Electrically Distributed Anti-Torque (EDAT) by Bell Helicopter

"ttyymmnn" (ttyymmnn) 02/21/2020 at 10:58 • Filed to: Planelopnik

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Some engineer over at Bell had the brilliant  idea to essentially place a quad-copter on the tail of a Bell 429 helicopter. The four electrically-driven fans replace the single mechanically linked tail rotor of the traditional helicopter. Power for the fans is generated by the turbine engines that drive the main rotor, and the blades of the fans are fixed. To go in different directions, the fans just reverse their spin, and it’s all controlled by the flight computer . Bell says that the helo can operate safely with just a single fan. Pretty cool.

The Warzone has a big writeup about it.

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TheRealBicycleBuck > ttyymmnn 02/21/2020 at 11:12

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I wonder how they perform in a power loss scenario. A lack of a mechanical connection would make tail control during autorotation impossible.

Snuze: Needs another Swede > TheRealBicycleBuck 02/21/2020 at 11:15

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One would hope they have a battery backup  system for just that reason. Using modern lithium chemistry batteries it should be possible without adding to much weight. 

ttyymmnn > TheRealBicycleBuck 02/21/2020 at 11:19

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What Snuze said. I’m guessing there is a battery back up that would provide at least enough juice, even to just two rotors, to make a safe landing. This helo also has twin engines, which makes a complete power loss, well, 50% less likely, I suppose. 

facw > TheRealBicycleBuck 02/21/2020 at 11:19

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It’s a good question. One assumes they would either need battery backup, or they’d need to generate power from the rotor side of the free hub (or whatever it is that lets it rotate freely). They could use the rotation to generate power from the tail rotors, but it seems like you shouldn’t be able to generate enough power that way to stop rotation (and of course as soon as you stop spinning, you are no longer generating any power again under that scenario).

Ash78, voting early and often > ttyymmnn 02/21/2020 at 11:19

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Cool, but not quite NOTAR-level cool.

https://en.wikipedia.org/wiki/NOTAR

ttyymmnn > Ash78, voting early and often 02/21/2020 at 11:21

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Don’t see too many NOTARs, though. 

user314 > ttyymmnn 02/21/2020 at 11:24

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Neat. Keeps the benefits of a Fenstron assembly while mitigating some of the later system’s cons. 

ttyymmnn > user314 02/21/2020 at 11:25

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It is also touted as being quieter. 

Ash78, voting early and often > ttyymmnn 02/21/2020 at 11:27

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Exactly...I always wondered why, but then the internet rescued me.

Apparently it’s complicated (multiple systems working together vs a simple blade) , somewhat inefficient, and reduces max cruise.

Check out the secon d reply here, very detailed:

https://aviation.stackexchange.com/questions/39136/helicopters-why-hasnt-notar-been-more-popular

If only EssExTee could be so grossly incandescent > ttyymmnn 02/21/2020 at 11:38

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So if one rotor is enough, why four? I know we want redundancy in aircraft but quadruple is kinda silly when most copters don’t even have a single backup  for the tail rotor.

ttyymmnn > Ash78, voting early and often 02/21/2020 at 11:39

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Excellent info. Thanks. 

Chariotoflove > ttyymmnn 02/21/2020 at 11:40

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I suspect the big determinant of whether this tech makes it to successful production will be Bell’s ability to make it cost effective to purchase. They’ll have to get the system to be at least a manageable premium over the current system. 

MonkeePuzzle > ttyymmnn 02/21/2020 at 11:40

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seems only logical. smart move

surely it deletes a number of moving mechanical parts in and to the tail. and perhaps provides a modicum of redundancy to allow for failure. 

ttyymmnn > If only EssExTee could be so grossly incandescent 02/21/2020 at 11:40

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Maybe more anti-torque from four? Redundancy? Electric engine would be too big for one? I’m just guessing. 

user314 > ttyymmnn 02/21/2020 at 11:42

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If only the Testors “Stingbat” had been real...

If only EssExTee could be so grossly incandescent > ttyymmnn 02/21/2020 at 11:43

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If the motor is too big for one, you just scale it down (also the article you linked says each rotor has a motor) . I guess anti-torque makes sense, i.e. one rotor might be functional but the response from four is optimal. Still looks dumb though.

ttyymmnn > user314 02/21/2020 at 11:46

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Remember this?

gmporschenut also a fan of hondas > If only EssExTee could be so grossly incandescent 02/21/2020 at 11:47

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Skimming the article, I think so 1or 2 could be in neutral, so you wouldn’t have to wait for the powered fans to stop before reversing. 

gmctavish needs more space > gmporschenut also a fan of hondas 02/21/2020 at 11:58

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So it’s like the DCT of tail rotors

Silfa Fifta Dianoer > ttyymmnn 02/21/2020 at 12:02

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Thank you, this greatly increased my knowledge

MasterMario - Keeper of the V8s > If only EssExTee could be so grossly incandescent 02/21/2020 at 12:11

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My guess was going to be that 4 are needed for peak performance, but one is still enough to maintain control.

user314 > ttyymmnn 02/21/2020 at 12:14

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I have two of them, one in the black “operational” config and another in gray with the bubble “trainer” canopy.

I’ve also got the Monogram “F-19"

The Testors “MiG-37B ”

The Testors SR-75/XR-7

and I had the Revell ATB as a young lad

ttyymmnn > user314 02/21/2020 at 12:22

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What’s interesting is how they were really on the right track, with as little official information as there was at the time.

CobraJoe > If only EssExTee could be so grossly incandescent 02/21/2020 at 14:16

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What’s the efficiency of one small rotor working near maximum power vs one larger rotor working at 1/4 power?

BaconSandwich is tasty. > ttyymmnn 02/21/2020 at 14:53

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My brother had one of those!

TheRealBicycleBuck > Snuze: Needs another Swede 02/21/2020 at 18:35

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A battery backup would be an adequate solution if they lost turbine power, but what if they had an electrical failure? They would be in a really bad place if a power surge took out some important fuses. 

TheRealBicycleBuck > ttyymmnn 02/21/2020 at 18:39

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An electrical failure would take out the control systems as well as power to the tail rotors. In other fly-by-wire aircraft they have a mechanical (perhaps hydraulic)  linkage for backup or at the very least, a way to eject from the aircraft.

TheRealBicycleBuck > gmporschenut also a fan of hondas 02/21/2020 at 18:40

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It said they are fixed-pitch, so there may be two for each direction. 

ttyymmnn > TheRealBicycleBuck 02/21/2020 at 18:54

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The F-35 doesn’t. Nor does it have a single steam gauge in the cockpit. It’s got batteries that basically run things long enough for you to point the jet towards home and punch out (as per your last point). This thing’s got two turbines, so here’s hoping you don’t have a double engine failure. I suppose if the electrical system failed somehow, then there would be no flight computer, probably no engine software, etc, so it wouldn’t really matter. Conjecture on my part, though. 

TheRealBicycleBuck > ttyymmnn 02/21/2020 at 19:28

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A way to escape the aircraft if the fly-by-wire system fails is the second option, as you noted. Two turbines aren’t likely to fail, but the common fuel system might. A computer failure or an electrical failure might not take out the power to the tail, but it would kill the control system. That’s a really bad thing when there’s no way to escape due to the blender overhead.

gmporschenut also a fan of hondas > TheRealBicycleBuck 02/21/2020 at 20:53

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“ EDAT’s four rotors have fixed-pitch blades that can spin either forward or backward. Bell says that this means its electrically-powered and controlled system can more precisely and dynamically change how much anti-torque force it’s putting out.” reversible

I think they may want to prevent forward/reverse spinning as that could cause overheating and burnout sooner .  

gmporschenut also a fan of hondas > CobraJoe 02/21/2020 at 21:07

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problem with one large rotor is it then has rotational inertia that will take longer to slow and thus cause thrust in a direction you don’t want. at the same time the large rotor in the other direction will take longer to accelerate and provide thrust in the oppostite direction. Also the single larger propellor will have a greater angular momentum so 2 smaller props can accelerate/deaccelerate faster than a single larger prop.

TheRealBicycleBuck > gmporschenut also a fan of hondas 02/21/2020 at 22:26

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Must’ve missed that. 

SBA Thanks You For All The Fish > ttyymmnn 02/22/2020 at 12:09

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Better spatial use of the tail area, most likely. Plus some redund ancy.

SBA Thanks You For All The Fish > ttyymmnn 02/22/2020 at 12:31

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BTW— the answer to “why four rotors” is right in the article— and it’s brilliant. Four fans have FAR less rotational inertia than a single larger fan, over even duals.

So you have much more responsive torque management-and-control in the tail.

brilliant.

sn4cktimes > ttyymmnn 02/22/2020 at 13:29

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It looks like 3 would have reduced the tail size quite a lot... Or maybe would just more appealing to my brain.

ttyymmnn > sn4cktimes 02/22/2020 at 13:47

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Click on the Warzone article and see all of the other ideas they filed patents for. 

sn4cktimes > ttyymmnn 02/22/2020 at 13:51

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Too many blades. But I guess if you’re gonna patent “something”, go all out.

ttyymmnn > sn4cktimes 02/22/2020 at 14:58

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It could have been worse.

Snuze: Needs another Swede > TheRealBicycleBuck 02/24/2020 at 06:36

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Thats a good point. I don’t know anything about modern helicopter flight controls, but are they all hydraulic/mechanical, or are they fly by wire? I ask this because I suspect a power surge like you are describing could mess up a lot of other important stuff.

Also, I would guess as part of a robust design, they have something equivalent to a “Battle Short.” We had this in the Navy on key pieces of electrical equipment and basically it bypassed all the safeties and interlocks and ran the machine directly off the powered bus. It was only ever to be used in extreme situations because it put the machine and in some cases the operator in danger, but if the choice is possibly break a machine  or lose a submarine and her crew , you’re gonna press the BS button.

TheRealBicycleBuck > Snuze: Needs another Swede 02/24/2020 at 07:40

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I did a little digging and learned that most turbine-powered helicopters have hydraulic controls with assist . Most piston powered helicopters have a mechanical linkage. They have an accumulator to provide assist in the event of power loss, but most can be actuated without the assist. If the controls are too heavy without assist, they are required to have two independent hydraulic systems.

I originally thought that most were mechanical with hydraulic assist. As far as I can tell, there are only a couple of fly-by-wire helicopters out there, one military and one civilian. 

Snuze: Needs another Swede > TheRealBicycleBuck 02/24/2020 at 09:25

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That’s interesting, I didn’t know that.  I knew the old ones were hydraulic or mechanical but didn’t know that it varied by power type (piston or turbine) or that so few were fly by wire.