Hoo boy, lots of things going on in this thread.
Q- I attended a seminar a few months back in which the Wright Brothers' wind tunnel and drag and lift force balances were examined. The goal was to build exact replicas of the balances and test them in a modern wind tunnel. I think it took something like a team of aero and mech engineers a month to build the balances even with pictures and plans of the original. Not only that, but original numbers the Wrights recorded for the drag over a flat plate were accurate to I believe the hundreth's position. Plus, the lady brought along the actual flat plate and cambered #12 airfoil the Wright Brothers' used in their tests. It was like looking at a Holy Grail of sorts.
What requires engineers is designing an aircraft with certain flight characteristics. Long, thin wings are good for long-distance steady flight, whereas short, thick wings are good for maneuverability. Swept wings are good for speed, etc. etc. Or, in the case of the stealth aircraft (ex: F-117), designing systems that make a plane that would otherwise be completely unstable for flight stable. You think the Wright brothers thought about things like washout and swept wings when trying to get up in the air?
Nebula- What requires engineers and physicists is the need to understand what is going on with a aircraft and try to resolve the aerodynamic issues with all the other problems like structural, payload, etc. Yes, long thin wings give low drag. But how long do you make them? What about the internal structure? Where's the fuel tank and how does that affect the shape, what about control surfaces, high lift devices, a hundred other variables that all need balancing. You can't just say, we need an airplane that goes fast, so let's use swept wings. The X-15 did not use highly swept wings; short stubby ones were found to give all the lift needed with the least drag.
The role of the engineer is to take a set of requirements, or mission parameters, and to design an airplane to fit them, not the other way around. On other words, the shape of the F-117 did not dictate stealth, the need for stealth dictated the shape of the airframe. To do this, the engineer needs to understand everything that can be expected to happen to the aircraft, and he needs to be able to balance hundreds of competiting interests against each other until he finally arrives at something that he thinks is the best suited to fit the mission parameters.
Yes, you're right, you can reduce aerodynamics to four fundamental forces: lift, drag, thrust and weight. And if you want to, you can design a R/C trainer pretty easy. Anyone can with about two hours of research. But that's only because you are making an assumption to ignore basically everything that's happening to that aircraft except lift, thrust, and weight. And that's okay, because no human life is involved, or very much money, nor is any advanced or experimental concept being tested, plus we basically know everything about that particular flight regime. But the moment you decide to try something that is even a little bit new, that's when you start to become an engineer.
By the way, the Wright Brothers did think about washout. They even used it in the Flyer, in the form of controllable wing warping to get roll control. Anyways, enough with the essay assignment.