Ducted-fan lifters have some really ugly problems. Per the wikipedia article:
Less efficient than a propeller at cruise (at lower thrust level).
Good efficiency requires very small clearances between the blade tips and the duct.
Requires high RPM and minimal vibration.
Complex duct design, and weight increase even if constructed from advanced composites.
At high angle of attack, parts of the duct will stall and produce aerodynamic drag.
The last two are the biggest problems. Weight and the fact that the ducted thruster partially stalls if the airflow over it is at a great enough angle to the intake of the duct. It’s part of why the Moller SkyCar has never progressed past a tethered hover.
Thank you gentlemen, those are excellent pieces of information answering a layman’s question. Here’s another.
Regarding saving lives, and crashworthiness, I’ve often wondered this of conventional helicopters and passenger aircraft of any size for that matter:
If they can drop a tank or large piece of field gear from a cargo plane via a parachute, why can’t they similarly lower a relatively light disabled aircraft, or fuselage, to the ground at 20MPH instead of 200?
The helicopter could have the “explosive bolts” on the rotor hub, and a braking mechanism on the tail rotor, allowing a clean drop of the core of the aircraft.
They’ve had “rocket fired parachutes” on ultralights for quite some time now.
It seems preserving the irreplacable human cargo, and maybe even the plane, would be well worth the weight penalty or additional cost.