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Comment by WalterBright | Hacker News Reader

An airplane is a vehicle that wants to fly, a helicopter wants to crash. A helicopter is inherently unstable and requires constant adjustment. It has multiple single points of failure, any one of which will result inevitably in a crash. This is dealt with by insanely expensive quality control, constant inspections, and constant maintenance.

The quadcopter doesn't improve on this, it makes it worse. It has 4 engines - if one engine fails, it crashes. It has inherently 1/4 of the reliability of a single engine helicopter. Losing one rotor blade will also cause a crash, so its 1/4 of the reliability there as well. QA, maintenance, and overhauls will cost 4x as much.

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I always thought that thanks to this http://en.wikipedia.org/wiki/Autorotation helicopters are safer than even some airplanes - unless you manage to turn them upside down midair, that is :-).

http://www.youtube.com/watch?v=YlkKfqUTnyk I know it's not full scale, but apparently autorotation can be achieved even inverted. No idea if the swashplate on a real helicopter could invert all the way, but I seem to recall the apache AH-64d could fly inverted.

http://spectrum.ieee.org/automaton/robotics/aerial-robots/ev...

stable flight is not impossible with the loss of a motor on a quadrotor platform. it's currently stuck in labs, but the dynamics are doable.

That kind of stable flight is ok for an unmanned vehicle, but I don't think a passenger/pilot would be delighted abut that kind of accelerations and spin.

I guess if it's a choice between smashing into the ground and short period of spinning whilst an automated system landed the vehicle, I think I know what I'd go for.

Depending on how fast you are spinning, I imagine the deceleration on landing, for a human passenger would be lethal or life threatening.

It might be better to include a parachute above the rotors.

The Cirrus SR22 single engine aircraft has this (their system's called CAPS.) It lets you sail to the ground in the event of some catastrophic failure preventing you from landing the aircraft safely. http://en.wikipedia.org/wiki/Cirrus_SR22

Would the airplane parachute be scalable to large commercial jets? I assume the fuel costs of carrying the extra parachute weight are too great but curious about the engineering.

Nobody has made a parachute remotely large enough. The engineering challenges are quite unknown.

I suspect the parachute would be far too heavy. Also, jets fly very fast, and the jerk when the chute opens would likely rip things apart.

The text and video make it unclear what is happening - does it try to spin the machine so the centrifugal force will straighten it out?

if one motor fails on a quadcopter, it can be saved [1] ... so that might increase reliability when compared to an helicopter.

[1] http://diydrones.com/profiles/blogs/new-algorithm-can-save-a...

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