Sorry, but I don't subscribe to the 'flat plate' theory. There is a reason that almost every commercial (and most military) aircraft have leading edge slats to generate lift at lower speeds (by making the top of the wing more convex and the bottom of the wing more concave).
If pure 'flat plate' theory was valid, then all those aircraft speeding down the runway with the leading edge of their wings canted downwards 20 or so degrees would result in the airplanes simply being pushed towards the ground and never lifting off...
And Boeing, Airbus et al would build planes with flat slab wings mounted at a 45 degree angle to the airflow, because that would give the maximum lift by the 'flat plate' theory, wouldn't it?
Not that I disbelieve that a flat slab cannot generate lift - but that it is probably a very inefficient way to generate lift compared to the standard aerofoil shape.
And as I have mentioned elsewhere on here - I have flown inverted a few times, and to do so take a tremendous amount of forward pressure on the control stick to even try and attempt to hold altitude while inverted, in order to counteract the wings natural (slight) positive AoA and the tendency for the wing to move towards it upper surface. In fact, most of the aircraft I have flown would not be able to sustain inverted flight at all. The fact that full aerobatic and military jets do, is because they (as I explained earlier) usually don't have that curved 'fish' shape cross section, but are usually symmetrically shaped on the top and bottom of the wing.
To whit, I've had the fortune to fly an old DH Tiger Moth biplane - on that little baby, when you approach the stalling point, you can actually see the the canvas on top of the bottom wing bulge and contort with pressure differential, and you can hear the sucking sounds as the airflow struggles to 'stick' to the wing. There is a little movement on the bottom surface of the top wing too, but not as pronounced.
I'd be interested to see in this thread, who here has actually studied aeronautical engineering, or flown actual aircraft, and who is relying on YT videos or a pure theoretical approach to come up with these theories?
Also interestingly, I believe most of the textbooks I used at flight school were filled with data from NASA and other US military branches with regards to flight dynamics etc., and here on this thread we see articles from NASA (albeit aimed at K-12 audience rather than trainee pilots) basically disproving their earlier academic research.
> I'd be interested to see in this thread, who here has actually studied aeronautical engineering
I studied Aerospace Engineering (PhD in Aerodynamics), and I stay out of internet conversations over "how" lift is generated. For me it is one of those topics that is just not worth debating. It seems that people get _really_ attached to their personally preferred theory of lift.
Seconded. Masters in ASE, written my own vortex lattice code from scratch.
"Wings generate lift by changing the velocity of the flow around them" seems general and correct but the why part is pretty tricky without notions of continuity and conservation laws. And vorticity helps a lot, too.
You should write a blog entry on current theory, and post "I'm an expert, here are the current theory(ies), I will not debate about it", or point to a wikipedia page that is accurate in your opinion.
Flight is a complex system, there are multiple variables effecting it. And yet half the responses here are regurgitated from grade school without references.
Its a somewhat common joke in our office that if you ask 3 researchers "What is lift?" you'll get 5 answers (and probably a bit of an argument).
I think "It's complicated" and "Why do you need to know?" are often the only appropriate answers, as context is important. I've read some "aerodynamics for pilots" type books that from a research point of view I considered to be, to some degree, wrong. But ultimately they were _right_ in that they taught the pilot exactly what they needed to know.
In a way it reminds me of electricity. I know enough to design and make simple circuitry, but I know electrical engineers and physicists that could run rings around me at both the circuit design level and the "That's not how electricity works, you idiot!" level.
> I have flown inverted a few times, and to do so take a tremendous amount of forward pressure on the control stick to even try and attempt to hold altitude while inverted, in order to counteract the wings natural (slight) positive AoA and the tendency for the wing to move towards it upper surface.
I don't think that is right. The tail wing has a different angle of attack than the main wing. On the order of one degree I think. This is so to give a self stabilizing effekt. When flying upside down you have to compensate heavily to avoid what would be a destabilizing effect.
The horizontal stabilizer of most aircraft has a negative angle of attack and produces downforce, not lift in straight and level flight. This allows the center of gravity to be forward of the wing's center of lift by moving the overall center of lift forward. The result is a tendency to pitch down if airspeed decreases without other control inputs, countering the reduced airspeed.
Flying inverted in a relatively stable aircraft requires a lot of forward pressure because for the inverted aircraft's wing to have a positive angle of attack, the horizontal stabilizer has an even larger positive angle of attack. The pilot must counter this with the elevator to establish a stable ratio of lift to downforce.
As an aside, modern aerobatic aircraft are often rigged 0,0,0 (wing incidence, tail incidence, dihedral), so level flight will need equal elevator deflection in the appropriate direction.
Less efficient - but makes for symmetrical performance.
> The fact that full aerobatic and military jets do, is because they usually don't have that curved 'fish' shape cross section, but are usually symmetrically shaped on the top and bottom of the wing.
Fair enough, it is symmetrical, but still has a lot of shape to it - only time I've been inverted was in a grob 103, and was a passenger for that part of the flight, here's the cross section of it's little sister which is also fully aerobatic:
Agreed, that's why I said it'd still work. But the shape does contribute to its efficiency, otherwise manufacturers wouldn't spend money trying out different shapes, adding winglet etc...
A bit late to reply, but I had to think of your post while spending some hours idly staring at at the top of an airliner wing today. Slats (and non-flat airfoils in general, I suspect) are there to allow a harder angle of attack ("amount of pointing up relative to the direction of movement") without stalling.
You can push the air hard on the underside, but on the top side, you have to gently accelerate the flow downwards, or else it forms vortices and you suddenly lose a significant fraction of the amount of air you would otherwise deflect downwards.
If pure 'flat plate' theory was valid, then all those aircraft speeding down the runway with the leading edge of their wings canted downwards 20 or so degrees would result in the airplanes simply being pushed towards the ground and never lifting off...
And Boeing, Airbus et al would build planes with flat slab wings mounted at a 45 degree angle to the airflow, because that would give the maximum lift by the 'flat plate' theory, wouldn't it?
Not that I disbelieve that a flat slab cannot generate lift - but that it is probably a very inefficient way to generate lift compared to the standard aerofoil shape.
[0] - https://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/Bo...
[1] - https://www.metabunk.org/sk/20141127-081301-jrgr5.jpg