on the outside of the curve, or if you want to interpret it another way, the pressure will be lower on the inside. Nev

I would stay away from pressure explanations. pressure is a result of lift not the cause. Always start with the simplest example-in tis case a flat plate wing. Increase AOA from a=zero and you have lift as a reaction force to turning the air. pressure is a result of AOA not wing shape.

 

 

 

 

[completeaerogeek]

If equal transit time worked you would have no drag. You can't get something for nothing. There is no reason to believe particles which separate have any reason to get together later after passing through some processing independently. It would be a baseless assumption. For air to move through a curved path there must always be more pressure on the outside of the curve, or if you want to interpret it another way, the pressure will be lower on the inside. Nev

Well most of us do, but I think the geek seems to be implying that there are instructors who don't.

There are lots of instructors still teaching this. I have seen it personally and encountered it while teaching. It is very prevalent. I have met airline pilots who believe it and it is still included in TV shows about flying. and by flying schools who put videos on the web. Search for yourself. They are easy to find.

 

 

 

 

[completeaerogeek]

Settle down, I agree with you. All I was trying to say is that I don't understand the point that was being made in the original reference to sprintcar wings.

Hi Aro - -Apologies - that was not was not aimed at you but at Mr Turbo

 

 

[completeaerogeek]

Well since I'm just a poor country boy who had to leave school at the age of 26 to help out on the farm perhaps you could explain why this would be so classic, GIVEN your description, which you now appear to be correcting?In particular a Sprintcar with an upside down aerofoil to your description, and I quoted it precisely - where the resulting effect is DOWN.

 

An airliner, which has a supercritical wing flies because the resulting effect is UP

 

I suppose there could be some airliners fitted with upside down aerofoils, but I've never seen one, and that was the context of my comment that Sprintcar wings have nothing to do with airliners, rather than an attempt to provide another start to the endless belt of your assumption that "they are just an aerofoil turning the airflow to create a reaction force", minus Bernoulli once again, of course.

MR Turbo- a physical reaction is not dependent on orientation of reaction. Are you really that obtuse or are you trying to upset people? For your information- SC aerofoils ARE what you would erroneously call 'upside down' aerofoils.

 

All that matters is the direction of the total reaction force. By your reasoning a plane that aileron rolled upside down would fall out of the sky.... I don't think you should be around aircraft...

 

 

 

[completeaerogeek]

I said sprintcar wings have nothing to do with an airliner. Probably what I should have said is that sprint car wings are curved on the bottom for a totally different reason than the wings on an airliner.

How can I make this any clearer. IT IS EXACTLY THE SAME PHYSICAL PRINCIPLE AND THE CURVED SHAPES PERFORM EXACTLY THE SAME FUNCTION.

 

They change the direction of the air to suit whatever purpose is intended...

 

 

[robinsm]

Jeez mate, dont shout. We hear you. Remember others dont have the fantastic academic and aviation theoretical background you obviously have. Most of us backwoods members of the idiots union just want to fly. Why it flies in an interesting argument, but thank goodness they do. Given that there have been a number of theories over the years as to why things fly, (referred to as the suck it up, or, blow it up theories,) it is refreshing to hear that we were all wrong. Please publish your insights in the scientific journals as I am sure the experts would love to be informed.

 

 

[completeaerogeek]

My apologies.

 

It was intended to Mr Turbo only was the end of a long and very silly series of statements he made including numerous statements attacking me when I am just trying to help. If you follow his statements you will see what I mean.

 

I too was taught the these silly theories in the RAAF many years ago and when I found out I was wrong I delved into it a bit deeper.

 

Teaching undergraduates aiming to be airline pilots for the last 3 years has made me se how widespread this nonsense it so I just trying to offer information so people can be better informed.

 

I began this thread-(see the first post) to help people understand what is actually happening because the more we know as pilots, the better we will be and the safer we will stay.

 

The experts have known these stories were rubbish for years. If you see my first post, I uploaded a video from Cambridge University and references from NASA. The problem has been that there have never been any alternate theories accepted by the experts. These stories have been made up by people who don't understand how tings work. If you believe things that are entirely wrong it can cause problems particularly at low airspeed/altitude.

 

When we see accidents like AF447, Asiana 214 and Colgan 3407 where the primary cause for the accident was pilots mishandling the aircraft, it does make me wonder if they understand what they are actually doing.

 

Anyway apologies and thanks for your feedback.

 

Cheers

 

 

[Admin]

@completeaerogeek please watch the tone and language used in your posts and refresh yourself with the Site Rules before you post again otherwise some moderation of your posts will occur

[Admin]

PS, you may also like to look at the Tutorials we have here on Recreational Flying under the menu item "Resources" developed over many years by our resident guru John Brandon

 

 

[turboplanner]

In all of my statements (please correct me) I have said 'flatter' not flat. See the A380 profile attached. Distance has nothing to do with anything.

Happy to correct you; I'll even bold the "flat" if you like.

 

Well SC wings were a real change maker. Curved on the bottom and flat on top. Messes with some people's heads!

[Guernsey]

Thanks everyone I have learned a great deal from these post....very uplifting indeed.

 

Alan.

 

 

[eightyknots]

Thanks everyone I have learned a great deal from these post....very uplifting indeed.Alan.

No one wrote anything with gravity on this thread.

 

 

[turboplanner]

It seems to have stalled.

 

 

[metalman]

It seems to have stalled.

Wouldn't start a victory dance just yet, he may have just grown tired of trying to educate the flat earth society

 

 

[bexrbetter]

Wouldn't start a victory dance just yet, he may have just grown tired of trying to educate the flat earth society

He answered a question no one asked and then expects everyone to fall over themselves praising him at the foot of his plinth.

 

Now excuse me, I'm late for a witch trial, anyone got a spare duck?

 

 

[metalman]

He answered a question no one asked and then expects everyone to fall over themselves praising him at the foot of his plinth.Now excuse me, I'm late for a witch trial, anyone got a spare duck?

Precisely why I've stayed right out of it, that and care factor zero,,,just thought it would be a bit early to be doing a jig

 

 

[Admin]

Moving right along now folks, it is an interesting subject along with many "physics" style questions, all answers that we need to use when flying so please discuss the subject and not the man!!!

 

 

[Dafydd Llewellyn]

Well SC wings were a real change maker. Curved on the bottom and flat on top. Messes with some people's heads!

I suspect you are confusing a Whitcomb Supercritical airfoil

http://crgis.ndc.nasa.gov/crgis/images/5/59/Review_SC_Airfoils.pdf

 

with a Sonic Rooftop airfoil

 

http://aerostudents.com/files/aircraftDesignAndOperation/examAnswers20100122.pdf

 

The latter is used near the wing root on swept-wing high-subsonic aircraft to prevent the concentration of the pressure distribution towards the trailing edge, which is a peculiarity of swept-back wings.

 

 

[ahlocks]

There has to be a conveyer belt in that wing somewhere...

 

 

[completeaerogeek]

Sprint car/F1

 

Yeah, nah, they don't - you're out of your league now, stick to your 1 dimensional aircraft thinking.

Ahh yes they do. Please provide the physical laws under which the sprintcar wings work differently? Be specific now.

 

Might have some trouble there as the rules for fluid dynamics apply to ALL solid objects... Oh and aircraft fly in 3D not 1D

 

 

[completeaerogeek]

I suspect you are confusing a Whitcomb Supercritical airfoilhttp://crgis.ndc.nasa.gov/crgis/images/5/59/Review_SC_Airfoils.pdf

with a Sonic Rooftop airfoil

 

http://aerostudents.com/files/aircraftDesignAndOperation/examAnswers20100122.pdf

 

The latter is used near the wing root on swept-wing high-subsonic aircraft to prevent the concentration of the pressure distribution towards the trailing edge, which is a peculiarity of swept-back wings.

 

 

 

 

Happy to correct you; I'll even bold the "flat" if you like.

Happy to correct you; I'll even bold the "flat" if you like.

My apologies. Must have been lazy fingers. The diagrams I have supplied clearly show flatter and that is what I have said in the remainder of my posts.

 

 

[completeaerogeek]

I suspect you are confusing a Whitcomb Supercritical airfoil http://crgis.ndc.nasa.gov/crgis/images/5/59/Review_SC_Airfoils.pdf

with a Sonic Rooftop airfoil

 

http://aerostudents.com/files/aircraftDesignAndOperation/examAnswers20100122.pdf

 

The latter is used near the wing root on swept-wing high-subsonic aircraft to prevent the concentration of the pressure distribution towards the trailing edge, which is a peculiarity of swept-back wings.

I don't think so. Please find attached the A380 wing plot. SC wings are designed to reduce the density change above the wing as air approached M1.0. The do this by minimising upper surface camber and therefore the angular change as the air changes direction at the leading edge, the reduction in density drop means that the local speed of sound is not lowered as much as on a conventional wing and this reduces standing shock wave size.

 

 

 

 

[completeaerogeek]

A wing curved on the bottom and flat on the top produces a downforce, as in the Sprintcar wing - the teaching is correct.I'm saying his description is incorrect. A Supercritical Wing is a complex shape and not just flat on the top and curved on the bottom.

 

A Supercritical Wing does camber on the top, just a lesser amount than a conventional aerofoil, and its complex shape underneath is designed to offset the lesser camber by creating more downforce. I've attached a diagramme comparison of a conventional aerofoil and supercritical aerofoil from the NASA website.

You are really grasping at straws not. A small amount of camber on top. It is much flatter on top than underneath which kind of blows up convention explanations of lift now doesn't it?