how engineers design the airfoil?

Question

what factors are necessay?

Answer 1

The various terms related to airfoils are defined below:
1. The mean camber line is a line drawn half way between the upper and lower surfaces.
2. The chord line is a straight line connecting the leading and trailing edges of the airfoil, at the ends of the mean camber line.
3. The chord is the length of the chord line and is the characteristic dimension of the airfoil section
4. The maximum thickness and the location of maximum thickness are expressed as a percentage of the chord

http://en.wikipedia.org/wiki/Airfoil#Thin_Airfoil_Theory

Answer 2

These days, airfoils are designed using computational fluid dynamics programs running on super computers. The idea is to modelize the airflow around the wing for the various phase of the flight, taking into account the perturbations brought by the presence of other elements of the aircraft, like engine nacelles, control surfaces, the fuselage itself, etc.
Since modern airliners fly at transonic speed, it is essential to minimize the shock wave coming from the airflow of the upper surface slowing down through the speed of sound (the airflow on the upper surface speeds up, this is what cause the pressure drop that creates lift), the gentler the deceleration, the less energy is absorbed by the shock wave.
Therefore, modern airfoils aim at keeping the airflow on the upper surface to a speed that is as constant as possible, and to very progressively allow it to slow down towards the trailing edge. The contours have to be very accurately designed, and a modern wing will have airfoil shape that change continuously from root to tip.

Answer 3

Air foil designed for lifting the plane that according with air velocity and geometric wing so the area up wing more wider than down wing that the air pressure in the down wing bigger than up wing

Answer 4

Here is a fun one to use.

http://www.lerc.nasa.gov/WWW/K-12/FoilSim/index.html

Answer 5

No joke. They studied birds.