Although experiments with rotary winged aircraft may be traced back to Leonardo da Vinci, successful flights were not achieved until the 1930s, and it was not until 1941 that the first practical, full size helicopter was built by lgor Sikorsky. Model enthusiasts are notably quick to emulate full-size aviation achievements, but were not as successful with rotary wing aircraft, and it was not until 1968 that the first fully controllable R/C model helicopter appeared, built by Dr. Dieter Schluter of West Germany.
Bigger engines require more fuel and more weight! Increasing the angle of the rotor blades in the airflow produces more lift, up to a point but this also increases the drag of the blade, which now requires more power to move it at the required speed. All problems were eventually overcome and the fully controllable R/C model helicopter had arrived.
There were, however, no short cuts in its development: engines, drive gears, rotor blades, control methods, etc all had to follow a similar design to full-size helicopter and be built to the same exacting standards or perhaps closer to the mechanism design of the full-size helicopter.
So how difficult is the model helicopter to control in fight? Well, it has been described as similar to balancing a steel ball on a knife edge whale riding a bicycle! more on that when you visit Model Aeronautics for Dodos by following the link in my resource box.