Originally Posted by
Procrastinus
Lift comes from deflecting air downwards - that's my simple understanding!!
chik'n-egg
thin foil theory works by the deflection.
bound vortex results in a defection
bernouilli keeps the FAA happy, even if it is rong as often as it is Wright.
Kutta-Joukowski theorem within the framework of inviscid potential flow theory is pretty good, needs add ons in more complex conditions.
backspin, slice, topspin...slats..., flaps... etc, Bernoulli falls short, as it does for unvented spoiler effects, (why there is usually a gap at the base of the spoiler or vent holes or slots...)
Zhukovsky's elegant conformal transformation is nice 'n eezy;
morphing circulation theory into lifting line gives good results, still a lot easier than a RANS/URANS/DES/LES numerical solution of lift, which will look a fair bit like any of these, but will function in low speed, and high speed cases, and will model stuff like compressibility, supercritical design fairly well, although it can be said that a lot of pretty simple potential flow code will give a fair approximation of pressure and velocity distributions. Dreese's code, Ilon Kroo's PANDA etc were nice n easy and give good results. Doc Pats Multi surf and visual foil is a bit more advanced, but it would be nice to have more cells, it is a step up from javafoil, which is surprisingly good. Going to Ansys, MSC, Simscale, Siemens, Dassault etc gives pretty good outcomes and other than needing a large pot of cash to use the code and a similar size bucket of loot for the core time, gives answers that apart from frequently having artefacts avoids answering the question of Bernoulli or newtonian reactions at play.
Whatever works and explains what you are playing with, alternatively, whatever the FAA says.
What will normally ness with the mind of the observer is that what happens at the trailing edge of a foil is as important or more to what happens at the front, and it affects the flow at the front of the foil in real time, and is not "spooky action at a distance", but arises due to the fact that one of the things above is not like the other, one of these is just not the same... etc...
