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skadi
19th Feb 2020, 12:21
Strange design :hmm:

Bell 429 Fenestron (https://m.facebook.com/story.php?story_fbid=3728807067159823&id=100000916985248)

skadi

mindsweeper
19th Feb 2020, 14:18
Electric perhaps?

GrayHorizonsHeli
19th Feb 2020, 19:19
such a crappy video to tell, but perhaps its just camouflage painting techniques so that you have trouble telling the design from a distance as most auto manufacturers do.
I cant see 4 small fans being anywhere near efficient to carry out the task required.

Bravo73
19th Feb 2020, 20:14
My money is on 'fake news', TBH.

Well, I never. Mildly gobsmacked. :O

krypton_john
19th Feb 2020, 21:21
such a crappy video to tell, but perhaps its just camouflage painting techniques so that you have trouble telling the design from a distance as most auto manufacturers do.
I cant see 4 small fans being anywhere near efficient to carry out the task required.

Indeed. I can't imagine any benefit but can think of several detractions for this idea. 4 fans have 4 times as many parts to maintain. Small fans have to spin faster than large fans so are noisy and stressed. 4 fans mean 4 times the risk of something failing and high speed moving parts failing is very dangerous.

LTP90
19th Feb 2020, 23:04
I cant post URLs yet, but verticalmag has the story. 4 electric motors driving fixed pitch blades at varying RPMs

GrayHorizonsHeli
19th Feb 2020, 23:04
guess I was wrong, and it's too early for april fools day

https://youtu.be/ttBEhFhyM1c

https://www.verticalmag.com/news/bell-electrically-distributed-anti-torque-edat/?fbclid=IwAR374AObzn4jC0RCMqvKMGrk9JjdCGwQrK9rClNVGMAH4eOFkX LR7vvPFp0

jimjim1
19th Feb 2020, 23:52
Indeed. I can't imagine any benefit but can think of several detractions for this idea. 4 fans have 4 times as many parts to maintain. Small fans have to spin faster than large fans so are noisy and stressed. 4 fans mean 4 times the risk of something failing and high speed moving parts failing is very dangerous.

As mindsweeper alluded to if they are electric many of these objections turn into advantages.

Much fewer parts, especially moving parts, and possible redundant operation. Losing a singe motor is not necessarily a catastrophe. I have no idea how the number might work out for such a drive system but it doesn't seem completely ridiculous anymore. If it were possible to get rid of variable pitch blades then such a system would be even more attractive, however that may be straying into the ridiculous:)

Google for -- helicopter electric tail rotor

Helicopter Electric Tail Rotor (http://www.launchpnt.com/portfolio/transportation/helicopter-electric-tail-rotor)
"to meet the requirements of an electric tail rotor drive for the Bell 206A/B helicopter as part of a recent Navy SBIR Phase I Award. "

https://www.navysbir.com/13_1/171.htm
"Bell 206 helicopter ... The drive system is estimated to add 7 to 9 kg to the vehicle while increasing vehicle efficiency, reliability, flyability, and operational performance"

FH1100 Pilot
20th Feb 2020, 00:59
As mindsweeper alluded to if they are electric many of these objections turn into advantages.

Much fewer parts, especially moving parts, and possible redundant operation. Losing a singe motor is not necessarily a catastrophe. I have no idea how the number might work out for such a drive system but it doesn't seem completely ridiculous anymore. If it were possible to get rid of variable pitch blades then such a system would be even more attractive, however that may be straying into the ridiculous:)

From the Vertical Magazine article...
“In a nutshell, we removed all of the conventional mechanical anti-torque components — which is gearboxes, driveshafts and tail rotor hub and blades — and replaced it with four electric motors and fans,” Eric Sinusas, program director of light aircraft at Bell, told Vertical. “They are fixed-pitch blades and they’re changing rpm constantly.”

Ascend Charlie
20th Feb 2020, 01:13
In forward flight at speed, they might even be able to turn them off?

How much bigger is the generator to run them? How long can the battery run them if Gen stops? Total electric failure might be a worry...

jimjim1
20th Feb 2020, 01:58
From the Vertical Magazine article...

Thanks,
I was a while writing my post and did not re-visit to see if there were relevant updates:-)

Thing is, if an Electric Transmission works for the tail rotor then it will surely work for that other even peskier rotor?

Electric tail rotor is a dead end since if the main rotor is electrified similarly there is no need for a tail rotor at all. Of course Bell and Airbus are on the case. e.g. see Bell Nexus

Ascend Charlie
20th Feb 2020, 04:24
if the main rotor is electrified similarly there is no need for a tail rotor at all.

Isaac Newton might have something to say about that. Electric motor mounted on fuselage, drives rotor one way, fuselage must rotate the other way.

The only way around it was like the Djinn, using jet reaction motors on each blade tip. Interesting idea, but horrendously noisy.

RichiRich
20th Feb 2020, 06:09
In forward flight at speed, they might even be able to turn them off?

How much bigger is the generator to run them? How long can the battery run them if Gen stops? Total electric failure might be a worry...

Why generator schould stop? Generator is continously powered from main gearbox. I like this idea and I see many profits from this design.

Bell_ringer
20th Feb 2020, 07:02
Why generator schould stop? Generator is continously powered from main gearbox. I like this idea and I see many profits from this design.

Generators can fail, are there redundant gennies or is there battery backup?

Autonomous Collectiv
20th Feb 2020, 07:33
I suspect that there would also be more engine power available to drive the main rotor if not having to send it down the back with the associated loses. When I first read the thread I wondered if they would shut down one or multiple/all of the fans in the cruise. I don't like it visually but guess its an idea that is inevitable given the advances in electric motors, the multiple fans would provide redundancy. And I agree with Charles, main rotor will require anti-torque

RichiRich
20th Feb 2020, 07:55
Generators can fail, are there redundant gennies or is there battery backup?
I think there will be more than one generator for powering the tail rotor system.

Autonomous Collectiv
20th Feb 2020, 08:03
I guess it would also reduce noise as most helicopter noise comes from the tail rotor

cattletruck
20th Feb 2020, 09:17
Interesting points covered such that it can be turned off in cruise, it can be quieter, etc. It could even be turned off with skids on ground, collective fully down and with mains turning for that extra safety. What I'd like to know is how authoritative is it over the original one, especially with a gusting wind abeam. Being fixed pitch I guess they can spin the motors in reverse if the anti-torque ain't enough. Being electric also makes it susceptible to the water ingress and will need extra environmental testing.
I guess you don't even a long tail anymore and just have a stubby tail with 2 of these things either side of the stabiliser. Computer controlled heading would also a doddle to install.

Having said all that I'm still not convinced.

Autonomous Collectiv
20th Feb 2020, 09:32
Interesting points covered such that it can be turned off in cruise, it can be quieter, etc. It could even be turned off with skids on ground, collective fully down and with mains turning for that extra safety. What I'd like to know is how authoritative is it over the original one, especially with a gusting wind abeam. Being fixed pitch I guess they can spin the motors in reverse if the anti-torque ain't enough. Being electric also makes it susceptible to the water ingress and will need extra environmental testing.
I guess you don't even a long tail anymore and just have a stubby tail with 2 of these things either side of the stabiliser. Computer controlled heading would also a doddle to install.

Having said all that I'm still not convinced.

More great points, the more you think about this I expect the more advantages will present. It's only a hop, skip and a jump to the Avatar type contra rotating fans. As long as the power source can replenish the batteries quicker than the fans can deplete them the only limit is imagination.

Bell_ringer
20th Feb 2020, 09:40
Would be interested to understand the difference in weight and CoG for this experimental configuration and what the increased surface area does to handling.
A fly by wire tail rotor system does allow for some interesting options for improved stability.
Bell could be onto a good idea, though it could look a bit sexier.
Still, not as fugly as fenestron :E

skadi
20th Feb 2020, 10:17
A fly by wire tail rotor system does allow for some interesting options for improved stability.
Bell could be onto a good idea, though it could look a bit sexier.
Still, not as fugly as fenestron :E

Designed with composite it could look better than this riveted sheet aluminium. But the latter is easier and cheaper to construct as prototype...

skadi

SimFlightTest
20th Feb 2020, 13:53
Being fixed pitch fans, I wonder how the system will perform during autorotation where it will have to produce both positive and negative thrust in order to control yaw? I would imagine the negative thrust scenario might have a different subjective feel to the pilot because of inefficiencies associated with the fans running backwards.

Also, the system might feel a bit laggy as the fans change rpm. If any of you fly RC helis, the difference in response is night and day between a fixed-pitch rotor and a rotor with collective. Having 4 smaller fans, compared to one larger fan, might mitigate this issue a bit, however, because of the ability of the smaller fans to respond more quickly.

Tango and Cash
20th Feb 2020, 14:22
How to keep engineers busy during a long Canadian winter?

Aussierob
20th Feb 2020, 21:20
Redundant generators. Each engine has one and you now have the no longer required tail rotor drive to use as a generator drive. I think three would be plenty. I assume each motor would have its own speed controller as well. A battery back up is probably unnecessary.

tartare
20th Feb 2020, 21:23
Would be interested to understand the difference in weight and CoG for this experimental configuration and what the increased surface area does to handling.
A fly by wire tail rotor system does allow for some interesting options for improved stability.
Bell could be onto a good idea, though it could look a bit sexier.
Still, not as fugly as fenestron :E

Oh, I don't know - I reckon that looks a darn sight more fugly than a fenestron!
Assume you'd still have problems with running out of tail rotor power/authority in certain situations...?

Winemaker
20th Feb 2020, 22:09
I guess you don't even a long tail anymore and just have a stubby tail with 2 of these things either side of the stabiliser.

Curious SLF here. If you moved the tail rotor(s) closer to the main rotor wouldn't you have to put more power through them because of their shorter moment arm? Halve the distance and you would need to double the torque....

Ascend Charlie
20th Feb 2020, 22:36
Most machines need a vertical fin for directional stability, and to stop it from bumping into the main rotor, it is on a boom that gets it away from under the disc. Minimum length that does the job.

Lurching
21st Feb 2020, 09:13
I'd imagine a system like this would be easy to configure so that the aircraft held a particular heading when no pedal input is introduced.
If the pedals now become switches to adjust the speed of the fans, surely it would be easy to connect this to the compass also.

cattletruck
21st Feb 2020, 09:16
That video of the helicopter transitioning sideways along the runway is not convincing enough for me. I would really like to see the machine doing 360 pedal turns both ways while moving along the runway at that speed, now that would really be impressive.

Curious SLF here. If you moved the tail rotor(s) closer to the main rotor wouldn't you have to put more power through them because of their shorter moment arm? Halve the distance and you would need to double the torque....

Yes, you are quite correct in that the length of the tail increases the moment of the force. But in my suggestion you will have two of them which doubles the power however its not really that simplistic. The reason I suggested a shorter tail was more for the convenience in handling in tight spaces.

Ascend Charlie
21st Feb 2020, 09:52
That video of the helicopter transitioning sideways along the runway is not convincing enough for me.

Same for me, it looked like he was moving downwind, a lot easier than into wind.

CTR
21st Feb 2020, 14:15
Have our expectations for new technologies become unrealistic?

Bell has just flown the worlds first electric distributed fan anti torque system. This was not achieved on some unmanned drone, or a tiny ultralight helicopter. Test flights completed so far were not limited to just hovering or flights from a remote desert.

The Bell 429 EDAT is a full size piloted twin engine helicopter. Flights took place from a commercial airport and over populated areas. This remarkable achievement required full consideration in the design of pilot safety, surrounding population safety, and Transport Canada (Canuck FAA).

Have we become so used to seeing computer-generated graphics and small unmanned drones of unrealistic electric aircraft that many people now cannot appreciate a real advancement in aviation?

Of course EDAT is nowhere near ready for a production helicopter application. But what Bell has achieved should be congratulated and not dismissed. Especially at such a early stage of technology development.

Kudos to the Canucks!!!

Phoinix
21st Feb 2020, 15:23
I'm usualy the one to pursue new technology but this is ridiculous. Probably just another thing they will stick to the 407 and 412, add another letter to the type and say it's now as modern as any other helicopter...

Arnie Madsen
22nd Feb 2020, 06:53
(To my surprise) I like the looks of it .... and if they mold it in composites it could look even better .... also very slender from a rear-view compared to the original 4-blade TR which uses 2 sets of blades stacked side-by-side (pic below).

And to be able to stop the TR on the ground would be an advantage .... as well as a good sales and marketing tool for Bell to promote "safety" for passenger operations ..... very often people who sign those big helicopter checks are themselves not pilots so advertising safety to them has more sizzle than technical stuff .

Wish we knew the volts the electric motors require ..... if the same as the standard Bell starter-generator-battery it would simplify everything .... and if needed , they could simply mount an extra generator on the TR output quill on the main transmission ..... and for redundancy a larger battery

Just thinking out loud .... and in my opinion the whole electric TR system would be much simpler and dependable .... it is very rare for industrial electric generators or motors to fail.

.
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/423x556/bell_429_a_454be98585f4d0973713b51886fc0041f7c83427.jpg
https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/490x598/bell_429_c_rear_v_de9c7ee04f62fd9114a22ac3e3b3868a74f3d496.j pg
https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/504x546/bell_429_e_electric_e5677b71a4f25d10dd010b9b3c51940258590818 .jpg

jimjim1
22nd Feb 2020, 08:23
Isaac Newton might have something to say about that. Electric motor mounted on fuselage, drives rotor one way, fuselage must rotate the other way.

The only way around it was like the Djinn, using jet reaction motors on each blade tip. Interesting idea, but horrendously noisy.

Not exactly. If the main rotor is replaced in the same manner as the tail rotor, that is, with a four rotor set. Then someone somewhere might just come up with an idea as to how the tail rotor might be eliminated.

Bell_ringer
22nd Feb 2020, 08:57
Not exactly. If the main rotor is replaced in the same manner as the tail rotor, that is, with a four rotor set. Then someone somewhere might just come up with an idea as to how the tail rotor might be eliminated.

they already have, why do you think they dropped the “helicopter” and became Bell flight.

https://www.bellflight.com/products/bell-nexus

Flying Bull
22nd Feb 2020, 13:22
Hi
I guess, its Bell approach to incorporate a fenestron type tail rotor - without infringing Airbus patents.
Unfortunately, with fixed blades and variable speeds there might be some high pitch noises - which the original fenestron had also - but was overcome by the unequal spacing of the blades.
I´m also not sure, how well speed changes will cope witch quick demands of power?
And - with different speeds of the fans there will be different speeds of the airflow - while with a "conventional" fenestron/tailrotor (roughly) only the amount of air is altered.
Advantage is the removal of gears - but I´m not quite sure, if that will also be a weight benefit, cause wires which can take high amps as well as electric motors and additional generators will weight.
So I´m skeptical - don´t like the look either.
From an engineering point I really don´t see an advantage from four fans - compared to one bigger one.

aa777888
22nd Feb 2020, 13:42
As both an engineer and a helicopter pilot I think this is brilliant. It will be simpler, safer, lighter, more reliable, less noisy, and less expensive.

I am curious about the fan acceleration/deceleration curves. That seems a bit challenging, but clearly Bell would want this anti-torque mechanism to be at least as, if not more, responsive than existing methods.

Claims of zero tail rotor speed on the ground are interesting, but one wonders how this will be sorted out for operation on low friction surfaces like water, snow and ice (currently of significant concern to me every flying day this winter :)).

I am curious about the exact weight trade-off. The tail intuitively looks lighter and sleeker than a gearbox, control rod, swash plate, pitch links and normal tail rotor. Wiring will not be any heavier than a drive shaft and probably lighter. But the weight of redundant generators and motor controllers located at the main gearbox is of interest. We could take a gander at the size of the motors if we had a little data: how much horsepower (or KW if your prefer) does the tail rotor require on this helicopter?

jimjim1
22nd Feb 2020, 13:54
they already have, why do you think they dropped the “helicopter” and became Bell flight.
https://www.bellflight.com/products/bell-nexus

Thanks, my message was a bit too obtuse, I should have spelled it all out. I think I mentioned the nexus further above.

All interesting stuff. It seems that helicopters of the current configuration may not be around for too long. Depends of course on the exact way the numbers work out but it would seem that a lot of the single points of failure of helicopters could be removed by the use of electric transmissions.

By the Way Electric Transmissions are not new.
https://en.wikipedia.org/wiki/Diesel_locomotive#First_functional_diesel_vehicles
"In 1914, world's first functional diesel–electric railcars were produced"

CTR
22nd Feb 2020, 16:26
Hi
I guess, its Bell approach to incorporate a fenestron type tail rotor - without infringing Airbus patents.
Unfortunately, with fixed blades and variable speeds there might be some high pitch noises - which the original fenestron had also - but was overcome by the unequal spacing of the blades.
I´m also not sure, how well speed changes will cope witch quick demands of power?
And - with different speeds of the fans there will be different speeds of the airflow - while with a "conventional" fenestron/tailrotor (roughly) only the amount of air is altered....e.

Actually, most of Airbus’s Fenstrom patents expired over a decade ago. this includes the unequal blade spacing. That’s why you see some small light sport helicopters with them.

NASA published some articles on electric distributed propulsion and the noise reduction benefits a few years back. In one article they described how operating multiple fans at different speeds reduces the apparent noise by spreading the frequency tones of the noise. Equivalent to playing a cord with multiple soft notes on a piano versus one loud note. I believe this is what Bell is trying to do with their EDAT.

Noise also increases with rotor tip speed, even in a duct. With electric motors driving fans, when thrust is not needed the fans can be reduced in speed, or even stopped. Not something that can be done with a conventional gear driven rotor.

As far as control response, as the Drive article notes, this is the reason for using 4 fans. Reducing individual fan inertia using multiple fans allows for rapid speed changes. If you watch some of the large quad drones maneuver, you will see this concept is already in use.

bellblade2014
23rd Feb 2020, 02:36
Thanks, my message was a bit too obtuse, I should have spelled it all out. I think I mentioned the nexus further above.

All interesting stuff. It seems that helicopters of the current configuration may not be around for too long. Depends of course on the exact way the numbers work out but it would seem that a lot of the single points of failure of helicopters could be removed by the use of electric transmissions.

By the Way Electric Transmissions are not new.
https://en.wikipedia.org/wiki/Diesel_locomotive#First_functional_diesel_vehicles
"In 1914, world's first functional diesel–electric railcars were produced"

not to be the naysayer, but there is no way they put this on a very pricey 429 unless they absolutely had to. Meaning the single engine Bell products likely didn’t have the electrical capacity to drive the generators and associated electrical claptrap. I’m betting this was because they needed to add huge generators which would push the prototype into a twin engine beast and explain the odd choice of putting this on one of the more expensive Bell variants instead of A 505 or 407.

That doesn’t account for any eventual complexity required to certify the system. Keep in mind there are zero fly by wire civil certified helicopters in existence. Adding an FBW system like this would have flight critical software, redundancy requirements all along the routing of the tail boom and a requirement for no “common mode” failures. That generally means 4 identical fans and motors would not be easily qualified with in flight critical applications because they were not designed for such a purpose.

I bet it is heavier than the system it replaces by a large margin... increases susceptibility to common mode critical failures like software, lightning or EMI.... and substantially less efficient from a pure energy transfer perspective... lots of physics to combat to prove me wrong here.

im glad Bell is investing some money in commercial space though. This seems like a real project as opposed to the FCX1 thing they showed a few years ago... so that’s nice.

dangermouse
23rd Feb 2020, 11:58
So let's not read too much in to it, frankly we'll done Bell forgetting some real size flight hardware to this stage. I suspect the 4 motor choice is a combination of redundancy, noise, weight, heat dissipation and response reasons. I know other manufacturers are looking at electric tail control but this is the first I have heard using more than 1 rotor, a very elegant solution in my opinion as the motor is likely to be the weak link in the chain reliability wise, cabling, generators and control systems have aircraft qualification already. Would be very interesting to see how it handles in crosswords above the minimum spec point (17kts). BTW what is the normal low speed envelope for the 429?

DM🐀

IFMU
23rd Feb 2020, 14:28
That doesn’t account for any eventual complexity required to certify the system. Keep in mind there are zero fly by wire civil certified helicopters in existence. Adding an FBW system like this would have flight critical software, redundancy requirements all along the routing of the tail boom and a requirement for no “common mode” failures. That generally means 4 identical fans and motors would not be easily qualified with in flight critical applications because they were not designed for such a purpose.

I bet it is heavier than the system it replaces by a large margin... increases susceptibility to common mode critical failures like software, lightning or EMI.... and substantially less efficient from a pure energy transfer perspective... lots of physics to combat to prove me wrong here.

im glad Bell is investing some money in commercial space though. This seems like a real project as opposed to the FCX1 thing they showed a few years ago... so that’s nice.

Well said bellblade2014 and captures my thoughts closely. Still cool they built and flew it. Taking IR&D to flight test is a sign of a healthy engineering department and good leadership.

airsail
23rd Feb 2020, 20:19
Four layers of redundancy with four electric motors. Considerable weight saving at the rear, C of G moving forward. More streamlined than current options. Large reduction in maintenance requirements, current systems are complex and heavy.
10-15% Power saving that is now available for lift rather than yaw control.
Well worth more investment and testing.

CTR
23rd Feb 2020, 20:28
I think of the Bell EDAT as a baby step for their Nexus air taxi. How will you ever FAA certify something like an all electric quad tilt rotor aircraft when you can’t certify an electric tail rotor on a conventional helicopter?

riff_raff
23rd Feb 2020, 20:35
dangermouse -

Your comment regarding the number of motors and reliability/failure rates is correct. Below is a typical fault tree for an electro-mechanical flight control actuation system. The threshold for primary flight control applications (like a helicopter tail rotor) is 1x10^-9 failures/flight hour. As you can see the least reliable parts of the system are the motor power electronics and controllers. A system like this would probably require 3 or more independent and isolated power/control circuits, and fault tolerant multi-phase motors. Fixed pitch blades are less efficient, but eliminate the need for very high reliability (and complex) actuators.


https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/355x272/capture_36fff152a71ca63fcfd9307ffba70cd302109973.png

JimEli
23rd Feb 2020, 20:39
dangermouse -

Your comment regarding the number of motors and reliability/failure rates is correct. Below is a typical fault tree for an electro-mechanical flight control actuation system. The threshold for primary flight control applications (like a helicopter tail rotor) is 1x10^-9 failures/flight hour. As you can see the least reliable parts of the system are the motor power electronics and controllers. A system like this would probably require 3 or more independent and isolated power/control circuits, and fault tolerant multi-phase motors. Fixed pitch blades are less efficient, but eliminate the need for very high reliability (and complex) actuators.


https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/355x272/capture_36fff152a71ca63fcfd9307ffba70cd302109973.pngrate

AND [4 of each] ...

IFMU
23rd Feb 2020, 22:11
But that does not address common mode software or firmware failures.

CTR
23rd Feb 2020, 22:35
Dangermouse and Riff Raff, the math is not that simple, or the whole requirements story.

First, loss of tail rotor control on most FAA certified helicopters is not classified as catastrophic, requiring 1E-9 probability of failure. Loss of tail rotor control is typically classified as hazardous, requiring only 1E-7 probability of failure. For Part 29 certification, the cyclic and collective controls however a catastrophic classification is correct.

Second, the Bell 429 is a Part 27 certified helicopter. For Part 27 certification flight controls a FEMCA is not required. However it is required under Part 29. I admit for new and novel technologies this is a gray area.

Third, the analysis you are providing as a reference is for a screw EMA actuator. You can delete the screws from the probability analysis. Additionally bearing failures are easily mitigated by use of redundant bearings or bushings, along with a sensor to detect primary bearing failure. So the probability of a dual simultaneous bearing failure is not even worth considering. Finally, main reason screw actuators are not used in aircraft primary flight controls is the difficulty in mitigating the common mode jam failure of a single screw. Configure two or three actuators in parallel, one actuator jams the assembly. Configure two or three actuators in series you end up with a very long actuator.

This is a big reason the Bell EDAT makes sense. In the event of one jammed fan, the remaining fans performance are not impacted.

bellblade2014
24th Feb 2020, 01:07
Dangermouse and Riff Raff, the math is not that simple, or the whole requirements story.

First, loss of tail rotor control on most FAA certified helicopters is not classified as catastrophic, requiring 1E-9 probability of failure. Loss of tail rotor control is typically classified as hazardous, requiring only 1E-7 probability of failure. For Part 29 certification, the cyclic and collective controls however a catastrophic classification is correct.

Second, the Bell 429 is a Part 27 certified helicopter. For Part 27 certification flight controls a FEMCA is not required. However it is required under Part 29. I admit for new and novel technologies this is a gray area.

Third, the analysis you are providing as a reference is for a screw EMA actuator. You can delete the screws from the probability analysis. Additionally bearing failures are easily mitigated by use of redundant bearings or bushings, along with a sensor to detect primary bearing failure. So the probability of a dual simultaneous bearing failure is not even worth considering. Finally, main reason screw actuators are not used in aircraft primary flight controls is the difficulty in mitigating the common mode jam failure of a single screw. Configure two or three actuators in parallel, one actuator jams the assembly. Configure two or three actuators in series you end up with a very long actuator.

This is a big reason the Bell EDAT makes sense. In the event of one jammed fan, the remaining fans performance are not impacted.

Common mode failures including software, EMI, HIRF, Lightning (IEL in particular), and latent manufacturing defect will all be tough to meet for this application.

The energy efficiency argument is tricky though... the engine>>>generator>>>distribution>>>motor is quite inefficient vs straight mechanical power transfer... losses are very small along a traditional series of bearings and gears.

cant wait to see those performance numbers.

CTR
24th Feb 2020, 10:58
Common mode failures including software, EMI, HIRF, Lightning (IEL in particular), and latent manufacturing defect will all be tough to meet for this application.

The energy efficiency argument is tricky though... Fully agree on all points. But as stated earlier, EDAT is a good baby step for electric distributed propulsion. Because if you can’t do an electric tail rotor requiring only 1×E-7, how will you ever do an all electric EVTOL requiring a probability of failure better than 1XE-9?

bellblade2014
24th Feb 2020, 15:10
Fully agree on all points. But as stated earlier, EDAT is a good baby step for electric distributed propulsion. Because if you can’t do an electric tail rotor requiring only 1×E-7, how will you ever do an all electric EVTOL requiring a probability of failure better than 1XE-9?


phenomenal question. I do not have faith in full electric EVTOL in the next 3 generations of occupants. I believe we will have at least one full generation of residents on Mars before we have full electric EVTOL’s FAA certified for part 135 equivalent operation. Technical risks abound and the civil certification mountain is getting much worse not better. The 737MAX will take a horrendous process to new heights (or lows). Just one example, it has long been an embarrassment to take approved and in Service STC’s and get them incorporated into an aircraft TC. That’s literally an approved change getting incorporated in an approved aircraft. These processes get denied all the time for stuff like.... Lithium BATTERIES! Should be easy to get approval to power the whole ship with them!

As long as the regulatory environment continues it’s profound misplaced emphasis on process over substance, EVTOL’s will be only used in Kit or Experimental applications... and helicopters have a bright and vibrant future!

Arnie Madsen
25th Feb 2020, 07:39
I confess to being an old school helicopter guy and find the battery-electric drones swarming the sky quite irksome.

However we must give those enthusiastic drone-youth some credit .... here is a prototype battery-electric they built to carry a passenger .... they are not hindered by anything ... probably no one told them it wouldn't work so they just went ahead and did it. Filmed at an old Zeppelin hangar in Germany I think

It is an 18 minute video .... and at 15:00 flies outdoors with a lightweight dummy .

Will be interesting to see if it will actually carry a passenger , and of course battery life will likely be under 30 minutes and not very practical as far as helicopters go.

Have to give these fellows some admiration ... not only that ... they are already self-trained to fly it by remote control ... I think I am jealous .... haaaa !!! ... and I doubt they have a multi-million dollar helicopter engineering department backing them .... they are more like video-game enthusiasts.

Anyway , it gives some credence to using several small electric motors with plastic propellers like the Bell 429 experiment.

https://www.youtube.com/watch?time_continue=1135&v=6xJ27BtlM0c&feature=emb_logo

skadi
25th Feb 2020, 10:42
Will be interesting to see if it will actually carry a passenger .....

Here you go.... :}

https://m.youtube.com/watch?v=s-DghXJp3J4

skadi

212man
25th Feb 2020, 11:08
Filmed at an old Zeppelin hangar in Germany I think
Well they say that in the video, but it certainly doesn't look like it - maybe for a small modern airship

skadi
25th Feb 2020, 11:38
Well they say that in the video, but it certainly doesn't look like it - maybe for a small modern airship

There are hangars in Germany for modern airships in Friedrichshafen and Essen-Mühlheim, the first one could fit...

skadi

mickjoebill
29th Feb 2020, 00:32
Presumably, without the fuss of a long drive shaft, a folding tail is a doddle! if so, a desirable feature?


mjb

MLH
1st Mar 2020, 17:09
To clear up a misconception, the electrically powered fans still present a load to the engine.

CTR
1st Mar 2020, 18:10
To clear up a misconception, the electrically powered fans still present a load to the engine.

Correct. In fact when hovering the electric fans will impose a higher engine load than a conventional shaft driven tail rotor due to the lower efficiency of electrics.

However as forward speed increases, the electric fan speeds can be reduced or even stopped. Therefore the electric fan load on the engines can drop below that of a conventional shaft driven tail rotor.

Another factor to be considered is the impact of reduction in main rotor speed to reduce noise. Many helicopters today have the capability of reducing rotor speed to reduce noise. This results in reduced lift capacity and engine efficiency. The ability to reduce the tail rotor speed independent of the main rotor speed may allow for additional performance benefits.

MLH
1st Mar 2020, 21:00
I suspect that a flat pitched conventional TR in cruise does not pull much power.

SuperF
1st Mar 2020, 21:37
Correct. In fact when hovering the electric fans will impose a higher engine load than a conventional shaft driven tail rotor due to the lower efficiency of electrics.

However as forward speed increases, the electric fan speeds can be reduced or even stopped. Therefore the electric fan load on the engines can drop below that of a conventional shaft driven tail rotor.

Another factor to be considered is the impact of reduction in main rotor speed to reduce noise. Many helicopters today have the capability of reducing rotor speed to reduce noise. This results in reduced lift capacity and engine efficiency. The ability to reduce the tail rotor speed independent of the main rotor speed may allow for additional performance benefits.

Just a question Re the above comment?

For doing what a lot of helicopters actually do, would a conventional tail rotor be better? A lot of helicopters are already maxed out when lifting heavy loads close to operating limits, and pushing a bit too much TR causes spikes that the computer loves to record for you. AS350 being an example. If the electric fans will draw more power than conventional TR, then surely they would be worse in these situations? As forward speed increases the draw on the conventional TR also decreases, but they aren't near the limits at this point.

So for operations such as Fire fighting, Utility, construction, Agricultural, lifting, logging, SAR if lots of winching, etc a conventional TR would probably be better??

CTR
2nd Mar 2020, 00:21
So for operations such as Fire fighting, Utility, construction, Agricultural, lifting, logging, SAR if lots of winching, etc a conventional TR would probably be better??

Correct. That is also why you don’t see helicopters with Fenstroms and Notars being used for these missions.

No solution fits every mission.

CTR
2nd Mar 2020, 00:32
I suspect that a flat pitched conventional TR in cruise does not pull much power.

It matters what you consider “much”. Adding in the open tail rotor additional drag, I wouldn’t be surprised at 30+ HP. A 407 tail rotor consumes about 70 HP in cruise.