As long as you keep referring to the static pressure on top of an airfoil as a vacuum I’m not able to take anything you claim seriously (whether true or not). I doubt you are an engineer if you truly believe the pressure on top of a wing to be a vacuum (absence of air) or even a partial vacuum.
You are reasoning that the Newton theory is incorrect based on your assumption that an asymmetrical wing at 0 degrees AOA not having higher than ambient pressure below the wing because no air is impinging on the lower surface. The wing is still producing lift and this, according to you, proves that the static pressure theory is correct and the Newton theory is wrong? The Newton theory does not (necessarily) explain the presence of lift due to airflow impinging on the wing lower surface when the aircraft is in motion and at an angle, the Newton theory is primarily based on the airflow changing its direction (up and downwash) due to the airfoil shape, angle and motion and thereby creating an equal and opposite reaction to the airflow being deflected downward (lift).
To be clear you can’t see those two theories separate from each other, without the change in airflow direction, there will be no change in speed and therefore no change in static pressure. I think the two theories complement each other and don’t necessarily proof one or the other is wrong. They are called theories for a reason, even experts don’t fully agree how lift is created. I’ve been a flight instructor for years, we still use the Continuity law (V x A = C) for incompressible - subsonic airflow together with the Bernoulli principle (Ps + Pd = C) to explain pressure difference causing lift. But as said before, this theory does not cover everything, its a simplification.
Came in late to the party, did anyone answer the OPs question instead of arguing? Angle of Attack (AOA) is the angle between the relative airflow and the wing chord line. Its effect on lift is covered together with wing shape (chamber, thickness / chord ratio, swept, straight, tapered, elliptical wing etc.) in Lift Coefficient (CL). Lift formula:
L = 1/2 x rho x V2 x CL x S
In which 1/2 x rho x V2 is the kinetic energy (1/2 x m x V2 must sound familiar) you can’t really define the mass of the air therefore we replace M by the rho which means air density (mass per m3 of air). CL includes the angle of attack and wingshape etc., S is wing surface area. On the CL - alpha (angle of attack) graph below you can see the relationship between alpha (angle of attack) and the lift coefficient (CL) for an asymmetric wing profile:
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Nijntje91: “As long as you keep referring to the static pressure on top of an airfoil as a vacuum I’m not able to take anything you claim seriously (whether true or not).”
I don’t recall anybody stating there is static pressure on top of the wings. I mentioned there is a “vacuum” created on top of the wing in quotes. Why did I write them in quotes? If you are an engineer, you know that there is no true “vacuum” in this universe. Even in deep space, there is radiation all over the place.
Perhaps you got confused since I mentioned “Statics” and “Dynamics” which are fundamental courses all engineers go through to study bodies at rest and bodies in motion. I studied both and it doesn’t hurt my feelings if you don’t believe me or the NASA links I’ve posted.
Have a nice day.
I am stating there is (a reduction of) static pressure on top of the wings. You are referring to it as a vacuum numerous times with and without quotations. Point being, its not a vacuum, far from a partial vacuum even and therefore plain wrong to call it as such. On top of the wing there will be a reduction in static pressure coupled with a higher pressure (in some conditions higher than ambient) below the wing this pressure difference is what creates lift.
Yes NASA is a credible source obviously but you are not pointing to scientific studies but rather articles aimed for the average person to understand, therefore its simplified. As I said, even pilot ATPL textbooks use a simplified version to explain how lift is created.
Interesting tangent, what does actually happen with the air density on top of the wing as compared to below the wing, assuming subsonic airflow? Pressure reduces on top of the wing, as a result temperature reduces. I dare to say the air density itself wouldn’t be all that different between the upper and lower surface of the wing hence why it is wrong to call it a vacuum. According to the continuity law the product of velocity x cross section remains constant, air particles resist compression (air is considered incompressible at sub sonic airspeeds) and therefore dynamic pressure increases with a reduction in static pressure (total pressure = constant), the amount (and therefore mass) of air particles in any given volume of air remains constant in my mind?
“You are referring to it as a vacuum numerous times with and without quotations.” - Nijntje91
" NASA is a credible source obviously but you are not pointing to scientific studies" - Nijntje91
Oh my bad, so sorry for not putting some of them in quotes. LOL.
Really? You mean NASA is publishing non-science backed documents on their site? That’s news to me…
FYI, a vacuum does not have to be a perfect vacuum.
The condition you are referring to is a perfect vacuum.
Anything below atmospheric pressure is a type of vacuum.
I was a long time operator in an electrical generating station.
Vacuum there is used to change steam back to water.
Lots of gages there to measure just how much vacuum we were drawing.
Problem is that you guys are only referring to the static pressure (which is lower on top of a wing), it does not tell the complete picture as the air density (mass per volume of air) is not that different between the upper and lower wing surface, the “mass flow” is different due to difference in airflow velocity between the wing upper and lower surface. I’m quite sure you can’t speak of a vacuum with regard to airfoils.
Edit: I thought it was an interesting discussion actually, ashame the topic has been closed…
“Problem is that you guys are only referring to the static pressure (which is lower on top of a wing)” - Nijntje91
Looks like you didn’t read the thread carefully and I don’t blame you. It’s quite long. You can state your argument here but I’m still comfortable with what I learned in engineering school and the science backed NASA article I posted.
The original question has been answered:
Doesn’t matter how the flame wars started here but I prefer to close this topic before someone try to go too far.
