Electric tail rotor; an alternative?

[GrayHorizonsHeli]

Originally Posted by dClbydalpha

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.

[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????

[chopjock]

Originally Posted by 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????

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.

[dClbydalpha]

Originally Posted by Pilot DAR

... 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]

Originally Posted by 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?

google helped me find this:
https://www.flyingmag.com/news/two-place-electric-cessna-172-skyhawk

[krypton_john]

Originally Posted by dClbydalpha

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]

Originally Posted by chopjock

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]

Originally Posted by hoodie

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

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!