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]

The change in pressure distribution is about 70% decrease on the top of a conventional airfoil and 30% increase on the bottom (as well as some areas of pressure decrease on the bottom.)

Depending on what one considers, the full weight has to be carried on the bottom as air hasn't got tensile properties, but if one is designing for loads, you need a stronger surface on the top as the differential is higher.

 

[LittleInch]

Then strictly speaking the answer is none.

What I think you mean is what percent of the total lift force is generated by the top surface. Answer apparently 70%.

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

 

[MintJulep]

It's not a simple question, it's simplistic.

There can't be a top without a bottom.

Lift is generated by a differential, acting at the mid-surface between top and bottom.

 

[verymadmac]

Now if one seals the wing, and installs a single vent, if that vent is pointing forward or aft or vented to the upper or lower surface, where does the lift get transmitted to the wing!

 

[rb1957]

I agree with MJ, that you can't have the upper surface pressure without the lower. I agree that lift is the resultant of differential pressures on the two surfaces. But we can still say that lower surface pressure resultant is about 70% of the total resultant.

If you vent the lower surface to the upper, then you'll lose a lot of the lower surface pressure.

The situation is different for flaps, where the slot reenergizes the flow over the flap.

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

 

[enginesrus]

Similar to airfoil shaped race cars, that are a form of lifting body. The answer is there is very little lifting effect.
The lift that seems to be ignored is all on the bottom of the wing. It is the angle of the air impact cushion or relative wind that the wing skips upon just like a rock skipping on water.
There are symmetrical wings with the same shape above and below, and there are aerobatic planes that fly upside down.
A wing can create lift with zero airflow over the top, in a laboratory.
Flaps? They "CUP" the wing, to hold more air under the wing, it has nothing to do with the top.
Just drive down the road and stick your hand out the window at say 50 mph, you will feel what causes the lift. Yes mimic a wing with it.

 

[SwinnyGG]

So... you started this thread to teach everyone how wings REALLY work? Is that it?

 

[WKTaylor]

OK, so... enginesrus...

Loads/forces due to lift are generated by + and - pressure distributions over the length of the wing-chord... which is a function of airfoil shape, angle of attack and air-velocity. Of course, this does not account for real-world factors... such as excrescence [friction] drag, laminar/separated flow... and in the case of a real-wing, the wing-tip vortices, torque and pressure distribution changes due to control surface deflections... and loads due to mass/inertia, etc...

Of course the span-wise sum of all loads [in discrete load-case 'sets'] defines the forces over the wing as an entity for various flight conditions.

Google "airfoil pressure distribution images"

https://www.google.com/search?q=airfoil+pressure+distribution+images

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]

so you disagree with the "lift from circulation" theory ? What theory is this you're proposing ?

what is this "the angle of the air impact cushion" ?? never heard of it before ?

"A wing can create lift with zero airflow over the top, in a laboratory." ... okm I'll bite ... 'cause it isn't acting as a wing, but is a deflector ... simple fluid momentum.

"Flaps? They "CUP" the wing, to hold more air under the wing, it has nothing to do with the top." ... seriously WTF ? flaps increase the camber of the airfoil

"Just drive down the road and stick your hand out the window at say 50 mph, you will feel what causes the lift. Yes mimic a wing with it." ... yes, I think we all play with this one ... I know I do (as a passenger, mostly. Your hand could be acting like a wing (with circulation) or like a deflector. We have to be careful with how we interpret experiments (uncontrolled) that we can perform, our 1st hand experience of the world. Careful, that way "flat earth" comes ...


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

 

[MintJulep]

Newton vs. Bernoulli cage match!

 

[waross]

Airflow over the wing top causes a reduction of pressure. Multiply the average pressure reduction (partial vacuum) by the area and you will get the lift contribution of the top of the wing.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[enginesrus]

Has anyone seen a flat wing airplane?
Or maybe just a simple paper thin wing, paper airplane.
No airflow over a wing there causing a pressure difference.
And again what about a symmetrical wing with the same curvature on the bottom as the top?

 

[3DDave]

A symmetrical wing at 0 degrees AoA produces no lift. To produce lift it tilts up to increase the amount of curvature above the stagnation point and decrease the amount of curvature below the stagnation point.

 

[SwinnyGG]

And again what about a symmetrical wing with the same curvature on the bottom as the top?

Symmetrical wings can fly because they operate at a non-zero angle of attack.

'Regular' non-symmetrical wings sections also operate at some not-zero angle of attack; they don't perform well inverted because the way they are shaped for high efficiency in the mode of operation they are designed for means that if you flip them upside down, you would need huge angles of attack for them to work properly.

Symmetrical wings work on aerobatic planes because they are designed to function at relatively small angles of attack which are still possible to achieve when the fuselage is upside-down, without putting the airframe into some crazy attitude which would cause damage or generate a boatload of drag.

The two surfaces which form the rear section of an airfoil are not parallel, whether the section is symmetrical or not. As a result, for any possible symmetrical airfoil section, there is a range of AoA values from zero up to the divergence angle of the trailing edge where no part of the airfoil is oblique to the flow, BUT the length of the streamline over the top is longer than the streamline over the bottom - meaning there will be a pressure differential generated if the airfoil is moving. Pressure differential means lift.

Next time you watch an aerobatic plane flying, pay attention. You'll notice that the mean camber line - for a symmetrical airfoil, the centerline - of the wing is not parallel to the centerline of the airframe. It's angled down a few degrees in the rear, so that in level forward flight the airframe is parallel to the direction of travel and the wing has a few degrees of positive AoA. In inverted level flight, the airframe will be 'tail low' to the point where the airfoil is moving at roughly the same AoA as it was when not inverted. The airframe is tail low because the mean camber line and airframe centerline are not parallel to each other. In the real world, in inverted level flight, the ailerons will be trimmed slightly nose-down as well, which reduces the necessary AoA to keep the aircraft level. So the amount of 'tail down' attitude you would expect to see in level inverted flight would be slightly less than the angle between the airfoil centerline and the centerline of the airframe.

 

[rb1957]

@enginesrus ... again, what theory do you support (since you deny the commonly held aerodynamic theory we all seem to support) ?



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

 

[LittleInch]

what theory do you support

The earth is flat
Perpetual motion is possible and being hidden by the oil companies
Alien beings are upon us in large numbers and even run the government
Lizard men rule the world ( and live in Denver international airport)
No one ever landed on the moon
Covid is caused by 5G masts
Birds can't fly ( they are surveillance drones)

Get the picture here?

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

 

[drawoh]

Has anyone seen a flat wing airplane?

Google Sleek Streak.

Bernoulli theory and the air vectoring theory are not mutually exclusive. If an aircraft mysteriously does something to the air that generates lift, air has to be vectored downwards. I have worked out the behaviour of what I call a Bernoulli airfoil, flat on the bottom, with a circle section as the top surface. At zero angle of attack, it generates lift. Round off the leading edge (messing up my angle of attack model) and move the top of the curve forward, you have something that looks like a Clark[ ]Y airfoil. Particularly after they brought in cantilever wings in the 1920s, an airfoil section must do three things...

[ol]
[li]...generate lots of lift[/li]
[li]...generate minimal drag[/li]
[li]...function as a structural section.[/li]
[/ol]

My impression is that most of this stuff was worked out by guys playing with wind tunnels. CFD came along decades later.

--
JHG

 

[rb1957]

Bernoulli airfoil ... sure it'll generate lift (at zero incidence) ... 'cause it has a curved camber-line (along the mid-thickness line). This was figured out in the early 1900s by a bunch of aerodynamicists (like Prandtl) supported by wind tunnels, then much later CFD.

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

 

[enginesrus]

A symmetrical wing at 0 degrees AoA produces no lift. To produce lift it tilts up to increase the amount of curvature above the stagnation point and decrease the amount of curvature below the stagnation point.

The tilting up in the front of the wing, allows for air pressure under the wing, that causes lift. If said wing had a box where no airflow was allowed over the top but only the bottom, in a wind tunnel, it would produce lift,(as long as turbulence was controlled,) when tilting up as mentioned.
My theory is simply based on logic.
A wing can be likened to a boat on a plane on water, skipping along on a higher pressure surface.