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?

 

[btrueblood]

"the subject has been taught wrong even in college classes"

Gosh oh gee, then why do Boeing and Airbus keep hiring grads from the Guggenheim schools, both of which companies (amongst other Western makers) keep making the highest performing aircraft in the world?

 

[rb1957]

I read the OP as "engines are us".

We should understand that our theory of flight can be fundamentally wrong, and still produce valid results.

Consider gravity. Newton's view of gravity as a force has allowed us to send satellites into space, perform grav assist manoeuvres, and intercept a planet millions of miles away; a voyage taking years. But Einstein's Relativity theorises that this gravitational "force" is a manifestation of curvature of space-time. So Newton whilst being practically correct (correct in our "real" world) is fundamentally flawed. Another view is that Newton is correct, and Einstein is "just" explaining why the gravitational force is there in the first place.

Umm ... things are weightless in orbit, cause of the orbit dynamics, but things in orbit should be experiencing a lower gravitational "force" ('cause they're further from the Earth's surface). Gravity on the moon is 1/6th of Earth's gravity, 'cause the mass of the moon is less ('cause the curvature of space-time is less). I wonder how the curvature of space-time is away from the Earth's surface. At the Lagrange points the gravitational "force" of the Sun is balanced by the Earth ... does this mean that space-time is "flat" ?

It is possible (likely ?) that some new idea will come along that will change the basic theory of aerodynamics, but this should "condense" to our current theory in our real world (so that the difference is philosophical rather than practical) or else show that our real world is just a "lucky" co-incidence (and we have tuning factors that allow us to match the real world).

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

 

[btrueblood]

At the Lagrange points the gravitational "force" of the Sun is balanced by the Earth ... does this mean that space-time is "flat" ?

Sure, if you can call the top side of a saddle "flat". Or, let's say it's flat for certain limits of flatness.

"It is possible (likely ?) that some new idea will come along that will change the basic theory of aerodynamics, but this should "condense" to our current theory in our real world"

Funnily enough, condensed matter physics at the bleeding edge is studying Bose-Einstein condensates, the most interesting examples of which are superfluids. In "real world aerodynamics" - somebody said lift happens because real world fluids are sticky (have viscosity). Helium below ~2 Kelvin is a "superfluid", i.e. has a vanishingly small viscosity and displays strange behavior (will flow up the wall of a container). Technically, you cannot have fluid dynamic drag or lift in a superfluid. Not sure if that has been experimentally confirmed, but I would love to get funds and build a superfluid helium wind tunnel so we can test it, you with me Rb?

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

Fun stuff.

As far as a "single theory of flight", there really isn't one. There are patched solutions that work in general across the variety of flow regimes from very low Re and Mach no. (bumblebee flying) to the opposite extreme of space shuttle re-entry (very high Re and Mach). Very different maths used. And generally, there are few fully theoretical solutions of fluid flow problems, more usually it's a jumble of partial numerical solutions, a lot of scale model testing, and a fairly large chunk of real world testing.

 

[rb1957]

yes, and that (multiple theories optimised for different regimes) indicates that we don't have a full understanding of the basic processes ... a unified theory of aerodynamics. But we do have a good engineering understanding of "everyday" aerodynamics

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

 

[btrueblood]

"we don't have a full understanding of the basic processes ... a unified theory of aerodynamics."

Hmm...not sure I'd go that far? We know (or think we do) the underlying equations (Navier Stokes), but the solution is not tractable (except in a few cases) with our current math capabilities. We have found pretty darn good approximations, and can link them back to the theory, so far at least. It's fun to see the direct NS solutions progressing year over year in the computational aero field.

 

[Brian Malone]

Popular Mechanics magazine happens to have a story in the July/August 2023 issue that is about paper plane flight. It does not go into great detail but it says the flat surface of a paper plane wing develops lift differently than a standard airfoil; vortex lift is involved for the paper plane. A similar situation applies to flight of many items: Frisbees, birds, bees, tree seeds, etc. I did not see the actual article on the Pop Mech website but I do not have a subscription so it could be behind their paywall. I purchased a hard copy to read the whole story.

 

[Ng2020]

Good segue:
I'd like to see the OPs theory on how appropriately placed vortex generators on the upper surface,( or for that matter, divergent trailing edges, blown flaps), lead to real and measurable increases in lift.

Then he or she can present it to AIAA, NASA, Boeing/Airbus flight sciences...

Or maybe TSAGI.

Enjoy.

 

[WKTaylor]

Ng2020...

"Or maybe TSAGI."?????

OK... I'll bite... what is 'TSAGI'??



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

 

[rb1957]

from wiki ...
"The Central Aerohydrodynamic Institute (also (Zhukovsky) Central Institute of Aerodynamics, Russian: Центра́льный аэрогидродинами́ческий институ́т, ЦАГИ, romanized: Tsentral'nyy Aerogidrodinamicheskiy Institut, TsAGI) was founded in Moscow by Russian aviation pioneer Nikolai Yegorovich Zhukovsky on December 1, 1918."

will, you need to figure out this internet thing and goggle ... smile

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

 

[WKTaylor]

Rb... Dohhhhh...

Ah... I see cried the blind man... Ng's reference to my [prior] 'Russian' reference...

I was being a bit 'engineerdy' when I Googled TSAGI... and got TsAGI... DANG. I thot Ng was giving us a wink/nod with a contraction like YGBSM...



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

 

[debodine]

I was too late (entered USAF in 1973) to ever work a Wild Weasel aircraft, but once when some other pingers and I got in trouble during basic training for USAF at Lackland AFB, TX, our punishment was to wash and wax the F-105 Thunderchief on display in front of our barracks. At that time of course, I did not know about the Wild Weasels, or that the F-105 had been uses for Wild Weasels. And although I didn't know that YGBSM was their motto, YGBSM was what we all bitched when we saw the size of our punishment...but the YGBSM was voiced VERY quietly so the drill sergeant could not hear us.

 

[WKTaylor]

GI's default-to-using the BAD/IMPOLITE names/contractions for 'things' and 'situations', etc...

79FS Wild Weasel mission patch...

Alas we are drifting-off-topic...

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

 

[btrueblood]

Nah, not so much. WW aircraft and pilots are always fun topics.

 

[rb1957]

ah, back in a time when people could be sensible ... SNAFU, FUBAR ...

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

 

[Brian Malone]

NASA's Glenn Research Center has introductory articles on aeronautics:

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/learn-about-aerodynamics/

Lift:

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/bernoulli-and-newton/#lift

Lift using Wright Brothers' airfoil in discussion:

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/lift-3/

The false 'equal transit time' / 'longer flow path' explanation for the increased air velocity and low pressure on the top surface of a wing was very common years ago.

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/foilw1/

I don't know if it is still used in modern texts but some science 'facts' are hard to eliminate being repeated even when there is extensive proof of their fallacy. Cases in point: female praying mantises always eating the male after mating, lemmings suicide, coriolis effect on bath water drains, etc.

Various other incorrect theories for lift are also discussed on the NASA GRC website. 'Skipping stone theory':

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/foilw2/

'Venturi theory':

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/venturi-theory/

 

[SwinnyGG]

The false 'equal transit time' / 'longer flow path' explanation for the increased air velocity and low pressure on the top surface of a wing was very common years ago.

The Bernoulli approach is still taught - but only (at least in my experience) at the introductory level before students are ready to be exposed to Navier-Stokes and more advanced compressibility solutions.

The uneducated seem to cry foul, but this is how all science is taught. Initially you learn basic concepts which are only true based certain basic assumptions which don't represent the real world. Once you understand those, you learn more complicated models.

 

[Brian Malone]

enginesrus, OP, you often seem to be hell-bent on trashing degreed individuals and/or accepted and proven knowledge/technology but I am digging the discussion this thread has produced. I was not familiar with the flow turning and fluid compressibility theory of flight - it makes a lot of sense and captures all conditions of flight and not just specific regimes.

 

[Brian Malone]

Then again - there is the exception condition of vortex lift . . .

 

[rb1957]

we have a perfectly good theory for every day flight conditions. We have special optimised solutions for uncommon regimes. I'm guessing the uninitiated don't appreciate the nuance and conclude if we don't have one theory for all then we have no theory ? But to say "I'm going to replace the entire theory that works well for everyday situations with what I feel on my hand and with logic" ... yeah, that flies in the face of professional engineering.

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

 

[btrueblood]

One of the toughest things to wrap your head around as an engineering student - look at the wing root fillets on modern aircraft. Why are they there? You would expect to see more drag from adding cross section area in the flow direction? It's not really clear until you watch some wind tunnel video to see the flow results with varying amounts of fillet added. Interference flows are not an intuitive result, you really need to spend some time with the NS or Euler equations to see what's going on.