I am a former pilot and still love keeping my fingers in aviation, especially homebuilt aircraft. One company, Team Mini-Max offers their aircraft plans free of charge. You need to provide personal information, but I have never received anything from them without my asking.
Understand that these plans are to build an FAA-legal aircraft than a person can fly, but I thought maybe one of you might want to scale to 10% and have a great project for yourself or your children.
Free plans are downloaded HERE. They come in a Zipped file and contain 29 pdf’s of plans and manuals.