Achim,
I wonder what would have happened if Heiko had lived a bit longer than he did. But it was an interesting concept.
Does the prototype still exist? It might be nice for an exhibition somewhere.
@Peter Yes, but single-engined fixed wing is really not that different in this. Until you get high enough to turn back (or open a parachute), your options are limited and going forward might mean flying into a canyon or a forest. If it happens in a helicopter, you are relying on a crash protection. IIRC for the little Cabri even 2.000 fpm fall is considered survivable (that doesn’t mean you’ll walk away, but you shouldn’t be “toast”). PS: And hovering close to ground is not that different from slowly flying close to ground.
BTW: the tilt rotor designs would work well with a chute. That seems to be the best way to address safety concerns.
VTOL is a daft idea for general transport. The energy required to hover/vertical lift is huge, very much limiting payload. Most helicopters only ever lift vertically when constrained by site space.
The tilt rotors all have complex and expensive gearing systems allowing a single engine to drive both rotors in he case of a failure. The early Osprey accidents were similar to the USMC’s high accident rates when introducing the Harrier – in both cases they were the first major operator of aircraft with new and unusual handling qualities in the transition between thrust and wing lift regimes and learned general operating principles and lessons that had not been identified in the flight testing phase.
The twin fixed forward facing rotors together with a normal disc deal with a different issue – maximum speed. Helicopters are limited to a maximum airspeed of around 220kias as at greater air speeds the airflow over the forward-going rotor blade becomes transonic creating all sorts of nasty effects. The forward thrusting propellers increase forward speed and allow a lower main rotor RPM delaying the onset of transonic effects to a higher IAS.
Josh, you completely ignored the fact that newer designs use electric motors for the tilt rotors. That is a game changer.
single-engined fixed wing is really not that different in this
I don’t think so, because a SEP can always be landed from any phase of flight, without damage (if the terrain below is suitable), assuming the pilot does the right things. Whereas a helicopter will get smashed up if you get a sudden and total loss of power in specific scenarios and nothing can be done about it – other than avoid those scenarios. That’s why one usually sees helis (especially Robinsons) accelerating at very low level before climbing.
I should think noise will keep VTOL operations from becoming common. Noise from the engine(s) can be atacked, especially in a petrol/electric hybrid; noise from propellers/rotors will be much harder.
Electric motors will definitely help, but designs like the XTI are pie in the sky CAD mock ups. You will still face the same payload issues with vertical launches.
I also suspect that the requirement for separate electric motors in the pods with rotors and generating hardware in the form of gas turbines would offset a large portion if not all of the weight savings in mechanical transmission.
Peter wrote:
if the terrain below is suitable
That is the very important caveat, isn’t it. Not all runways are long enough and not all have a nice terrain at the end. And even then it’s a question of how much you’re pushing the limits.
I don’t know what Robinsons are capable of and I’m not interested in finding out, I just don’t like them. When really low, you have to be quick and you’re actually using inertia of the rotor system (you are essentially performing the final stage of autorotation). The issue with going up is that you don’t have enough energy in it and while entering autorotation might be possible, there is a good chance you’ll just be too slow to react. So you pick up airspeed instead which will make entering autorotation easier (you will have enough speed to flare). And then climb. You don’t want too much airspeed too low either (again, a good chance you’d be too slow to properly react). If you’re afraid of losing power, don’t go into a “coffin corner”.
Having a high inertia rotor system is a clear advantage in this. The important bit here is whether you can take off and land without a visit to the aforementioned corner. 
And what operational limitations it places on you.
Unfortunately an accident happened with the AW 609, killing the two test pilots on board :-(
http://www.flyingmag.com/technique/accidents/test-pilots-killed-aw609-crash
