I recently got into a debate with an idiot about what makes airplanes fly. He expounded his belief in the correct answer which was completely wrong and despite my constant attempts to disprove his idea and indicate the correct one, he would not believe me. It seems that there is a strongly believed and widespread misconception about what makes airplanes fly. So, without giving away the real answer, I come to /sci/ to ask the general populous here what they think causes airplanes to stay aloft. Who thinks what and why?
Whenever you board a plane there is a pure mathematician also on board, usually acting as just another traveler.
This pure mathematician has an IQ that is over 300 and has a creativity and logic abbility that is unmeasurable so this pure concentrated brilliance makes the plane fly.
Of course, the mathematician is too busy writing his proof as to control the plane, which is why we got pilots which are trained specifically to manipulate the power of the mathematician's mind so that they give the correct direction and speed desired for the flight.
These pure mathematicians that work in planes usually start with a salary of 300k.
I work as an airframe maintainer and everyone at work thinks it to do with differential pressure but im more convinced it has to do with newtons laws where the plane is oriented such that the angle deflects the fluid causing a net upward force
From what I understand, an airplane generates lift from the difference in air pressure between the top and bottom of the wing. The air needs to move faster and farther along the drop than on the bottom, so the wing air pressure above is less than the air pressure below. The result is that the wings effectively "skim" off the lower air while simultaneously being sucked up by the semi-vacuum above
I think the prevalence of the "incorrect" answer is because both are actually correct, but to different degrees.
The shape of the air foil DOES generate a small amount of lift and make the plane slightly more efficient, but the MAJORITY is from the "angle of attack" letting the plane skim off the air. That's why an airplane can fly upside down for example.
Saying that air pressure differences doesn't exist at all and have an impact is also untrue.
The pressure distribution on an airfoil causes lift. The air's momentum is altered, yes. But the mechanism by which air causes a force on the airfoil is pressure and shear. You can think of it either way.
The pressure difference is negligible and even debatable if it even exists. The common statement is that the air travels faster over the top than the bottom thus creating lower pressures. But real field testing shows the air under the bottom can actually travel faster.
In either case, the air being directed down probably contributes 99% of the force or more.
Because airfoils are better shaped to direct air downwards. Flat wings can't direct air downwards unless the plane is tilted up very slightly which isn't generally a stable orientation of the plane.
Newton's third law. As I've said in previous threads, there's actually an entire Wikipedia article on the subject.
In what universe does this make sense.....
It fucking is?
Jesus fucking christ, I couldn't tell you the math or physics behind it, but I can grasp the concept without it being introduced to me. Just like people speak their language with great levels of proficiency without knowing what all the cooky names for each 'part of speech' that some nerds in a basement cooked up to try and explain something.
POINT BEING, In what fucking universe do people perceive a sucking motion when the plane flies?
>I work as an airframe maintainer and everyone at work thinks it to do with differential pressure but im more convinced it has to do with newtons laws where the plane is oriented such that the angle deflects the fluid causing a net upward force
It's both. The shape and angle of the wing with relation to the airflow causes the airflow to redirect, which results in differential pressure on the wing as the equal and opposite reaction to the wing redirecting the airflow. Make sense?
>The air needs to move faster and farther along the top than on the bottom,
That's the myth (often taught in schools)..
Flying wings like the B2 actually have the curve on the bottom.
The real key is the angle of the wing. As long as the front is a little higher than the back air "piles up" under the wing, creating a high pressure area,
I'm a NEET but incredulously I believe that I know more about airfoils than most on this board simply because as part of my interest in RC aircraft I have spent a solid year studying nothing but airfoils and propeller thrust as opposed to say an undergrad who skimmed over it in a few lessons. Anyway lets not argue about that just listen to what I have to say; The short answer is that it's Newton's 2nd Law. I know this because I can calculate lift to over 80% accuracy using purely an application of that law. The long answer is that there is an additional component arising from the curvature of the airfoil cross-section. I know this because a wing will still generate some lift at zero angle of attack. However the Bernoulli explanation is bullshit, there is no maths to back it up, it's just an explanation that seems to make sense when you say it out loud. The additional lift is generated by the streamline curving. If you solve the Euler Equationsand by extension the Navier-Stokes Equations for curved flow you get the result
As you can see, increasing the radius of curvature, r increases the pressure differential, dP/dr. This can be seen in hurricanes, the eye is low pressure no? I have studied the Euler Equations it is true.
The final piece of evidence is that ducting a propeller not only increases it's thrust but causes it to be dynamically stable. The thrust increase can be explained away by the prevention of tip vortex losses but the stabilization can only be explained by the creation of low pressure over the lip of the duct which causes the underside to float on a ring of high pressure.
So to summarize, it's mostly just reaction thrust but there is some lift from a pressure differential.
Yes, that's called angle of attack, but it's certainly not the main cause of lifting force. If it were, then the roofs of houses wouldn't fly up during high winds.
Most houses have angled roofs, and even if the winds are passing perpendicular to the peak of the sloped roof, creating a force downward (as seen in pic related), they still go up.
This is because the pressure pushing up on the roof (~14 psi) from inside the house is far greater than the pressure above the roof, which is being mitigated due to the extreme airflow. The pressure differential creates a net force upward, and if the differential is great enough, the roof flies up.
It's readily available information, I didn't feel like a citation was necessary for something that I'm confident a 2 second google search would yield results for.
As a secondary citation, since you seem to be arguing against the very notion that roofs fly off in heavy windstorms, I urge you to literally just look at the picture of the aftermath of a tornado, or hurricane.
Anyway, even without houses being airtight, the differences in pressure are still enough so that the structural integrity of the roof must be compromised. That much you can't deny. And it doesn't imply anything about the velocity vector of the wind, simply that the velocity is great enough to create a pressure differential.
For fucks sake man, do you know how frustrating it is to see a mongoloid arguing with someone who is trying to tell you something that I explained clearly in a post in this thread is? Like I spewed out all that info and nobody read it, they just continued to spout bullshit. Read my fucking post here I'll link it to you >>7837464
there is the fucking equation right there that tells you curving a streamline causes a pressure differential. Seriously fuck this board, full of pseudointellectual dickheads.
But that's not a complete model for aerodynamics. A plane can maintain a horizontal flight, with a descent far lower than would be expected of something undergoing purely newtonian forces, being gravity and whatever vertical drag is being supplied by the wings.
A plane would have a far faster descent were its wings to be simple slats rather than shaped wings.
The force from a pressure differential is very observable and if it weren't, then generations of aerospace engineers wouldn't agree that shaping wings on efficiently designed aircraft was a priority.
I saw your post after I had already made mine, sorry about that, but I do know that frustration, friend.
You're probably far better qualified to actually be explaining this anyway, I haven't taken any kind of engineering/physics course for 2 years
>The air needs to move faster and farther along the drop than on the bottom
There's no reason for the air to move over the top in the same time it takes to move under the bottom, and in fact the air usually takes less time to move over the top. There is a speed difference, but it originates via friction with the trailing edge of the wing.
I used to go to /x/ for scientific discussion before I knew there was a /sci/ board
this place is significantly better, and sometimes I'll find a gem like you hiding in the sands of jargon-spouting gender studies students.
>I don't know why I browse this board it's so frustrating.
because you are a worm who cannot achieve anything in his life. go in bar, try to be noticed by a girl and eat her pussy. do not try to be something that you are not.
>/x/ for scientific discussion
Really? The few times I've been there it's been all demons.
>sometimes I'll find a gem like you
Aww thanks, that's the nicest thing anyone has ever said to me on 4chan.
>Going to a bar for sex
That's retarded, go to a brothel, it actually works out cheaper. Let's do the maths:
>Go to bar every night 7 days a week
>£10 entry fee + £10 taxi + £20 drinks
>£40 a day
>Get lucky say twice a week
>(40*7)/2 = £140 cost of sex
>Go to brothel
>£30 cost of sex
"scientific discussion" may be strong wording for what actually happened.
Basically I ended up being the person who would try to explain phenomena scientifically, and ended up being called a government shill 90% of the time.
I swear some of them think that the entire basis of our understanding of mathematics and science is a conspiracy carefully crafted by lizards.
As for being nice, I guess I'm just the only one not in a foul mood.
>I work as an airframe maintainer and everyone at work thinks it to do with differential pressure but im more convinced it has to do with newtons laws where the plane is oriented such that the angle deflects the fluid causing a net upward force
they are both right. lift coefficient scales linearly with angle of attack. but drag coefficient scales exponentially. thats why we do simulations and wind tunnel shit, because where the two meet is when your plane stalls.
its a combination of bernoulli principle and what op thinks (newton drag?)... depending on the plane design preferences and what the pilot is doing (i.e. landing, takeoff, maneuvering, etc.)
but the lowest drag/most efficient setup (i.e. cruising) would try and balance only the bernoulli force with gravity with minimal cross sectional area perpendicular to the direction of travel (drag).
in other words, op troll fail, or is a dumbass.
a simple google image search of wing design gives the correct answer.
For my part, when young, I thought it was angle of attack. In a later mechanics class I was told it was higher speed over the wing creating vacuum. Believed that for 20 years. Want to shoot that engineering lecturer now. A pox on them all.
Everywhere are thousands of little Master Yodas thinking theyre lifting the X-Wing but its actually just a plane
Over the years we have managed to train these Yodas into the flight paths we know and love today. Some Yodas have been specialised for military purposes and are a required fitting on modern jets.
>All these people claiming pressure differential is somehow an invalid explanation or is outright false
Just stop. Both are entirely true (with the exceptions of the equal times fallacy and that surface curvature is necessary for lift). A wing DOES produce lift by deflecting airflow in accordance with Newton's laws (see circulation theory/Prandtl lifting line theory), AAAAAAAAAND there exists a pressure differential between the top and bottom of the wing (see thin airfoil theory). Not only are both contributing to the phenomenon of lift, but in fact both are FUNDAMENTALLY RELATED, as the airflow cannot be redirected without some variation of pressure; nor can a difference of pressure exist in an open system without flow being accelerated/redirected.
BOTH EXPLANATIONS ARE VALID.
It's not a myth, per se, but it's incorrect to attribute lift directly TO the difference in air speed between the top and bottom. It's more accurate to say the difference in speed is a BYPRODUCT of lift. If you're producing lift by deflecting air, the top surface of the wing WILL have lower pressure than the bottom surface, and by Bernoulli's principle, the air on top will be traveling faster than the air on the bottom as a result.
It's not entirely wrong to think that. Air "pushes" on all surfaces of the wing, but since the wing is angled and/or cambered causing air to be deflected, the pressure on the bottom surface is greater than the pressure on the top surface.
because of the geometry of the wing while the craft is in flight air above the wing takes a longer path than air below.
this causes an increase in velocity, which constitutes a decrease in preassure.
the result is a preassure differential between the region below and above the wing.
this differential means the air on the bottom tends to expand upward catching the wing along with it, not unlike how a sail catches wind
because electrical engines don't exist.
you're also clearly not an engineer yourself otherwise you'd realise that modern combustion engines have a fuck tonne of electrical features that MEs would be completely unable to design.
>the air on top will be traveling faster than the air on the bottom as a result.
this alone does not explain the contribution to the lift though. how do you turn a different velocity into a force ?
>this alone does not explain the contribution to the lift though.
Well, not very explicitly, no. That's why I said it's more of a byproduct than anything else (though, through the principles of fluid mechanics, if you have the velocity flowfield you absolutely CAN still derive the pressure field and aerodynamic force from it).
Bernoulli's venturi effect combined with Newton's 3rd law. There's a reactive force combined with a generated low pressure environment on top of the foil. There's a trade off in lift per speed, in the sense that the tensile modulus of the wing surface can not handle the drag coefficient of high-lift/high-speed. Impellers and turbines work on the same principles.
Also turbulence in aircraft is usually due to atmosphere barometric change in air pressure around various lifting surfaces of the vehicle, combines with the change of relative speed in head-wind.
>the tensile modulus of the wing surface can not handle the drag coefficient
Materials fag here, can you explain more? It sounds like you are suggesting the mechanical properties of the composites used for wings are the limiting factor in aeroplane speed?
..don't forget the passenger belief factor. The very belief that the plane can and will fly causes the quantum waveform to collapse in a favourable way for the plane to stay in air.
the bernoulli vs defelection debate... lol
they are both correct, both will help you fly.
the airfoil is more efficient by far however.
for those who deny bernoulli please explain the Magnus effect
Bernoulli's venturi principle, and newton's second and third law.
In relative head wind, propagated by the thrust of the propulsion system, a faster flow is diverged over the wing. This creates lift, proportional to the pressure differential of the upper and lower wing surfaces.
The reason a plane is able to take off a treadmill is that the tires act like sleeveless bearing, and the prop engine is pulling the plane forward, generating that needed relative head wind.
If you had zero friction, you could bolt a house fan on a 1 ton block of granite and have it incrementally move forward. Than again, there's no such thing as zero friction, even in the vacuum of space, where it really is negligible.
The reason it isn't solely the angle of attack is that the wing is not designed to resist the forward thrust of propulsion. The propulsion system is there to lurch the aircraft forward with enough speed to create a pressure difference to create enough upward force to defeat the downward force of gravity.
>it's incorrect to attribute lift directly TO the difference in air speed between the top and bottom. It's more accurate to say the difference in speed is a BYPRODUCT of lift
Change the velocity of a fluid and the pressure will change (pic related). On the other hand, a pressure that differs from what you'd predict from the velocity field is carried away rapidly as sound waves.
Aerospace engineer here
Lift is the name given to all forces which push a body "up". Usually, in mechanics of flight, a body fixed coordinate system is used to enforce this condition. The geometry of aerofoils is designed to maximize this effect. You can easily derive the relevant results at a very preliminary and rough level yourself by learning complex potentials and the Joukowski transform coupled with control volume analysis. The pressure coefficient distribution across the surface of an aerofoil dictstes its life characteristics and the bottom line is that pressure below>pressure above which means net force upwards is produced.
However, other parts of a conventional aeroplane generate these forces as well and it typically takes CFD simulations to find the exact magnitude of these effects due to our inability to solve the Navier Stokes equations analytically.
Your friend is a crackpot.
Airfoils generate lift because they divert air downwards at an angle of about 10*. They change the direction of the air because of the angle of attack. If the air hits the airfoil at an angle then the airfoil will scoop through the air and because vacuums are impossible air has to fill the space behind the wing. The air tries to follow its surface and it does, although the pressure will be much lower on the top. If the angle is too great the air will not be able to follow the surface and will begin to tumble and spin which removes lift. We call that "stall".
TL;DR air moves down after the wing and that's what makes the wing go up. Newton's third law + Coanda effect + no vacuums are allowed
None of them specifically , as you couldn't lift 30 kilo plane with it. But I heard something about some kind of spins that happen on the upper side of the wing, which contribute to total lift. Also, aerodynamics is a bitch.
if one side was actually a higher pressure in this diagram, it would push whatever is in the bottom out.
This lower pressure shit is just an old meme, lift is generated by pushing air downwards
The datum used for an airfoil is kind of arbitrary (the chord line is usually used, but not always), and therefore "zero AoA" is equally arbitrary. Every airfoil DOES, however, have a zero-lift axis, which - if used as the datum - does obviously make that statement true.
Redirection of air can only occur if there's a pressure differential. You're wrong to assume they're mutually-exclusive.
Technically lift is the net component of aerodynamic force that is perpendicular to the (far-field) air velocity vector. It needn't be necessarily "up," it can also be centripetal or potentially in any direction perpendicular to the object's motion. Even drag can be "up" if the object is descending vertically, as with a parachute.
>if one side was actually a higher pressure in this diagram, it would push whatever is in the bottom out.
Except no, because gravity.
Does the layman really not understand how significant the angle of attack of a wing is? How would they explain how a propeller works? Or a helicopter. Shit I had this figured out at 13 making airplanes and helicopters with functioning swash plates in fucking gmod
>How would they explain how a propeller works? Or a helicopter.
The old equal-transit fallacy could still "explain" for those, since both still have airfoiled blades (and the layman wouldn't know that a helicopter rotor uses symmetrical profiles). The better question is, how do these people think paper airplanes work?
It's not a combination. Both the lift calculated from Bernoulli's principle and the lift you'd calculate by seeing how much air is deflected downward individually equal the entire lift on the plane. Angle of attack is not a separate thing from Bernoulli's principle, it is included. Changing the angle of attack changes the speed difference between above and below the wing.
>Angle of attack is not a separate thing from Bernoulli's principle
yes it is. bernoulli's is a oversimplified conservation of energy balance. angle of attack deals with conservation of momentum and impulse.
look up what a half reaction turbine is.
>bernoulli's is a oversimplified conservation of energy balance.
It neglects viscosity but is a good approximation in this case.
>angle of attack deals with conservation of momentum and impulse.
If you think a wing at zero angle of attack can generate lift without deflecting air downward, you're just fucking wrong, mate.
>It's not a combination. Both the lift calculated from Bernoulli's principle and the lift you'd calculate by seeing how much air is deflected downward individually equal the entire lift on the plane.
>It's not a combination.
>Both the lift calculated from Bernoulli's principle and the lift you'd calculate by seeing how much air is deflected downward individually equal the entire lift on the plane.
>Both... equal the entire lift
failing to comprehend the definition of combination...
== priceless ==
here's a goodie for you
>If you think a wing at zero angle of attack can generate lift without deflecting air downward, you're just fucking wrong, mate.
did you not read what i just said? i never claimed anything of the sort. the ratio of impulsive/reactive forces is a real thing in fluid mechanics. a good example of a device with an R of ~1 is a pelton wheel. the R value of airplane wings is dependant on the angle of attack, and while it can never be zero, it can be pretty close.
Let me clarify: If you think a wing at zero angle of attack can generate lift without imparting downward momentum to the air precisely equal to the lift on the plane, you are fucking wrong.
You are also wrong if you believe that the lift calculated from Bernoulli's principle does not depend on the angle of attack.
If you claim there is some important lift-generating mechanism in airplanes due to effects neglected in Bernoulli's principle, feel free to explain it, but "reaction forces" / "conservation of momentum" is not such a mechanism. Bernoulli neglects compression and viscosity, not the third law.
I agree with this f-a-m. This is my type of f-a-m.
He understand that one doesn't even need to know physics/chemistry to understand why stuff is the way it is and how it interacts. It's innate to us humans.
As an example, you don't need to know that matter is negatively charged because of the excessive amount of electrons, it's just purely logical to us that there has to be something that causes matter to be positively or negatively charged, an existing imbalance of matter, particles, electrons call it whatever... and the function of science is to unlock that innate understanding we all possess.
its because the speed of the plane is greater than the rate at which is falls back to the earth. imagine this - throwing a baseball really far and eventually its going to fall? but what if you throw it so hard that it never has to reach earth, based on the gradient of the ground. eventually, the curve of the earth and diagonal fall of the baseball will become parallel, keeping it in the air. it all has to do with a galileo and huygens discovery in the 18th century by the way.
yeah they are. static pressure and dynamic pressure are governed by different parameters. the shape of an air foil changes the static pressure of the fluid while its camber angle and angle of attack change the momentum.
fluids can be not moving and have a pressure differential. this pressure differential can push on the bottom of a wing and is completely independent of whether the air is deflected downards. its a change in the energy of the fluid, not a change in its momentum.
downwash is 3 dimensional, and has a component caused by that static pressure differential. the high pressure air is on the bottom and is trying to flow to the top, and because of vorticity is directed downwards. downwash is the sum of that plus the air that is directed downward off the trailing edge of the wing.
Not an aero dude, but I've heard that the Bernoulli explanation isn't accurate. Moreso it's just the angle of the wing causing downward deflection of air -> conservation of momentum keeps the plane up. This would explain why planes can fly upside down, since they can move the ailerons to redirect flow.
Aero is dope and I wish I knew more. I'm a MechE though
You're describing perfectly the principle of content vacuum pressure troll thread lift. Bullshit is lighter than meat. This difference drives lighter copypasta and troll threads up the board, while driving denser discussion threads down to page 10.
*assuming incompressible flow
air does indeed end up traveling faster under the wing than above it, resulting in a decrease in dynamic pressure and an increase in static pressure, providing lift, according to bernouilles equation or however you spell that.
Angle of attack plays a major role, which is why symmetric airfoils are possible, but even then it's mainly pressure differentials caused by a changing camber line. I don't know who put the idea in your head that pressure is not part of flight, but they were wrong.
Of course, in incompressible flow all bets are off, I think lift at that point is mainly generated by shockwaves.
No, we don't. At distances away from an aerofoil, we use isentropic flow equations. Near an aerofoil, you have to go balls deep and use Navier Stokes to find the flow field, but if you just want to calculate, say, lift, you can calculte it to a very high degree of accuracy using Prandtl-Meyer shock expansion theory.
v<<c assumption is usually made to assume incompressible flows. This will be extremely off, considering the effects of compressibility usually start being considered in aerodynamics at around 0.3 Mach number. A typical passenger jet cruises at M=0.85.
Typically, at these mach numbers, shockwaves can form on aerofoils which makes even Bernoulli and all the related isentropic equations etc derived from it useless due to the existence of non isentropic nature of shockwaves. These flows basically necessitate CFD or Prandtl-Meyer Shock Expansion theory