>  Looking at that, I assume that altitude is not controlled in the same
> way as in a real helicopter, ie. by changing the angle of attack of the
> rotor blades. Instead, I assume that in this case it's done by changing
> the speed of rotation?

Yes, this is common with (almost) all 4-channel helicopters, the altitude is 
controlled by the speed of the rotor, not the angle of the blades.

>  Also in a real helicopter pitching and rolling is done by changing the
> angle of attack of the blades differently at different positions,

Actually in the model here it works the same as a real helicopter, the swash 
plate is tilted forward and backwards or left and right by two servos (the 
red circular part with the attachments to the vertical rods), then the black 
plastic part sits on top and rotates with the rotor.  As it rotates it 
pushes levers to change the angle of attack of the blades.

The difference to a real helicopter is that the model doesn't have any way 
to adjust the average pitch over a rotation, amongst other things this means 
you can't generate negative lift, which is needed to fly upside down.

There are more sophisticated models with 5 and 6 channels that work exactly 
the same way as real helicopters, and of course then allow upside down 
flight.

> but here I assume it's done with those small blades.

No that's just a stabilizer bar and it spins with the main rotor, offset by 
90 degrees.  It is connected in a certain way to help cancel out any 
external forces on the rotor.  In small models it is pretty much essential 
to allow them to be controlled by humans!

> Yawing is probably done
> in the same way in both.

Yes.

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