I am reading an aerodynamics textbook (Introduction to Aerodynamics by Anderson). I am still in the chapters that deal with subsonic aerodynamics, which seems to have a focus on life-sized manned aircraft. I am wondering: are there major differences in the consideration of aerodynamics when designing model aircraft as opposed to life-sized manned aircraft?
The largest difference is that in Reynolds number, which is the same issue that wind tunnel models have. The Reynolds number is linear in length, which for the wing is the chord length. So for example, a quarter-scale model will have a Reynolds number equal to one-forth that of the full-scale aircraft (in the same atmospheric conditions). The reason this matters is that airflow tends to transition from laminar to turbulent at a specific Reynolds number, so if one uses the same airfoil on the model as in the full-scale aircraft, then usually the performance will be different near stall (usually much worse). That is why reduced-scale models usually change to an airfoil that is designed for lower Reynolds numbers.
BTW, Intro to Aerodynamics by Anderson is excellent. That was my first textbook when I started aero engineering over 30 years ago.