Explain this, Veeky Forums
I am dumb but I think simple logic proves airfoils are designed upside down.
The curved surface on the top would displace more air, creating a higher pressure than the flat surface on the bottom. This means that the lower pressure area on the bottom of the foil would suck the aircraft downwards, instead of upwards.
Am I just stupid? I don't get this at all. Please help. Assume the angle of attack is totally flat and the flat foil is totally flat also.
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In this picture it's perfectly clear that the top surface has a greater surface area than the bottom, meaning it displaces more atoms and would have greater pressure on it....
Right?
>Assume the angle of attack is totally flat
That's not how wings work, senpai.
...and that's pretty much the answer to your question.
It's dynamic pressure, and since sum of dynamic and static pressure in.given area is constant, static pressure is pulling the wing from above and pushing from below.
Here's another picture confusing me.
These are hydrofoils, basically airfoils for underwater use.
The front foil is designed like the foils in the other two pictures, and they show they work by pushing water downwards behind the foil.
Does this mean I'm right about airfoils being sucked downwards but the lifting effect comes from the trail it leaves?
I'm confused.
In this picture, the rear hydrofoil is upside down compared to the front, probably for stability reasons?
No idea.
Look, here's a fucking NASA link saying our current theories on foils are inadequate and may be wrong.
As you'll see in ALL the pictures I've posted, the angle of attack is ZERO DEGREES. I think that's how you'd say it.
Basically, I'm trying to say the wing is heading directly into the air perfectly flat, with no angle.
I guess I'm trying to say is, what would a foil look like if it was designed to fly straight into the wind?
No flaps, just the shape.
Thanks.
Any idea what the most efficient airfoil design is for zero angle of attack?
OP here...
I guess that while there is more matter displaced by the top surface of the foil, the drop off creates a vacuum at speed which cancels out the effect?
I read that the lift produced by a foil like in the OP pic will produce virtually no lift at zero angle of attack, but at speed it seems pretty much any conventional foil will create around 1-2% lift at zero angle of attack if it's going fast enough.
I never understood the Bernoulli lift explanation. Why does air need to meet at the same point? Why does air accelerate when it has a longer distance to pass compared to air below.
I always thought it's mostly just air striking the bottom surface at an angle creating lift, and some other minor effects.
>I never understood the Bernoulli lift explanation.
That's because neither did your teachers. Read the following link:
iopscience.iop.org
>Why does air need to meet at the same point?
Good question. It doesn't. See pic related.
I thought teacher's stopped giving that explanation long ago.
common misconceptions
1. the particle/streams which are separated at the tip of the airfoil don't meet at the end of it ==> the flow above is faster than under the airfoil
2. there is no suction, only pushing forces; suction is an illusion of our senses. there is the difference between two pressure areas which results in a net force
3. oldschool videos for gain and profit
youtube.com
youtube.com
protip: wings don't work primarily by using Bernoulli principle
OP here, my thoughts exactly.
I think the vast, vast majority of flight is actually based around angle of attack.
Actually according the your picture...
THE FLOW OF AIR ABOVE THE FOIL IS SLOWER THAN THE FLOW BENEATH IT.
And to top it off, the only lift it's generating is because of the angle of attack.
And the icing on the cake is, with no angle of attack, the thing would NOT produce any lift at any speed. In fact it would sink.
According to the pic, the greatest resistance is on top of the foil because the particles are DENSER than the particles below.
This thread is living proof that we have been doing it WRONG. Foil design has been WRONG for decades because people believe ANYTHING a guy with a degree says.
No, no, you see, when you move through the air with that, the wing still moves through, say 5 meters of air, right, but because there's a bump on the top, 5 meters of air must COVER maybe like 5.5m of wing. So the air on top moves faster.
Since it moves faster, the particles are more spread out, and that creates a vacuum-like state of lower air pressure, so it WOULD get sucked UP instead.
The airflow on the bottom moves 5m of win in 5 meters, but the airflow on top might move like 5.5m of wing in 5m.
You see?
You are correct.
Anyone who thinks Bernoulli is responsible for lift, tell me how can planes fly upside down? You can't. It's all about angle of attack and minimizing drag.
Look at this picture
It's obvious the airflow flows faster because the bottom plane is shorter and has the least resistance.
Thanks.
So, redesigned foils could actually provide lift with zero angle of attack, and be more fuel efficient?
What? No. An airfoil can provide lift at 0 AoA, but where the hell did the fuel efficiency part come from?
Airfoils are pretty much 99.99999% optimized for their use cases.
Alot of flying upside down has to do with the shape of the airfoil and raw engine power. Stunt planes use a symmetrical airfoil and a strong engine to stay inverted for instance. Its why stunt planes feel comfy inverted while a 747 tries to fall out of the sky when upside down. For those of you that disagree about engine power being as big of a factor as im making it out to be, then how does a rocket fly? Just power alone.
Not exactly. An aircraft can achieve flight even if you never pulled back on the stick and just kept accelerating down the runway. The plane will feel lighter and lighter until it just lifts off the ground.
(Source: my own aircraft. A C172)
Aaaaaand all those foils utilize an angle of attack.
I'm talking about no angle of attack.
I'm wanting to design a retractable hydrofoil, and it will tuck away better if it has a 0° angle of attack.
That's because the wings are ANGLED.
Here again, I forgot to mention that even with no angle of attack it seems standard foils produce a very very small percentage of lift with no angle of attack, and speed is what gives those foils fight.
Angled as in its dihedral? Or angled in relation to the ground? Because its landing gear is tricycle gear so no AoA until you pull back on the stick and drop the tail.
Angled relative to the wind.
Like when you stick you're hand out the window of a car on the interstate, and you angle you're hand so it moves up or down, but keep it flat and it doesn't move up or down.
Depends on the Reynolds number.
>I want to design a device that does not do the one thing that makes it work
Hey guys. Despite scoffing at all my aero projects as "basic and stupid" looking at this thread not many people here can describe how an airfoil works. Pretty sad really that you posture yourself as an ubermensch genius yet can't even answer a basic aerodynamics question.
Anyway chiding aside, The Bernoulli (air moving faster on top) explanation is not true. An airfoil works due to a combination of deflecting air downwards (Newton) and the fact that air over the top is curved (Euler). Literally the first page of any aerodynamics book will tell you that curving a streamline causes a pressure drop. The describing relation deltaP/deltaN = rho*v^/r where deltaN is the thickness of the air being curved and r is the radius of curvature. This is easily derived from Euler's Equations. This is why unsymmetrical airfoils generate lift at zero angle of attack. However if the curve is too sharp the flow will separate and cause turbulence. This depends on the flow conditions (reynolds number) and is why one airfoil camber doesn't work well in all circumstances.
So yeah I'm pretty triggered that whenever I post a basic aerodynamics problem I get told to fuck off because it's "babby homework-tier" yet when someone asks how a wing works nobody even knows this. Even the other day no-one could say how an axial compressor works when someone asked despite everyone here allegedly being "physics experts" Veeky Forums is really far up it's own ass.
No
You can easily prove this is not the case by first taking a rotating cylinder (i.e. a forced vortex), convert it into an aerofoil shape via the Joukowski transform and compute the flow field around it via complex potentials. While this does not account for boundary layer effects (i.e. viscosity) or compressibility, it is a good approximation nonetheless.
Alternatively, if you wanna go balls deep, take an aerofoil shape and compute lift by the Prandtl -Meyer shock expansion theory.
You'll see both will yield a lift force up.
Cambered aerofoils generate lift even at 0 AoA.