The reason we don't see retreating blade stall on models is our relatively slow foward speeds compared to full scale. Not much chance of stalling a blade at our 70-80 mph speeds. Anyone remember the Cheyenne heli that the army never built? They managed to relieve that trouble by slowing the main rotor to a comparative crawl and let the stubby wings take over some of the load and used a pusher propeller configuration if memory serves me correct? Kind of resembled a gyrocopter with the rotor disk almost flat going 268 mph. Pretty impressive but never got produced. Ground resonance on the other hand is one of those things that dosen't seem to translate to smaller scale by virtue I would guess of our incredibely rigid airframes and rotor blades. In full scale vibration would kill the airframes if they were half as rigid as our models. Same thing with the flapping blades vs solid feathering spindles. A full scale Bell looks kind of loosy goosey when you compare it to our rigid rotor setups in models. I understand not all are alike, but most of the popular models are this way.