Why Full Scale Helicopters are not using Electric Motor Tail Rotor Unit?

I agree, actually, the current development status of power transmissions electrically compared to mechanically gives it many advantages. In my point of view, the transmission efficiency would call for the better benefit, in addition to all the advantages you mentioned. Some sort of electric control boxes would be required for power control and switch to backup systems, but indeed, feasible.

I'd also add that trains transmission are applying electric motors in each wagon, distributing the power transmission in all the assembly, and with better transmission efficiency based on the generator+motors efficiency X many transmission gears with lower efficiency in the mechanical way. The new generation of cars also will benefit from it.

Regarding helicopters, I'm affraid the problem is not essentially technical, but also legal and investment cost X estimated return time. Remember that keeping a series of mechanical transmissions and gearboxes in an airborne system is always work consuming and costly, and sells a lot of spare parts... well, the electrical control boxes and accessories are also expensive enough to spare and keep. They fail with far more working time, it makes them interesting. At least when you can sell or lease-back the aircraft before they fail...

I think the time will come. Take as an example the next aircraft generation based on the bleedless concept to add for engine fuel consumption enhancement. No pneumatics, no distributed hydraulics. Only powerfull generators on engines and APU. Everything is electric, or used a small electric pump or compressor buit-in to make the accessory work. This concept is around for at least 10 years, and is not already incorporated to assembly lines.

In aviation, everything is always slow. There are never quick upgrades or developments, but a series of improvements, design changes, always followed by thousands of flight hours of testing and certifications. Unless you are talking about experimental-general aviation. In this case, there are bold pilots...

Good point. Indeed, a simpler system and enclosed in the power package inside the fuselage. But, the transmission still has a dedicated power output for the fan. Maybe some model could be benefited by a flexible fan mounting location if it could be electrical driven. Or, even thr source of the gases for the anti-torque effect could be provided by the engine exhaust... Just wandering.

Hello lynlynch,

hope all is well?

The 'NOTAR' sounds a lot simpler than having any kind of drive at the tail of a helicopter for sure! It is also very clever stuff! Congrats on listing the sites and a good answer

GA to you sir!

bb

Thanks. All is well. Today is my youngest grandchild's first birthday.

Hope all is well with you, too.

The NOTAR system also has a much lower acoustic signature than conventional tail rotor equipped choppers. It is more expensive than a tail fan though.

Lyn

Hello lynlynch,

Congrats on your youngest grand child's first Birthday!

Finding it hard to concentrate after the breakdown a few months ago but, I hope to get better in time, thanks!

I wonder why it has taken so long to take off, (forgive the unintentional pun) as the first type of helicopter to use this type of thing was in 1945? Way before the Hughs Aircraft Corp built the model was it in the 80's or 90's?

bb

Thanks bhrescobar and lynlynch for your great comments

I am familar with NOTAR which was developed approximately 30 years ago; however, almost all the single rotor helicopters being produced in the last 30 years still use Tail Rotors. Which makes me wonder if the NOTAR concept is inferior to the tail rotor in performance and/or cost.

I agree with bhrescobar that the future will be electric. However, as was mentioned it will be slow to change.

Disclaimer: I don't work for Boeing, but, the most outstanding aspect of NOTAR is, if you back your chopper into a tree/pole/cliff, you might not die, if you are lucky. You could back one of these into a tree that would take down a tail rotor chopper and fly away with little or no damage.

Oh I wholly agree that simpler is better. But in the debate between electric and mechanical that is also why mechanical is likely to be more reliable. I don't know if they are yet using electrical surface controls on planes. My sense is most of them are hydraulic with redundancy again for the same reason as well as perhaps power. Electric isn't going to match hydraulic in power to weight ratio and that would seem to be an issue with the tail rotor. It is probably less weight in the tail section to transmit the power there mechanically than to produce it locally electrically.

Back in the '80s, McDonnell Douglas proposed ducted air instead of a tail rotor for the RAH-66 Comanche for exactly the reason cited by lynlynch. It lost out to a "fan-in-fin" model proposed by Boeing/Sikorsky. That is, the fan was entirely surrounded by the tail fin, much like a muffin fan. Much more survivable in trees than an external rotor, but nowhere near as good as the ducted air. Nevertheless, the fan-in-fin won out.

Not implying that the tail rotor configuration was the deciding factor. That decision was way above my pay scale and I have no idea on what the decision was based.

Just detailing some history.

emc_c

I believe it is the torque factor as well, in direct/immediate relation to driving horsepower, response time as well. Torgue requirements of electric fan vs weight. A huge motor would be required to supply the required torque. Lifting off with full or overweight load requires massive anti torque requirements to tail rotor and motor size I am sure would be prohibitive in tail section, so weight comes in as well as size requirements.

ga

EXCELLENT!! This is the reason "Why Full scale Helicopters are not using Electric Motor Tail Rotor Unit!!"

Thank you Bill H. That is a very good point about mechanical tail rotor they are directly and positively coupled to the main rotor. And I believe you are correct about human passengers and the need for proven reliability. I have been reading about all the effort be expended to prove out face gear technology for the Apache AH-64D.

I am also not a helicopter pilot, which makes me wonder what they do if the problem is the lockup of the Main Gearbox. It would be great if there were some experience helicopter pilots to critique our thoughts.

Also, I am thinking that another benefit if the Tail Rotor Generator fails, a redundant source for the electric motor tail rotor could be the main generator; however, this probably would require shutdown of non-critical, non-safety-of-flight systems.

I cannot imagine the gearbox locking up and there not being a whole lot of things that break in a very very rapid succession. most importantly I would think there would be a shear pin on the rotor so that it continues to spin, it is the ONLY flight surface on which the passengers lives lives depend, a freespinning rotor shaft still allows the pilot to perform the autorotation fall and emergency landing cushion effect. I have experienced this on more than one occasion and owe my life to trained calm pilots.

I think the point made earlier about the weight of motors necessary to achieve the torque required in the tail rotor and the weight of generators, Not even addressing reduncency systems is a valid concern, the mechanical system could actually be lighter and therefore better.

My father was in an early British army helicopter in Germany when the gearbox locked up immediately after takeoff. Fortunately they were close to the ground but the impact was very heavy. Apparently the drain plug on the gearbox had fallen out. The pilot found something to serve as a plug and some oil, refilled the gearbox and flew back to base! However he flew alone as my father refused to travel any further with him.

I bekieve you to be correct, altho a very debateable requirement for survivability.

I don't know how technical you are but have u ever thought of the torque required for those tail rotors - the size and weight - of the electric motor required as well as the generator and its weight to drive it?

The electric motor needed would pull the back of the chopper down so much that I doubt you have any idea based on having asked this question. Next you could start to consider to drive the main rotor electrically also.

Your idea would make things first heavier and second more complex thus increasing failure possibilities.

Furthermore, these vehicles need to have their net weight kept to the minimum rather than increase it for the disadvantage of their payloads.

Remember we're not talking about a locomotive where the extra weight can help with traction!

I'd suggest you to get rid of this illusion rather contemplating on taking it to the patent & design office.

Next dumb question!

Did YOU even bother to read fully the original message? He said this was a thought; he ended with a request to benefit from the experience of others.

I sure as heck hope you do not speak to your staff in the tone of your reply, otherwise you must go thru a huge change over of staff and coworkers. The whole Idea of CR4 is engineers helping each other, to support and improve, to help see the larger pictures or the fine detail oft overlooked, but NOT TO MAKE THEM CHOOSE A NEW CAREER PATH.

I am ashamed of your answer on behalf of the many good folks here who want to share knowlege, to help foster and direct creative thinking and to encourage those who want to learn, explore and grow. By the way, that is an important word, 'encourage', not to be confused with 'discourage', maybe you should look them both up!!!

SHAME ON YOU - if you are going to be that negative and insulting, please refrain from future answers, yours contributed nothing to this string.

and one last post script and I prepair to submit this: I hope you are not a parent.

I did read his postings but I also do recall when I joined that this is a place where you come for more serious answers to more serious questions.

You do not need to answer on my behalf!

He wasn't being aggressive...or rude.....you are though!!

Thank you nd I did not mean to be rude however, as more people join in they all seem to agree on the extra weight problem that I was talking about.

Hey, you - stop being sentimental! It is a dumb question anyway you have to admit that.

There are no dumb questions. Only inquiring minds.

Going by his questions, I believe Gannet has little experience with helicopters other than the toys he was describing, so there's no harm in him just asking. There's no need to go overboard in telling him off, especially since this forum is open to everyone, not just professional engineers and scientists. It's possible that Gannet may not even be an engineer, so these are factors he's unaware of. If you want to vent your frustrations on anyone, please direct them at a more deserving target, such as one of the umpteen overunity and HHO scammers who rear their ugly head here ever so often. It's these guys who deserve to be slammed hard for their stupid ideas.

Well put!!

I didn't see it on CR4, but I'm with you about the eels.......there would have been two of us calling the idea stupid (at least!)

Hi emc c,

I tried to apologise to the poor b....about my alleged 'rude temper' but perhaps he'll never get to read it anyway.

The 'pet electric eels' story really made me laugh and enjoyed it.

However, your thoughts about having electric rudder control on the tail of a black-hawk is just not be better then the current method/s.

The weight of the drive shaft (hollow or not) is not that bad because it is just a few meters long spread over and <20mm in diameter. The associated gear with this mechanism is not more than the one you'd need btw the turbine nd the generator to produce the juice for the electric tail rotor. Then you'd still need an electric control device btw the gen and the tail motor. (Hence the pilot was right when he said 'he wouldn't trust an electrical system'.)

What is even worse that to swing the tail to left or right you would not be able to do it by switching the direction of the tail rotor-motor but still would have to do it by the tilting of the blades, as it is done currently.

Now if you add all these issues up you have nothing to gain but to loose.

The adaptation of hydraulics started to weigh in when things became larger and heavier and the human muscle power was insufficient to deal with things (see power steering in cars).

In other words - could you tilt the main propeller blades directly with your legs' muscle power on a chopper? I hardly think so.

Of course hydraulics isn't necessarily used if there's a better method available.

Finally, I can apologise once more for the shake of everybody but this is it..........no more because some of you don't think straight enough to see things properly.

Let's be honest, if the OP's idea was a feasible one then the designers would have resorted to it long before he even knew it. Designers normally want to make things efficient and, above all, simple to keep things reliable.

Beg to differ on a few technical issues.

The hollow driveshaft is at least four inches in diameter on the Blackhawk. I don't know what you mean by a few meters long but I ballpark it at ten meters, end-to-end.

You state that an electric drive would still require pitch control on the tail rotor blades, but consider the advantage you have if you suddenly want to turn the aircraft. Right now, all you have is a mechanical linkage from the engine driving the main rotor - lots of inertia there. But with an electric drive, you simply up the voltage to the motor, in concert with changing blade pitch. Seems like you could whip the tail around very quickly that way.

As to your final point, the Blackhawk is a 1978 design. Comanche was late '80s. Apache is seventies vintage. It would not be surprising to me, seeing how much else has gone from mechanical to hydraulic to electric, to one day see tail rotors running off an electric drive. That it hasn't been done yet doesn't mean it's a bad idea, it just means the technology wasn't there yet when the last bird was designed.

emc_c

"The hollow driveshaft is at least four inches in diameter on the Blackhawk. I don't know what you mean by a few meters long but I ballpark it at ten meters, end-to-end."

That's exactly the size and length of water pipe missing from a near by water board's stockpile.

The last time......I have visited one of your aircraft carriers, where the helicopters had their tails folded in two for parking, I could easily see at the folding point both the coupler and the size of the tail rotor's solid shaft that looked no more than 20mm. The length of most of the helis' body would have been barely 10meters let alone their tail sections.

"But with an electric drive, you simply up the voltage to the motor, in concert with changing blade pitch. Seems like you could whip the tail around very quickly that way."

The response time of the motor would be slower than the current method's due to the momentum of the rotor assy (including the prop on it), right? (Even if you consider using ironless-rotor-motor, where the rotor's weight considerably lighter, won't give you an immediate jump in its use for this purpose not to mention the generator issues we have talked about already.)

I saw many links here to support this argument but, if you noticed, most concepts are pretty much ancient and obsolete because they weren't feasible.

What I said so far is to let the OP know about the current pit falls on the matter he raised.

What tomorrow's technology may bring is another matter but, as I see it, none of you have that under the belt yet, have you?

So, - please do not exaggerate!! Some of us have enough clue to use plain logic to imagine what is going on, even if it is you who see choppers on the daily basis.

I often noticed at many forums of cr4 they're heavily infiltrated by field service tech/eng who are struggling in every day life at work because they do not have the basics mastered adequately.

Were you a bench tech/eng then you would be compelled to know things better (not always though) not to mention if you were a PRACTICING design engineer.

No hard feeling - eh?

The UH-60 fuselage is fifteen meters long, and the driveshaft starts over the crew compartment, and travels down the spine, then back up to the top of the tail. Ten meters is an estimate, but the fifteen meter fuselage number is a specification.

The four-inch drive shaft diameter is a guess based on memory, but it is way closer than your 20 mm wag. 20 mm is less than an inch, and even I (an electrical type) know that a sub-one inch hollow driveshaft running several meters isn't going to do the job of turning a three-meter tail rotor.

As far as motor inertia, I know that it is a fact that helicopter rescue hoists have been going from hydraulic to electrical, both for less maintenance, and also for better control, which means less inertia, not more.

Some more advice for isti80: Keep it professional and courteous. If you are going to try to slam people, have all your facts lined up and triple-checked.

emc_c

The length of the tail rotor shaft I only pointed out for saying is spread over a certain distance (from gear-box down to the tail) rather than falls on the tip of the tail like that dirty big electric motor would to drive the tail rotor.

I saw marine helicopters on aircraft carriers and I give you credit now rapidly dropping the size of the tail shaft from 4" to.....Many stub-axles are barely 20mm and they are exposed to a lot more bidirectional dynamic stress than the tail shaft on those birds despite their sizes.

Like I said, the total weight of the tail-rotor shaft doesn't sit out there on the tip of the tail, regardless how long and heavy they are, as the total weight of the electric motor would.

If the winch on the rescue helicopter is no longer driven by hydro-motor as used to be, you say, is understandable but not due to the inertia. It is due to reliability and controllability. It is also a much smaller motor than the size of the electric tail-motor would need to be and it is situated on the fuselage not far from center gravity where the main rotor axle is.

The problem with electric motors is they need magnets or iron cores which both heavy and that makes them unsuitable for aircrafts on a 'Full Scale". And this is the underlying answer to the OP's question ("Why Full Scale Helicopters are not using Electric Motor Tail Rotor Unit?").

The only light weight electric motor is the piezo-motor, but, that is for precision work and is a low rev motor.

I did not drop my estimate of the size of the tail rotor drive shaft. It is an estimate based on memory - I didn't measure it, so I can't say for sure. Here are pictures of a composite replacement for the metal drive shaft. Look carefully at the lower right hand picture, and then try telling me that is anywhere near 20 mm. The replacement has to fit in the same place, so it isn't any larger than the metal shaft I saw. My four inch estimate looks pretty good to me.

emc_c

My answer # 85 is final for you.

We're just drifting away from the original topic here simply because you have now found something better to argue about. One day have a look at the tail section of a marine helicopter where it folds. Do not hold it against me if you find something different in size than what I saw because some choppers are smaller and some are larger.

You might be suprised to see that helicopters may have different size parts compared with each other for the same purpose.

The real debate here is the weight issue of the electric motor and the generator and how it would pread over the craft rather than the size of the current tail rotor shaft. They are fine as they are and that is why they're being used as opposed to the OPs electric motor concept.

We really have changed direction with this Blog when I see such comments as:-

Do not hold it against me if you find something different in size than what I saw because some choppers are smaller and some are larger.

Exactly what I have always maintained, "mine is only a small one, but it SMELLS like a big one!!!!"

or :-

.......... may have different size parts compared with each other for the same purpose.

Theme no.1 raises its head again, even on CR4!!!!

I never worked on a UH-60 before, but I have worked on the UH-1B, UH-1H, and As-332M. You are correct: the typical tail rotor shaft is approximately 4 inches in diameter, give or take an inch. Being much bigger than the Hueys, the tail rotor shaft of the As-332M Super Puma has a larger diameter (approximately 4¹/₂" inches). Since the UH-60 Blackhawk is approximately the same size as the As-332M, the shaft should be about the same size. Of course, 20mm is still possible if the shaft is solid, not hollow. I have never encountered a tail rotor shaft that's solid before, but there's no reason why not apart from weight, and even that may be less of a problem with a small diameter shaft.

What is even worse that to swing the tail to left or right you would not be able to do it by switching the direction of the tail rotor-motor but still would have to do it by the tilting of the blades, as it is done currently.

Not true. You need a variable speed motor, not a variable pitch fan. With no mechanical connection to the main rotor the fan will have to be variable speed to compensate for differences in torque with speed changes, etc.

Sorry if I missed this comment by someone else.

LL

The weight of drive shafts, ( very thin wall) and coupling cups (light alloys) and flex gears, also light alloys is slight compared to electric motors. The grease to fill each coupling is near the weight of the coupling itself. They are gear couplings that allow for flex and expansion/contraction upon + or - torque. while transmitting revolutions back to each successive gear box. A very light but strong direct= power output system. Far less than an electric motor fan combo needed for larger applications.

Lets say a speed racing helo would do well with elec/fan but no lifting ability above its own weight at best.

Also, I believe blade direction/pitch is restricted as to travel, say for arguement...90/10 or less as torque override is primary........that is why pilots have one leg larger than the other...or ride a sportster with kick start.

emc_c Thanks for all your excellent input on the subject a lot of food for thought. I am still trying to digest it all.

I'll probably have questions and comments tomorrow

Thanks again

Unbelievable... emc_c, it's time for you to get a job.

Not to pile on, but, I thought the question was very well put, in comparison to the truly dumb posts we see.

It started a good amount of conversation and we all learned something about choppers.

I ALREADY KNOW EVERYTHING NEEDED ABOUT MY CHOPPER, thank you!!!!

Thanks RicinCinci for sharing your knowledge.

And your candor in sharing "I as a pilot I would be resistant to trusting my health to an non-coupled tail rotor of electrical nature."

I was wondering what helicopter pilots do if the Main Gearbox should lockup?

Thanks again RicinCinti. It is great that you are here to share this experience

Therefore, if I understand correctly during auto-rotation when the main rotor is not creating any torque the tail rotor needs to be stopped and the tail fin weathervanes your course.

In most conventional Helicopters, the main and the tail rotors are mechanically linked, stopping the tail rotor is not an option.

Also, although you drop like a stone (to rev up the main rotor, get some energy into it) at first, you may still need to "aim" the chopper in a particular direction for the emergency landing, without the tail rotor this would not be possible.....

Depends on the air frame and transmission design. Some have a clutch you have to disengage others use the overrunning clutch like an automatic transmission Sprag clutch. One old bird had the tail rotor driven from the top of the transmission above the clutch so it always turned with the rotor. When we went over the different airframes that was always one of the inspection points.

We have heard here of auto rotation on failure of the helicopter engine or gear box.

Nonetheless, not a word as to the auto-gyro, which has no tail rotor and which gets its lift from auto rotation.

My guess is that the puller or pusher prop providing forward motion also in providing that motion provides the force line that keeps the entire air craft from rotating.

Is that correct?

Can the auto-gyro hover and how does that work?

j.

Auto gyros cannot lift off vertically nor hover. The horizontal rotor must be moving forward to provide lift. Before takeoff the pilot has to crank the horizontal rotor up with a hand crank, or by hand, then pour on the power to increase the H rotor speed with forward motion.

Sorry,

Didn't mean to answer someone else's question.

As far as I am aware, an Autogiro can only land almost vertically. Otherwise it flys mostly like a conventional aeroplane.....

There is an interesting link on Wikipedia that should be read:-

http://en.wikipedia.org/wiki/Autogiro

Yes, you are correct.

Just a thought.

Although I fully understand the pilots wish for a hard mechanical connection between the lift rotor and the tail rotor as insurance, leaving that aside it seems the rotation lock between the two rotors could be achieved in an electrical system simply by synching them on the basis of electrical frequency although that does not preclude their unlocking given an electrical control failure.

j.

So, I will toss in my two cents. I know only rudimentary elements of helicopter design and flying. Everyone here brings up good ideas, fosters the thought process, which got me thinking......if helicopters already have some sort of hydraulics ( I don't know if they do) why not a hydraulic drive motor? Easily controlled for speed, just two lines and a valve or so, and if the pump is driven from the main motor, or the rotor, you could still have some contol as long as the pump is turning. Just thought I would throw that out there and look for the replies.

Cheers!!

mastrsmth: ( again weight is the bad guy here, liquids are heavy as are wall of transmittal plumbing.

Electric drive works on ships and submarines, where weight is not a serious problem.

A Chopper is particularly sensitive to excess weight. An electric drive would be far heavier than the present mechanical drive.

The point about the rotation of the tail rotor in an auto-rotation landing is a good one. That would probably not be available for an electric drive.

Unless a major breakthrough is made in the weight of electric motors, we are unlikely to see them driving tail rotors.

(Such a breakthrough would also be a boon for the electric car industry, making wheel in hub designs a proposition. Currently the unsprung weight involved plays havoc with suspension performance and road holding. Both are heavily affected by the sprung/unsprung weight ratio.)

I apologise for going over board in my first response to you however, I did mean my nswers to your question as some of the basics to consider.

Osborne83 Thanks for your assessment of the articles.

The intermediate tail rotor gearbox is usually a 45 degree gearbox located at the root of the vertical stabilizer.

As for mechanical power transmission weight for the tail rotor, I was assuming that the electric motor would weigh approximately the same as the tail rotor gearbox. That the generator would be direct drive; thus, eliminating tail rotor speed reducing section of the main gearbox and possibly lighter in weight because at a much higher speed will result in lower torque for same horsepower. Also as stated before the elimination of the drive shafting, bearings, coupling, hangers, and intermediate gearbox. I was actually thinking that a heavy lift helicopter like the JHL would be an excellent model for performing a quantitative detail analysis.

Fewer parts besides increasing the likelihood of reliability, it also decreases non-recurring and recurring acquisition costs, and maintenance cost.

My qualitative assessment of vulnerability is based on the smaller cross-sectional area of the power cables. I remember that there was a big push back in the 80s for 5000 psi hydraulic systems because it result in smaller hydraulic tubes that would be less vulnerable.

Backup electrical power source – what I was trying to state is that the tail rotor generator would have excess capacity most of the time and could be used as a secondary electrical power source.

Right, I forgot about the "up the vertical" shaft.

I still think that the mass of a motor of sufficient power to drive the tailrotor would be problematic. While the total mass of the mechanical drive system will likely be more than that of an electrical system, it is a distributed mass. The full mass of the motor would be at the extreme tail.

I'm not saying that it can't be done, but it certainly isn't as simple as in a model or even a UAV. Convincing the certification authorities might be problematic. The military would likely be more receptive to the idea.

The figure in the previous reply is from

Bellocchio, Andrew T.; 200512; DRIVE SYSTEM DESIGN METHODOLOGY FOR A SINGLE MAIN ROTOR HEAVY LIFT HELICOPTER; Georgia Institute of Technology

which is available at http://etd.gatech.edu/theses/available/etd-11212005-112322/unrestricted/bellocchio_andrew_t_200512_mast.pdf

imho:

ducted air is the most reliable system.

i worked on the tuna fleet out of San Diego: used choppers to hunt for fish. i lubed the tail rotor assy every day. Bell 47's..

sometimes the best system isn't used , " because it wasn't invented here "..

you LOL.. but ..

ie: winglets: a proven fact to decrease vortices from wingtips, but it's taken 50 years before planes started showing up ( regularly ) with winglets incorporated.

i tend to think if it wasn't for the $$ of fuel that they would still be considered a novelty.

.o2

Ts say that NOTAR (ducted air) is the most reliable leads to a point not yet made: it is NOT more expensive just because it will cost more to build it. Total Cost of Ownership (TCO) represents the true "cost", and it includes all the maintenance costs. NOTAR would tend to have lower maintenance costs, probably enough to lower TCO below that for mechanical tail rotors. Has anyone seen a study that included all the costs?

Interesting question and comments , i still dont know why contra,rotating main blades is a bad idea . There would be no need for a tail rotor .

The Ruskies managed to come up with a reliable transmission on the old Tupolev Bear bomber in the sixties were the US could not .

What say ye .?

The TU-95 bear was developed during the same period as the B-52 in the USA. And the B-52 followed the already jet-propelled B-47. What would be the point of developing contra-rotating blade system when our bombers had gone to jet propulsion?

emc_c

I really dont know why they went this way , but they did .

I have to assume the beautiful B47 was years ahead of what the Soviet Union could produce at the time .

They might have been concentrating on the same rocket booster that everyone is still trying to get a ride on fifty years later !

My only point was ... the Soviets developed a reliable turbo prop. transmission to allow high powered contra/rotatation in the 1960s.

Britain produced the Fairey "Gannet" to run from carriers. It had counter rotating props and worked well.

It wasn't fast but it was intended as a surveillance plane, an early AWAC I suppose.

As far as helicopters are concerned, I agree that counter rotating main rotors and no tail rotor or boom should be a big advantage and I'm not sure why the system hasn't been developed and generally used.

Anyone know what the problems are which have prevented it's adoption?

I do not understand either why contra-rotating rotors are not considered.

I thought you maybe interested in these sites:

From 1958 http://www.gyrodynehelicopters.com/coaxial_benefits.htm

another site which seems to leverage off this is http://www.freewing.net/coaxial_choice.html

and also for airplanes such as:

From 1931 http://www.air-racing-history.com/aircraft/Macchi-Castoli%20MC%2072.htm

From 1946 http://www.aviastar.org/air/usa/convair_tradewind.php

Enjoy

This is from memory only, but contra rotating props are not efficient with respect to at least one point, moving air in one direction and then instantly (almost!) reversing this by around 90° is a waste of energy. Air has a weight to be fully considered.

The extra complexity of the gearing required, leads to further losses.....however small....

Remember also that extra complexity, introduces further areas for possible failures......and increased costs......

This leads me to the conclusion that these extra losses/costs have been noted by most manufacturers and deemed not worth having.

It would be interesting to see if anyone can either support this (or not!) with some easily verifiable facts.....

Hi Andy Germany

After leaving the rotor, the air has a whirl velocity which is basically lost energy.

A counter-rotating rotor recovers this energy and the air leaves with virtually zero whirl.

When done with ducted fans, there is a significant efficiency improvement.

The only reason I can think of against counter rotation for a chopper is that, because of low disc loading, the pressure rise required is too low to enable a 2 stage rotor to be efficient.

Otherwise, I can't think of any reason why they are not used extensively on helicopters.

If your comments are true, then the reasons must lie with efficiency losses of the gearboxes, extra weight and complexity......every kilo more, is a kilo less fuel.....

Kaman K-Max made in U.S.A...For heavy lifting but in current production.

How about EMP? rescuing stragglers near a nuclear blast and then the tail rotor stops due to the EMP

What's EMP?

Electro Magnetic Pulse.

The secondary damage that a atom bomb does when it explodes. Transistor equipment (when switched on), unless specially designed NOT to be affected will be severely damaged and will not work afterwards.

A relatively small Atom bomb, dropped over the north sea, would damage every single (switched on) transistor radio in about 10 countries......

Valve equipment will continue working, which is why the Warsaw Pact countries continued to supply their armies with valve radio transmitters and receivers up to fairly recently!!

Now I know why the MiGs used to have tiny valves only on board instead of solid state devices.

I would strongly suggest we forget about EMP for this topic string - as this is so far out on the proverbial "but what if" limb as to carry no impact on the topic of why mechanical vs electric tail rotors.

You see, the EMP occurs at the time of the bomb going off like the shock wave - yes, it is very temporary but destructive.

The tail rotor method of drive is not a relavent concern, If it were electric it would only be one more little concern. the motor would stop, EMP would take out the electroinic fuel injection system, the gyros, the elec. sync gear, navigation equipment and even the pilots wrist watch. he would have total total shut-down of everything on the bird that had a circuit board, believe me, the tail rotor would only be one more little swear word coming out of his mouth in a very very long string of words.

Every car on the road would stop if it has electronic ignition, all computers would fry, except those specially shielded, etc.

Besides, if you are rescuing folks near a nuclear blast - and another goes off and you are impacted by EMP, THEN YOU SHOULD PROBABLY NOT BE UP IN THE AIR AT THE T IME ANYWAY!!!

Electric motor itself is immune to EMP unless the pulse is strong enough to induce sufficient current to start melting conductors or frying insulation. In this case the pilot's brain would fry anyway.

Any electronic controls however would be toast unless specially shielded.

I have just found this when searched for "electric tail rotor" instead of electric motor tail rotor"

SATCON TECHNOLOGY CORP Topic#- 89-020 ID# 89AVS012

71 ROGERS ST Office: AVSCOM

CAMBRIDGE. MA 02142 Contract #: DAAJ02-92-C-0003

Phone: (617) 661-8942 PI: JAMES R. DOWNER

Title: ELECTRIC TAIL ROTOR DRIVE

Abstract. During Phase 1, the Direct Electric Tail Rotor Integrated Drive (DETRID) concept was shokn to fe not only feasible, but competitive on a per-unit-weight basis with the existing hardware. DETRID is a concept identified by the Army ti chminate current difficulties with the tail rotor drive train of many helicopters. DETRID replaces a system of gearboxcs, couplings, shafts, and bearings with in electric motor which directly drives the tail rotor blades. The promising rcstLIts of Phase I suggest that the program proceed into the next Phase, which is to demonstrate the DETRID concept both in the laboratory and oln an actual tail section in a wind tunnel. SatCon Technology Corporation proposes to continue to develop a DETRID systcm for the UH60A by designing, fabricating, and testing a prototype of the baseline motor identified in Phase I By use of Government-furnished equipment and rental of a specialty test facility, SatCon will be able to demonstrate the DETRID motor at full scale both on a dynamometer an integrated into an actual UH60A tail section.

Interestingly (to me at least) the RN used a small plane, with contra rotating props, called the "Fairy Gannet", to deliver mail and do other mundane jobs......before this time it was used in an AS role....

It was penetratingly loud and slow!!!!

It was also a name given in the RN for comrades who ate anything and too much of it!!

Is your Avatar anything to do with this aircraft? Or eating? Just a thought at your cost!!!

See the following link for more details:-

http://www.thunder-and-lightnings.co.uk/gannet/history.php

SatCon Applied Technology has a patent (1990) on what they called "self-driving tail rotor" to view see attach link

http://www.freepatentsonline.com/4953811.html

I am very pleased how this thread developed and all the great ideas and comments.

I plan to do a detail trade study to see how a electric vs mechanical tail rotor drive compares using the JHL as model and would like to share with everybody the development of that trade study for your comments.

I believe it is our job as engineers to always challenge the "status quo" and look for paradigm shifts.

@Gannet: Have you made any progress with your trade study. I would definitely be interested to share my knowledge and enter into a more detailed discussion. I am working for a gearbox company that produces main, intermediate and tail rotor gearboxes and earns a considerable fraction of its money from the maintenance work on those components. On the other hand, I personally am working on electrical (instead of hydraulic) (main) rotor control with the ultimate goal to get rid of the swashplate and all the mechanical linkages of today's rotor control systems. Therefore, going more-electric would be fully in-line with my R&D work.