1. Helicopters are technically VTOL, but what you'd really want is something that can transition between vertical takeoff and horizontal flight using conventional wings, which is much more efficient and stable when travelling from A to B.

2. VTOL requires engines which provide very high thrust and very short response time during vertical ascent. This is incredibly hard to do using combustion engines - which includes hydrogen - but trivial using electric engines, which is why every cheap drone can easily fly using only vertically mounted propellers.

> VTOL requires engines which provide very high thrust and very short response time during vertical ascent

Not necessarily. That's how you do it with electric multirotors, because it's simple and electric motors are good at it. With turbine powered VTOLs, the rotor blades are actuated to change their angle of attack, and consequently how much lift they're producing, using swashplates and cyclic controls. That's what traditional helicopters do, and what tiltrotors like the V-22 do too.

Incidentally I think tiltrotors are what you're describing as the VTOL ideal; they take off like helicopters then transition into horizontal flight using conventional (albeit stubby) wings. They're not exactly a runaway success and have had a rocky history, but they do work.

>the rotor blades are actuated to change their angle of attack, and consequently how much lift they're producing, using swashplates and cyclic controls

Correct, but that is just the workaround to achieve more immediate thrust variability from a combustion engine - which in turn made these aircraft insanely complex and highly expensive to operate. An electric motor can immediately give you the required torque over a wide range of speeds, finally making these designs safe and possibly even economical. Batteries are the only reason why we aren't seeing these things everywhere and a tiltrotor capable of VTOL and winged horizontal flight could finally make them viable.

> Correct, but that is just the workaround to achieve more immediate thrust variability from a combustion engine

Well no, it's not just a work-around to the thrust response of combustion engines. Cyclic control is also how traditional rotorcraft control their pitch and roll. It actually works quite well, helicopters are a huge success and the main reason why tiltrotors aren't more popular is because helicopters are generally good enough; nobody really needs the extra endurance of a tiltrotor enough to make the extra complexity worth it. In most cases when you need more range, a fixed wing aircraft is better. The intersection of "needs to be VTOL" and "needs better range than a helicopter" seems to be "military".

Anyway, saying that Helicopters are "technically" VTOLs is silly; they are VTOLs in every sense of the term. If you think they aren't in some way VTOLs then you're operating with some pet definition of VTOL. You seem to think electric multirotors are the ideal form of VTOL and anything other than that doesn't really count... but VTOL doesn't mean that. VTOL means vertical takeoff and landing. Helicopters are VTOL, not just technically but conceptually, spiritually, and in every other sense you can conceive of.

> Batteries are the only reason why we aren't seeing these things everywhere and a tiltrotor capable of VTOL and winged horizontal flight could finally make them viable.

I disagree. Electric VTOLs perform much worse than electric fixed-wing airplanes, and always will. Fixed wing electric airplanes don't have the power or endurance to do much that's useful. That's the upper bound for VTOL performance, and it sucks.

There is so much mechanical complexity in the existing tiltrotor systems. Especially with the V-22, where each turbine can cross-drive the other rotor.

Another area where electric propulsion shines. You can simply drive each propeller with its own motor and not blow up your weight/complexity budget even if you go crazy with the number of fans line Lilium did. That's precisely why almost noone bothered with tiltrotors until batteries became so good that they are almost useful for flying aircraft.

1. I'm interested in the economics of this vs helicopters. Why would someone buy one? Is it cheaper? Faster? More energy efficient per mile?

2. Hydrogen fuel cells drive an electric motor, no combustion needed. Battery weight seems to be a huge factor for VTOL. Hydrogen drones can easily fly for hours for example.

Also what about safety? Helicopters can be landed even in case of power failure.