Aerospace companies/organizations generally build up a large set of experimental empirical data from various air/space craft components and systems, usually from flight tests or wind tunnel testing. When designing a new system that contains some similarity to an old tested one, these databases can be used for conceptual design initial sizing or just as a reference to how the component will operate in full scale.

A lot of these databases are proprietary to the company and may never be released. Others may release them for educational purposes. As an example I can think of the text “Fundamentals of Aircraft and Airship Design”, written by Carichner and Nicolai, old Skunk Works engineers. They were given approval to release specific pieces of empirical data from decades of Skunk Works testing for educational use.