What have you been on??????
One engine under one wing, and two engines under the other..????? Don't think so...although german wartime engineers did come up with quite some assymetric aircraft, several of which have been flown quite succesfully.
Anyway. To answer your question Vinovalentino:
From an operational point of view, an airline would not want two different type of engines under one aircraft. For fleet commonality [sp?] reasons, airlines tend to stay with the least number of engine-types possible, even over different aircraft types [B767, B747]. If possible at all, you want to reduce the number of aircraft types and the number of engine types in your fleet. Introducing another engine type in one aircraft is an absolute maintenance nightmare! No go!
However, besides the maintenance issue, there is absolutely no reason at all which would exclude a different engine spec for the #2 position on a tri-jet. No problemo at all. Please note that this is NOT considered as being assymetrical engine configuration!
Even Boeing was [and maybe still is] looking at this option to increase the 777 potential. The idea was to install a big ass APU, which would deliver several thousands of pounds of thrust [only required at take-off and initial climb sector], thereby increasing MTOW without going to even larger engines [115000 lbs+] under the wing. During cruise APU power would not be required.
Current commercial aircraft tends toward twins...which is not the most natural platform for assymetric engine installation....
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