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AIRFOIL DIAGRAMS

[JPG: bad and good textbook diagrams]

fig. 1
Incorrect diagram in grade K-6 textbooks. In the lefthand diagram, the air approaches the wing horizontally and also leaves the wing horizontally. This violates Newton's laws, since by F=ma there cannot be a lifting force unless air is accelerated downwards. The wing must deflect the horizontally-moving air downwards, as shown in the righthand diagram.






[GIF:smoke pulses travelling across 
airfoil]

fig. 2
Actual windtunnel photograph of air flowing around a wing. Pulsed smoke streams illustrate that the parcels of air which are divided by the leading edge DO NOT recombine at the trailing edge. Therefor the "wing shape" explanation of lifting force falls apart.

(This image was made by late Aerodynamicist Alexander Lippish, The German Me-163 creator, at Collins Radio windtunnels, USA, in 1953. It was published in his book. Alexander Lippish was an expert on smoke in windtunnels and his smoketrails were world-famous.)


[GIF:sequential images of a single smoke pulse]

fig. 3
A flim clip of a windtunnel experiment depicts a single "plane" of smoky air as it approaches a thin airfoil and is sliced into upper and lower portions. Note that this airfoil is NOT "curved above and flat below." Instead the upper and lower surfaces are approximately equal in length. Note that the air flowing above the wing quickly outraces the air flowing below. The air flowing above and below the wing never rejoin again. The real reason for the rapid flow of air above the wing is never explained in "Bernoulli"-based textbooks.

(This image is made by Aerodynamist Martin-Ingelman Sundberg at KTH windtunnels in 1992. Sundberg, who first saw syncronized smokepulses when visiting a windtunnel maker in USA 1962, made this smokepulse video to show how ICAO pilot education was wrong in explaining winglift with "airflow longer path over wing".)



[GIF: Lift created at zero attack?]

fig. 4
The confusing aspects of "airfoil shape" shown here can totally obscure the true nature of aerodynamic lift.

Many authors point out that asymmetrical airfoils give positive lift even if the angle of attack is zero. They offer this in order to prove that "wing shape", and not "attack angle" should be the explanation of choice. But there is a problem here. To determine if an airfoil is tilted, we cannot rely on construction of the geometrical attack angle. Geometrical attack angle is very sensitive to tiny bumps on the wing's leading edge, since tiny bumps can change where we draw the main 'chord.' Yet tiny bumps on the leading edge can have little effect on deflection of air, while the tilting of the airfoil shown in the fourth section can have an enormous effect upon the deflection of air and upon lifting force. SMALL FEATURES ON THE LEADING EDGE CAN CAUSE US TO TILT THE ENTIRE WING, WHILE WE DENY THAT WE HAVE DONE SO.

To determine the effective attack angle, we cannot trust the simple geometrical rules. To determine whether an asymmetrical wing is REALLY set to zero angle of attack, we instead must inspect the trailing edge of the airfoil to see if it directs the air downwards.


[JPG: Simulation of smoke pulses on SAAB aircraft wing]

fig. 5
Fluid simulation from Saab Aircraft shows phase lag between upper and lower air parcels after an airfoil has passed. Air travels much faster over the top of the airfoil, and then it never rejoins the air which has travelled below. Note that the airfoil has deflected the air downwards.

(This image is a Navier-Stokes 2D airflow calculation around a SAAB 340 wing made by Aerodynamist Krister Karling,SAAB Aerospace)


[GIF: Simulation of wing at three angles, showing airflow delay]

fig. 6
An air flow simulation from J. S. Denker's SEE HOW IT FLYS, in the Airfoils chapter.

Note that the asymmetrical (cambered) wing at the top of the diagram has been adjusted to produce zero lifting force. There is no "slip" or "phase delay" between upper and lower airflows. In the middle and bottom diagrams, the angle of attack is progressively increased, which also creates an increasing lifting force. The increasing angle of attack also increases the phase delay between upper and lower air flows.

So not only is the common "wingshape / Bernoulli" explanation wrong, but it even covers up some of the most interesting phenomena in airfoil physics: the fact that the time delay between upper and lower airflows is proportional to the attack angle and the lifting force!

Links to other photos

 





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