as take-off weight, takeoff and landing speed and distance, minimum and maximum flight speed, flight range and height.
Also I choose engine parameters.
I calculate the forces and moments forces and moments acting on the plane using the formulas and plot graphs and diagrams.
I define configuration of plane and make 3D-model.
Results
What about my value to work I design airplanes.
The aircraft I have designed must be safe and comfortable for passengers and crew, it must comply with technical specification.
Only a few of the designed aircraft are implemented in life, but it is very important at the development stage to determine the viability of a new idea.