As full-scale aircraft or as models / UAVs / drones? Is anyone working on making these real or are they fundamentally flawed designs, or needing new materials to be invented?
I presume you're talking about the fictional Aerospatiale SA-2 Samson. From that page:
Ducted fan VTOL aircraft have been flown since at least the 1960s. A notable example was the Bell X-22, a quad-ducted fan experimental aircraft built for the US military. It has no relation to the later V-22 Osprey tiltrotor. Though successful, no military aircraft since have used that technology.
The Bell X-22 looked like this:
which has similar overall characteristics to the SA-2 depictions.
They are feasible in as much as the atmosphere on "Pandora" is thicker and the force of gravity is lighter. C.f. Avatar Wiki
This allows for both large winged reptiles (?) and smaller tiltrotors than are possible on our current earth.1
1 There is evidence that our atmosphere was more oxygen-rich in the geologic past and may have been thicker, allowing for similarly large reptiles.
Yes, they are certainly feasible. In fact, one basically exists already: the V-22 Osprey.
The main difference being that the V-22 has ailerons for roll control and wings for lift in forward flight.
Power isn't a problem, it's just a multirotor helicopter... think Chinook, on a different axis. And control, for the most part, isn't a major issue.
Differential power to the two motors provides Roll control, similar to a quadcopter
Rotating the rotors slightly forward/back and/or something similar to a cyclic on a conventional helicopter allows (similar to the Osprey tiltrotor):
- Forward/reverse flight (if tilted together)
- Yaw control (if tilted in opposing directions... think tank tracks
If attached in away that they can be angled up/down, pivoting on the attachment to the fuselage, the vehicle can "strafe" (ie lateral sideways movement)
Pitch when in forward/reverse flight is provided by the tail stabilisers. In the hover it could presumably be controlled to some extent by means similar to a conventional helicopter's cyclic, shifting weight, or by an additional small rotor near the tail, if you didn't want to be 100% true to the movie model
Here's a working model, for example. I don't believe there are any full size models, but the Osprey is "close enough" to prove the concept.