Comment by sokoloff | Hacker News Reader

Comment by sokoloff | Hacker News Reader

I'm a pilot and owner of general aviation aircraft. I simply don't understand the appeal of a flying car. It's going to inevitably be a compromise design and likely suck at both being a car and at being an aircraft.

Aircraft "want" to be lightweight and low-drag and crashworthiness (and expense) is not a significant design parameter. Cars need to be crashworthy as they are frequently bumping into each other.

I can fly into nearly any airport and have ground transportation easily available. Certainly at any good-sized airport, of which there are hundreds more than are served by airlines.

If that ground transportation suffers a minor collision, no matter, my airplane ride home is unaffected. If my flying car is damaged in a ground collision, I'm stuck finding another way home and coordinating repairs from a distance. I don't want to maintain my car to the standards required of aircraft. (Want an engine overhauled for my airplane? It's going to cost more than the median new car. Not bragging; mostly just complaining. Want the annual [invasive] inspection done? In most cases, that's going to be a $3-5K bill, minimum.)

I welcome the interest and hope some of that rubs off on general aviation interest, but I don't see flying cars as anything more practical than a gimmick.

Prediction: the media will be the only ones to make significant money from flying cars.

I'm curious as to what the crash safety features in a flying car would even be. Emergency balloons? Parachutes? A collision at flying speeds is going to be bad for the riders, but the sudden stop after the resulting long fall will likely prove far more fatal.

How do you design for that? It seems the general trend in Aviation is that you don't; if you're falling that rapidly, things have gone so far south that you're just considered dead on arrival. (Best to get out of the plane quickly, and activate your parachute.) But I'm no pilot; I'd love some more experienced input on this. I think the idea of flying cars is ridiculously silly for the safety problems alone.

No one designs for mid-air collisions. Mid-air collisions are almost vanishingly rare outside of the airport traffic pattern. If flying cars became popular, they would increase, but still, it's a very, very large sky.

Cirrus (and some homebuilts) have the BRS airframe parachute system. Quick checking the Cirrus record, it seems like 3 Cirri have had mid-air collisions; in 2 of those, the occupants were saved by the BRS system; in the other, all aboard the Cirrus perished.

Aircraft crashworthiness is predicated on surviving an under-control arrival with terra firma, possibly after an engine failure. That is the source of the restriction on stall speed in the landing configuration of single-engine airplanes of 61 knots (~70 mph) or in the case of LSAs 45 knots (~52 mph). Shoulder belts are one of the most important factors for survivable aircraft accidents. There's a somewhat common saying, "Aircraft that crash upright and under control have survivors on board." The vast majority of aircraft crashes have zero fatalities (typically over 80% are non-fatal).

> but still, it's a very, very large sky

How are you assuming flying cars would work? Because I picture flows of "air traffic" along prescribed "air roads", not arbitrary free three-dimensional movement. Which, obviously, allows for (at the very least) rear-ending.

To oversimplify hugely, if you look at commercial aviation, that's near enough how it works. But it's all controlled by ATC who give you a height, direction and maintain separation. A flight plan must have been filed before the flight so ATC know your route. So take all that huge sky and force the planes down little corridors :)

Flying cars are much more likely to be VFR flights in uncontrolled airspace. Go where you like, tell no one, don't hit anyone, stay out of controlled airspace and in sight of ground, responsibility rests with pilot.

I'd be very surprised to see enough flying cars around to reach high enough density to raise risk noticeably outside already high traffic areas.

> Shoulder belts

My dad (AF flight instructor) relates that crew in a fighter often release the shoulder harness but keep the lap belt on while taxiing. One day, a fighter with a tandem crew taxied off the runway into the mud, the nosegear stuck in the mud, and the jet dug its nose into the ground.

The guy in front, who had left his shoulder harness on, walked away. The guy in back didn't, and had his brains splashed all over the instrument panel.

After seeing that, my dad never took off his shoulder harness until the airplane was parked and the engines were shut down.

Most ultralight / sport aviation airplanes now come equipped with ballistic parachutes. Thew work very good if you know how/when to use them.

Yours is a first world answer.. In other worlds where roads are not as available & geographical conditions are complex, a flying car would be wonderful. Imagine Amazon jungle or an Island hopper or areas of extensive land with poor/constantly interrupted roads.. (All found where I currently live)

And flying cars would be easier than just building a basic road? How many people are living in the jungle but want flying cars?

Also you can already buy a cheap helicopter today if you just need to get around rural places.

There's nothing cheap about a helicopter.

An airplane wants to fly, a helicopter wants to crash. The expense for the latter comes from fighting that tendency.

Autogyros (https://en.wikipedia.org/wiki/Autogyro) are very safe and cheap, compared to planes and helicopters. Plus they are very simple mechanically, so for the third-world scenario seems a good fit. They require a takeoff and landing road, though.

But flying cars are going to be cheap enough for the jungle people?

Jungle, outback, and tundra environments have flying cars. They're called bush planes.

They land on rough, largely unimproved strips, or bare dirt, snow, or water. No, you don't drive them much, other than taxiing around the landing zone or airport, these are places with few or no roads, or far too many miles to go between spaces.

Australia, Alaska, Brazil, and similar places.

If you're interested in take-off and landing capabilities, there are truly impressive videos to be found on YouTube. With an unloaded plane and steep slope or high wind, a roll of 5-7 meters is possible.

The cars that tend to drive in such areas are heavy and robust -- Land Rovers, Jeeps, and technicals. Those make poor planes. Any aircraft subject to road conditions would shake itself to pieces.

Put landing strips where you need them and fly to them. It's far more effective. Given the terrain, it's also actually not all that more fuel-consumptive, see earlier comments about effective aircraft fuel efficiency.

" 110 mile per hour airspeed"

I guess there's something alluring about pulling out of your driveway and being in the air within 10 minutes then arriving at your destination 150 miles away within 90 minutes after leaving your house. The world just became a lot smaller.

Now, what we actually get might be a lot different but who doesn't want that flexibility? Personally, i think we need autonomous vehicles before we fill the sky's with hundreds of thousands of "cars".

I get the "world got smaller" aspect; it's a big part of why I fly. Interesting that that 110 mph is an appealing speed. I guess I'd just forgotten as almost all airplanes bigger than a Piper Cub will outrun 110mph. Ours does well over 200mph and the kids still complain about how long it takes to get to grandma's house. :)

Put 110 mph airspeed into a 26 knot headwind and you'll see cars in the left lane of the highway passing you. Winter winds are regularly 40 knots or more at altitude. Into those winds, Priuses in the right-lane will be passing you. ;)

LSA rules limit the airplane to a maximum of 2 seats, further hampering the utility. (I'm trying to stay engineer-neutral and not go full Debbie Downer, but it's hard.)

Most people travel at 65mph, traffic allowing. Why wouldn't almost doubling that be desirable? Throw in the ability to fly in a direct path and it's even faster than driving. NYC to Maine, for example, is a painful drive. I wouldn't mind flying my car there for a long weekend.

I haven't looked in becoming a pilot in many years. It seemed expensive, not so convenient, and a bit dangerous. You need to spend some money to get a fast "Dr Killer"

https://aviatorcollege.wordpress.com/2010/06/25/why-is-the-“...

Doctors have killed more Bonanzas than Bonanzas have killed Doctors.

For your NYC to Maine trip, you're going to need to have good weather to get there and good weather to get back (although the option to drive back might be handy). You're also most likely going to have to navigate out from under the NYC airspace on the ground.

Private (personal) flying is expensive, not always convenient, and is a bit dangerous. You're absolutely right, though you can mitigate the risk fairly effectively (>75% of the crashes are pilot-caused or pilot-responsible at least), the cost is variable (you can rent at least to start, though that adds inconvenience), and the convenience is variable (there are ways to trade money for convenience).

Do you live adjacent to a GA airport? Where else could one expand the wings, accelerate, and take off with their flying car?

That's not really very fast at all. Most cars can easily go faster than that, the only limits are the human drivers and their pesky problems with reacting quickly enough at high speeds. Sure, no car could go that fast in a city but I'd be surprised if people were going to be happy with large amounts of people flying over residential areas so your flying car might be grounded by regulations/etc inside cities anyway.

If you want to make the world smaller than the most cost effective solution might be to enforce a common standard for networked cars and ban human drivers from motorways.

Cars regularly go >125mph (at least on the few bits of German Autobahn that have no speed limits) and while that is an insanely stupid thing to do with human drivers and their awful reaction speeds + their inability to know the intention of other drivers, a 125mph highway could be achieved via networked computer driven cars (and excluding human driving,of course) with significantly less effort than it would take to make flying cars available to anybody but a select few.

It's not very fast at all if forced to follow roads. It's a big deal if you can fly in a near straight line.

And while, yes, you can drive fast on the autobahn and similar, most of us don't live right next to a freeway and go to/from places directly on a freeway, so the average speed will tend to be far lower.

To take some extreme examples: average traffic speeds in London are below 20mph, with certain congested parts well below that.

We will never get to 125mph+ everywhere on the ground, because car drivers is not the limiting factor, but other factors such as pedestrian safety in residential areas etc.

in fully automated traffic, we can get 2x the current speed, even 3x in congested areas, and probably no traffic jams ever again.

it's not a straight line performance, but considering how 'little' is needed (capable ai-drive) compared to complete overhaul of almost everything just that people can fly around and land somewhere... much more realistic goal

This assumes the only limit is congestion, which it isn't. E.g. roads near me will soon be 20mph to intentionally make it undesirable to use them for through traffic past peoples houses, and to reduce pedestrian accidents.

In Central London, 3x means maybe reaching 30mph, but increasing parts of Central London are also getting 20mph, and while it might very well be that safer automated cars would make it viable to bring that back up to 30mph, you can't travel in a straight line or anything resembling it in the most central parts of London.

E.g. in the most central part there is a single road covering the city centre East/West (Oxford Street), which is also restricted to taxis and buses (and it's still one of the most congested roads in town). To travel the same distance East/West, you need to drive a substantial distance along heavily congested roads South/North, or drive through a maze of smaller back streets and deal with traffic lights and pedestrians haphazardly crossing all over the place, so actual speed measured by straight line between starting point and destination is a tiny fraction of the driving speed for a lot of locations in the centre... It's not uncommon for it to be faster to walk even when there isn't much congestion, depending on where you are going from/to.

So while there may be plenty of places where being able to fly won't be worth it, there are certainly also locations where "just" 100mph would still beat even automated cars by several times if you don't need to spend time driving somewhere dedicated to take off/land. This latter is the biggest caveat - if your "flying car" is really a "drivable convertible plane" that needs something resembling a runway, a heavily congested city core won't exactly be ideal.

Though saying that, even my old commutes in to London were far slower on average than 100mph when taking the bus + train, despite bus + train beating driving a regular car by a massive margin, and that was between locations with far less congestion than the centre.

Just wondering: How many miles per gallon does a small propeller plane fly?

My A36TN gets about 13 mpg in "go fast mode" (205-210 mph true airspeed). I can slow it down and get better than 17 mpg, but rarely do. That's for a six-seat, single (large, turbocharged) engine airplane.

My first plane, a Cessna 182, got about the same ~13 mpg at ~160mph, due to having a much worse drag profile and a less efficient engine.

Twin engine airplanes get a little more than half of that (feeding two engines, not going all that much faster). Going faster hurts mileage by about the square of the ratio of speeds; slower helps by that same ratio. (10% faster takes 33% more fuel burn per time, making specific range (mpg) 21% worse.) Slowing down 20% can often increase mileage by more than 35%. (It's not perfectly quadratic, ground ops consume fuel, and takeoff/climb is still expensive in terms of mileage.)

Obviously, headwinds hurt mpg and tailwinds help. You have more headwinds than tailwinds (mathematical fact, not just pilot grousing).

Someone has to ask: Why do you have more headwinds than tailwinds?

Simplest explanation: Take a 100 mph airplane and fly 100 miles in 25 mph winds, then fly 100 miles back.

You'll fly upwind for 80 minutes at 75 mph groundspeed and downwind for 48 minutes at 125 mph groundspeed. Your overall average speed will be 93.75 mph.

Additional factor: even a "pure" crosswind will turn partially into a headwind, as you need to crab (angle the nose) into the wind to make your desired ground track, meaning your downrange distance becomes the cosine of the crab angle, making (1 - cosine[angle]) * airspeed the effective/induced headwind.

Thanks. A bit like how a 10% investment loss in year one followed by a 10% gain in year two leaves you worse than even.

That's quite good considering the speed and that you also go more direct line compared to a car.

I got 360 miles for 27 gallons over the weekend, so basically 13 mph.

However there are modern two seated designs based on gliders that will triple that and still go 130mph.

Depends what you are flying, how much weight/passengers etc.. The sinus I fly gives me 31mpg running on car gas.. but it only carries 2 people + 20kg of cargo.

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