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As I just posted in the other comment: Lift is the asymmetry of a solid turning the air (explains both camber and AoA). Mass flow continuity means speed must increase proportional to the constriction A1/A2. (ratio of two cross-sectional areas: incoming flow and the constriction area presented to that flow) This speed increase drives a conservation of energy, static pressure drop: pressure = constant - (1/2)x(mass density)x(v)^2 The total pressure difference is equal to lift. Which forces air mass down, also equal to lift: P x A = F = ma = d(mv)dt Or the force of pressure (as force per unit area times area), equals the change in vertical momentum of the air (again, both equal to lift). This directly ties asymmetry as the fundamental principle to both the "Bernoulli issue" and the "Newton issue". No need to get lost in the common circular logic

So your errors appear to be that you haven't sorted out your issues with the following beliefs: 1)"because the “equal time” assumption is wrong 2)"If you work through the calculations, the “path length” theory doesn’t produce enough pressure drop, or fast enough air over the top, or enough lift! I'll leave you with something I wrote elsewhere: quick summary: Lift is the asymmetry of a solid turning the air (explains both camber and AoA). Mass flow continuity means speed must increase proportional to the constriction A1/A2. (ratio of two cross-sectional areas: incoming flow and the constriction area presented to that flow) This speed increase drives a conservation of energy, static pressure drop: pressure = constant - (1/2)x(mass density)x(v)^2 The total pressure difference is equal to lift. Which forces air mass down, also equal to lift: P x A = F = ma = d(mv)dt Or the force of pressure (as force per unit area times area), equals the change in vertical momentum of the air (again, both equal to lift). This directly ties asymmetry as the fundamental principle to both the "Bernoulli issue" and the "Newton issue". No need to get lost in the common circular logic

The problem is you take the mention of path distance difference as me advocating equal transit time, but I do not. Transit time is not equal, as I showed in my illustrations the air going over reaches the trialing edge before the air going under. Also the point of the video was never to argue a lift creation theory, but to show that the argument I countered is a logical fallacy. It doesn't matter if the wing is upside down, symmetrical or flat, the path length over the top (that is the side pointing skywards with a positive AoA) is always longer due to the stagnation point that shifts with AoA. And it has nothing to do with equal transit time.

@@LetsGoAviate Thank you for replying! I apologize, I looked for the transit time in the video and missed it at 7:51 (although you show it without comment), and since the "distance over/under" simplistic description of lift creation is usually tied to equal transit times + Bernoulli, I thought you were going there. You opened your video with: "If lift is created as a result of pressure differential from air flowing over the top of the wing having a longer path than air flowing underneath, then an airplane wing wouldn't be able to fly upside down". Your illustrations focused on airflow in the immediate vicinity of the wing surface - indeed, you talked quite a bit about the stagnation point. The problem is that lift is not, as such, "created as a result of air flowing (directly) over the top of the wing having a longer path." If you make a very thin airfoil (like a boat sail) with a fairly sharp leading edge, the stagnation point at the leading edge barely moves with angle of attack, and the path lengths (immediately) over and under are almost identical. If path length near the surface mattered, those airfoils should produce very little lift - and yet they produce substantial amounts of it. Of course we could make a more sophisticated version of your point, and talk about air flowing near, but not immediately next to the wing. Air doesn't just separate at the leading edge stagnation point; the flow begins to separate some distance ahead of it. You can draw a line ahead of the wing, such that air on one side of it will go below the wing and air on the other side will go above. When you do that, even for a sail-type wing the air going over the low-pressure side, but away from the surface of the sail, will take a longer path - this is often described as the result of "circulation" produced by the wing. Maybe that was the point you were getting to?

@@davetime5234 Agreed. If you deflect air downwards, then there will be an equal and opposite reaction, which we call Lift (Newton). There is only a tiny amount of air in direct contact with the wing. To "deflect air downward" in any meaningful way, it must deflect a certain amount of air near the wing as well. The only way to deflect air that is not in direct contact with the wing, is through air pressure. If air below the wing is being deflected down, the pressure must be high in the upper part of the airmass and low in the lower part, so that the pressure difference pushes downward on the airmass. Since the air well below the wing is at atmospheric pressure, the pressure directly under the wing must therefore be at higher than atmospheric pressure. Similarly, if air above the wing is being deflected down, the pressure must again be higher up high and lower down low. Since the air well above the wing is at atmospheric pressure, the air directly above the wing must therefore be lower than atmospheric pressure. So the air just above the wing must be at lower-than-atmospheric pressure and the air just below the wing must be at higher-than-atmospheric pressure, and there is a pressure differential between the top and bottom of the wing (which pushes upward on the wing - Newton's equal reaction). Air moving to flow above the wing experiences pressure declining ahead of it as it starts passing over the wing, then rising again until it gets back to atmospheric pressure. This causes the air to accelerate (as the pressure falls) and then decelerate (as the pressure rises). It ultimately returns to the same speed behind the wing as it had ahead of it, but everywhere in between the accelerated air moves faster than the overall airflow. Meanwhile the air moving to flow below the wing experiences pressure rising ahead of it as it starts passing under the wing, then falling again until it gets back to atmospheric pressure. This causes the air to decelerate (as the pressure rises) and then accelerate (as the pressure falls). It ultimately returns to the same speed behind the wing as it had ahead of it, but everywhere in between it is moving slower than that. This is all consistent with Bernoulli's observations about fluid flows. It also means that a lifting wing will cause the air molecules that go above the wing to get to the trailing edge faster than air molecules that go below the wing, EVEN IF the path length over the upper surface of the wing is longer (but also if it is not). These things happen at the same time. They are inseparable. If you produce a pressure difference above and below an object, it will deflect air flowing around it downwards AND air flowing over it will move faster than air flowing under it. If an object deflects air flowing around it downward, then it will have a pressure difference above and below it and air flowing over it will move faster. If an object accelerates air flowing over it and decelerates air flowing under it (like a backspinning tennis ball), then it will have a pressure difference above and below and it will deflect air downward (and generate lift). It's not Bernoulli OR Newton; it's Bernoulli AND Newton.

Single blade is more efficient, but has very limited power absorbtion. The blade can only be made a limited length before tip speeds become and issue. And if making the chord wider to add power absorbtion, it loses efficiency, and there would be a crossover point where it would be more efficient to add a second blade, than making the single blade chord wider. And same 2 vs 3 blade, 3 vs 4 blade etc.

Single blade is more efficient, but not because of less disturbed air. The propeller pushes the wake backwards, so by the time the 2nd or 3rd blade gets to that point, it hits new undisturbed air. So perhaps a myth that I will cover in the next one. Blades has efficiency losses, noise, bending etc, so less blades is more efficient. But this is fairly minor compared to the fact that more blades have more power absorbtion potential. Someone said it's thrust that pushes the plane, not efficiency, and 1 blade has very limited power absorbtion or thrust, regardless of higher efficiency.

@@LetsGoAviate Hey its exactly what I said, the single blade runs in less disturbed air, or cleaner air. The plane moves forward, so it runs is less disturbed air.

Pusher config engines/propellers have a few disadvantages, but aerodynamically speakiing it doesn't get "clean" and undisturbed air like a tractor propeller does, with the air first having to pass over the fuselage and wings before reaching the propeller. The pusher prop thus passes though the wake of the plane, which results in non-uniform speed of the air hitting the propeller, which reduces propeller efficiency.

@@LetsGoAviate so it's a trade-off between the plane going through a slipstream and the propeller having access to to undisturbed air. Thanks for the explanation!

Yeeees! Since the equation of drag is the same as lift, the faster propeller slipstream not only increases drag as a function of V^2, but also lift. In the context of the video however, that faster propeller slipstream of the smaller diameter, faster spinning propeller is more concentrated over the fuselage that creates very little lift, and misses most of the wings, flaps and slats. A slower spinning, larger diameter propellers slipstream is slower, but spread out over a wider area, and will go over a larger portion of the airplanes wings, flaps and slats. So there is no real increase in lift by going for a faster spinning, slower diameter prop. On STOL one would want the largest possible diameter prop spinning right up to the max tip speed of mach 0.8, even closer to 0.9, to make use of this increased lift from the propeller slipstream.

Yes that was on purpose, as that complicates explanation. With constant speed/variable pitch taken into account, everything in the video is still valid, but the optimum thrust airspeed limitations removed that a fixed pitch prop would have. If interested, I covered the aerodynamics and thrust of variable pitch extensively in this video : kzbin.info/www/bejne/nqfFoJxsrJaNb6Msi=ekW1tPhCBASyH86H

Yes I went into quite the tangeant that an upside down wing needs a bigger AoA (i.e. dropping the tail) than a right-side-up wing.

Asymmetry of shape to the relative airflow is the fundamental condition causing lift. If you understand the implication of asymmetry, thin vs thick vs shaped wings all comes into the proper perspective. Does the entire configuration add to a total asymmetry or not. That's really the only condition that counts.

Correct, the shape of the upper surface is not necessary for lift (a flat wing can fly too), but the upper surface is instrumental in creating lift. Air pushing the wing up is not sufficient in explaining lift.

The amount of pressure that dropped on top that "pulls up" is considerably more than the pressure that has increased on the bottom "Pushing up". If you can't explain the top pressure drop, you really haven't explained anything. The up force is caused by an asymmetry of shape (both shape fixed by camber and adjustable shape determined by angle of attack) turning the air enough to equal that up force. The pressure difference which pulls down the air due to the asymmetry, is mostly from the pressure drop on top.

​@@davetime5234 This. The assymetry caused by the AoA, not necessarily wing shape.

@@davetime5234 Things that happen in air fall under fluid dynamics. Have you ever seen how water skis work?

@@LetsGoAviate Yes, thank you for pointing out I need to clarify what I meant by "shape": the total asymmetric "shape": angle of attack asymmetrical "shape" and/or asymmetrical camber shape. AoA allows us to modulate total asymmetrical "shape" to coax varying amounts of lift from a fixed structural shape of an airfoil, for the practical needs of changes in VS, IAS, and load. (I edited the original)

More blades are always quieter. Two blades make a racket.

You can experiment as you like as long as there is an STC for each prop you fit. Take a look the STC's for the Cessna 172 for example, you have 2 and 3 blade options, of various blade lengths. Depending on the engine and model of Cessna 172, you can fit certain Hartzell, McCauly, MT prop, Sensenich and possibly more. That's certified aircraft. On most experimental there are virtually no propeller legal restrictions.

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That's not entirely a misconception, because drag exists. In a world with no drag and spherical cows, where the aircraft is not accelerating, they wouldn't interfere.

I agree but most common propellers (US manufactured) are referred to, sold and talked about in inches. We also talk about power in hp, not kw, altitude in feet, not meters. It's aviation standards.

Maybe see some of the latest news regarding this engine. Besides, this video is more about the engineering of the engine, flying or not, which is unique in aviation. And I'd like to see the video mine is a repeat of 😉

What you explained doesn't explain lift, but what you explained does require a pressure difference to explain it: the mass of water is accelerated into a change in direction by a pressure difference. So, in terms of physics, unfortunately, you are wrong on two counts.

I was trying to point out that lift is mostly a upper surface phenomenon, and has way less to do with pressure differences between the upper and lower surfaces of the wing.

So close! But the point was actually that angle of attack makes the path over the top longer (top being the side pointing skywards with a positive AoA)...regardless of the shape, regardless of being upside down or right side up.

@@LetsGoAviate Okay. But if I make a paper plane, it still flies, even if its wings are flat. Why?

​@@alexanderhugestrand The same way any wing creates lift. Give the paper plane wing a positive AoA and it will create a pressure differential. Since it's a flat wing, the pressure differential is minimal and the lift force is minimal, but it doesn't matter, the weight of the paper plane is minimal. How does a paper plane wing create a pressure differential if its flat? The same way any wing does, just not as efficiently as a cambered wing. As soon as the paper plane wing has a positive AoA, the forward stagnation point move down, creating a longer path and lower pressure over the wing than under the wing. On a flat paper plane wing the stagnation point movment will be minimal, fractions of a millimeter probably, but that incredibly small amount is enough to make a 5 gram piece of paper defy gravity until it loses airspeed.

@@LetsGoAviate Is that explanation true for kites as well? I mean, it's easy to explain how a flat surface can be pushed by the wind, using only Newton's laws and forces applied by the wind. No pressure differential needed. UPDATE: There will always be a difference in pressure, of course. But not for the reason that one path is longer than the other. If you shoot particles on one side of a surface, you will apply a force to it, i.e. adding a higher pressure on that side. The other side will obviously have a lower pressure.

​@@alexanderhugestrand Yes it is the same. Most kick against it, but the reality is lift can be described with a few different theories that are correct. Newtons laws (2nd and 3rd) are valid ways to describe lift, but that doesn't mean the pressure differential theory is incorrect, because it is also valid. My opinion is there are too many emphasis on correct and incorrect, instead of realising lift is complex and not fully explainable with a single theory. Like you said, there will always be higher pressure below the kite or wing, and that the air "pushing it up" will be a part of it, on a kite probably more than a wing, but as NASA says (I'm quoting) "Neglecting the upper surface's part in turning the flow leads to an incorrect theory of lift" which I very much agree with. As for the longer path, it doesn't "create" lift, it enables lift, as it contributes to the pressure differential (on a kite too). The equal transit theory doesn't have to be true for the longer path over the top to be true.