Dear Keesje, I have been following your developments on Airliners and find your idea's very interesting.
I congratulate you for the time and passion you spend on this project.
I agree with you that the twin double-decker is the solution for economical travel and I 've been thinking about it some times already.
The only problem I see in your project is the single engine take-off performance and the APTU. There are 3 problems:
-Considering that the APTU is a CFM-56 class system, and using it only at critical moments such as tkof would make it a waste of weight as these engines usually weigh around 6000lbs.
-Considering your design of the air intake through a pipe placed at 90 degree angle to the airflow, the engine air intake will not be sufficient to provide the full-rated thrust. Also, the 90 degree angle air intake angle will create extensive drag. Even if the angle is decreased, these problems will not be entirely eliminated.
-Placing an engine device in the aft section is troublesome due to the different control surfaces present in that area: elevators, rudders. Several uncontained engine failures have resulted in crashes...
The engine failure at take-off is a difficult argument.
This is my solution:
If an engine that has failed could be used as a ram/rocket jet engine, the argument would be no more. These sort of engines burn alot more fuel in shorter periods, which means that you can get rid of all that fuel you'd like to get rid of, and at the same time generate enormous thrust that will enable the aircraft to climb. If engines could be designed in this way, the one engine inoperative problem would be no more.
I'm putting a copyright on this idea
Procedure will be easy: engine failure/X-feed selection/full-fuel injection/continuous ignition/establish climb speed,...
The B757 at manchester that suffered a contained EF is a good example showing that this could work.