The search query is a symptom of a larger issue: expensive technical textbooks locking out hobbyists. However, Gudmundsson’s publisher has taken steps to make this accessible (eBook rentals, Kindle, and Google Play).

[PDF] General Aviation Aircraft Design by Snorri Gudmundsson

If you are a student at a university with an engineering library, you likely have free access via ScienceDirect. You can download a PDF chapter by chapter (which is technically the "full" text).