Airplanes, how to they work?

>I'm a fuckin retard, the post
What do you think happens when you change your angle of attack? You change the pressures about the airfoil. Lift isn't the force resulting from the air pushing on the bottom of the airfoil, it is the resulting force from the pressure differential caused by the low pressure above the airfoil. Two examples to prove this:

A positive-camber airfoil will generate positive lift even at a negative angle of attack, pic related (or page 28 in )

The buffet before a stall is the alternating separation and reattachment of the boundary layer on the upper half of the airfoil along the trailing edge. This causes the wing to alternate between a stalled and unstalled condition. If lift were a reactionary force the buffet wouldn't occur.

t. Commercial multi engine pilot

*Partially* true. Each airfoil has a different lift coefficient at 0 deg angle of attack. Ideal airfoils have a 2pi/radian lift-AoA slope. However, 3D wing effects and other viscous phenomena mean that the 2pi figure is never reached and a lift curve slope value dependent on the airfoil exists.

Therefore, the particular AoA you are at is indeed very important for the lift characteristics of a wing, but ultimately how much lift you get is a combination of airfoil cross section, wing taper ratio, twist, sweep and dihedral. Admittedly, things change as we go high supersonic, where you can even have a thin wedge as a wing. You won't be doing any fancy manuevers at this Mach no anyway, for both aerodynamic and structural reasons.

Thrust to weight ratio is an important parameter in aircraft design, especially military, for performance purposes. A good wing and a good engine are both useless without each other.

One last extremely important issue is stall/boundary layer separation. There's nothing that can send a fighter pilot to his grave faster than unexpectedly stalling and therefore losing lift and a massive increase in drag. Again, the AoA at this occurs is almost always entirely a wing matter. Plus, smart aerodynamic design can turn stalling strategically into an advantage-see the crazy post stall manuevers Russian Su-27 family fighters can do.

-t. Aero engineering student at world top 5 school

>A good wing and a good engine are both useless without each other
I'll take 'gliders' for 200, Alex

>smart aerodynamic design
>see the crazy post stall manuevers Russian Su-27 family fighters can do
That's entirely thrust-dependent, not aerodynamic. The wing remains in an accelerated stall condition during those maneuvers until the AoA is reduced below the critical value.

Bernoulli's equation.

But it's not mainly due to pressure difference, the tilt of the wing is of bigger importance.

There are exactly two forces in fluid mechanics: pressure and shear. And shear is always parallel to the flow, while lift is defined as perpendicular to the flow. Thus, lift must manifest through the pressure field, and Bernoulli is a valid equation to describe that.

The mechanism, be it shape of the wing (bullshit) or the Kutta Condition (better), is secondary to the rediculous claim of yours that lift doesn't come from pressure.

>aircraft flying upside down
Now what.

Then if you want to spend LOTS of time understanding this sort of shit, get into why different kite designs fly.

Starter screed -- peterlynnhimself.com/Why_Kites_Dont_Fly.php

You can still achieve a positive coefficient of lift with an inverted airfoil, it just depends on the camber and angle of attack.

The shape of the wing assists in improving additional lift, but isn't strictly necessary.

It helps a bit, but you don't NEED it.

>the shape of the wing isn't necessary
Tell me why a wing uses an airfoil instead of a flat plate.

Does Henry's law also hold for the solubility of gases in other gases.

Aerobatic aircraft often do not.

A symmetrical airfoil is still an airfoil. They are used because they have the same coefficient of lift inverted as they do right side up.

They work by pushing air down. That is the simplest explaination. There is some subtly with wing shape, and angle of attack, but that is the basic idea.

they provide more lift so the plane can carry more cargo.

not like that. You need an angle of attack

Wrong. Lift is the resulting force created by the pressure differential between the upper side (low pressure) and the lower side (high pressure). It is not a reactionary force from air hitting the bottom of the wing.

See pic related. A symmetrical airfoil will produce no lift at 0° AoA, but a cambered airfoil will.

>Lift is the resulting force created by the pressure differential between the upper side (low pressure) and the lower side (high pressure).
True.
>It is not a reactionary force from air hitting the bottom of the wing.
False. Every force has a reaction.

>>It is not a reactionary force from air hitting the bottom of the wing.
>False. Every force has a reaction.
That said, if someone is visualizing the air bouncing off the wing like a ball, that is just as wrong as the equal-time fallacy. The air flows parallel to the surface of the wing.

Biggest problem with this diagram: Air behind the wing is drawn as flowing up!

How do you explain having to nose down at certain speeds if you have a lot of lift?

Yes, but that is not lift. That is just the deflection of the relative wind, which is not the reason an airfoil generates lift.

What is not lift? Lift, or its reaction force? Certainly the reaction to lift is not lift. But lift is the reaction to the reaction to lift.

Another poster in this thread has already explained that lift must manifest from the pressure field: that shear is parallel with the flow, and that this is approximately orthogonal to lift on an airfoil at low angles of attack. Given this as a starting point, I would encourage you to inspect the Navier-Stokes Equations: the substantial derivative of velocity - the acceleration of the fluid - multiplied by the density of the fluid is equal to the pressure gradient (neglecting gravity and shear). This is essentially equivalent to "F=ma".

When you say "it isn't the deflection, its the pressure", or if someone else says "its not the pressure its the deflection", you are literally claiming "its not the left-hand side of the equation, its the right-hand side". Well, believe it or not, it has to be both, or we can't call it an equation. You cannot have a pressure differential without a deflection of the flow, and you cannot deflect the flow without a pressure differential. Both streamline curvature and pressure difference are equivalent, perfectly acceptable descriptions.

Flat plate airfoils, sharp-leading-edge, and round-trailing-edge airfoils all exist. Helicopter rotors at bad advance-ratios basically go 'backwards' through the flow. You still generate lift, but you have poor stall characteristics and for round trailing-edges you have some unwanted pressure recovery.

>It is not a reactionary force from air hitting the bottom of the wing.
LOL what the the hell do you think pressure is, magic?

You do realize that air flow is a macroscopic phenomenon and does not mean that air molecules are not hitting the wing right? The only way to exert pressure on something is to be in contact with it.

The idea I was attempting to get across is that lift is not simply a result of the air hitting the bottom of the airfoil and pushing it upwards, so I suppose I could've worded it better.

Of course they all exist, but its extremely rare that you find any of those nowadays, save for sharp leading edge airfoils, but that is specific to aircraft designed for supersonic operation. They will typically be supplemented with lift-improving devices, like slats or flaps which change the camber of the airfoil.

You're correct. That said, I have seen people trying to compute lift by imagining molecules hitting the wing at relative wind speed and bouncing off at an angle. Which isn't correct. That's what I was trying to describe and failed at. And I agree that isn't implied by "hitting".

>In high speed aircraft that use delta wings, the wing shape means almost nothing

The shape of a delta wing is very important. For instance, at low-speed, delta wings produce a strong coherent leading-edge vortex which significantly augments lift, and delays static stall. Spanwise flow, achieved from the high sweep angle, is required to stabilize these vortices, but the resulting small aspect ratio means that low-speed manoeuvres requires extremely high angles-of-attack (thankfully stall is delayed as stated earlier). What you should mean to say, I hope, is that the profile cross-section is less important. This is less wrong, but it is not true either.

Newton predicted that the lift on an airfoil would be proportional to the square of the sine of the angle of attack, as the flow would just be deflected parallel to the chord. Newton cannot be blamed for this error; there was no knowledge of vortex flows in his era. But this is essentially your claim if you are to suggest the profile is unimportant. A delta wing, even at high speeds, still must generate a circulation, and in fact, it generates this circulation even better than a low-speed straight-wing of similar aspect ratio, as it has not only the linear alpha-term you would expect from potential flow, but a sine-square-alpha term from leading-edge suction (as Polhamus showed in the 60s).

>When I fly, I don't give a shit about things like "wing stall" because I fly via angle of attack for the given airspeed.
This is even more nonsense. We could talk about wing stall in terms of boundary layer separation or whatever you like, but a nice practical definition is when your lift starts to decrease with increasing angle of attack. The idea that you 'don't care about stall' because you fly 'via angle of attack' suggests you don't understand either. Pilots seriously are some of the worst-educated people I've ever met regarding aerodynamics.

Some of us bother to learn it but the few idiots make all of us pilots look bad.

maybe above the karman line

>you 'don't care about stall' because you fly 'via angle of attack'

Obviously he flies rockets

Any explanations from physicists rather than pilots?

Nah the pilot's completely correct. You can use a brick as a wing it would still work. The only important thing is ANGLE OF ATTACK!! Pressure and Bernooblees equation is not the rael world. Only pilots would know

You don't need to be an aerodynamicist to fly a plane; I'm happy with pilots knowing the way their control inputs affect the aircraft handling intuitively without significant physical understanding. My issue is in this misplaced confidence.

Most pilots I've met, despite having little to no formal aerodynamic training, are completely sure that they have a full understanding of the fluid mechanics of aircraft. As an aerodynamicist, I imagine it's a bit like a system administrator walking into Intel and telling them he knows all about CPU architecture and circuit-level design because he operates big computers for a living. Piloting is already an important and valuable skill and profession, you don't have to be physicists too.

I have had formal education on this stuff though, I have taken classes on physics, aerodynamics, aircraft performance, energy management, and systems; many pilots have not. It's just annoying when people lump us pilots together as idiots when it comes to this stuff. I love learning about aerodynamics then taking that knowledge up and seeing it first hand in the plane, it ties it all together. But when the other pilot says wing shape means nothing and a brick can do the same as an airfoil it makes me want to whip my phone through the window.

ITT: We dont know how the fuck flight is possible but it is some how

To simply put it:
Because air takes a longer distance to cover the "curved upper surface" of an airplane, the pressure on top of the airplane decreases thus leading to greater velocity and blah blah blah conservation of momentum blah blah it lifts

Certainly not like that