Combined turbopro and jet ?
I don't know if I dreamt this or what, but suddenly it appeared to me as an idea to "take a twin turboprop and mount a jet engine in the tail". I am just a pilot, not an engineer, so maybe some clever head here can either tell me that is has already been done, or why it has never been tried.
I think the advantages of jet and turboprop engines could both be derived of such a mix, making it a more (fuel) efficient, economical and flexible aircraft.
For certification purposes it should be called a jet aircraft (with regard to legislative matters), or the most limiting of the two from case to case.
Advantages of the turboprop
Better braking capability in the air (discing the props instead of using spoilers)
Closer to "instant power" than a jet (go-around, windshear etc)
Better fuel performance at low levels
Shorter take-off and landing distances (but that is probably mainly due to wing construction of the TP)
Advantages of the jet
Better fuel economy on cruise at higher levels
Faster speed at higher levels
Higher service altitude
Advantages to the combination
Three engined - no ETOPS hazzle
Combined fuel economy and top speed/performance
Two cheaper turboprop units, yet having jet performance
Disadvantages
If the jet pushes the aircraft faster at higher speeds, would the props then be of any use, or just making drag and extra weight, or could the right prop with the right pitch still be effective enough to be of any use?
Well, just a thought ...