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Comment by satori99 | Hacker News Reader

> All of the flying car concepts, which are like drones big enough to hold humans, promise to be better than helicopters. Helicopters are expensive to maintain, noisy to fly and require trained pilots.

They forgot to add helicopters can also auto-gyrate in the event of engine failure.

Quad-copter drones probably just crash.

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>Helicopters are expensive to maintain, noisy to fly and require trained pilots.

This part really puzzles me, I mean I guess they're better than helicopters but all those thing apply to flying cars as well, just to a lesser degree.

Getting some flying cars won't be cheap, maintaining them might be cheaper than a chopper but still not very cheap.

And if you're going to pilot one of these, and carry people around I guarantee you will have to be licensed and trained in piloting one. The regulations won't be as loose as with drones.

As for the noise, well this isn't exactly quiet.... https://youtu.be/cmdilp9LM0E?t=67

Sure it might not be as bad as a helicopter but you also rarely have two dozen helicopters zipping around near ground level. While the whole plan is to have these zipping around everywhere.

I imagine a ridesharing / uber-like model will be dominant compared to private ownership and personal piloting. But these things are going to be incredibly annoying and disruptive -- the various drone delivery efforts already seem loud and stress-inducing. I imagine airspace restrictions on these are going to become common in the near-ish future.

>As for the noise, well this isn't exactly quiet....

I remember listening to Elon Musk dismissing flying cars for this reason.

I wonder if asymmetric blades like in fans could work and if they would be any good for reducing the noise.

Also reduces thrust.

There has been a good deal of economic incentive for finding ways to reduce the noise of the fans in turbofans for a long time. the relatively recent introduction of chevrons on the exit end of fan nacelles shows how even minor improvements are pursued. It is unlikely that an opportunity for significant improvement has been overlooked.

Well he wasn't wrong. Rotorcraft operations are or will be banned in many populated areas for exactly that reason. If they have to move a high volume of air it's going to be extremely noisy no matter what tricks they play with blade shape or whatever.

He also makes the excellent points that keeping them in the air is very energy intensive and that they pose a risk to those underneath them, in case of failure or something falling off them.

Electric motors with fixed pitch rotors are much simpler mechanically than piston/turbine engines and fully articulated rotor blades.

Furthermore, with the drones, you have fly by wire, with control inputs translated into manoeuvring in a simple manner, so pilots will require much less skill.

For example, one has to log a certain number of landings in a helicopter. In a Volocopter, you'd literally just slide a button on the control stick up to take off, then slide it down to land, and do that N times, and you've passed that part of the requirements.

Most drones can compensate to account for issues. My drone has hit a tree a few times, self-balanced and continued flight. It's flown fine through heavy wind/rain with cracked propellers (that I've replaced after noticing). There's a video out there of someone throwing cushions at, or suspending weights from, a consumer drone and it takes the hits and re-stabilises.

High-end drones have battery redundancy, six props to account for failures, parachute systems, etc.

From what I have read and seen a drone with only 4 props has almost no chance of recovery if one prop fails. This is also why drones for high end expensive video have six or eight props to prevent a catastrophic failure resulting in loss of equipment.

There are algorithmic solutions to maintaining some semblance of flight with a damaged quad copter, even down to one remaining prop, however it involves spinning the entire air-frame to stay aloft -- which means it is probably not suitable for a human passenger drone

https://newatlas.com/quadcopter-failure-algorithm/30031/

Scale matters. Compare a small animal falling and a large animal falling (i.e. compare what happens when they hit the ground). A "drone" large enough to carry a human or two will be much more heavily damaged by an impact that appears to be similar to one that leaves a much smaller drone intact.

A parachute system only helps if you are high enough. Looks like the flying thingys we are talking about here will be close to obstacles a lot and not very high up much of the time given how they are to be used.

Battery redundancy: The scale argument again. This is an order of magnitude harder to achieve on a much larger man-carrying "drone".

> Battery redundancy: The scale argument again. This is an order of magnitude harder to achieve on a much larger man-carrying "drone".

Isn't it much easier because you have capacity (weight carrying ability) for many more cells, and the chances too many of them fail is much lower? If you have 3 cells, 1 of them can fail at any given time, and you're left with 66% of power, but if you have 200 cells, and 1 or 2 of them fail, you don't even notice. How do you mean that it's harder? Electric cars certainly don't seem to have any problems with this and their batteries are much more reliable than the ones available for drone usage.

Also with big size/capacity you can easily include additional systems like temperature control which increase reliability because they don't weigh as much in relationship to the whole vechicle.

> Isn't it much easier because you have place for many more cells

Don't think space (not the biggest issue here as you say), think weight, power and the ratio.

Yes, of course. I was using "space" as a more general term, as in "capacity". Should have been more clear.

Human-scale drones would have much more powerful batteries and room for redundancy. More powerful motors and blades.

If a helicopter is doing it with a single main rotor, I'd be surprised if it can't work with a hexacopter and redundancy.

I'd be more worried about noise. A consumer drone is noisy enough, though mostly just noticeable because it's a new thing people are yet to get used to.

If you drop a mouse down a mineshaft it will likely have a bit of a jolt on impact, then scurry away looking for some bit of cheese. If you drop a horse down a mineshaft there will be horsebits splattered on a very large area around the point of impact. Noise problems are inherent to fast spinning rotors, gravity is where the real problems are, and redundancy in drones is more along the lines of controlled crashes than emergency landings. I'd be very much worried about the performance of the system if one or more rotors failed to do their job.

Helicopters auto-rotation is not at all comparable to a drone with one or more failed rotors, a helicopter that is autorotating is comparable to a gyrocopter, it will fly relatively well, a drone with one or more failed rotors will not fly well or even at all.

Maybe they could put an airbag at the underside of the vehicle for when it flies a few meters above the ground

One thing I've always wondered is why is it so hard to make a self-flying helicopter? Helicopters already exist, can carry much heavier weights than most multirotors, and have other pro's (like being able to auto-gyrate). Is there some reason we haven't automated the flying of those and are instead going for multirotors?

Or do they exist but just aren't sexy enough to make headlines?

They do exist for military purposes;

https://en.wikipedia.org/wiki/Northrop_Grumman_MQ-8_Fire_Sco...

https://www.engadget.com/2019/07/09/us-navy-mq-8c-fire-scout...

Almost certainly if the blades cannot vary pitch.

That's why this design is not a quadcopter, it is technically an octocopter.

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