I read a lot of books about airplanes and flying. I also read books about World War 2, and how the airplane was further developed during that time. Learning history is almost as important as learning the math and science. It allows you to understand why we build airplanes. Of course, you'll need to study math and science to get the background to design and test aircraft, and become an engineer.
History is also important, for the reasons stated earlier.
It's also important to learn about, and understand human behavior and political thinking. Not only is this important in selling your program to the government, but it is also critical to getting people to work together to build and test your airplane. It is a team effort. Playing on a football, baseball or basketball team helps develop that sense of mutual effort. It can also be accomplished by working on a big project such as a play or a community service project.