Speed is not a problem with RC helicopters
But something that can give them longer range and better efficiency is worth looking at.
I would guess the tiltrotor aircraft is probably more efficient in cruise flight. The helicopter probably provides greater flexibility in it’s operational range, far greater stability in slow speed flight, and is more practical for applications requiring VTOL. In the world of full-size the tilt-rotor V-22 has been one of the most expensive maintenance nightmares in the history of military aircraft, outside of the Apache helicopter. So practicality is a huge issue when looking at various designs.
The reason I brought up the induced flow issue is because the change in induced flow thru the main rotor is what makes the tail rotor become very efficient on a conventional heli in ETL. If it’s the same this should apply to a tail-mounted thruster prop as well. And might be the reason the X2 design achieved the same flight speed on less shaft power consumed per kg of aircraft weight vs the x3 design, despite the fact it is using coaxial rotors. I’m fairly convinced it would be possible in a RC design, with the proper mixing, to build one that uses the tail rotor as a conventional in hover and slow speed. And transistions to the tail rotor providing thrust in high speed flight. And do it with a single main rotor.
And there are other things that could be done to improve aerodynamic efficiency such as using a “speed” fuselage like the Daiblo in the video. Or using a ducted fan-type tail rotor aka the Kamov Ka-62. And using more efficient main rotor blade designs, which I have already played with. At the quite low disc loading our RC heli’s fly at, they are already quite efficient, very high-performance machines. I’m convinced it will take a combination of things that improve the aerodynamic efficiency of the airframe and main rotor beyond simply bolting on thrusters.