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Comment by aphextron | Hacker News Reader

As a pilot I would never step foot in this thing. The thought of being in an aircraft with zero aerodynamic control, or ability to glide in a dead stick situation is a complete nightmare. It doesn't matter how redundant your systems are if you have a fundamentally unstable airframe with no yaw control. In a total power loss situation, you must have some type of glide profile. All other forms of aircraft have this. Such a design would be fine for drones, but this will never carry humans.

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Rockets, balloons, most military aircraft? Shove a ballistic parachute on it.

> "Rockets, balloons, most military aircraft? Shove a ballistic parachute on it."

As far as I know, no rocket or military fighter jet has ever been certified to carry paying passengers for exactly this reason. We're talking about shuttling people around, not highly trained test pilots.

Balloons are actually far safer than fixed wing aircraft for other reasons. It would take a complete loss of the canopy for a balloon to fall out of the sky. When they run out of fuel, they just drift slowly to the ground.

Ballistic parachutes are a last resort option, and add a large amount of weight and complexity to the aircraft. Not to mention that they do not scale up to larger passenger aircraft. It's not even comparable to the safety afforded by a stable airframe.

You cant dead stick a cessna in an urban environment, and current ballistic parachutes aren't that heavy.

https://aviation.stackexchange.com/questions/24946/what-is-t...

>You cant dead stick a cessna in an urban environment, and current ballistic parachutes aren't that heavy.

Except a ballistic parachute does absolutely nothing for you in the scenario where > 90% of accidents happen: take off and landing. Even the most advanced BRS systems on Cirrus planes require 1000 feet AGL. There's simply no getting around the basic physics of this problem.

Yeah but dead sticking is less effective during take off and landing as well.

I watched someone who wouldn't make the runway (pilot error, didn't switch the fuel tanks fully on approach) dead stick onto a perpendicular highway.

With a light plane, you can do a lot with a dead stick. They have remarkably generous glide slopes (nearish to a mile horizontal travel for every 1,000 vertical feet). Not to mention being inherently stable whether under power or not.

Well a 0/0 safety system seems like a solvable problem in the scheme of things. airbag + chute? Who knows.

You can't dead stick most aircraft in an urban environment. Unless you are Sully...

Let me clarify that, you can dead stick a cessna and land it outside your local bar in NYC (someone did) but its not easy.

https://en.wikipedia.org/wiki/Thomas_Fitzpatrick_(pilot)

https://cityroom.blogs.nytimes.com/2013/06/04/long-ago-a-pil...

Once a parachute is deployed there is no control among many high rise buildings.

On the technology page under the safety first section they talk about a parachute being installed as a last resort.

If equipped with a parachute like a Cirrus I would not be so scared of it. In its current iteration it's about as scary as the eHang giant octocopter.

Parachutes generally need 1K feet to be effective, and VTOL cabs will operate at fairly low altitudes. Maybe there are special ops low-altitude parachute designs that can be adapted for airframes.

As a non-pilot, that's ultimately the reality every time we fly already. Sure there's redundancy, but ultimately if things go wrong all we can do is sit powerlessly in our chair as the ground roars up at us.

The post is talking about unpowered glide profile - the vast majority of air travel is in commercial jetliners which can and do glide, providing a major advantage in case of problems.

How is the glide profile any worse than a helicopter's?

Helicopters glide or 'autorotate' tolerably well after engine or driveshaft failure, at least enough to land controllably.

In the R22 two-seater the best glide ratio is about 4:1 ( 4ft horizontal for 1ft drop ) and those at my local airfield practice autorotation to landing all day long.

Apparently the worst helicopters for autorotation are those with Kamov's superimposed coaxial rotor system, which struggle to reach 2:1 for some aerodynamic reason I don't know.

In a helo you can attempt auto-rotation, which while tricky at least gives you a fighting chance.

>How is the glide profile any worse than a helicopter's?

This is a common misconception. Helicopters can glide to a landing just like airplanes.

Helicopters glide quite nicely. Learning to autorotate is something you learn early on when getting your license.

Is this dissimilar to a helicopter though?

Helicopters can auto-rotate, "gliding" on the momentum of the main rotor. This allows for a controllable landing under loss of power.

There have been rare cases where a mechanical failure seizes the main rotor, such as the crash of the WNBC news chopper (N8617B) in 1986. This particular incident was caused by poor maintenance, however.

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

http://www.check-six.com/Crash_Sites/Dornacker-N8617B.htm

A helicopter can auto-rotate, though that's really the least-bad option if you're in that sort of situation. It turns an assuredly fatal scenario into a hopefully, maybe, possibly survivable one: https://aviation.stackexchange.com/questions/14605/how-does-...

Here's a demonstration: https://www.youtube.com/watch?v=BTqu9iMiPIU

Haha! That Neil DeGrasse Tyson, what a dummy.

(Good sport, though. And I also thought a helicopter would drop like a rock without power.)

It drops like a rock if the Jesus Nut (https://en.wikipedia.org/wiki/Jesus_nut) fails, but that situation is freakishly rare.

So similar to how a maple seed glides?

Not really. Watch the video. A maple seed has less control over how it spins.

Roughly as dissimilar as a sack of bricks versus a helicopter. Those small ducted fans will do absolutely nothing while you fall down. Maybe they'll spin a little bit to recharge the batteries, sort of a built in confusion generator for the people doing the autopsy: "Why didn't they just land the thing, it's got some charge left?".

Where do people get the idea that helicopters just fall from the sky when there's a power failure?

Do people think that others are flying around everyday in machines that will likely kill them in case of a malfunction? Is the media is covering up all the helicopter related fatalities?

People just don't realize there is such a thing as auto-rotation.

Yes, that is exactly what I thought. Me and Neal DeGrasse Tyson!

The plane they are planning to build looks like it could glide by itself.

This guy!

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