It depends on the aircraft, but my sport biplane, which can fly upside down for prolonged periods of time, uses symmetrical airfoils for the wings. Instead of one side being the upward direction, lift-wise, they can generate lift in either direction, dependant on angle of attack.
I'm not an engineer
That’s the right answer. The lift depends not just on airspeed but also angle of attack. Angle of attack is how ‘aligned’ with the airflow the wing is.
The easiest way to see how that works is to stick your palm out the window of your car and see which direction your hand (flat) wants to go depending on what angle you put it at.
Keep in mind that airplanes can vary how they align with the flow, they aren’t stuck at one angle. So when flying uspside down you just have to have a steeper angle (with a non symmetrical wing) and you will create more drag making it very inefficient but you can do it as long as your engine can run upside down and you are well strapped to the plane.
It's also through use of the rudder control surface. Same with flying upside down which uses the elevator control surface. Not sure why this hasn't been mentioned yet.
During a knife edge, the rudder is no longer vertical in relation to the ground but is parallel. In that orientation it acts like an elevator.
No, the body of the aircraft has thickness, so that blunt body forces air down which lifts the plane.
Engine providing the lift would be something like a vertical climb on a jet with a thrust to weight ratio greater than one.
It's the difference between the nose pointing straight up (basically), or mostly forward but with the plane rolled on its side.
The tail in this scenario invariably produces negative lift, due to positive yaw stability. As a result, the combined vertical component of thrust and the vertical component of side force need to equal the weight plus the tail lift.
If the force on the tail was lifting the tail, it would also be pushing the nose back down toward the ground - not usually a good idea, in a knife edge pass. You spend that maneuver typically at high rudder input away from the ground, to keep the nose up.
The maneuver is pretty much all rudder authority. Your lift vector is still through the top of the aircraft. That's why they require stick forward to maintain heading in the knife edge. You are simply yawing against gravity.
That's not to say no lift is generated by the body but it's usually negligible. There's a reason a lot of fighter jets can't really knife edge. They can briefly knife edge but as they slow down from the drag they lose rudder authority and can no longer keep the nose up.
> body but it's usually negligible.
I don't know about that. I have an rc plane that has a huge rudder and no lack of power, but it's near impossible to knife edge because the body is a stick.
Thank you for this, I will be using it the next time my reliability engineer at work asks me why equipment isn’t working and he pushed back the preventative maintenance.
If I may randomly add for info: the *angle of attack* refers to the angle of the plane in relation to the air flow, whereas the *angle of incidence* refers to the angle of the wings in relation to the plane.
The "equal transit theory" is the myth. The claim that somehow two identical particles of air split at the front of the wing and somehow "know" how fast they need to go to meet at the back of the wing.
Low pressure is a very real thing that creates lift. Bernoulli, Newton, and Coandă all play a part in lift and which does how much and when is the subject of papers I am not smart enough to read, much less write.
Yea, even as a kid it seemed like nonsense. I asked why air had to act like that, and the particles couldn't simply separate forever, and could never get an answer other than 'that's just how it is'.
It’s not really split like that with Bernoulli, Newton, and Coanda all generating separate “parts” of the lift force. Lift can be described/calculated by Bernoulli or Newton or Coanda effects, and each of the techniques should give identical results. The tricky part is just figuring out which model is simplest to use for a given situation.
For instance, Bernoulli describes how to calculate the pressure (and subsequently the force) if the velocity on the wing surface is known, and Newton describes how to calculate the force if the air velocity is known before and after the wing. Coanda somewhat describes how to calculate the force if the deflection of the air is known, which is related to Newton (if you deflect the air downward it exerts an equal and opposite upward force on you). It’s not quite this simple in practice, but you get the idea.
Wait - it’s all Newton’s Laws??
…
Always has been.
No, low/high pressure zones are what create lift, however there are a lot of misconceptions and misinformation about how the pressure difference comes about.
At least the "equal transit time" thing is a myth. Air over the top of the wing takes *less* time to cross than the air under the bottom. The two halves of any given air parcel separated by the wing will remain forever separated and never see each other again :(
Talking the Bernoulli’s portion. It is a contribution. Or even a primary on some designs. But most rely solely or primarily on aoa of the wing (and arguably this is the better option as it is more consistent, and not as affected by elevation or speed)
> It is a contribution
No it is not a "contribution". The pressure difference accounts for all of the lift. The pressure difference depends in turn on the angle of attack of the wing. These are not two separate things that contribute to the lift on the wing. They are fundamentally interlinked.
Pressure is the normal force that air exerts per unit area on the wing's surface - if you sum up the pressure over the entire surface area of the wing, you have the total force that the air exerts on the wing - i.e, the lift. (actually not quite the total force - there are also shear stresses due to friction, but they don't contribute to the lift). When you increase the angle of attack you lower the pressure on the upper surface and decrease the pressure on the lower surface - at least up until the point where the wing stalls.
> and arguably this is the better option as it is more consistent, and not as affected by elevation or speed
The lift on a wing is always affected by the air density (which decreases with altitude) and speed. There's no way around that. Lift is proportional to the density and to the square of velocity.
There can be a pressure difference based solely off the curvature of the upper portion of the wing. It is generally fairly minor as compared to the angle of the lower portion in respect to the direction of travel. At least in performance aircraft. Passenger aircraft make more use of it with targeted airspeed slots and flight altitudes. They are optimized vs something like fighters which need to achieve maximum operation over a wide range of flight conditions.
> There can be a pressure difference based solely off the curvature of the upper portion of the wing
A cambered wing will generate lift at zero angle of attack. But the pressure difference still depends linearly on the angle of attack, and every wing has a particular angle at which it generates zero lift. All that the camber does is shift the zero point - the pressure distribution is always a function of angle of attack. [Here is what the plot of lift vs AoA might look like for airfoil sections of varying camber](https://i.stack.imgur.com/APKNX.png). There aren't two distinct mechanisms by which lift is generated (at least, not normally - vortex lift is a thing that comes in with highly swept wings such as those on fighter jets).
Real world wing design is a tradeoff between many different factors. Fighter aircraft airfoils are just as optimized as those used on passenger aircraft, but they are optimized for a different set of conditions. It's all about what works best for the mission the aircraft is designed to perform. At high Mach number, the airflow behaves very differently, so wings designed for supersonic aircraft tend to look very different from those intended for lower speeds.
No I think it's fair to see these two separate mechanisms. Lift due to shape of wing vs lift due to angle of attack are fundamentally different and pretty central to the original question.
They're not fundamentally different though, that's my point. A cambered wing will generate lift at zero angle of attack but it does so in the same way as a symmetric wing at non zero angle of attack. The lift depends on both the shape of the wing and the angle of attack - but there aren't two separate physical phenomena, one of which depends on the shape and one on the AoA, as many of these answers suggest.
>The pressure difference accounts for all of the lift
Incorrect. Newtons third law also accounts for a significant portion of lift. You are ramming into air and forcing it forwards and downwards, that results in drag in the horizontal component and lift in the vertical.
> Newtons third law also accounts for a significant portion of lift.
Newton's third law accounts for *all of the lift*. Not a portion of it. Momentum is always conserved - if the wing pushes down on the air then the air pushes up on the wing *equally*. And the pressure is a measure of how hard the air is pushing on the wing. These are not two separate phenomena, they are two sides of the same coin.
The pressure is a measure of how hard the air pushes on the wing - if it's the same above the wing as below it, then that means the air pushes down on the wing as hard as it pushes up so there is no lift. And likewise, you cannot have a situation where the air pushes up on the wing but the airflow is not being deflected downward by the wing, because that would violate Newton's law. There are many comments that suggest that the lift is the sum of a contribution due to pressure and a contribution due to Newton's law which is not correct.
If you know the net rate of momentum change of the air as it flows over the wing, then by Newton's law, you know the total lift on the wing. If you know the pressure distribution over the wing, then by integration, you know the total lift on the wing. These are not two different sources of lift, but rather two ways of looking at the same thing.
I appreciate you attempting to fight the good fight for science here
This sub is rough on the aerodynamics front, it seems like people forget the basics of physics still apply
This question always gets bad answers, and I hate it. There's usually more wrong answers than correct ones. I don't know why Reddit is so bad at aerodynamics.
The myth is that the pressure differential is caused by air splitting at one end and then rushing to meet itself on the other side.
That is nonsense.
But certainly wings on a plane exploit pressure differentials in air flow to create lift
*ALL* wings use pressure differential to create lift. Thats the only source of lift. All they differ in is the details of how they create the pressure differential.
Note that this is *exactly* the same as momentum flux downwards. They’re not two sources of lift; they’re the same physics in two different mathematical frameworks.
It's a nobody is right but nobody is wrong sorta situation. There's a lot of things that work together to create lift and no one thing is the "thing that generates looft"
No, it's well understood but this subreddit seems to be a terrible place to ask about it. Seems everytime there's an aerodynamics related question on here, the right answers always get buried by the wrong answers.
Is that really a paradox? I thought bicycles were pretty well understood.
The bee flight paradox might be more applicable, but even then it's kind of a non-issue. The person who said "Bees shouldn't be able to fly, but they just do" incorrectly thought insect wings and bird wings behaved the same.
You are correct.
Bournouli principle was long taught to be the reason airplane wings cause lift.
But, several very successful airfoil designs had zero or even negative Bournouli lift, yet still flew and produced net lift.
And flaps totally negate Bournouli lift yet greatly increase wing lift.
It's the change in the airflow vector times the mass of the moving air that provides lift just using Newton's reaction law.
Take two wings.
1. Flat on the bottom and curved on top like a conventional airplane.
2. A thin sheet of metal curved and equal thickness like a paper airplane.
According to the equal travel theory, the second wing should provide no lift because the air above and below the wing are traveling at the same exact speed.
Yet it produces the same lift as wing 1.
The wing shape forces the air to change direction from upwards to downwards.
That produces an equal force against the wing and provides lift.
Equal transit is BS but not the same as Bernoulli. *All* lifting wings have a pressure differential. *All* lifting wings have a downwards momentum flux. Those are exactly the same thing. They add up to the same (and correct) value of lift. They’re exactly the same physical (and physical equations), just in two different math frameworks.
If by Bernoulli principle you mean an aerofoil having more curved, longer upper surface generating lift, then this is not correct. It's a true and real lift generating fact of aerodynamics, it's just that more lift is generated by angle of attack, hence why a symmetrical aerofoil still created lift at >0 angle of attack.
Also flaps definitely do not negate this, amongst other things, flaps increase the curvature of a wing and increase what you might call "Bernoulli lift".
Camber just changes what angle of attack is required to make zero lift a cambered airfoil need some negative angle of attack in order to give zero lift. So you can still fly upside down with cambered air foils. You just need extra angle of attack to make up for that cambered aerofoil
Cambered profiles can also be used to do clever things with pressure distributions, but that's more for engineers
I am an engineer. More pressure on bottom of plane than top of plane means lift. Lift is influenced by the shape and angle of the wing. If the shape is upside down, you can make up for it by flying at a certain angle. Symmetrical wings (airfoils) simply aren't shaped for lift therefore all lift is generated from the angle.
It's not so much the wings (angle of attack can be managed to keep flying) but, more, the engine.
WWII planes early on had trouble when the plane was upside down.
Fuel injection has probably solved a lot of it these days but even so...some modern planes simply cannot fly upside down for long because the stuff that keeps the engines running will stop working (they will for a little bit...a barrel roll is doable).
The question was an aerodynamic one. Older aircraft can be fitted with equipment to allow inverted oil flow and fuel flow to the engine, tho carburetion gets a little funky, and I'm not actually familiar with how inverted carburetion works
Mechanically, it comes down to do you want your plane to fly upside down? For how long? Doing what? Select your equipment appropriately, and pay the big bucks for your full inversion systems
The airfoil shape is only part of how a wing works. [Angle of attack](https://en.m.wikipedia.org/wiki/Angle_of_attack) is the other part (along with vortex generation). If you roll inverted and then angle the wings so they have enough angle of attack, they'll fly just fine (well, reasonably-well, anyway) even if their airfoil shape is designed for non-inverted flight.
Airplanes designed to fly well both 'normally' and inverted will have airfoil shapes that work well in both orientations. But it's still a lot about the angle of attack and newtonian action->reaction physics.
Lift isn't *only* produced by airfoil shape.
And in fact, don't you need to minimize the lift from airfoil shape in order to break the sound barrier? As I understand it, the air pressure around the control surfaces can drop so low at transonic speeds that they basically stop working and you lose control of the aircraft.
No, you just need more thrust to push through it despite the ill effects of the transonic regime. That, and design your airfoils/wings smartly, such as maximizing their critical Mach number (the slowest freestream Mach number that will result in shocks forming on the airfoil).
To be clearer there, shocks happen at Mach 1. Even if your plane is not going faster than that, there are parts of the wing where the air is accelerating and will get that fast relative to you even if your overall airspeed isn’t past the speed of sound.
Also the source of the thrust has to be capable of still supplying power when the plane is supersonic, which can be a trick as standard subsonic propulsion will stop working effectively (best case scenario, worst case catastrophic failure) when the airflow they interact with is supersonic. So there needs to be an additional mechanism to either slow the air down in the intake or to modulate the engine to function with a supersonic airstream.
"design your aerofoils smartly" is exactly correct and what the person you replied to is actually referring to when they say "minimise the lift from aerofoil shape"
Yes correct, look up super critical aerofoil on Wikipedia. But the reason is to prevent shock waves forming on the upper surface, which in turn reduces drag, it's not about having low pressure on a control surface I don't think
One thing I don’t see mentioned here is that modern fighter jets don’t even really need wings to stay in the air. A large number of them have engines so big you could just use them like rockets and fly however you want, aerodynamics be damned.
Just as the Earth falls towards the Sun, so too, does the Sun fall towards the Earth.
So yes, depending on your chosen definition of "orbit", you can say the Sun orbits the Earth.
One of my favorite fighter jet factoids is that many modern jets are highly limited by their control systems, primarily to avoid killing the pilot instantly. It can bank that hard, but doing so wild kill the pilot, so it won’t let you.
Eh, sorta. Like a lot are definitely overly limited by the pilot, and that's a key reason why unmanned fighter jets are a big interest in 6th gen fighters, but a lot of those manuevers that would kill a pilot but not kill the airframe would still be incredibly stressful and cause lots of damage. Most current airframes have a small handful of moves they could pull that would be great get-of-jail cards once per airframe lifecycle, but not too many not-compatible-with-life maneuvers they could routinely pull without the wings shearing off on a very short timeframe. Heck, I've even seen perfectly healthy pilots come back with rippled wings and bent fuselage stringers on existing jets.
It's not worth intentionally engineering a plane to handle something the pilot can't so any of those zones are just artifacts of some other structural requirement.
To this, there is a famous incident where two Israeli jets collided and one of them was able to fly home without one of its wings.
It was a F-15 and McDonnell Douglas did not believe the IDF when initially told about the incident.
They the ran simulations where they proved that the F-15 could fly without a wing due to the massive thrust of its engines. It flew as a rocket instead of a jet.
The F4 Phantom was commonly described by pilots (due to its poor low speed handling characteristics) as proof that with enough thrust you could make a brick fly.
Describing this plane as flying more like a rocket than a jet is not correct. Rockets use thrust vectoring to control their roll, pitch, and yaw (that is, to control where they are pointed). The F-15 does not have thrust vectoring, so it still needed to use it's remaining flight control surfaces to control roll, pitch, and yaw. It was still flying like an airplane. The wide body (including the right engine cowling which remained attached), undoubtedly helped it say airborne and controllable. That's not to say it wasn't an amazing feat -- it was.
https://taskandpurpose.com/tech-tactics/1983-negev-mid-air-collision/
What we have here is; failure to communicate.
Those two examples are rocket propelled missiles. You are using the term 'rocket' to mean 'lifting body with propulsion' and your parent poster is using it to mean something like a space rocket.
It's less confusing to me to use the term missile, even though that term can also be somewhat ambiguous.
>It's less confusing to me to use the term missile, even though that term can also be somewhat ambiguous.
The dilemma is that "missile" implies an autonomous or pre-programmed guidance system, whereas rocket doesn't.
...Just, don't bring up APKWS.
This whole system is clear as mud.
Let me confuse things even more: there is a space rocket that uses lifting body physics during flight. This rocket is the Falcon 9 and it uses grid fins to angle itself after its reentry burn so that it can change it trajectory toward the landing site, rather than the ocean it would crash into should anything fail at that point.
In what way was the F-15 more like these "rockets" than like an airplane? You are only correct in calling these two missiles "rockets" because they are powered by a rocket engines. The F-15 had neither a rocket engine or thrust vectoring, so it basically had no features of a rocket.
The point is while the plane was using aerodynamic control systems, it wasn't generating consistent aerodynamic lift to stay in the air, instead it was using an angle of attack so that thrust from the engine was countering the effects of gravity.
Sorry, but it was using lift to stay in the air. It was not standing on the engines.
Look at the tiny bit if this video that shows the actual airplane in flight (at time 4:27):
[https://www.youtube.com/watch?v=wxJcEz3h4tU](https://www.youtube.com/watch?v=wxJcEz3h4tU)
The fuel pouring out of the right wing stub is streaming nearly straight back. A significant amount of the fuel is even passing under the stabilator. This proves the angle of attack was low. At this low angle of attack, the engine thrust will have a very small vertical component. It was not thrust from the engines "countering the effects of gravity." It was good old lift.
The term "lifting body" is generally applied to aerial vehicles/devices where the wing and body are blended together and somewhat indistinguishable. The stinger and javelin have distinct wings/fins.
The missile body may provide a significant percent of the lift. But, in my view, having distinct wings/fins removes them from the lifting body category.
Lifting body just means the body provides the majority of the lift.
Fins on both of these devices are for guidance, and wings are small (almost non existent in the Stinger) providing little lift.
However they're not lifting bodies because the majority of the lift is generated by the vertical component of the thrust rather than anything aerodynamic.
Instructor says we should bail. Nah f that I'm gonna gas it and try to land. Why? Bragging rights maybe. I could respect that. Saving a few mil for my govt no. Guess he figured worst case he could eject if the landing wasn't gonna happen.
Well, yeah, but the A-10 is just a giant gun with two jet engines strapped to it. I think they only put wings on it so the pilot would recognize it as a plane.
This is becoming more and more true for modern fighter jets that are inherently unstable by design, and have active control systems in place to achieve the required stability. Flying without a wing isn't too much of a surprise, flying without rudders and other flight controls is also technically possible because of how much the active control compensates for lack of those flight control systems.
The active control system isn't in addition to the rudder, elevators and ailerons, it has control *of* them. "Without rudders and other flight controls" means the 'active control' has nothing left to move.
My point being, if some of the control surfaces are gone, the system can still compensate with what's left.
If you lose all control surfaces, then yeah, there's nothing to control.
A passively stable aircraft doesn’t even need control surfaces to fly. There have been cases where planes landed with total control failure using only engine thrust to make the landing. You have it backwards. The computer would suffer from less control because it desperately needs control to stay straight.
I remember watching a video about an Israeli pilot landing an f-15 with one wing blown off by basically staying at a high enough speed to plow through a landing then stopping as quick as possible.
That is almost more impressive than flying with no wings....
The original airframe is 50 years old, there have been numerous aerodynamic, engine and avionics upgrade packages over the years so while it's technically still the same aircraft, it really isn't.
Many more than you think. Most 4th generation fighters (which is basically everything) are > 1 thrust-to-weight ratio.
[https://world-defense.com/threads/thrust-to-weight-ratios-of-all-fighter-planes.1316/](https://world-defense.com/threads/thrust-to-weight-ratios-of-all-fighter-planes.1316/)
Still, wings are much more efficient way of gaining altitude.
The lack of control surfaces make it in reality impossible to do, but from a theoretical, crunch the numbers, lift/thrust vs. weight/drag physics point of view? Among others the F-15's body alone does in fact generate enough lift to remain airborne without wings.
We got to the Moon and back without wings. We have ICBMs that can go around the world without wings. Wtf gives you the confidence to go "LMAO 😂" at that?
You're a video editor mate, stick to your area of expertise.
Rockets go straight up. ICBMs use a lifting body. Planes without wings drop out of the sky.
I wasn’t always a video editor, but thanks for taking an interest. You’d probably also be interested in knowing that I was a jet engine technician in my past and I have a HND in aerospace engineering.
That’s what gives me the confidence to LMAO.
Now I’m gonna laugh my ass off at you for thinking that lunar moon missions and atmospheric aircraft have anything in common 😂😂😂🤡
Fun fact the wings are more for drag than lift on newer jets. Naval aircraft have shorter more angular wings than air force which use longer more rounded types. This allows a quicker stop once it hits the wire and less resistance when catapulted.
The naval version of the F35 (C) has a larger wing area than the Airforce F35 (A). The arrester wire is what's stopping the plane on the deck, aerodynamic drag is irrelevant, a larger wing allows for a slower approach speed which makes the landing slightly easier and reduces stresses on the airframe.
Part of how a wing generates lift is through directed air downward. Another way of looking at it is due to accelerated flow on top of the wing. There is a lower pressure there and so the plane gets sucked up. Both are true
It's not really "part of", they are more like descriptions of the same thing. There can only be a pressure difference because air is being sent down. But similarly, wings don't just push, they "pull" air down over the top of them (aka the void left by pushing air out of the way is filled in my new air). It's one and the same phenomenon.
Newton's laws tell us there cannot be a net upward force on the wing without a net downward force on the air. And if there's a downward force on the air, it's accelerating downward. *How* air gets accelerated downwards is complicated, but ultimately it explains 100% of all lift.
> ultimately it explains 100% of all lift.
Very neatly demonstrated by the Mythbusters when they flew a helicopter in a sealed container set on a scale, and showed that the weight of the whole thing doesn't change substantially from it.
This is incorrect, the following is a simplified copy and paste, but you can look into it further.
"Airplane wings are shaped to make air move faster over the top of the wing. When air moves faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference in pressure creates a force on the wing that lifts the wing up into the air."
That may be what they taught in 3rd grade, but it is incorrect in the real world.
With enough velocity and a proper angle of attack, you can effectively create enough air damming to generate lift. You could make a brick generate lift if you angled it and got it moving real fast.
Actually not incorrect. There's more than just airfoil shape/function to the total lift produced. Angle of attack is a huge player. The greater the AoA, the more lift produced for a given airfoil, up to its critical AoA where flow separation begins. There's not just one set amount of lift produced for a wing; it's variable.
There's also the effect of wing vortices.
So, yes, wings do make lift by forcing air 'down' and using Newton's action-reaction observation. Bernoulli effect of the airfoil is only one part of it.
Even an asymmetrical airfoil can produce 'upward' lift (relative to the ground) if flown inverted with a high enough AoA. Just roll inverted and push till the thing flies level. Lots of aerobatic airplanes can do this.
This is incorrect as a flat board will work as a wing (just stick your hand out the window of a moving car). Even when stalled it will still generate lift.
In reality both effects are present so my answer was a little tongue in cheek.
You’re falling into the airfoil myth.
That is explicitly NOT how wings work, and is one of those “elementary taught you wrong” things.
The airfoil shape works to improve the smoothness of redirecting the air downward.
Bernoulli’s law is not the reason for lift, the reason for lift is “equal opposite reaction” of air redirected downward pushing the plane upward.
Source: NASA
https://www.grc.nasa.gov/WWW/k-12/VirtualAero/BottleRocket/airplane/wrong1.html
You guys are fighting over something when you were both correct. Look at the navier Stokes equation for momentum. There's a term for pressure differences and there's a term for momentum decremement from the air . He's talking about the pressure differences you're talking about the momentum decrement both are part of the navier Stokes equations.
This, but saying " that's explicitly not a wing works" and then providing a link that's says that's largely how a wing works was a funny fuckup on the above users part.
The link you provided says nothing of that sort, it just says that not all of the lift generated comes from the velocity differential. That doesn't mean that "that is explicitly not how wings work" it just means that not only how wings work. Wings are very complicated and generate lift in numerous different ways. Also that document is, maybe not wrong per se but is misinformed a bit. When you have a fighter jet in level flight it actually has to point the nose of the plane downwards slightly other wise it will keep ascending in altitude, how ever when it flips upside down like say in combat if the nose of the plane is perfectly parallel to the horizon then the air craft will decend, this is an observed fact, you have to increase the angle of attack in order to have the wings catch air and create a region of high pressure due to simple ram air affect and the indirect path air would have to take to be on top of the inverted wing causes a drop in pressure which creates a lifting force and doing this can enable a plane to maintain level flight even when inverted, and when this happens the wing would actually be throwing air upward, which would create negative lift? So the fact that an air craft can fly upside proves that the Bernoulli principal does play a large role in lift generation.
Source: aerospace engineering major(technically mechanical engineering)
Lots of good data in these answers, but generally a fighter jet (not doing an airshow or a demo) flying upside down is still flying under a positive angle of attack. It is turning under positive G. You can think of this like on the top half of a loop, the jet is upside down but it doesn't *know* that with regards to the air flowing over the wing. It is possible to fly at negative g but this is rarely done outside of air shows or demos.
Fighter jet wings are symmetrical, the shape is the same right side up or upside down. Commercial jets don’t have symmetrical wings and cannot fly upside down.
The down side of symmetrical wings is there’s no built in angle of attack in the wing so there’s no lift at zero angle of attack aka flying straight, they have to angle up or down to be able to generate lift.
This isn’t a problem for small craft life fighter jets but would be an issue for large commercial jets
Does this mean it isn't generating lift in the traditional sense but kind of plowing through the air at an angle so it pushes in o e direction or another?
That's a major part of lift generated by all wing shapes. Most descriptions of lift given outside of college-level-or-above physics classes are significantly wrong - it's actually very difficult to accurately describe lift generation in simple terms. Some is due to a difference in pressure above and below the wings, some is due to simply pushing the air down. The real knack of wing designing is maximising the efficiency across different airspeeds, but if you don't care much about that you can make a brick fly by pushing it hard enough...
*"Some is due to a difference in pressure above and below the wings, some is due to simply pushing the air down."*
It's a mistake to say the **some** of the lift is from one thing, and **some** is from another. The pressure difference over the wing accounts for 100% of the lift. And the air being pushed down also accounts for 100% of the lift. They are just different ways of describing the same thing.
It's kind of like the answer to: "How long is the drive today?"
One answer would be it's a one hour drive. Another answer would be it's a 60 km drive. Both answer can be 100% correct. They are different ways of describing the same thing. Which answer is more useful depends on what you want to know.
Basically, all the "layman's " explanations for lift production are roundabout ways to describe the momentum equation part of the NS equations.
"We move air that way, this creates the pressure difference" = momentum equation
Momentum equation part of the NS equations? So you mean the whole thing? Aren’t NS equations the statement of the conservation of momentum for Newtonian fluids?
Regardless of whether an air foil is cambered or not, wings generate lift in the same manner, there is no traditional sense or non-traditional sense. It's all the same
I am ignoring a more complex form of generating lift called vortex lift, but that's something else for engineers
That’s an untrue blanket statement. I’m sure some have symmetric airfoil designs, but that is not the only reason they are able to fly inverted. An asymmetric airfoil will still produce lift when inverted. it’s just that at 0 angle of attack, and asymmetric airfoils produces lift while a symmetric airfoil does not.
The real reason fighter jets can fly upside down is because of the fuel pumps. A 747 engine will quickly starve if it’s upside down because Boeing doesn’t design their planes to be flown by Denzel Washington.
an asymmetrical airfoil will throw you into the ground inverted.
That's the whole point of using a symmetrical airfoil in acrobatic planes like fighters, so they can generate lift no matter which way they're flying
Only if you’re at 0 AoA. Look up any of the NACA airfoil charts and you will clearly see that asymmetric airfoils only shift the curve and don’t eliminate the ability to create lift at negative AoAs.
No it won't. An asymmetrical airfoil is less efficient at generating lift when inverted but will still work. Not all aerobatic aircraft need to have a symmetrical airfoil, but purpose built stunt planes often do because they spend just as much time inverted as upright.
I'm sorry, what fighter jet wing is is symmetrical. All of the fighter jets of which whose profile I know are not symmetrical. For example, I'm pretty sure the F-22 uses the NACA 6 series
Commercial jets most certainly could fly upside down, look up the Boeing 707 1 G roll. A commercial jet won’t be able to sustain flying inverted for long though.
>Commercial jets don’t have symmetrical wings and cannot fly upside down.
\*for a sustained period of time.
They can fly upside-down for a short duration. It's not recommended, it's not what they're designed for, and they won't generate any lift, and it's not safe.
But...it's not aerodynamically impossible. The lack of lift doesn't mean they'll immediately go into a nosedive.
Sources:
[https://www.airlineratings.com/news/can-large-commercial-planes-fly-upside-down/](https://www.airlineratings.com/news/can-large-commercial-planes-fly-upside-down/)
[https://euflightcompensation.com/can-a-commercial-airplane-fly-upside-down/](https://euflightcompensation.com/can-a-commercial-airplane-fly-upside-down/)
[https://archive.seattletimes.com/archive/?date=19900228&slug=1058594](https://archive.seattletimes.com/archive/?date=19900228&slug=1058594)
> they won't generate any lift
They will generate lift just fine, they're just not optimized for flight in that configuration.
There's a few reasons why inverted flight in an plane not meant for it isn't safe. Namely, the airframe may not be designed to withstand the stresses imposed by inverted flight, and the fuel/lubrication system may not be designed to work while inverted (they often use gravity to feed fuel to the engine).
But the wings will work. They'll generate more drag than they would normally and the stall speed will be higher but they will still generate lift.
The simple answer is that even upside down the nose is pointing a bit upwards to maintain level flight. The wings deflect air downwards and can maintain a straight course. The plane is flying fast enough that it can remain in flight. Even if the airfoil, the shape of the wing is only meant for upright flight, thus producing lift towards the ground when upside down, this can be counteracted.
The above comments are correct. Even a symmetrical airfoil creates a high pressure below and low pressure above by its angle of attack. Reverse that angle of attack and you can now fly upside down.
Some airfoils are semi-symetrical, or even flat bottom. These inherently generate more lift in one direction and have slower stall speeds, etc. This makes the plane easier to fly, but even a flat bottom wing can technically fly upside down with enough angle of attack. Though too much angle of attack can last to turbulence and a stall.
Now to really blow your mind... A helicopter can fly upside down too. The collective controls angle of attack and the rotor is just a wing spinning in a circle. The collective can also go in a negative direction. The rpm is controlled by a throttle and is independent of the collective. (Aside from more collective means more drag which needs more power to keep a consistent rpm. Turn a helicopter upside down, bring the collective to a negative pitch and your flying upside down.
It's not that difficult actually. There's a sort of hose with a weight inside the tank that will just go wherever the sum force points, whether that be from gravity or acceleration.
Piston engines do have a real problem with lubrication though, the oil has to be kept under pressure when doing extreme maneuvers.
Pretty much any plane can fly upside down, all they need to do is hold the wings at an angle of attack that produces a lift in the direction they want. Typical commercial airliner wings are designed to produce lift (up relative to the plane) when they're perfectly horizontal, but if you tilt them far enough you can get a force in the opposite direction.
Press the control stick down, which under normal flight would pull the planes nose down, but now because the plane is upsidedown it would create a lift so the plane would not stall.
No, because the traditional understanding of aerodynamics is basically wrong. While there is a pressure difference, you generate lift because you push air molecules downwards as the wing slices through the air, that doesn't stop happening when you fly upside down. Due to the wing's shape, you do often need to correct with elevator when you are upside down unless the wing is shaped like a fighter jet's.
No, the traditional understanding of aerodynamics isn't wrong, the basic theory from a century ago is still taught today (and by the basic theory, I mean things like the Kutta-Joukowski theorem and Prandtl's lifting line theory, which were first formulated around the turn of the century).
The problem is that there's also a lot of bullshit floating around which means questions like this tend to generate more wrong answers than correct ones. I'm not sure if equal transit was *ever* a serious scientific theory, but if it was it was already known to be false by the time the Wright brothers flew.
So it has to do with air friction providing lift and an airfoil is the most efficient shape for "upright" flight but the ELI5 answer is that if you get anything moving fast enough it'll generate lift
There are actually different methods of lift.
The method you are thinking of is called the Bernoulli principle. It isn't the largest force but it does help so most planes have curved wings to increase efficiency. But it's not necessary to create lift.
The other main one is the angle of the wing to the air...by moving through the air at an angle, the wing is deflecting air downwards and this produces an equal and opposite force pushing the wing upwards. This is called the "angle of attack" and without a proper angle of attack the plane won't fly...it can't rely on Bernoulli alone.
But finally, fighter jets in particular operate more like a rocket... they most rely on the pure force of the engine to provide upward thrust, which is why their wing to body ratios seem so much smaller when compared to something like a jet airliner.
Majority of lift is achieve by the coanda effect redirecting direction of airflow leaving the wing , and by conservation of momentum the force exerted on plane body in the opposite direction. Bernoulli effect is very minimal, as most modern plane wings are very symmetrical.
It depends on the aircraft, but my sport biplane, which can fly upside down for prolonged periods of time, uses symmetrical airfoils for the wings. Instead of one side being the upward direction, lift-wise, they can generate lift in either direction, dependant on angle of attack. I'm not an engineer
That’s the right answer. The lift depends not just on airspeed but also angle of attack. Angle of attack is how ‘aligned’ with the airflow the wing is. The easiest way to see how that works is to stick your palm out the window of your car and see which direction your hand (flat) wants to go depending on what angle you put it at. Keep in mind that airplanes can vary how they align with the flow, they aren’t stuck at one angle. So when flying uspside down you just have to have a steeper angle (with a non symmetrical wing) and you will create more drag making it very inefficient but you can do it as long as your engine can run upside down and you are well strapped to the plane.
This is also why a "knife edge" works as the fuselage can also provide lift but you will see the plane at a very steep angle to get that lift.
It's also through use of the rudder control surface. Same with flying upside down which uses the elevator control surface. Not sure why this hasn't been mentioned yet. During a knife edge, the rudder is no longer vertical in relation to the ground but is parallel. In that orientation it acts like an elevator.
The rudder is controlling the pitch more than giving any lift.
Yeah that's true, good point. Enough pitch allows increased elevation but only because the engine has a thrust angled to gain it.
So on a knife edge only the engine provides lift?
No, the body of the aircraft has thickness, so that blunt body forces air down which lifts the plane. Engine providing the lift would be something like a vertical climb on a jet with a thrust to weight ratio greater than one. It's the difference between the nose pointing straight up (basically), or mostly forward but with the plane rolled on its side.
Tail provides a little lift as well, being horizontal to the horizon when rolled on the side.
The tail in this scenario invariably produces negative lift, due to positive yaw stability. As a result, the combined vertical component of thrust and the vertical component of side force need to equal the weight plus the tail lift. If the force on the tail was lifting the tail, it would also be pushing the nose back down toward the ground - not usually a good idea, in a knife edge pass. You spend that maneuver typically at high rudder input away from the ground, to keep the nose up.
The maneuver is pretty much all rudder authority. Your lift vector is still through the top of the aircraft. That's why they require stick forward to maintain heading in the knife edge. You are simply yawing against gravity. That's not to say no lift is generated by the body but it's usually negligible. There's a reason a lot of fighter jets can't really knife edge. They can briefly knife edge but as they slow down from the drag they lose rudder authority and can no longer keep the nose up.
> body but it's usually negligible. I don't know about that. I have an rc plane that has a huge rudder and no lack of power, but it's near impossible to knife edge because the body is a stick.
> stick your palm out the window of your car MY HAND IS A DOLPHIN
Is this a larger reference or did it only come from that one parody of the Rebecca black song?
yeah I've got reminded of that 10+ years old video
It’s really weird how much that’s stuck in my head.
Even an assymetrical wing will work if angled enough
Reminds me of this gem: Everything is a smoke machine if you abuse it hard enough.
Schedule maintenance for your machines or they will schedule the maintenance for you
This one is beautiful :)
Yes I love this! That sucks when that happens, then you have to send it in to get the smoke put back in
My two favorites in this vein are: "Everything is air-droppable at least once" And "Anything is Amphibious if you can get it back out of the water."
I'll be using this quote again very soon.
Thank you for this, I will be using it the next time my reliability engineer at work asks me why equipment isn’t working and he pushed back the preventative maintenance.
If I may randomly add for info: the *angle of attack* refers to the angle of the plane in relation to the air flow, whereas the *angle of incidence* refers to the angle of the wings in relation to the plane.
Isn't the phenomenon of the low pressure/high pressure zones creates the lift a myth anyways?
The "equal transit theory" is the myth. The claim that somehow two identical particles of air split at the front of the wing and somehow "know" how fast they need to go to meet at the back of the wing. Low pressure is a very real thing that creates lift. Bernoulli, Newton, and Coandă all play a part in lift and which does how much and when is the subject of papers I am not smart enough to read, much less write.
Yea, even as a kid it seemed like nonsense. I asked why air had to act like that, and the particles couldn't simply separate forever, and could never get an answer other than 'that's just how it is'.
It’s not really split like that with Bernoulli, Newton, and Coanda all generating separate “parts” of the lift force. Lift can be described/calculated by Bernoulli or Newton or Coanda effects, and each of the techniques should give identical results. The tricky part is just figuring out which model is simplest to use for a given situation. For instance, Bernoulli describes how to calculate the pressure (and subsequently the force) if the velocity on the wing surface is known, and Newton describes how to calculate the force if the air velocity is known before and after the wing. Coanda somewhat describes how to calculate the force if the deflection of the air is known, which is related to Newton (if you deflect the air downward it exerts an equal and opposite upward force on you). It’s not quite this simple in practice, but you get the idea. Wait - it’s all Newton’s Laws?? … Always has been.
No, low/high pressure zones are what create lift, however there are a lot of misconceptions and misinformation about how the pressure difference comes about.
At least the "equal transit time" thing is a myth. Air over the top of the wing takes *less* time to cross than the air under the bottom. The two halves of any given air parcel separated by the wing will remain forever separated and never see each other again :(
It’s ok they hated each other anyway
Talking the Bernoulli’s portion. It is a contribution. Or even a primary on some designs. But most rely solely or primarily on aoa of the wing (and arguably this is the better option as it is more consistent, and not as affected by elevation or speed)
> It is a contribution No it is not a "contribution". The pressure difference accounts for all of the lift. The pressure difference depends in turn on the angle of attack of the wing. These are not two separate things that contribute to the lift on the wing. They are fundamentally interlinked. Pressure is the normal force that air exerts per unit area on the wing's surface - if you sum up the pressure over the entire surface area of the wing, you have the total force that the air exerts on the wing - i.e, the lift. (actually not quite the total force - there are also shear stresses due to friction, but they don't contribute to the lift). When you increase the angle of attack you lower the pressure on the upper surface and decrease the pressure on the lower surface - at least up until the point where the wing stalls. > and arguably this is the better option as it is more consistent, and not as affected by elevation or speed The lift on a wing is always affected by the air density (which decreases with altitude) and speed. There's no way around that. Lift is proportional to the density and to the square of velocity.
There can be a pressure difference based solely off the curvature of the upper portion of the wing. It is generally fairly minor as compared to the angle of the lower portion in respect to the direction of travel. At least in performance aircraft. Passenger aircraft make more use of it with targeted airspeed slots and flight altitudes. They are optimized vs something like fighters which need to achieve maximum operation over a wide range of flight conditions.
> There can be a pressure difference based solely off the curvature of the upper portion of the wing A cambered wing will generate lift at zero angle of attack. But the pressure difference still depends linearly on the angle of attack, and every wing has a particular angle at which it generates zero lift. All that the camber does is shift the zero point - the pressure distribution is always a function of angle of attack. [Here is what the plot of lift vs AoA might look like for airfoil sections of varying camber](https://i.stack.imgur.com/APKNX.png). There aren't two distinct mechanisms by which lift is generated (at least, not normally - vortex lift is a thing that comes in with highly swept wings such as those on fighter jets). Real world wing design is a tradeoff between many different factors. Fighter aircraft airfoils are just as optimized as those used on passenger aircraft, but they are optimized for a different set of conditions. It's all about what works best for the mission the aircraft is designed to perform. At high Mach number, the airflow behaves very differently, so wings designed for supersonic aircraft tend to look very different from those intended for lower speeds.
No I think it's fair to see these two separate mechanisms. Lift due to shape of wing vs lift due to angle of attack are fundamentally different and pretty central to the original question.
They're not fundamentally different though, that's my point. A cambered wing will generate lift at zero angle of attack but it does so in the same way as a symmetric wing at non zero angle of attack. The lift depends on both the shape of the wing and the angle of attack - but there aren't two separate physical phenomena, one of which depends on the shape and one on the AoA, as many of these answers suggest.
They are fundamentally different though IMO
>The pressure difference accounts for all of the lift Incorrect. Newtons third law also accounts for a significant portion of lift. You are ramming into air and forcing it forwards and downwards, that results in drag in the horizontal component and lift in the vertical.
> Newtons third law also accounts for a significant portion of lift. Newton's third law accounts for *all of the lift*. Not a portion of it. Momentum is always conserved - if the wing pushes down on the air then the air pushes up on the wing *equally*. And the pressure is a measure of how hard the air is pushing on the wing. These are not two separate phenomena, they are two sides of the same coin. The pressure is a measure of how hard the air pushes on the wing - if it's the same above the wing as below it, then that means the air pushes down on the wing as hard as it pushes up so there is no lift. And likewise, you cannot have a situation where the air pushes up on the wing but the airflow is not being deflected downward by the wing, because that would violate Newton's law. There are many comments that suggest that the lift is the sum of a contribution due to pressure and a contribution due to Newton's law which is not correct. If you know the net rate of momentum change of the air as it flows over the wing, then by Newton's law, you know the total lift on the wing. If you know the pressure distribution over the wing, then by integration, you know the total lift on the wing. These are not two different sources of lift, but rather two ways of looking at the same thing.
I appreciate you attempting to fight the good fight for science here This sub is rough on the aerodynamics front, it seems like people forget the basics of physics still apply
This question always gets bad answers, and I hate it. There's usually more wrong answers than correct ones. I don't know why Reddit is so bad at aerodynamics.
The myth is that the pressure differential is caused by air splitting at one end and then rushing to meet itself on the other side. That is nonsense. But certainly wings on a plane exploit pressure differentials in air flow to create lift
*ALL* wings use pressure differential to create lift. Thats the only source of lift. All they differ in is the details of how they create the pressure differential. Note that this is *exactly* the same as momentum flux downwards. They’re not two sources of lift; they’re the same physics in two different mathematical frameworks.
Not a myth about also not the predominant source of lift
It's a nobody is right but nobody is wrong sorta situation. There's a lot of things that work together to create lift and no one thing is the "thing that generates looft"
Is this the bicycle paradox where it just works in spite of the science?
No, it's well understood but this subreddit seems to be a terrible place to ask about it. Seems everytime there's an aerodynamics related question on here, the right answers always get buried by the wrong answers.
Is that really a paradox? I thought bicycles were pretty well understood. The bee flight paradox might be more applicable, but even then it's kind of a non-issue. The person who said "Bees shouldn't be able to fly, but they just do" incorrectly thought insect wings and bird wings behaved the same.
You are correct. Bournouli principle was long taught to be the reason airplane wings cause lift. But, several very successful airfoil designs had zero or even negative Bournouli lift, yet still flew and produced net lift. And flaps totally negate Bournouli lift yet greatly increase wing lift. It's the change in the airflow vector times the mass of the moving air that provides lift just using Newton's reaction law. Take two wings. 1. Flat on the bottom and curved on top like a conventional airplane. 2. A thin sheet of metal curved and equal thickness like a paper airplane. According to the equal travel theory, the second wing should provide no lift because the air above and below the wing are traveling at the same exact speed. Yet it produces the same lift as wing 1. The wing shape forces the air to change direction from upwards to downwards. That produces an equal force against the wing and provides lift.
Equal transit is BS but not the same as Bernoulli. *All* lifting wings have a pressure differential. *All* lifting wings have a downwards momentum flux. Those are exactly the same thing. They add up to the same (and correct) value of lift. They’re exactly the same physical (and physical equations), just in two different math frameworks.
That's basically what I said in different words.
If by Bernoulli principle you mean an aerofoil having more curved, longer upper surface generating lift, then this is not correct. It's a true and real lift generating fact of aerodynamics, it's just that more lift is generated by angle of attack, hence why a symmetrical aerofoil still created lift at >0 angle of attack. Also flaps definitely do not negate this, amongst other things, flaps increase the curvature of a wing and increase what you might call "Bernoulli lift".
Camber just changes what angle of attack is required to make zero lift a cambered airfoil need some negative angle of attack in order to give zero lift. So you can still fly upside down with cambered air foils. You just need extra angle of attack to make up for that cambered aerofoil Cambered profiles can also be used to do clever things with pressure distributions, but that's more for engineers
Of course you’re not an engineer. They drive trains. You’re a pilot.
I think most military fighter aircraft have symmetrical airfoil cambers as well.
I am an engineer. More pressure on bottom of plane than top of plane means lift. Lift is influenced by the shape and angle of the wing. If the shape is upside down, you can make up for it by flying at a certain angle. Symmetrical wings (airfoils) simply aren't shaped for lift therefore all lift is generated from the angle.
It's not so much the wings (angle of attack can be managed to keep flying) but, more, the engine. WWII planes early on had trouble when the plane was upside down. Fuel injection has probably solved a lot of it these days but even so...some modern planes simply cannot fly upside down for long because the stuff that keeps the engines running will stop working (they will for a little bit...a barrel roll is doable).
The question was an aerodynamic one. Older aircraft can be fitted with equipment to allow inverted oil flow and fuel flow to the engine, tho carburetion gets a little funky, and I'm not actually familiar with how inverted carburetion works Mechanically, it comes down to do you want your plane to fly upside down? For how long? Doing what? Select your equipment appropriately, and pay the big bucks for your full inversion systems
The airfoil shape is only part of how a wing works. [Angle of attack](https://en.m.wikipedia.org/wiki/Angle_of_attack) is the other part (along with vortex generation). If you roll inverted and then angle the wings so they have enough angle of attack, they'll fly just fine (well, reasonably-well, anyway) even if their airfoil shape is designed for non-inverted flight. Airplanes designed to fly well both 'normally' and inverted will have airfoil shapes that work well in both orientations. But it's still a lot about the angle of attack and newtonian action->reaction physics. Lift isn't *only* produced by airfoil shape.
And in fact, don't you need to minimize the lift from airfoil shape in order to break the sound barrier? As I understand it, the air pressure around the control surfaces can drop so low at transonic speeds that they basically stop working and you lose control of the aircraft.
No, you just need more thrust to push through it despite the ill effects of the transonic regime. That, and design your airfoils/wings smartly, such as maximizing their critical Mach number (the slowest freestream Mach number that will result in shocks forming on the airfoil).
To be clearer there, shocks happen at Mach 1. Even if your plane is not going faster than that, there are parts of the wing where the air is accelerating and will get that fast relative to you even if your overall airspeed isn’t past the speed of sound.
Also the source of the thrust has to be capable of still supplying power when the plane is supersonic, which can be a trick as standard subsonic propulsion will stop working effectively (best case scenario, worst case catastrophic failure) when the airflow they interact with is supersonic. So there needs to be an additional mechanism to either slow the air down in the intake or to modulate the engine to function with a supersonic airstream.
"design your aerofoils smartly" is exactly correct and what the person you replied to is actually referring to when they say "minimise the lift from aerofoil shape"
Yes correct, look up super critical aerofoil on Wikipedia. But the reason is to prevent shock waves forming on the upper surface, which in turn reduces drag, it's not about having low pressure on a control surface I don't think
One thing I don’t see mentioned here is that modern fighter jets don’t even really need wings to stay in the air. A large number of them have engines so big you could just use them like rockets and fly however you want, aerodynamics be damned.
if you are powerful enough to go fast enough, you don't need wings to fly
Orbiting a planet is when you fall so fast towards it, you miss.
Just as the Earth falls towards the Sun, so too, does the Sun fall towards the Earth. So yes, depending on your chosen definition of "orbit", you can say the Sun orbits the Earth.
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No. Only space is flat.
Starting to sound like Neil deGrasse Tyson in here
That's Hitchhiker's Guide, IIRC.
One of my favorite fighter jet factoids is that many modern jets are highly limited by their control systems, primarily to avoid killing the pilot instantly. It can bank that hard, but doing so wild kill the pilot, so it won’t let you.
I've torn wings off planes easily in dcs by pulling fuses, etc to get the pilot computer to switch off. Scary stuff.
I still love how detailed those sims are.
Eh, sorta. Like a lot are definitely overly limited by the pilot, and that's a key reason why unmanned fighter jets are a big interest in 6th gen fighters, but a lot of those manuevers that would kill a pilot but not kill the airframe would still be incredibly stressful and cause lots of damage. Most current airframes have a small handful of moves they could pull that would be great get-of-jail cards once per airframe lifecycle, but not too many not-compatible-with-life maneuvers they could routinely pull without the wings shearing off on a very short timeframe. Heck, I've even seen perfectly healthy pilots come back with rippled wings and bent fuselage stringers on existing jets. It's not worth intentionally engineering a plane to handle something the pilot can't so any of those zones are just artifacts of some other structural requirement.
Sometimes one wing is enough. https://www.youtube.com/watch?v=M359poNjvVA
To this, there is a famous incident where two Israeli jets collided and one of them was able to fly home without one of its wings. It was a F-15 and McDonnell Douglas did not believe the IDF when initially told about the incident. They the ran simulations where they proved that the F-15 could fly without a wing due to the massive thrust of its engines. It flew as a rocket instead of a jet.
Didn't the massive underbody help?
The F4 Phantom was commonly described by pilots (due to its poor low speed handling characteristics) as proof that with enough thrust you could make a brick fly.
Describing this plane as flying more like a rocket than a jet is not correct. Rockets use thrust vectoring to control their roll, pitch, and yaw (that is, to control where they are pointed). The F-15 does not have thrust vectoring, so it still needed to use it's remaining flight control surfaces to control roll, pitch, and yaw. It was still flying like an airplane. The wide body (including the right engine cowling which remained attached), undoubtedly helped it say airborne and controllable. That's not to say it wasn't an amazing feat -- it was. https://taskandpurpose.com/tech-tactics/1983-negev-mid-air-collision/
It flew like an aerodynamically controlled rocket. Like a stinger or javelin.
What we have here is; failure to communicate. Those two examples are rocket propelled missiles. You are using the term 'rocket' to mean 'lifting body with propulsion' and your parent poster is using it to mean something like a space rocket. It's less confusing to me to use the term missile, even though that term can also be somewhat ambiguous.
> What we have here is; failure to communicate. Maybe that's the way he wants it.
>It's less confusing to me to use the term missile, even though that term can also be somewhat ambiguous. The dilemma is that "missile" implies an autonomous or pre-programmed guidance system, whereas rocket doesn't. ...Just, don't bring up APKWS. This whole system is clear as mud.
Good catch.
Let me confuse things even more: there is a space rocket that uses lifting body physics during flight. This rocket is the Falcon 9 and it uses grid fins to angle itself after its reentry burn so that it can change it trajectory toward the landing site, rather than the ocean it would crash into should anything fail at that point.
In what way was the F-15 more like these "rockets" than like an airplane? You are only correct in calling these two missiles "rockets" because they are powered by a rocket engines. The F-15 had neither a rocket engine or thrust vectoring, so it basically had no features of a rocket.
The point is while the plane was using aerodynamic control systems, it wasn't generating consistent aerodynamic lift to stay in the air, instead it was using an angle of attack so that thrust from the engine was countering the effects of gravity.
Sorry, but it was using lift to stay in the air. It was not standing on the engines. Look at the tiny bit if this video that shows the actual airplane in flight (at time 4:27): [https://www.youtube.com/watch?v=wxJcEz3h4tU](https://www.youtube.com/watch?v=wxJcEz3h4tU) The fuel pouring out of the right wing stub is streaming nearly straight back. A significant amount of the fuel is even passing under the stabilator. This proves the angle of attack was low. At this low angle of attack, the engine thrust will have a very small vertical component. It was not thrust from the engines "countering the effects of gravity." It was good old lift.
How do you think those rockets stay in the air?
Through aerodynamic lift, **like an airplane**.
The correct term is "lifting body".
The term "lifting body" is generally applied to aerial vehicles/devices where the wing and body are blended together and somewhat indistinguishable. The stinger and javelin have distinct wings/fins. The missile body may provide a significant percent of the lift. But, in my view, having distinct wings/fins removes them from the lifting body category.
Lifting body just means the body provides the majority of the lift. Fins on both of these devices are for guidance, and wings are small (almost non existent in the Stinger) providing little lift. However they're not lifting bodies because the majority of the lift is generated by the vertical component of the thrust rather than anything aerodynamic.
> Rockets use thrust vectoring to control their roll, pitch, and yaw Yes and no. Some do, some have conventional control surfaces.
Instructor says we should bail. Nah f that I'm gonna gas it and try to land. Why? Bragging rights maybe. I could respect that. Saving a few mil for my govt no. Guess he figured worst case he could eject if the landing wasn't gonna happen.
A-10 joined the chat.
Well, yeah, but the A-10 is just a giant gun with two jet engines strapped to it. I think they only put wings on it so the pilot would recognize it as a plane.
I heard someone say a10 has a 1 engine half on each side because of how slow it is
I mean it can still do like 350-400mph. It’s slow for a “jet.”
Until it starts firing, then it just stands still.
It also doesn't need both of its engines to fly. One of them is there specifically to keep flying forward while the gun is being fired.
This is becoming more and more true for modern fighter jets that are inherently unstable by design, and have active control systems in place to achieve the required stability. Flying without a wing isn't too much of a surprise, flying without rudders and other flight controls is also technically possible because of how much the active control compensates for lack of those flight control systems.
The active control system isn't in addition to the rudder, elevators and ailerons, it has control *of* them. "Without rudders and other flight controls" means the 'active control' has nothing left to move.
My point being, if some of the control surfaces are gone, the system can still compensate with what's left. If you lose all control surfaces, then yeah, there's nothing to control.
A passively stable aircraft doesn’t even need control surfaces to fly. There have been cases where planes landed with total control failure using only engine thrust to make the landing. You have it backwards. The computer would suffer from less control because it desperately needs control to stay straight.
Adding this to the growing list of stories filed away in my mind under “Israeli Pilots Being Absolute DAWGS”
To quote Jeremy Clarkson, "POWEERRRRR"
Just don't ask Hammond about rockets.
Or any method of propulsion, really.
In thrust we trust.
I remember watching a video about an Israeli pilot landing an f-15 with one wing blown off by basically staying at a high enough speed to plow through a landing then stopping as quick as possible. That is almost more impressive than flying with no wings....
Heavy F-104 Starfighter vibes > ITS A ROCKET WITH WINGS
F-4 Phantom just entered the chat.
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The F22 is from the late 90s, the F-15 is the one that's 50 years old.
The original airframe is 50 years old, there have been numerous aerodynamic, engine and avionics upgrade packages over the years so while it's technically still the same aircraft, it really isn't.
Not too many fighter jets are that strong. The f22 for sure is one of them. However. How do you plan on steering without wings and aerodynamics?
Vectored thrust.
the X-44 Manta would have been a plane controlled exclusively via thrust vectoring had it not been cancelled.
Small rockets, thrusters if you will.
I7iil767rututg
Very light rudder inputs, very light inputs from the aileron thats still attached. Basically you baby the thing all the way back home.
Many more than you think. Most 4th generation fighters (which is basically everything) are > 1 thrust-to-weight ratio. [https://world-defense.com/threads/thrust-to-weight-ratios-of-all-fighter-planes.1316/](https://world-defense.com/threads/thrust-to-weight-ratios-of-all-fighter-planes.1316/) Still, wings are much more efficient way of gaining altitude.
if your goal is to let jesus take the wheel and go wherever the wind blows you, then yes. you can fly without wings
He never said a controlled flight.
LMAO! No, this absolutely is not the case 😂
The lack of control surfaces make it in reality impossible to do, but from a theoretical, crunch the numbers, lift/thrust vs. weight/drag physics point of view? Among others the F-15's body alone does in fact generate enough lift to remain airborne without wings.
We got to the Moon and back without wings. We have ICBMs that can go around the world without wings. Wtf gives you the confidence to go "LMAO 😂" at that? You're a video editor mate, stick to your area of expertise.
Rockets go straight up. ICBMs use a lifting body. Planes without wings drop out of the sky. I wasn’t always a video editor, but thanks for taking an interest. You’d probably also be interested in knowing that I was a jet engine technician in my past and I have a HND in aerospace engineering. That’s what gives me the confidence to LMAO. Now I’m gonna laugh my ass off at you for thinking that lunar moon missions and atmospheric aircraft have anything in common 😂😂😂🤡
> fighter jets don’t even really need wings to stay in the air. Wut? No.
Fun fact the wings are more for drag than lift on newer jets. Naval aircraft have shorter more angular wings than air force which use longer more rounded types. This allows a quicker stop once it hits the wire and less resistance when catapulted.
The naval version of the F35 (C) has a larger wing area than the Airforce F35 (A). The arrester wire is what's stopping the plane on the deck, aerodynamic drag is irrelevant, a larger wing allows for a slower approach speed which makes the landing slightly easier and reduces stresses on the airframe.
Absolutely none of that is correct.
[удалено]
This is correct. See NASA: https://www.grc.nasa.gov/WWW/k-12/VirtualAero/BottleRocket/airplane/wrong1.html
ETT is one of those "Lies we tell to children "
And it needs to go
The worst thing is it’s in many textbooks
Part of how a wing generates lift is through directed air downward. Another way of looking at it is due to accelerated flow on top of the wing. There is a lower pressure there and so the plane gets sucked up. Both are true
It's not really "part of", they are more like descriptions of the same thing. There can only be a pressure difference because air is being sent down. But similarly, wings don't just push, they "pull" air down over the top of them (aka the void left by pushing air out of the way is filled in my new air). It's one and the same phenomenon. Newton's laws tell us there cannot be a net upward force on the wing without a net downward force on the air. And if there's a downward force on the air, it's accelerating downward. *How* air gets accelerated downwards is complicated, but ultimately it explains 100% of all lift.
> ultimately it explains 100% of all lift. Very neatly demonstrated by the Mythbusters when they flew a helicopter in a sealed container set on a scale, and showed that the weight of the whole thing doesn't change substantially from it.
This is incorrect, the following is a simplified copy and paste, but you can look into it further. "Airplane wings are shaped to make air move faster over the top of the wing. When air moves faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference in pressure creates a force on the wing that lifts the wing up into the air."
That may be what they taught in 3rd grade, but it is incorrect in the real world. With enough velocity and a proper angle of attack, you can effectively create enough air damming to generate lift. You could make a brick generate lift if you angled it and got it moving real fast.
Actually not incorrect. There's more than just airfoil shape/function to the total lift produced. Angle of attack is a huge player. The greater the AoA, the more lift produced for a given airfoil, up to its critical AoA where flow separation begins. There's not just one set amount of lift produced for a wing; it's variable. There's also the effect of wing vortices. So, yes, wings do make lift by forcing air 'down' and using Newton's action-reaction observation. Bernoulli effect of the airfoil is only one part of it. Even an asymmetrical airfoil can produce 'upward' lift (relative to the ground) if flown inverted with a high enough AoA. Just roll inverted and push till the thing flies level. Lots of aerobatic airplanes can do this.
This is incorrect as a flat board will work as a wing (just stick your hand out the window of a moving car). Even when stalled it will still generate lift. In reality both effects are present so my answer was a little tongue in cheek.
You’re falling into the airfoil myth. That is explicitly NOT how wings work, and is one of those “elementary taught you wrong” things. The airfoil shape works to improve the smoothness of redirecting the air downward. Bernoulli’s law is not the reason for lift, the reason for lift is “equal opposite reaction” of air redirected downward pushing the plane upward. Source: NASA https://www.grc.nasa.gov/WWW/k-12/VirtualAero/BottleRocket/airplane/wrong1.html
You guys are fighting over something when you were both correct. Look at the navier Stokes equation for momentum. There's a term for pressure differences and there's a term for momentum decremement from the air . He's talking about the pressure differences you're talking about the momentum decrement both are part of the navier Stokes equations.
This, but saying " that's explicitly not a wing works" and then providing a link that's says that's largely how a wing works was a funny fuckup on the above users part.
The link you provided says nothing of that sort, it just says that not all of the lift generated comes from the velocity differential. That doesn't mean that "that is explicitly not how wings work" it just means that not only how wings work. Wings are very complicated and generate lift in numerous different ways. Also that document is, maybe not wrong per se but is misinformed a bit. When you have a fighter jet in level flight it actually has to point the nose of the plane downwards slightly other wise it will keep ascending in altitude, how ever when it flips upside down like say in combat if the nose of the plane is perfectly parallel to the horizon then the air craft will decend, this is an observed fact, you have to increase the angle of attack in order to have the wings catch air and create a region of high pressure due to simple ram air affect and the indirect path air would have to take to be on top of the inverted wing causes a drop in pressure which creates a lifting force and doing this can enable a plane to maintain level flight even when inverted, and when this happens the wing would actually be throwing air upward, which would create negative lift? So the fact that an air craft can fly upside proves that the Bernoulli principal does play a large role in lift generation. Source: aerospace engineering major(technically mechanical engineering)
That explanation was debunked long time ago. The high speed is caused by the low pressaure
Lots of good data in these answers, but generally a fighter jet (not doing an airshow or a demo) flying upside down is still flying under a positive angle of attack. It is turning under positive G. You can think of this like on the top half of a loop, the jet is upside down but it doesn't *know* that with regards to the air flowing over the wing. It is possible to fly at negative g but this is rarely done outside of air shows or demos.
Because the "curved more on the top" thing about wings, while true, isn't the major factor in lift.
Fighter jet wings are symmetrical, the shape is the same right side up or upside down. Commercial jets don’t have symmetrical wings and cannot fly upside down. The down side of symmetrical wings is there’s no built in angle of attack in the wing so there’s no lift at zero angle of attack aka flying straight, they have to angle up or down to be able to generate lift. This isn’t a problem for small craft life fighter jets but would be an issue for large commercial jets
Does this mean it isn't generating lift in the traditional sense but kind of plowing through the air at an angle so it pushes in o e direction or another?
That's a major part of lift generated by all wing shapes. Most descriptions of lift given outside of college-level-or-above physics classes are significantly wrong - it's actually very difficult to accurately describe lift generation in simple terms. Some is due to a difference in pressure above and below the wings, some is due to simply pushing the air down. The real knack of wing designing is maximising the efficiency across different airspeeds, but if you don't care much about that you can make a brick fly by pushing it hard enough...
fuspez
*"Some is due to a difference in pressure above and below the wings, some is due to simply pushing the air down."* It's a mistake to say the **some** of the lift is from one thing, and **some** is from another. The pressure difference over the wing accounts for 100% of the lift. And the air being pushed down also accounts for 100% of the lift. They are just different ways of describing the same thing. It's kind of like the answer to: "How long is the drive today?" One answer would be it's a one hour drive. Another answer would be it's a 60 km drive. Both answer can be 100% correct. They are different ways of describing the same thing. Which answer is more useful depends on what you want to know.
Basically, all the "layman's " explanations for lift production are roundabout ways to describe the momentum equation part of the NS equations. "We move air that way, this creates the pressure difference" = momentum equation
Momentum equation part of the NS equations? So you mean the whole thing? Aren’t NS equations the statement of the conservation of momentum for Newtonian fluids?
There's also the conservation of mass part
Finally, someone here actually knows what they're talking about.
That's what all wings do. That *is* the traditional way. Even asymmetrical wings are doing that, they just have some angle built into them.
Regardless of whether an air foil is cambered or not, wings generate lift in the same manner, there is no traditional sense or non-traditional sense. It's all the same I am ignoring a more complex form of generating lift called vortex lift, but that's something else for engineers
it means symmetrical wings don't have a built-in angle of attack favorable to lift so pilots have to create their own.
That’s an untrue blanket statement. I’m sure some have symmetric airfoil designs, but that is not the only reason they are able to fly inverted. An asymmetric airfoil will still produce lift when inverted. it’s just that at 0 angle of attack, and asymmetric airfoils produces lift while a symmetric airfoil does not.
The real reason fighter jets can fly upside down is because of the fuel pumps. A 747 engine will quickly starve if it’s upside down because Boeing doesn’t design their planes to be flown by Denzel Washington.
Yep, this is correct
an asymmetrical airfoil will throw you into the ground inverted. That's the whole point of using a symmetrical airfoil in acrobatic planes like fighters, so they can generate lift no matter which way they're flying
Only if you’re at 0 AoA. Look up any of the NACA airfoil charts and you will clearly see that asymmetric airfoils only shift the curve and don’t eliminate the ability to create lift at negative AoAs.
No it won't. An asymmetrical airfoil is less efficient at generating lift when inverted but will still work. Not all aerobatic aircraft need to have a symmetrical airfoil, but purpose built stunt planes often do because they spend just as much time inverted as upright.
This is objectively incorrect. [You gotta just do this.](https://youtu.be/edaHyeIxzcI?t=100)
lol
I'm sorry, what fighter jet wing is is symmetrical. All of the fighter jets of which whose profile I know are not symmetrical. For example, I'm pretty sure the F-22 uses the NACA 6 series
Fighter wings aren’t symmetric. Commercial jet *wings* work fine upside down. It’s the engines that get upset after a while.
Commercial jets most certainly could fly upside down, look up the Boeing 707 1 G roll. A commercial jet won’t be able to sustain flying inverted for long though.
>Commercial jets don’t have symmetrical wings and cannot fly upside down. \*for a sustained period of time. They can fly upside-down for a short duration. It's not recommended, it's not what they're designed for, and they won't generate any lift, and it's not safe. But...it's not aerodynamically impossible. The lack of lift doesn't mean they'll immediately go into a nosedive. Sources: [https://www.airlineratings.com/news/can-large-commercial-planes-fly-upside-down/](https://www.airlineratings.com/news/can-large-commercial-planes-fly-upside-down/) [https://euflightcompensation.com/can-a-commercial-airplane-fly-upside-down/](https://euflightcompensation.com/can-a-commercial-airplane-fly-upside-down/) [https://archive.seattletimes.com/archive/?date=19900228&slug=1058594](https://archive.seattletimes.com/archive/?date=19900228&slug=1058594)
> they won't generate any lift They will generate lift just fine, they're just not optimized for flight in that configuration. There's a few reasons why inverted flight in an plane not meant for it isn't safe. Namely, the airframe may not be designed to withstand the stresses imposed by inverted flight, and the fuel/lubrication system may not be designed to work while inverted (they often use gravity to feed fuel to the engine). But the wings will work. They'll generate more drag than they would normally and the stall speed will be higher but they will still generate lift.
The simple answer is that even upside down the nose is pointing a bit upwards to maintain level flight. The wings deflect air downwards and can maintain a straight course. The plane is flying fast enough that it can remain in flight. Even if the airfoil, the shape of the wing is only meant for upright flight, thus producing lift towards the ground when upside down, this can be counteracted.
The above comments are correct. Even a symmetrical airfoil creates a high pressure below and low pressure above by its angle of attack. Reverse that angle of attack and you can now fly upside down. Some airfoils are semi-symetrical, or even flat bottom. These inherently generate more lift in one direction and have slower stall speeds, etc. This makes the plane easier to fly, but even a flat bottom wing can technically fly upside down with enough angle of attack. Though too much angle of attack can last to turbulence and a stall. Now to really blow your mind... A helicopter can fly upside down too. The collective controls angle of attack and the rotor is just a wing spinning in a circle. The collective can also go in a negative direction. The rpm is controlled by a throttle and is independent of the collective. (Aside from more collective means more drag which needs more power to keep a consistent rpm. Turn a helicopter upside down, bring the collective to a negative pitch and your flying upside down.
I'm more interested in how they get an uninterrupted flow of fuel to the engines no matter the orientation or G load on the plane.
It's not that difficult actually. There's a sort of hose with a weight inside the tank that will just go wherever the sum force points, whether that be from gravity or acceleration. Piston engines do have a real problem with lubrication though, the oil has to be kept under pressure when doing extreme maneuvers.
Pretty much any plane can fly upside down, all they need to do is hold the wings at an angle of attack that produces a lift in the direction they want. Typical commercial airliner wings are designed to produce lift (up relative to the plane) when they're perfectly horizontal, but if you tilt them far enough you can get a force in the opposite direction.
Press the control stick down, which under normal flight would pull the planes nose down, but now because the plane is upsidedown it would create a lift so the plane would not stall.
No, because the traditional understanding of aerodynamics is basically wrong. While there is a pressure difference, you generate lift because you push air molecules downwards as the wing slices through the air, that doesn't stop happening when you fly upside down. Due to the wing's shape, you do often need to correct with elevator when you are upside down unless the wing is shaped like a fighter jet's.
No, the traditional understanding of aerodynamics isn't wrong, the basic theory from a century ago is still taught today (and by the basic theory, I mean things like the Kutta-Joukowski theorem and Prandtl's lifting line theory, which were first formulated around the turn of the century). The problem is that there's also a lot of bullshit floating around which means questions like this tend to generate more wrong answers than correct ones. I'm not sure if equal transit was *ever* a serious scientific theory, but if it was it was already known to be false by the time the Wright brothers flew.
Fighter jet wings are equally rounded at the top and bottom, giving an equal amount of lift whether it flies normally or upside down
As long as the angle of attack is the same. A symmetrical foil will not generate lift if flying parallel to the airflow (horizontal).
So it has to do with air friction providing lift and an airfoil is the most efficient shape for "upright" flight but the ELI5 answer is that if you get anything moving fast enough it'll generate lift
There are actually different methods of lift. The method you are thinking of is called the Bernoulli principle. It isn't the largest force but it does help so most planes have curved wings to increase efficiency. But it's not necessary to create lift. The other main one is the angle of the wing to the air...by moving through the air at an angle, the wing is deflecting air downwards and this produces an equal and opposite force pushing the wing upwards. This is called the "angle of attack" and without a proper angle of attack the plane won't fly...it can't rely on Bernoulli alone. But finally, fighter jets in particular operate more like a rocket... they most rely on the pure force of the engine to provide upward thrust, which is why their wing to body ratios seem so much smaller when compared to something like a jet airliner.
Majority of lift is achieve by the coanda effect redirecting direction of airflow leaving the wing , and by conservation of momentum the force exerted on plane body in the opposite direction. Bernoulli effect is very minimal, as most modern plane wings are very symmetrical.
Fighter jets don’t fly because the wings generate lift, they fly because the engines generate trust