Electric tail rotor; an alternative?
 

Chopjock, the RAF SAR Wessex which crashed into the lake in Wales with cadet passengers on board had a tail rotor dis-connectable coupling failure.
First of all you complained that a tail rotor drive system is too unreliable but now you want to make it more complicated and therefore by definition less reliable...what sort of logic is that?

Everybody relax, the above statement should make it perfectly clear that he's just trolling you.

There is a cure for Trolls.

Friends don't let friends troll.

Seems to me that an electric tail rotor is a rather good idea.

Chopjock should show us his design for the Fail Safe Helicopter....one that cannot have any kind of failure.....then explain how to sell them, maintain them, and operate them as he seems to have all the answers.

Only until someone forgets to switch it on, or the motor, the switch or the wiring fails...

Same is true of engines, fuel, hydraulics, gearboxes etc. hence the need for safety critical design.

You could have it on by default with the ability to switch it off if you want, like when in the cruise or during an un commanded full pedal emergency...

Think a switch is a bit simple, but there would be a number of means of control. Of course the main reason to move to electric is environmental, but it does offer other potential advantages.

An electric tail rotor could be switched off in the cruise and yaw control achieved by a simple aeroplane style rudder. It would save energy, reduce noise and help significantly with component life. Overall, I think this could be a winner

I think so too, powered by a generator run off the main engine(s).

Actually, why not the main rotor too? They do it in ships so why not aircraft?

Would take a lot of development though...... Elon Musk?

Almost instantaneous torque.... giro stabilised?

Perhaps start a new thread to discuss?

But you would need it on for takeoff and landing, which is where your argument began. Even if you have lost sight of that, I haven't.

Yes of course. I did say simply switch it off when not needed... (Obviously switch it back on again when required). A bit like you do with the gear.

Or, you could have a less complicated design turned by a simple and very reliable mechanical driveshaft and have an aerodynamic tailfin which allows the pitch of the blades to be reduced to near neutral in cruise flight.

But wait, someone already thought of that...

Or an even simpler design with direct drive electric motors and no gearboxes at all?

An electric motor would need to supply a lot of horsepower and it might be just as heavy as a gearbox. The aircraft would also need at least one large generator to supply power to it. Stopping a rotor blade in flight comes with its own set of aerodynamic problems.
But anything is possible, all engineering design is a compromise and let's not forget that most things in engineering have been tried already. There's nothing much simpler than a driveshaft turning a gearbox.

A single turbine generator with battery backup to provide "instantaneous" torque and sufficient reserve to get safely on the ground in the event of generator failure? Would probably be good to have a sprag clutch too.

I thought this was just a joke/trolling, but since it seems that some of you are serious:

I can see only one thing that speaks for an electric TR and that is that you wouldn't need pitch controlled blades. I'll mention a few things that come to mind that speaks against it, although I'm sure there are many more:

• I'm sure there's a lot of computer control in most modern helicopters already, but this would have to be entirely computer controlled to be at all flyable. That would open up a new can of worms when it comes to safety. I know that "fly-by-wire" is popular these days, but personally I only consider it "safe" as long as everybody is equipped with ejection seats.
• The reason they use electric motors on ships is first and foremost because it's difficult to get the mechanical energy to where you want it. Imagine the arrangement of driveshafts and gears that would be needed to transfer the power from the engine(s) to multiple azimuth thrusters placed on different locations, some probably near the bow. On trains they often do the same, but from what I understand that's for similar reasons (you want drive on as many wheels as possible because trains generally have bad traction) and because making gearboxes that can take the punishment over time is difficult. However you twist it, converting mechanical energy into electrical energy and then back again means that you'll both have a lot of extra potential points of failure and waste a significant part of the energy. Driveshafts and gearboxes waste energy too (through friction in bearings etc.), but considering how simple (geometrically) this is on a helicopter I'm convinced that using driveshafts and gearboxes is much more efficient.
• There's nothing inherently "environmental friendly" about electrical motors. It all depends on what form the energy is available in to start with. If you use a combustion engine to turn fuel into energy, you have mechanical energy as the source. What is considered "environmental unfriendly" is the combustion engine itself, converting the energy to electricity after the engine makes no sense (although some cars do this to ride the hype). If you have electricity as the power source using for example a battery or fuel cells, things are very different.
• As mentioned above, the only "gain" by using an electrical TR that I can see it that you wouldn't need pitch controlled blades. That said, changing the pitch is very quick and doesn't take a lot of power. The RPM is already there, ready to be used. A fixed pitch blade rotor would have to vary the RPM instead, and I believe this would be much too slow to be practical due to the inertia in the rotor. I guess that if you could make it by some revolutionary new hyped nano-materials that's stronger than steel but weighs nothing, the inertia problem could be overcome. I don't know of any such materials outside the world of hype though.

In addition I'd just like to mention that I believe Elon Musk's strongest asset is his ability to create hype and "impress people" enough to invest in him. I think time will reveal a different picture of him, and I certainly wouldn't like to fly anything designed or built by him or anyone like him.

Sorry as this seems to have drifted from the main thread.

The advantages of an electric tail rotor is that it can run at speeds independent of the main rotor. This allows the design to not be limited to one compromise. It, importantly, gives greater control over noise.

The assumption that a motor would be as heavy as a TGB, IGB, MGB tail pickoff and driveshaft is not one that I would make.

Great discussion chaps, but don't put your patent applications in just yet, think you've been beaten to it... If I'm not mistaken the team at Leonardo won an award for their work from the RAeS the other evening as well!

My point exactly ... the technology is already available. The concept of an electric tail rotor is not a reason to dismiss someone's statements.

I would have been surprised if someone wasn't working on it..... Boeing too? Airbus? Robinson?

Most things have already been tried as already mentioned in this thread. What would surprise me is if an electric tail rotor would be competitive when it comes to reliability and efficiency as long as the power plant is a combustion engine.

Here is a paper on the model shown in the youtube clip, although I didn't see much of interest in there: http://www.cleansky.eu/sites/default...3_-_eletad.pdf

It's obvious that an electrical TR could be made, it would probably be much cheaper to produce than the current mechanical solutions as well. What I seriously question is whether it would be "competitive" with regards to the criteria that matter, especially when it comes to safety. How would you do a autorotation with an electrical tail rotor?

Nadar
You do know you can autorotate with or without a working tail rotor right?

Nadar, there are efficiencies to be gained by the ability to vary tail rotor speed. It allows a designer to move the compromise points. Plus as I stated before the ability to tailor the noise footprint.

As to autorotation, how much torque is the tail rotor dealing?

That depends on if you want to turn (left or right) and keep the aircraft in balance.

Irrespective of how the turning rotor is actually powered, it still needs a blade pitch control system. Varying the speed of rotation isn't the full answer.

Accepted, but say as a ROM % of that in powered hover?

I also wonder why the assumption that an electric tail rotor wouldn't work in autorotation?

Fully agree with that! But having control of both is not a bad thing.

a) I'm not familiar with the term ROM%

b) Did anyone assume it wouldn't work in autorotation? I certainly didn't. However, the tail rotor would still absorb a lot of energy even in autorotation so presumably its electrical power generator would need to be driven by the main rotor transmission, or a very large capacity battery would be required if engine driven generators no longer provided electrical power.

Presumably you could get away from powering an electric tail rotor all the way down in autorotation until just before the flare when it's time to spool it back up again to assist a little later with the run on...

Surely you cannot be serious?

I would think battery. Battery technology is going forward in leaps and bounds so maybe not so big

ShyTorque, my apologies, ROM is Rough Order of Magnitude. I ask because this determines the power demand at a critical phase.
Nadar seems to have implied that auto with an ETR would be different to "conventional". I'm not sure why this would be the case, in auto I would presume a design where the MGB is still driving the generators. Question for my own interest, how many helicopters out there revert to battery when in autorotation and how many retain electrical generation?

note: during "conventional" autorotation, the tail rotor is powered by the MGB.

That's what you would do with the gear isn't it? OK just kidding..

OMG there are dozens of chop jocks now, invading this thread!
What happened to the original thread FFS?
Electric TR's. Where do these people come from? :sad:

I had a small RC helicopter with an electric tail rotor once. Worked fine until it sparked a few times and stop dead.
I dont think this helps any. Just thought I would share
playing it safe since the mods deleted my last post

How much did you pay for it? What kind of certification did you get with it?