A mechanical tail rotor runs at constant speed whatever the thrust requirement. At zero thrust, it’s still eating a fair amount of power.
Oskar's fixed pitch, variable speed electric drive eats zero power at zero thrust. That’s the difference. A constant speed, variable pitch electric drive would be less efficient than a mechanical drive.
Group,
There is a big difference between someone that just works in helicopter theory some of the time and someone that actually is a Commercial helicopter pilot with over 5000 hours of flight time and designed, built, tested, and manufactured a respectable number of helicopters as well as has experienced about every emergency and nonemergency situation in a multitude of different types of helicopters.
Theories have their place, but actual real-world practicality will win the day, every time. Don't get me wrong. I encourage people to experiment, but there are norms that in the end, must be met.
1. The fact is, I can comfortably hold a properly designed tail rotor and gearbox in one hand, as well as the aluminum tail rotor shaft and bearings. It is only a few pounds. It is simple and reliable and is not affected by electronic interference or shorts.
2. The power loss from bearings and gears in a properly designed shaft-driven tail rotor system is 3% or less, not significant.
3. The batteries or power generation system, as well as the props, motors, controllers, and control input modules that would be necessary to fly 3.5 to 4 hours would be far heavier than a tail rotor system driven by a shaft.
4. For the helicopter to maintain flight stability, it will still need the proper size of horizontal and vertical stabilizers, so there is no saving of weight by being able to discard them in lue of an electrical system. With the proper size horizontal stabilizer, you only require 5% or less of the total power being generated for cruise flight speeds using a shaft-driven antitorque system. Without the horizontal stabilizer, you will still require 10% or more of total power being generated for antitorque.
5. With a battery-powered tail rotor system, you may indeed use 100% of the total power generated for lift in the main rotor system. However, to carry around enough batteries to last 3.5 to 4 hours of flight time, every time you fly and to meet every condition would require that 15% power you thought you would save just to left the extra battery weight. Sure, flying more in forward-flight would save battery power so you need less battery weight, but now you have limited the very thing that was unique to helicopters in the first place... Indefinite hover time.
5. With an electric-powered tail rotor system, now you take a standard refueling time of fewer than 5 minutes and turn it into perhaps hours. That alone is not practical, plus now you have to have an extension cord and charger with you on the helicopter, which also adds to the overall weight, or you can't freely fly from airport to airport, again not practical.
6. More importantly than any other characteristic of helicopter performance is how well it handles in an emergency, like a loss of power situation. In the event of power loss, you need to enter autorotation. With a shaft-driven tail rotor system, the main rotor blades are powering the tail rotor, and you have an instant reversal of thrust available to yaw the aircraft in the directions required without any hesitations, while the blades continue turning the same direction in rotation. With the electric tail rotor driven system, you would have to rely on the motors and propellers being able to overcome inertia, stop immediately, build back RPM (making more inertia to overcome) and turn the other direction every time yaw needs to be corrected, which may need to be done several times a second during the emergency. Your propellers are designed to thrust efficiently in one direction, but not the other, therefore yaw control when you need it the "fastest and mostest" will not be fully available.
Therefore, after taking a logical approach after looking over the effects, drawbacks, and characteristics of each mode of operation, it becomes clear that an electrically powered tail rotor system has no real advantages over the traditional time-proven shaft driven tail rotor, and in fact has disadvantages.