how do they make airplane designs?

Used to be a lot harder...but now a days they just use various airplane design software like Solidworks, RC Cad, Autocad ,etc, NASA. Some are even free

http://www.rccad.com/

http://www.simviation.com/fsdesign_aircraft1.htm

http://www.grc.nasa.gov/WWW/K-12/freesoftware_page...

http://www.google.com/#hl=en&source=hp&q=airplane+...

Software figures out airfoil shapes to wings and tells you how long the fuselage has to be in proportion to the wings. It figures out how much engine power you need for what ever your load is.

You can change the shape of a section of the aircraft and the design software will make adjustments to the wingspan and power requirements and so forth.

You can design it and "fly" it in a simulated wind tunnel to see how it handles or any problems.

But bottom line, you have to know aerodynamics well to know where to start drawing, even on a screen. You have to know pretty closely what payload (people + luggage) you want to carry. In other words, you can't put 400 people in an airplane that looks like a fighter jet.

The software is nice because it plots the lines for you and does the math required to make complex curves and airflow equations. But you still have to know aerodynamics, otherwise it is trial and error forever trying to get a flying ability (and landing)

1

The purpose of the plane

dry Weight load and max load limit

Fuel load.

Size needed

lift needed

drag

power needed

design

cost.