> Hi everybody. I’m a disegner of fast bikes (for speed records) and
> this is one of my recent ideas (modyfied centaur (it had two
> wheels before)). It has drive from hands and legs. Very beta
> drawing, just idea.
Sounds cool - very cool.
> I wold love to hear from unicycle experts :
I’m nowhere near an expert, but I’m going to stick my oar in anyway 
> 1. would it be ridable?
One thing I’ve learnt on these forums is that almost anything is ridable
No matter how crazy an invention, there’s always going to be someone who can handle it.
I bet many people would be able to ride it sitting upright and not using the hand cranks. Transferring to hand cranking too would be interesting - you’d have to be going slow enough that you could grab hold of the cranks.
Riding this would require decent balance - you wouldn’t be able to flail your arms around
I don’t know how much hand cranking would disrupt one’s balance…
What wheelsize were you thinking of? 36" wheels seem to be popular for speed / distance riding, although geared 29ers have some merits too.
Oh, and a little safety point: it’d be really nice if you could fall off the front of this without getting your feet tangled in any machinery
Although given you’re unlikely to be able to run out of a speed record attempt maybe that’s not so important!
> 2. are there hubs with integrated planetary gear for unicycles?
Yes, see http://schlumpfdrive.com and search the forum history for Harper’s Blueshift and uni.5.
The Schlumpf hub is shiftable on the fly, Harper’s hubs offer a choice of two ratios you can change with a toolkit (by adjusting the torque arm if I remember correctly - which I may not do).
Also, look for PurplePhaze which achieves much higher ratios using a jackshaft system. Again adjustable using a toolkit, but a bit more work. It also featured a “tuck” handlebar arrangement, vaguely like your proposal (without the hand drive). OuttaPhaze is a proposed production variant of this design.
> 3. would it be possible to turn?
If it could be ridden, then it could be turned.
> I like this bike bacause it’s simple and has good aerodynamics =>
> high speed.