The definitive answer on Lift?

[Dave_Jackson]

There are differing reasons given for how an airfoil causes lift.

The attached Web page is an easy to read description of the airfoil, its shape, and how it creates lift. The printable version might make for interesting reading on a lazy Sunday.

http://jef.raskincenter.org/published/coanda_effect.html#_2

[Graviman]

Einstein's aerofoil made me chuckle - i'd never heard about that one...

http://jef.raskincenter.org/main/published/img/coanda_img/conda11.gif

From this site (http://www.mathpages.com/home/kmath258/kmath258.htm)


Incidentally, during the first world war when Albert Einstein was a professor in Berlin he wrote a paper in which he offered an explanation of aerodynamic lift. (This was in 1916, shortly after he completed the general theory of relativity.) He began “Where does the lift come from that allows airplanes and birds to fly?”, and went on to say he could not find even the most primitive answer in the published literature – which shows how little acquainted he was with the literature. In any case, Einstein decided the explanation for lift was the Bernoulli effect, and he sent a detailed proposal to a German aircraft company for a “humped wing, shaped like a cat’s back” which, he asserted, would provide maximum lift with minimum drag. As part of the effort to develop improved weapons for the German war effort, the company (Luftverkehrsgesellschaft, or LVG) actually constructed a prototype, which was flight tested by Paul Georg Erhardt, one of the pioneers of German aviation and head of the experimental department of LVG. Alas, the plane was a fiasco, barely able to get off the ground, and Erhardt considered himself lucky to have survived the test. Years later Einstein recalled the incident in a letter to Erhardt, saying “that is what can happen to a man who thinks a lot but reads little”.


Well, i found studying aerodynamic maths harder than special rel (but general rel is definately harder still). So, perhaps that little oversight should just be seen as a demonstration of his interest in the field of aeronautics. ;)

Mart

[Shawn Coyle]

At considerable risk of re-opening what must be old wounds (which one is older - 'how lift is created' or 'flying into wind and then turning downwind'?)
this website has by far the best explanation I've found -

http://www.av8n.com/how/htm/airfoils.html

[Graviman]

That's a useful site, Shawn. The main lesson that sticks in my mind about aerodynamics is that it is a complex area, where the best that can be done is to approximate the physics. The fact that computer intensive CFD is still producing design improvements demonstrates this.

The way i came to understand lift is:
1. Coanda effect causes air to follow aerofoil shape (boundary layer rotates air into surface).
2. Aerofoil shape in flow causes a circulation component around foil.
3. Circulation around foil causes lift force, as per Bernoulli equations.
4. Finite wing span allows unbounded tip vortices.
5. Tip vortices produce overall downwash across wing.
6. Overall downwash requires additional increase in AOA, and thus produces induced drag.
7. The wing circulation component and tip vortex are part of a horseshow vortex, producing a downwash within the vortex.

The maths can get very heavy, and often obscures the underlying principles.
Basically a wing throws air at the ground...

Mart