Airliners.net

Listed advantages
* Can turn them off while on the ground, saving fuel and noise, and increasing safety
* Redundancy, in case of failure or battle damage
* Much quieter in the air
* Fewer mechanical components
* They can be controlled more precisely, for better/quicker handling
* Fuel efficacy. They cost less to run




https://www.flightglobal.com/helicopter ... 76.article

There is alot of BS in that article. As someone who used to regularly fly RC heli's with driven tails and electric tails, I can say that: Electric tails have slower reaction times, they will more subject to failure (which is why you seen 4 in that full scale aircraft), and It doesn't change the efficiency as much as they let on (on the rc scale you might get 30 more seconds of flight time for the same size heli).

For those who think these things will differ on full scale, remember what hobby is responsible for the urban transport developments of the past 5 years. Everything electric has gotten the vast majority of it's innovation from RC.

426Shadow wrote:

There is alot of BS in that article. As someone who used to regularly fly RC heli's with driven tails and electric tails, I can say that: Electric tails have slower reaction times, they will more subject to failure (which is why you seen 4 in that full scale aircraft), and It doesn't change the efficiency as much as they let on (on the rc scale you might get 30 more seconds of flight time for the same size heli).

For those who think these things will differ on full scale, remember what hobby is responsible for the urban transport developments of the past 5 years. Everything electric has gotten the vast majority of it's innovation from RC.

I’m skeptical that a full sized helicopter will mirror the experiences in RC. RC have provided a lot of improvements where no one else was doing it. I suspect that the innovation will start to increasingly come from the top down.

snasteve wrote:

I’m skeptical that a full sized helicopter will mirror the experiences in RC. RC have provided a lot of improvements where no one else was doing it. I suspect that the innovation will start to increasingly come from the top down.

Look at it this way. Power to weight ratio goes to RC, acceleration in all directions goes to RC, Inertia goes to full scale but that isn't what you want when controlling thrust becomes a factor of rpm changes so again RC wins in fine controls. The only way the electric tail rotor will fully succeed in full scale is if the tail is electric driven but the pitch is still controllable and at that point you are better off just driving the tail as a typical helicopter would.

426Shadow wrote:

snasteve wrote:

I’m skeptical that a full sized helicopter will mirror the experiences in RC. RC have provided a lot of improvements where no one else was doing it. I suspect that the innovation will start to increasingly come from the top down.

Look at it this way. Power to weight ratio goes to RC, acceleration in all directions goes to RC, Inertia goes to full scale but that isn't what you want when controlling thrust becomes a factor of rpm changes so again RC wins in fine controls. The only way the electric tail rotor will fully succeed in full scale is if the tail is electric driven but the pitch is still controllable and at that point you are better off just driving the tail as a typical helicopter would.

Not really obvious. As far as I understand, normal tail rotor is driven directly by turbine, with torque transferred through a long shaft and some gearboxes - to turn rotation axis 90 deg, if nothing else.
Replacing that mechanics with electric power transfer may be beneficial for things like weight and maintenance, if nothing else. I am not saying it is - but dismissing things upfront is not obvious as well.

At least one of the co-axial copters competing for FARA has the rear prop (forward thrust) electrically powered. Now I cannot find the article. Possibly the Raider or Raider X or possibly the SB>1 Defiant.

426Shadow wrote:

snasteve wrote:

I’m skeptical that a full sized helicopter will mirror the experiences in RC. RC have provided a lot of improvements where no one else was doing it. I suspect that the innovation will start to increasingly come from the top down.

Look at it this way. Power to weight ratio goes to RC, acceleration in all directions goes to RC, Inertia goes to full scale but that isn't what you want when controlling thrust becomes a factor of rpm changes so again RC wins in fine controls. The only way the electric tail rotor will fully succeed in full scale is if the tail is electric driven but the pitch is still controllable and at that point you are better off just driving the tail as a typical helicopter would.

Well, we're watching video of a full scale helicopter flying with it.

As some points mentioned by others, this does reduce mechanical complexity:
- No need for a gear set and output from the main gearbox. The gearbox could likely be made smaller and lighter.
- no gearbox at the tail.
- No driveshaft along the tailboom needing bearing supports, flex plates. Also the tailboom geometry would have more freedom as you don't need to find a way to run a shaft along it. Or cover the shaft.
- many small/medium helicopters still use control rods to control the pitch of the tail rotor. This gets replaced by a harness. Simpler & lighter once again
- FBW control only needs to speedup or slowdown one or multiple fans, is no longer dependent on the power setting of the engines.
- Redundancy: if one fan fails, there is still authority available.
- Likely less maintenance, especially inspection

reduced weight/complexity should lead to lower costs as well

Safety:

- On the ground you can keep the engine running at ground idle with the main rotor still turning, but have the tail rotor completely stopped.

I think this will work out long term.

basspaul wrote:

- No need for a gear set and output from the main gearbox. The gearbox could likely be made smaller and lighter.
- no gearbox at the tail.
- No driveshaft along the tailboom needing bearing supports, flex plates. Also the tailboom geometry would have more freedom as you don't need to find a way to run a shaft along it. Or cover the shaft.

The only point that doesn't address is autorotation
,

zeke wrote:

basspaul wrote:

- No need for a gear set and output from the main gearbox. The gearbox could likely be made smaller and lighter.
- no gearbox at the tail.
- No driveshaft along the tailboom needing bearing supports, flex plates. Also the tailboom geometry would have more freedom as you don't need to find a way to run a shaft along it. Or cover the shaft.

The only point that doesn't address is autorotation
,

The FBW would need to have functionality for this, of course. But I doubt Bell hasn't thought about it.

basspaul wrote:

The FBW would need to have functionality for this, of course. But I doubt Bell hasn't thought about it.

The energy to drive the tail rotor comes from the autorotation of the main rotor through the gearbox. Without an engine, what would power electric motors for an autorotation ?

zeke wrote:

basspaul wrote:

The FBW would need to have functionality for this, of course. But I doubt Bell hasn't thought about it.

The energy to drive the tail rotor comes from the autorotation of the main rotor through the gearbox. Without an engine, what would power electric motors for an autorotation ?

The battery is still available, possibly a dedicated one for it would be needed for certification.

Time will see if this is a success, but it's certainly interesting.

zeke wrote:

basspaul wrote:

The FBW would need to have functionality for this, of course. But I doubt Bell hasn't thought about it.

The energy to drive the tail rotor comes from the autorotation of the main rotor through the gearbox. Without an engine, what would power electric motors for an autorotation ?

A good question. As far as I understand, helicopters don't have a clutch/disconnect between trubine(s) and main rotor. So autorotation should still rotate entire powertrain, probably including generator(s).
A follow-up question is generator(s) failure, though, and how that compares to probability of tailshaft/gearbox(es) failure.
Battery may or may not have enough capacity for meaningful backup time.