Meaningless aerodynamics and related physics discussion

[masraum]

Originally Posted by GH85Carrera

Like a lot of kids, I got into model airplanes. I built a kit with the classes 0.049 engine on it and learned the basics of U-control. I moved up to a .35 and a balsa wood airplane. It had a wing shape that was the same top or bottom. My Air Force pilot father said it can't fly. But the power to weight ratio was more than enough to fly with ease and I had a lot of fun with it. And yes, even when the engine ran out of gas it would glide down just fine to a safe landing.

Seems that would have to be due to downwash and Newton's 3rd.

[island911]

Originally Posted by RobFrost

Planes get lift by sending air downwards, it's simple Newtonian mechanics. There are two ways of looking at this, which are in a way the same thing.

A. Most wings have a convex top which forces the air to move faster round the outside of the circle. Whenever a fluid moves faster it has lower pressure, so the pressure difference from top to bottom of the wing manifests as lift.

And B. Wings usually have an upwards angle of attack to the direction of travel, I.e. the back of the wing is lower than the front.

Both a and b work by sending air downwards as the plane moves forwards. But a curved wing with a level angle of attack would still generate lift.

Sent from my SM-G988B using Tapatalk

Originally Posted by hbueno

That sums it up.

So then you two are saying that a flat-bottom (or also convex bottomed) wing with a level angle of attack would not generate lift?

I mean, the leading edge stagnation point of say a NACA 2412 is inline with the trailing edge at zero angle of attack yet it provides positive lift.

How does this wing have a net downward throw?

[cockerpunk]

Originally Posted by RobFrost

Planes get lift by sending air downwards, it's simple Newtonian mechanics. There are two ways of looking at this, which are in a way the same thing.

A. Most wings have a convex top which forces the air to move faster round the outside of the circle. Whenever a fluid moves faster it has lower pressure, so the pressure difference from top to bottom of the wing manifests as lift.

And B. Wings usually have an upwards angle of attack to the direction of travel, I.e. the back of the wing is lower than the front.

Both a and b work by sending air downwards as the plane moves forwards. But a curved wing with a level angle of attack would still generate lift.

Sent from my SM-G988B using Tapatalk

its not a mystery, this is why.

[cockerpunk]

Originally Posted by island911

So then you two are saying that a flat-bottom (or also convex bottomed) wing with a level angle of attack would not generate lift?

I mean, the leading edge stagnation point of say a NACA 2412 is inline with the trailing edge at zero angle of attack yet it provides positive lift.

How does this wing have a net downward throw?

because the air on top is going faster.

net doward throw is a simplified answer, and not a true determiner. useful, but not the be all end all determiner. lift is a force, a force is generated by pressure over an area. you can generate a pressure differential with the shape of the wing, or with the angle of the wing, but both methods create a pressure differential, higher on the bottom, lower on the top (until stall).

[nota]

get a sail boat to play with

the results of totally screwing up
are you stop or go backwards
vs in an aircraft stall = crash

driving forces are the same

[cockerpunk]

Originally Posted by GH85Carrera

Like a lot of kids, I got into model airplanes. I built a kit with the classes 0.049 engine on it and learned the basics of U-control. I moved up to a .35 and a balsa wood airplane. It had a wing shape that was the same top or bottom. My Air Force pilot father said it can't fly. But the power to weight ratio was more than enough to fly with ease and I had a lot of fun with it. And yes, even when the engine ran out of gas it would glide down just fine to a safe landing.

its important to note that static angle of attack is a stability characteristic built into many model and light duty aircraft. ergo, the wing could be flat on both sides (like a balsa glider with stamped flat wings), and with enough power, it would fly. you can make damn near anything fly with enough power.

[masraum]

Originally Posted by island911

So then you two are saying that a flat-bottom (or also convex bottomed) wing with a level angle of attack would not generate lift?

I mean, the leading edge stagnation point of say a NACA 2412 is inline with the trailing edge at zero angle of attack yet it provides positive lift.

How does this wing have a net downward throw?

Great question, and I look forward to the answer. Just looking at and thinking about things (because intuition is clearly the best source of knowledge for physics and aerodynamics), the top edge of the wing comes down to the trailing edge of the wing at a greater angle than the lower edge of the wing. And the air going over the top of the wing is moving faster than the air over the bottom, so that air will follow Newtons 1st law and overpower the slower air under the bottom, still causing a downwash that creates lift?

Like I said before, growing up, I'd only ever heard the Bernoulli speed/pressure theory of lift. Back about 2007 I heard the downwash theory. I've since heard that the truth is a combination of the two, and that science isn't really 100% on it.

[island911]

Originally Posted by cockerpunk

because the air on top is going faster. ..

Why is it going faster? Because it's getting pushed forward faster by the leading edge?

I mean, the air is still until the plane flies into it. The air is going to be pushed forward and up by the top side of the wing.

[cockerpunk]

the aero dynamics question that always blows my mind, is the super sonic flows esp around high performance jet intakes. using certain design principles you can arrive at an intake design that significantly multiplies the thrust of the engine at super sonic speeds by basically removing the air in front of the engine, and the whole thing is then sucked forward, rather than pushed by the thrust of the engine. this is counter intuitive because the intake designs primary design goal is to slow the air before the compressor. because the compressor will stall/explode if fed super sonic air. well, at least turbo compressor jets (ie not scram or ram jets)

super sonic flows are facinating and a key reason why i became an engineer. i have wanted to experiment at work with super sonic flows in metal, but the science isnt there yet. someday maybe.

[cockerpunk]

Originally Posted by island911

Why is it going faster? Because it's getting pushed forward faster by the leading edge?

I mean, the air is still until the plane flies into it. The air is going to be pushed forward and up by the top side of the wing.

the air is not pushed forward and up until flow separates (ie it stalls). the flow stays attached, and follows the profile of the wing.

[island911]

Originally Posted by masraum

Great question, and I look forward to the answer. Just looking at and thinking about things ... I've since heard that the truth is a combination of the two, and that science isn't really 100% on it.

ding ding ding...

Yes, multiple forces at play.

IOW, it's not "one thing."

See "Lifting bodies" for example.

Then there are wave pulses that keep bees in the air.

[masraum]

Originally Posted by island911

ding ding ding...

Yes, multiple forces at play.

IOW, it's not "one thing."

See "Lifting bodies" for example.

Then there are wave pulses that keep bees in the air.

Magic pixie dust keeps bees in the air. Duh! Pixies love honey.

[Hads930]

[island911]

Originally Posted by cockerpunk

the air is not pushed forward and up until flow separates (ie it stalls). the flow stays attached, and follows the profile of the wing.

You clearly believe that you have a good mental model of "the flow stays attached" yet I see that you do not. You are simply regurgitating an engineering concept that is used as tool for categorizing general flow types. IOW, all "attached flows" are not equal.

Oh, and the air (even when laminar about the foil) is absolutely pushed forward and upward by the leading edge. (mind your reference frame.)

[cockerpunk]

Originally Posted by island911

You clearly believe that you have a good mental model of "the flow stays attached" yet I see that you do not. You are simply regurgitating an engineering concept that is used as tool for categorizing general flow types. IOW, all "attached flows" are not equal.

Oh, and the air (even when laminar about the foil) is absolutely pushed forward and upward by the leading edge. (mind your reference frame.)

i didn't say all attached flows are equal.

we were discussing mass flow rate directions (ie "downflow"), not pressure distributions. the mass flow until stall is not upwards and forward, it is rearward.

[island911]

[cockerpunk]

Originally Posted by island911

yup, as i said, its about pressure distribution, not "down flow"

https://peer.asee.org/aerodynamic-performance-of-the-naca-2412-airfoil-at-low-reynolds-number.pdf

[island911]

Originally Posted by cockerpunk

yup, as i said, its about pressure distribution, not "down flow"

You just said the the opposite

Originally Posted by cockerpunk

its not a mystery, this [RobFrost Downward throw] is why.

Originally Posted by cockerpunk

because the air on top is going faster.

net doward throw is a simplified answer...

SMH.

[cockerpunk]

Originally Posted by island911

You just said the the opposite



SMH.

i mean you edited out the part about pressure distributions. its clear you have an ax to grind with me from PARF and didnt read the post and/or dont care what i said.

this is the post which clearly says that pressure distribution is the important thing when computing lift:

"net doward throw is a simplified answer, and not a true determiner. useful, but not the be all end all determiner. lift is a force, a force is generated by pressure over an area. you can generate a pressure differential with the shape of the wing, or with the angle of the wing, but both methods create a pressure differential, higher on the bottom, lower on the top (until stall)."

bolded for emphasis.

either you didnt read it, or you didnt care and decided to lie about my post.

[MBAtarga]

But what if the plane is on a treadmill?