Introductory Fluid Mechanics L21 p5 - Lift Force

[@Juefriki]

Thank you so much sir, you have no idea how much of a help you've been during this quarantine times where I still had to study and do exams at University, I passed thanks to you!

[@Lichugunti]

Thank you a lor sir Hugo, this series definetly has awakened a lot of interest in fluid mechanics in me. Your overview and expalantions is the best source i ever found for this course.

[@samankhajehzadeh4445]

Thank you very much for your contribution to the world Ron.

[@marshallm.7421]

Completed the whole series Hail Lord Hugo! Thanks a lot

[@AK-gg5nh]

Thank you! Excellent course as usual.

[@Observ45er]

I just ran across this video and see this is very misleading. .. Neither Bernoulli's Principle. nor Equation says anything about the speed/velocity relative to a surface. .. This kind of explanation runs afoul of physics fundamentals, because if you measure these velocities relative to the ground (moving wing), as a wing goes by, the air under the wing is actually faster than the upper air. Yet, the air above the wing is accelerated more than below. Bernoulli is about changes in velocity which is acceleration. . Velocity is dependent upon the observer's inertial frame of reference, whereas, acceleration is not. From the fixed air reference, that lower air is accelerated forward for a longer time (starting in the upwash before the wing arrives), reaching a higher forward speed. It also winds up far from its starting point in the direction of flight. The air above is also first accelerated forward in the upwash ahead of the wing, but accelerated rearward, completely REVERSING DIRECTION and travels in the opposite direction of flight. It is accelerated much more (than the lower air because of the horizontal Pressure Gradient), but finishes at a lower REARWARD velocity - and winds up close to where it started before the wing arrived. This is from measured data. This is not speculation from trying to apply physics. . I fail to see how people don't understand this actual data and the reasons. . See Fig. 7 here: rxesywwbdscllwpn.quora.com/

[@mikhail8853]

finished the whole series!

[@SteveNoskowicz]

There are two major errors in this starting around time 10:30: .. - Bernoulli's Equation is for two locations along a *single flow*, not two independent flows. . - Bernoulli says NOTING about flow relative to a surface or anything else, only between two locations along a SINGLE flow. .. Measured data shows that relative to the air/ground, the lower flow is accelerated to a higher speed than the upper air. .. YES! The lower air is faster!! - relative to the air mass/ground.!!... .. On the other hand, the upper flow goes from moving in the direction of flight AHEAD of the wing (upwash) to completely stopping and reversing direction as the wing passes under it; then traveling in the OPPOSITE direction of flight (relative to the ground/air), but at a LOWER rearward speed than the lower air's forward speed. .. Thus, the lower air is moving FASTER than the upper air relative to the stationary air mass. That is actual data on a wing. .. Bernoulli is about ACCELERATION, *NOT* speed.

[@tahy59]

I pay thousands of dollars for tuition each year and end up coming to watch youtube to learn

[@PDattaTV]

Thanks, Prof.

[@antiquarian1773]

do you even lift bro

[@mokhtarjamal6096]

Thank you so much! it helped alot

[@karankantyadav4400]

sir please make more videos on mechanical engineering subjects.

[@tuethich1429]

Hi, I have a question. we also know at stall point: Lift force begin to decrease and Vup approximate zero .But we have Bernoulli equation Pup -Pdown=1/2 * rho (Vdown ^2-Vup^2). If Vup ->0 , P will increase. it means that at stall point Lift force does not decrease. Could you please explain it to me?

[@SteveNoskowicz]

You cannot use Bernoulli on two different flows. It is for two locations along a single flow. Therefore it deals with ACCELERATION of the flow. It does not deal with speed, nor does it say anything about speed relative to any surface. . . . . . . . There are two major errors in this starting around time 10:30: .. - Bernoulli's Equation is for two locations along a *single flow*, not two independent flows. . - Bernoulli says NOTING about flow relative to a surface or anything else, only between two locations along a SINGLE flow. .. Measured data shows that relative to the air/ground, the lower flow is accelerated to a higher speed than the upper air. .. YES! The lower air is faster!! - relative to the air mass/ground.!!... .. On the other hand, the upper flow goes from moving in the direction of flight AHEAD of the wing (upwash) to completely stopping and reversing direction as the wing passes under it; then traveling in the OPPOSITE direction of flight (relative to the ground/air), but at a LOWER rearward speed than the lower air's forward speed. .. Thus, the lower air is moving FASTER than the upper air relative to the stationary air mass. That is actual data on a wing. .. Bernoulli is about ACCELERATION, NOT speed.

[@DzahierulAliemy]

Thank you sir.

[@Observ45er]

I just ran across this video and see this is very misleading. .. Neither Bernoulli's Principle. nor Equation says anything about the speed/velocity relative to a surface. .. This kind of explanation runs afoul of physics fundamentals, because if you measure these velocities relative to the ground (moving wing), as a wing goes by, the air under the wing is actually faster than the upper air. Yet, the air above the wing is accelerated more than below. Bernoulli is about changes in velocity which is acceleration. . Velocity is dependent upon the observer's inertial frame of reference, whereas, acceleration is not. From the fixed air reference, that lower air is accelerated forward for a longer time (starting in the upwash before the wing arrives), reaching a higher forward speed. It also winds up far from its starting point in the direction of flight. The air above is also first accelerated forward in the upwash ahead of the wing, but accelerated rearward, completely REVERSING DIRECTION and travels in the opposite direction of flight. It is accelerated much more (than the lower air because of the horizontal Pressure Gradient), but finishes at a lower REARWARD velocity - and winds up close to where it started before the wing arrived. This is from measured data. This is not speculation from trying to apply physics. . I fail to see how people don't understand this actual data and the reasons. . See Fig. 7 here: rxesywwbdscllwpn.quora.com/

[@vg23air]

calm down sheldon, have a cookie

[@Observ45er]

@@vg23air Says the KZbin-made expert. . .

[@vg23air]

@@Observ45er exactly

[@Observ45er]

@@vg23air Do you have anything intelligent to say?

[@vlatkopopovski2685]

The authors have two wrong scientific approaches: researching the creation of Lift force and Low pressure at upper side of the wing, relative to the ground surface and Earth. I explain the aerodynamic cavitation and existence of Lee side aerocavern, and creation of Aerodynamic force.

[@vlatkopopovski2685]

The force object receives is always normal to the contact surface and air pressure always acts normal to the surface of the body. This has long been well known, and I don't know why in flight theories and aerodynamics books this is (mostly) omitted.