Background: At Hamburg University of Applied Sciences an EXCEL/VBA tool called PreSTo - Preliminary Sizing Tool was developed. PreSTo is divided into several modules that deal with every step in aircraft design: preliminary sizing (discussed here), cabin and fuselage, wing, high lift, empennage, landing gear, mass and CG, drag and DOC calculation. --- The Problem: Design parameters (aspect ratio, maximum lift coefficients, ...) are the engineer's choice. Especially for inexperienced students it is difficult to choose all required design parameters. The best combination of design parameters leading to a good design needs to be found. --- The Solution: To formally optimize the aircraft design parameters and present these optimized values to the student as a starting point. To combine formal optimization with subsequent interactive and experience driven aircraft design.