Airplane wing ? 5

[enginesrus]

With all the constant talk about lift and airflow over the top of a wing.
I have one simple question, on average what is the percentage of airplane weight supported by the top of the wing?

 

[3DDave]

It would produce about 30% of the lift compared to allowing air to flow over the top.

 

[enginesrus]

Take a flat blade ceiling fan, similar to a propeller, propellers don't suck the plane through the sky, they push it.


It would produce about 30% of the lift compared to allowing air to flow over the top.
Do you have wind tunnel data for that statement?

When a submarine uses its control surfaces it is the water pressure that is acting on them not a vacuum assist. Especially at say 2 mph or less.

When a bird fly's it uses its wings to bite into the air and push down creating a higher pressure.

 

[3DDave]

It's been a while since I plotted the pressure distribution over a pressure-ported airfoil, but somewhere I think that I do, but similar data is widely available.

Back the fan blades with a disk and see what happens to the flow.

 

[rb1957]

"My theory is simply based on logic" ... sorry, you can't say that, well not here you can't.

You've said our theory of lift is Wrong. I've asked you to explain your theory. "logic" is not a theory. Can you calculate the lift of a wing, not a fanciful shape, an actual shape.
Say you had a wing 10' long, 1' chord, say 4deg incidence, 100fps airspeed ... what lift would it generate ? Does anything else need to be defined ?

The motion of a bird's wing, and so how it generates lift, is very different to an airplane's wing. Although you can compare a soaring bird (where the wing isn't flapping) to an airplane. I would expect that in that case the soaring bird's wing has the same pressure distribution as an airplane's wing. Can you demonstrate your proposition ?

For a propeller, the "upper" surface suction and the "lower" surface pressure do generate thrust. "upper" and "lower" are defined by the rotation of the blade.

A submarine's fins are the same as an airplane's wings; they are typically (by observation) symmetric foils, which produce lift by incidence. what's this "vacuum assist" you talk about?

What's your point with "No airflow over a wing there causing a pressure difference." ? Are you saying that an airfoil (however you want it to be) sitting on the ground with no airflow around it, won't produce lift ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[LittleInch]

Stop feeding the troll folks.....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[rb1957]

I came here for a good argument.

No you didn't, you came here for an argument.

Yes, but that isn't mere contradiction. An argument is a logical set of statements intended to support a proposition. Contradiction is merely the automatic gain-saying of whatever the other person said.

No it isn't.

...


"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[RoarkS]

My $.02. Newton is wrong... look at a vapor cloud on the top of a wing. Bernoulli is wrong... the air column does not create the opposing nozzle boundary (equal transit time does not exist!).

A wing curves the airflow around it because air is slightly sticky.

The curve acts just like the bend in a sheetmetal part. The wing is the neutral line of the bend. Everything above the neutral line puts tension in the material... or flow field. This has the effect of lowering the static pressure because its stressing the flow field ( or streamline if you need to think of it like that) out. Everything below the neutral line is in compression, thus causing an increase in pressure because the flow streamline is running into something causing it to back up because of the forced inflection. Back to the sticky part... Because it is slightly sticky that forces there to be a gradient between top and bottom... typically at the leading edge and trailing edge when we have decent air flow and its not separated (intentionally or not) Thus a well designed lifting wing puts most of the lower pressure on top, and higher pressure on bottom.

Fun starts when you start to go fast enough... again that little bit of sticky gets more important... you cant think of curvature anymore because you don't have time for that and you have to look at the instantaneous slope of what the airflow is hitting. If it's positive slope, you increase pressure and compress the flow field to the point of forming a shock wave. If it's a negative slope you loose pressure and get expansion.

Even more fun is when the curvature causes tension fast enough suddenly the air starts to care about instantaneous slope of what it's hitting.

How much one side does vs the other... (insert flight variables here). whichever side has the best PSI*SI wins.

 

[rb1957]

ok, i'll bite ... is there a name for this theory or is it your own idea ?

"A wing curves the airflow around it because air is slightly sticky." ... does "sticky" mean the same as "boundary layer" or "viscosity" ? but then that is flow circulation theory.

"look at a vapor cloud on the top of a wing" ... do you mean the condensation that accompanies a shock wave ?

same as I asked the OP ... apply your ideas to a wing, and show how much lift it'll generate.


"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[IRstuff]

A wing curves the airflow around it because air is slightly sticky.

That's the description of the Coanda effect, isn't it?

https://en.wikipedia.org/wiki/Coandă_effect

That is supposedly the mechanism by which Bernoulli effect is helped out, through the momentum of the topside air flow being directed downward balancing the resultant lift

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[drawoh]

Here is a photograph of a Junkers J2, the second cantilever aircraft ever built, minus its wing.

What we tend to ignore when we discuss early monoplane airfoils, is the requirement that the wing have an efficient structural shape. This aircraft had a 120HP engine, and a gross weight of 2500lb. The contemporary Sopwith Camel with similar power weighed around 1500lb gross.

If an airfoil is grossly asymmetric like this one, you can use Bernoulli's equation to calculate lift, and get a reasonable approximation. By World War[ ]II, people had tested airfoils in wind tunnels, and they had worked out shapes that were less asymmetric, that had good lift/drag ratios, and that were not analyzable by Bernoulli's equation.

--
JHG

 

[rb1957]

contrast the thick mainplane, with the very thin (almost planar) tailplane. Of course the tailplane generates it's lift with down incidence and with a large elevator.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[enginesrus]

How is that over the top airflow at say 5 times the speed of sound?
Again fly your hand out a car window at 50 or so MPH. What is pushing up or down your hand, just feel it.


Why can't some have a discussion without the name calling? I've been here for years.



According to a fellow here the pressure reduction over the top of the wing only accounts for 2% of pressure differential lift.

https://www.avsim.com/forums/topic/4217-bernoullis-principle-some-myths/

Its the force from the forward movement and angle of attack that creates the high pressure under the wing. The main reason for a curve in the wing section is for the spar. So that 30% is wrong.

 

[LittleInch]

enginesrus,

You may indeed have been here sometime, but you started this post with "one simple question" which was answered some time ago ( now 31 posts later) and yet you persist in apparently ignoring all the responses and decades of theory established in experiments. Then you take one person on a thread which is equally non conclusive and just random people spouting unsubstantiated "theories" and say it proves whatever point it is you are trying to make - and I've got lost as to what that is.

So sure, your presumably flat hand deflects air down and there is a resultant force up or vice versa. However this creates huge amounts of drag which forces your hand backwards. If indeed you could make your hand the shape of a wing with a curved top surface and less curved bottom surface ( rather difficult) you would get the same effect, but less drag.

I remind you that this forum is a "Professional forum and technical support for engineers for Aircraft engineering."

I would strongly recommend to any other posters that they simply don't reply and let this thread die its natural and overlong death.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[enginesrus]

Funny how some have no interest in learning something new.
Just do the search, the subject has been taught wrong even in college classes, its not just ME saying it.

 

[SwinnyGG]

Funny how some have no interest in learning something new.

You never post 'something new'. Your posts are pretty much always either stumping for some random climate engineering conspiracy theory website, or 'asking questions' about very well known engineering or physics processes and then calling everyone idiots when their correct explanations don't make sense to you.

I, for one, and happy to see others besides me grow tired of it.

 

[LiftDivergence]

Hi all,

Here is a great video by a Boeing tech fellow on common misconceptions in aerodynamics:

https://www.youtube.com/watch?v=QKCK4lJLQHU

He goes over many fallacies in the conceptions of how lift works.

In actuality both the Newtonian and Bernoulli explanations are incomplete. Generally the Bernoulli "explanation" relies on the fallacy of equal transit times for fluid elements, and the notion of "stream tube pinching" both of which have no physical basis.

This video goes over the mechanics of lift in the most complete way I have seen.

Keep em' Flying
//Fight Corrosion!

 

[3DDave]

Oh, no, not avsim vs actual data I actually saw on actual manometers. If a plank worked nature would have kept planks, like on insects in very low Reynolds number flow, and not gone to all the trouble of smooth airfoil shapes on birds.

The pressure increase under the wing is much smaller than the decrease on top. Mach flow changes that, but not enough below 0.8M to give up the nice curved wings.

Technically it's not possible to work out the performance of an airfoil by Bernoulli's equation because one needs to know the velocity distribution - that distribution is not a constant over the wing. You can look at the pressure distribution from testing and find the local airspeed, but no one cares, because the critical thing is pressure reversals which indicate stall and those are measured directly.

Even then, the majority of wind tunnel work doesn't bother with either one - they just create a lift, drag, and pitch-moment chart with respect to Angle of Attack, and normalize for dynamic pressure to use the coefficients in overall aircraft performance.

If anyone cares more they use smoke-streams added to see if the airfoil has unwanted or unexpected flow detachment; stall.

None of the rest is "new."

There are computational methods, such a panel flow, to get into the ballpark, and they compute airspeed from momentum and use Bernoulli's equation to generate the pressure distribution.

It's taught "wrong" because people continue to repeat bad explanations, often from the same seemingly plausible, but incorrect diagrams drawn by illustrators. Even from 20 year old zombie discussions from non-aerodynamicists. Be glad that "theory of lift" isn't what aircraft design is based on and that Bernoulli's equation, so useful in understanding incompressible flow, is simpler than what is required to deal with flow above about M 0.3 on up.

 

[rb1957]

I have a really neat picture (somewhere !?) of a model of the EAP (what became the Euro-Fighter) in a water tunnel, with different coloured flow streams. very nice !

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Brian Malone]

Doug McLean's presentation is very interesting. I will have to check out his book. I am certain much of it I will not fully understand. But his presentation is encouraging that I will be able follow his logic on the explanations of misreprentations, especially the equal transit theory.

 

[WKTaylor]

Here are the few examples of a flat-wing 'aircraft' I could conceive of... fun toys... otherwise no practical value except for teaching children.

For hundreds of reasons... aerodynamically and structures wise for instance... flat wings and stabilizers surface have ZERO practical value... for starters.

We have all given enginesrus some good insights and comments and solid technical insights on this topic... from mature/practical perspectives as professionals... and all this appears to be swept-aside by the OP looking for 'Q-magic'.

NOW, lets get real... I have to concur with LittleInch... let's stop playing games with this obvious 'non-aero enginesrus' [engines Russia?]... and consider this an interesting discuss among ourselves...

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov