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Comment by nercury | Hacker News Reader

Helicopter?

Not a helicopter - an autogyro. The rotor on the top is not driven (literally just spins freely on a bearing). Forward motion pushes air through it, which keeps it spinning and that keeps the aircraft up. In effect the rotor acts like a wing (forward motion results in lift), but without the ability to stall.

I'm learning to fly an autogyro in the UK. They're great fun to fly, and in theory safer than a plane because the short landing distance means that in event of engine failure you have a much greater selection of places to land (in practice modern safe autogyros have only been around 5-10 years so we don't have enough data to compare).

Can they land safely after engine fails and any electric/hydraulic assists are also gone?

In the case of an engine failure, a helicopter trades its potential energy (altitude) to kinetic energy by allowing the passing air (as it 'falls') to spin the rotors. This is the helicopter's equivalent of gliding, more or less. The condition is called auto-rotation. Gyros are always in a state of auto-rotation, so if the engine quits they simply begin trading potential energy for kinetic energy, which they're really good at.

Yes they can. There are no hydraulic assists between the stick and the the rotor head, or between pedals and rudder - straight mechanical linkage.

The only electric (or in some cases pneumatic) assist is the pitch trim. In event of failure that would usually stay in the same place, but in the worst case where it moves to one end of the spectrum you can absolutely control the aircraft against it (your arm just gets a bit tired after a while maintaining the pressure).

Yes. They're small enough to not need power-assisted controls.

It doesn't feel possible that the propeller is enough to provide such forward motion that is also used to push the vehicle up

Why not? That's exactly what happens in a plane (or a microlight, or powered parachute).

Well I'm by no means well versed in physics, but my mental model of lift would suggest wings + forward velocity generate a lot more than rotors + forward velocity, and that planes move a lot faster than autogyros, so there's more forward velocity to utilize for lift.

Given how much power appears to go into making helicopters rise, its surprising to see an autogyro do it without actually powering the main rotor.

(fwiw, I'm not arguing that I'm correct. obviously I'm wrong).

There is another push/pull propeller that moves plane forward and that one is driven by engine.

Well, the seeds of a maple tree fall a lot more slowly when they're rotating so clearly there's some kind of lift being generated. To fly you 'just' need to replicate that effect and forcibly push more air through the rotor than just gravity would.

Autogyro. Looks quite cool https://youtu.be/RFpNTykIYM0?t=132

A helicopter that can also drive on wheels and that is rated for driving on public roads.

So no, it's not a helicopter, is a car/helicopter hybrid, a.k.a. flying car.

Not only a flying car, a flying _dutchcar_, which is way more interesting.

Not a helicopter at all, see this comment: https://news.ycombinator.com/item?id=24918402

There is no engine connected to the blades, it is an autogyro. They are not so uncommon here in Europe, most of them I have seen has been home-build.

Off-topic: some UAV prototypes developed in Europe during the 80s and the beginning of 90s was of the type autogyro, because of its simplicity and short take-off and landing distances.

For those interested, there is no engine connected to the blades while in flight. Most gyros have is a linkage called the pre-rotator with a clutch that you engage while stationary on the ground. This allows you to get the rotor to about two thirds of the speed needed for take off at which point you release it, and then do a take off roll to build speed and rotor speed.

This is also how the UAVs in the 90s did it too, but with a screwdriver instead.

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