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What to Do After Finding Hot Connectors on Overhead Power Lines (2017) [video] (youtube.com)
312 points by camtarn 5 months ago | hide | past | web | favorite | 198 comments

This video shows an aerial line crew (lineworker and pilot in a helicopter) bypassing a high-resistance splice in a 220kV overhead power line, attaching a large bolt-on shunt while the line is still live. The lineworker sits on a platform on the outside of the helicopter while doing the work, in an incredible demonstration of precision helicopter hovering.

It is hard to overstate how difficult it is to hover a helicopter this precisely for this long. Helicopters are dynamically unstable. If you take your hands off the controls, they start to flip over almost immediately and become unrecoverable within 2-3 seconds.

The best analogy I've heard: imagine trying to stand on a basketball. Now imagine trying to stand on a basketball without flailing your arms around. Now imagine trying to do that for half an hour while someone's life depends on you not screwing up even for a single second.

Okay I've actually flown helicopters, and it's not that hard. Harder than fixed-wing, but much easier than standing on a basketball.

If I read your parent correctly, you need to compare standing on a basketball, not with flying a helicopter, but with precision hovering one.

Fair enough. Hovering is definitely harder than forward motion, because among other things the tail boom acts as a weathervane during forward motion. But hovering is still easier than standing on a basketball. I've done the former, and I can't imagine even trying to do the latter.

Are you rated for the Basketball? How many hours have you logged on the basketball? /s

I got my "single basketball on grass" rating a couple of years ago, and have been meaning to schedule a checkride for my "single basketball on hardcourt" endorsement for a long time, but honestly I don't know when I'd ever use it.

Exactly. Flying a moving helicopter is not hard. A helicopter is much more stable while moving forward than while hovering. (And for the record, I am mainly a fixed wing pilot but I have also flown a helicopter.)

It's a common misconception that learning to stand on a ball is difficult to do, you can actually learn all the basics in a few hours. Most of the hours you need for your endorsement is spent on things like balance recovery, finding a safe place to fall, and interacting with other ball-standers. Keeping your balance becomes second nature after 60 hours or so.

I would wager that it's easier to hover a helicopter than a fixed wing aircraft.

:) It can be done! (If your point of reference is the ground.)


I have not actually flown a helicopter, but every time I tried one in MS Flight Simulator, I promptly lost my balance, flipped over and crashed directly after taking off.

However, it may be that using some other form of control than a mouse works better.

I've bought a joystick (some inexpensive HOTAS set actually [1]) specifically for playing helicopter sims. It makes a world of a difference. I mean, still hard, but suddenly approachable at all and fun. And notably, all the hand movements you do must be super tiny. According to youtube, that's how it is on real helis too.

[1] namely, Thrustmaster T-Flight HOTAS X, IIRC

The real thing is easier than a simulator. The sensory inputs that come from your butt are invaluable and impossible to reproduce in a desktop simulator.

Plus you're very highly-motivated to stay alive.

> I've actually flown helicopters, and it's not that hard.

When all helicopters are quad, tailless, designs flying will be much easier.

Good point. However big quads can't work exactly like little quads. They'll still need collective pitch, which is mechanically more complicated than just throttling rotor power the way little quads do it. Big rotors cannot change RPM quick enough to keep the thing stable. (I expect people are trying, but it's gonna take huge power fluxes to make it work. Easier just to build collective controls.)

They can’t do computer based stabilization?

They can. I remember a field trip back in university (maybe even high school, it was years ago) to an emergency response center. They had a medevac helicopter with auto-hover, where the pilot could just hit 'position hold' and it would hover there while they winched someone to safety.

I'd imagine the reason a DJI drone's capabilities are so much greater than those of a helicopter carrying passengers is that the former can fall out of the sky every now and then and it's no big deal. The latter has to pass a whole lot of rigorous FAA (or equivalent) testing.

There are also aerodynamic realities. There are limits on the performance of quadcopters. To get heavylift performance, say over 10000lbs, a quad will need to be huge, requiring lots of heavy arms. A single big rotor, with variable pitch, is much easier and more efficient at such scales.

I havent seen a quad that can autorotate, a necessary emergency trick if you want to carry people. When the power fails on a quad it just falls. Traditional helos can actually glide to a controlled landing.

the lack of ability to fly with one engine out, in a quad, is why most of the human-carrying systems proposed such as the eHang unit are what's known as an X8 configuration. Four arms, eight motors in a coaxial configuration on each arm. Can fly and land with a dead motor.

This one can fly with just one rotor running:


Admittedly it would be a pretty terrifying ride to the ground, but preferable to plummeting. There’s a lot of rotational energy in the aircraft though.

I think there’s probably significant scope for improvement in redundancy of these systems.

But can they fly with all the motors dead? What if they loose the supply of power from the battery system? A standard config can deal with that senario.

I am not aware of any multicopter design that can autorotate. Something like this with a tilt wing approach probably has some ability to glide:


They could. They just need variable pitch (aka collective) on all the blades. And this needs to be actuated by a different power system so that it remains operational when the main power stops. Helicopters use hydraulics, or even manual power.

Autorotation is where helicopters get their speed/altitude restrictions when carrying passengers. They generally are not allowed to hover at low altitude because from there they cannot safely autorotate onto the ground. If drones want to carry people, or carry heavy things over people, then they will need to develop some sort of plan. Total engine failure should never result in the total loss of the aircraft.

Over a sufficiently long and thorough testing period, I think x8 design multirotors with eight or more motors/props will prove to have a statistical rate of motor failure much lower than the incidence of single engine failure in small to mid size internal combustion engine and turbine helicopters.

It would have to monumentally better before I'd get into one that didn't have a backup plan. The motors could be 100% reliable, but the possibility of loosing power due to maintenance or control issues remains. A perfectly good motor is useless if the cable feeding it electricity shorts out.

> I'd imagine the reason a DJI drone's capabilities are so much greater than those of a helicopter carrying passengers is that the former can fall out of the sky every now and then and it's no big deal. The latter has to pass a whole lot of rigorous FAA (or equivalent) testing.

This reminded me of another comment I read recently, and I was actually able to remember where I read it! https://news.ycombinator.com/item?id=17723107

> Hi- I used to work in regulated pharma and I want to be clear: " The core problem is that the FDA-approved devices are optimized not for getting the best result, but for ensuring the manufacturer can't be blamed if something goes wrong" is a misleading statement. The reason everything is regulated is that sometimes things do go wrong, and it's necessary to have root cause attribution so the problem can be remedied and a fix deployed, and, if somebody did something illegal or dumb, they can be sanctioned.

(The quoted part of this comment, itself from a previous comment, is the part I found relevant, but I quoted the whole thing (reply and all) because I found the whole thing interesting.)

I think I can naively say with confidence that aviation and medical certification are very similarly rigorous.

So, it sounds to me that the autohover functionality you describe was perhaps the equivalent of Tesla "Autopilot" (which really amounts to auto-steer). The context of doing rescue lifesaving over sea is indeed very stringent, but at the same time, it's not going to be the end of the world if the helicopter moves around a bit, because it's in the open air. And if the situation is dire - strong crosswinds, or someone in critical condition - the pilot's training probably instructs them not to use it.

In this situation, letting the controls go for 2-3 seconds (as per the other comments here) is going to mean an unrecoverable crash, and perhaps a rotor blade might cut one of the cables and then you have 220kV waving everywhere, hitting other power lines, touching the ground..... no. You just find the best pilots that can hover Really Well™, and pay them metric stupid amounts of money so they don't go anywhere else.

Now I'm wondering if the pilots hold hovering competitions, in the same way people in the military frequently do target practice.

> Now I'm wondering if the pilots hold hovering competitions, in the same way people in the military frequently do target practice.

Yes. Have a read of "Rescue Pilot" by Jerry Grayson. It's a great read. He describes how they used to practise hovering with a single front wheel resting on the top of a particular coastal rock formation. It was a competition in the sense that one crew upped the ante by managing to balance their tail wheel on the rock, so the rest of the crews followed.

[1] https://www.bloomsbury.com/au/rescue-pilot-9781472918840/

Edit: Another link: http://rescuepilot.net/

They also open beer bottles with the skids to demonstrate precision control: https://www.youtube.com/results?search_query=helicopter+beer...

Similarly, some fire departments will do dexterity exercises like playing Jenga with rescue tools ("jaws of life" - https://www.jawsoflife.com/), and similar with ladder trucks and building blocks.

Wow, I just read the first chapter via https://issuu.com/bloomsburypublishing/docs/rescue_pilot.

Yet another book to add to the wishlist... I'm gonna need a job that gives me a bit of spare time, the pile is getting pretty big, haha.

The Vulcan bit leapt out at me; I've also read Vulcan 607! That book was purely technical; I would have appreciated an explanation about the political upheaval going on with the RAF at the time as well, I had absolutely no idea.

I had no idea hovering over sea is as complex as it is - of course everything underneath the helicopter is going up and down. So the helicopter needs to match that if it doesn't want to whomp onto the deck as it lands. Hah.

And so, in the same vein, hovering over a ship doing rescue operations is clearly going to preclude the use of the kind of autopilot described in the GGP comment.

I've been interested in the idea of flying since I was about 15, but I've been dragging my feet on getting involved for years (I'm 27 now) - if I love it, I'll be depressed I can't afford to dive right in, but if I hate it or can't get my head around the flight controls (I have poor hand-eye coordination, a lot of visual things don't "click" for me, and I can't keep an RC helicopter in the air), I'm not sure if I'd handle the let-down. Because of the expense involved I'm a bit on the fence about it.

Various health issues are why I didn't go the RAAF route a long time ago. (I'm not even sure what to name my condition - I've briefly described it at https://news.ycombinator.com/item?id=15005811 and https://news.ycombinator.com/item?id=17780498.)

I wonder why they don't instead suspend the line worker something like 50 feet below the helicopter to give themselves more margin for error. I guess the current method must be reliable enough that they don't bother.

Then you’d have two problems. There’s more wind up there than on the ground. The lineman would get blown around. Imagine a yo-yo tied to a drone hovering above the top of a tall tree. Now try to hold the yo-yo perfectly on a leaf.

That would mean a rope or similar, so the helicopter can actually take off.. that's not going to be stable!

At the end of the day, any mistake at 5 foot or 50 foot away is likely to be fatal!

Maybe to give the pilot a better view?

Auto-hover technology does exist, but it's not common. Also the pilot has to be able to do it manually in case the autopilot fails, and so most pilots will elect to do it manually at least some of the time just to stay in practice.

Perhaps the smart thing would be to practice in situations where an error does not cause someone else to get electrocuted.

A fair point, but you wouldn't get electrocuted in this case. You'd die when the helicopter crashed. (Not that that makes a lot of difference.)

More to the point, helicopters and power lines have both been around a lot longer than helicopter autohover technology, and aviation is an inherently conservative enterprise. Even if these sorts of repairs are being done using autohover today (I don't know) they were surely flown manually in the past.

UPDATE: I asked this question on /r/flying and got this response from an actual helicopter pilot:


"In a low energy state like an OGE hover, and especially when doing dangerous work like utility (as in the video), live hoists, etc we are almost always handflying. You would be surprised at how few helicopters out there are even capable of auto-hovering. We have an IAHAAS system on the Pave Hawk which in theory can do things like auto hover, auto land, maintain radalt and baro altitudes, even fly zero vis approaches etc. but we don't trust it. I have personally seen it do some sketchy things like virtually departing us from controlled flight during a steady hover for literally no reason."

Isn’t AFCS with hold position capability pretty much standard these days?

What does it mean for an autopilot to fail, in this case? We're not talking about an automatic guidance system, like in fixed-wing aircraft. We're talking about a thing that translates high-level commands on the stick to low-level commands to the motors, like a car's automatic transmission.

Cars with automatic transmission don't have a "backup manual transmission" for when the automatic transmission fails. The automatic transmission doesn't fail.

> What does it mean for an autopilot to fail, in this case? We're not talking about an automatic guidance system, like in fixed-wing aircraft.

Actually, that is exactly what we're talking about. Why would you doubt it? You not only need to keep the helicopter oriented, you need to keep it in the same place, i.e. you need it to follow a zero-velocity trajectory. Why would you think that this is any different from a regular autopilot?

An automatic guidance system in a fixed-wing aircraft is given a route with waypoints, and autonomously navigates between them. It needs to know things about horizons, Great Circles, collision-avoiding altitude change plans, least-time routing, reachability of nearby airports given available fuel weight, etc. There's no real way to implement this with anything less than a CPU with a full (realtime) OS and a software stack on it, full of complex pre-baked databases, with multiple inter-related components from different vendors in the mix. It's frail. Of course it needs a backup.

The kind of system I'm talking about here, on the other hand, is essentially a physical model of the three available controls and how they interact to move the aircraft (and thus predict how the aircraft will be moved); combined with actuator-sensors, accelerometers, and gyroscopes to read off how the aircraft is being affected by those controls (and thus correct the prediction)—enabling you to translate linear movement of a flight-stick to linear movement of the helicopter. It's a dynamic torque model feeding a control system, with a user-supplied reference point. You can make an ASIC that does that and put it through fuzz-testing for literally every potential input combination it'll ever receive.

Yes, said ASIC might physically fail (even after you've done an extensive burn-in test)—but, given the tolerances we have in making ruggedized solid-state electronics these days, vs. the tolerances we have in making mechanical systems, it'd be the least likely part in the control chain to fail.

It is obvious you have never actually flown a real plane, and you have no familiarity with actual aircraft avionics. There are so many errors in what you said above that I don't have the time to correct them all.

It is true that state-of-the-art navigation systems operate the way you described. But airplanes have been flying for over 100 years, and there have been autopilots for nearly all of them (the earliest autopilot dates back to 1912). The vast majority of airplanes flying today do not have state-of-the-art systems.

You are just picking random descriptions of autopilot systems.

Helicopters can also have advanced and full integrated routing systems that will complete an entire trip from A to B, just as fixed-wings can have a simplistic input-to-output linked autopilot that just aims to keep the plane level and with the same heading.

So yes, an advanced system is more complicated than a simple system, but both systems can fail. And since that is inevitable, it's usually better to have a complex system with redundancy that will tolerate failure, than a simple system with no backup that will lead to catastrophe.

it is not the electronic chips that cause an autopilot to fail (in most cases). the primary failure mode is 'something else', meaning a failure in the mechanical equipment connected to the environment.

Not having a backup doesn’t not mean that no failure is possible, that is a very odd thing to say.

Automatic transmissions fail all the time, and then the car stops moving. Ok for cars but serious problem for flight so these aircraft have multiple automatic and manual redundancies.

Helicopter autopilots are indeed full guidance systems like fixed wing aircraft, but they can hold the craft in hover position because it's just another flying position possible for helicopters, but it is still actively flying.

I misspoke. What I meant is, the ASIC controlling the automatic transmission—the thing that makes it "an automatic transmission"—doesn't fail. It's just a simple bit of solid-state electronics. It'll probably outlive the car.

Other parts of the automatic transmission system fail, sure, but those parts are the same parts that are in a manual transmission. (Because, after all, in modern cars, a manual transmission's control system still ends up as signals sent to an electronic gearbox.)

So, like I said—in modern cars, where you've just got an electronic gearbox anyway, there's no sense in having both the ASIC issuing control-commands to the electronic gearbox, and a backup manual stick for issuing the same commands. If there's any fault in the system, it's far, far more likely to come from the stick's mechanism breaking down and issuing spurious commands, than from the ASIC breaking down and issuing spurious commands. And more likely than either is the gearbox getting messed up because it's sitting in a hot, dirty engine compartment.

"the ASIC controlling the automatic transmission—the thing that makes it "an automatic transmission"—doesn't fail"

In 2018, it is possible to have a car with an ECU that is 30 years old, and I happen to have one. Solder joints can go bad over time, and repairing the control unit is a thing that people do on cars like mine. If I was looking forwards regarding some other bit of electronics, I would probably worry about capacitors too.

All electronics can fail, and those failures can be unpredictable. A bad batch of capacitors can pop during the slightest surge of current. Age can also contribute. Car ECUs used to be built to be as simple as possible (which also cuts down on manufacturing costs) - this had the nice side effect of making them extremely reliable. And if they fail, it's an inconvenience, but rarely life-or-death.

Autopilot systems, however, are only as good as the people who program them. A helicopter, as mentioned elsewhere, is dynamically unstable and requires so many tiny inputs to maintain steady flight, let alone hovering. Just like in Teslas that 'nope' out of their Autopilot systems back to the driver milliseconds before a crash, a pilot has precious little time to retake control should the electronics fail.

Car ECU keeping your car moving in one dimension (forwards) - fairly safe to let a computer take over, minimal danger if it fails.

Autonomous technology keeping your car moving in two dimensions (forwards AND steering) - very complex, very little time to retake control in a failure scenario, very dangerous.

Autopilot keeping your helicopter moving in three dimensions - I think you get the idea by now :)

The distinction you're talking about is analog vs digital, as in mechanical linkages vs fly-by-wire, but it's a distinction with much difference as most systems are a mixture of both these days.

Either way, failure is not unique and can happen in either domain. There are plenty of examples of electronics failing and again it is strange to say that they don't. Silicon chips might not move but they are physical products that can overheat or short-circuit or just break.

Aircraft are much more critical than cars and the reason they have multiple completely redundant systems is precisely because things do fail all the time.

> ...the reason they have multiple completely redundant systems is precisely because things do fail all the time.

To be sure, it's not because they fail all the time, but to probabilistically address the risk that if Murphy does come knocking, consequences won't be immediately catastrophic.

We're talking about different spectrums. I'm saying that "things" in general fail all the time, not always on a single plane or flight.

Different spectrums, indeed.

I only meant to clarify that aircraft redundant systems exist because failure mode consequences would be catastrophic with unacceptably high probability otherwise; not simply because things in general fail all the time, as was asserted.

It's a subtle yet significant difference that other readers in passing may not recognize.

>Because, after all, in modern cars, a manual transmission's control system still ends up as signals sent to an electronic gearbox.

No, they don’t (so long as you are talking about stick-shift and not paddle shift).

The solid state electronics absolutely can and do fail. There's a reason why modern large aircraft typically have three redundant ADIRUs...

> There's a reason why modern large aircraft typically have three redundant ADIRUs...

That has more to do with aggregate risk management predominantly driven by predicted MTBF, failure mode analysis, and safety criticality levels.

> automatic transmission doesn't fail

Um, what kind of car do you drive?

And all those transmission repair shops are doing... what, exactly?

The transmission does fail. It doesn’t have a backup because the consequences of the failure don’t justify the cost of the backup.

It is possible, and done in some cases. Check out Bell 525 for example

The pilot has to be there anyway, right? So where's the profit in fixing this? And so it doesn't get done..

The profit can be in reducing errors, being better than human control, etc. which can reduce time spent on the line

At the cost of turning every automation problem into a worst case disaster.

Until the technology is good enough for taking the pilot away, it's not a gain.

>Until the technology is good enough for taking the pilot away, it's not a gain.

If that were true modern airlines wouldn't have autopilot.

Airplane pilots have plenty of time for fixing any problem that may appear mid-flight. It's because of this that airplanes don't have autopilots landing or taking them off.

And by the way, there's an ongoing discussion on airplane groups about all the new failure modes created by the autopilot-pilot interface. It creates plenty of problems.

Modern anything wouldn’t have anything.

There's no inherently intractable reason aircraft "need" human pilots when autopilots are faster, better and make fewer errors. At this stage, an aircraft guider would be able to instruct the aircraft as to what's needed. At some point in the future, AI/ML/DL will replace that role entirely such that the lineman communicates with the aircraft directly. Then, as a further iteration (40-100 years), the lineman is also replaced by robotics on a drone-like platform.

No to the first part. At the risk of sounding flippant, this is one of those cases where the aviation industry really does better than you’d think. Humans do make errors, but, for you to apply ML to fix it, you need to make a lot more errors of all possible types to build robust training data. Sure, it may happen one day, but until then we are dependent on pilots and pilot aids. People are just much faster and more capable at coping with novel, or rare situations.

Regarding drones, I suspect that you are at least partly right. There is a lot of interest already in drones as inspection platforms. Perhaps they will go farther as drones get more commercial aviation clearance.

Which makes me wonder: are there different classes of heliopter piloting license? Maybe one for commercial passenger flight, one for forest firefighting, one for work on overhead power lines, one for acrobatics, one for search-and-rescue? Maybe it’s different per government?

I’m not really into aviation and don’t have any helicopter pilot friend.

Yes, you can get the same grades of helicopter license as you can a fixed-wing license: private, commercial, and airline-transport pilot. Most people who get a commercial and an ATP also pick up an instructor rating along the way, but that is mostly orthogonal to the other three.

Ah, ok. So the classes are not very special-purpose (e.g. firefighting vs search-and-rescue), at least where you’re from.

Those are just the official FAA requirements. There are additional requirements for speciality occupations mandated by industry and insurance standards. See e.g.:


That sounds like deadly accidents should be happening every week.

I call bullshit on this analogy.

If it required similar skills to a human standing on a basketball, then a Helicopter is an monumental engineering failure.

> then a Helicopter is an monumental engineering failure.

That's baffling. Engineering is the art of compromise. The helicopter _does_ have many compromises in it's design, but it's benefits are unmatched by other aerial vehicles. In other words, the benefits outweigh the negatives.

If you don't believe me, go to your nearest general aviation airport, hire a training helicopter and an instructor, and try it yourself.

Other Pilots have already commented - it is nowhere as difficult as balancing on a Basketball.

I saw a crew like this at work once. No idea what they were working on, but they were doing it to lines that crossed over the highway I was driving on. I was moving at highway speed, so my mind didn't really have a chance to boggle until I was already past. Those helicopter pilots must have a very steady hand.

> Those helicopter pilots must have a very steady hand.

Piloting a helicopter in general requires an incredibly steady hand on unintuitive controls that interact with each other in ways that are difficult to predict[1]. Being able to do that with high precision, a disturbingly small margin of error, and fatal consequences for almost any error is basically a superpower.

[1] SmarterEveryDay has an interesting video[2] about learning to hover a helicopter, which apparently requires trying to hover (badly) until the brain learns how to abstract away all of the complexity.

[2] https://www.youtube.com/watch?v=eXR1olg_I0w

> very steady hand

I don't know the first thing about helicopters, but the negative feedback circuits that keep things steady in many applications, from power supply voltages to Segways, could help with that.

It's a very simple basic concept that has been around for many decades, even before analog electronics, never mind digital devices: https://en.wikipedia.org/wiki/Negative_feedback

(I repeat I do not know if they are available in helicopters. It may well be the pilot doing it by hand the hard way.)

> It's a very simple basic concept

I mean, sure, the general concept of feedback is "simple" and applicable to helicopters, in the same way that addition is "simple" and applicable to planetary orbital dynamics.

But even basic control theory – what you'd need to actually stabilize a dynamic system as complex as a helicopter – fills a textbook or two, and the field is still evolving. [1]

Not to mention that the whole concept of "hovering" is damn difficult for a machine to quantify. You'd need LIDAR and/or visual tracking systems to accurately hold your place in all six dimensions well enough to keep a worker next to a powerline, and only in the past decade have those even become good enough for use in land-based vehicles.

[1] https://en.wikipedia.org/wiki/Control_theory

"But even basic control theory – what you'd need to actually stabilize a dynamic system as complex as a helicopter – fills a textbook or two, and the field is still evolving."

I am not that good at math, but I feel like if I was trying to solve that problem, it should be as simple as finding someone smart and saying "use a Kalman filter"...

In one sense I can't say it's "simple" or "basic" because I can't do it, but I'm under the impression that it is a manageable solved problem that can be summarized in four words. Is that wrong?

Yes, in exactly the same sense that "building a bridge is simple because I can say 'use a truss' to a smart person" is wrong. Things having names doesn't automatically make them simple.

There are – like I said – entire textbooks on the subject – and why it is complex – if you are genuinely interested. I mean, heck, there's two textbooks alone about one particular system I randomly found on Wikipedia [1].

However to directly address your misconception, Kalman filters are not control systems. They are related to control theory, and are used to provide inputs to control systems. But control theory is its own thing, and there is no "general" solution to correctly control any given system.

[1] https://en.wikipedia.org/wiki/Furuta_pendulum

Regarding your pendulum example - wouldn't it be significantly simpler if you had a closed-loop system with sensors feeding back information? What I was suggesting about Kalman filters was that instead of using a "proper" analysis, is it possibly more practical to just add some cheap sensors and combine their output to tell the actuator what to do?

In a lot of fields, elegant analysis has given way to cheap brute-force application of computers that is easier to generalize - that's what I'm fumbling at here.

After all, if you or I try to balance a pencil on our fingertip, we are not doing the math on that wikipedia page in our heads. We are in fact using something more akin to the brute force method - sense, synthesize, act, repeat.

I'm not an expert in controls, but it's an area that interests me and I've taken a couple classes. It's true that the theory of linear, time-invariant systems is pretty complete. In that very limited framework, you can basically make a system behave in any way you want. The interesting thing is all the various infuriating ways in which real systems fail to be linear. Those nonlinearities can be accounted for, but now you no longer have a turn-key solution. Furthermore, there really is no such thing as the optimal controller. It all depends on the objective function you are trying to optimize. How much do you value a fast response time versus strong disturbance-rejection? Would operating the system that way cause undue wear and tear over the service lifetime? Would it cause danger or discomfort to human passengers (if any)? How sensitive is system behavior to uncertainty in model parameters? It's obvious that the design objectives involved in building an air-to-air missile are very different from those involved in building an elevator. But explicating them and translating them into an actual controller requires a great deal of care.

I disagree with most of your comment, but explaining why will require several paragraphs of background.

You can read Maxwell's On Governors from 1868 and see that, although it explores their math in some detail, it doesn't attempt to generalize beyond braking or otherwise slowing down steam-engines: https://www.maths.ed.ac.uk/~v1ranick/papers/maxwell1.pdf

So, although devices with negative feedback had been built for centuries — and many natural or simple artificial objects can be usefully analyzed in terms of feedback — the general idea of negative feedback as such seems to date from the 1920s, and apparently Black discovered its usefulness in 1927. The idea was so outlandish at the time that his patent was initially rejected as describing a useless invention — why would you want to reduce the gain of an amplifier? It wasn't public until 1933.

After Black's invention, which upgraded FDM for long-distance telephony (the "carrier system") from three voice channels per wire up to nine, then dramatically more, and permitting long-distance circuits with a sequence of 34 repeaters, rather than, say, three.

Bennett's "A history of control engineering, 1930–1955" discusses this history in detail; find it at your favorite library.

At the same time, in 1922, Minorsky formalized PID control, which gets into negative feedback from a different angle, that of automatic ship steering.

Black's, Minorsky's, and earlier negative-feedback designs were not generalized into a general theory of negative feedback until the work of Nyquist and others in the 1930s — most prominently, Wiener!

Nowadays, explicitly designed negative feedback is far more ubiquitous than your comment suggests. By far the most common analog circuit component, for example, is an op-amp, which is almost invariably applied with negative feedback; also, though, negative feedback is central to nearly any kind of homeostasis, optimization, or stable static mechanical equilibrium. So, for example, we have negative feedback in TCP bandwidth usage, in glucemia, and in your toilet tank. Parkinsonian tremors — the opposite of your "very steady hand" — are now being analyzed as oscillations in a negative feedback system involved in human motor control, though the theory is not yet fully mainstream in neuroscience.

As for "digital devices", those date back at least to Leibniz; they are far older than analog electronics, which in turn are a couple of decades older than the concept of negative feedback.

I agree with your detailed disagreement ;-)

But I get the feeling that a large part of the audience here is not that aware of those possibilities - I was just pointing in that general direction.

Computerized stability control systems exist, are quite prevalent, and have a thriving open source community.

Check out: https://github.com/betaflight/betaflight/wiki

Granted, it's for hobby scale drones, but the same principles apply.

The physics involved in multi-rotor drones (or even counter rotating dual rotor toy-level RC helicopters) is significantly different from single rotor+stabilizer helicopters in that there is at least in theory point where the thing is dynamically stable.

For what it's worth many toy RC helis exist with collective pitch tail rotor setups and full feedback stabilization - it started with tailrotor yaw hold automation and now they can stabilize in all axes. Check out something like Blade mCPx

The dynamics, which are not just the rigid body dynamics plus the aerodynamics of the vehicle but also include many structural modes of the rotorhead and blades, are not scale invariant. An RC helicopter is proportionally stiffer in certain degrees of freedom by an order of magnitude (in rotor angular velocity and thrust:weight ratio e.g.), and so can ignore dynamical factors that dominate the control and structural sizing for manned helicopters.

Do you think a PID control would would fail to be able to accommodate those dynamic factors?

The physics involved in multi-rotor drones and fixed wing aircraft are quite different. However, there is control software that works on either.


The underlying differences in how they fly aren't that relevant. You have a six-axis IMU, various controls that influence how the craft behaves in those axes and various PID loops that influence the controls.

I don't really understand the downvotes. Obviously, having a type certificated auto-pilot for a commercial helicopter is a world apart from the flight control system for a hobby-scale drone, but the gap between them has nothing to do with the technology and everything to do with the process of type certification.

My point is that it's pretty impressive what these software projects are able to achieve with sub $100 MCUs. Some of them now have 32khz control loops with 32khz IMU sampling. Anyone that's ever peeked under the hood of a commercial auto-pilot would be amazed by that.

I thought quadrocopters were so unstable that flying one without a PD controller, or better a full PID, would lead to a crash within seconds. A Helicopter, possibly only of the counterrotating coaxial variant, should not be affected by this instability, I think.

That's correct. The controllers use full PID loops for each axis.

I've been having a stressful week (thus far) at work and this video really puts things into perspective.

That lineman deserves a raise, no matter what he makes. He falls in the category of workers who are lowered into nuclear reactors to cleans things up.

A year or two back they recently did maintenance on a majority of the high voltage towers in the greenway behind my house.

They sent out flyers to all the residents a few days ahead. This video shows once splice. I can't imagine the crew (or crews) that were working the miles of lines behind our house doing this for multiple days in a row.

This kind of splice repair should be rare. It only needs doing when the original splice was badly done.


I just watched it... this feels like deja-vu...

For those who are interested, the helicopter is an MD-500. They're well known for being very stable and have pretty good control feel through mechanical-only linkages. As such, they're fairly popular for this kind of precision work. Another big application is aerial tree trimming: https://www.youtube.com/watch?v=OXcIqR01_d0

I couldn't help but burst out laughing when the voiceover dude explained, "The pilot and the lineman are both doing an outstanding job despite very high wind conditions." Who on earth decides that very high wind conditions are a good time to hover your helicopter connected to a 230,000-volt power line? Couldn't they postpone the job for a day or two until the winds die down?

The arc when the helicopter finally disconnects from the power line is pretty astounding. To the lineman, it's all in a day's work, I guess.

It kind of looks like they are in a plains state somewhere. Having lived in the midwest nearly all my life, I can say with confidence that you are going to spend a lot of time waiting if you are waiting for a calm day.

They probably just make sure the wind isn't gusting too much.

It's actually eastern Pennsylvania, the helicopter has a Pennsylvania Power and Light (PPL) logo on it. If you look carefully in the background you can see the Delaware Water Gap in the mountains.

Nevertheless, it's the same for the weather, Fall/Winter is gonna be windy enough you can't wait around for it.

Also probably the calm winds come when it's 5°F outside.

Possibly not? The high resistance splices are producing heat and at some point I believe they fail, which could affect the whole grid.

When they get to 220C they are going to fail pretty quick.

At those kinds of temperatures, oxidation is much faster, and you'll get heating and cooling stresses causing micro fractures as the load on the line goes up and down.

As the resistance increases even a little, the temperature will increase more, making the above effects even worse.

> hover your helicopter connected to a 230,000-volt power line?

Not an issue when any electrical ground is at a far distance.

As another commenter noted the plain states are likely to have wind most all the time.

Also there will be more wind at 200 feet than at ground level

Two things: "very high wind conditions" is a rather relative term (and could e.g. mean "very high within the parameters that are still considered safe"), and we also don't know about the urgency of that job.

All in all, I wouldn't extrapolate too much from that little statement.

I also wish they ended the video with three or four middle-aged actors and actresses, in household settings, visibly demonstrating how much they enjoy consuming electricity, before turning to the camera and saying, “Thanks, Clampstar!

This is excellent.

I don't understand why there's an arc at the end when the lineman disconnects and pulls away the safety rod. That's there to keep the helicopter at the same potential as the transmission line, right? So why's there a potential difference when the safety rod is withdrawn?

It's a low-current arc. The circuit is completed by the capacitance between the helicopter and the ground.

Assuming a spherical helicopter 1M in radius, the capacitance to ground is

  >>> 4 * pi * 8.8e-12
The current, at 220 kV and 60 Hz can be calculated

  >>> 60 * 2 * pi * 220e3 * 1.1058406140636071e-10
or 9 milliamps. Enough to feel a good tingle. The power in the arc is

  >>> 220e3 * 0.009171625977844317
or 2 kilowatts, so you can see the arc in daylight.

I chuckled at "Assuming a spherical helicopter".

This is how you know the parent is an engineer.

Nah, physicist. If parent was an engineer, he's just reference the row and column from some table of helicopter capacitances. ("See p.34, table 7 for the MD-500. The one in the video is a 530, but close enough")

Good point.

At least it's not flying in a vacuum.

FYI, and not that it matters, I think your current is off by a factor of 2/pi. There's no 2*pi in the current formula because the 60 Hz is the full frequency not the angular frequency. And there's an extra factor of 4 because in each full cycle sine wave there are four 220 kV steps: 0-220, 220-0, 0-(-220), (-200)-0.

(and all of this of course assumes that the metal helicopter has low enough resistance to charge up to the full voltage)

The current through a capacitor is I = ωC, where ω is in radians per second (ie, 2𝜋 60 Hz).

I think 220 kV is the RMS voltage, so you get RMS current from the formula above. Peak voltage would be √2 * 220 kV.

Indeed, both the capacitor and the arc are in series, so actual current and power is somewhat less. As the arc grows longer, there should be an optimum length where you get 1/√2 of the maximum power.

Thank you for this.

Thank you! I wanted to calculate this, so I'm glad you did.

It's an AC line, so when the helicopter retracts it will get a static charge instead of fluctuating in sync with the line, giving an immediate potential difference.

I have no source for this, just amateur reasoning.

It's very likely capacitance. At 200kV even a couple dozen meters above ground the capacitance would be enough to get a couple microamps over an arch (it would likely tickle a bit).

AC makes isolating rather complicated since increasing your resistance to ground naturally turns you into a capacitor which acts like a resistor in AC (which is why thin rubber soles on your shoes don't protect you, you want think ones to increase resistance and decrease capacitance) so a small current will flow.

At high voltage this small current can still be transmitted over an plasmaarc.

Assuming it is an AC line, it is inductance

My understanding is that it's caused from the rotorblades moving through the air.

Apparently there are other factors as well. This StackExchange answer can address it better than I can:


I have to admit, it was a fascinating video. The precision of the helicopter pilot is amazing. Just one wrong move though and both are dead. Surely there's a less risky way of doing this?

How did the lineworker and helicopter not get electrocuted? Is it because they attached themselves to the transmission line, similar to how a squirrel doesn't get electrocuted? Or were the lines taken down or something (I find that hard to believe but maybe). At those levels, if they were at the same voltage as the lines, isn't there still a risk of arcing to another line?

The only way to do it with less risk would be to shut down the line, which would be tremendously expensive and might still result in more risk, since power outages can kill.

It doesn’t look like the safest job in the world, but a lot of crazy-looking things can be reduced to tolerable levels of risk with lots of training and good, methodical procedures.

After all, packing a couple hundred people into a pressurized tube six miles above the ground is pretty crazy too, and used to be fairly dangerous, but these days it’s the safest way to get from A to B.

AFAIK many crawler robots can place shunts on live lines automatically, without any risk. I wonder what's the advantage of doing it manually from a helicopter.

How do you get the robots onto the line, and how far can they travel? They might not be capable of handling a sudden problem in a remote area. Although I really don't know, as I just learned of their existence from your comment!

Those I know of are advertised as semi-autonomous and capable to move over any distance for days or weeks; the line provides both power and communications. Robots are put there in a traditional way, by line workers climbing the towers, then the operator controls them remotely if needed. Some models also appear to have a winch for the tools and spare parts if a problem is found.

I have no idea if they work as well as advertised though, hence the question.

I've seen those things crawling along a nearby power line a couple times, although these particular ones seemed too small to be able to do anything besides inspecting the line with a camera/sensors. I'm not in the US though, things are different here, we don't use aerial transport on every occasion.

EDIT: on a further inspection, the robots seem to have issues with crawling over more complex line sections, and are used mainly on very high voltage lines. Apparently, the tech is still in its infancy.

One pretty significant application 15 years ago of crawler robots (and the only one I've seen in person) was suspending optical fiber cables on the ground cables of VHV lines.

I saw a video where the lineman was actually left on the line by the pilot (hanging in some kind of rescue harness), then retrieved when the work was done. He could move along the line using it like a zipline. I guess it depends on the malfunction and the way it's solved; an overheated line connector is not something you want to touch or hang on.

Not sure what they do if the line to be fixed is not the one on the top (fixing one of the lower lines would mean the helicopter interferes with the upper lines).

> There is only 3 things I have ever been afraid of; electricity, heights, and women. And I am married too.

There isn't a less risky way of doing this. This is actually safer because there is no contact with ground, removing the voltage potential (which is also why they make contact with the line, to keep the voltage potential as close to zero as possible).

Yes, most definitely. They still have to be careful about that. I expect it's an easy thing to avoid unless you're working on an inside conductor.

For conductors that the helicopter cannot safely hover close enough to for the line worker to work on from the helicopter, they sling load the worker below the helicopter, lower him down to the conductor he needs to work on, and he attaches himself to the conductor and detaches from the helicopter, and the helicopter moves away from the lines.

When the work is done, the above is reversed to extract the worker.

There's a segment showing this in "Modern Marvels" episode S11E45, "Wiring America" starting at 23:44 [1].

I've also seen a documentary somewhere [2] that was similar but more focused specifically on line work. That had a clip showing a worker being lowered to a particularly difficult to reach conductor. There were at least 3 horizontal layers of conductors, with at least 3 parallel conductors in each layers, and the one needing work was in the middle horizontally and had at last 2 layers above it.

For that one, they had several dry wooden poles connected end to end to form a kind of chain. They put this together in a dry area, then had a crew carry the pole chain outside careful to not let it touch the ground, so it would not get wet from the morning dew on the ground. One end was attached to the helicopter, which slowly started lifting it, with the crew that was holding it making sure to not release segments until they were sure they would not swing into the ground on the way up. Finally, the line worker was attached to the last segment. From then on, it was similar to the segment from Modern Marvels.

They used the dry wooden pole chain because there was no way to reach the work conductor without whatever was suspending the worker simultaneously touch two of the above conductors, so it was imperative that this not short out things.

I believe they used a pole chain rather than some non-conducting rope because a rope can get tangled in things or wrap around things. The pole chain consists of rigid segments, which are not going to get wrapped around anything.

[1] https://youtu.be/vuRNs50VMJ0?t=23m44s

[2] Probably on the History Channel or Discovery Channel.

The whole thing is a conductor. Those lines are insulated only by air.

Edit: Misreading on my part. Parent meant "a line closer to the tower" not "a conductor within the line."

Pretty sure by "inside conductor" he means one of the lines closer to the tower. In the video I think he's working on the outermost conductor, i.e. the one furthest from the tower.

Ah, good point. Grandparent is correct. Carry on!

The lineman (and my guess is the pilot too) wear a conducting and fire retardant suit made of metal threads. This essentially acts as a Faraday cage.

The lineworker and helicopter don't get electrocuted for the same reason that birds don't.

There is no way to ground (other than capacitance which likely causes the arcs you see in the video)

According to a comment elsehwere based on capacitance the amount of current flowing is rather low and not immediately dangerous.

Here's an article on the pilots/flying: https://www.verticalmag.com/features/highvaluecargo/

As an inventor how does one convince oneself to allow overhead wires carrying life threatening currents or any other such inventions. There exists so many inventions I would never pursue even if it occurred to me first, yet they exist and make our lives better.

No inventor sat down at a blank slate and said "Hey, let's string 700KV power lines across the country on huge towers".

Overhead powerlines developed gradually from an overhead line running power from one side of someone's lab to the other, to power running between buildings, to city wide distribution and beyond. As time went on, the powerlines got larger and higher voltage.

There aren't a lot of options -- underground powerlines are possible, but they have their own disadvantages so are not a clear-cut winner.

One also has to take account the historical context. When humanity started to use electricity for practical applications (ie. telegraph) there was no practical alternative to overhead wires isolated by ceramic bushings and air. Reasonably low-cost and durable cable insulation materials were invented around the WW2.

I suppose someone figured that, after a point, the only question is how far your red mist will be spread should you have contact with a line. I mean, I'll put money on the fact that you're sitting in a room right now with nearly-exposed electrical contacts that can kill you. I guess it's not a great leap from there to "go ahead and hang them overhead, and try to make sure they won't fall down".

OTOH, the only thing I've ever seen take down high tension towers was an ice storm so bad, they collapsed under the weight.

It happened here in 1998 in Montreal, Quebec

It did cost over $2B to rebuild the network.


Yeah overhead on a strong tower is probably the best place for them. Underground they're way more likely to get hit accidentally and if the shielding failed it'd be impossible to tell where the danger was from the surface without specialized equipment.

underground is more resilient to damage but harder to do maintenance and actually much more expensive at the distribution level

It would also increase the cost a lot due to the digging and actually requiring insulation that will hold up where the overhead lines are bare aluminum insulated by air.

Exactly. It's mostly cost that keeps underground transmission lines limited to very specific situations. I forget the exact figure, but underground transmission is something like 20x the cost of above ground.

A lot of pylons went down during the 2016 South Australian blackout, no ice required.


"The strong winds and lightning strikes look to have damaged power transmission towers"

ahem, I never said that only ice was required. But those towers didn't just fall over on a calm summer's day. :-)

What's the alternative. Burying them is arguably more dangerous because the insulation failing would make the area immensely dangerous with no obvious signs. The power needs to get from generation to consumer somehow and high voltage lines are good for long distances.

For an incredible read about just how bizarre fixing underground power distribution can become, check out this classic: https://www.jwz.org/blog/2002/11/engineering-pornography/

Here's the tl;dr version: https://hackaday.com/2015/07/27/find-and-repair-a-230kv-800a...

Make sure you copy and paste the jwz link, just clicking it redirects to an imgur picture.

For those that don't know, you can get around jwz's referrer redirection by opening the link incongnito.

I never knew I could be enthralled by a faulty power line. What a story!

Haha a jwz link those are great.

Can someone explain to a software person why this wouldn't basically just ground the power?

Grounding doesn't make the electricity magically disappear - for large voltages and currents, it's difficult to dissipate.

For example, if you'd simply stick a high voltage line into the ground, then there would be a voltage gradient between the ground voltage far away and (almost) the line voltage directly at the place where you stuck it; and since the earth isn't a very good conductor (compared to e.g. yourself), if you walk towards it, then the "step voltage" between your leg closest to the wire and the other leg can be sufficient to kill you.

If you do ever find yourself in that kind of situation (powerline draped over vehicle or similar), solution one, the way to go, is "don't exit the vehicle".

That being unavoidable (vehicle on fire, etc.), don't walk away from the vehicle, jump, two feet at a time, and keep jumping that way, until you're a good distance away. This avoids you ending in a situation where you have that step voltage between the voltage rings.

At the voltages involved in power transmission the "grounding" will cause an arc that'll do a lot of damage and take the transmission line out of service until it's dug up and fixed. And that takes awhile and costs a lot of money not to mention lost revenue while the transmission line is out of service.

Above ground is the way to go since it's cheaper to construct and much easier to service when things go wrong.

Unfortunately cost would have been a factor. High voltage, low current is going to lose less in transmission so it’s hard to justify a less dangerous option if it means paying way more to make up for wasted energy.

How do you feel about automobiles, then? Lot more deaths from cars than from power lines

Oh, I am not saying they are bad (overall). Just that, if it didn't exist before then I would never be able to convince myself to pursue doing that.

More importantly I want to understand how to let go of such inhibitions (and thoughts) of not pursuing such ideas..

What caused the line to overheat in the first place, requiring a splice?

Usually (internal) damage, caused by wind, rain, ice, etc. Could also be a manufacturing flaw.

The damaged section will have a higher electrical resistance than what it was designed for, and as a result that section will dissipate more energy (heat). The splice/patch effectively increases the cross sectional area, which will lower the resistance, which will lower the dissipated energy, which will lower the heat.

The new splice also simply offers a lower resistance path full stop so most of the electricity will flow through the new splice instead of the damaged splice.

There was a video a few years ago that explained how this works: https://www.youtube.com/watch?v=r_1T2_l43Xo

Reminds me of one of my favorite youtube videos of all time


I sincerely hope it's the actual lineman talking and that he takes a job in voice work when he retires.

This got me interested into what it takes to become lineman. For Canada, it's: - extended driver's license requirements - some high school requirements (graduate, math and sciences) - physically fit year-round - pre-apprenticeship program - 3 year apprenticeship program, $30 pay - standard trade rate is $40

You probably get good benefits and disability securities, and overtime pay. But it means working in dangerous, frequently laborious, conditions, working away from home all over the province/country, and working frequent overtime. Makes me scratch my head when the people holding the infrastructure together get compensated so little.

> Makes me scratch my head when the people holding the infrastructure together get compensated so little.

Because they are very far away from where value is captured. That's a seriously annoying part of the way capitalism as we know it works: you only get paid a substantial fraction of the value created if you are near the point of value capture. That's why sales people tend to earn well.

In the overhead camera views, you can see about half a roll of duct tape on the lineman's helmet to hold the go-pro on, eg https://youtu.be/piQpLL5nD18?t=1m47s

Although looking closer, it looks like it's the flexistrap type mount put over a smooth helmet, so makes sense.

Point is, kludges are everywhere!

A) That's electrical tape, I believe, and all the more appropriately so.

B) you can also see someone holding the other camera on the ground, as well, which is interesting to see.

Don't you measure electrical resistance between two points? How is the guy measuring resistance on the line at a particular point?

If you look closely at the rod there's a separate wire sticking out the side about 10 cms. It probably measures impedance over that 10 cm space. You can definitely see him use it to measure impedance between the line and the clamp, but the first one is hard to see because it's behind the clamp. The second is far easier.

Voltage drop?

I had the pleasure of watching something like this a couple of weeks ago on I90 in southern Minnesota. I came upon what looked like a helicopter entangled in the transmission lines, but after slowing down and opening the window, it was obvious the pilot was skillfully hovering there on purpose. It was impressive to see!

Sometimes I wonder why I have convinced myself that a desk job is the way to go. Then I remember that thats 220kV haha

I’ve learned that massive injury is actually less scary than mild or moderate injury because your body is overwhelmed, and you don’t really feel anything.

Yes, being dead does hurt less than a papercut.

I do not appreciate the useless dismissive statement. I’m talking about something intense I’ve experienced personally, and you are being rude.

Just because you are talking about it doesn't mean it automatically commands compassion or respect, and I am not saying this to be rude.

There's some great videos of installing spacers on multi-100kV live lines and of the Bond villian tree-trimmers.

Couldn't we use something like that on wildfires for chopping down trees quickly?

Like a big chain?

If you're referring to the helicopter,I believe they already have helicopter mounted saw blades for trimming trees, in particular, for transmission line corridors.

See here: https://youtu.be/Pla06PO6Odk

What what happens at 2:57 in the vid. Did you spot the large spark?

I missed that, but it's also not all that surprising.

The first thing they do is attach the platform to the cable. They use the "wand thing" first, so that their hands are away from the inevitable sparks, and allow the platform he's sitting on to equalise (voltage wise) with the wire. In other words, he's sitting on a platform thats 10k or more volts! Once equalised, a hook is attached - this is also conductive.

Once the job is done, the wand thing comes back out - the hook is detached, without sparks as their is an alternative path for the electricity through the wand, and then the wand is slowly removed.

Linemen are nuts!

how much do those guys make?

Came for the video, stayed for the comments.

Multiple passes on 20 bolts on each side? Does it really have to be that complicated?

You need multiple passes, because while doing the first pass, contact is still being made on an angle. Tie all the nuts at least once, then you won't have an angle and will be able to tighten better.

Same like you should do on your car wheel. First put them all ass much as you can without force, then apply force. In a star bolt pattern.

I suspect the other element is that if the line fails completely in the middle, the new splice is now structurally critical to holding the line up - so you need it to be as good, or better, than the original manufactured line.

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