Hacker News Reader

Comment by lisper | Hacker News Reader

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.

View on HN

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.)

https://www.youtube.com/watch?v=7vP13XPMNfc

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:

https://youtu.be/gfkRCzgHGq8

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:

https://youtu.be/gJrKmMM7vW0

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:

https://www.reddit.com/r/flying/comments/998c8b/helicopter_p...

"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?

No.

https://www.reddit.com/r/flying/comments/998c8b/helicopter_p...

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.:

https://www.reddit.com/r/flying/comments/3zzajl/fire_pilots/

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.

Reply on news.ycombinator.com