Electric tail rotor; an alternative?

[chopjock]

I think they are all doing it wrong. It would be much simpler if there was an electric motor out on the boom and simply switch it off when not needed...

[ShyTorque]

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?

[Nadar]

I think they are all doing it wrong. It would be much simpler if there was an electric motor out on the boom and simply switch it off when not needed...


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

[SASless]

There is a cure for Trolls.

Friends don't let friends troll.

[Twist & Shout]

Trolling makes sarcasm look like genius.
Only practiced by the wittless.

[dClbydalpha]

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

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

[SASless]

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.

[ShyTorque]

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

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

[dClbydalpha]

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.

[chopjock]

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

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...

[dClbydalpha]

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.

[jellycopter]

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

[gevans35]

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

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?

[gevans35]

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...

Almost instantaneous torque.... giro stabilised?

Perhaps start a new thread to discuss?

[ShyTorque]

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...

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.

[chopjock]

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.

[ShyTorque]

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

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...

[gevans35]

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?

[ShyTorque]

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.

[gevans35]

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.

[Nadar]

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?

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.

[dClbydalpha]

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.

[PPRuNeUser0211]

YouTube linky: electric tail rotor

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!

[dClbydalpha]

YouTube linky: electric tail rotor (https://youtu.be/-LIH_6581QE)

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.

[gevans35]

YouTube linky: electric tail rotor (https://youtu.be/-LIH_6581QE)

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!

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

[Nadar]

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/files/documents/grc_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?

[chopjock]

Nadar
How would you do a autorotation with an electrical tail rotor?

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

[dClbydalpha]

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?

[ShyTorque]

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.

[dClbydalpha]

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

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?

[dClbydalpha]

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.

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

[ShyTorque]

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?

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.

[chopjock]

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...

[ShyTorque]

Surely you cannot be serious?

[gevans35]

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

[dClbydalpha]

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.

[chopjock]

Surely you cannot be serious?

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

[Thomas coupling]

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:

[GrayHorizonsHeli]

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

[dClbydalpha]

I had a small RC helicopter with an electric tail rotor once. Worked fine until it sparked a few times and stop dead.


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

[gevans35]

Some interesting reading.

Overview of NASA Electrified Aircraft Propulsion Research for Large Subsonic Transports.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20180000361.pdf

GRC3: Integration of Innovative Electrical Systems for Rotorcraft (pages 12 & 13)
http://cleansky.eu/sites/default/files/documents/publishable_summary_-_grc_periodic_report_2015.pdf

But are helicopters the future?
http://evtol.news

Upcoming lecture by Nick Lappos.
https://vtol.org/news/lappos-selected-as-2019-nikolsky-lecturer
.

[tigerfish]

Sadly TC, as so often is the case, this forum has been invaded by many armchair flyers who have no idea about actual operational Air operations . Best leave to their playtime air ops games!

TF

[dClbydalpha]

Sadly TC, as so often is the case, this forum has been invaded by many armchair flyers who have no idea about actual operational Air operations . Best leave to their playtime air ops games!

TF
Or those who have no idea how these magnificent flying machines are designed or certified.

[Nadar]

Just to make it clear, my comment about autorotation was with the assumption that the generator would then be dead, and putting enough heavy and possibly explosive batteries in a helicopter to have that as a backup doesn't seem remotely realistic to me. I didn't think of that the gearbox could drive the generator, which I realize now would be the only sensible thing to do.

The autorotation comment was just meant as an example of new problems that would arise with such a "hybrid" system. I still think the main points are that I can't imagine that such a system as a total would be as reliable as a driveshaft and a gearbox, and that it would be much less efficient. I could be wrong, but I still have a hard time seriously thinking of electrifying the TR to reduce the risk of failure.

[RVDT]

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

Very true except the levels of controllability will be different - there is a certain amount of drag within the drivetrain and auxiliary systems (HYD pumps, cooling fans, sometimes generators or alternators etc ) that are driven that will induce the cab to catch up with the main rotor. Also noticeable when you flare to prior to touchdown. Without a TR it will be a bit messy.

[Robbiee]

https://youtu.be/-05wY41ht1s

[cattletruck]

Suppose you have to hover next to a cliff or hangar with some serious crosswind. Consider the following:
Is a fixed pitch variable speed electric motor dynamic enough to hold the tail steady? What about tail rotor rpm wind down when the gusts abate, do you need tail rotor brakes?
Perhaps variable pitch constant speed is the better electric option of the two. Now how do you manage power available on two different systems. Will the electric motor run out of puff while the coal burners are just warming up? Are bigger electric motors needed along with all the penalties that introduces?

Some of us like to roll the helicopter in tiny amounts just using the pedals, will the electric fan at the back take this away from us?

Now if you are gunna stick an electric fan at the back at least allow it to pivot around 90 degrees to provide forward thrust.

[GrayHorizonsHeli]

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


I overpayed obviously. I thought Walmart had the best price, but then I found it at Best Buy for less. #rippedoff
there was a sticker inside the airframe. Mostly in Chinese that had Insp.45 on it. I assume this was the manufacturer QA inspector. I bet he knows his stuff.
the things I learned on this thing would shame Chuck Aaron and his 105. He's got nothing on me.

[gevans35]

First they ignore you, then they laugh at you, then they fight you, then you win.

Mahatma Gandhi

[timprice]

I like this idea, main problem I can see is the tail rotor will have to keep spinning in flight otherwise there could be damage to the tail rotor blades or mechanism during start up and slow down.
Perhaps a ducted one would be superior????:rolleyes:

[chopjock]

I like this idea, main problem I can see is the tail rotor will have to keep spinning in flight otherwise there could be damage to the tail rotor blades or mechanism during start up and slow down.
Perhaps a ducted one would be superior????:rolleyes:

Could be designed to windmill as a generator perhaps?

[Hughes500]

if these things that might appear ludicrous aren't looked at then nothing goes forward. I remember my basic rotary wing instructor at Wallop told me ( he started as a Sycamore pilot ) that they thought it was impossible to put a gas turbine in a helicopter when he started in the 1950's. That idea was obviously a non starter as well

[Pilot DAR]

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.

I'd like to see the weights. I'm imagining a pretty heavy motor, compared to the present drivetrain, plus the need for either a heavy generator, or batteries, and some heavy wire. By placing the heavy motor at the end of the tailboom, the tailboom will have to be made much more strong, thus heavy itself, and that will create an undesirable mass distribution for the whole fuselage. The available torque of a motor to drive an effective tail rotor would have to be immense to accelerate the tail rotor RPM commensurate with the pilot's possible sudden application of lots of pedal. For aircraft which carry batteries as a power source to replace fuel, a disadvantage is that when the batteries become discharged, they don't weigh any less. The component and control for electric motors would have to satisfy a evaluation of reliability to the standards of 27/29.1301 and 1309, which is daunting.

I am a helicopter pilot, and have undertaken design studies for an electric powered Cessna 172 STC (program may continue) and an electric powered R22 (program will not continue). Electric power in aviation has a bright future, in a rather narrow band of application, which I opine does not include helicopters in the foreseeable future.

[dClbydalpha]

Let's not get too ambitious. Simply replacing the mechanical drive gives enough options for now.

If we're blue sky thinking I'd look at a ducted fan that could rotate to become a pusher.

[gevans35]

Electric power in aviation has a bright future, in a rather narrow band of application, which I opine does not include helicopters in the foreseeable future.

I would agree with you if it's pure electric power, but a hybrid VTOL aircraft powered by electric motors, with a battery or capacitors, replenished by a gas turbine or diesel generator, may be viable in the not to distant future?

Edit: Here's an example...
https://newatlas.com/rolls-royce-evtol-air-taxi/55466/
.

[dClbydalpha]

... which I opine does not include helicopters in the foreseeable future.
That depends on the advantages gained, I personally think that an ETR brings a lot to the table in terms of efficiency and noise.

Motors, generators and actuators are already used, so we know how to design for certification, nothing daunting there.

As has been pointed out previously the technology is already here. It's simply about the investment.

[Uplinker]

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.
I don’t accept your first premise - an electrically driven tail rotor, (whether feasible or not), could still be manually controlled.

As to fly-by-wire; so I take it that you don’t fly on any Airbus and only on some Boeings and turbo-props?

Airbus 320 family and 330 each have 5 FBW computers, and can remain flying aloft without any of them.

PS: can helicopters have ejection seats ??

[Washeduprotorgypsy]

PIlot DAR,

I am curious to know the weight and horsepower of an electric motor suited to a Cessna 172 retrofit.

CAn you give us a ballpark range?

[GrayHorizonsHeli]

I vote for ion propulsion. It's way cooler.
imagine the 505 as the launch model? Damn conflicted feelings there. Butt ugly but cool.

[GrayHorizonsHeli]

PIlot DAR,

I am curious to know the weight and horsepower of an electric motor suited to a Cessna 172 retrofit.

CAn you give us a ballpark range?
google helped me find this:
https://www.flyingmag.com/news/two-place-electric-cessna-172-skyhawk

[krypton_john]

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

The big problem I see is that in autorotation the main rotor still drives the tail rotor in perfect synchronisation. That won't work for an electric driven TR.

[Pilot DAR]

Motors, generators and actuators are already used, so we know how to design for certification, nothing daunting there.
As has been pointed out previously the technology is already here. It's simply about the investment.

I agree that we're getting there, in terms of fly by wire, and criticality of electric components. However, when an electric motor replaces the very commonly accepted tail rotor driveshaft and gearboxes, the criticality will be perceived at a higher level. Let alone the unusual method of control (if it's even practical), the reliability of the motor system will have to be demonstrated to a new level. Such a design initiative will be labeled as novel and unusual, and held to an unusually vigorous standard. The present motors and generators (FBW notwithstanding) are certified as secondary systems whose failure can be managed by procedure. I perceive that investors would ask why they should invest an immense amount of money to certify a novel system which really only trades known and understood problems for unknown problems, without really solving any problems.

The project I was hired to advance toward certification for a motor powered 172 considered a purpose built 150HP electric motor. Though I saw designs and detailed drawings, the project never got to the point of producing a motor for installation (they took a lot of measurements though!). It was to be about 10% heavier than the Lycoming O-320 it would replace. The battery pack was a bit more of a challenge, though not insurmountable. Certification had a path forward with the authority, I had a number of discussions as to the proposed certification basis, and general agreement. That was doable - but it was a single engine airplane, where the failure mode was no worse (and really not much different) that the original design. I am confident this will happen for airplanes, it just requires a meeting of battery capacity, and airplane utility. It costs too much to keep a training airplane offline for hours to recharge it, and changing out very heavy batteries discharged for charged is problematic. During the planning of the 172 project, I did tell my client that they should install the motor as the primary power source in an R22, and not carry batteries, just a long power cord to the corner of the apron. Of course, you couldn't fly the R22 anywhere that way, but we spend a lot of time simply practicing hovering, so it could simply be a hovering trainer, which never gets higher than ten feet, nor leaves the apron. People liked the concept, but we did not get that far. Someone will.....

In the mean time, I'm very comfortable with shaft driven tail rotors/fans, we have more pressing product improvements to work on.

[chopjock]

P D
Let alone the unusual method of control (if it's even practical)

KISS Just on or off constant rpm with a servo controlled FBW variable pitch rotor should do it.

[hoodie]

KISS Just on or off constant rpm with a servo controlled FBW variable pitch rotor should do it.
The word "just" is doing a heck of a lot of work in that sentence.

I don't think you understand the complexities inherent in a "FBW variable pitch rotor", of which only one - but a big one - is safety critical software and electronic hardware.

[chopjock]

The word "just" is doing a heck of a lot of work in that sentence.

I don't think you understand the complexities inherent in a "FBW variable pitch rotor", of which only one - but a big one - is safety critical software and electronic hardware.

Ok perhaps "just" a pushrod then...

[Pilot DAR]

Just on or off constant rpm with a servo controlled FBW variable pitch rotor should do it.

Or a constant (to the main transmission) RPM, pilot controlled (pushrod, no FBW) variable pitch rotor - even more simple!

Yeah, that word "just"... It always makes my ears perk up when it's not accompanied with a comprehensive plan for certification. That's because I'm one of the people who may be asked to sign a certificate approving it later, and that does not happen lightly! It's great to innovate and aspire to new technology. But when doing that pushes the thinking of aircraft certification, it's a long and expensive process of demonstration of design compliance - or worse, petitioning for a change in the design standards to enable certification of an aircraft with novel features. The Bell XV-15 was the poster child for having to evolve design standards which were outside the box, and that is still a driveshaft type design!

[abgd]

It may not be the daftest idea. A quick google throws up this:

Helicopter Electric Tail Rotor (http://www.launchpnt.com/portfolio/transportation/helicopter-electric-tail-rotor)

Motors for model aircraft will often manage about 6-7 horsepower/Kg so if an R22 has a 120hP engine you might want a 30 horsepower motor - so 6kg for the motor and 6kg for the generator and a kilo or two for the control electronics. You would considerably simplify the gearbox and be able to do without an alternator. You might want to play with adding a small battery - large enough to transition from forward flight to the hover, then land, for added reliability and perhaps to give a little extra oomph for take off. On the back of an envelope it's feasible.

If you wanted to use fixed pitch tailrotors to reduce mechanical complexity you'd have to make them small and light in order to be responsive enough so you may wish to use several small rotors rather than one large one.

However even in electric radio controlled helicopters it's normal to link the main rotor and tail rotor mechanically and separate motors are only rarely used. The exception would be for very small models with constant pitch tail rotors where the complexity of making tiny variable pitch rotors would be prohibitive.

[chopjock]

PD
Or a constant (to the main transmission) RPM, pilot controlled (pushrod, no FBW) variable pitch rotor - even more simple!


I understand exactly. However in the current situation there is no option to disconnect drive in event of stuck / full un commanded pedal. An electric option could do this.

[Pilot DAR]

However in the current situation there is no option to disconnect drive in event of stuck / full un commanded pedal.

Funny this should come up. During my training, I asked my instructor how often a helicopter suffered a stuck pedal. He said he'd never heard of it in 21,000 hours of his flying. I asked then why so much focus on yaw control failures. He said he'd asked the same question during instructor training, and why no training for stuck cyclic or collective (also apparently extremely rare. There was no good answer to the question. The stuck pedal training seems a solutions looking for a problem. It's fun training though! 'Builds skills!

So now we introduce a tail rotor emergency turn off switch (guarded, I hope). What if a spinning pilot cannot reach it? What if it suffers unintended operation? 'Seems to introduce more failure modes than it solves!

[dClbydalpha]

The big problem I see is that in autorotation the main rotor still drives the tail rotor in perfect synchronisation. That won't work for an electric driven TR.
Firstly, why wouldn't it work for an ETR?
Secondly, why do you want the tail rotor driven in "perfect synchronisation" with the main rotor?

[419]

I think that the obvious question to ask is:
If an electrically driven tail rotor could be made as reliable as a shaft driven one and it was around about the same price, same weight and had benefits such as lower maintenance costs, why isn't such a system in use already?

[dClbydalpha]

... But when doing that pushes the thinking of aircraft certification ...

That's exactly what is being asked by the authorities. As well as a strive for efficiency, the push to an ETR is environmental. It can make an impact on the noise footprint, critical in approving modern air operations.

There are already electric motors and actuators on the critical parts list, you can't choose to ignore all the FBW advancements and the lessons learned. We know how to design, build and certify using redundant feeds and multiple wingdings isolated electrically and thermally. It is not a big step in to the unknown ... not saying it is cheap, but if the regulations allow for a competitive advantage to be gained then the business case will follow. I am most definitely not advocating using RPM alone or stopping the TR in flight. But changing RPM allows optimisation to particular phases of flight.

Thanks for sharing the weight estimate. I came up with a similar %delta for the ETR. The motor about 25kg, the feeds another 10kg and the generator 40kg. So 75kg replacing about 65kg. So a weight gain, but I am convinced that the MGB could be further simplified and you have greater choice over where the generator is placed.

[Lonewolf_50]

Funny this should come up. During my training, I asked my instructor how often a helicopter suffered a stuck pedal. He said he'd never heard of it in 21,000 hours of his flying. I asked then why so much focus on yaw control failures. He said he'd asked the same question during instructor training, and why no training for stuck cyclic or collective (also apparently extremely rare. There was no good answer to the question. The stuck pedal training seems a solutions looking for a problem. It's fun training though! 'Builds skills! Not quite.
When you are dealing with servos and hydraulic fluids some odd things can happen.
For example, on the UH-60 Black Hawk there is a cable/pulley/spring tensioning lash up in the Tail Rotor Servo Assembly that, if it fails, leads the TR Blades to neutral pitch. (I read up on a rare case of this occurring a few years ago. The commentary from the Blackhawk experts did note that it was very rare, and an internal bit failed ...). I am trying to recall if there was a tail servo hardover in a Seahawk back in the distant past that led to a "stuck pedals" approach ... but memory is fading there.

There were some mechanical conditions I vaguely recall that would lead to flat pitch or stuck pitch in the Huey ages ago when I went through flight training (TH-1E and TH-1L models, I don't have the manuals for them anymore).
It may be that your instructor was being "model specific" in his observations.

[dClbydalpha]

I think that the obvious question to ask is:
If an electrically driven tail rotor could be made as reliable as a shaft driven one and it was around about the same price, same weight and had benefits such as lower maintenance costs, why isn't such a system in use already?

The simple answer is the advances in technology driven by the hybrid and electric vehicle markets over the past decade now make production of such a system feasible. The operational environment is changing which may make it attractive to the market place. Hence the new interest and why a system has been ground tested.

... I asked then why so much focus on yaw control failures. He said he'd asked the same question during instructor training, and why no training for stuck cyclic or collective (also apparently extremely rare. There was no good answer to the question...

I'm not sure how you'd train to cope with anything that causes a stuck main rotor actuator.

...
There were some mechanical conditions I vaguely recall that would lead to flat pitch or stuck pitch ...

Control rod failure is one that immediately comes to mind.

[gevans35]

I'm not sure how you'd train to cope with anything that causes a stuck main rotor actuator.

Stuck collective is manageable , depending on position, cyclic less so.

[JohnDixson]

Lonewolf, I suspect that there is some misinformation out there, as the tail rotor control quadrant basic design purpose in life not as you described. Rather, that quadrant and associated large spring is designed to address the loss of a cable side to ballistic damage od maintenance error. As long as one cable remains intact, the pilot flies the remaining cable against the spring and almost 100% authority is retained. What you referred to was that the basic tail rotor assembly is two, crosswise mounted paddles with four blades, and the built-in blade angles are set up to generally match the tail rotor requirements between 40 and 120 or 130 ( can't remember now ) KIAS with reasonable sideslip, as in where one might be if all the tail hydraulics were lost. That situation was flown ( both stages of the TR servo depressurized ) and we were almost able ( in this failure mode one would still have the yaw boost servo which is up forward ) to get back to a hover but could not stop the right yaw drift below 10-15 kts.

[Lonewolf_50]

Lonewolf, I suspect that there is some misinformation out there,
More like bad memory.
Yes, your point on the neutral position is part of what I was trying to get at.
I was trying to describe the TR servo assembly. Failure there, not just a cable failure, would render any inputs moot I think. The tail quadrant caution light would illuminate if one of the two failed. (there are 1st stage and 2d stage) Not, as noted, a common problem.
As you describe it, yes, 40 and 120 ring a bell. (I seem to recall that as the number in the NATOPS).
The recent failure I tried to describe was a failure inside the servo assembly itself, actually, the quadrant, on the ground, so they never got into a hover. Physical failure. There's a point around which it all pivots, on which the cable guards are mounted. I need to go back and see if I can find notes on that. Will post if I can find them. I think it was that sleeve/post that failed.
As I remember that system, John, without hydraulics you can't move the paddles. Your point on the servos triggers some old memory.
If you lose hydraulics in that channel, I don't recall that you can move the paddles without boost.
But now I need to go and look at the old NATOPS systems diagrams. I am pretty sure that in that flight control, the Blackhawk and Seahawk are alike enough. No CILA, though, in the Black Hawk.
As to the training, you guys were test pilots.
What they didn't want people doing, operationally, was coming into a hover with inability to control the nose, and not having the tail authority to control the aircraft down close to the ground. The run on / stuck pedals approach was considered lower risk, as well as the benefit of letting the cross wind assist in holding the nose position as one got close to the ground so you could get slower before touchdown.

I guess my point, badly made, was that you need to know the specific failures that will leave you with loss of controlability even if you don't have loss of drive/thrust. Each model will have its own quirks. The blythe "we only do it because it's fun training" I don't think is a responsible position to take.

[JohnDixson]

A design function that the Hawks have is a backup ( #3 ) hydraulic pump that is electrically driven, and is the same as the two primary pumps in flow/pressure capability, and this pump backs up the first stage pump pressure to the TR servo 1st stage, hence there is triple redundancy, source-wise for hydraulic pressure back at the TR servo.

As to your remark about doing it because its fun training is well taken here, as it was possible ( or at least used to be ) to depressurize both tail rotor servo stages by pulling the backup pump c/b, deselecting the #1 Primary servo and selecting the tail rotor LDI switch. . At least I think that was the sequence. It did succeed in depressurizing both stages as we intended. Anyhow, after that flight there was some reconsideration by the senior mechanical controls engineers, who were concerned that a switch back to a pressurized system with a bunch of pedal force being applied, would create a cable whiplash that might result in the cable coming off the intermediate cable attachment devices. Hence your point is very good advice.

[krypton_john]

Firstly, why wouldn't it work for an ETR?
Secondly, why do you want the tail rotor driven in "perfect synchronisation" with the main rotor?

First: With engine out what's generating sufficient energy to drive the TR?

Second: To keep the TR in the correct RPM range.

[chopjock]

First: With engine out what's generating sufficient energy to drive the TR?



How long does an autorotation take? A couple of minutes perhaps? So not a very large capacity required then.

Second: To keep the TR in the correct RPM range.

Or drive the generator from the transmission...

[abgd]

The other reason you don't need a lot of power to the tail during autorotation is that you don't have to overcome the torque of the main rotor. A smallish battery would be enough.

I completely understand PilotDAR's point about thinking about certification throughout the design process, but there's still a big difference between discussing innovations that obey the laws of physics and those that don't.

[Pilot DAR]

I'm not sure how you'd train to cope with anything that causes a stuck main rotor actuator.

I trained for stuck collective and it was manageable. Helicopters have a few more vulnerable lift, thrust and control elements than airplanes do. A lot of design consideration has gone into maximizing reliability, and creating compensating systems or flying techniques. Generally, they work, and if indeed, helicopters were flown like airplanes (avoiding hovering), more failures would be more manageable, but then it would kind of defeat the basis for choosing a helicopter for the role. Helicopter operations by their nature require accepting some additional operating risk, and vulnerability. For my experience, a main transmission driven tail rotor/fan provides the greatest opportunity to design out failure points and increase reliability.

[Washeduprotorgypsy]

Seeing as this thread is a slapstick offshoot of the Leicester aw169 thread. And using 10-15 % Q as TR power consumption on an aw169 , AEO xmsn rating of 1500 hp. The electric motor off the Cessna 172 will substitute nicely for a electric driven tr on the aw169 , though coming up short by 70 hp if you take 15% Q to be closer to what the mechanically driven version can muster.

So you add the weight of a an Lyco 0-320(+10%) ..~300 lbs on to the tail end, ~350 lbs for the generator, ~600 lbs nose ballast , 400 lbs structural reinforcement. Voila....a perfect locomotive. A little sluggish in pitch when the electronic motor control gets buggy and the need for speed in the necessary autorotation occurs. There is no reason this can't work.

You would expect an electric motor employed in human carriage at altitude to be quite reliable , say close to what the failure rates on an elevator motor might be. Speak to your millwright or elevator buddies as to what a cutting edge gearless motor in the 150 hp department might weigh......~2000 lbs. Making it aviation grade, you build the frame out of aluminium and use titanium bolts.~1700 lbs. I don't want wreck it for Star Wars fans around Christmas time but this I is fantastic ground bound technology.

[[email protected]]

I trained for stuck collective and it was manageable. only if the collective is stuck in mid-power position or close to it - did you try it at very high power or very low power? Presumably it was on a single with a hand-throttle rather than a FADEC twin.

Washeduprotorgypsy - finally, the voice of reason:ok:

[gevans35]

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1024x768/head_in_sand_1024x768_95a05e9e53f86b936c6007d2561e1a61d59fb2 0e.png

[GrayHorizonsHeli]

Thanks Gypsy for the morning laugh lol

[dClbydalpha]

Seeing as this thread is a slapstick offshoot of the Leicester aw169 thread. And using 10-15 % Q as TR power consumption on an aw169 , AEO xmsn rating of 1500 hp. The electric motor off the Cessna 172 will substitute nicely for a electric driven tr on the aw169 , though coming up short by 70 hp if you take 15% Q to be closer to what the mechanically driven version can muster.

So you add the weight of a an Lyco 0-320(+10%) ..~300 lbs on to the tail end, ~350 lbs for the generator, ~600 lbs nose ballast , 400 lbs structural reinforcement. Voila....a perfect locomotive. A little sluggish in pitch when the electronic motor control gets buggy and the need for speed in the necessary autorotation occurs. There is no reason this can't work.

You would expect an electric motor employed in human carriage at altitude to be quite reliable , say close to what the failure rates on an elevator motor might be. Speak to your millwright or elevator buddies as to what a cutting edge gearless motor in the 150 hp department might weigh......~2000 lbs. Making it aviation grade, you build the frame out of aluminium and use titanium bolts.~1700 lbs. I don't want wreck it for Star Wars fans around Christmas time but this I is fantastic ground bound technology.


Not sure where you are plucking your numbers from. 1 hp / lb electric motors have been available for over a decade. 3 hp / lb electric motors have been flying for a couple of years. Changes your numbers somewhat, particularly when you consider you are taking out two gearboxes a driveshaft and its supports.



Washeduprotorgypsy - finally, the voice of reason:ok:
Cognitive bias at its best.

"A steamship can never cross the Atlantic for it would consume more coal than it can carry."

[[email protected]]

Where is the battery going to go and how much will it weigh?

The answer to most problems lies in battery technology and therefore size/weight vs power. In the future maybe but now????

Much the same is the improvements in steamship technology and efficiency did but it's not an overnight solution.

[SASless]

"A steamship can never cross the Atlantic for it would consume more coal than it can carry."


For sure some steamships took on more sea water than they could carry!

[dClbydalpha]

Where is the battery going to go and how much will it weigh?

The answer to most problems lies in battery technology and therefore size/weight vs power. In the future maybe but now????

Much the same is the improvements in steamship technology and efficiency did but it's not an overnight solution.

It's not an overnight solution, we started many years ago, it just seems that very few people recognise it.

This thread isn't about the All Electric Rotorcraft it is about an Electric Tail Rotor so for the moment generator driven I would suggest. Battery technology is advancing, but I expect FW to take the lead on all electric flight. Don't dismiss the ETR because of battery technology.

[[email protected]]

but I expect FW to take the lead on all electric flight. Don't dismiss the ETR because of battery technology perhaps because you can cover the wings and the top of the fuselage with solar panels - you haven't got that surface area on a RW.

If you are going for a generator you will need to drive it mechanically (MRGB most likely) = more weight/more complexity and the single point of failure ceases to be in the TR drive chain (as with conventional TR) but at the drive for the generator - how is that so much better?

You could take a NOTAR and bolt the generator on in place of the fan but you still have a mechanical TR/Fenestron at the other end - again what progress/advantage?

Perhaps just improve design/maintenance so people can't leave the nut off the end of the TR servo arm..........

[dClbydalpha]

Crab, I think the FW will see commercial benefits sooner, as the efficiency improvement is possibly greater.

The MGB already drives the TRDS and so no real added complexity... in fact layout could be made simpler.

There would still be multiple generators, in fact I envisage load balancing. For example I can't see the need for full RIPS concurrent with long periods of high TR demand

[petit plateau]

Seeing as this thread is a slapstick offshoot of the Leicester aw169 thread. And using 10-15 % Q as TR power consumption on an aw169 , AEO xmsn rating of 1500 hp. The electric motor off the Cessna 172 will substitute nicely for a electric driven tr on the aw169 , though coming up short by 70 hp if you take 15% Q to be closer to what the mechanically driven version can muster.

So you add the weight of a an Lyco 0-320(+10%) ..~300 lbs on to the tail end, ~350 lbs for the generator, ~600 lbs nose ballast , 400 lbs structural reinforcement. Voila....a perfect locomotive. A little sluggish in pitch when the electronic motor control gets buggy and the need for speed in the necessary autorotation occurs. There is no reason this can't work.

You would expect an electric motor employed in human carriage at altitude to be quite reliable , say close to what the failure rates on an elevator motor might be. Speak to your millwright or elevator buddies as to what a cutting edge gearless motor in the 150 hp department might weigh......~2000 lbs. Making it aviation grade, you build the frame out of aluminium and use titanium bolts.~1700 lbs. I don't want wreck it for Star Wars fans around Christmas time but this I is fantastic ground bound technology.




Tesla Model S motor weight is 70 lbs for 362 hp (see https://chargedevs.com/newswire/elon-musk-cooling-not-power-to-weight-ratio-is-the-challenge-with-ac-induction-motors/). Compare that with your stated 2000 lbs for 150 hp.

[[email protected]]

dClbydalpha - The MGB already drives the TRDS and so no real added complexity. that is my point, you have replaced a well functioning mechanical system (TR drive failures are rare) with an electric one which is just as likely to fail, so what is the advantage?

Petit plateau - but how much do the TESLA batteries weigh?

[dClbydalpha]

dClbydalpha so what is the advantage?


Better control of noise footprint.
Less moving parts.
Less maintenance.
Less unfriendly lubricant.
No need for TRDS alignment.
More freedom in tail rotor design compromise.
More options in MGB layout.

I'm sure there are more.

Why keep asking about battery weight? A claim was made earlier about motor weight ... I think people are answering that and that alone.

[chopjock]

dClbydalpha - so what is the advantage?



Better control of noise footprint.
Less moving parts.
Less maintenance.
Less unfriendly lubricant.
No need for TRDS alignment.
More freedom in tail rotor design compromise.
More options in MGB layout.

I'm sure there are more.


Able to switch it off in event of un commanded full pedal...

[GrayHorizonsHeli]

Tesla Model S motor weight is 70 lbs for 362 hp (see https://chargedevs.com/newswire/elon-musk-cooling-not-power-to-weight-ratio-is-the-challenge-with-ac-induction-motors/). Compare that with your stated 2000 lbs for 150 hp.


and how big will your generator need to be to power that beast? seeing pics of the tesla motor, it's the size of a large beer cooler, or to be more accurate the size of many americans beer bellies.
there's the battery with mood killing weight option to charge up and store that huge thirsty electrical appetite, or an equally sized (if not bigger) generator needed to power the motor live. And the bigger the generator, the bigger the power robbed, and the bigger turbine engine required to drive it all...its all relative isnt it? And relatively speaking, it all just keeps getting bigger and heavier.

I'm no electrical wizard by any means, but to get that published HP, knowing they use a 100KWh battery, thats alot of juice to be squeezed from a small bolt on generator.

[dClbydalpha]

I'm no electrical wizard by any means, but to get that published HP, knowing they use a 100KWh battery, thats alot of juice to be squeezed from a small bolt on generator.

90 kVA is about 40 kg already in use. Full RIPS takes some juice too.

[[email protected]]

Better control of noise footprint.
Less moving parts.
Less maintenance.
Less unfriendly lubricant.
No need for TRDS alignment.
More freedom in tail rotor design compromise.
More options in MGB layout. but will you match the power and controllability of a conventional TR? No one is going to give up performance just to replace a system that is both reliable and mature technology.


I'm sure there are plenty of problems with maintaining electric motors in the aviation environment and Elon Musk already acknowledges the issues with cooling high performance motors.

As to noise footprint - the TR still has to move the air whether it is driven my a driveshaft or an electric motor and the unequally spaced blades that already exist in modern TR, especially Fenestrons, have already significantly reduce noise footprint,

It seems an odd solution to a problem that hardly exists, especially since the crash that sparked this discussion doesn't look likely to be a TR drive failure anyway.

BTW I wouldn't hold up RIPS as a great success - it is very power hungry and heavy.

[dClbydalpha]

but will you match the power and controllability of a conventional TR?

... Elon Musk already acknowledges the issues with cooling high performance motors.

... It seems an odd solution to a problem that hardly exists ...

BTW I wouldn't hold up RIPS as a great success - it is very power hungry and heavy.

Yes, why wouldn't it? Simply changing the means of providing the rotation won't reduce performance. If anything it gives the potential for greater control.

Cooling high performance motors is where the major advancements in design and production have occurred. HEVs are major driver for this.

A problem that industry have been asked to provide solutions to. So somebody thinks it exists.

BTW RIPS is an example where industry has moved to make helicopters more viable. It being power hungry is exactly my point.

The technology is here, the engineering is possible. The question is whether the economics will move us in this direction or elsewhere.

[ShyTorque]

BTW RIPS is an example where industry has moved to make helicopters more viable. It being power hungry is exactly my point.

The technology is here, the engineering is possible. The question is whether the economics will move us in this direction or elsewhere.

Indeed. Fitting RIPS adds so much weight to some aircraft that some operators have decided against buying it as an option, because they prefer more usable payload.

[dClbydalpha]

Indeed. Fitting RIPS adds so much weight to some aircraft that some operators have decided against buying it as an option, because they prefer more usable payload.
And for others it allows them to operate in conditions not previously possible and therefore increasing usability of their asset. As a Customer, you take your choice.

[[email protected]]

Except that it is not reliable so you can end up committed to an IFR transit in icing conditions and then find yourself without ice protection - have you seen how many pages of malfunctions there are in the 139 QRH just for IPS?

And you lose a valuable vibration absorber which can cause AP/AFCS problems.

Just the sort of issues you want with an electric TR..............

The idea that something is better just because it is electric and new is just fanciful. However, if the advances in electric motor and battery technology were as fast as computer growth and processing power, we might see some viable alternatives but we still struggle with generation and storage for electric power.

How well are electric cars going to do in UK with a National Grid generating system that creaks at the seams on a still winter morning when consumer demand is high and generation output maximums are reached?

[dClbydalpha]

The idea that something is better just because it is electric and new is just fanciful. However, if the advances in electric motor and battery technology were as fast as computer growth and processing power, we might see some viable alternatives but we still struggle with generation and storage for electric power.


The idea that because something is new it is somehow less capable or even a "fantasy" is also false. Massive advancements have been made in electric technology. Serious research began a decade ago, full scale ground testing of an ETR last year. An ETR first and foremost must meet the requirements of being a tail rotor, hence the careful development. If regulations or operations give an advantage to an ETR equipped aircraft, then it will happen. However I think that we are gradually moving towards all electric aircraft, the VTOL version is unlikely to look like a conventional helicopter, development may therefore diverge.

Out of personal interest what rate of RIPS failures are people experiencing?

[ShyTorque]

And for others it allows them to operate in conditions not previously possible and therefore increasing usability of their asset. As a Customer, you take your choice.

Of course, that's why it was designed in the first place, but it has proved to be at a possibly unexpectedly high cost, both financially and as an aircraft payload penalty.
But surely the question here is: why add complication to replace a well proven, simple mechanical tail rotor system that has proved very reliable for decades? It's worth bearing in mind that many tail rotor failures have been caused by external damage - these failures will still occur on an electrically driven system. In my experience (having been flying helicopters for a living for just coming up to forty years and fixed wing for some years prior to that), the items that have proven most unreliable on all the aircraft I've flown have mainly been electrical or electronic. Same with the road vehicles I've been driving since the 1960s. Water ingress is a perpetual issue as well as mechanical ones. Well designed gearboxes are very reliable indeed because they are so simple. Electric motors and generators are not so reliable and need more maintenance.

As far as "saving the environment" goes, noise reduction has been mentioned more than once. From what I've seen very recently, relatively straightforward innovations in rotor blade design seem to be a very good way forward.

[dClbydalpha]

As far as "saving the environment" goes, noise reduction has been mentioned more than once. From what I've seen very recently, relatively straightforward innovations in rotor blade design seem to be a very good way forward.

Nothing is straightforward. The fact that these innovations are even happening shows the will to move forward. ETR is one of a number of initiatives as you say.

Real advantages may be gained in new designs where the geometric constraint of a TRDS doesn't apply. However see my previous response on all electric, that step may never come.

[petit plateau]

dClbydalpha - that is my point, you have replaced a well functioning mechanical system (TR drive failures are rare) with an electric one which is just as likely to fail, so what is the advantage?

Petit plateau - but how much do the TESLA batteries weigh?

My understanding is that the original poster is proposing an electrical transmission for the tail rotor rather than the existing conventional transmission, i.e. no batteries involved. To do this one would need to have the corresponding increase in generation, which crudely will be approximately equal in weight to the motor (assuming that the existing generator is operating near its design limit and so does not have the requisite spare capacity). So that would be (say) 70lbs for (a 150hp generator + a 150hp motor). Still a long way different than the objection raised of 2000 lbs for 150 hp system.

You can go further and propose to relocate the prime mover to wherever is convenient in the aircraft (i.e. low rather than high, or whatever) and put an electric drive on the main rotor(s) with an electrical transmission. Sort of the helicopter equivalent of a diesel-electric ship main propulsion, for much the same reasons. As a further refinement you then only need to put a few small/light batteries in the system and you can run the prime mover over a much narrower rpm band and still handle transient peak power loads; such a system typically has a better fuel economy. Taking an approach like this might be interesting if folk are having problems designing gearboxes, which I understand they are. Tilt wing transmissions are also complex and heavy and have awkward failure modes.

This is an interesting time to be a designer.

[gevans35]

My thoughts exactly.

[dClbydalpha]

This is an interesting time to be a designer.

As in " may you live In interesting times" 😁.

The ETR generation is not exclusive with the rest of the generation system. For a lot of the time the ETR will not be at peak load, when it is, other systems may not. A thorough ELA will show this and it may be that the weight penalty for RIPS can be shared with ETR, just a thought?

In my opinion I wouldn't go anywhere near electric main rotor for a conventional setup.

[gevans35]

https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/624x351/x57_cc484f68b5ce34449b5eaf5d0bb414d95ff67740.jpg
https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1232x694/rolls_royce_evtol_air_taxi_1_6c7014c23cc649a469ec293e2cb3d69 c6d7bd672.jpg


In my opinion I wouldn't go anywhere near electric main rotor for a conventional setup.

An opinion shared by NASA and Rolls Royce who are suggesting electric tilt rotor designs.

[[email protected]]

Real advantages may be gained in new designs where the geometric constraint of a TRDS doesn't apply. However see my previous response on all electric, that step may never come. Those already exist in the form of NOTAR, Twin rotor (Chinook) and contra-rotating MRs so it's not exactly ground breaking.

If it's not a good idea for the MR, why is it such a great one for thew TR?

Everyone would like to see a helicopter replacement that looks like a scaled up drone or quadcopter but to give it a useful payload is a long way from fruition.

[jellycopter]

Crab, my initial post at #12 explains why it may be good idea.

A fenestron type ETR could be stopped in forward flight and yaw control achieved by a simple rudder. Massive increase in component life and reliability.
​​​​​​
in the event of engine failure, any yaw in the descent could be controlled by rudder. The ETR would automatically spool up quickly under battery power for the vinegar strokes at the end.

Under normal ops, a conventional variable pitch mechanism would be used.

If made as a 'smart' system, the AW169-type failure could be mitigated by computer controlled reversal of direction of rotation with variable RPM to effect emergency yaw control. All of this is technically feasible today. If the pedals were driven to full deflection and held there, an ETR could be computer controlled to lock the heading. Heading could be managed by autopilot-type hdg bug on the HSI for example. Any excess rate of rotation could trigger a heading lock function.

Food for thought, or just fantasy?

JJ

[dClbydalpha]

Those already exist in the form of NOTAR, Twin rotor (Chinook) and contra-rotating MRs so it's not exactly ground breaking.

If it's not a good idea for the MR, why is it such a great one for thew TR?

Everyone would like to see a helicopter replacement that looks like a scaled up drone or quadcopter but to give it a useful payload is a long way from fruition.

Who said it was groundbreaking? NOTAR has its issues and advantages. As does Tandem, and coaxial, and contra... It doesn't have to be groundbreaking to be useful. This thread started because one poster was accused of trolling for suggesting an ETR... numerous others have weighed in that it isn't practical. In fact we now seem to have reached a point where it is, it's just a case of whether it offers sufficient advantage to move from the status quo. Are you unable to see the advantages of an ETR or is it having assessed it judge it isn't worth it?

I thought the reason to avoid the MR was covered in my earlier posts. That would be close enough to the all-electric aircraft, which I don't believe will look like a helicopter, so no point going down that branch - even if a continuously variable rotor has its attractions.

Quad, Quad tilt ... who knows what will emerge over the next 10 years?

[chopjock]

I thought the reason to avoid the MR was covered in my earlier posts.

One advantage of a MR setup could be only one engine required (Turbine generator) to give twin engine confidence (Battery back up for 10 minutes)...

[JohnDixson]

Are the proposed electric tilt-rotor designs cross-shafted?

[gevans35]

Are the proposed electric tilt-rotor designs cross-shafted?


I don't know for sure but I doubt it. I assumed they rely on the multiple motors for redundancy, but I could be wrong.

Here's a bit more info on the RR one which they say could be flying in the early to mid 2020s.

https://robbreport.com/motors/aviation/rolls-royce-hybrid-vtol-concept-farnborough-2806843/

And NASA.

https://data.nasa.gov/dataset/Hybrid-Electric-Propulsion-System-for-a-4-Passenge/6x4v-g98n

[dClbydalpha]

One advantage of a MR setup could be only one engine required (Turbine generator) to give twin engine confidence (Battery back up for 10 minutes)...
Once you've redesigned that much I suspect there are much better configurations than the conventional layout.


Are the proposed electric tilt-rotor designs cross-shafted?

I'm not sure there would be a need. I can't recall whether Project Zero was.

[GrayHorizonsHeli]

Welcome to Erector by Meccano ® The original inventor brand! (http://www.meccano.com/product/p20722/20-models-set---aerial-rescue)

I'll let you know how my trial runs go when I electrify this thing.

https://d1whcn1ntmec99.cloudfront.net/images/catalog/products/meccano/i18n/en_ca/20-models-set-aerial-rescue/full1.jpg

[ShyTorque]

If the pedals were driven to full deflection and held there,

I don't think this is necessarily what occurred in the 169 accident. Depending on the actual failure, the tail rotor servo control valve going to full deflection doesn't necessarily mean that the pedals are driven at all. The pilot may have held full opposite pedal but the servo could have run away in the opposite direction to his input.

[[email protected]]

Are you unable to see the advantages of an ETR or is it having assessed it judge it isn't worth it? The advantages seem purely theoretical and you have yet to establish the need for an ETR.

Millions of hours flown with the conventional tail rotor in all aspects of the helicopters versatile roles and the number of TR failures and malfunctions is very small.

One crash with an as yet undetermined cause but some form of TR issue and you are proposing ETR as the saviour to that scenario and ignoring the realities of system failure/loss of power in the ETR, not to mention that many of the solutions, such as jelly's, ignore the amount of time many helicopters spend in the hover as opposed to the high speed cruise.

Keep on with your blue-sky thinking but I will be surprised if we see ETR in the next 10 years at least.

[dClbydalpha]

The advantages seem purely theoretical and you have yet to establish the need for an ETR.

Millions of hours flown with the conventional tail rotor in all aspects of the helicopters versatile roles and the number of TR failures and malfunctions is very small.

One crash with an as yet undetermined cause but some form of TR issue and you are proposing ETR as the saviour to that scenario and ignoring the realities of system failure/loss of power in the ETR, not to mention that many of the solutions, such as jelly's, ignore the amount of time many helicopters spend in the hover as opposed to the high speed cruise.

Keep on with your blue-sky thinking but I will be surprised if we see ETR in the next 10 years at least.

At what point have I ever proposed an ETR as a solution to tail rotor failure?

Why do you say I don't consider system failure or loss of power? The motor will meet the required failure rate as will the generation system. They are already multiple redundant systems.

All things start as theoretical. However analysis and testing so far have backed up the theory. Do you believe there are no practical advantages to a variable speed rotor?

I will continue, thanks, as long as there is a commercial incentive. I don't establish the need, that's done by either regulation or operational requirement. Whether that will happen with an ETR is out of my hands, but so far it has been worthy of attention up to an iron bird.

[Washeduprotorgypsy]

Grey horizons, glad you enjoyed. I always feel equally reassured when making consumer purchases with the Inspector #45 tag.

Pilots en mass around the world are finally getting their biggest wishes met with the advent of the ETR. They can live with the chronic lower back problems from the cruddy seating, if only the archaic driveshafts and gearboxes would disappear.

So...back to this locomotive.

We have got power to weight figures for electric motors being flung around the conversation with nary a mention of duty cycle, never mind record in service. Kinda of like sailors arguing where mean sea level sits in 100 foot seas....amusing but pointless.

Seeing as we are improving the type , I think it fair to ask the new ETR model to have the ability to hover at max continuous for prolonged periods. So using the aw169 as our testbed once again, this occurs at 1350 hp. So using 15% of Max continuous Q as being TR consumption again........ 200 hp.

Sure electronic motor controls have made leaps and bounds in the past couple decades. Complete control of the waveforms operating within the stators of a synchronous motor allowing near perfect efficiency of the principles of electromagnetic induction. Have the ground bound and efficiency obsessed , industrial process industries not innovated and taken advantage of this? Of course they have, sparing no amount of complexity in order to achieve efficiency of power. Lighting fast microprocessors paired with power transistors and resistors, all guided by millions of lines of possibly conflicted computer code.....what kind off fault or failure mode could possibly present itself? So much better than a clunky old driveshaft and gearbox, and there are no bearings to fail in an electric motor. Even If there were , you just use mag/lev tech.(Always use a laser to do the same job a builders string has been doing for the past 10,000 yrs...so much cooler and its called "progress".)

After perfect efficiency has been obtained in controlling the repulsive electro magnetic forces between the rotor and stator where do you find your power density gains? Higher voltages through better cooling(.....like all the practical geometries haven't been tried yet) Insulation that doesn't melt or crack, and conductors that don't melt or heat up too much. I know that if we just stretch a little harder cold fusion , super conductors, super steel the weight of feathers are just around the bend....but in the meantime we are stuck with good old copper. Yes even consumer grade products like Tesla and Dyson. Though I feel we are on the cusp of a wave of stc's replacing the 1930's vintage, starter genies still on most helicopters with beer can size , LED backlit , hollow plastic ones accomplishing the same thing.

So we need an electric motor based on the best of industrially vetted technology to operate consistently at 200 hp to mirror our max continuous hover missions for SAR or aerial work. Doing a little window shopping I came up with this https://www.ziehl-abegg.com/us/en/product-range/ventilation-systems/axial-fans/maxvent-owlet/. (Pg.44 of 66)

A drop in fenestron. Good looking, scimitar-scalloped blades , meets all the euro engineering approvals. 1.4 m diam. Bout right for the back end of a aw169. Power to weight for continuous duty? 50 hp at the svelte weight of 637 kg. Ahh but all that steel fat to be trimmed. Shes's gonna need some beefing up in the motor (4x 50) I think it's a fair trade off to add all that extra copper and substitute steel for aerospace material and call it even ~650 kg....she 'll taxi like a freight train because thats all She'll ever do.

I guess until the next invention comes along we are stuck with the practical limit of the electric motor being a quadcopter the size of most windscreens. Send me enough money and I'll build you one to ride in. You can't beat em join em.

[[email protected]]

Where is that Like button again..........:)

[petit plateau]

So we need an electric motor based on the best of industrially vetted technology to operate consistently at 200 hp to mirror our max continuous hover missions for SAR or aerial work. Doing a little window shopping I came up with this https://www.ziehl-abegg.com/us/en/product-range/ventilation-systems/axial-fans/maxvent-owlet/. (Pg.44 of 66)

A drop in fenestron. Good looking, scimitar-scalloped blades , meets all the euro engineering approvals. 1.4 m diam. Bout right for the back end of a aw169. Power to weight for continuous duty? 50 hp at the svelte weight of 637 kg. Ahh but all that steel fat to be trimmed. Shes's gonna need some beefing up in the motor (4x 50) I think it's a fair trade off to add all that extra copper and substitute steel for aerospace material and call it even ~650 kg....she 'll taxi like a freight train because thats all She'll ever do.

If the Tesla motor I referenced was built like that industrial fan you pulled up, then the Tesla S car would be about the size and shape of the freight train you are imagining. Instead that Tesla motor, scaled to your stated needs of 150hp was "(say) 70lbs for (a 150hp generator + a 150hp motor)" based on "Tesla Model S motor weight is 70 lbs for 362 hp". You appear to now be moving the goalposts out to 200hp. Fair enough, I can do that sum.

But so that the design goal does not move around, what is the weight of the power takeoff & shafting & control & gearboxes for the tail rotor on the AW169 ? And how long do you expect to sit in the hover for at that power ?

[gevans35]

I guess until the next invention comes along we are stuck with the practical limit of the electric motor being a quadcopter the size of most windscreens. Send me enough money and I'll build you one to ride in. You can't beat em join em.

Maybe you're correct, but organisations such as NASA, Rolls Royce, Bell and others would appear to disagree with you.

[dClbydalpha]

The Siemens motor in the Extra 330 LE is rated at 260 kW continuous and is 50kg. But don't let facts get in the way of plucking random numbers out of thin air.

[[email protected]]

The 330LE is constructed with light-weight materials and is suitable for 20-minute flights, including take-off, climbing and five minutes of full throttle flight.that's very useful.......

The electric 20-minuters..........

[gevans35]

Battery capacity?

[petit plateau]

Battery capacity?

"Extra 330LE aircraft are powered by an electric SP260D motor with a power output of 260kW (348hp). The electric motor was developed by Siemens with support from Germany’s Aeronautics Research Program (LuFo). The motor can drive propellers directly without the use of a transmission, and can deliver 2,500 revolutions per minute at rational speeds. It has a continuous torque of 1,000nm and link voltage of 580v. The motor has a maximum coolant inlet temperature of 90°C and efficiency of 95%. The aircraft features two battery packs, each with 14 high-power Li-Ion battery modules with a capacity of 18.6kWh. The aircraft’s motor weighs 50kg including airscrew bearings, and has a low power-to-weight ratio of five kilowatts per kilogram, which was achieved with the use of new simulation techniques and sophisticated lightweight construction." from https://www.aerospace-technology.com/projects/extra-330le-electric-aircraft/

What is the weight of conventional tail rotor transmission, power offtake, controls, etc ?

[dClbydalpha]

that's very useful.......

The electric 20-minuters..........
So at least you now acknowledge the existence of a suitable motor with an appropriate continuous rating.

Now where's that like button

[[email protected]]

So at least you now acknowledge the existence of a suitable motor with an appropriate continuous rating. hmmm, not quite - 5 mins at max continuous isn't going to cut the mustard in pretty much any helicopter role and a 20 minute max life????

Why haven't Extra elected to use a generator with a prop in the slipstream on it? Cooling issue perhaps with going longer than 20 minutes?

It is a small step in the right direction but a very long way from challenging a conventional TR.

[gevans35]

Does one need more than 5 minutes continuous, would 30 minutes at 90% suffice?

I read 20 minutes as battery life, the ETR application would be generator driven.

Surely a prop in the slipstream makes no sense... drag?

[[email protected]]

Does one need more than 5 minutes continuous, would 30 minutes at 90% suffice?I've spent over an hour in the hover at max continuous, so no, it isn't enough.

The 20 minute limitation clearly is battery life on the Extra which is why I asked about a generator as you suggest for ETR - if the answer to that is cooling then you would have to keep 'resting' your ETR to stop it overheating.

[gevans35]

I've spent over an hour in the hover at max continuous, so no, it isn't enough.

The 20 minute limitation clearly is battery life on the Extra which is why I asked about a generator as you suggest for ETR - if the answer to that is cooling then you would have to keep 'resting' your ETR to stop it overheating.

I wouldn't get too hung up on the "Extra" motor, that was designed for an aerobatic aeroplane. An ETR would need a motor optimised for that application and rated/de-rated to provide 100% continuous output for OGE hover if that is what is necessary. The "Extra" application is just an indication that a suitable motor could be sourced.

I doubt that Leonardo would have developed a prototype ETR and ground tested it if they didn't see any advantage, or think it had a chance of working in flight.

[dClbydalpha]

hmmm, not quite - 5 mins at max continuous isn't going to cut the mustard in pretty much any helicopter role and a 20 minute max life????

Why haven't Extra elected to use a generator with a prop in the slipstream on it? Cooling issue perhaps with going longer than 20 minutes?

It is a small step in the right direction but a very long way from challenging a conventional TR.

I'm struggling to understand your interpretation of "continuous". The motors I have encountered have a continuous rating, a five minute max rating (~125%) and a five second emergency rating (~160%).

I'll say again the technology is available. In my personal opinion the research into flux, isolation and thermal flow modelling over the past few years is exceptional.

So Crab, there is an ETR that can do everything your mechanical TR can do ( let's face it it would have to otherwise it wouldn't be flyable)

Disadvantages
Not yet certified.
Needs electrical source, changing the safety case for the EPGDS.

Advantages
Less installation constraints.
Simpler installation and maintenance.
Power sharing with other systems.
Easily varied rotor speed.

For a number of years I looked at a variable speed tail rotor, but mechanically the penalty was just too much. The ETR changes the equation. ... I admit that I don't know whether it changes it enough, time will tell.

[jimjim1]

Advantages

Easy change to dual (or more) redundant tail rotors as suggested here -
https://publicapps.caa.co.uk/docs/33/CAPAP2003_01.PDF
CAA PAPER 2003/1

[ShyTorque]

JimJim1,

The twin tail rotor concept was thought of very many years ago. From a purely academic/theoretical point of view, a tail rotor at each end of the helicopter would be a better design. But it wouldn't be convenient. Early designers realised that the single tail rotor at the rear end was a necessary compromise.

[[email protected]]

DcL - I'll take your word for the advancement of the technology - I'm just a guy who flys helicopters for a living not a boffin. but given these constraints Disadvantages
Not yet certified.
Needs electrical source, changing the safety case for the EPGDS. how close are we really to seeing ETR in production?

[abgd]

I have always liked this method of implementing twin tailrotors. They're not mounted on the tail, admittedly. (https://cnet4.cbsistatic.com/img/T9JWLabNrF3m3l8n5IjpS-aSlWM=/2010/09/29/67f1d2eb-fdbf-11e2-8c7c-d4ae52e62bcc/X3_DIGIT-03665_001s.jpg)

I don't know whether they provide redundancy in this case, but as a concept I don't see why it couldn't.

[ShyTorque]

That machine isn't very practical, for a number of reasons discussed here a long time ago.

[dClbydalpha]

DcL - I'll take your word for the advancement of the technology - I'm just a guy who flys helicopters for a living not a boffin. but given these constraints how close are we really to seeing ETR in production?
Caveat that this is my personal WAG. If there is a will, I reckon 18 months to free flight. Realistically 3 years to an available production item. 5 years to realise the advantages?
The thing I see is that technology is advancing so fast that the move to hybrid and all electric may mean it's not worth the short term investments for just an ETR. Hence my comments about the next 10 years.

As I say, my opinion only .

[SASless]

I have been reliably informed the UH-60 Blackhawk Tail Rotor can demand as much as 800 Horsepower.

How much would a 24VDC Electric Motor weigh in order to provide that much output?

What kind of gearing/gearbox/shafting would it require?

What Electric Load would it have to have feeding it....and what would the Generator/Alternator weigh for that?

Where would you place the Electric Motor along the Tail Boom not to have a CG Issue?


Let's carry this a bit further......what size motor would be required to power the CH-47F's Aft Rotor considering it already has two 4700 shp Engines driving the rotor system now.

[IFMU]

How much would a 24VDC Electric Motor weigh in order to provide that much output?
What kind of gearing/gearbox/shafting would it require?
What Electric Load would it have to have feeding it....and what would the Generator/Alternator weigh for that?
it would not be 24VDC. More likely higher voltage AC.
800 HP is close to 600 kVA. A 250kVA B787 generator weighs a bit less than 300 lbs IIRC. Motors and generators are similar machines, so figure something like 600 lbs, unless somebody comes up with better technology. You should not need a gearbox for the UH60 tail rotor speed range with an electric motor.
you would need a big honking generator to run that 800 HP motor.

[JohnDixson]

I think SAS wrote “ as much as.....” so that 800 number would be treated as a peak value, not steady state.

[SASless]

Brother Dixson is correct that the demand would vary with the amount of Tail Rotor Thrust being applied or in the Chinook example what the Aft Rotor Head demand range could be from setting stationary on the Ground to lifting at Max Allowable Gross Weight.

If you think you need a big generator for the Hawk Tail Rotor....the Chinook application would be really huge!

[gevans35]

Chinook is a different ball game, as is V22, although large hybrid VTOL multi motor tilt wing transport aircraft are suggested in various NASA articles.

[Davey Emcee]

I expect James Dyson could find a solution.:)

[Ascend Charlie]

...Dyson sucks...

[ShyTorque]

But nothing sucks like an Electrolux.

[mickjoebill]

If someone did come up with a bolt on spin recovery system (not a parachute!) for existing helicopters, would the industry adopt it?

Here is one hypothetical scenario:
Bolt on apparatus with no or min adaptions required to the air frame. Derigable.
Operates independently
Weight 30 kg (moving CoG rear of mast.)
Engauges automatically
Low maintenance
No other use but for countering the high speed yaw on light and medium helicopters.

At what price would such a safety device be considered too expensive?

For reference, we saw that despite the obvious benifits of crash resistant fuel cells for the r44, they were not widely retrofitted as a matter of free choice, due to cost.


mjb

[Ascend Charlie]

30 kg on the tail would be a sizeable CG change - we used to put 10kg there to counter a massive camera on the nose. Without a camera, and 30 kg on the tail - fuggeddabardit!

Automatic engagement just invites undemanded deployment - that would be exciting.

No use for it, other than the 1:1million chance of a tail fail - no thank you, rather have 30kg more payload and a workable CG for the 999,999 other flights.