It's only illegal if they pull you over right as you cross the Potomac by the National Mall, start questioning you, search your car, and find a fully assembled 15" drone in the trunk, an antenna in the back seat, a 2-liter bottle of Mountain Dew Code Red on the passenger floorboard mostly full of deep orange liquid, and 40 empty food coloring bottles in the glove box.
"No, Officer, I was just planning on using the drone to film myself doing a challenge of chugging a soda with 5 tablespoons of cayenne pepper in it, on America's front lawn."